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Last updated: 5/3/11
This list includes resources for understanding the functions
and benefits of riparian
buffers, especially those functions and benefits seen in
different widths (for example, a 50 foot versus a 300 foot
buffer). Baker, ME, Weller, DE, Jordan, TE. 2006.
Improved methods for quantifying potential nutrient
interception by riparian buffers. LANDSCAPE ECOLOGY, 21 (8):
1327-1345.
Abstract: Efforts to quantify the effects
of riparian buffers on watershed nutrient discharges have been
confounded by a commonly used analysis, which estimates buffer
potential as the percentage of forest or wetland within a
fixed distance of streams. Effective landscape metrics must
instead be developed based on a clear conceptual model and
quantified at the appropriate spatial scale. We develop new
metrics for riparian buffers in two stages of increasing
functional specificity to ask: (1) Which riparian metrics are
more distinct from measures of whole watershed land cover? (2)
Do functional riparian metrics provide different information
than fixed-distance metrics? (3) How do these patterns vary
within and among different physiographic settings? Using
publicly available geographic data, we studied 503 watersheds
in four different physiographic provinces of the Chesapeake
Bay Drainage. In addition to traditional fixed-distance
measures, we calculated mean buffer width, gap frequency, and
measures of variation in buffer width using both
“unconstrained” metrics and “flow-path” metrics constrained by
surface topography. There were distinct patterns of
relationship between watershed and near-stream land cover in
each physiographic province and strong correlations with
watershed land cover confounded fixed-distance metrics.
Flow-path metrics were more independent of watershed land
cover than either fixed-distance or unconstrained measures,
but both functional metrics provided greater detail,
interpretability, and flexibility than the fixed-distance
approach. Potential applications of the new metrics include
exploring the potential for land cover patterns to influence
water quality, accounting for buffers in statistical nutrient
models, quantifying spatial patterns for process-based
modeling, and targeting management actions such as buffer
restoration.
Carline, RF,
Walsh, MC. 2007. Responses to riparian restoration in the
Spring Creek watershed, central Pennsylvania. RESTORATION
ECOLOGY, 15 (4): 731-742.
Abstract:
Riparian treatments, consisting of 3- to 4-m buffer strips,
stream bank stabilization, and rock-lined stream crossings,
were installed in two streams with livestock grazing to reduce
sediment loading and stream bank erosion. Cedar Run and Slab
Cabin Run, the treatment streams, and Spring Creek, an
adjacent reference stream without riparian grazing, were
monitored prior to (1991–1992) and 3–5 years after (2001–2003)
riparian buffer installation to assess channel morphology,
stream substrate composition, suspended sediments, and
macroinvertebrate communities. Few changes were found in
channel widths and depths, but channel-structuring flow events
were rare in the drought period after restoration. Stream bank
vegetation increased from 50% or less to 100% in nearly all
formerly grazed riparian buffers. The proportion of fine
sediments in stream substrates decreased in Cedar Run but not
in Slab Cabin Run. After riparian treatments, suspended
sediments during base flow and storm flow decreased 47–87% in
both streams. Macroinvertebrate diversity did not improve
after restoration in either treated stream. Relative to Spring
Creek, macroinvertebrate densities increased in both treated
streams by the end of the posttreatment sampling period.
Despite drought conditions that may have altered physical and
biological effects of riparian treatments, goals of the
riparian restoration to minimize erosion and sedimentation
were met. A relatively narrow grass buffer along 2.4 km of
each stream was effective in improving water quality, stream
substrates, and some biological metrics.
Clinton, BD,
et al. 2010. Can structural and functional characteristics
be used to identify riparian zone width in southern
Appalachian headwater catchments? CANADIAN JOURNAL OF
FOREST RESEARCH, 40 (2): 235-253.
We
characterized structural and functional attributes along
hillslope gradients in headwater catchments We endeavored to
identify parameters that described significant transitions
along the hillslope On each of four catchments, we installed
eight 50 m transects perpendicular to the stream. Structural
attributes included woody and herbaceous vegetation: woody
debris and forest floor mass. nitrogen (N) and carbon (C),
total soil C and N. litterfall amount and quality by species:
and microclimatic conditions Functional attributes included
litter decomposition, soil microarthropods. soil CO2
evolution, soil solution chemistry, and soil extractable N
Forest floor mass, N and C, and soil depth increased with
distance from the stream and transitioned between 10 and 20 m
In contrast, litterfall N rate (kilograms of nitrogen per
hectare per day), downed woody debris, soil A-horizon C and N.
and soil solution NO3 concentration all decreased with
distance, and exhibited significant transitions. Certain
overstory species were more abundant in the uplands than near
the stream Herbaceous diversity and richness were similar
across the hillslope, but species distributions varied in
response to hillslope moisture content. Taken together, these
results suggest that at 10-20 m from the stream, transitions
occur that separate riparian from upland conditions and may
provide valuable insight into riparian zone definition
Costello, D,
Lamberti, G. 2008. Non-native earthworms in riparian soils
increase nitrogen flux into adjacent aquatic ecosystems. OECOLOGIA, 158 (3): 499-510.
Abstract:
Riparian zones are an important transition between terrestrial
and aquatic ecosystems, and they function in nutrient cycling
and removal. Non-native earthworms invading earthworm-free
areas of North America can affect nutrient cycling in upland
soils and have the potential to affect it in riparian soils.
We examined how the presence of earthworms can affect riparian
nutrient cycling and nutrient delivery to streams. Two
mesocosm experiments were conducted to determine how (1) the
biomass of earthworms and (2) earthworm species can affect
nutrient flux from riparian zones to nearby streams and how
this flux can affect streamwater nutrients and periphyton
growth. In separate experiments, riparian soil cores were
amended with one of four mixed earthworm biomasses (0, 4, 10,
or 23 g m−2 ash-free dry mass) or with one of three earthworm
species (Aporrectodea caliginosa, Lumbricus terrestris, L.
rubellus) or no earthworm species. Riparian soil cores were
coupled to artificial streams, and over a 36-day period, we
measured nutrient leaching rates, in-stream nutrient
concentrations, and periphyton growth. Ammonium leaching
increased with increasing biomass and was greatest from the A.
caliginosa treatments. Nitrate leaching increased through time
and increased at a greater rate with higher biomass and from
cores containing A. caliginosa. We suggest that the overall
response of increased nitrate leaching [90% of total nitrogen
(N)] was due to a combination of ammonium excretion and
burrowing by earthworms, which increased nitrification rates.
During both experiments, periphyton biomass increased through
time but did not differ across treatments despite high
in-stream inorganic N. Through time, in-stream phosphorus (P)
concentration declined to <5 μg l−1, and periphyton growth was
likely P-limited. We conclude that activities of non-native
earthworms (particularly A. caliginosa) can alter
biogeochemical cycling in riparian zones, potentially reducing
the N-buffering capacity of riparian zones and altering
stoichiometric relationships in adjacent aquatic ecosystems.
DeWalle, DR.
2010. Modeling Stream Shade: Riparian Buffer Height and
Density as Important as Buffer Width. JOURNAL OF THE
AMERICAN WATER RESOURCES ASSOCIATION, 46 (2): 323-333.
).
A
theoretical model was developed to explore impacts of varying
buffer zone characteristics on shading of small streams using
a path-length form of Beer's law to represent the transmission
of direct beam solar radiation through vegetation. Impacts of
varying buffer zone height, width, and radiation extinction
coefficients (surrogate for buffer density) on shading were
determined for E-W and N-S stream azimuths in infinitely long
stream sections at 40 degrees N on the summer solstice.
Increases in buffer width produced little additional shading
beyond buffer widths of 6-7 m for E-W streams due to shifts in
solar beam pathway from the sides to the tops of the buffers.
Buffers on the north bank of E-W streams produced 30% of daily
shade, while the south-bank buffer produced 70% of total daily
shade. For N-S streams an optimum buffer width was
less-clearly defined, but a buffer width of about 18-20 m
produced about 85-90% of total predicted shade. The model
results supported past field studies showing buffer widths of
9-11 m were sufficient for stream temperature control.
Regardless of stream azimuth, increases in buffer height and
extinction coefficient (buffer density) were found to
substantially increase shading up to the maximum tree height
and stand density likely encountered in the field. Model
results suggest that at least 80% shade on small streams up to
6-m wide can be achieved in mid-latitudes with relatively
narrow 12-m wide buffers, regardless of stream azimuth, as
long as buffers are tall (approximate to 30 m) and dense (leaf
area index approximate to 6). Although wide buffers may be
preferred to provide other benefits, results suggest that
increasing buffer widths beyond about 12 m will have a limited
effect on stream shade at mid-latitudes and that greater
emphasis should be placed on the creation of dense, tall
buffers to maximize stream shading.
Diebel, M et
al. 2009. Landscape Planning for Agricultural Nonpoint Source
Pollution Reduction III: Assessing Phosphorus and Sediment
Reduction Potential. ENVIRONMENTAL MANAGEMENT, 43 (1): 69-83.
Abstract: Riparian
buffers have the potential to improve stream water quality in
agricultural landscapes. This potential may vary in response
to landscape characteristics such as soils, topography, land
use, and human activities, including legacies of historical
land management. We built a predictive model to estimate the
sediment and phosphorus load reduction that should be
achievable following the implementation of riparian buffers;
then we estimated load reduction potential for a set of 1598
watersheds (average 54 km2) in Wisconsin. Our
results indicate that land cover is generally the most
important driver of constituent loads in Wisconsin streams,
but its influence varies among pollutants and according to the
scale at which it is measured. Physiographic (drainage
density) variation also influenced sediment and phosphorus
loads. The effect of historical land use on present-day
channel erosion and variation in soil texture are the most
important sources of phosphorus and sediment that riparian
buffers cannot attenuate. However, in most watersheds, a large
proportion (approximately 70%) of these pollutants can be
eliminated from streams with buffers. Cumulative frequency
distributions of load reduction potential indicate that
targeting pollution reduction in the highest 10% of Wisconsin
watersheds would reduce total phosphorus and sediment loads in
the entire state by approximately 20%. These results support
our approach of geographically targeting nonpoint source
pollution reduction at multiple scales, including the
watershed scale.
Dosskey, MG,
et al. 2010. The Role of Riparian Vegetation in Protecting
and Improving Chemical Water Quality in Streams. JOURNAL
OF THE AMERICAN WATER RESOURCES ASSOCIATION, 46 (2): 261-277.
We review
the research literature and summarize the major processes by
which riparian vegetation influences chemical water quality in
streams, as well as how these processes vary among vegetation
types, and discuss how these processes respond to removal and
restoration of riparian vegetation and thereby determine the
timing and level of response in stream water quality. Our
emphasis is on the role that riparian vegetation plays in
protecting streams from nonpoint source pollutants and in
improving the quality of degraded stream water. Riparian
vegetation influences stream water chemistry through diverse
processes including direct chemical uptake and indirect
influences such as by supply of organic matter to soils and
channels, modification of water movement, and stabilization of
soil. Some processes are more strongly expressed under certain
site conditions, such as denitrification where groundwater is
shallow, and by certain kinds of vegetation, such as channel
stabilization by large wood and nutrient uptake by
faster-growing species. Whether stream chemistry can be
managed effectively through deliberate selection and
management of vegetation type, however, remains uncertain
because few studies have been conducted on broad suites of
processes that may include compensating or reinforcing
interactions. Scant research has focused directly on the
response of stream water chemistry to the loss of riparian
vegetation or its restoration. Our analysis suggests that the
level and time frame of a response to restoration depends
strongly on the degree and time frame of vegetation loss.
Legacy effects of past vegetation can continue to influence
water quality for many years or decades and control the
potential level and timing of water quality improvement after
vegetation is restored. Through the collective action of many
processes, vegetation exerts substantial influence over the
well-documented effect that riparian zones have on stream
water quality. However, the degree to which stream water
quality can be managed through the management of riparian
vegetation remains to be clarified. An understanding of the
underlying processes is important for effectively using
vegetation condition as an indicator of water quality
protection and for accurately gauging prospects for water
quality improvement through restoration of permanent
vegetation.
Dosskey, MG,
Helmers, MJ, Eisenhauer, DE. 2008. A design aid for
determining width of filter strips. JOURNAL OF SOIL AND WATER
CONSERVATION, 63 (4): 232-241.
Abstract: Watershed planners need a tool for
determining width of filter strips that is accurate enough
for developing cost-effective site designs and easy enough
to use for making quick determinations on a large number and
variety of sites. This study employed the process-based
Vegetative Filter Strip Model to evaluate the relationship
between filter strip width and trapping efficiency for
sediment and water and to produce a design aid for use where
specific water quality targets must be met. Model
simulations illustrate that relatively narrow filter strips
can have high impact in some situations, while in others
even a modest impact cannot be achieved at any practical
width. A graphical design aid was developed for estimating
the width needed to achieve target trapping efficiencies for
different pollutants under a broad range of agricultural
site conditions. Using the model simulations for sediment
and water, a graph was produced containing a family of seven
lines that divide the full range of possible relationships
between width and trapping efficiency into fairly even
increments. Simple rules guide the selection of one line
that best describes a given field situation by considering
field length and cover management, slope, and soil texture.
Relationships for sediment-bound and dissolved pollutants
are interpreted from the modeled relationships for sediment
and water. Interpolation between lines can refine the
results and account for additional variables, if needed. The
design aid is easy to use, accounts for several major
variables that determine filter strip performance, and is
based on a validated, process-based, mathematical model.
This design aid strikes a balance between accuracy and
utility that fills a wide gap between existing design guides
and mathematical models.
Ficetola, GF,
Padoa-Schioppa, E., De Bernardi, F. 2009. Influence of
Landscape Elements in Riparian Buffers on the Conservation of Semiaquatic Amphibians. CONSERVATION BIOLOGY, 23 (1): 114-123.
Abstract:
Studies on riparian buffers have usually focused on the amount
of land needed as habitat for the terrestrial life stages of
semiaquatic species. Nevertheless, the landscape surrounding
wetlands is also important for other key processes, such as
dispersal and the dynamics of metapopulations. Multiple
elements that influence these processes should therefore be
considered in the delineation of buffers. We analyzed
landscape elements (forest cover, density of roads, and
hydrographic network) in concentric buffers to evaluate the
scale at which they influence stream amphibians in 77 distinct
landscapes. To evaluate whether our results could be
generalized to other contexts, we determined whether they were
consistent across the study areas. Amphibians required buffers
of 100–400 m of suitable terrestrial habitat, but
interspecific differences in the amount of habitat were large.
The presence of amphibians was related to roads and the
hydrographic network at larger spatial scales (300–1500 m),
which suggests that wider buffers are needed with these
elements. This pattern probably arose because these elements
influence dispersal and metapopulation persistence, processes
that occur at large spatial scales. Furthermore, in some
cases, analyses performed on different sets of landscapes
provided different results, which suggests caution should be
used when conservation recommendations are applied to
disparate areas. Establishment of riparian buffers should not
be focused only on riparian habitat, but should take a
landscape perspective because semiaquatic species use multiple
elements for different functions. This
approach can be complex because different landscape elements
require different spatial extents. Nevertheless, a shift of
attention toward the management of different elements at
multiple spatial scales is necessary for the long-term
persistence of populations.
Ghermandi, A
et al. 2009. Model-based assessment of shading effect by
riparian vegetation on river water quality. ECOLOGICAL
ENGINEERING, 35 (1): 92-104.
Abstract:
Shading by riparian vegetation affects incident solar
radiation and water temperature in small- and moderate-size
streams, and is thus an important component in the influence
of forested riparian buffers on streams. The water quality
effects of riparian shading are largely unknown. A simulation
study was carried out to evaluate the effect of shading on six
water quality variables in a moderate-size Belgian river
stretch. A dynamic modelling approach making use of the River
Water Quality Model No. 1 was chosen to represent the system.
The scenarios developed indicate that shading may be an
effective tool in controlling stream eutrophication (44%
reduction in phytoplankton productivity in the simulated
stretch) but has a limited effect on dissolved oxygen,
chemical oxygen demand, nitrates, ammonium nitrogen, and
phosphates. Results suggest that shading can effectively be
implemented as a direct management strategy to improve water
quality conditions in small and moderate-size watercourses
that are exposed to excessive algal growth during summer
periods.
Gorsevski,
PV, et al. 2008. Dynamic riparian buffer widths from potential
non-point source pollution areas in forested watersheds. FOREST ECOLOGY AND MANAGEMENT, 256 (4): 664-673.
Abstract:
Efforts to manage National Forests in the USA for wood
production, while protecting water quality, are currently
constrained by models that do not address the temporal
dynamics of variable non-point source (NPS) areas. NPS areas
are diffuse sources of contaminants contributed mostly by
runoff as a result of different land use activities. Riparian
vegetative buffers are often used to control contaminants from
NPS areas but defining suitable widths require different
policy considerations. In this study, the approach for
defining suitable buffer widths is to apply a distributed
process-based model that predicts potential NPS areas prone to
generating runoff in relation to overland flow distances. A
case study of the concept was applied to the 72 km2 Pete King
watershed located in the Clearwater National Forest (CNF) in
central Idaho, USA. This grid modeling approach is based on a
Geographic Information System (GIS) and it integrates the soil
moisture routing (SMR) model with probabilistic analysis. The
SMR model is a daily water balance model that simulates the
hydrology of forested watersheds using real or stochastically
generated climate data, a digital elevation model, soil, and
land use data. The probabilistic analysis incorporates the
variability of soil depth and accounts for uncertainties
associated with the prediction of NPS areas using Monte Carlo
simulation. A 1-year simulation for the case study location
was performed to examine the spatial and temporal changes in
NPS areas prone to generating runoff. The results of the
simulation indicate that the seasonal variability of saturated
areas determines the spatial dynamics of the potential NPS
pollution. Use of this model for the design of riparian buffer
widths would increase the effectiveness of decision-making in
forest management and planning by mapping or delineating NPS
areas likely to transport contaminants to perennial surface
water bodies.
Hairston-Strang, A. 2010. Assessing forest buffer functions
after five years : final report. Maryland Department of
Natural Resources, Forest Service. Available online at
http://www.dnr.state.md.us/irc/docs/00016298.pdf
Hazlett, P
et al. 2008. The importance of catchment slope to soil water N
and C concentrations in riparian zones: implications for
riparian buffer width. CANADIAN JOURNAL OF FOREST RESEARCH, 38
(1): 16-30.
Abstract:
Buffer zones are an important component of forest-management
strategies and are thought to reduce the impact of nutrients
released after harvesting on water quality. Conceptually,
steep slopes have shorter water residence times than shallow
slopes, have a reduced capacity to moderate water quality, and
therefore, require wider buffers. Carbon and N concentrations
in riparian zone shallow soil water at 30 cm depth and lake
water were measured on shallow and steep slopes at the Esker
Lakes Research Area in northeastern Ontario to determine if
nutrient concentrations were correlated to catchment terrain
attributes. Field measured slope, slope class obtained from a
triangular irregular network model, and upslope contributing
area and topographic index calculated from a digital elevation
model were calculated for each sampling location. Modeled
terrain properties, including those currently used during
forest-management planning, were not significantly correlated
with soil water N and C concentrations, whereas only dissolved
organic carbon levels were significantly greater on field
measured steep slopes. Forest species composition and soil N
levels were positively correlated with soil water N
concentrations. These results from the undisturbed boreal
ecosystem highlight the potential limitation of using only
catchment slope as a tool for prescribing riparian buffers
during harvesting when considering terrestrial nutrient
export.
Horwitz, RJ
et al. 2008. Effects of riparian vegetation and watershed
urbanization on fishes in streams of the mid-Atlantic piedmont
(USA). JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, 44
(3): 724-741.
Abstract:
The joint influences of riparian vegetation and urbanization
on fish assemblages were analyzed by depletion sampling in
paired forested and nonforested reaches of 25 small streams
along an urbanization gradient. Nonforested reaches were
narrower than their forested counterparts, so densities based
on surface area differ from linear densities (based on reach
length). Linear densities (based on number or biomass of fish)
of American eel, white sucker and tesselated darter, and the
proportion of biomass of benthic invertivores were
significantly higher in nonforested reaches, while linear
densities of margined madtom and the number of pool species
were significantly higher in forested reaches. Observed
riparian effects may reflect differences in habitat and algal
productivity between forested and nonforested reaches. These
results suggest that relatively small-scale riparian
restoration projects can affect local geomorphology and the
abundance of fish. Dense vegetative cover in riparian zones
and similar or analogous habitats in both forested and
nonforested reaches, the relatively small scale of the
nonforested reaches, and the low statistical power to detect
differences in abundance of rare species may have limited the
observed differences between forested and nonforested reaches.
There was a strong urbanization gradient, with reductions of
intolerant species and increases of tolerant species and
omnivores with increasing urbanization. Interactions between
riparian vegetation type and urbanization were found for
blacknose dace, creek chub, tesselated darter, and the
proportion of biomass of lithophilic spawners. The study did
not provide consistent support for the hypotheses that
responses of fish to riparian vegetation would be overwhelmed
by urban degradation or insignificant at low urbanization.
Hunt, PG,
Matheny, TA, Ro, KS. 2007. Nitrous oxide accumulation in soils
from riparian buffers of a coastal plain
watershed-carbon/nitrogen ratio control. JOURNAL OF
ENVIRONMENTAL QUALITY, 36 (5): 1368-1376.
Abstract: Riparian buffers are used throughout the world
for the protection of water bodies from nonpoint-source
nitrogen pollution. Few studies of riparian or treatment
wetland denitrification consider the production of nitrous
oxide (N2O). The objectives of this research were to
ascertain the level of potential N2O production in riparian
buffers and identify controlling factors for N2O
accumulations within riparian soils of an agricultural
watershed in the southeastern Coastal Plain of the USA. Soil
samples were obtained from ten sites (site types) with
different agronomic management and landscape position.
Denitrification enzyme activity (DEA) was measured by the
acetylene inhibition method. Nitrous oxide accumulations
were measured after incubation with and without acetylene
(baseline N2O production). The mean DEA (with acetylene) was
59 microg N2O-N kg(-1) soil h(-1) for all soil samples from
the watershed. If no acetylene was added to block conversion
of N2O to N2, only 15 microg N2O-N kg(-1) soil h(-1) were
accumulated. Half of the samples accumulated no N2O. The
highest level of denitrification was found in the soil
surface layers and in buffers impacted by either livestock
waste or nitrogen from legume production. Nitrous oxide
accumulations (with acetylene inhibition) were correlated to
soil nitrogen (r2=0.59). Without acetylene inhibition,
correlations with soil and site characteristics were lower.
Nitrous oxide accumulations were found to be essentially
zero, if the soil C/N ratios>25. Soil C/N ratios may be an
easily measured and widely applicable parameter for
identification of potential hot spots of N2O productions
from riparian buffers.
Kline, M,
Cahoon, B. 2010. Protecting River Corridors in Vermont.
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, 46 (2):
227-236.
The Vermont
Agency of Natural Resources' current strategy for restoring
aquatic habitat, water quality, and riparian ecosystem
services is the protection of fluvial geomorphic-based river
corridors and associated wetland and floodplain attributes and
functions. Vermont has assessed over 1,350 miles of stream
channels to determine how natural processes have been modified
by channel management activities, corridor encroachments, and
land use/land cover changes. Nearly three quarters of Vermont
field-assessed reaches are incised limiting access to
floodplains and thus reducing important ecosystem services
such as flood and erosion hazard mitigation, sediment storage,
and nutrient uptake. River corridor planning is conducted with
geomorphic data to identify opportunities and constraints to
mitigating the effects of physical stressors. Corridors are
sized based on the meander belt width and assigned a
sensitivity rating based on the likelihood of channel
adjustment due to stressors. The approach adopted by Vermont
is fundamentally based on restoring fluvial processes
associated with dynamic equilibrium, and associated habitat
features. Managing toward fluvial equilibrium is taking hold
across Vermont through adoption of municipal fluvial erosion
hazard zoning and purchase of river corridor easements, or
local channel and floodplain management rights. These tools
signify a shift away from primarily active management
approaches of varying success that largely worked against
natural river form and process, to a current community-based,
primarily passive approach to accommodate floodplain
reestablishment through fluvial processes.
Knight, KW,
et al. 2010. Ability of Remnant Riparian Forests, With and
Without Grass Filters, to Buffer Concentrated Surface Runoff.
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, 46 (2):
311-322.
Riparian
forest buffers established according to accepted conservation
practice standards have been recommended as one of the most
effective tools for mitigating nonpoint source pollution. The
midwestern United States is characterized by many kilometers
of narrow, naturally occurring forests along streams. However,
little is known about the relative effectiveness of these
remnant forests compared with these newly established buffers.
This study compared the ability of naturally occurring remnant
forests with and without adjacent planted grass filters to
buffer concentrated flow paths (CFPs) originating in crop
fields along first- and second-order streams in three
northeast Missouri watersheds. Remnant forests breached by
runoff through CFPs were narrower than those that dispersed
100% of the CFPs. Remnant forests with adjacent grass buffers
were nearly twice the width as those without grass filters. We
also found that CFPs, which developed within remnant forests
and at the base of in-field grass waterways, were potential
sources of sediments to streams. Methods to mitigate these
CFPs warrant further investigation. Our study suggests that
although these natural remnant forests provide substantial
buffering capacity, both improved management and/or the
addition of an adjacent grass filter would improve water
quality by reducing sediment loss to streams. Inferences can
be used to inform the design and management of similar
conservation buffer systems within the region.
Liu, XM,
Mang, XY, Zhang, MH. 2008. Major factors influencing the
efficacy of vegetated buffers on sediment trapping: A review
and analysis. JOURNAL OF ENVIRONMENTAL QUALITY, 37 (5):
1667-1674.
Abstract:
Sediment is a major agricultural pollutant threatening water
quality. Vegetated buffers, including vegetative filter
strips, riparian buffers, and grassed waterways, are best
management practices (BMPs) installed in many areas to filter
sediments from tailwaters, and deter sediment transport to
water bodies. Along with reducing sediment transport, the
filters also help trap sediment bound nutrients and
pesticides. The objectives of this study were: (i) to review
vegetated buffer efficacy on sediment trapping, and (ii) to
develop statistical models to investigate the major factors
influencing sediment trapping. A range of sediment trapping
efficacies was found in a review of over 80 representative BMP
experiments. A synthesis of the literature regarding the
effects of vegetated buffers on sediment trapping is needed.
The meta-analysis results based on the limited data showed
that buffer width and slope are two major factors influencing
BMPs efficacy of vegetated buffers on sediment trapping.
Regardless of the area ratio of buffer to agricultural field,
a 10 m buffer and a 9% slope optimized the sediment trapping
capability of vegetated buffers.
Liu, Y,
Yang, W, Wang, X. 2007. GIS-based integration of SWAT and REMM
for estimating water quality benefits of riparian buffers in
agricultural watersheds. TRANSACTIONS OF THE ASABE, 50 (5):
1549-1563.
Abstract: The Soil and Water Assessment Tool (SWAT) is a
process-based, watershed-scale model with a hydrologic
response unit (HRU) as the basic computation element, which
makes it difficult to accurately represent riparian buffers
using their physical parameters (e.g., vegetation
structure). On the other hand, the field-scale Riparian
Ecosystem Management Model (REMM) provides the opportunity
to consider details of hydrologic processes within a
riparian buffer zone. However, the runoff and its associated
constituents from the upland area that is hydraulically
connected to the riparian buffer zone must be provided as
inputs into REMM. The rationale proposed here is that the
integration of SWAT and REMM would improve the assessment of
riparian buffers, which is vital to watershed management but
which has not been described in the literature. The
objective of this study was to develop a GIS interface that
integrated SWAT and REMM for estimating water quality
benefits of riparian buffers in agricultural watersheds. For
modeling purposes, the interface subdivided a watershed into
a number of sub-basins, each of which was further subdivided
into drainage areas of isolated impoundments (e.g.,
wetlands), concentrated flow, and riparian buffers using
available GIS data. As a result, riparian buffers received
runoff and associated pollutants from corresponding
contribution areas to mimic actual field conditions. The
interface facilitated transferring the SWAT outputs into
REMM and computing the site characteristic parameters (e.g.,
length and width) of the riparian buffers. The outputs from
subsequent REMM runs were in turn taken as inputs into SWAT
for channel routing and further simulation. The interface
was used to assess water quality benefits of riparian
buffers in the Lower Canagagigue Creek watershed located in
southern Ontario, Canada. The results indicated that the
existing riparian buffer system achieved a 27.9% abatement
in sediment and a 37.4% reduction in total phosphorus. The
model runs demonstrated that the GIS interface was easy to
use and could serve as a protocol for integrating models
with distinctly different spatial scales.
Madden, SS,
Robinson, GR, Arnason, JG. 2007. Spatial variation in
stream water quality in relation to riparian buffer dimensions
in a rural watershed of eastern New York state. NORTHEASTERN
NATURALIST, 14 (4): 605-618.
Abstract: Studies of forested rural
watersheds provide estimates of background contamination for
comparison with streams and rivers in other settings. We
performed a landscape analysis and measured major dissolved
ions and benthic macroinvertebrates for a small rural
watershed in Albany County, NY, to determine spatial
variation in water quality. An estimated 73% of the surface
cover is post-agricultural forest, with only 2.3% of the
watershed covered by roads and other impervious surfaces.
Although water quality was consistently high in most of the
creek, we detected three relatively distinct zones separated
by impoundments; zonation was most apparent in relative
concentrations of major ions, less so with benthic
macroinvertebrate community similarity. At ten sample
stations, buffer size, measured as upstream land cover and
distance to nearest road, did not correlate well with
chemical water quality indicators. In particular, we found
the highest levels of chloride, indicative of road-salt
contamination, in areas of maximum forest buffer. Small
feeder creeks that drain nearby roads may function as
“leaks” in otherwise well-buffered watersheds with low road
densities.
Mankin, KR
et al. 2007. Grass-shrub riparian buffer removal of sediment,
phosphorus, and nitrogen from simulated runoff. JOURNAL OF
THE AMERICAN WATER RESOURCES ASSOCIATION, 43 (5): 1108-1116.
Abstract:
Riparian buffer forests and vegetative filter strips are
widely recommended for improving surface water quality, but
grass-shrub riparian buffer system (RBSs) are less well
studied. The objective of this study was to assess the
influence of buffer width and vegetation type on the key
processes and overall reductions of total suspended solids (TSS),
phosphorus (P), and nitrogen (N) from simulated runoff passed
through established (7-year old) RBSs. Nine 1-m RBS plots,
with three replicates of three vegetation types (all natural
selection grasses, two-segment buffer with native grasses and
plum shrub, and two-segment buffer with natural selection
grasses and plum shrub) and widths ranging from 8.3 to 16.1 m,
received simulated runoff having 4,433 mg/1 TSS from on-site
soil, 1.6 mg/1 total P, and 20 mg/1 total N. Flow-weighted
samples were collected by using Runoff Sampling System (ROSS)
units. The buffers were very efficient in removal of
sediments, N, and P, with removal efficiencies strongly linked
to infiltration. Mass and concentration reductions averaged
99.7% and 97.9% for TSS, 91.8% and 42.9% for total P, and
92.1% and 44.4% for total N. Infiltration alone could account
for >75% of TSS removal, >90% of total P removal, and >90% of
total N removal. Vegetation type induced significant
differences in removal of TSS, total P, and total N. These
results demonstrate that adequately designed and implemented
grass-shrub buffers with widths of only 8 m provide for water
quality improvement, particularly if adequate infiltration is
achieved.
Marczak,
Laurie B., Takashi Sakamaki, Shannon L. Turvey, Isabelle
Deguise, Sylvia L. R. Wood, John S. Richardson. 2010.
Are forested buffers an effective conservation strategy for
riparian fauna? An assessment using meta-analysis. Ecological
Applications. 20(1): 126-134.
Abstract:
Historically, forested riparian buffers have been created to
provide protection for aquatic organisms and aquatic ecosystem
functions. Increasingly, new and existing riparian buffers are
being used also to meet terrestrial conservation requirements.
To test the effectiveness of riparian buffers for conserving
terrestrial fauna, we conducted a meta-analysis using
published data from 397 comparisons of species abundance in
riparian buffers and unharvested (reference) riparian sites.
The response of terrestrial species to riparian buffers was
not consistent between taxonomic groups; bird and arthropod
abundances were significantly greater in buffers relative to
unharvested areas, whereas amphibian abundance decreased.
Edge-preferring species were more abundant in buffer sites
than reference sites, whereas species associated with interior
habitat were not significantly different in abundance. The
degree of buffer effect on animal abundance was unrelated to
buffer width; wider buffers did not result in greater
similarity between reference and buffer sites. However,
responses to buffer treatment were more variable in buffers
<50 m wide, a commonly prescribed width in many management
plans. Our results indicate that current buffer prescriptions
do not maintain most terrestrial organisms in buffer strips at
levels comparable to undisturbed sites.
Mayer, P.M.,
S.K. Reynolds, M.D. McCutchen, and T.J. Canfield. Riparian
buffer width, vegetative cover, and nitrogen removal
effectiveness: A review of current science and regulations.
EPA/600/R-05/118. Cincinnati, OH, U.S. Environmental
Protection Agency, 2006.
Available online.
Riparian
zones, the vegetated region adjacent to streams and wetlands,
are thought to be effective at intercepting and controlling
nitrogen loads entering water bodies. Buffer width may be
positively related to nitrogen removal effectiveness by
influencing nitrogen retention through plant sequestration or
removal through microbial denitrification. We surveyed
peer-reviewed scientific literature containing data on
riparian buffers and nitrogen concentration in streams and
groundwater of riparian zones to identify causation and trends
in the relationship between buffer width and nitrogen removal
capacity. We also examined Federal and State regulations
regarding riparian buffer widths to determine if such
legislation reflects the current scientific understanding of
buffer effectiveness. Nitrogen removal effectiveness varied
widely among riparian zones studied. Subsurface removal of
nitrogen was efficient but did not appear to be related to
buffer width. Surface removal of nitrogen was partly related
to buffer width and was generally inefficient, removing only a
small fraction of the total nitrogen flowing through soil
surface layers. While some narrow buffers (1-15 m) removed
significant proportions of nitrogen, narrow buffers actually
contributed to nitrogen loads in riparian zones in some cases.
Wider buffers (>50 m) more consistently removed significant
portions of nitrogen entering a riparian zone. Buffers of
various vegetation types were equally effective at removing
nitrogen in the subsurface but not in surface flow. The
general lack of vegetation type or buffer width effects on
nitrogen removal, especially in the subsurface, suggests that
soil type, watershed hydrology (e.g., soil saturation,
groundwater flow paths, etc.), and subsurface biogeochemistry
(organic carbon supply, high nitrate inputs) may be more
important factors dictating nitrogen concentrations due to
their influence on denitrification. State and Federal
guidelines for buffer width also varied widely but were
generally consistent with the peer-reviewed literature on
effective buffer width, recommending or mandating buffers
~7-100 m wide. Proper design, placement, and protection of
buffers are critical to buffer effectiveness. To maintain
maximum effectiveness, buffer integrity should be protected
against soil compaction, loss of vegetation, and stream
incision. Maintaining buffers around stream headwaters will
likely be most effective at maintaining overall watershed
water quality while restoring degraded riparian zones, and
stream channels may improve nitrogen removal capacity.
Riparian buffers are a “best management practice” (BMP) that
should be used in conjunction with a comprehensive watershed
management plan that includes control and reduction of point
and non-point sources of nitrogen from atmospheric,
terrestrial, and aquatic inputs.
McCarty, GW
et al. 2008. Water quality and conservation practice effects
in the Choptank River watershed. JOURNAL OF SOIL AND WATER
CONSERVATION, 63 (6): 461-474.
Abstract:
The Choptank River is an estuary, tributary of the Chesapeake
Bay, and an ecosystem in decline due partly to excessive
nutrient and sediment loads from agriculture. The Conservation
Effects Assessment Project for the Choptank River watershed
was established to evaluate the effectiveness of conservation
practices on water quality within this watershed. Several
measurement frameworks are being used to assess conservation
practices. Nutrients (nitrogen and phosphorus) and herbicides
(atrazine and metolachlor) are monitored within 15 small,
agricultural subwatersheds and periodically in the lower
portions of the river estuary. Initial results indicate that
land use within these subwatersheds is a major determinant of
nutrient concentration in streams. In addition, the 18O
isotope signature of nitrate was used to provide a landscape
assessment of denitrification processes in the presence of the
variable land use. Herbicide concentrations were not
correlated to land use, suggesting that herbicide delivery to
the streams is influenced by other factors and/or processes.
Remote sensing technologies have been used to scale point
measurements of best management practice effectiveness from
field to subwatershed and watershed scales. Optical satellite
(SPOT-5) data and ground-level measurements have been shown to
be effective for monitoring nutrient uptake by winter cover
crops in fields with a wide range of management practices.
Synthetic Aperture Radar (RADARSAT-1) data have been shown to
detect and to characterize accurately the hydrology (hydroperiod)
of forested wetlands at landscape and watershed scales. These
multiple approaches are providing actual data for assessment
of conservation practices and to help producers, natural
resource managers, and policy makers maintain agricultural
production while protecting this unique estuary.
McIlroy, SK
et al. 2008. Identifying Linkages Between Land Use,
Geomorphology, and Aquatic Habitat in a Mixed-Use Watershed.
ENVIRONMENTAL MANAGEMENT, 42 (5): 867-876.
Abstract:
The potential impacts of land use on large woody debris (LWD)
were examined in Sourdough Creek Watershed, a rapidly growing
area encompassing Bozeman, Montana, USA. We identified six
land classes within a 250 m buffer extending on either side of
Sourdough Creek and assessed aquatic habitat and
geomorphologic variables within each class. All LWD pieces
were counted, and we examined 14 other variables, including
undercut bank, sinuosity, and substrate composition. LWD
numbers were generally low and ranged from 0 to 8.2 pieces per
50 m of stream. Linear regression showed that LWD increased
with distance from headwaters, riparian forest width, and
sinuosity in four of the six land classes. Statistically
significant differences between land classes for many aquatic
habitat and geomorphologic variables indicated the impacts of
different land uses on stream structure. We also found that
practices such as active wood removal played a key role in LWD
abundance. This finding suggests that managers should
prioritize public education and outreach concerning the
importance of in-stream wood, especially in mixed-use
watersheds where wood is removed for either aesthetic reasons
or to prevent stream flooding.
Newbold, JD
et al. 2010. Water Quality Functions of a 15-Year-Old
Riparian Forest Buffer System. JOURNAL OF THE AMERICAN
WATER RESOURCES ASSOCIATION, 46 (2): 299-310.
We monitored
long-term water quality responses to the implementation of a
three-zone Riparian Forest Buffer System (RFBS) in
southeastern Pennsylvania. The RFBS, established in 1992 in a
15-ha agricultural (row crop) watershed, consists of: Zone 1,
a streamside strip (similar to 10 m wide) of permanent woody
vegetation for stream habitat protection; Zone 2, an 18- to
20-m-wide strip reforested in hardwoods upslope from Zone 2;
and Zone 3, a 6- to 10-m-wide grass filter strip in which a
level lip spreader was constructed. The monitoring design used
paired watersheds supplemented by mass balance estimates of
nutrient and sediment removal within the treated watershed.
Tree growth was initially delayed by drought and deer damage,
but increased after more aggressive deer protection (1.5 m
polypropylene shelters or wire mesh protectors) was
instituted. Basal tree area increased similar to 20-fold
between 1998 and 2006, and canopy cover reached 59% in 2006.
For streamwater nitrate, the paired watershed comparison was
complicated by variations in both the reference stream
concentrations and in upslope groundwater nitrate
concentrations, but did show that streamwater nitrate
concentrations in the RFBS watershed declined relative to the
reference stream from 2002 through the end of the study in
early 2007. A subsurface nitrate budget yielded an average
nitrate removal by the RFBS of 90 kg/ha/year, or 26% of
upslope subsurface inputs, for the years 1997 through 2006.
There was no evidence from the paired watershed comparison
that the RFBS affected streamwater phosphorus concentration.
However, groundwater phosphorus did decline within the buffer.
Overland flow sampling of 23 storms between 1997 and 2006
showed that total suspended solids concentration in water
exiting the RFBS to the stream was on average 43% lower than
in water entering the RFBS from the tilled field. Particulate
phosphorus concentration was lower by 22%, but this removal
was balanced by a 26% increase in soluble reactive phosphorus
so that there was no net effect on total phosphorus.
Shandas, V
and Alberti, M. 2009. Exploring the role of vegetation
fragmentation on aquatic conditions: Linking upland with
riparian areas in Puget Sound lowland streams. LANDSCAPE
AND URBAN PLANNING, 90 (1-2): 66-75.
Abstract: A
controversial issue in managing urbanizing watersheds is
determining the scale at which conservation measures should be
implemented. Current “best practices” suggest establishing
riparian buffers along stream corridors and limiting
impervious surfaces to prevent degradation of instream
biological conditions. While there is increasing evidence that
the amount of land covers (e.g., impervious surface,
vegetation) has an impact on instream aquatic conditions, the
effect of upland vegetation fragmentation on aquatic
conditions requires further study. By using landscape metrics
to quantity vegetation amount and distribution at the riparian
and watershed scales, and a macroinvertebrate index to
describe aquatic conditions, this study presents empirical
evidence about the interactions between riparian and upland
vegetation as they affect instream biological condition of 51
nested watersheds in the Puget Sound lowland. We ask if the
fragmentation of vegetation within a watershed helps predict
instream biological condition. In addition, we hypothesize
that the fragmentation of vegetation at the riparian and
watershed scales affects instream biological condition. Using
parametric and non-parametric statistical analyses to test
relationships, our findings suggest that the fragmentation of
upland vegetation and the total amount of riparian vegetation
explain the greatest amount of variation in aquatic
conditions. These results help frame a management approach for
conserving upland areas of vegetation through the use of land
use planning techniques.
Smith, TA, Osmond, DL, Gilliam, JW. 2006.
Riparian buffer width and nitrate removal in a lagoon-effluent
irrigated agricultural area. JOURNAL OF SOIL AND WATER
CONSERVATION, 61 (5): 273-281.
Abstract: The ideal buffer width required
to maximize water quality benefits while minimizing
unnecessary land utilization is difficult to determine. This
study examined the effect of increasing buffer width on
nitrate (NO3-N) reduction in shallow groundwater in the middle
Coastal Plain of North Carolina. The study site was a
streamside buffer zone where previous research determined the
buffer did not sufficiently reduce NO3-N discharge to stream
water. Buffer width was increased from 9 to 30 m (30 to 98 ft)
by fencing out cattle and allowing volunteer vegetation to
emerge, thus forming a grass and shrub buffer along the newly
widened area. Buffer functions were assessed by comparing
groundwater NO3-N concentrations from this new system with the
same area prior to widening. A significant increase in percent
NO3-N reduction was observed in shallow (0.8 to 1.2 m; 2.6 to
4.0 ft) groundwater on the east (34.7 percent to 95.0 percent;
p = 0.02) side of stream, most likely due to an increase (p =
0.01) in dissolved organic carbon (C) at this depth. Reduction
at the 30-m (98-ft) width in shallow groundwater at the west
side of stream was measured at 93.3 percent, although this was
not a statistically significant increase from the 9-m (30-ft)
width (53.1 percent; p = 0.2). Percent NO3-N reduction was
less efficient in deep (2.4 to 4.5 m; 7.9 to 14.5 ft)
groundwater, although a significant increase (-37.8 percent to
39.2 percent; p = 0.003) at the east side of stream was
observed. Reduction on the west side at this depth
significantly decreased (19.5 percent to -5.1 percent; p =
0.05) suggesting that the deeper confining layer along this
side of stream allowed groundwater to bypass the zone of high
dissolved organic C enhanced by riparian vegetation, thus
minimizing the effects of buffer widening in this area. Stream
sampling indicated no significant difference in upstream and
downstream NO3-N between the two buffer widths (p = 0.61).
Although increasing the buffer width did improve reduction in
some areas, the severity of the groundwater NO3-N situation at
this site was not completely resolved by increasing the buffer
width to 30 m (98 ft).
Speiran, GK.
2010. Effects of Groundwater-Flow Paths On Nitrate
Concentrations Across Two Riparian Forest Corridors.
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, 46 (2):
246-260.
Groundwater
levels, apparent age, and chemistry from field sites and
groundwater-flow modeling of hypothetical aquifers
collectively indicate that groundwater-flow paths contribute
to differences in nitrate concentrations across riparian
corridors. At sites in Virginia (one coastal and one
Piedmont), lowland forested wetlands separate upland fields
from nearby surface waters (an estuary and a stream). At the
coastal site, nitrate concentrations near the water table
decreased from more than 10 mg/l beneath fields to 2 mg/l
beneath a riparian forest buffer because recharge through the
buffer forced water with concentrations greater than 5 mg/l to
flow deeper beneath the buffer. Diurnal changes in groundwater
levels up to 0.25 meters at the coastal site reflect flow from
the water table into unsaturated soil where roots remove water
and nitrate dissolved in it. Decreases in aquifer thickness
caused by declines in the water table and decreases in
horizontal hydraulic gradients from the uplands to the
wetlands indicate that more than 95% of the groundwater
discharged to the wetlands. Such discharge through organic
soil can reduce nitrate concentrations by denitrification.
Model simulations are consistent with field results, showing
downward flow approaching toe slopes and surface waters to
which groundwater discharges. These effects show the
importance of buffer placement over use of fixed-width,
streamside buffers to control nitrate concentrations.
Stutter, MI,
Langan, SJ, Lumsdon, DG. 2009. Vegetated Buffer Strips Can
Lead to Increased Release of Phosphorus to Waters: A
Biogeochemical Assessment of the Mechanisms. ENVIRONMENTAL
SCIENCE & TECHNOLOGY, 43 (6): 1858-1863.
Abstract:
Establishing vegetated buffer strips (VBS) between cropland
and watercourses is currently promoted as a principal control
of diffuse pollution transport. However, we lack the
mechanistic understanding to evaluate P retention in VBS and
predict risks of P transport to aquatic ecosystems. We
observed that VBS establishment led to enhanced rates of soil
P cycling, increasing soil P solubility and the potential
amount leached to watercourses. Soil in VBS, relative to
adjacent fields, had increased inorganic P solubility indices,
dissolved organic P, phosphatase enzyme activity, microbial
diversity, and biomass P. Small relative increases in the pool
of soil P rendered labile had disproportionate effects on the
P available for leaching. We propose a mechanism whereby the
establishment of VBS on previous agricultural land causes a
diversifying plant-microbial system which can access previous
immobilized soil P from past fertilization or trapped sediment
P. Laboratory experiments suggested that sediment-P inputs to
VBS were insufficient alone to increase P solubility without
biological cycling. Results show that VBS management may
require strategies, for example, harvesting vegetation, to
offset biochemical processes that can increase the
susceptibility of VBS soil P to move to adjoining streams.
Sutton, AJ, Fisher, TR, Gustafson, AB.
2010. Effects of Restored Stream Buffers on Water Quality
in Non-tidal Streams in the Choptank River Basin. WATER
AIR AND SOIL POLLUTION, 208 (1-4): 101-118.
Restoration of riparian buffers is an
important component of nutrient reduction strategies in the
Chesapeake Bay watershed. In 1998, Maryland adopted a
Conservation Reserve Enhancement Program (CREP), which
provides financial incentives to take agricultural land out of
production to plant streamside vegetation. Between 1998 and
2005, 1-30% of streamside vegetation (average = 11%), was
restored to forest or managed grass in 15 agriculturally
dominated sub-basins in the Choptank River basin, a tributary
of Chesapeake Bay. Pre-existing forested buffers represented
10-48% of the streamside (average = 33%), for a total of
12-61% buffered streamsides (average = 44%). Using multi-year
water quality data collected before and after CREP
implementation (1986, 2003-2006), we were unable to detect
significant effects of CREP on baseflow nutrient
concentrations based on the area of restored buffer, the
percentage of restored streamside, or the percentage of total
riparian buffer in the sub-basins (p > 0.05). Although CREP
increased the average buffered streamside from 33% in the
1990s to 44% by 2005, N and P concentrations have not changed
or have increased in some streams over the last 20 years.
Reductions may not have occurred for the following reasons:
(1) buffer age, width, and connectivity (gaps) between buffers
are also important to nutrient reductions; (2) agricultural
nutrient inputs may have increased during this period; and (3)
riparian buffer restoration was not extensive enough by 2005
to have measurable affects on the stream water quality in
these sub-basins. Significant effects of CREP may yet be
resolved as the current CREP buffers mature; however, water
quality data through 2006 in the Choptank basin do not yet
show any significant effects.
Tomer, MD et al. 2009. Methods to
prioritize placement of riparian buffers for improved water
quality. AGROFORESTRY SYSTEMS, 75 (1): 17-25.
Abstract: Agroforestry buffers in
riparian zones can improve stream water quality, provided they
intercept and remove contaminants from surface runoff and/or
shallow groundwater. Soils, topography, surficial geology, and
hydrology determine the capability of forest buffers to
intercept and treat these flows. This paper describes two
landscape analysis techniques for identifying and mapping
locations where agroforestry buffers can effectively improve
water quality. One technique employs soil survey information
to rank soil map units for how effectively a buffer, when
sited on them, would trap sediment from adjacent cropped
fields. Results allow soil map units to be compared for
relative effectiveness of buffers for improving water quality
and, thereby, to prioritize locations for buffer
establishment. A second technique uses topographic and
streamflow information to help identify locations where
buffers are most likely to intercept water moving towards
streams. For example, the topographic wetness index, an
indicator of potential soil saturation on given terrain,
identifies where buffers can readily intercept surface runoff
and/or shallow groundwater flows. Maps based on this index can
be useful for site-specific buffer placement at farm and
small-watershed scales. A case study utilizing this technique
shows that riparian forests likely have the greatest potential
to improve water quality along first-order streams, rather
than larger streams. The two methods are complementary and
could be combined, pending the outcome of future research.
Both approaches also use data that are publicly available in
the US. The information can guide projects and programs at
scales ranging from farm-scale planning to regional policy
implementation.
Vidon, P. et al. 2010. Hot Spots and
Hot Moments in Riparian Zones: Potential for Improved Water
Quality Management. JOURNAL OF THE AMERICAN WATER
RESOURCES ASSOCIATION, 46 (2): 278-298.
Biogeochemical and hydrological processes
in riparian zones regulate contaminant movement to receiving
waters and often mitigate the impact of upland sources of
contaminants on water quality. These heterogeneous processes
have recently been conceptualized as "hot spots and moments"
of retention, degradation, or production. Nevertheless,
studies investigating the importance of hot phenomena (spots
and moments) in riparian zones have thus far largely focused
on nitrogen (N) despite compelling evidence that a variety of
elements, chemicals, and particulate contaminant cycles are
subject to the influence of both biogeochemical and transport
hot spots and moments. In addition to N, this review
summarizes current knowledge for phosphorus, organic matter,
pesticides, and mercury across riparian zones, identifies
variables controlling the occurrence and magnitude of hot
phenomena in riparian zones for these contaminants, and
discusses the implications for riparian zone management of
recognizing the importance of hot phenomena in annual solute
budgets at the watershed scale. Examples are presented to show
that biogeochemical process-driven hot spots and moments occur
along the stream/riparian zone/upland interface for a wide
variety of constituents. A basic understanding of the possible
co-occurrence of hot spots and moments for a variety of
contaminants in riparian systems will increase our
understanding of the influence of riparian zones on water
quality and guide management strategies to enhance nutrient or
pollutant removal at the landscape scale.
Walter, MT et al. 2009. New Paradigm for
Sizing Riparian Buffers to Reduce Risks of Polluted Storm
Water: Practical Synthesis. JOURNAL OF IRRIGATION AND DRAINAGE
ENGINEERING-ASCE, 135 (2): 200-209.
Abstract: Riparian buffers are
commonly promoted to protect stream water quality. A
common conceptual assumption is that buffers “intercept”
and treat upland runoff. As a shift in paradigm, it
is proposed instead that riparian buffers should be
recognized as the parts of the landscape that most
frequently generate storm runoff. Thus, water
quality can be protected from contaminated storm runoff by
disassociating riparian buffers from potentially
polluting activities. This paper reviews and
synthesizes some simple engineering approaches that can be
used to delineate riparian buffers for rural
watersheds based on risk of generating runoff.
Although reference is made to specific future research
that may improve the proposed methods for delineating
riparian buffers, the approaches described here
provide planners and engineers with a set of
currently available scientifically defensible tools. It is
recommended that planners and engineers use
available rainfall and stream discharge data to
parameterize the buffer-sizing equations and use
variable-width buffers, based on a topographic
index, to achieve a realistic representation of
runoff generating areas.
Watson, TK,
et al. 2010. Groundwater Denitrification Capacity of
Riparian Zones in Suburban and Agricultural Watersheds.
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, 46 (2):
237-245.
We evaluated
the relationship of dominant watershed land use to the
structure and nitrogen (N) sink function of riparian zones. We
focused on groundwater denitrification capacity, water table
dynamics, and the presence and pattern of organically enriched
deposits. We used the push-pull method (measurement of
15N-enriched denitrification gases derived from an introduced
groundwater plume of 15N-enriched nitrate) to evaluate
groundwater denitrification capacity on nine forested wetland
riparian sites developed in alluvial or outwash parent
materials in southern New England. Three replicate sites were
located in each of the three watershed types, those with
substantial (1) irrigated agriculture, (2) suburban
development, and (3) forest. Soil morphology and water table
dynamics were assessed at each site. We found significantly
lower mean annual water tables at sites within watersheds with
substantial irrigated agriculture or suburban development than
forested watersheds. Water table dynamics were more variable
at sites within suburban watersheds, especially during the
summer. Groundwater denitrification capacity was significantly
greater at sites within forested watersheds than in watersheds
with substantial irrigated agriculture. Because of the high
degree of variability observed in riparian sites within
suburban watersheds, groundwater denitrification capacity was
not significantly different from either forested or
agricultural watersheds. The highly variable patterns of
organically enriched deposits and water tables at sites within
suburban watersheds suggests that depositional events are
irregular, limiting the predictability of groundwater N
dynamics in these riparian zones. The variability of riparian
N removal in watersheds with extensive suburbia or irrigated
agriculture argues for N management strategies emphasizing
effective N source controls in these settings.
Wilkerson,
E; Hagan, JM; Siegel, D; Whitman, AA. 2006. The effectiveness
of different buffer widths for protecting headwater stream
temperature in Maine. FOREST SCIENCE, 52 (3): 221-231.
Abstract: We
evaluated the effect of timber harvesting on summer water
temperature in first-order headwater streams in western Maine.
Fifteen streams were assigned to one of five treatments: (1)
clearcutting with no stream buffer; (2) clearcutting with
11-m, partially harvested buffers, both sides; (3)
clearcutting with 23-m, partially harvested buffers; (4)
partial cuts with no designated buffer; and (5) unharvested
controls. Over a 3-year period we measured summer water
temperature hourly before and after harvesting, above and
below the harvest zone. Streams without a buffer showed the
greatest increase in mean weekly maximum temperatures
following harvesting (1.4-4.4°C). Streams with an 11-m buffer
showed minor, but not significant, increases (1.0-1.4°C).
Streams with a 23-m buffer, partial-harvest treatment, and
control streams showed no changes following harvest. The mean
weekly maximum temperatures never exceeded the thermal stress
limit for brook trout (25°C) in any treatment group. The mean
daily temperature fluctuations for streams without buffers
increased from 1.5°C/day to 3.8°C/day, while with 11-m buffers
fluctuations increased nonsignificantly by 0.5-0.7°C/day.
Water temperatures 100 m below the harvest zone in the
no-buffer treatment were elevated above preharvest levels. We
concluded that water temperature in small headwater streams is
protected from the effects of clearcutting by an 11-m buffer
(with >60% canopy retention).
Wilkerson,
E, Hagan, JM, Whitman, AA. 2010. The effectiveness of
different buffer widths for protecting water quality and macroinvertebrate and periphyton assemblages of headwater
streams in Maine, USA. Canadian Journal of Fisheries and
Aquatic Sciences 67(1): 177-190.
Abstract: We
evaluated the effect of timber harvesting on water quality and
macroinvertebrate and periphyton assemblages in first-order
streams in Maine, USA. Fifteen streams were assigned to one of
five treatments: clearcutting without a stream buffer,
clearcutting with 11m buffers, clearcutting with 23m buffers,
partial harvesting with no designated buffer, and unharvested
controls. Harvest blocks on both sides of the stream were 6ha
and partial harvesting within buffers was allowed. Specific
conductivity, pH, dissolved oxygen, turbidity, and soluble
reactive phosphorus did not change significantly for 3 years
after harvesting in all treatments. Unbuffered streams had
significantly elevated concentrations of chlorophylla
as well as increased abundance of algal feeding organisms (Diperta
Cricotopus and Diptera Psectrocladius). Streams
with 11m buffers had substantial (10-fold) but nonsignificant
increases in chlorophylla. No other significant changes
were detected in other treatment groups. In all treatment
groups, the dominant taxa (periphyton Achnanthes
minutissimum and macroinvertebrate Chironomidae) are
adapted to disturbed environments. We attribute the limited
harvest-induced changes to lack of soil disturbance within 8m
of the stream, the small (≤40%) proportion of watersheds
harvested, and the resilient nature of aquatic organisms.
However, small-scale changes may not be detected due to the
small sample size, an inherent limitation of field-based
studies.
Woodward, KB et al. 2009. Nitrate
removal, denitrification and nitrous oxide production in the
riparian zone of an ephemeral stream. SOIL BIOLOGY &
BIOCHEMISTRY, 41 (4): 671-680.
Abstract: Riparian zones are important
features of the landscape that can buffer waterways from
non-point sources of nitrogen pollution. Studies of perennial
streams have identified denitrification as one of the dominant
mechanisms by which this can occur. This study aimed to assess
nitrate removal within the riparian zone of an ephemeral
stream and characterise the processes responsible,
particularly denitrification, using both in-situ and
laboratory techniques. To quantify rates of groundwater
nitrate removal and denitrification in-situ, nitrate was added
to two separate injection–capture well networks in a perched
riparian aquifer of a low order ephemeral stream in South East
Queensland, Australia. Both networks also received bromide as
a conservative tracer and one received acetylene to inhibit
the last step of denitrification. An average of 77 ± 2% and 98
± 1% of the added nitrate was removed within a distance of 40
cm from the injection wells (networks with acetylene and
without, respectively). Based on rates of N2O production in
the network with added acetylene, denitrification was not a
major mechanism of nitrate loss, accounting for only 3% of
removal. Reduction of nitrate to ammonium was also not a major
pathway in either network, contributing <4%. Relatively high
concentrations of oxygen in the aquifer following recent
filling by stream water may have reduced the importance of
these two anaerobic pathways. Alternatively, denitrification
may have been underestimated using the in-situ acetylene block
technique. In the laboratory, soils taken from two depths at
each well network were incubated with four nitrate-N
treatments (ranging from ambient concentration to an addition
of 15 mg N l−1), with and without added acetylene. Potential
rates of denitrification, N2O production and N2O:N2 ratios
increased with nitrate additions, particularly in shallow
soils. Potential rates of denitrification observed in the
laboratory were equivalent in magnitude to nitrate removal
measured in the field (mean 0.26 ± 0.12 mg N kg of dry soil−1
d−1), but were two orders of magnitude greater than
denitrification measured in the field with added acetylene.
The relative importance of assimilatory vs. dissimilatory
processes of nitrate removal depends on environmental
conditions in the aquifer, particularly hydrology and its
effects on dissolved oxygen concentrations. Depending on
seasonal conditions, aquifers of ephemeral streams like the
study site are likely to fluctuate between oxic and anoxic
conditions; nevertheless they may still function as effective
buffers. While denitrification to N2 is a desirable outcome
from a management perspective, assimilation into biomass can
provide a rapid sink for nitrate, thus helping to reduce
short-term delivery of nitrate downstream. Longer-term studies
are needed to determine the overall effectiveness of riparian
buffers associated with ephemeral streams in mitigating
nitrate loads reaching downstream ecosystems.
Yamada, T et al. 2007. Groundwater
nitrate following installation of a vegetated riparian buffer.
SCIENCE OF THE TOTAL ENVIRONMENT, 385 (1-3): 297-309.
Abstract: Substantial questions remain
about the time required for groundwater nitrate to be reduced
below 10 mg L− 1 following establishment of vegetated riparian
buffers. The objective of this study was to document changes
in groundwater nitrate–nitrogen (NO3–N) concentrations that
occurred within a few years of planting a riparian buffer. In
2000 and 2001 a buffer was planted adjacent to a first-order
stream in the deep loess region of western Iowa with strips of
walnut and cottonwood trees, alfalfa and brome grass, and
switch grass. Non-parametric statistics showed significant
declines in NO3–N concentrations in shallow groundwater
following buffer establishment, especially mid 2003 and later.
The dissolved oxygen generally was > 5 mg L− 1 beneath the
buffer, and neither NO3–N nor DO changed significantly under a
non-buffered control area. These short-term changes in
groundwater NO3–N provide evidence that vegetated riparian
buffers may yield local water-quality benefits within a few
years of planting.
Zhang, XY, et al. 2010. A Review of
Vegetated Buffers and a Meta-analysis of Their Mitigation
Efficacy in Reducing Nonpoint Source Pollution. JOURNAL OF
ENVIRONMENTAL QUALITY, 39 (1): 76-84.
Vegetated buffers are a well-studied and
widely used agricultural management practice for reducing
nonpoint-source pollution. A wealth of literature provides
experimental data on their mitigation efficacy. This paper
aggregated many of these results and performed a meta-analysis
to quantify, the relationships between pollutant removal
efficacy and buffer width, buffer slope, soil type, and
vegetation type. Theoretical models for removal efficacy (Y)
vs. buffer width (w) were derived and tested against data from
the surveyed literature using statistical analyses. A model of
the form Y = K x (1 - e(-bxw)), (0 < K <= 100) Successfully
captured the relationship between buffer width and pollutant
removal, where K reflects the maximum removal efficacy of the
buffer and b reflects its probability to remove any single
particle of pollutant in a unit distance. Buffer width alone
explains 37, 60, 44, and 35% of the total variance in removal
efficacy for sediment, pesticides, N, and P, respectively.
Buffer slope was linearly associated with sediment removal
efficacy either positively (when slope <= 10%) or negatively
(when slope > 10%). Buffers composed of trees have higher N
and P removal efficacy than buffers composed of grasses or
mixtures of grasses and trees. Soil drainage type did not show
a significant effect on pollutant removal efficacy. Based on
our analysis, a 30-m buffer under favorable slope conditions
(approximate to 10%) removes more than 85% of all the studied
pollutants. These models predicting optimal buffer width/slope
can be instrumental in the design, implementation, and
modeling of vegetated buffers for treating agricultural
runoff.
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