Chesapeake Bay Monitoring
"Monitoring for Management Actions"

8. pollutant inputs

Nutrients, organic material, sediment and other pollutants are introduced to the Chesapeake Bay from a variety of sources. These are generally separated into two broad classes, point and nonpoint sources. Point sources, as the name implies, are inputs with a specific point of entry into the system. Municipal sewage and industrial discharges are examples of the major point sources of pollutants to the Bay. Nonpoint sources do not have a readily identifiable point of entry to the system or they may have many, diffuse points of entry to the system. Rain water runoff and ground water discharges are examples of the major nonpoint sources of pollutants to the Bay.

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All of these inputs must be effectively monitored in order to document the present pollutant loadings to the Bay and to track the progress of cleanup efforts. In addition, the point of entry, chemical form, magnitude and timing of the inputs are important information required to understand and evaluate the impact of the pollutants on water quality.

Maryland has been monitoring the major point sources of pollutants to the waters of the state for many years. The severity of the water quality impacts of many point source discharges warranted immediate attention to regulate and control the discharges. Over the years these regulatory and monitoring efforts have been steadily upgraded. Under the recent Chesapeake Bay initiatives, point source monitoring efforts are being further improved.

Nonpoint sources present a different sort of regulatory and monitoring problem due to the diffuse and unpredictable nature of the inputs. The situation is further complicated by the critical role that largely uncontrollable natural weather patterns play in determining nonpoint source pollution. As many point sources have been brought under control, the importance of nonpoint sources has become more evident and efforts to control and monitor nonpoint sources have been significantly increased.


The pollutant input monitoring program described here is divided into three major components; 1) municipal point sources, primarily sewage treatment facilities; 2) industrial point source discharges, of a variety of types; and 3) river inputs, the combined result of many upstream, point and nonpoint source pollutant inputs.

Municipal Point Source Monitoring Program

Point source discharges are regulated in Maryland by the Office of Environmental Programs as part of the federally mandated National Pollutant Discharge Elimination System (NPDES) which is administered by the U.S. Environmental Protection Agency (EPA). The OEP monitoring program for point source discharges was developed to meet the specific requirements of NPDES and EPA. The entire program is based on establishing and enforcing specific discharge permits. As part of its regulatory responsibility, OEP issues discharge permits and reviews monitoring data to assure compliance with the permits.

Several types of monitoring approaches are taken for municipal sewage discharges. The most comprehensive monitoring is carried out by the dischargers themselves. Daily sampling and records of effluent parameters and operational indices are generally required. To verify this self monitoring, OEP personnel conduct periodic compliance monitoring at varying frequencies depending on permit conditions, discharge volume and type of treatment process used. Onsite reviews of plant operation are also conducted regularly by OEP engineers.

The new Maryland Chesapeake Bay initiatives affecting municipal point sources are directed toward improving the operation of municipal sewage treatment plants through improved financial management and operator training, improved regulation and monitoring of industrial discharges which go into the municipal waste stream to be treated at sewage treatment facilities, and enhanced compliance enforcement efforts. However, the major focus of the existing point source monitoring efforts, that is, to verify the individual discharger's compliance with permit conditions did not change.

In the evaluation of water quality impacts of point source pollution the compliance monitoring data dealing with effluent flows and concentrations of associated nutrients are of primary concern. The bulk of the effluent monitoring data is collected by the plant operators. These data are periodically verified by comparison with State monitoring data. In the past, the effluent data for groups of plants have been complied only periodically to provide Bay or watershed point source loading estimates for specific planning purposes. In conjunction with the enhanced water quality monitoring activities in the Bay and its tidal tributaries, the data are now being complied on an annual basis.

Industrial Point Source Monitoring Program

In contrast to municipal sewage discharges, the nature of industrial discharges is much more variable. As a result, a more individually tailored discharge monitoring program is required based on the permit requirements for the individual discharger. In general terms, however, the industrial point source monitoring takes the same combination of approaches as used for municipal monitoring. Compliance evaluation inspections are done by OEP engineers to review records and plant operating procedures. Performance audit inspections are conducted to provide quality assurance and to review the discharger's self monitoring activities. Compliance sampling inspections are done to independently analyze the effluent and verify the results of self monitoring data.

As in the case of the municipal point source monitoring, Chesapeake Bay initiatives for the industrial program are focused on improving discharge permit compliance. In addition, biological evaluation of toxic waste discharges using bioassay techniques is being tested as an added regulatory tool for managing industrial discharges into Maryland's streams. The emphasis is on permit compliance for the individual discharger. The data are generally sufficient for Bay-wide, water quality evaluation needs. However, efforts are currently underway to enhance the monitoring where necessary to provide additional information on discharges.

River Input Monitoring Program

As a result of Maryland's Chesapeake Bay initiatives, the river input monitoring program has been enhanced considerably to provide more accurate data for evaluating sediment and nutrient loading to the Bay from its surrounding watersheds. Prior to the start of the new monitoring program in July 1984, routine water quality monitoring of streams in Maryland by OEP was primarily limited to monthly grab samples. With the new monitoring program, regular storm runoff sampling efforts are now being conducted on four major rivers in Maryland.

River inputs present a difficult monitoring problem because of the number of streams and rivers discharging to the Bay and the unpredictable nature of storm events and associated river flows. There are too many streams and rivers discharging to the Bay for it to be practical to monitor them all. In addition, the characteristics of water flowing in a river are constantly changing in response to rainfall in the watershed. Just as it is not practical to monitor every river flowing into the Bay, it is not practical to continuously monitor all water quality characteristics over time.

River flows can generally be divided into two basic categories, base flow and storm events. Under base flow conditions the river is fed primarily from groundwater and the volume of water and its water quality characteristics are relatively stable. During a storm event, however, the volume of water flowing in a river increases tremendously as base flow is supplemented and overwhelmed by direct runoff of rainfall. As the river rises and falls the concentrations of pollutants in the water can change radically. Thus, it is necessary to take numerous samples during the course of the storm to get an accurate estimate of the pollutant load from a particular storm. Because the volume of water delivered to the estuary is much greater during storm events, the loads of associated pollutants are also much larger than loads carried by base flow.

With careful selection of sampling locations and time of sampling it is possible to characterize a number of rivers for a range of conditions and then extrapolate the data to fill in the gaps in sampling coverage. The rivers that are being monitored have been selected to capture runoff from as much of the Bay watershed as possible and to obtain the maximum coverage of the range of different sources of runoff to the Bay and its tributary estuaries. Sampling times are chosen to emphasize storm events, when the majority of the river input loads are delivered to the Bay. The percentage of the total nutrient and sediment loads associated with these river flows is not as easily determined.

Each watershed has unique characteristics that may significantly influence the loads delivered by each river. In order to accurately extrapolate the monitoring data to cover unmonitored tributaries to the Bay, various approaches can be taken. Approaches range from simple flow based extrapolation of loading data (e.g. 80% of the flow delivers 80% of the load) to sophisticated watershed computer models. All of these involve assumptions about the transferability of water quality data from one watershed to another and are thus subject to considerable interpretation and debate.


In order to facilitate a comparison of the Chesapeake Bay river input monitoring program with the point source monitoring program, the results are presented together. It must be clearly understood that the loading estimates discussed below are not to be taken as a complete inventory of the nutrient inputs to the Bay. What is represented are the river input loads (point and nonpoint sources) for four rivers, representing 80% of the fresh surface water flow into Maryland's portion of the Chesapeake Bay, and the point source loads discharging into the Bay drainage area that are not measured by the river input monitoring program. The nonpoint source nutrient loads from the unmonitored 20% of the flow, the atmosphere, ground water, sediments and other potentially significant sources of nutrients have not been presented here.

In addition, the results shown for both river inputs and point sources indicate the amounts discharge at the location, or in the region indicated. The loads do not necessarily reach the mainstem of the Bay itself. For example, the impact on the Chesapeake Bay of the nutrient loads at the head of the Potomac estuary are substantially moderated by the natural processing which occurs in the Potomac estuary before any of that load reaches the Bay. In order to assess the relative impact of these loads on various regions of the Chesapeake Bay, so many factors must be taken into account that the problem is best addressed using complex mathematical models. Modeling efforts are presently underway in the Bay and a number of its tributary estuaries in order to carefully address these problems.

Maps 13 and 14 show the major river and point source nitrogen and phosphorus inputs to the Chesapeake Bay in Maryland for the period 1978 through 1985. River inputs include both point and nonpoint source pollutants discharged upstream of the monitoring stations. Point source inputs shown include only those point sources not captured by the river input monitoring stations.

Click on the map for a larger view of Map 13

Click on the map for a larger view of Map 14

Point source nutrient load estimates have been compiled from a number of sources including the EPA Chesapeake Bay Program, Metropolitan Washington Council of Governments and OEP compliance monitoring data. Historical point source load estimates were only available for certain years. However, since point source loads are fairly stable for extended periods, the gaps in the data presented here do not prevent a meaningful comparison with the river input data.

Even though population and associated sewage flows have increased since 1980, dramatic reductions in point source phosphorus loads have been achieved in the upper Bay western shore and Potomac regions where phosphorus loads have been reduced by 46 and 89 percent respectively. This has been accomplished largely through the installation of improved treatment processes directed at removing phosphorus from the effluent of the major municipal sewage treatment plants. Over the same period, point source nitrogen loads did not change appreciably. Improved treatment processes, although they are not directed at nitrogen removal, have provided some removal and have permitted the nitrogen loads to be relatively stable in the face of increasing flows.

The 1984 and 1985 river input load estimates shown here are reasonably accurate since they result from the analysis of the expanded monitoring data base. However, because of the lack of a comprehensive historical data base, river input annual estimates for the years prior to the initiation of this monitoring program are not as accurate. In particular, estimates for high flow years are less accurate because of the greater uncertainty in predicting storm flow pollutant concentrations as opposed to low flow pollutant concentrations. Estimates for the Potomac, and 1979 and 1980 estimates for the Susquehanna are an exception. These are based on more complete data and are more accurate than other historical load estimates.

The annual variation of the river input data is clear, but there is significant seasonal variability as well. Based on the results of the river input monitoring program, the total nitrogen and total phosphorus loads have been estimated on a seasonal basis for 1984-85. Figure 20 is a set of bar charts showing the flow, total nitrogen and total phosphorus loads contributed by the four rivers during winter (Jan-Mar), spring (Apr-Jun), summer (Jul-Sep) and fall (Oct-Dec) of 1984 and 1985 (note: the loading scale for the Patuxent and Choptank is 100 times smaller than the Susquehanna and Potomac).

Figure 20.  Seasonal inputs of flow, total nitrogen and total phosphorus for the river input monitoring stations on the Susquehanna, Potomac, Patuxent and Choptank Rivers.

Click on Figure 20 for a larger view

During the course of a year the amount of water and the associated nutrient loads discharged by a river can vary considerably. This is particularly noticeable during the 1984-85 monitoring period when flows averaged 10 - 30% above average in 1984 and 10 - 50% below average in 1985. The seasonality of the flow and associated nutrient loads can be clearly seen. In general, the winter and spring flows and nutrient loads are very high compared to summer and fall contributions. However, as noted earlier, from one year to the next, considerable variation occurs. For example, summer and fall of 1984 had relatively high flows and winter and spring of 1985 had relatively low flows. As a result the winter/spring peak in nutrient loads is not nearly as dramatic as occurred in calendar year 1984.

River flow during the summer of 1985 was well below average (40-50%) and nutrient loads were extremely low as a result. The fall of 1985 was unique, particularly on the Potomac, where the occurrence of a major flood caused unusually high nutrient loads to be delivered to the head of the Potomac estuary.

Despite the uncertainty in the annual estimates for years prior to 1984, the data presented here serves to illustrate the magnitude and extreme year to year and seasonal variability in river input nutrient loads. In general, the highest loads occur during periods of higher rainfall, but flow alone cannot be accurately used as a surrogate for nutrient loadings.

Comparison of the flows and nutrient loads delivered by the four rivers reveals some interesting points. Over the 1984-85 period the Susquehanna contributed 73% of the flow, 76% of the total nitrogen (TN) and only 66% of the total phosphorus (TP), while the Potomac contributed 26%, 23% and 32% for flow, TN and TP respectively. This indicates that on average during this period the Susquehanna was relatively rich in nitrogen and the Potomac was relative rich in phosphorus. The Patuxent contributed 0.6% of the flow, 0.9% of the TN and 1.9% of the TP and was thus rich in both nitrogen and phosphorus. The Choptank contributed 0.2% for flow, TN and TP.

These observed differences in the characteristics of the discharge from the four basins are the result of the interaction of a number of factors. Each river is unique because of the variability of both natural and anthropogenic characteristics of the drainage basins. Physiographic (land surface slope, soil type, geology) and meteorologic characteristics differ from basin to basin and are basically unaffected by human activity. Other important factors - land use practices, population density and point source discharges are definitely attributed to people. More detailed analysis of these factors and the characteristics of the river flow produced is necessary to begin to deal with the unique problems facing each river.

The presentation given above also permits a simple comparison of the river input and point source loads discharging directly to tidal waters of the Chesapeake Bay. Without taking into account all of the other sources of nutrients to the system, the chemical form of the nutrient input and the location of the discharge, it is not realistic to attempt to quantitatively evaluate the relative importance of these inputs. Nevertheless, some general observations can be made.

River input and point source data are shown with a standard scale on Maps 13 and 14 to emphasize the relative magnitude of the loads. It is clear that for both nitrogen and phosphorus the river inputs from the Susquehanna and Potomac are the major source of nutrients to the system. However, because the magnitude of the river input varies considerably from year to year depending on rainfall, the river inputs are of variable significance in the annual nutrient loading budget of the Bay.

For example, the major nutrient inputs to the upper Bay above its confluence with the Patuxent, are the Susquehanna River and point sources from the Western and most of the Eastern Shore. For this part of the Bay in 1984, a high runoff year, the Susquehanna River inputs of nitrogen and phosphorus were respectively 20 and 8 times the combined Western and Eastern Shore point source inputs. In 1985, a low runoff year, the nitrogen and phosphorus inputs were 7.5 and 2.5 times the point source inputs.

Comparison of the point and nonpoint loading on a seasonal basis further illustrates the importance of runoff in affecting the balance of nutrient inputs to the Bay. In the upper Bay, river inputs from the Susquehanna reached a minimum in the summer of 1985. During this period, point source loads of nitrogen and phosphorus were comparable to Susquehanna River inputs.


  • Since 1980 dramatic reductions in phosphorus loadings from point sources discharging into the tidal waters of Chesapeake Bay have been achieved in spite of increasing population and associated sewage flows.
  • Nitrogen loads from the same point sources have been held fairly stable in the face of increasing sewage flows.
  • River inputs of nutrients vary tremendously from year to year and seasonally, generally in correspondence to changes in river flow.
  • River flow by itself does not completely determine nutrient load. Each watershed has unique characteristics which affect the exact proportions of nutrient loads and make simple extrapolations of the data inaccurate.
  • On an annual average load basis, river inputs far exceed point source inputs to tidal waters. In low flow years this dominance of river input loads is less pronounced and in low flow seasons the river inputs and point source inputs may be comparable.
  • Although it is not possible to quantitatively evaluate the relative water quality impacts of the various sources of nutrients to the Bay at the present time, data is now being collected which will permit this analysis to be made.

a.    Preface
b.   Acknowledgements
1.   Introduction
2.   Understanding The Bay's Problems
3.   Program Description
4.   Chemical and Physical Properties
5.   Plankton
6.   Benthic Organisms
7.   Ecosystem Processes
8.   Pollutant Inputs
9.   Management Strategies and the Role of Monitoring
10. Glossary

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