Results for the
Middle and Lower Potomac Basins

The nutrient limitation model was used to predict nutrient limitation for the thirteen stations in the Middle and Lower Potomac Basins. Results for each station are summarized for the most recent three-year period (2001-2003) by season: winter (December-February), spring (March-May), summer (July-September) and fall (October-November). Overall, riverflow is a strong factor in determining seasonal limitation patterns throughout the river. The uppermost stations show patterns typical of turbid, nutrient enriched areas where nutrient limitation occurs primarily in the warmer/low riverflow periods (Fisher and Gustafson 2002). The two stations most downstream show the pattern typical of mesohaline areas, where river discharge dictates a seasonal pattern of limitation due to low light/temperatures in winter, high dissolved inorganic nitrogen/dissolved inorganic phosphorus in high river discharge in the spring, large fluxes of dissolved inorganic phosphorus fluxes from the sediments under anoxic conditions in the summer, and turnover of the water column in the fall (Fisher and Gustafson 2002 filename: 2002_level1_report.pdf, 11,982 kb).
Bay Monitoring Info:
Water Quality Data
"Eyes on the Bay"
River Input
Water & Habitat
Nutrient Limitation
Ecosystem Processes
Benthos
Phytoplankton
Zooplankton
Bay Grasses
Tidal Fish
Research Vessel Kerhin
Chesapeake Bay Home
Bays & Streams Home
DNR Home


Managers can use these predictions to assess what management approach will be the most effective for controlling excess phytoplankton growth. Interpreting the results can be a little counter-intuitive, however. Remember that nitrogen limited means that phosphorus is in excess. Initially, it would seem that the best management strategy would be to reduce phosphorus inputs. However, it may actually be more cost effective to further reduce nitrogen inputs to increase the amount of ‘unbalance’ in the relative proportions of nutrients so that phytoplankton growth is even more limited. When used along with other information available from the water quality and watershed management programs, these predictions will allow managers to make more cost-effective management decisions.

Upper Piscataway Creek (PIS0033) – On an annual basis, phytoplankton growth is nutrient saturated (light limited or no limitation) more than 95% of the time. In the fall, there is nitrogen limitation approximately 20% of the time. Total and dissolved inorganic nitrogen concentrations are relatively good and improving (decreasing). Total phosphorus and dissolved inorganic phosphorus concentrations are relatively fair and dissolved inorganic phosphorus is improving (decreasing). The ratio of total nitrogen to total phosphorus is decreasing. Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios are low in summer and fall, indicating nitrogen limitation may be possible in those seasons. Together, this information suggests that further reductions in nitrogen concentrations will help limit phytoplankton growth at this location. Reductions in phosphorus concentrations in all seasons are needed to bring the system into better balance and to potentially limit growth in the spring.

graph showing Piscataway Creek PIS0033graph showing Piscataway Creek XFB1986

Lower Piscataway Creek (XFB1986) – On an annual basis, phytoplankton growth is nutrient saturated (light limited or no limitation) approximately 90% of the time. There is phosphorus limitation for a small percentage of the time in the spring and summer (less than 10% and approximately 15%, respectively). Fall and winter growth is always nutrient saturated. Total and dissolved inorganic nitrogen concentrations are relatively poor but improving (decreasing). Total phosphorus concentration is relatively good and dissolved inorganic phosphorus concentration is relatively fair. The ratio of total nitrogen to total phosphorus and the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus are both decreasing. The dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is high, particularly in the winter. Together, this information suggests that reductions in phosphorus in all seasons will help to limit phytoplankton growth at this location. Much larger nitrogen reductions will be needed to allow nitrogen limitation in this portion of Piscataway Creek.

Off Piscataway Creek (TF2.1) - On an annual basis, phytoplankton growth is nutrient saturated (light limited or no limitation) almost 95% of the time. There is phosphorus limitation for a small percentage of the time in the spring and summer (approximately 5% and approximately 10%, respectively). Fall and winter growth is always nutrient saturated. Total and dissolved inorganic nitrogen concentrations are relatively poor but improving (decreasing). Total phosphorus concentration is relatively good and dissolved inorganic phosphorus concentration is relatively fair. The ratio of total nitrogen to total phosphorus and the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus are both decreasing. The dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is moderate in the winter. Together, this information suggests that reductions in phosphorus in all seasons will help to limit phytoplankton growth at this location. Much larger nitrogen reductions will be needed to allow nitrogen limitation in the summer and fall.

graph showing Potomac Off Piscataway TF2.1graph showing Potomac at Marshall Hall TF2.2

Marshall Hall (TF2.2) - Annual phytoplankton growth is nutrient saturated (light limited or no limitation) almost 95% of the time at this station. Spring and summer growth is phosphorus limited approximately 5% of the time; fall growth are phosphorus limited approximately 10% of the time. Total and dissolved inorganic nitrogen concentrations are relatively poor but improving (decreasing). Total phosphorus concentration is relatively good and dissolved inorganic phosphorus concentration is relatively fair. The ratio of total nitrogen to total phosphorus and the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus are both decreasing. The dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is moderate except in the winter and fall when it is high. Together, this information suggests that reductions in phosphorus in all seasons will help to limit phytoplankton growth at this location. Larger nitrogen reductions will be needed to help bring the system into better balance and may lead to nitrogen limitation in the summer.

Indian Head (TF2.3) - Annual phytoplankton growth nutrient saturated (light limited or no limitation) 95% of the time at this station. Spring growth is phosphorus limited 20% of the time. Total and dissolved inorganic nitrogen concentrations are relatively poor but improving (decreasing). Total phosphorus concentration is relatively good and dissolved inorganic phosphorus concentration is relatively fair. The ratio of total nitrogen to total phosphorus is decreasing. The dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is high in winter and spring, indicating phosphorus limitation may be possible in these seasons. This information suggests that reductions in phosphorus in winter and spring will help to limit phytoplankton growth at this location. Dissolved inorganic nitrogen concentrations are moderate in summer, suggesting that nitrogen reductions might lead to nitrogen limitation in that season. Larger nitrogen reductions will be needed to help bring the system into better balance and may lead to nitrogen limitation in the fall.

graph showing Potomac at Indian Head TF2.3graph showing Potomac at Quantico TF2.4

Quantico (TF2.4) - Annual phytoplankton growth is nutrient saturated (light limited or no limitation) more than 95% of the time at this location. Spring growth is phosphorus limited almost 15% of the time. Total nitrogen concentration is relatively fair but dissolved inorganic nitrogen concentration is relatively poor; both are improving (decreasing). Total phosphorus concentration is relatively good and dissolved inorganic phosphorus concentration is relatively fair. The ratio of total nitrogen to total phosphorus is decreasing. The dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is low in summer and moderate in winter and spring. Together, this information suggests that reductions in phosphorus in winter and spring will help to limit phytoplankton growth at this location. Larger nitrogen reductions will be needed to help bring the system into better balance and may lead to nitrogen limitation in the summer and fall.

Upper Matawoman Creek (MAT0078) – On an annual basis, phytoplankton growth is nutrient saturated (light limited or no limitation) more than 80% of the time, nitrogen limited almost 15% of the time, and phosphorus limited less than 5% of the time. Summer and fall growth is nitrogen limited approximately 25% and 30% of the time, respectively, and phosphorus limited less than 10% of the time. Total and dissolved inorganic nitrogen concentrations are good; total nitrogen concentration is improving (decreasing). Total and dissolved inorganic phosphorus concentrations are all good and both are improving (decreasing). Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is increasing; this ratio is currently low, especially in summer and fall indicating that phosphorus is in excess relative to nitrogen at this location. Further reductions in nitrogen will increase the occurrences of nitrogen limitation in the summer and fall. Continued reductions in phosphorus will be needed to allow phosphorus limitation to occur in the winter and spring.

graph showing Mattawoman Creek MAT0078graph showing Mattawoman Creek MAT0016

Lower Matawoman Creek (MAT0016) - On an annual basis, phytoplankton growth is nutrient saturated (light limited or no limitation) approximately 90% of the time. Winter growth is phosphorus limited almost 15% of the time and otherwise nutrient saturated. Spring growth is phosphorus limited approximately 5% of the time and is otherwise nutrient saturated. Summer growth is nitrogen limited almost 10% of the time and phosphorus limited less than 5% of the time. Fall growth is nutrient saturated. Total and dissolved inorganic nitrogen concentrations are relatively fair and improving (decreasing), and total and dissolved inorganic phosphorus concentrations are relatively good. The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is high in winter and spring and low in summer. However, dissolved inorganic nitrogen concentrations are still too high in summer for nitrogen limitation to occur frequently. Further reductions in nitrogen will increase the occurrences of nitrogen limitation in the summer and may allow nitrogen limitation to occur in the fall. Reductions in phosphorus will be needed to increase phosphorus limitation in the winter and spring.

Smith Point (RET2.1) – On an annual basis, phytoplankton growth is nutrient saturated (light limited or no limitation) almost 95% of the time. Spring growth is phosphorus limited approximately 5% of the time. Summer growth is nitrogen limited approximately 10% of the time. Total nitrogen concentration is relatively fair but dissolved inorganic nitrogen concentration is poor; both are improving (decreasing). Total phosphorus concentration is relatively fair and dissolved inorganic phosphorus concentration is relatively poor. The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is decreasing. Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is low in summer and moderate in other seasons; dissolved inorganic nitrogen concentrations are still to high for nitrogen limitation to occur. Further reductions in nitrogen will increase the occurrences of nitrogen limitation in the summer and may allow nitrogen limitation to occur in the fall. Reductions in phosphorus will be needed to increase the occurrence of phosphorus limitation, especially in the spring.

graph showing the Potomac at Smith Point RET2.1graph showing the Potomac at Maryland Point RET2.2

Maryland Point (RET2.2) – On an annual basis, phytoplankton growth is nutrient saturated (light limited or no limitation) 90% of the time. Spring growth is phosphorus limited approximately 5% of the time. Summer growth is nitrogen limited approximately 20% of the time. Total nitrogen concentration is relatively fair but dissolved inorganic nitrogen concentration is relatively poor; both are improving (decreasing). Total phosphorus concentration is relatively fair but dissolved inorganic phosphorus concentration is poor. The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is moderate in winter and spring, suggesting phosphorus limitation may be able to occur during this part of the year. This ratio is low in summer and fall and suggests nitrogen limitation may be able to occur. Further reductions in nitrogen will increase the occurrences of nitrogen limitation in the summer and may allow nitrogen limitation to occur in the fall. Reductions in phosphorus will be needed to allow phosphorus limitation to occur, especially in the spring.

Morgantown Bridge-Rt. 301 (RET2.4) - On an annual basis, phytoplankton growth is nutrient saturated (light limited or no limitation) approximately 65% of the time, and nitrogen limited 20% of the time and phosphorus limited approximately 15% of the time. Winter growth is entirely nutrient saturated. Spring growth is phosphorus limited 40% of the time. Summer growth is nitrogen limited almost 55% of the time and phosphorus limited approximately 5% of the time. Fall growth is nitrogen limited about 10% of the time. Total nitrogen, dissolved inorganic nitrogen concentrations are relatively poor but improving (decreasing); total phosphorus and dissolved inorganic phosphorus concentrations are relatively poor. The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is high in the winter and spring (indicating phosphorus limitation can occur) and low in the summer and fall (indicating nitrogen limitation can occur). Further reductions in nitrogen will increase the occurrences of nitrogen limitation in the summer and fall. Additional reductions in phosphorus may allow phosphorus limitation in the winter and increase occurrences in spring.

graph showing the Potomac at Morgantown RET2.4graph showing the Potomac at Ragged Point LE2.2

Ragged Point (LE2.2) – On an annual basis, phytoplankton growth is nitrogen limited approximately 55% of the time and phosphorus limited almost 35% of the time. Winter growth is nitrogen limited almost 35% of the time. Spring growth is phosphorus limited approximately 65% of the time and nitrogen limited approximately 30% of the time. Summer growth is nitrogen limited 85% of the time and is otherwise phosphorus limited. Fall growth is nitrogen limited 60% of the time and phosphorus limited 40% of the time. Total nitrogen concentration is relatively fair and dissolved inorganic nitrogen is relatively good and is improving (decreasing). Total phosphorus concentration is relatively fair and dissolved inorganic phosphorus concentration is relatively good and improving (decreasing). The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is decreasing. Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios are low in summer and fall (suggests nitrogen limitation can occur) and high in spring (suggests phosphorus limitation can occur). Dissolved inorganic nitrogen concentration is also low in winter, suggesting nitrogen limitation could occur. This information indicates that further reductions in nitrogen will further limit algal growth in the summer and fall, and may increase the occurrences of nitrogen limitation in the winter and spring. Additional reductions in phosphorus will increase the phosphorus limitation in all seasons.

graph showing the Potomac at Point Lookout LE2.3

Point Lookout (LE2.3) – On an annual basis, phytoplankton growth is nitrogen limited approximately 60% of the time and phosphorus limited almost 30% of the time. Winter growth is nitrogen limited approximately 15% of the time and phosphorus limited approximately 15% of the time. Spring growth is phosphorus limited 55% of the time and nitrogen limited more than 35% of the time. Summer growth is nitrogen limited more than 95% of the time. Fall growth is nitrogen limited 50% of the time and phosphorus limited 50% of the time. Total and dissolved inorganic nitrogen concentrations are relatively good; total and dissolved inorganic phosphorus concentrations are relatively good and total phosphorus is improving (decreasing). The ratio of total nitrogen to total phosphorus and the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus are both decreasing. The dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is low in winter and fall (suggesting nitrogen limitation) and moderate in spring (suggesting phosphorus limitation). Further reductions in nitrogen will further limit algal growth in the summer and fall, and increase the occurrences of nitrogen limitation in the winter and spring. Additional reductions in phosphorus will increase the phosphorus limitation in all seasons.

For more information, please contact Renee Karrh
at (410) 260-8628.

Search Maryland DNR

Search www.dnr.state.md.us


Restoration and Protection | Bay Grasses | Harmful Algae | Bay Monitoring
Bay Life Guide | Bay Education

Return to the Maryland DNR Home Page.
Your opinion counts! Take a survey!