Results for the
Lower Eastern Shore Basin

The nutrient limitation models models were used to predict nutrient limitation for the ten stations in the Lower Eastern Shore. Results 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). 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.
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Rivers

Upper Nanticoke River (ET6.1) - On an annual basis, phytoplankton growth is phosphorus limited more than 50% of the time and otherwise is nutrient saturated (light limited or no limitation). Winter growth is entirely nutrient saturated; spring growth is phosphorus limited more than 80% of the time. In the summer and fall, growth is phosphorus limited approximately 80% and almost 40% of the time, respectively, and otherwise is nutrient saturated. Total and dissolved inorganic nitrogen concentrations are relatively poor and degrading (increasing). Total and phosphorus concentration is relatively good and dissolved inorganic phosphorus concentration is relatively fair; total phosphorus concentration is improving (decreasing). The ratio of total nitrogen to total phosphorus is increasing. The dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios are extremely high in winter, spring and fall, indicating that nitrogen is in great excess at this station. Additional phosphorus limitation is possible in the winter, spring and fall with continued decreases in phosphorus concentrations. Very large reductions in nitrogen concentrations are needed to match the reductions in phosphorus and might allow for nitrogen limitation to occur in summer.

graph showing Upper Nanticoke River et6.1graph showing Lower Nanticoke River et6.2

Lower Nanticoke River (ET6.2) - On an annual basis, phytoplankton growth is phosphorus limited more than 60% of the time, nitrogen limited more than 10% of the time, and nutrient saturated (light limited or no limitation) 25% of the time. In the winter, phytoplankton growth is phosphorus limited approximately 35% of the time and is otherwise nutrient saturated. In the spring, growth is phosphorus limited 80% of the time ad is otherwise nutrient saturated. In summer, phytoplankton growth is nitrogen limited 35% of the time and phosphorus limited 65% of the time. In the fall, phytoplankton growth is phosphorus limited almost 60% of the time and nitrogen limited less than 10% of the time. Total and dissolved inorganic nitrogen and total and dissolved inorganic phosphorus concentrations are relatively poor. Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios are extremely high in winter and high in spring, corresponding to the strong phosphorus limitation at this station. Reductions in phosphorus concentrations in the winter and spring and nitrogen concentrations in the summer and fall will help further limit phytoplankton growth in this portion of the Nanticoke.

Wicomico River (ET7.1) – On an annual basis, phytoplankton growth is phosphorus limited almost 55% and nitrogen limited more than 20% of the time. In the winter, growth is phosphorus limited about 30% of the time and otherwise is nutrient saturated. In the spring, growth is phosphorus limited almost 90% of the time. In summer, phytoplankton growth is nitrogen limited 60% of the time and phosphorus limited 40% of the time. In the fall, phytoplankton growth is phosphorus limited more than 55% of the time and nitrogen limited almost 15% of the time. Total and dissolved inorganic nitrogen concentrations are relatively poor but total nitrogen concentration is improving (decreasing). Total and dissolved inorganic phosphorus concentrations are relatively poor but total phosphorus concentration is improving (decreasing). The ratio of total nitrogen to total phosphorus is increasing. Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios are very high in winter and high in spring, corresponding to strong phosphorus limitation in these seasons. Continued reductions in phosphorus concentrations in the winter and spring and nitrogen concentrations in the summer and fall will help further limit phytoplankton growth in this portion of the Wicomico.

graph showing Wicomico River et7.1graph showing Manokin River et8.1

Manokin River (ET8.1) – On an annual basis, phytoplankton growth is nitrogen limited more than 60%, phosphorus limited more than 10%, and nutrient saturated (light limited or no limitation) 25% of the time. In the winter, growth is nitrogen limited more than 15% and phosphorus limited more than 5% of the time, and otherwise is nutrient saturated. Growth in spring is nitrogen limited about 65% of the time and phosphorus limited about 20% of the time. Summer growth is entirely nitrogen limited. In fall, growth is nitrogen limited more than 65% of the time and phosphorus limited about 35% of the time. Total nitrogen, total phosphorus and dissolved inorganic phosphorus concentrations are relatively fair, and dissolved inorganic nitrogen concentration is both relatively good. Dissolved organic phosphorus concentration is degrading (increasing). The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is decreasing. This ratio is low in winter, summer and spring, and dissolved inorganic nitrogen concentrations are low throughout the year, corresponding to the strong nitrogen limitation at this station. Reductions in nitrogen would further limit phytoplankton growth at this station, while reductions in phosphorus will help bring the system into better balance, particularly in the spring.

Big Annemessex (ET9.1) - On an annual basis, phytoplankton growth is nitrogen limited 75% and phosphorus limited almost 15% of the time. Winter growth is nitrogen limited almost 35% of the time and is otherwise nutrient saturated (light limited or no limitation). In the spring, growth is nitrogen limited more than 65% of the time and otherwise phosphorus limited. In the summer, growth is entirely nitrogen limited. In the fall, growth is nitrogen limited about 85% of the time and phosphorus limited about 15% of the time. Total nitrogen, dissolved inorganic nitrogen, total phosphorus and dissolved inorganic phosphorus concentrations are all relatively good. Dissolved inorganic nitrogen concentration is 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 all seasons, as is dissolved inorganic nitrogen concentration, corresponding to the strong nitrogen limitation at this station. Continued reductions in nitrogen would further limit phytoplankton growth at this station, while reductions in phosphorus will help bring the system into better balance, particularly in the winter and spring.

graph showing Big Annemessex River et9.1graph showing Pocomoke River et10.1

Pocomoke River (ET10.1) – Phytoplankton growth is nutrient saturated (light limited or no limitation) almost 95% of the time, with only occasional nitrogen or phosphorus limitation in summer (more than 5% and approximately 15% of the summer samples, respectively). Total nitrogen, dissolved inorganic nitrogen and total phosphorus concentrations are relatively fair and total nitrogen concentration is improving (decreasing); dissolved inorganic phosphorus concentrations are relatively poor. This is a blackwater system, where light limitation is high due to dark color of the water. The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus are low in summer and fall, but dissolved inorganic nitrogen concentrations are high, indicating excess phosphorus in this system. Continued reductions in nitrogen would increase the occurrences of nitrogen limitation and further limit phytoplankton growth in this portion of the Pocomoke. Reductions in phosphorus will help bring the system into better balance throughout the year..

Embayments

Fishing Bay (EE3.0) – On an annual basis, phytoplankton growth is nitrogen limited almost 50% of the time and phosphorus limited more than 25% of the time. In the winter, growth is nutrient saturated (light limited or no limitation) about 80% of the time and nitrogen limited about 20% of the time. In the spring, phytoplankton growth is phosphorus limited about 65% of the time and nitrogen limitation about 35% of the time. Summer growth is nitrogen limited more than 80% of the time and phosphorus limited almost 20% of the time. Fall growth is nitrogen limited more than 65% of the time and phosphorus limited the remainder of the time. Total nitrogen and total phosphorus concentrations are both relatively fair; dissolved inorganic nitrogen and dissolved inorganic phosphorus concentrations are relatively good, and dissolved inorganic nitrogen concentration is improving (decreasing). The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is decreasing; this ratio is relatively low in summer and fall; dissolved inorganic nitrogen concentrations are low in all seasons. Continued reductions in nitrogen would enhance nitrogen limitation, especially in the spring. Reductions in phosphorus will help bring the system into better balance, particularly in the winter and spring.

graph showing Fishing Bay ee3.0graph showing North Tangier Sound ee3.1

North Tangier Sound (EE3.1) – On an annual basis, phytoplankton growth is nitrogen limited and phosphorus limited about 40% of the time each. In the winter, growth is nutrient saturated (light limited or no limitation) about 85% of the time and nitrogen limited almost 15% of the time. In the spring, phytoplankton growth is phosphorus limited almost 90% of the time and nitrogen limited about 10% of the time. Summer growth is nitrogen limited 80% of the time and otherwise is phosphorus limited. Fall growth is nitrogen limited 50% and phosphorus limited 50% of the time. Total nitrogen and dissolved inorganic nitrogen concentrations are relatively fair and total phosphorus and dissolved inorganic phosphorus concentrations are relatively good. Total phosphorus and dissolved inorganic nitrogen concentrations are improving (decreasing). Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios are low in summer and fall and moderate in summer. Continued reductions in nitrogen would further limit phytoplankton growth at this station in the winter, summer and fall. Continued reductions in phosphorus will help bring the system into better balance and will increase the occurrence of phosphorus limitation in the winter and spring.

South Tangier Sound (EE3.2) – On an annual basis, phytoplankton growth is nitrogen limited almost 55% of the time and phosphorus limited almost 30% of the time. In the winter, growth is nitrogen limited 30% of the time, phosphorus limited about 5% of the time, and nutrient saturated more than 60% of the time. In the spring, summer and fall, growth is nitrogen limited 50%, 80% and 60% of the time of the time, respectively and is otherwise phosphorus limited. Total nitrogen, dissolved inorganic nitrogen, total phosphorus and dissolved inorganic phosphorus concentrations are all relatively good; dissolved inorganic nitrogen concentration is improving (decreasing). The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is decreasing; this ratio is very low in all seasons, consistent with the strong nitrogen limitation at this station. Continued reductions in nitrogen would further limit phytoplankton growth at this station throughout the year. Reductions in phosphorus will help bring the system into better balance and will increase the occurrence of phosphorus limitation in the winter and spring.

graph showing South Tangier Sound ee3.2graph showing Pocomoke Sound ee3.3

Pocomoke Sound (EE3.3) – Spring, summer and fall growth is nitrogen limited 60%, 90% and almost 85% of the time, respectively, and otherwise is phosphorus limited (no samples are collected in winter). Total nitrogen and total phosphorus concentrations are relatively fair; dissolved inorganic nitrogen and dissolved inorganic phosphorus concentrations are relatively good and dissolved inorganic nitrogen concentration is improving (decreasing). The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is decreasing; this ratio is very low in summer and fall, consistent with the strong nitrogen limitation at this station. Continued reductions in nitrogen would further limit phytoplankton growth at this station throughout the year. Reductions in phosphorus will help bring the system into better balance and will increase the occurrence of phosphorus limitation in the winter and spring.

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

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