Results for the
Lower Western Shore Basin

The nutrient limitation models were used to predict nutrient limitation for the five stations in the Lower Western 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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Magothy River (WT6.1) - On an annual basis, phytoplankton growth is nitrogen limited 35% and phosphorus limited about 50% of the time. In the winter, phytoplankton growth is nutrient saturated (light limited or no limitation) 85% of the time and nitrogen and phosphorus limited less than 10% of the time. In the spring, growth is phosphorus limited about 90% of the time and nitrogen limited about 10% of the time. In the summer, phytoplankton growth is nitrogen limited more than 75% of the time and otherwise is phosphorus limited. In the fall, growth is phosphorus limited almost 65% of the time and nitrogen limited approximately 35% of the time. Total nitrogen concentration is relatively poor and total phosphorus, dissolved inorganic nitrogen and dissolved inorganic phosphorus concentrations are relatively fair. Total nitrogen, dissolved inorganic nitrogen and total phosphorus concentrations are all improving (decreasing). The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is decreasing. The dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is low in the summer, consistent with the strong nitrogen limitation in that season. Continued reductions in nitrogen would further limit phytoplankton growth at this station, while continued reductions in phosphorus will help bring the system into better balance, particularly in the winter.

graph showing Magothy River wt6.1graph showing Severn River wt7.1

Severn River (WT7.1) - On an annual basis, phytoplankton growth is nitrogen limited 40% and phosphorus limited almost 35% of the time. In the winter, phytoplankton growth is nutrient saturated (light limited or no limitation) about 85% of the time, nitrogen limited and phosphorus limited more than 5% of the time each. In the spring, growth is phosphorus limited almost 90% of the time and is otherwise nutrient saturated. In the summer, phytoplankton growth is nitrogen limited almost 90% of the time and otherwise is phosphorus limited. In the fall, growth is nitrogen limited almost 60% of the time and phosphorus limited 25% of the time. Total nitrogen and total phosphorus concentrations are relatively fair and dissolved inorganic nitrogen and dissolved inorganic phosphorus concentrations are relatively good. Total nitrogen, dissolved inorganic nitrogen and total phosphorus concentrations are all improving (decreasing). Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is also decreasing. This ratio is low in the summer, consistent with the strong nitrogen limitation. Continued reductions in nitrogen would further limit phytoplankton growth at this station, while continued reductions in phosphorus will help bring the system into better balance, particularly in the winter.

South River (WT8.1) - On an annual basis, phytoplankton growth is nitrogen limited more than 70% of the time and nutrient saturated (light limited or no limitation) about 20% of the time. In the winter, phytoplankton growth is nitrogen limited almost 35% of the time and is otherwise nutrient saturated. In the spring, phytoplankton growth is nitrogen limited 40% of the time and phosphorus limited 20% of the time. In the summer phytoplankton growth is nitrogen limited. In the fall, growth is nitrogen limited almost 95% of the time and otherwise is phosphorus limited. Total nitrogen and dissolved inorganic phosphorus concentrations are relatively fair and dissolved inorganic nitrogen concentration is relatively good; total phosphorus concentration is relatively poor. Dissolved inorganic nitrogen and total phosphorus concentrations are improving (decreasing). Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios are low all year, especially in summer. Continued reductions in nitrogen would further limit algal production and continued reductions in phosphorus would help bring the system into better balance.

graph showing South River wt8.1graph showing Rhode River wt8.2

Rhode River (WT8.2) - On an annual basis, phytoplankton growth is nitrogen limited more than 70% of the time and is phosphorus limited more than 15% of the time. In winter, phytoplankton growth is nitrogen limited 25% of the time, phosphorus limited almost 10% of the time, and nutrient saturated more than 65% of the time. In spring, growth is nitrogen limited 55% of the time and phosphorus limited 45% of the time. In the summer, phytoplankton growth is entirely nitrogen limited. In the fall, growth is more than 90% nitrogen limited and otherwise is phosphorus limited. Total nitrogen, total phosphorus and dissolved inorganic phosphorus concentrations are relatively fair and dissolved inorganic nitrogen concentration is relatively good. Dissolved inorganic nitrogen and total phosphorus concentrations are improving (decreasing). This ratio is low all year, especially in the summer, consistent with the strong nitrogen limitation at this station. Continued reductions in nitrogen would further limit algal production and continued reductions in phosphorus would help bring the system into better balance.

West River (WT8.3) - On an annual basis, phytoplankton growth is nitrogen limited 60% of the time and phosphorus limited more than 20% of the time. In the winter, phytoplankton growth is nitrogen limited about 20% of the time and is otherwise nutrient saturated (light limited or no limitation). In spring, growth is nitrogen limited more than 35% of the time and phosphorus limited 50% of the time. In the summer, phytoplankton growth is entirely nitrogen limited. In fall, growth is nitrogen limited approximately 65% of the time and phosphorus limited 35% of the time. Total nitrogen and total phosphorus concentrations are relatively fair and dissolved inorganic nitrogen and dissolved inorganic phosphorus concentrations are relatively good. Total phosphorus concentration is improving (decreasing). Dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is decreasing. This ratio is low in winter, summer and fall, consistent with the strong nitrogen limitation at this station. Continued reductions in phosphorus concentrations in addition to reductions in nitrogen will further reduce phytoplankton growth and bring the system into better balance.

graph showing West River wt8.3

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

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