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Results for the Patapsco-Back Basin |
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| The nutrient limitation models were used to predict nutrient limitation for the stations in the Patapsco and the Back Rivers. 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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Back River (WT4.1) - On an annual basis, phytoplankton growth is nutrient saturated (light limited or no limitation) almost 70%, nitrogen limited more than 10% of the time and phosphorus limited almost 20% of the year. Winter growth is entirely nutrient saturated. In spring, growth is phosphorus limited 20% of the time and nitrogen limited 10% of the time. In summer, growth is nitrogen limited about 30% of the time and phosphorus limited 5% of the time. In fall, growth is phosphorus limited 45% of the time and otherwise is nutrient saturated. Total nitrogen, dissolved inorganic nitrogen, total phosphorus and dissolved inorganic phosphorus concentrations are all relatively poor at this station, but total nitrogen and dissolved inorganic nitrogen concentrations are improving (decreasing). The ratio of total nitrogen to total phosphorus and the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios are both decreasing. The dissolved inorganic nitrogen to dissolved inorganic phosphorus ratio is relatively high in the fall which suggests that reductions in phosphorus may be the most effective means of controlling phytoplankton growth in that season. This ratio is low in summer (suggesting possible nitrogen limitation), but dissolved inorganic nitrogen concentration is still high. Continued reductions in nitrogen will further increase occurrences of nitrogen limitation in the summer. Reductions in both nutrients will be needed to limit growth in the winter and spring..
Patapsco River (WT5.1) – On an annual basis, phytoplankton growth is phosphorus limited almost 50% of the time and nitrogen limited 20% of the time. Winter growth is nutrient saturated (light limited or no limitation). In the spring, growth is phosphorus limited almost 75% of the time. In the summer, phytoplankton growth is nitrogen limited 50% of the time and phosphorus limited 50% of the time. In the fall, growth is phosphorus limited 50% of the time and nitrogen limited approximately 15% of the time. Total nitrogen, dissolved inorganic nitrogen, and total phosphorus concentrations are all relatively poor but are improving (decreasing); dissolved inorganic phosphorus concentration is fair. The ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus is decreasing; this ratio is relatively high in the winter, which suggests that reductions in phosphorus may be the most effective means of controlling phytoplankton growth in that season. This ratio is low in summer (suggesting possible nitrogen limitation), but dissolved inorganic nitrogen concentration is still high Reductions in nitrogen will further increase occurrences of nitrogen limitation in the summer. . For more information, please contact
Renee
Karrh |
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