Low winter and spring flow may lead to better conditions this summer
Nutrient loading related to river flow
The Susquehanna River is the single largest source of nitrogen and phosphorus discharging into Chesapeake Bay. These nutrients have a significant effect on the dissolved oxygen and Prorocentrum forecasts. Susquehanna River flows during the first five months of 2009 were characterized by two large peak flows in late February and mid-March, which were higher than normal. Following the mid-March peak, Susquehanna river flows were substantially lower than average.
Susquehanna River daily mean flow rates for January through June 2009 compared to the long-term average. Flow data supplied by USGS and are still provisional.
Provisional Susquehanna River total nitrogen loads (fall-line) for the January to May 2009 period were below average. The low nitrogen loads are unusual for this time of year. However, the loads follow the low flow from the Susquehanna (above). The lower-than-average nitrogen load estimates are the reason hypoxic volume is predicted to be relatively small (average) this summer.
Susquehanna River total nitrogen loads (fall-line) for the period of January to May for 2009 and the long-term average for the same months. Provisional data supplied by USGS.
The forecasts do not account for unseasonable late spring or summer conditions, but represent the best available prediction based on past and present conditions.
This summer it is predicted that:
The anoxic condition (no dissolved oxygen) in the Bay's mainstem is predicted to be poor this summer, with the average anoxic volume forecast to be 0.54 ± 0.33 km3. Compared to the previous 24 summers, 2009 could have the 2nd smallest anoxic volume if this prediction holds true.
The average volume of hypoxic water (Dissolved Oxygen ≤2 mg·L-1) in Chesapeake Bay this July is predicted to be 5.1 km3, with a 95% probability that the hypoxic volume will be between 2.7 and 7.4 km3. Compared to past years (1985 to 2008), this July is expected to have the 3rd lowest hypoxic volume. This forecast is based on a model that was developed to assess the impacts of changes in nitrogen loads on Chesapeake Bay hypoxia (Scavia et al 2006).
Low to moderate severity Microcystis blooms are forecast to occur in the tidal Potomac River this summer; 9% ± 2% of samples collected over the summer are predicted to have levels that are considered to be "bloom" concentrations (>10,000 cells·mL-1). Typical sample collection during summer for the affected region is 72 samples. If this prediction holds true, this summer would be ranked as the 8th best (or 11th worst) among the last 18 years of monitoring.
Prorocentrum blooms are predicted to occur in the lower reaches of the Patuxent River in June. Blooms are also predicted to occur in June in Baltimore Harbor. At this stage, no blooms are predicted to occur in the late summer and fall period in the forecast regions.