The actual amount of nitrogen entering the Bay in 2005 was close to 370 million pounds. That figure is about 200 million pounds more than the 175 million pound goal for nitrogen.
It was also close to the average nitrogen “load” to the Bay since 1990—which signals that nutrient reduction efforts still have a long ways to go.
A similar estimate for phosphorus showed that about 26.1 million pounds entered the Bay in 2005 compared with an average of 21.8 million pounds since 1990.
Part of the reason for the figure was river flow. Although the average flow into the Bay was near normal for 2005, the flows during individual months were anything but average. Several months, especially early in the year, were far wetter than normal, while several other months, particularly in the summer, were drier than normal.
The amount of nutrients moved during those wetter-than-normal conditions tend to more than offset the reduced nutrient movement during drier periods. That is especially true for phosphorus, which is often bound with sediment. Disproportionate amounts move downstream during very high-flow conditions.
The loading estimates come from a recently developed technique by the Bay Program that uses a hybrid of modeling and monitoring data.
The technique uses monitored nutrient and sediment loads entering tidal rivers from the nine major upstream waterways that feed the Bay. Altogether, that network monitors nutrient runoff from 78 percent of the watershed. It does not include runoff from most of the Coastal Plain areas east of Interstate 95, which goes directly into tidal waters.
To estimate loads from the Coastal Plain, the EPA’s Bay Program uses projections from its Watershed Model. The model typically estimates nutrient movement under “normal” hydrology, so those figures have to be adjusted to correspond with the river flow conditions observed in the monitoring network. Also added to the figures are estimates of nutrient discharges from point sources, such as wastewater treatment plants, located in the Coastal Plain.