Monitoring of the Bay’s nontidal rivers offered a mixed verdict for 2003. Near-record flows left the Chesapeake awash in nutrients and sediment during 2003. Yet when adjusted for flow, nutrient concentrations in many, though not all, of the watershed’s major rivers had declining trends.
That was not much of a silver lining for fish, crabs and grass beds, which were hard hit by huge amount of nutrients and sediment swept into the Bay by the third highest level of river flow recorded since 1937.
As a result, the acreage of underwater grass beds was knocked back 30 percent from 2002 levels, the largest single-year decrease ever observed. In addition, the deep waters of the Bay had some of the most severe, and extensive, areas of oxygen-depleted water on record.
In all, nontidal rivers—which drain about 60 percent of the watershed—delivered about 350 million pounds of nitrogen to the Bay in 2003, along with 30 million pounds of phosphorus, according to estimates by the U.S. Geological Survey. That’s more than would come from the entire watershed in a “normal” year. (Monitoring nutrients from tidal rivers and creeks in the coastal plain portion of the watershed is difficult because of the back-and-forth tidal movement of water.)
Those nutrient loads are determined by the concentration of nutrients and sediment in the water, and the amount of river flow headed toward the Bay.
When adjusted for river flow, USGS scientists say monitoring shows decreasing nitrogen concentrations for the Potomac and rivers to the north, but no trend—or increasing trends—in rivers to the south. The phosphorus picture was more mixed, with a decreasing trends in most of the Susquehanna, the Patuxent, the Rappahannock and the James, and , increasing, or no trends in other rivers.
While declining, these measured concentrations still remain far above historic levels. A recent analysis by a team of Bay scientists found that nitrogen concentrations in the Susquehanna, while falling since 1985, were still 10 times greater than those in streams draining forested areas.
Ultimately, it is critical that nutrient concentrations be reduced to the point that water quality is not determined primarily by weather patterns. That’s because the determination of whether the Bay attains its new water quality standards will be made with real-world monitoring, not virtual-world models or flow-adjusted concentration estimates.