In the past two years, state and federal officials undertook an extensive review of common nutrient reduction practices around the watershed.
The result: New scientific data showed some were not as effective as previously thought. Others were doing better than earlier believed.
As a result, sharp-eyed readers who saved a similar report from the January-February 2001 Bay Journal may notice some unexpected changes.
Runoff from urban areas, which had been increasing in the earlier figures, now show no change for nitrogen and a decline for phosphorus. Agricultural figures show overall increases for phosphorus since the earlier report, and increases for nitrogen in many basins.
In the real world, the agricultural nutrient loads didn’t suddenly increase, and the urban loads did not magically decrease. Rather, the differences reflect a change in the way the Bay Program is now crediting some nutrient reduction actions.
To measure cleanup progress, state and federal officials assign different levels of nutrient reduction effectiveness to various runoff control techniques, known as best management practices, which are used on agricultural, urban or other lands. Then, they keep track of how widely those practices are implemented.
Recent studies, though, suggest that the nutrient control effectiveness of some widely used agricultural best management practices, such as farm conservation plans and nutrient management plans, were overly optimistic.
After the review, the effectiveness of a number of other practices were also reduced, while some—such as cover crops planted soon after harvest—were increased.
That didn’t change the amount of actions that had taken place on the land; but it did change modeled estimates of the amount of nutrient reductions that resulted from those actions.
As part of the review, officials began to give credits for the use of phytase feed additives, which reduce phosphorus concentrations in poultry and hog wastes, and for a yield reserve program in which farmers apply nitrogen at levels below that recommended by the nutrient management plan. Nutrient reduction credits were also added for wetland restoration and several other practices. Watershedwide, however, those changes did not outweigh the changes in effectiveness for other practices.
Because of those adjustments, phosphorus from agricultural lands was estimated to have contributed 9.2 million pounds of phosphorus to the Bay in 2002, while the old figures estimated 7.9 million pounds in 2000.
Likewise, the “other agriculture” category—which covers activities related to animal farming.
Operations—contributed 28.5 million pounds of nitrogen in the 2002 figures, compared with 27.9 million in 2000. Changes are even more dramatic within some river basins.
The story was different for urban areas, where revisions included nutrient reductions for several new types of stormwater control practices, and officials more thoroughly estimating how widely existing practices were being implemented.
In 2000, nitrogen loads to the Bay from urban runoff were estimated to have increased 17 percent from 1985. The 2002 figures show no change in nitrogen loads since 1985. For phosphorus, the 2000 figures had shown no change from 1985, but the 2002 figures now show a 15 percent reduction.
Again, that doesn’t mean the nutrient levels dramatically changed from those areas in reality—only that the method for counting actions changed.
The changes were prompted because of a recognition that in some areas, modeled changes in nutrient levels were at odds with water quality monitoring information. Getting the modeled numbers right is important because—as stated elsewhere—while the Watershed Model is the scorecard by which progress is counted, actual monitoring will determine whether the water quality goals are being met.