An estimated 92% of water quality degradation in the Tar-Pamlico River Basin of North Carolina is attributed to nutrient-laden runoff, a large portion of which is contributed by agricultural activities. The Tar-Pamlico Agricultural Rule mandates that agricultural operations in the basin collectively achieve and maintain no net increase in total phosphorus (P) loading over 1991 P levels. In order to accomplish this, the development of a strategy that accounts for P losses and gains from agricultural activities in the basin was required. Quantitative accounting of P loading is not possible due to the complexity of P behavior and transport within a watershed and the lack of data quantifying the various mechanisms of P loss and retention. Therefore, we designed an approach which documents trends in land use and management related to agriculture in the basin. Relative changes in land-use practices that either increase or decrease the risk of P loss were tracked from 1991 to the present. Because of the reliance on historical county-level data, there are many sources of error involved with the data used, most notably the assumption that crops and livestock are uniformly distributed throughout each county. The use of soil test P data is also problematic due to the biased nature in which soil samples are collected by land owners as well as the temporal and spatial variability of soil test P. Relative changes from 1991 to the present were estimated for the following factors: cropland acreage, livestock numbers, manure P content, land uses that reduce the risk of P loss, BMP implementation, as well as soil test P. Results of our approach show either no change or only a slight increase in P inputs to the basin, while the use of conservation practices to prevent P loss greatly increased during the period of interest.
See more of Phosphorus Chemistry in Soils: II. P Fluxes in Soil and Water Systems
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See more of The ASA-CSSA-SSSA International Annual Meetings (November 6-10, 2005)