Submitted to: Transactions of the ASAE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2003
Publication Date: 11/18/2003
Citation: NOVAK, J.M., STONE, K.C., WATTS, D.W., JOHNSON, M.H. DISSOLVED PHOSPHORUS TRANSPORT IN STREAM FLOW FROM AN AGRICULTURALLY INTENSIVE SOUTHEASTERN COASTAL PLAIN WATERSHED. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 2003. v. 46. p. 1355-1363. Interpretive Summary: Intensive agricultural including concentrated livestock operations use large amounts of nutrients. Thus, there is a potential for excess nutrients in sensitive ecosystems such as the eastern coastal plain where high rainfall, sandy soils, and coastal estuaries occur. In order to balance the needs of intensive agricultural production and sensitive ecosystems, it is important to understand the interactions of excessive nutrients, rainfall, runoff, and stream flows. To address some of these potential problems, we conducted a 2-year study to measure stream water phosphorus concentrations and amounts transported during different stream flow events from a North Carolina watershed. We found that under normal rainfall events and low stream flows, little phosphorus concentrations and amounts occur in the stream system. On the other hand, intense storms from high rainfalls can increase runoff P losses and raise stream flows that accelerate the amount of phosphorus transported out of the watershed.
Technical Abstract: In many states with concentrated animal production, soils used for manure disposal frequently have accumulated soil phosphorus (P) in excess to plant nutritional requirements. During storms off-site P movement from soils high in P into surface water systems can increase P export to downstream Coastal ecosystems and potentially jeopardize water quality. We characterized fluvial dissolved phosphorus (DP) concentrations and transport trends from an agriculturally intensive Coastal Plain watershed under different stream flow conditions by measuring DP concentrations and flow over a two-year period. Stream flow was separated into base flow and storm flow conditions for the whole watershed and on a subwatershed basis. Between 78 and 97% of the annual stream flow from all subwatersheds occurred under storm flow conditions. More DP was exported under storm flow than base flow rates. DP concentrations at each outlet were not significantly influenced by stream flow rates. A series of intense summer storms in June and July 1995 produced sufficient rainfall and runoff conditions to increase stream flow to transport almost 250 kg of DP at the outlet (78% of the annual fluvial DP load) during this short period. Regression analyses showed that there was a strong linear relationship between log stream water flow and log DP exported. Our results show that high stream water flow will accelerate fluvial DP transport from an agriculturally intensive watershed and that exported stream DP loads can be reasonably predicted using stream water flow rates.