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United States Department of Agriculture

Agricultural Research Service

Title: Flow Proportional and Time Composite Estimates of Nutrient Loading from An Eastern Coastal Plain Watershed

item Stone, Kenneth
item Johnson, Melvin
item Novak, Jeffrey
item Watts, Donald
item Hunt, Patrick

Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: July 13, 1998
Publication Date: N/A

Technical Abstract: The balance between resources expended and information obtained is an integral aspect of water quality investigations. As part of a Water Quality Demonstration Project in the eastern Coastal Plain, we monitored stream water quality at the watershed outlet. Four methods of assessing stream water quality were compared. These methods were time-composite sampling with continuous flow measurements (TC), flow-proportional samplin with independent measurement of flow (FP), grab sampling with instantaneous flow measurements (IG), and grab sampling for quality assurance/quality control checks using daily USGS flow measurements (UG). Flow measurements using the TC and IG methods were highly correlated (r**2=0.97). Because of more intensive measurements during high flow, the FP method measured higher flow rates during the sampling period. For all four methods, nitrate-N and ammonia-N concentrations were not correlated to stream flow. Because of the significantly higher flow, the FP method predicted significantly highe mass loading rates for both nitrate-N and ammonia-N. Grab sampling (IG and UG) and the TC methods were not significantly different for the entire study period, however, a few monthly differences were significantly different. These results suggest that an appropriate sampling method should adequately weight sampling of both storm and base flows.

Last Modified: 4/22/2015