Water Quantity and Quality from a Small Georgia Pasture During 1998-2009: Impact of Drought

Proceedings of the 2011 Georgia Water Resources Conference, April 11, 12, and 13, 2011, Athens, Georgia.The water quality impact of pasture grazing in the Piedmont, which generally occurs under low-input management, is not well studied. Cattle, hydrologic and water quality data were collected from 1999 to 2009 from a rotationally grazed 7.8-ha pasture near Watkinsville Georgia. Grazing occurred during 69 time periods, with 20 to 225 head of cattle grazing 1 to 71 days each period. Mean cattle days (head of cattle x days spent) was 182.4 ha⁻¹ grazing-period⁻¹. Drought occurred with 7 of the 11 years having below average annual rainfall. Runoff events were limited to 20 during 86 months of below average rainfall (deficit period) compared with 54 during 46 months of the non-deficit period. Instrument problems limited sample collection to 43-47 out of possible 67 events from 2000-2009. Across all data, mean event flow weighted concentration (FWC) in mg L⁻¹ was < 1.0 for nitrate-nitrogen (NO₃-N) and ammonium-nitrogen (NH₄- N), 3.7 for total nitrogen (TN), 9.1 for total organic carbon (TOC), 2.0 for ortho-P (PO₄4-P), 2.4 for total P (TP), 0.23 for iron (Fe), and 0.06 for aluminum (Al). Nutrient loads in kg ha⁻¹ event⁻¹ averaged 0.04 for NO₃-N, 0.03 for NH₄-N, 0.19 for TN, 0.54 for TOC, 0.11 for (PO₄4-P, and TP, 0.02 for Fe, and 0.01 for Al. Peak nutrient concentrations and loads occurred during calving season and/or when monthly rainfall was above average. Total load was 3 to 6 times greater from non-deficit than deficit periods. Concentrations of N were well below drinking water standards. Nevertheless observed N and P losses could pose risk of eutrophication because it can be stimulated at low concentrations. Such long-term data are needed to help states set or refine water quality standards.Sponsored by: Georgia Environmental Protection Division U.S. Geological Survey, Georgia Water Science Center U.S. Department of Agriculture, Natural Resources Conservation Service Georgia Institute of Technology, Georgia Water Resources Institute The University of Georgia, Water Resources FacultyThis book was published by Warnell School of Forestry and Natural Resources, The University of Georgia, Athens, Georgia 30602-2152. The views and statements advanced in this publication are solely those of the authors and do not represent official views or policies of The University of Georgia, the U.S. Geological Survey, the Georgia Water Research Institute as authorized by the Water Research Institutes Authorization Act of 1990 (P.L. 101-307) or the other conference sponsors