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Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASAE. 47(5): 1457-1463. (doi: 10.13031/2013.17626) @2004
Authors:   K. W. King, R. D. Harmel
Keywords:   Bermuda grass, Concentration, Monitoring, Water quality

Water quality loadings are generally calculated without knowledge of the relationship of the calculated loads to the total loads. A laboratory runoff study was designed and conducted to compare total loads with loads calculated from time- based sampling strategies. Total loads were measured by capturing all the runoff from 2.2 m2 Bermuda grass (Cynodon dactylon L. Pers.) sod plots with 5% slope and analyzing for NO3+NO2-N and NH4-N. Runoff samples were also manually collected on 1 min intervals during 2 h overland flow events. Total loads were compared to time-discrete and time-composite sampling strategies. The strategies included time-discrete sampling at 1, 2, 3, 4, 5, 10, 15, and 30 min and composite sampling that included 2, 3, 4, and 5 aliquots per composite sample based on the same time-discrete intervals. In addition, loads were also calculated from a composite sample derived from aliquots collected at 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 min intervals. The calculated load of NO3+NO2-N and NH4-N was not significantly different (. = 0.05) from the total load when using time-discrete sampling at 1, 2, or 3 min time intervals. No significant difference (. = 0.05) from the total load was found when using a composite approach with 2, 3, 4, or 5 aliquots collected at 1, 2, or 3 min time intervals or when using a composite sample with aliquots collected on a 1 min interval. To preserve the total load from plot-scale studies, more intensive sampling is required. The results from this study will facilitate the selection of time-based sampling strategies for plot-scale studies.

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