COMPARING SAMPLING SCHEMES FOR MONITORING POLLUTANT EXPORT FROM A DAIRY PASTURE¹

Abstract

Dairy cow pastures and feeding areas around barns can be a significant source of nonpoint source pollutants to nearby streams. To help document the significance of these sources, nutrient export in streamfiow from a 56.7‐ha, mostly agricultural, watershed located in southwestern North Carolina was monitored from August 1994 to January 1996. Total nitrogen and phosphorus export rates from the upper, predominantly pasture, part of the watershed were 18.0 and 1.4 kg/ha/yr, respectively, as measured by weekly grab sampling and 18.7 and 4.9 kg/halyr, respectively, as measured from storm event monitoring. Nitrogen and phosphorus export rates for the area between the monitoring sites, which included overgrazed cow holding and feeding areas and farm buildings, were 376 and 86 kgfhalyr, respectively, for grab sampling and 351 and 160 kg/ha/yr, respectively, for storm event monitoring. To estimate the amount of reduction from nonpoint source controls necessary to effect a significant reduction in pollutant loading, statistical analyses of the load data were conducted. The analyses for the five pollutants monitored showed that total suspended solids would require the greatest reduction (34.6 percent for weekly grab and 33.6 percent for storm) in loading after the implementation of controls for statistical significance. Nitrate plus nitrite was found to require the least reduction (12.6 percent for weekly grab). Pollutant export rates computed from weekly grab samples and storm event samples used separately were compared to corresponding export rates computed from combining grab and storm event samples to assess the differences in monitoring schemes.

Characterizing deep soils from an impacted subtropical isolated wetland: implications for phosphorus storage

“…With open access to wetlands and ditches, cattle can increase nutrient pollution by depositing manure into surface waters (Bottcher et al 1999;Alloush et al 2003) or by stimulating nutrient release from sediments stirred up by cattle activity (Line et al 1998). Heavy stocking can also lead to the reduction in vegetation cover and an increase in soil erosion (Capece et al 2007).…”

Errors of flux integration methods for solutes in grab samples of runoff water, as compared to flow-proportional sampling

“…This requires both an appropriate sampling scheme and a correct numerical integration of discharge and concentrations. Several studies have been published comparing different sampling schemes and/or integration methods, either in a mathematical approach (Cohn, 1995;Schwartz and Naiman, 1999) or based on empirical measurements (Johnson, 1979;Dolan et al, 1981;Walling and Webb, 1985;Dann et al, 1986;Preston et al, 1992;Thomas and Lewis, 1993;Swistock et al, 1997;Webb et al, 1997;Bukaveckas et al, 1998;Line et al, 1998;Robertson and Roerish, 1999;Smart et al, 1999;Stone et al, 2000;Horowitz et al, 2001;Coats et al, 2002;Cooper and Watts, 2002). Comparisons usually consider both the accuracy (low systematic error, i.e.…”

Spatial and Time Distribution of Dairy Cattle Excreta in an Intensive Pasture System

“…Nonpoint‐source pollution can occur from pasturelands and conventional drylots as the result of surface water runoff during rain storm events. According to Line et al (1998), dairy farms can contribute significant sources of nonpoint‐source pollution. Goetz (1999) found that nutrient pollution in runoff was much greater from a conventional drylot system than from a grazing system.…”