Nonpoint-source pollutant load reductions associated with livestock exclusion
-
-
Authors: D. E. Line, W. A. Harman, G. D. Jennings, E. J. Thompson, and D. L. Osmond
Date: 2000
Journal: Journal of Environmental Quality
Volume: 29
Number: 6
Pages: 1882-1890
Summary of Methods: Water quality was measured before and after improvements were made in two grazed pastures. An alternate water source was installed in a lightly grazed pasture, and an alternate water source, riparian fencing and plantings were installed in a heavily grazed pasture. The alternate water source did not significantly reduce the amount of pollutants entering the stream from the lightly grazed pasture. However, the The effectiveness of best management practices (BMP, including livestock exclusion, alternative water sources and planting trees on riparian corridor (or natural revegetation) in reducing sediment, nitrogen, and phosphorus loading rates was examined on a watershed in the Piedmont region, North Carolina. The watershed was divided into a lightly grazed upper pasture (Site D) and a heavily grazed lower pasture (between Site D and E). In both pastures an alternative watering system was installed on ridges and continuous discharge measurements were taken from August 1994 to September of 1998 at site D and E. Livestock were excluded from the stream in the lower pasture by a riparian fence installed in February 1996. A considerable amount of volunteer vegetation (willows, cattails, grasses and a variety of weeds) grew in the riparian corridor after livestock were excluded. Grab samples were collected weekly and analyzed for nitrite + nitrate nitrogen, total Kjeldahl nitrogen (TKN), total phosphorus (TP), total suspended solids (TSS), and total solids (TS). Soil cores were collected (10 on floodplain and 10 on terrace) just before establishment of riparian pasture and in May of the third year after establishment to measure bulk density and saturated hydraulic conductivity.
Article Summary / Main Points: Implementation of an alternative watering system and livestock exclusion fencing reduced weekly discharge and loading rates of sediment, nitrate + nitrite N, TKN, TP, TSS, and TS while the alternate watering system alone decreased rates of nitrate + nitrite N and TSS loads. Best management practices were effective at reducing loads of TKN, TP, and TSS but less effective at decreasing the nitrate and nitrite load. The weekly discharge during the December- February and March-May periods were greatest for post-BMP implementation compared to pre-BMP for the lightly grazed, unfenced site. Discharge was not different for post- and pre-BMP for the heavily grazed, fenced site. Nonpoint-source pollutant loads from the heavily grazed pasture were reduced with livestock exclusion and subsequent riparian vegetation re-establishment. Bulk density of soils in the riparian corridor was lower on the fenced riparian corridor at both the terrace and the floodplain stage after fencing. Soil saturated hydraulic conductivity increased after fencing on the terrace site indicating an increase in infiltration.
Vegetation Types: Riparian and Wetlands
MLRA Ecoregions: 136 Southern Piedmont
Agrovoc Control Words: Riparian zones Grazing Nonpoint pollution
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: grazing, water pollution, sediment load, riparian fencing, grazing intensity, alternative water source, watershed
Annotation: The results from this study are applicable to native watersheds and pastures from all areas. Application of these results should be applied with caution as only one stream was tested and each BMP was tested at a different grazing intensity. Further research is required to clearly evaluate the effectiveness of only off-site water development alone or paired with fencing the riparian corridor and revegetation. Riparian area fencing limits livestock access to the stream and prevents mechanical breakdown of streambanks. Additional research has shown that periodic, short-term grazing by livestock in these riparian corridors can limit the amount of invasive weeds moving into an area so size of these riparian corridors is very important. This is part of a larger study by Line in 2003 (T Am Soc Ag Eng:287-293) also available in the RSIS database.
-
Get article
Cite article with DOI
-