Jordan Lake (Reservoir), located in central North Carolina, is a 5,650-ha impoundment with a 436,860-ha watershed of which 18% was urban, 20% agricultural, and 56% forested. Like many lakes in the eastern U.S., the use of this water resource is being threatened by excessive nutrient inputs. A proposed nutrient reduction strategy set overall nitrogen (N) and phosphorus (P) load reduction goals for the watershed at 8-35% for N and 5% for P. Because much of the agricultural land in the watershed was used for pasture, the initial focus of reduction efforts was on pastures with livestock exclusion fencing identified as having the most potential. The objective of this project was to document the effectiveness of a combination of livestock exclusion fencing and nutrient management implemented on a beef cattle pasture typical of pastures in the Jordan Lake watershed and of the Piedmont region of NC.
The paired watershed experimental approach used in this project, required simultaneous monitoring of two watersheds (treatment and control), during a calibration and a treatment period. The calibration period was from 12/30/07 to 10/5/11 and the treatment period was from 10/6/11 to 12/18/15. During both periods, the rainfall and quantity and quality of discharge were monitored continuously. Land use information (number of cattle, fertilization, soil test results) was collected at least annually. The treatment watershed (Past-treat) encompassed 54.5 ha all but 7.3 ha of which was used for beef cow pasture. The control watershed (Past-cont) encompassed 78.1 ha 39.5 ha of which was pasture, while most of the remainder (27.5 ha) was wooded.
In the treatment watershed the exclusion fenceline was constructed in October, 2011 about 3 m from the top of the streambank on either side and was limited to the main stream channel only (fig. 1b). Nutrient management was also implemented which eliminated P application as soil tests showed that there was adequate P in the soil to support the growth of pasture grasses such as fescue. In the control watershed, beef cattle had unlimited access to the stream channel during the entire project (fig. 1a). Monitoring included collecting flow-proportional samples during storm events and analyzing them for total Kjeldahl (TKN), ammonia (NH3-N), and inorganic (NOx-N) nitrogen as well as total phosphorus (TP) and total suspended solids (TSS).
Statistical analyses of storm event load data documented that during the post-fencing period, mass loading of TKN (34%), NH3-N (54%), TN (33%), TP (47%), and TSS (60%) was reduced significantly in the treatment relative to the control watershed, while storm discharge and NOx-N loads were not significantly different. These data showed that even a relatively narrow exclusion corridor implemented on only the main stream channel can significantly reduce the export of nitrogen, phosphorus, and sediment from a beef cattle pasture.
Evaluate livestock exclusion fencing at another Piedmont site with a wider exclusion corridor.
Daniel Line, Extension Specialist at NC State University
Deanna Osmond, Professor, NC State University
Published in J. Environmental Quality 45:1926-1932
This project received support from the National Institute of Food and Agriculture, U.S. Department of Agriculture, Integrated Water Quality Grant award 2011-0515 as well as funding from NCDEQ-DWR as pass-through funds from U.S. EPA 319.