Evaluating the Effectiveness of Best Management Practices to Reduce Nutrient Loadings from Beef Cattle Ranches to Lake Okeechobee

Cow-calf operations are a source of excessive Nitrogen (N) and Phosphorus (P) loadings in the Lake Okeechobee basin, Florida (USA). A study was conducted at a beef-cattle ranch to evaluate ditch fencing and culvert crossing (DFCC) as a best management practice (BMP) implemented to improve downstream water quality. The BMP was implemented within a ditch section of 170 m in the ranch. The concentrations and loadings of Dissolved Organic Nitrogen (DON), Total Nitrogen (TN), and Total Phosphorus (TP) were compared for a pre-BMP period (June-October, 2005) versus a post-BMP period (June-October, 2006-08) between the upstream and downstream nutrient loads from the BMP site. During the pre-BMP period, P loading was 123.10 kg higher at downstream as compared to that at upstream from the BMP site. During the post-BMP periods in 2006 and 2008, downstream loadings of P were 17.31 and 88.03 kg lower as compared to those upstream from the BMP site. Downstream P loading was 35% higher than that for the upstream during the pre-BMP period while downstream P loadings were 32 and 11% lower during the post-BMP periods of 2006 and 2008, respectively. There were net reductions of N loadings at the BMP site during the 2006 and 2008. Unusually dry conditions during 2007 resulted in the addition of P and N at the BMP site, probably due to the release of P and N from soil and aquatic plants. Average upstream and downstream TP loadings were 294.53 and 263.64 kg for the three post-BMP periods indicating 10% reduction of TP. On average, upstream and downstream TN loadings from the BMP site were 674.65 and 600.85 kg for the three post-BMP periods indicating an 11% reduction of TN. Overall, the BMP is costeffective in improving water quality downstream, with average capital costs for nutrient removal estimated at $7.74 to $22.05 per kg phosphorous, and $3.23 to $9.23 per kg nitrogen. These costs are an order of magnitude lower than the commonly used stormwater treatment areas.