Groundwater phosphorus in forage-based landscape with cow-calf operation

Forage-based cow-calf operations may have detrimental impacts on the chemical status of groundwater and streams and consequently on the ecological and environmental status of surrounding ecosystems. Assessing and controlling phosphorus (P) inputs are, thus, considered the key to reducing eutrophication and managing ecological integrity. In this paper, we monitored and evaluated P concentrations of groundwater (GW) compared to the concentration of surface water (SW) P in forage-based landscape with managed cow-calf operations for 3 years (2007-2009). Groundwater samples were collected from three landscape locations along the slope gradient (GW1 10-30% slope, GW2 5-10% slope, and GW3 0-5% slope). Surface water samples were collected from the seepage area (SW 0% slope) located at the bottom of the landscape. Of the total P collected (averaged across year) in the landscape, 62.64% was observed from the seepage area or SW compared with 37.36% from GW (GW1 = 8.01%; GW2 = 10.92%; GW3 = 18.43%). Phosphorus in GW ranged from 0.02 to 0.20 mg L(-1) while P concentration in SW ranged from 0.25 to 0.71 mg L(-1). The 3-year average of P in GW of 0.09 mg L(-1) was lower than the recommended goal or the Florida's numeric nutrients standards (NNS) of 0.12 mg P L(-1). The 3-year average of P concentration in SW of 0.45 mg L(-1) was about fourfold higher than the Florida's NNS value. Results suggest that cow-calf operation in pasture-based landscape would contribute more P to SW than in the GW. The risk of GW contamination by P from animal agriculture production system is limited, while the solid forms of P subject to loss via soil erosion could be the major water quality risk from P.