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United States Department of Agriculture

Agricultural Research Service

Research Project: MANAGING WATER AVAILABILITY AND QUALITY TO MAINTAIN OR INCREASE AGRICULTURAL PRODUCTION, CONSERVE NATURAL RESOURCES, AND ENHANCE ENVIRONMENT

Location: Coastal Plain Soil, Water and Plant Conservation Research

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

Authors
item Sigua, Gilbert
item Chase, Chadwick

Submitted to: Environmental Monitoring and Assessment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 25, 2013
Publication Date: January 13, 2014
Citation: Sigua, G.C., Chase, C.C. 2014. Groundwater phosphorus in forage-based landscape with cow-calf operation. Environmental Monitoring and Assessment. 186:1317-1326.

Interpretive Summary: Phosphorus (P) is an essential macronutrient that is required to meet global food requirements and make crop and livestock production profitable. While adequate levels of P soils are essential to grow crops, P has the potential to induce eutrophication in our water systems. In most cases, eutrophication has accelerated by increased inputs of P due to intensification of crop and animal production systems. Assessing and controlling 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 three 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. Based on the concentrations of P in GW (0.09 milligram per liter (mg/L) that were observed in our study, potential leaching of P under grazed bahiagrass pastures would not be harmful to water quality. However, the average concentration of P in SW of 0.45 mg/L is above the Environmental Protection Agency’s mean contamination level (MCL) (0.10 mg L-1) and this level could pose a harmful effect on the environment and, therefore, would require a continued and long-term monitoring and assessment. To effectively implement any best management practice (BMP), it is necessary to recognize the potential impact of agricultural P on SW and understand that different landscape locations and varying hydrologic conditions in forage-based landscape could affect the spatial and temporal variations of P losses at the watershed scale.

Technical Abstract: 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 three 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 while P concentration in SW ranged from 0.25 to 0.71 mg/L. The three-year average of P in GW of 0.09 mg/L was lower than the recommended goal or the EPA’s mean contamination level (MCL) value of 0.10 mg/L. The three-year average of P concentration in SW of 0.45 mg/L was four-fold higher than the EPA’s MCL 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.

Last Modified: 11/28/2014
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