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Title: IMPOUNDMENT WATER QUALITY FROM TWO MIXED LAND-USE AGRICULTURAL WATERSHEDS.

Author
item Daniel, John
item ELMENDORF, DAVID - UCO, EDMOND, OK

Submitted to: Proceedings of American Society of Agricultural Engineers
Publication Type: Proceedings
Publication Acceptance Date: 3/11/2002
Publication Date: 3/11/2002
Citation: N/A

Interpretive Summary: Surface impoundments are a common conservation practice used to inhibit erosion, thus improving downstream water quality, but they also may restrict nutrient movement. The objective of this study is to determine the effectiveness of nutrient removal by surface impoundments. Two grazed agricultural watersheds, one with an upstream dairy operation and one without, were studied. Both contain a stream drainage with four successiv surface impoundments, and each was dominated by grazed winter wheat and rangeland. Water samples from surface impoundments were collected monthly from winter to summer and analyzed for nitrate-nitrogen, bioavailable and water-soluble phosphorus. Results show no significant difference among watersheds in nitrate-nitrogen concentrations. While bioavailable and water-soluble phosphorus concentrations were found to be higher in the watershed associated with the dairy operation, phosphorus levels decreased with downstream impoundments. However, phosphorus levels are seasonally dependent. Decreasing levels of phosphorus downstream of the dairy suggest the surface impoundments mitigated some of the bioavailable and water- soluble phosphorus. Surface impoundments may provide a simple and cost effective approach to restricting nutrient movement.

Technical Abstract: Surface impoundments have been shown to improve downstream water quality by restricting soil erosion, but they also may be effective to inhibit nutrient movement. The objective of this study is to determine the effectiveness of nutrient removal by successive surface impoundments in a stream drainage. Two grazed agricultural watersheds, one with an upstream dairy operation and one without, were used. Both contain a stream drainag with four successive surface impoundments, and each utilized grazed winter- wheat and rangeland management practices. Water samples from surface impoundments were collected monthly from winter to summer and analyzed for nitrate-nitrogen, bioavailable (BAP) and water-soluble phosphorus (WSP). Nitrate-nitrogen concentrations for both watersheds showed no significant difference in impoundment position. BAP and WSP concentrations were found to be higher in the watershed associated with the dairy operation, but phosphorus levels were found to decrease in the downstream surface impoundments. However, BAP and WSP levels are seasonally dependent. Decreasing levels of nutrients downstream of the dairy operation suggest the surface impoundments mitigated some of the bioavailable and water- soluble phosphorus, suggesting and that surface impoundments may provide a simple and cost effective approach to restrict nutrient movement.