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Submitted to: Proceedings of the USCID Wetlands Seminar
Publication Type: Proceedings Publication Acceptance Date: 1/1/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Nonpoint sources of phosphorous from grazed meadows and wetlands have become an important issue. Best management practices such as vegetative filter strips and rotational grazing systems should reduce the total phosphorus loading in the streams, lakes, and reservoirs by reducing erosion. A case study of the Cascade Reservoir watershed in west- central Idaho was used in the development and application of a conceptual simulation model of phosphorus export from the ecosystem. Assuming best management practices are applied, a simple mass balance confirms that cattle grazing can remove significant amounts of phosphorus through cattle harvesting the forage and exporting phosphorus in bone and soft tissue growth. By varying forage yield, phosphorus concentration in the forage, phosphorus retention in the cattle, and other variables, the model predicted a range from 4 to 95 tons of phosphorus removed from the watershed annually. A moderate value of 3.3 lb phosphorus per acre per year was predicted. Technical Abstract: Elevated phosphorus (P) loading of wetlands, streams, lakes, and reservoirs can occur from nonpoint sources such as grazing of irrigated or naturally wet meadows and palustrine wetlands. The water entering Cascade Reservoir of west- central Idaho sometimes has elevated P concentrations (>0.050 ppm) and provides a P load of 54 tons P/yr. The use of best management practices such as rotational grazing, buffer strips next to wetlands, and proper irrigation management should reduce overland flow and streambank erosion. Livestock grazing should harvest and remove a significant amount of P from the ecosystem from incorpora- tion into bone and tissue mass of growing animals and beef export from the basin. About 44,000 ac of mostly flood- irrigated pasture land exists in the Cascade Reservoir watershed. The Phosphorus Uptake and Removal from Grazed Ecosystem (PURGE) model uses three separate methods to estimate P retention in cattle and using limits of the input variables, predicted that from 4 to 95 tons P could be removed annually from the Cascade watershed. With proper grazing management, cattle should be part of a long term solution to P loading and improvement of water quality in Cascade Reservoir. |
