Spring-water Nitrate Increased with Removal of Livestock Grazing in a California Oak Savanna |
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Authors: | Randall D Jackson Barbara Allen-Diaz Lawrence G Oates Kenneth W Tate |
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Institution: | (1) Department of Agronomy, University of Wisconsin-Madison, 1575 Linden Drive, Madison, Wisconsin 53706-1597, USA;(2) Ecosystem Sciences, University of California, Berkeley, 151 Hilgard Hall, Berkeley, California 94720-3110, USA;(3) Department of Agronomy and Range Science, University of California, Davis, One Shields Ave, Davis, California 95616, USA |
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Abstract: | We characterized spatial and temporal changes in nitrate concentrations of the leachate from annual grasslands and subsequently
emergent spring-waters and tested the effect of livestock grazing removal on them. Nitrate patterns indicated that annual
grassland soils are a likely N source to spring-fed wetlands, which appear to intercept and transform N along its hydrologic
path from upland soils to spring-fed, headwater streams. Aboveground biomass and soil N extractions suggested that removal
of livestock grazing from these wetlands impaired this function by allowing dead plant material to accumulate inhibiting plant
production (hence, plant N demand), resulting in elevated stream-water nitrate (NO3−) concentrations. Nitrous oxide (N2O) fluxes indicated that grazing removal may increase the relative importance of this N-loss pathway. Microbial biomass varied
with season but was not affected by grazing treatments suggesting that N2O losses were related to differences in NO3− availability rather than grazing effects on microbial community composition or their activity. Spring-fed wetlands provide
important ecosystem services such as plant uptake and denitrification at transition zones between terrestrial and aquatic
ecosystems. These N-retention and transformation functions may be enhanced through biomass harvesting by livestock. |
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Keywords: | water quality wetlands nitrogen loss livestock grazing mixed effects modeling Mediterranean ecosystems |
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