Ecology–Soil Relations — Abstract of Paper


Nitrogen Dynamics of Spring-fed Wetland Ecosystems of the Sierra Nevada Foothills Oak Woodland
Randall D. Jackson¹ and Barbara Allen-Diaz¹


Spring-fed wetlands are small, highly productive, patchy ecosystems nested within the oak woodland/annual grassland matrix of the Sierra Nevada foothills. In an effort to place these wetlands in a landscape context, we described seasonal variation (1999-2000 growing season) in nitrogen cycling parameters at 6 spring-fed wetland sites of the Sierra Nevada foothill oak woodlands. Ammonium and nitrate pool sizes covaried inversely with nitrate dominance (about 3 µg N g dry soil^-1) in autumn/winter during plant dormancy and ammonium dominance (about 6 µg N gds^-1) in spring/summer when wetland plants were beginning yearly production cycles. Nitrate is highly mobile in the vadose zone but can accumulate in the absence of plant growth during dry summer months in the annual grasslands surrounding these wetland systems. With the onset of autumn rains, much of this nitrate may be flushed down slope to spring systems. Spring-fed wetlands may act as either as sources, sinks, or as transformers of this exogenously derived nitrogen.