Authors: Keith E Schilling Peter Jacobson
Publish Date: 2008/01/23
Volume: 87, Issue: 2, Pages: 199-216
Abstract
It has been recognized that subsurface lithology plays an important role in controlling nutrient cycling and transport in riparian zones In Iowa and adjacent states the majority of alluvium preserved in small and moderate sized valleys consists of Holoceneage organicrich and finegrained loam In this paper we describe and evaluate spatial and temporal patterns of lithology and groundwater nutrient concentrations at a riparian well transect across Walnut Creek at the Neal Smith National Wildlife Refuge in Jasper County Iowa Land treatment on one side of the stream reduced the grass cover to bare ground and allowed assessment of the effects of land management on nutrient concentrations Results indicated that groundwater in Holocene alluvium is very nutrient rich with background concentrations of nitrogen phosphorus and dissolved organic carbon that exceed many environmentally sensitive criteria Average concentrations of ammonium exceeded 1 mg/l in several wells under grass cover whereas nitrate concentrations exceeded 20 mg/l in wells under bare ground Phosphate concentrations ranged from 01 to 13 mg/l and DOC concentrations exceeded 5 mg/l in many wells Denitrification channel incision land management and geologic age of alluvium were found to contribute to variable nutrient loading patterns at the site Study results indicated that riparian zones of incised streams downcutting through nutrientrich Holocene alluvium can potentially be a significant source of nutrient loadings to streams
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