Excess N-2 and denitrification in hyporheic porewaters and groundwaters of the San Joaquin River, California

Sarra E Hinshaw; Taiping Zhang; John A Harrison; Randy A Dahlgren

doi:10.1016/j.watres.2019.115161

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Excess N-2 and denitrification in hyporheic porewaters and groundwaters of the San Joaquin River, California

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Excess N-2 and denitrification in hyporheic porewaters and groundwaters of the San Joaquin River, California

Sarra E Hinshaw, Taiping Zhang, John A Harrison and Randy A Dahlgren

Water research (Oxford), Vol.168

01/01/2020

DOI: https://doi.org/10.1016/j.watres.2019.115161

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https://hdl.handle.net/2376/124107

PMID: 31654960

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Abstract

Engineering, Environmental

Environmental Sciences

Environmental Sciences & Ecology

Life Sciences & Biomedicine

Science & Technology

Water Resources

Engineering

Physical Sciences

Technology

The San Joaquin River (SJR) in California is purported to receive high nitrate loadings from surrounding agricultural lands through both surface and groundwater inputs. To investigate the potential removal of nitrate (NO3-) from surface and ground water sources, the spatial variations in dinitrogen (N-2) gas concentrations and direct measurements of sediment denitrification potential (DNP), with amended NO3- and carbon (C) treatments, were investigated in the summer along a 95-km reach of the San Joaquin River. Excess N-2 in hyporheic porewaters ranged from <0.1 to 8.65 mg L-1 and was significantly higher in porewaters from the 1.3 m (ground water source) versus 0.3 m (mixed surface and ground water) depths. In deep groundwater wells (3-7 m), median excess N-2 concentration was 5.39 mg L-1 (range = <0.1 -14.6 mg L-1). Excess N-2 concentrations were inversely correlated with dissolved oxygen and NO3- concentrations suggesting denitrification as an important process in the dominantly anaerobic sediments. Hyporheic porewater NO3- concentrations exceeded the detection limit of 0.01 mg L-1 in only 20% of the hyporheic porewaters, in spite of high NO3- concentrations measured in both surface waters (mean = 2.25 mg N L-1) and surrounding groundwaters. Sediment DNP rates averaged 253 and 297 mu g N kg(-1) hr(-1) for NO3- amended, and NO3- + C amended sediments, respectively, supporting the prevalence of denitrification in hyporheic sediments. Our results indicate that the hyporheic/riparian zones act as an anoxic barrier to nitrate transport from regional groundwater and as a location to remove NO3- from surface waters exchanging with the hyporheic zone. (C) 2019 Elsevier Ltd. All rights reserved.

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Title: Excess N-2 and denitrification in hyporheic porewaters and groundwaters of the San Joaquin River, California
Creators: Sarra E Hinshaw - University of California, Davis
Taiping Zhang - South China University of Technology
John A Harrison - Washington State University Vancouver
Randy A Dahlgren - University of California, Davis
Publication Details: Water research (Oxford), Vol.168
Academic Unit: Environment, School of the (CAS); Harrison Research Group: Global Change and Watershed Biochemistry
Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Number of pages: 12
Grant note: R09AC20040 / US Bureau of Reclamation Proposition 50 grant from the CALFED Drinking Water-Quality Program US Geological Survey (USGS)
Identifiers: 99900667908101842
Language: English
Resource Type: Journal article