Cross-scale controls on the in-stream dynamics of nitrate and turbidity in semiarid agricultural waterway networks

Alex J Webster; Mary L Cadenasso

doi:10.1016/j.jenvman.2020.110307

Cross-scale controls on the in-stream dynamics of nitrate and turbidity in semiarid agricultural waterway networks

J Environ Manage. 2020 May 15:262:110307. doi: 10.1016/j.jenvman.2020.110307. Epub 2020 Feb 29.

Authors

Alex J Webster¹, Mary L Cadenasso²

Affiliations

¹ University of Alaska, Fairbanks, Institute of Arctic Biology, Fairbanks, AK, USA; University of California Davis, Department of Plant Sciences, Davis, CA, USA. Electronic address: ajwebster2@alaska.edu.
² University of California Davis, Department of Plant Sciences, Davis, CA, USA.

PMID: 32250790
DOI: 10.1016/j.jenvman.2020.110307

Abstract

Stream and riparian zone networks embedded in agricultural landscapes provide a potential intervention point to ameliorate the negative effects of agricultural runoff by reducing transport of nitrate (NO₃^-) and suspended sediments (SS) downstream. However, our ability to support and promote NO₃^- and SS attenuation is limited by our understanding of vegetative and hydrogeomorphic controls in realistic management contexts. In addition, agricultural landscapes are heterogenous on multiple management scales, from farm field to regional water management scales, and the effect of these heterogeneities and how they interact across scales to affect vegetative and hydrogeomorphic controls is poorly explored in many settings. This is especially true in irrigated agricultural settings, where stream and riparian networks are entwined with and sensitive to water management systems. To fill these gaps, we related the vegetative and hydrogeomorphic features of 67 waterway reaches across two water management districts in the California Central Valley to reach-scale NO₃^- and turbidity attenuation and district-scale water quality patterns. We found that in-stream NO₃^- attenuation was rare, but, when it did occur, it was promoted by shallow and wide riparian banks, low flows, and high channel-edge denitrification potential. Nitrate concentrations were consistently higher in upstream reaches compared to water district outlets, suggesting that while exports from the district were low, agricultural runoff may impair within-district water resources. Turbidity attenuation was highly variable and unrelated to vegetative or hydrogeomorphic features, suggesting that onfield controls are crucial to managing suspended sediments. We conclude that waterway networks have the potential to mitigate the effects of agricultural NO₃^- runoff in this setting, but that more effective monitoring and adoption of NO₃^- attenuating features is needed. Using our findings, we make specific management and monitoring recommendations at both reach and water district scales.

Keywords: Agricultural streams; California Central Valley; Nitrate (NO(3)(-)); Semiarid irrigated agriculture; Turbidity; Water quality monitoring.

MeSH terms

Agriculture*
California
Environmental Monitoring
Nitrates*
Nitrogen Oxides
Water Supply

Substances

Nitrates
Nitrogen Oxides