Rainfall and conduit drainage combine to accelerate nitrate loss from a karst agroecosystem: insights from stable isotope tracing and high-frequency nitrate sensing

Yue, F.-J. , Li, S.-L., Waldron, S. , Wang, Z.-J., Oliver, D. M., Chen, X. and Liu, C.-Q. (2020) Rainfall and conduit drainage combine to accelerate nitrate loss from a karst agroecosystem: insights from stable isotope tracing and high-frequency nitrate sensing. Water Research, 186, 116388. (doi: 10.1016/j.watres.2020.116388) (PMID:32916623)

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Understanding where nitrate is mobilized from and under what conditions is required to reduce nitrate loss and protect water quality. Low frequency sampling may inadequately capture hydrological and biogeochemical processes that will influence nitrate behavior. We used high-frequency isotope sampling and in-situ nitrate sensing to explore nitrate export and transformation in a karst critical zone. Nitrate was mobilised during light rainfall, and transferred from soil layers to the karst matrix, where some nitrate was retained and denitrified. Nitrate isotopic composition changed rapidly during the rising limb of events and slowly during the falling limb. The main nitrate source was synthetic fertiliser (up to 80% during event flow), transported by conduit flow following high rainfall events, and this contribution increased significantly as discharge increased. Soil organic nitrogen contribution remained constant indicating at baseflow this is the primary source. Isotope source appointment of nitrate export revealed that synthetic fertilizer accounted for more than half of the total nitrate export, which is double that of the secondary source (soil organic nitrogen), providing valuable information to inform catchment management to reduce nitrate losses and fluvial loading. Careful land management and fertilizer use are necessary to avoid nitrate pollution in the karst agroecosystem, for example by timing fertilizer applications to allow for plant uptake of nitrate before rainfall can flush it from the soils into the karst and ultimately into catchment drainage.

Item Type:Articles
Additional Information:The authors would like to acknowledge funding from the National Natural Science Foundation of China , Grant/Award Number: 41571130072 and the UK Natural Environment Research Council, Grant/Award Number: NE/N007425/1.
Glasgow Author(s) Enlighten ID:Waldron, Professor Susan and Yue, Dr Fu-Jun
Authors: Yue, F.-J., Li, S.-L., Waldron, S., Wang, Z.-J., Oliver, D. M., Chen, X., and Liu, C.-Q.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Water Research
ISSN (Online):1879-2448
Published Online:03 September 2020
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in Water Research 186:116388
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
172384The transmissive critical zone: understanding the karst hydrology-biogeochemical interface for sustainable managementSusan WaldronNatural Environment Research Council (NERC)NE/N007425/1GES - Geography