Impact of water source dynamics on dissolved reactive phosphorus loadings in heterogenous karst agroecosystems with phosphatic limestones

Cory Radcliff, William I. Ford, Saeid Nazari, Christopher Shepard

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Karst landscapes underlain with phosphatic limestones are now recognized to be an important contributor of fluvial phosphorus (P) to coastal waters. Specifically, karst agroecosystems may be a hotspot for dissolved reactive P (DRP) due to chronic over-application of organic and inorganic fertilizers that create legacy P accumulation in surface soils. Nevertheless, few studies have assessed the hydrologic controls on DRP transport in these systems at the watershed scale, which is the focus of this study. We analysed soil moisture, soil water extractable P, and storm event hydrologic and water quality data from a small heterogenous karst watershed (10.7 km2) in the Inner-Bluegrass Region of Central Kentucky, USA. Four storm events were sampled in winter, 2020 and were analysed for flow pathways using hydrograph recession analysis and water source connectivity using a tracer-based unmixing model. Based on hydrograph separation results, multiple linear regression analysis was performed to assess drivers of DRP concentrations and loadings. Soil water extractable P results showed stark vertical gradients with greater concentrations at both the surface and deeper soil zones, and minimum concentrations in the root zone. Results for the storm event analysis showed that water source connectivity provided superior prediction of DRP concentrations over the flow pathway analysis, which reflected the heterogeneity of karst maturity masking intermediate flow pathways. Findings from the MLR and loading analysis suggest waters sourced from the soil/epikarst produced significantly higher loadings compared with phreatic and precipitation water source in the three largest events, although concentrations fell between the phreatic (low) and precipitation (high) sources. Findings highlight variable activation of matrix-macropore exchange at different depths throughout the event. Collectively these results suggest existing models and approaches to assess karst hydrology need revision to improve management strategies in this critical landscape.

Original languageEnglish
Article numbere14422
JournalHydrological Processes
Volume35
Issue number11
DOIs
StatePublished - Nov 2021

Bibliographical note

Funding Information:
The authors are grateful to Dan Barton and Drew McGill for help in data collection, analysis and site maintenance, and Aviv Brokman for assistance with statistical analysis of soils. We would like to thank the Kentucky Geological Survey, UK CAFE Division of Regulatory Services, the University of Arkansas Stable Isotope Laboratory, and the Kentucky Stable Isotope Geochemistry Laboratory for their efforts and assistance in sample processing and analysis. This work was supported by NSF EPSCOR 1632888, the USGS 104B program and the USDA National Institute of Food and Agriculture, Hatch project S‐1089. Partial support of the graduate student was provided by the Biosystems and Agricultural Engineering department at the University of Kentucky.

Funding Information:
The authors are grateful to Dan Barton and Drew McGill for help in data collection, analysis and site maintenance, and Aviv Brokman for assistance with statistical analysis of soils. We would like to thank the Kentucky Geological Survey, UK CAFE Division of Regulatory Services, the University of Arkansas Stable Isotope Laboratory, and the Kentucky Stable Isotope Geochemistry Laboratory for their efforts and assistance in sample processing and analysis. This work was supported by NSF EPSCOR 1632888, the USGS 104B program and the USDA National Institute of Food and Agriculture, Hatch project S-1089. Partial support of the graduate student was provided by the Biosystems and Agricultural Engineering department at the University of Kentucky.

Publisher Copyright:
© 2021 John Wiley & Sons Ltd.

Keywords

  • agriculture
  • dissolved reactive phosphorus
  • fertilization
  • isotopes
  • karst hydrology
  • phosphatic limestone
  • water quality
  • watershed

ASJC Scopus subject areas

  • Water Science and Technology

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