Long-term assessment of nutrient flow pathway dynamics and in-stream fate in a temperate karst agroecosystem watershed

William I. Ford, Admin Husic, Alex Fogle, Joseph Taraba

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

Nutrient dynamics in karst agroecosystems remain poorly understood, in part due to limited long-term nested datasets that can discriminate upland and in-stream processes. We present a 10-year dataset from a karst watershed in the Inner-Bluegrass Region of central Kentucky, consisting of nitrate (nitrate-N [NO3]), dissolved reactive phosphorus (DRP), total organic carbon (TOC), and total ammoniacal-N (TAN) measurements at nested spring and stream sites as well as flowrate at the watershed outlet. Hydrograph separation techniques were coupled with multiple linear regression and Empirical Mode Decomposition time-series analysis to determine significance of seasonal processes and to generate continuous estimates of nutrient pathway loadings. Further, we used model results of benthic algae growth and decomposition dynamics from a nearby watershed to assess if transient storage in algal biomass could explain differences in spring and downstream watershed nutrient loading. Results highlight statistically significant seasonality for all nutrients at stream sites, but only for NO3 at springs with longitudinal variability showing significant decreases occurring from spring to stream sites for NO3 and DRP, and significant increases for TOC and TAN. Pathway loading analysis highlighted the importance of slow flow pathways to source approximately 70% of DRP and 80% of NO3. Results for in-stream dynamics suggest that benthic autotroph dynamics can explain summer deviations for TOC, TAN, and DRP but not NO3. Regarding upland dynamics, our findings agree well with existing perceptions in karst for N pathways and upland source seasonality but deviate from perceptions that karst conduits are retentive of P, reflecting the limited buffering capacity of the soil profile and conduit sediments in the Inner-Bluegrass. Regarding in-stream fate, our findings highlighted the significance of seasonally driven nutrient processing in the bedrock-controlled streambed to influence nutrient fluxes at the watershed outlet. Contrary to existing perceptions, we found high N attenuation and an unexplained NO3 sink in the bedrock stream, leading us to postulate that floating macrophytes facilitate high rates of denitrification.

Original languageEnglish
Pages (from-to)1610-1628
Number of pages19
JournalHydrological Processes
Volume33
Issue number11
DOIs
StatePublished - May 30 2019

Bibliographical note

Funding Information:
The authors would like to thank the associate editor and three anonymous reviewers for their comments, which have greatly improved the quality of the manuscript. We gratefully acknowledge financial support of this research under National Science Foundation Award 1632888 which provided partial support for the corresponding author. This is publication No. 18‐05‐092 of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. This work is supported by the National Institute of Food and Agriculture, U. S. Department of Agriculture.

Funding Information:
The authors would like to thank the associate editor and three anonymous reviewers for their comments, which have greatly improved the quality of the manuscript. We gratefully acknowledge financial support of this research under National Science Foundation Award 1632888 which provided partial support for the corresponding author. This is publication No. 18-05-092 of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. This work is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture.

Publisher Copyright:
© 2019 John Wiley & Sons, Ltd.

Keywords

  • bedrock stream
  • hydrologic pathways
  • in-stream fate
  • karst agroecosystem watershed
  • nutrient loadings
  • time-series analysis

ASJC Scopus subject areas

  • Water Science and Technology

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