Impact of water source dynamics on dissolved reactive phosphorus loadings in heterogenous karst agroecosystems with phosphatic limestones. Issue 11 (23rd November 2021)

• Record Type: Journal Article
• Authors: Radcliff, Cory; Ford, William I.; Nazari, Saeid; Shepard, Christopher
• Is Part Of: Hydrological processes. Volume 35:Issue 11(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-23
• Subjects: agriculture -- dissolved reactive phosphorus -- fertilization -- isotopes -- karst hydrology -- phosphatic limestone -- water quality -- watershed; Hydrology -- Periodicals; Hydrology -- Research -- Periodicals; Hydrologic models -- Periodicals; Hydrological forecasting -- Periodicals; 631.432
• DOI: 10.1002/hyp.14422
• Languages: English
• ISSNs: 0885-6087

Abstract

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 km 2 ) 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. Abstract : Soil water extractable P profiles in the Inner‐Bluegrass region of Kentucky reflected anthropogenic and natural source contributions that varied with depth. Tracer‐based hydrograph separation enabled predictions of DRP loadings in a heterogenous karst watershed. Findings showed soil/epikarst water contributed the greatest DRP loadings, contrasting systems without P‐limestones, and highlighted a need to refine existing karst hydrological modelling approaches to account for variability in vertical soil layer connectivity within storm events.