Sediment carbon fate in phreatic karst (Part 1): Conceptual model development

Husic, Admin; Fox, James F.; Agouridis, Carmen T.; Currens, James C.; Ford, William I.; Taylor, C. James

doi:10.1016/j.jhydrol.2017.03.052

Cited by 24 publications

(36 citation statements)

References 81 publications

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“…Lastly, the timing of NO 3 − concentration peaks caused by storm events and seasonality are well matched by the surface and subsurface pathways (Figure ). The result demonstrates the pressure pulse of stormflow on the karst subsurface that can mirror the temporal response seen in surface streams (Husic, Fox, Agouridis, et al, ). Further, the multiple inferred pathways (i.e., quick flow, epikarst, and phreatic) introduce wide temporal variability in NO 3 − data results.…”

Section: Resultsmentioning

confidence: 52%

“…The fractions of stream water from soil and runoff origin can vary from event to event, but were selected in this study based on a range of values reported in the literature for karst using isotopic hydrograph separation (Buda & DeWalle, ) and two‐domain modeling (Long, ). Surface events in the Cane Run Watershed are short‐lived and often peak and recede within a day (i.e., the time step of the model; Husic, Fox, Agouridis, et al, ), providing support that an average value for the respective soil and runoff fractions can adequately portray mixing processes. Hydrologic model parameter sets were generated and evaluated over a wide range of values.…”

Section: Methodsmentioning

confidence: 99%

“…Quick flow pathways convey concentrated N recharge through tertiary porosity voids such as sinkholes, swallets, and estavelles. As is typical of many karst systems, surface streams are event‐activated and run dry for large parts of the year as a result of flow pirating by quick flow pathway karst features (Husic, Fox, Agouridis, et al, ). Diffuse recharge follows soil, epikarst, and phreatic zone pathways where storage volumes are several orders of magnitude greater than that of the quick flow pathways and have the potential to retain N (Bottrel & Atkinson, ; Williams, ).…”

Section: Methodsmentioning

confidence: 99%

“…The model simulates solute (nitrate, ammonium, and dissolved organic nitrogen) fate from recharge source to eventual downstream loading to the spring as well as the surface stream. We do not consider chemoautotrophic pathways as the study watershed is relatively rich in the energetically favorable organic carbon electron donor (Husic, Fox, Agouridis, et al, ; Husic, Fox, Ford, et al, ). Our study assumes temperate agricultural surface processes, mature karst subsurface development, coupled surface‐subsurface pathways, and daily mixing of solutes after accounting for mass changes.…”

Section: Methodsmentioning

confidence: 99%

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Nitrate Pathways, Processes, and Timing in an Agricultural Karst System: Development and Application of a Numerical Model

Husic

Fox

Adams

et al. 2019

Water Resources Research

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Nitrogen (N) contamination within agricultural‐karst landscapes and aquifers is widely reported; however, the complex hydrological pathways of karst make N fate difficult to ascertain. We developed a hydrologic and N numerical model for agricultural‐karst, including simulation of soil, epikarst, phreatic, and quick flow pathways as well as biochemical processes such as nitrification, mineralization, and denitrification. We tested the model on four years of nitrate (NO3−) data collected from a phreatic conduit and an overlying surface channel in the Cane Run watershed, Kentucky, USA. Model results indicate that slow to moderate flow pathways (phreatic and epikarst) dominate the N load and account for nearly 90% of downstream NO3− delivery. Further, quick flow pathways dilute NO3− concentrations relative to background aquifer levels. Net denitrification distributed across soil, epikarst, and phreatic water removes approximately 36% of the N inputs to the system at rates comparable to nonkarst systems. Evidence is provided by numerical modeling that NO3− accumulation via evapotranspiration in the soil followed by leaching through the epikarst acts as a control on spring NO3− concentration and loading. Compared to a fluvial‐dominated immature karst system, mature‐karst systems behave as natural detention basins for NO3−, temporarily delaying NO3− delivery to downstream waters and maintaining elevated NO3− concentrations for days to weeks after hydrologic activity ends. This study shows the efficacy of numerical modeling to elucidate complex pathways, processes, and timing of N in karst systems.

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Section: Resultsmentioning

confidence: 52%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Nitrate Pathways, Processes, and Timing in an Agricultural Karst System: Development and Application of a Numerical Model

Husic

Fox

Adams

et al. 2019

Water Resources Research

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“…Regarding in‐stream fate, agroecosystem streambeds often consist of exposed bedrock or thin surficial sediment deposits starkly contrasting the deep alluvial beds found in systems with predominant hyporheic zones (Fogle, Taraba, & Dinger, ; Ford & Fox, ; Husic, Fox, Agouridis, et al, ; Mellander et al, ). Recent studies have highlighted the impact of the surficial fine‐grained laminae, in both surface and phreatic conduit streambeds, on nutrient attenuation and transient storage (Ford & Fox, , ; Ford, Fox, & Pollock, ; Husic, Fox, Ford, et al, ; Husic, Fox, Agouridis, et al, ). Less is known about the role of exposed bedrock streambeds in low‐gradient regions.…”

Section: Introductionmentioning

confidence: 99%

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

Ford

Husic

Fogle

et al. 2019

Hydrological Processes

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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 [NO 3 − ]), 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 NO 3 − at springs with longitudinal variability showing significant decreases occurring from spring to stream sites for NO 3 − 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 NO 3 − . Results for in-stream dynamics suggest that benthic autotroph dynamics can explain summer deviations for TOC, TAN, and DRP but not NO 3 − . 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 NO 3 − sink in the bedrock stream, leading us to postulate that floating macrophytes facilitate high rates of denitrification. KEYWORDS bedrock stream, hydrologic pathways, in-stream fate, karst agroecosystem watershed, nutrient loadings, time-series analysis

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From cave to spring: Understanding transport of suspended sediment particles in a fully phreatic karst conduit using particle analysis and geochemical methods

Mueller,

Goldscheider,

Eiche

et al. 2023

Hydrological Processes

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Karst aquifers are vulnerable to contamination, especially in the context of heavy rainfall events. Contamination is often associated with turbidity that can originate from the soil zone, infiltrating surface waters or resuspension of previously deposited sediments within the aquifer. While turbidity events can be well monitored at karst springs, related information about the sediment origin and the spatiotemporal input function usually remain unknown. Thus, the mobility and attenuation of the particulate matter and associated pollutants can hardly be determined quantitatively. A tracer test with suspended cave sediments and solute tracers for comparison has hence been performed in a karst aquifer at the Blue Spring (Blautopf) in Southern Germany. The tracers were injected in the cave system, at the beginning of a fully phreatic karst conduit, and monitored at the spring after a travel distance of 1250 m. The particle‐size distribution was monitored using a particle counter and sediment samples were filtered with 0.45‐μm cellulose acetate filters. Particles on the filter were analysed for major and trace elements as well as rare earth elements (REE) by ICP‐MS after acid digestion. Results show that (1) sediment particles were transported faster than solutes, which was interpreted as a transport in the main flow path of the conduit, whereas conservative tracers tend to diffuse into smaller fissures as well. (2) All measured particles sizes were transported at similar flow velocities. (3) A transport associated to sediment particles could be shown for all measured elements. This study presents a methodological improvement of comparative sediment tracer tests as well as deeper insights into particle and element transport processes in karst aquifers, originating from previously deposited cave sediment. Results provide deeper knowledge into transport processes of sediment‐associated contaminants, such as heavy metals which may strongly be affected by the particle size. This knowledge contributes to a better management of karst water resources in the context of turbidity events.

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Sediment carbon fate in phreatic karst (Part 1): Conceptual model development

Cited by 24 publications

References 81 publications

Nitrate Pathways, Processes, and Timing in an Agricultural Karst System: Development and Application of a Numerical Model

Nitrate Pathways, Processes, and Timing in an Agricultural Karst System: Development and Application of a Numerical Model

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

From cave to spring: Understanding transport of suspended sediment particles in a fully phreatic karst conduit using particle analysis and geochemical methods

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