Potentiometric surface of the Upper Floridan aquifer in the Ichetucknee springshed and vicinity, northern Florida, September 2003

Sepulveda, A. Alejandro; Katz, Brian G.; Mahon, Gary L.

doi:10.3133/ofr20061031

Cited by 5 publications

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“…The ground‐water contributing area for Ichetucknee springs (the ISB) was delineated from a detailed potentiometric surface map of the UFA, which was developed using 94 water‐level measurements made by the Suwannee River Water Management District (SRWMD) in September 2003 (Sepulveda et al. , 2006).…”

Section: Description Of Ichetucknee Springs Basinmentioning

confidence: 99%

“…However, median nitrate-N concentrations >1 mg ⁄ l in ground water from 10 of 11 wells are related to the amount of fertilizer applied upgradient from the well. An arbitrary upgradient area, representing a generalized contributing recharge area for each well, was delineated by orienting a semicircle (1000-m radius) perpendicular to the ground-water flow direction obtained from the potentiometric map of the UFA (Sepulveda et al, 2006). The amount of N applied as fertilizers ranged from 4.9 to 13 kg ⁄ ha in these upgradient semicircular areas.…”

Section: Assessing Vulnerability To Nitrate Contamination From Fertilmentioning

confidence: 99%

“…The ground-water contributing area for Ichetucknee springs (the ISB) was delineated from a detailed potentiometric surface map of the UFA, which was developed using 94 water-level measurements made by the Suwannee River Water Management District (SRWMD) in September 2003 (Sepulveda et al, 2006). The ISB lies almost entirely within Columbia County in northern Florida, but a small portion along the west side of the Ichetucknee River and its headspring area, lies in adjacent Suwannee County, Florida, to the west.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Estimating Nitrogen Loading to Ground Water and Assessing Vulnerability to Nitrate Contamination in a Large Karstic Springs Basin, Florida¹

Katz

Sepulveda

Verdi

2009

J American Water Resour Assoc

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A nitrogen (N) mass‐balance budget was developed to assess the sources of N affecting increasing ground‐water nitrate concentrations in the 960‐km2 karstic Ichetucknee Springs basin. This budget included direct measurements of N species in rainfall, ground water, and spring waters, along with estimates of N loading from fertilizers, septic tanks, animal wastes, and the land application of treated municipal wastewater and residual solids. Based on a range of N leaching estimates, N loads to ground water ranged from 262,000 to 1.3 million kg/year; and were similar to N export from the basin in spring waters (266,000 kg/year) when 80‐90% N losses were assumed. Fertilizers applied to cropland, lawns, and pine stands contributed about 51% of the estimated total annual N load to ground water in the basin. Other sources contributed the following percentages of total N load to ground water: animal wastes, 27%; septic tanks, 12%; atmospheric deposition, 8%; and the land application of treated wastewater and biosolids, 2%. Due to below normal rainfall (97.3 cm) during the 12‐month rainfall collection period, N inputs from rainfall likely were about 30% lower than estimates for normal annual rainfall (136 cm). Low N‐isotope values for six spring waters (δ15N‐NO3 = 3.3 to 6.3‰) and elevated potassium concentrations in ground water and spring waters were consistent with the large N contribution from fertilizers. Given ground‐water residence times on the order of decades for spring waters, possible sinks for excess N inputs to the basin include N storage in the unsaturated zone and parts of the aquifer with relatively sluggish ground‐water movement and denitrification. A geographical‐based model of spatial loading from fertilizers indicated that areas most vulnerable to nitrate contamination were located in closed depressions containing sinkholes and other dissolution features in the southern half of the basin.

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Section: Description Of Ichetucknee Springs Basinmentioning

confidence: 99%

Section: Assessing Vulnerability To Nitrate Contamination From Fertilmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Estimating Nitrogen Loading to Ground Water and Assessing Vulnerability to Nitrate Contamination in a Large Karstic Springs Basin, Florida¹

Katz

Sepulveda

Verdi

2009

J American Water Resour Assoc

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“…The Ichetucknee springshed has a relatively well‐defined contributing area of approximately 960 km 2 , estimated by potentiometric surfaces from 2003 (Sepulveda, Katz, & Mahon, ) and using spatially distributed geochemical analyses (Champion & Upchurch, ). Groundwater flows predominantly from north‐east to south‐west and is primarily drained by the nine named springs and numerous seeps of the Ichetucknee Springs Group (Rosenau, Faulkner, Hendry, & Hull, ; Scott et al, ), which collect to form the Ichetucknee River (mean discharge 8.35 m 3 s −1 ; U.S. Geological Survey, ), which drains to the Santa Fe and Suwannee Rivers.…”

Section: Methodsmentioning

confidence: 99%

Spatially distributed denitrification in a karst springshed

Henson

Cohen

Graham

2019

Hydrological Processes

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Karst spring measurements assess biogeochemical processes occurring within groundwater contributing areas to springs (springsheds) but can only provide aggregated information. To better understand spatially distributed processes that comprise these aggregated measures, we investigated aquifer denitrification evidence in groundwater wells (n = 16) distributed throughout a springshed in the Upper Floridan aquifer in northern Florida. Aquifer geochemistry, nitrate isotopes, and dissolved gases were compared against similar measurements at the spring outlet to evaluate spatial heterogeneity of denitrification evidence in relation to land surface-aquifer connectivity.Sample locations spanned spatial variation in recharge processes (i.e., diffuse vs.focused recharge) and proximity to sources of denitrification reactants (e.g., wetlands).Although no distinct spatial pattern in denitrification was uncovered, excess dissolved N 2 gas measurements were only above detection in the unconfined springshed, with some evidence of a wetland proximity effect. Measured oxidation-reduction potential and dissolved oxygen poorly predicted denitrification, indicating that measured denitrification may be occurring upgradient from sampled wells. Despite dramatic spatial chemical heterogeneity across wells, mean values for recharge nitrate concentrations (0.02 to 5.56 mg N L −1 ) and excess N 2 from aquifer denitrification (below detection to 1.37 mg N L −1 ) corresponded reasonably with mean spring outlet measurements for initial nitrate (0.78 to 1.36 mg N L −1 ) and excess N 2 (0.15 to 1.04 mg N L −1 ). Congruence between groundwater and spring measurements indicates that combining sampling at the spring outlet and across the springshed is useful for understanding spatial aquifer denitrification. However, this approach would be improved with a high-density sampling network with transects of wells along distinct groundwater flow paths.

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“…Detailed geomorphic and hydrologic descriptions of Ichetucknee Springs and the local UFA have been previously reported [ Rosenau et al ., ; Scott et al ., ]. The springshed is approximately 960 km 2 [ Champion and Upchurch , ; Sepulveda et al ., ]. Locally, the UFA in the study area is predominantly unconfined, where limestone is not exposed at the surface, a thin layer of well to excessively drained sands is present [ Houston , ; Ceryak et al ., ].…”

Section: Methodsmentioning

confidence: 99%

Nitrate reduction mechanisms and rates in an unconfined eogenetic karst aquifer in two sites with different redox potential

et al. 2017

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This study integrates push‐pull tracer tests (PPTT) with microbial characterization of extracted water via quantitative polymerase chain reaction (qPCR) and reverse transcriptase qPCR (RT‐qPCR) of selected functional N transformation genes to quantify nitrate reduction mechanisms and rates in sites with different redox potential in a karst aquifer. PPTT treatments with nitrate (AN) and nitrate‐fumarate (ANC) were executed in two wells representing anoxic and oxic geochemical end‐members. Oxic aquifer zero‐order nitrate loss rates (mmol L−1 h−1) were similar for AN and ANC treatment, ranging from 0.03 ± 0.01 to 0.05 ± 0.01. Anoxic aquifer zero‐order nitrate loss rates ranged from 0.03 ± 0.02 (AN) to 0.13 ± 0.02 (ANC). Microbial characterization indicates mechanisms influencing these rates were dissimilatory nitrate reduction to ammonium (DNRA) at the anoxic site with AN treatment, assimilatory reduction of nitrate to ammonium (ANRA) with ANC treatment in the water column at both sites, and additional documented nitrate reduction that occurred in unsampled biofilms. With carbon treatment, total numbers of microbes (16S rRNA genes) significantly increased (fourteenfold to thirtyfold), supporting stimulated growth with resulting ANRA. Decreased DNRA gene concentrations (nrfA DNA) and increased DNRA activity ratio (nrfA‐cDNA/DNA) supported the assertion that DNRA occurred in the anoxic zone with AN and ANC treatment. Furthermore, decreased DNRA gene copy numbers at the anoxic site with ANC treatment suggests that DNRA microbes in the anoxic site are chemolithoautotrophic. Increased RT‐qPCR denitrification gene expression (nirK and nirS) was not observed in water samples, supporting that any observed NO3‐N loss due to denitrification may be occurring in unsampled microbial biofilms.

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Potentiometric surface of the Upper Floridan aquifer in the Ichetucknee springshed and vicinity, northern Florida, September 2003

Cited by 5 publications

References 0 publications

Estimating Nitrogen Loading to Ground Water and Assessing Vulnerability to Nitrate Contamination in a Large Karstic Springs Basin, Florida¹

Estimating Nitrogen Loading to Ground Water and Assessing Vulnerability to Nitrate Contamination in a Large Karstic Springs Basin, Florida¹

Spatially distributed denitrification in a karst springshed

Nitrate reduction mechanisms and rates in an unconfined eogenetic karst aquifer in two sites with different redox potential

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Potentiometric surface of the Upper Floridan aquifer in the Ichetucknee springshed and vicinity, northern Florida, September 2003

Cited by 5 publications

References 0 publications

Estimating Nitrogen Loading to Ground Water and Assessing Vulnerability to Nitrate Contamination in a Large Karstic Springs Basin, Florida1

Estimating Nitrogen Loading to Ground Water and Assessing Vulnerability to Nitrate Contamination in a Large Karstic Springs Basin, Florida1

Spatially distributed denitrification in a karst springshed

Nitrate reduction mechanisms and rates in an unconfined eogenetic karst aquifer in two sites with different redox potential

Contact Info

Product

Resources

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Estimating Nitrogen Loading to Ground Water and Assessing Vulnerability to Nitrate Contamination in a Large Karstic Springs Basin, Florida¹

Estimating Nitrogen Loading to Ground Water and Assessing Vulnerability to Nitrate Contamination in a Large Karstic Springs Basin, Florida¹