Relations between sinkhole density and anthropogenic contaminants in selected carbonate aquifers in the eastern United States

Abstract

The relation between sinkhole density and water quality was investigated in seven selected carbonate aquifers in the eastern United States. Sinkhole density for these aquifers was grouped into high ([25 sinkholes/ 100 km 2 ), medium (1-25 sinkholes/100 km 2 ), or low (\1 sinkhole/100 km 2 ) categories using a geographical information system that included four independent databases covering parts of Alabama, Florida, Missouri, Pennsylvania, and Tennessee. Field measurements and concentrations of major ions, nitrate, and selected pesticides in samples from 451 wells and 70 springs were included in the waterquality database. Data were collected as a part of the US Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program. Areas with high and medium sinkhole density had the greatest well depths and depths to water, the lowest concentrations of total dissolved solids and bicarbonate, the highest concentrations of dissolved oxygen, and the lowest partial pressure of CO 2 compared to areas with low sinkhole density. These chemical indicators are consistent conceptually with a conduit-flow-dominated system in areas with a high density of sinkholes and a diffuse-flow-dominated system in areas with a low density of sinkholes. Higher cave density and spring discharge in Pennsylvania also support the concept that the high sinkhole density areas are dominated by conduit-flow systems. Concentrations of nitrate-N were significantly higher (p \ 0.05) in areas with high and medium sinkhole density than in low sinkhole-density areas; when accounting for the variations in land use near the sampling sites, the high sinkhole-density area still had higher concentrations of nitrate-N than the low sinkholedensity area. Detection frequencies of atrazine, simazine, metolachlor, prometon, and the atrazine degradate deethylatrazine indicated a pattern similar to nitrate; highest pesticide detections were associated with high sinkhole-density areas. These patterns generally persisted when analyzing the detection frequency by land-use groups, particularly for agricultural land-use areas where pesticide use would be expected to be higher and more uniform areally compared to urban and forested areas. Although areas with agricultural land use and a high sinkhole density were most vulnerable (median nitrate-N concentration was 3.7 mg/L, 11% of samples exceeded 10 mg/L, and had the highest frequencies of pesticide detection), areas with agricultural land use and low sinkhole density still were vulnerable to contamination (median nitrate-N concentration was 1.5 mg/L, 8% of samples exceeded 10 mg/L, and had some of the highest frequencies of detections of pesticides). This may be due in part to incomplete or missing data regarding karst features (such as buried sinkholes, low-permeability material in bottom of sinkholes) that do not show up at the scales used for regional mapping and to inconsistent methods among states in karst feature delineation.

Density of karst depressions in Yucatán state, Mexico

“…Density maps of karst depressions have a wide range of applications. The different densities are indicative of the types of groundwater flow (Lindsey et al, 2010), and these characteristics should be included in models of groundwater flow (Kiraly, 2002;Parise et al, 2015a, b). In addition, density maps can also be used as precursors to tracer studies to identify preferential water flows to locate aquifer limits (Angel et al, 2004).…”

“…Several studies have focused on the analysis of the spatial distribution of karstic depressions. Density maps have been among the most common approaches (Denizman, 2003;Angel et al, 2004;Farfán González et al, 2010;Lindsey et al, 2010); there are also some studies on the typology of these landforms, differentiating between dolines, uvalas, and poljes (Plan et al, 2009;Siart et al, 2009;Goeppert et al, 2011;Fragoso-Servón et al, 2014;Pepe and Parise, 2014). These are important in land planning, mainly related to the vulnerability of aquifers to pollution, the risk of ground collapse and subsidence, and potential flooding.…”

Pesticide occurrence in groundwater and the physical characteristics in association with these detections in Ireland

“…Karst systems are very heterogeneous with many having solution features that can act as easy access points for water containing pesticides to enter the groundwater below. Sinking streams, closed depressions, and limestone pavement (exposed limestone bedrock surfaces with little to no soil cover (Williams 1966)) all allow direct access into the groundwater beneath, where water flows quickly through with little attenuation to outlets or springs (Coxon 2011;Lindsey et al 2010). Irish Carboniferous limestone aquifers have negligible primary permeability so groundwater flow is via solutionally widened fractures and cave conduits (Drew 2008).…”

The quality of our nation's waters: water quality in the Principal Aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions, eastern United States, 1993-2009

“…As a consequence, much of the water that reaches a well is very young. In addition, the presence of sinkholes favors oxic conditions, (41) making denitrification unlikely. The combination of direct infiltration of contaminants into the aquifer, rapid movement through the aquifer, and oxic conditions within the aquifer, coupled with large nitrogen inputs, explains the high nitrate concentrations in samples from the carbonate-rock aquifers.…”