Base flow hydrology and water quality of an Ozarks spring and associated recharge area, southern Missouri, USA

Abstract

Human activities in the karst Ozark Plateaus can impact water quality of springs where surface water is rapidly transferred to subsurface conduits. Bennett Spring, in southern Missouri, is the fourth largest spring in the state and supports local tourism activities. Questions regarding poorly functioning on-site wastewater systems (OWS) have raised concerns over the long-term water quality of the spring. This study reports the results of a surface water quality monitoring program in the recharge area where monthly samples were collected at base flow to identify potential pollution sources to the spring. Base flow hydrology of the recharge area was highly variable over the study period, which was drier than normal, causing an incomplete sampling record due to no flow conditions at some sites. For most of the year, nutrient levels were less than the eutrophic threshold (ET) of 0.075 mg/l total phosphorus (TP) and 1.5 mg/l total nitrogen (TN). Sites that consistently displayed concentrations of TP and TN higher than the ET were influenced by wastewater treatment plants (WTP) or OWS. Sites with nutrient concentrations above the ET were likely influenced by the re-release of nonpoint source related TP and TN delivered to streams during storm events. Water quality and discharge at the spring outlet remained consistent over the sampling period suggesting diffuse recharge from a deep aquifer source is able to dilute shallow ground water sources carrying nonpoint pollutants at base flow. Historical and regional data comparisons show these trends have been consistent over at least the last two decades.

Hydrogeology and hydrologic conditions of the Ozark Plateaus aquifer system

“…Locally, groundwater flow is generally from local topographic highs towards stream valleys, with surface streams serving as groundwater hydrologic boundaries; however, because of the karst hydrogeology of the Ozark system, surface-water basins and groundwater recharge areas do not always coincide (Brahana, 1997). The abundant occurrence of groundwater transfer across surfacewater drainage-basin divides has been observed in dye-tracing studies and drainage-area-discharge relations (Sullavan, 1974;Vineyard and Feder, 1982;Brahana and Davis, 1998;Mott and others, 2000;Owen and Pavlowsky, 2011). Consideration of interbasin movement of water is an important point for protection and management of groundwater because contributing zones are not apparent at the surface, and contaminants can be introduced into groundwater from unexpected locations.…”

“…Conversely, many surface-stream reaches also lose considerable amounts of water to the subsurface (termed "losing streams"). Delineating a precise boundary between groundwater and surface water is difficult and ill-advised from the standpoint of effective management and protection of the region's water resources (Owen and Pavlowsky, 2011). Springs are important discharge points for the Ozark system and tend to occur at contacts of units with varying permeability and near faults or monoclines or in structural lows (Mott and others, 2000).…”

“…Examples of such work include, but are not limited to, Vandike (1994), Davis and others (2000), Peterson and others (2000), Peterson and others (2002), Sauer and others (2002), Imes and others (2007), Owen and Pavlowsky (2011), Knierim and others (2013), and Knierim and others (2015). Although regional models show overall topographic control over shallow groundwater flow on a large scale (Imes and Emmett, 1994), groundwater flow on smaller scales follows unpredictable focused flow paths that are controlled less by topography and more by stratigraphy and structure (Brahana, 2011).…”

Quantifying the variability in Escherichia coli (E. coli) throughout storm events at a karst spring in northwestern Arkansas, United States

“…Sources of contamination in karst aquifers can include point sources, such as discharges from waste-water treatment plants (Owen and Pavlowsky 2011) and landfills (Kogovšek and Petrič 2013), or non-point sources, such as improperly functioning septic systems (Katz et al 2010;Owen and Pavlowsky 2011) and urban and agricultural run-off (Kresse et al in review;Boyer and Pasquarell 1999;Mahler et al 2000;Panno et al 2001;Pronk et al 2006;Reed et al 2011). Bacteria, inorganic compounds (including nutrients), and sediment are common contaminants in karst aquifers (Adamski et al 1995;Vesper 2007).…”

Increased Effluent Dosage Effects on On-Site Wastewater Treatment Systems of Differing Architecture Type

“…There are also many gas stations, mobile home parks, campsites, and individual homes that also rely on groundwater as a drinking water source. However, much of the topography in northwest Arkansas is karstic [3] [4]. Consequently, groundwater resources are susceptible to pollution from sources such as fertilizers and OWTSs [5].…”