Chapter 4 Habitats
4.2.6 Groundwater, Springs, and Subterranean Water Systems 4.2.6.1 Ecosystem Description
Groundwater is present throughout North Carolina at varying depths below the land surface. The traditional definition for groundwater is subsurface water that occurs beneath the water table in soils and geologic formations that are fully saturated (Freeze and Cherry 1979) . For this aquatic community description, we use the term “groundwater” to represent all subsurface waters generically, including saturated soils and underground streams. These systems may interact with or transition to other types of habitats (e.g., streams, lakes, wetlands) (Winter et al. 1998) which are described as separate natural communities in other sections of this chapter. Groundwater is subsurface water stored in a zone of soil saturation and occurs beneath the water table (Freeze and Cherry 1979; Fetter 2001) and differs from surface waters because of the absence of light and the fact that organic matter and oxygen are imported from the surface (Hahn 2009) . Groundwater recharge is the process where water infiltrated from the surface is added to the saturated zone; the top of the saturation zone is referred to as the water table (Domenico and Schwartz 1998; Campbell and Coes 2010) . Groundwater forms a water table that can lie at the ground’s surface and contribute to the baseflow of a stream, or it can be situated underground at varying depths, existing as subsurface flow. Some groundwater discharge is an interstitial habitat that is hydrologically linked to and contributes baseflow to wetlands, ponds, or lakes (Culver et al. 2012). Groundwater intersects with streams where the water table is at or slightly above the streambed (Gordon et al . 1992; Peterson and Rabeni 1996 ). Springs are points of focused groundwater discharged at a small point on the land surface (van der Kamp 1995; McGinley 2013) . They are generally stable in terms of water quality, temperature and flow (Fleury 2009) . Springs can also form at the spots where karst waters emerge from the local underground drainage system and develop on the surface or in caves (Fleury 2009) . They are made up of groundwater that has infiltrated at different times, from different places, and potentially under different conditions than currently exist (van der Kamp 1995) . In contrast, seeps discharge to a larger area than a spring (McGinley 2013) . Seepage springs are a diffuse discharge of gravity-fed water where the land surface is wet compared to surrounding areas, but there is no observable flow (Culver et al. 2012) . Springs feeding into creeks and rivers can provide coldwater microhabitats and, in some cases, can reduce overall water temperature. This in turn reduces thermal stress on aquatic species sensitive to warm waters. Subterranean water develops in permeable layers of soil, sand, and rock. A subterranean system that carries groundwater in sufficient quantity to provide usable water supplies is called an aquifer (Hynes 1983; Barnes-Svarney and Svarney 2004; Kokkonen et al. 2011). Coastal Plain groundwater is found primarily in porous sand and limestone (carbonate rock) and is regionally classified as being shallow unconfined (surficial) aquifers or deeper confined aquifers (Smith and Chapman 2005; USGS 2012a; Denver et al. 2014) . All aquifers have an impermeable layer beneath them that stops the groundwater from infiltrating farther. When the layers above it are permeable, it is an unconfined aquifer and when the permeable layer occurs between two impermeable layers, it
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2025 NC Wildlife Action Plan
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