A conceptual hydrologic model for a forested Carolina bay depressional wetland on the Coastal Plain of South Carolina, USA

Abstract

Abstract:This paper describes how climate influences the hydrology of an ephemeral depressional wetland. Surface water and groundwater elevation data were collected for 7 years in a Coastal Plain watershed in South Carolina USA containing depressional wetlands, known as Carolina bays. Rainfall and temperature data were compared with water-table well and piezometer data in and around one wetland. Using these data a conceptual model was created that describes the hydrology of the system under wet, dry, and drought conditions. The data suggest this wetland operates as a focal point for groundwater recharge under most climate conditions. During years of below-normal to normal rainfall the hydraulic gradient indicated the potential for groundwater recharge from the depression, whereas during years of above-normal rainfall, the hydraulic gradient between the adjacent upland, the wetland margin, and the wetland centre showed the potential for groundwater discharge into the wetland. Using high-resolution water-level measurements, this groundwater discharge condition was found to hold true even during individual rainfall events, especially under wet antecedent soil conditions. The dynamic nature of the hydrology in this Carolina bay clearly indicates it is not an isolated system as previously believed, and our groundwater data expand upon previous hydrologic investigations at similar sites which do not account for the role of groundwater in estimating the water budget of such systems.

Do geographically isolated wetlands influence landscape functions?

“…For others, particularly GIWs that typically lack a persistent surface connection, hydrological connectivity may be less obvious. It occurs via unidirectional, episodic, and transient surface connections when depression storage is seasonally filled (e.g., vernal pools) (42,65), or via slower moving subsurface flow paths (58,66,67). Despite uncertainty in quantifying timescales of hydrologic connectivity, GIWs have recently been shown to regulate (68,69) and stabilize (70) potentiometric gradients that generate base flow in streams.…”

“…These subsurface flow paths may be hard to see (71), but they are not speculative or insubstantial connections. Indeed, they are often large and quantifiable at both field and landscape scales (41,66,(72)(73)(74). Crucially, the timescales of such connections are longer than for surface flow paths (75), manifest in base flow generation and water chemistry, implying potentially decadal delays in observing downstream effects of both wetland degradation and restoration activities.…”

Modeling the potential impacts of climate change on the water table level of selected forested wetlands in the southeastern United States

“…The FL research site is located 33 km northeast of Gainesville in Alachua County of northern central Florida. The SC wetland is located in Bamberg County, South Carolina, representing a typical depressional wetland in the region (Pyzoha et al, 2008;Sun et al, 2006). The SC wetland was covered by naturally regenerated deciduous trees (i.e., water oak, willow oak) and was surrounded by deep, well-drained sand dominated by hardwood plantations and agricultural crops (Pyzoha et al, 2008;Sun et al, 2006).…”

“…To be consistent and reduce uncertainty of PET estimates, 1.2 was used for all five wetlands in this study. Artificially managed lower coastal plain forested wetland Sun et al (2010), Tian et al (2012Tian et al ( , 2015, Diggs (2004) Pyzoha et al (2008), Sun et al (2006) …”

Coastal Forests and Groundwater: Using Case Studies to Understand the Effects of Drivers and Stressors for Resource Management

“…In shallow water table settings, however, seemingly small changes in the water budget of the groundwater system may cause large changes in the surface hydrology, such as surface runoff, wetland water content, and groundwater discharge as baseflow to streams and rivers [23,34]. Figure 4 shows a conceptual diagram that illustrates how changing the water table position may affect a riparian zone or depression wetland [35]. Based on field visits, interpretations of geological surveys [31,36,37], and water-level data from piezometers in the region (Figure 2) [26,38], we estimate that, for the most part, this area does not have truly perched groundwater conditions and thus downward drainage is not limited geologically, but rather by the small downward hydraulic gradients in this flat, highwater-table landscape.…”