Characterizing hydrology and the importance of ground-water discharge in natural and constructed wetlands

Abstract

Although considered the most important component for the establishment and persistence of wetlands, hydrology has been hard to characterize and linkages between hydrology and other environmental conditions are often poorly understood. In this work, methods for characterizing a wetland's hydrology from hydrographs were developed, and the importance of ground water to the physical and geochemical conditions in the root zone was investigated. Detailed sampling of nearly continuous hydrographs showed that sites with greater ground-water discharge had higher water tables and more stable hydrographs, Subsampling of the continuous hydrograph failed to characterize the sites correctly, even though the wetland complex is located in a strong regional ground-water-discharge area. By comparing soil-moisture-potential measurements to the water-table hydrograph at one site, we noted that the amount of root-zone saturation was not necessarily driven by the water-table hydrograph but can be a result of other soil parameters (i.e., soil texture and associated capillary fringe). Ground-water discharge was not a significant determinant of maximum or average temperatures in the root zone. High ground-water discharge was associated with earliest date of thaw and shortest period of time that the root zone was frozen, however. Finally, the direction and magnitude of shallow ground-water flow was found to affect the migration and importance of a geochemical species. Areas of higher ground-water discharge had less downward penetration of CO~ generated in the root zone. In contrast, biotically derived CO: was able to penetrate the deeper ground-water system in areas of groundwater recharge. Although ground-water flows are difficult to characterize, understanding these components is critical to the success of wetland restoration and creation efforts.

Relating groundwater to seasonal wetlands in southeastern Wisconsin, USA

“…Depth-to-water below grade (land surface) was calculated by subtracting the difference between the top-of-casing and land surface elevations (same as riser height above grade) from the depth-to-water measurement. Periods of continuous root zone residence times were determined for each of the six water-table wells and each growing season using the method of Hunt et al (1999); for clarity the standard normal deviate has been converted to cumulative probability for plotting. Continuous lognormal distributions were fit to the residence time data.…”

“…Following the method described by Hunt et al (1999), each well hydrograph was analyzed to determine the contiguous periods of time where the water level was at or above the root zone, defined as 30 cm below ground surface, during the growing seasons. This method incorporates the small-scale temporal fluctuations that can play a significant role in the wetland hydrology and is more consistent with the characteristic hydrologic thresholds presented by the National Research Council (1995).…”

“…In recognition of the importance of this loss, appropriate identification, delineation, and management of remaining wetlands within the United States are needed to assess the effectiveness of wetland protection plans. However, our understanding of the fundamental components of wetlands (i.e., hydrology, soils, vegetation, and topography), and their interaction with each other, is often not sufficient to meet this goal (Hunt 1996;Hunt et al 1998Hunt et al , 1999, especially for wetlands that are only seasonally wet.…”

Water Table Depth, Surface Saturation, and Drought Response in Bog Turtle (Glyptemys muhlenbergii) Wetlands

“…Temperate zone fens are usually found on land that is slightly sloped, resulting in little inundation. Because of groundwater inflow, fens generally have more moderate water table fluctuations than wetlands dependent on periodic flood events or precipitation (Hunt et al 1999). Many fens in the southern Appalachians contain vegetation that is typical of acidic bogs such as sphagnum moss, which has been associated with bog turtle nesting (Mitchell 1994;Ernst and Lovich 2009).…”

Assessing the Influence of Drainage Pipe Removal on Wetland Hydrology Restoration: A Case Study

“…However, while many studies of wetland hydrology have been conducted (Schot and Wassen 1993, Hunt et al 1998, 1999a, 1999b, Winter 1992, few have addressed the effect of various wetland restoration techniques on the basic hydrological functioning of restored or reestablished wetlands. Studying the hydrological functioning of wetlands after restoration is critical in order to assess wetland restoration and to develop effective restoration practices.…”