The Effect of Land Use/Land Cover on Headwater-Slope Wetlands in Baldwin County, Alabama
Type of Degreethesis
Forestry and Wildlife Sciences
MetadataShow full item record
Land use and land cover (LULC) have been shown to greatly influence aquatic environments although very few studies have described the effect on headwater wetlands. The overall goal of this research was to assess the impact of LULC on headwater-slope wetlands and their associated functions. The objectives were to (1) assess the influence of LULC on the forested structure, composition and function as modeled by the hydrogeomorphic approach, and (2) evaluate the effects of LULC on specific wetland functions (carbon cycling and water storage) through direct measurement. Using 30 wetlands across a gradient of surrounding LULC, tree density, tree diameter, species cover, and soil value/chroma were measured. Prevalence index (PI) was calculated as an indicator of potential species shift due to change of hydroperiod related to changes in LULC within corresponding watersheds. Using the collected wetland data, functional capacity indices (FCI) were calculated using the hydrogeomorphic approach (HGM) for wetland wildlife habitat, organic carbon cycling, water storage and characteristic vegetative community. The presence of exotic species was significantly related to LULC with increases in Ligustrum sinense (Chinese privet) and Sapium sebiferum (Chinese tallow tree) as forested land cover decreased. Prevalence index, as well as, soil chroma decreased with forested land cover, potentially describing longer saturated soil conditions within wetlands whose watersheds were dominated by forests. The same level of significance did not occur when the FCI scores were evaluated as response variables to LULC. The HGM may not be suitable to describe impacts of shifts in land use because of inherent issues with the wetland hydrology variable used to calculate FCI scores. However, FCI describing wetland ability to provide characteristic wildlife habitat was significantly related to LULC. Although useful for regulatory purposes, HGM may require further development and validation before it should be utilized for scientific purposes. In the second part of this study, land use and soil data were utilized to calculate runoff curve numbers (CN) and used with site-specific precipitation data to calculate total runoff (Pe) produced within 15 wetland watersheds. Water level recorders were installed in each wetland and programmed to measure surface and ground water levels. Hydrologic metrics derived from these data included: Richard-Baker index (RB), water level rate of change (WLΔ), water level variability (standard deviation of measurements), and a measure of the percent of time the water table was within 20-cm of ground surface (WT20). Richard-Baker index was the only hydrological metric to be significantly related to land use and decreased with increasing CN. Bimonthly monitoring of forest floor carbon (CFF) and litter fall carbon (CLF) were conducted within each plot to determine if watershed runoff influenced the storage of forest litter fall. A significant relationship was detected between decreasing CFF with increased CN and Pe suggesting hydrologic export may be an important process in forest carbon dynamics where surrounding lands have been altered. Soil carbon was quantified in each wetland by collecting cores to a depth of 1m and processing 10-cm sections for carbon analysis. Increased duration of soil saturation resulted in decreasing bulk density, potentially describing the role of soil saturation in the storage of organic carbon.