Auburn University’s Chris Anderson is looking at nutrient retention at various headwater wetlands in Baldwin County, Ala., to quantify exactly how much of the naturally occurring filtration process is lost to excessive urban drainage. Anderson expects this study will provide some insight to city planners and concerned residents about the important ecological function of healthy wetlands.
A healthy headwater wetland takes in water from surrounding land and filters out impurities before eventually releasing cleaner water downstream. Storm drains in developed areas often bring in more water to a wetland than comes in naturally during rain events. The speed and volume at which the water enters the wetland can cause fast-moving streams to form, which makes the surrounding wetland soils dry up. When that happens, the microbes that live in the wetland soil no longer have the time and exposure they need to filter out the nutrients.
Abstract
This study will examine the influence of urban land use on headwater wetlands and their capacity to maintain and improve water quality along the Alabama and Mississippi coast. Current research has demonstrated that increasing urban land use within wetland catchments often cause these wetlands to shift hydrology from groundwater to surface water driven. For this study, a total of 3 headwater wetlands will be selected in southern Baldwin County, Alabama that are surrounded by varying intensity of urban development. Wetlands will be monitored over a 1-year period to evaluate nutrient and sediment reduction related to hydrological alternations in response to increasing urban development.
Wetland capacity to improve water quality will be based on measured reductions of nutrient (NH4/NH3, NO2, NO3, and TP) and sediments (TSS) loads into the wetland. Surface water and groundwater samples will be collected through a combination of grab samples and automatic sampling devices (i.e., ISCOs). Hydrographs of each wetland will be developed using automated water level recorders and discerned for groundwater and surface water contributions. Water quality and hydrological measurements will be used to calibrate and validate a process-based wetland model designed to estimate nutrient and sediment cycling. Our objective is to determine how urban intensity (and the tendency to increase surface water drainage) may reduce wetland capacity to improve/maintain water quality while improving our ability to predict and mitigate for urban impacts to water quality.
Through a series of outreach meetings with municipal planners, we will convey our findings, demonstrate the predictive model, and provide recommendations of planning and development practices that maintain wetland capacity to improve water quality emanating from urban areas.
Objectives
Because of their location on the landscape, headwater slope wetlands are likely critical ecosystems for maintaining water quality to coastal creeks. Our research objectives are to 1) determine how urban surroundings alter wetland hydrology and 2) determine and predict how urban surroundings may change wetland capacity to maintain or improve water quality. As a project objective, we seek to provide urban planners relevant information regarding the importance of headwater wetlands for coastal water protection.
Methodology
For this study, we will select three headwater wetlands in Baldwin County, Alabama that represent a range of surrounding urban land use conditions. We will evaluate how hydrologic shifts in these wetlands affect nutrient (NH4/NH3, NO2, NO3, and TP) and sediment (TSS) loadings into downstream creeks. Wetlands will be selected along a gradient of watershed conditions that range from no-urban land use (primarily forested) to one that is nearly or completely developed (primarily urban). Water level recorders (pressure transducers) will be established to characterize hydrology, evaluate baseflow levels relative to the ground surface, and examine hydrologic responses to storm events. For each wetland, we will also establish a water quality sampling stations along surface water inflows (i.e., urban ditches) and outflows (i.e., drainage into first order creeks).
Water emanating from each wetland will be sampled through a combination of baseflow grab samples and automatic stormflow samplers (i.e., ISCOs). We will utilize up to 3 shallow groundwater wells at the wetland/upland interface to sample incoming groundwater. All water will be analyzed for nutrients and sediment immediately after collection using laboratory facilities at the Week’s Bay National Estuarine Research Reserve (see support letter from WBNERR). Standard Methods (APHA 1998) will be followed during the course of sampling and lab analysis. To estimate nutrient/sediment loading, we will use continuously logged stage data, coupled with measured stage dependent flow measurements, to develop stage-discharge relations (rating curves). These rating curves will be used to make estimations of nutrient and sediment loading from the wetland. This information will be used to compare wetland inflow, outflow, and retention of nutrients/sediment during both baseflow and stormflow conditions. This data will also be used to calibrate/validate a recently developed process-based wetland model for nutrient and sediment cycling, developed by co-PI Kalin through collaboration with the U.S. EPA.
The validated wetland model will then be used to assess the functional capacities of wetlands which receive nutrient and sediment loads in hypothetical scenarios of increasing urban development. Inflow of nutrients and sediment to those wetlands from their respective watersheds will be estimated using the SWAT model. Using SWAT derived inputs of the hypothetical scenarios, we will model changes in water quality and change in wetland capacity to improve water quality.
This study will allow us to evaluate the ramification of continued urban development on the water quality of coastal creeks throughout the coastal Alabama and Mississippi region.
Rationale
Coastal wetlands are among the most important ecosystems in terms of their services to mankind (e.g., water quality improvement, water storage, habitat), but they are also among the most vulnerable. The most pressing issue leading to the loss of functional wetlands is increasing urban growth along the coast. For instance, in Baldwin County, Alabama there was a 42.9-percent increase in population from 1990 to 2000 and this trend is expected to continue in the future (BCPZD 2005). Headwater slope wetlands are predominantly forested wetlands at the headwaters of coastal creeks throughout Coastal Plain Alabama and Mississippi. They tend to occur on relatively flat terrain where gradual slopes move water slowly through them as shallow groundwater discharge. They are potentially critical components to the landscape because they occur at the interface of uplands and coastal creeks. As a result, these wetlands intercept draining waters and improve water quality before reaching local bay and oceanic waters. Further, urban areas in south Baldwin County commonly sit on watershed divides and therefore have the potential to adversely impact headwaters of coastal creeks.
For instance, the city of Foley sits at the divides of the Magnolia River, Bon Secour, and Wolf Bay watersheds. Similarly, a significant portion of Fairhope is along the boundary of the Fish River watershed. It is also important to note that receiving bays in this area have regional and national significance. Weeks Bay, the receiving bay of the Fish and Magnolia River watersheds, is designated as an Outstanding National Water, Wolf Bay recently became an Alabama Outstanding State Water, and the Bon Secour River watershed drains to the Bon Secour National Wildlife Refuge.
As the northern Gulf Coast continues to develop, headwater wetlands are expected to become increasingly impacted by filling, draining, and indirect hydrologic alterations. When urban surroundings increase, headwater wetland hydrology may shift causing them to become more surface water driven. Various urban attributes (greater impervious surface, stormwater drainage systems, etc.) tend to convey water quickly to streams and wetlands thereby increasing stormflow, reducing baseflow, and changing important ecosystem functions (Bledsoe and Watson 2001, Forman and Alexander 1998). With these alterations, there is the potential for severe changes in several biogeochemical and physical processes that influence downstream water quality. Consistent with the Mississippi-Alabama Sea Grant Consortium research priorities related to sustainable development, we seek to understand how land alteration in our coastal counties may compromise local water quality. Through a combination of field surveys and modeling, our goal is to explore how increasing urbanization changes headwater wetland hydrology and the capacity for wetlands to provide water quality improvement.
Results
Barksdale, W. F., Anderson, C. J., & Kalin, L. (2014). The influence of watershed run-off on the hydrology, forest floor litter and soil carbon of headwater wetlands. Echohydrology, 7(2), 803-814.
Barksdale, W.F., & Anderson, C. J. (2015). The influence of land use on forest structure, species composition, and soil conditions in headwater-slope wetlands of coastal Alabama, USA. International Journal of Biodiversity Science, Ecosystem Services & Management, 11(1).
Alix, Diane M., et al. "Evaluating the Effects of Land Use on Headwater Wetland Amphibian Assemblages in Coastal Alabama." Wetlands 34.5 (2014): 917-926.