Projects

Coastal development in the northern Gulf of Mexico: Linking drainage patterns and tidal creek habitats

End Date: 01/31/2020

What is the impact of urban stormwater runoff on fish in neighboring salt marsh habitats? Does urbanization in coastal watersheds affect habitat for resident fish? Christopher Anderson, Latif Kalin and Dennis DeVries of Auburn University are asking these critical questions about coastal development in Alabama and Mississippi. The team is exploring how runoff and nutrient loading from urban development changes salinity and dissolved oxygen in nearby salt marshes. They are also looking at species richness, diversity, abundance, overall condition of fish and dietary differences in fish to investigate how land use related changes in water quality shape resident fish populations. Through this study, the team hopes to inform stormwater policy and identify tidal creeks where reducing runoff can improve habitat.

Objectives

  1. To explore how runoff characteristics and nutrient loadings to tidal creeks affect creek salinity (Sal) and dissolved oxygen (DO) regimes.
  2. To distinguish how patterns of urban development in coastal watersheds relates to tidal creek Sal and DO using estimates of runoff and nutrient loading as the nexus.
  3. To determine whether urbanization in coastal watersheds will change the suitability of salt marsh habitat for resident fish.
  4. To demonstrate the impacts of coastal development on the health of coastal habitats to coastal communities in order to help them develop better stormwater policies.

Methodology

We will examine at least 12 tidal creeks influenced by a range of urban conditions typical of the region. At each creek, 3-4 fringing salt marshes will be selected for later fish sampling. Salt marshes will be selected of comparable size, vegetative composition and complexity. Along each creek (at a mid-point between marshes) Sal and DO will be monitored. Other habitat data collected will include marsh slope (at the creek interface), marsh stem density, and water.

We will predict freshwater input and N, P loadings from the tidal creeks using the SWAT model. Those outputs will then be used as input along with tide level, sea salinity and water temperature data into an ANN model to develop a model for Sal and DO predictions. By applying the model to historical climate data, we will determine Sal and DO over a much longer period, which will allow us to develop Sal and DO frequency graphs and other analyses that demonstrate the effect of urban LULC intensity on drainage patterns in the region.

Marshes within each creek will be sampled seasonally for resident fish. Fish will be trapped once per season. Fish collections will be used to determine species richness, diversity, and abundance per marsh. The length and weight of a subset of fish will be measured, and compared for potential differences in species condition between creeks. Stomach analyses will be conducted on a subset of fish to evaluate potential differences in diet related to land use. Statistical models will be conducted to evaluate the strength of relationship that Sal and DO have on fish assemblage and total biomass of fish per marsh. Other factors to be included in statistical models will include marsh and creek environmental data such as vegetative cover, sediment characteristics and slope.

Rationale

Salt marshes are critical habitats for Gulf of Mexico (GOM) fishes that contribute significantly to total fish landings both commercially and recreationally in the United States (Chesney et al. 2000). As human populations along the northern GOM coast continue to increase, it is important to know how this will affect critical habitats. Evidence from a recent study (Wedge et al. 2015, Wedge and Anderson 2017) suggests that even drainage from low- to moderately urban (i.e., residential) land use can influence nearby tidal creeks and their associated habitats. Specifically, urban tidal creeks were shown to have salinities that rapidly fluctuated and more often reached freshwater conditions compared to reference creeks draining forested watersheds.

Urbanization is known to increase runoff and stream flashiness while reducing the physicochemical condition of aquatic habitats (Walsh et al. 2005). In coastal areas, this may ultimately change the salinity (Sal), dissolved oxygen (DO) and nutrient regimes that determine marsh habitat suitability for fish. By better understanding the role of watershed runoff on tidal habitats, we can improve stormwater policy and identify urbanized tidal creeks that might be enhanced by reducing runoff retrospectively. This research is most relevant to the Focus Area: Healthy Coastal Ecosystems The proposed research project is intended to demonstrate the effect of increased urban storm water runoff to resident fish inhabiting the fringe salt marsh habitats of Alabama and Mississippi. Coastal watershed plans have been/are being developed for
local drainages along the GOM (e.g., http://www.mobilebaynep.com/the_watersheds). This research would determine the potential environmental gains of better storm water management. Among the watershed goals listed by the Mobile Bay National Estuarine Program for watershed health and resilience to:

  1. Reduce point and non-point source pollution (including storm water runoff and associated trash, nutrients, pathogens, and sedimentation) and remediate past effects of environmental degradation to reduce pollutant loads into Mobile Bay, Mississippi Sound and the Gulf of Mexico,
  2. Identify actions to reduce the incidence and impacts of invasive flora and fauna and improve habitats necessary to support healthy populations of fish and shellfish, and
  3. Identify vulnerabilities in the watershed from increased sea level rise, storm surge, temperature increases, and precipitation and improve watershed resiliency through adaptation strategies.