Impacts of land use and climate change on hydrologic processes in shallow aquatic ecosystems Clarisse Betancourt Roman Department of Environmental Science University of Puerto Rico- Rio Piedras Campus San Juan, PR, USA clarissebetancourt@gmail.com Maurice G. Estes, Jr. and Mohammad Z. Al- Hamdan Universities Space Research Association National Space Science and Technology Center Huntsville, AL, USA maury.g.estes@nasa.gov mohammad.alhamdan@nasa.gov Abstract- Mobile Bay is a significant resource for human uses with important implications on commercial fisheries, coastal development, industry and tourism. Submerged aquatic vegetation (SAV) provides habitat in the littoral zone important to Gulf fisheries. Alabama coastal systems have been increasing in population and this with LCLU change in the surrounding areas of the coast are causing changes in streamflow discharges. The change in river outflow can affect the quality of the water in the bay, which is essential to the health of the ecosystem. Watershed and hydrodynamic modeling has been performed to evaluate the impact of land use and climate change in Mobile and Baldwin counties on the aquatic ecosystem in Mobile Bay. Remote sensing data (Landsat Images) were used as model input for the LCLU scenarios for the years of 1992 and 2001. The Prescott Spatial Growth Model (PSGM) was used to project the 2030 land use scenario based on observed trends. The data provided by Intergovernmental Panel on Climate Change (IPCC) for the South region on future temperature and precipitation projections were used to create future climate scenarios of 2025 and 2050. Results indicate that the LCLU changes are increasing the freshwater flows into the Bay. The projected drier and hotter climate will decrease the freshwater flows into the Bay too. Variations in flow into the Bay can change the sediment loads, salinity and temperature of the water. These changes affect the normal conditions of the habitat, distribution and abundance of particular species of plants and the amount of light that SAVs need for survival. I. Introduction Mobile Bay is located along the southeastern coast of the United States in the state of Alabama and is considered the fourth largest estuary in the United States with an inflow of 1755 cubic meters of water per second (62,000 cubic feet per second) [1]. This large estuary receives 20 % of the freshwater supply in the United States [2]. The surface waters of Mobile Bay cover 1059 km² (409 mi²), and the average depth is about 3.048m (10 ft) [3][4]. Mobile Bay is the intermediary area between freshwater of the watershed and open water, the Gulf of Mexico. The primary opening of the Bay to the Gulf of Mexico is called the Main Pass and is located between Dauphin Island and the Fort Morgan Peninsula [5]. Mobile Bay is home to a large diversity of species and distinct habitats. Habitat types characterized in the Bay include soft sediments, seagrass beds, barrier island dune and inter-dune wetland swales, fresh and saltwater marshes, pitcher plant bogs, wet pine savannas, upland pine-oak forests, tidal marshes, cypress swamps, bottomland hardwoods forest and oyster reefs [5][6]. These habitats are essential food sources for species such as shrimp, oysters, and flounder. Because of its vital function as an ecosystem, the Clean Water Act of 1987 established Mobile Bay as a National Estuary in 1995 [7]. The Mobile Bay Estuary is a habitat to 46 species of mammals, 126 amphibians and reptiles, 355 species of birds and 337 saltwater and freshwater fish species [4]. The Bay has one of the richest freshwater fish populations in North America, however, 36 of the Bay’s 337 fish species are listed as at risk [4][8]. Also, Mobile Bay is a significant resource for human uses with important implications on commercial fisheries, coastal development, industry and tourism. The fish species in the Bay are commercially and recreationally important for the local and national economy [9]. Submerged aquatic vegetation (SAV) is an important natural resource in the Mobile Bay aquatic ecosystem. SAV provides forage for wintering waterfowl and food and habitat for many native, exotic and endangered species (sea turtles and manatees). Besides, SAV offer a nursery habitat for species and refuge from predators. SAV prevents erosion by buffering the impacts of waves, removing nutrients and other pollutants from river and runoff inputs to coastal areas, reducing wave energy and trapping sediment [10][11]. The SAV requires specific habitat characteristics to survive. The factors most relevant to the health of SAV are light, salinity, wave energy, and nutrients [11]. The major factor controlling distribution of SAV is the penetration of light through the water column [12]. Light penetration will be influenced by the quantity of sediment in the water column. The average condition in salinity for high salinity submerged aquatic vegetation is between 15 and 26 ppt; while freshwater SAV is from 1 to 2 ppt [13]. Fonseca et al, 1998 [14] analyzed the effect of wave exposure and currents on SAV coverage in Core Sound and found an inverse relationship between percent cover of SAV and wave exposure indices or current speed. Therefore with more wave exposure there is less coverage of SAV. The growth and availability of the SAV on bays could be affected by numerous factors including weather events, industrial pollutants, agricultural herbicides and decline in water quality. U.S. Government work not protected by U.S. copyright