Understanding the Ways of the Water

Tidal freshwater forested wetlands (TFFW) can be extensive in large river deltas influenced by estuary and river flows. There is increasing concern about the fate of these wetlands due to sea level rise (SLR) and other impacts along our coasts. The Mobile-Tensaw River Delta (MTRD) in southern Alabama is one of the largest deltas (~140,000 ha) in the United States. We initiated a study to better understand the MTRD and its relation to Mobile Bay. Nine continuous salinity/water level monitoring stations were installed and used to locate 47 plots (400 m2) for tidal forest community surveys. A multivariate hierarchical clustering approach discerned five distinct communities based on canopy tree importance values. Using the water stations and other available data, a machine learning approach (i.e., deep neural network and a Hybrid Convolutional Recurrent models) was used to successfully model salinity affecting TFFWs. Based on model outputs, sites further from river channels showed significant daily salinity variability (range > 8 PSU), while those closer to the channels had less variability and lower salinity (range < 5 PSU). Across the study area, there was < 10% probability that salinity will exceed 5 PSU across all the stations. Finally, to better understand connections between the MTRD and Mobile Bay, current and historical samples of bay sediments were analyzed. Bulk stable isotope ratios in sediments reflected terrestrial source dominance across MTRD sites (-30 to -28‰), with values increasing down Mobile Bay from north (-34 to -26‰) to south (-24 to 18‰). Preliminary analysis suggests seasonal and interannual differences were primarily driven by whether river discharge was low (< 1200 m3/s) or high (>2000m3/s) 30 days prior to sampling. Our results depict a highly complex MTRD-TFFW system and allow us to evaluate alterations expected with future SLR, river flows, and other changes.

The Grand Bay National Estuarine Research Reserve (GNDNERR) hosts 3,500 acres of Longleaf Pine Savanna undergoing various restoration processes (e.g. herbicide application and prescribed burns) upstream of 8,000 acres of estuarine habitat. While impacts of restoration on upland ecosystems have been well studied, effects on downstream ecosystems remain largely unknown. Since 2004, GNDNERR estuary has been monitored through the System Wide Monitoring Program for water quality, weather, and nutrients, with recent intermittent monitoring of fish, submerged aquatic vegetation, and birds. However, little recent research at GNDNERR has focused on the benthic zone, which plays a critical role in ecosystem functioning, in part facilitated by macrobenthic invertebrates. These invertebrates facilitate energy and material movement between the sediment and water column through bioturbation and secondary production, forming a key trophic link to higher levels. In addition, they are also a monitoring tool for managers as their small size, sessile and sensitive nature make them an ideal indicator of change within an ecosystem. This project, Downstream Effects of Restoration Activities, conducted from August 2023 to August 2024, aimed to investigate the ecological effects of upland restoration on downstream ecosystems. Sampling sites were plotted along transects (upper, middle, and lower) within five bayous downstream of a gradient of development and restoration activities. Monthly water quality (e.g., temperature, salinity, dissolved oxygen) and nutrient (e.g., NOx, PO4,Chlorophyll-a) samples, were analyzed in-house, whereas sediment and macrobenthic invertebrate samples were collected quarterly and analyzed at Dauphin Island Sea Lab (sediment) and at GNDERR (invertebrates). Here we present baseline characterization of the macrobenthic invertebrate community of the upper sites of Alabama (no restoration) and Middle Bayous (recent restoration), and Bangs Lake (industrial development). This novel dataset provides a baseline for resource managers on how the local benthic community is impacted by seasonality and shifts in water quality.

Mississippi is experiencing increased temperatures, flood-producing storms, and more extreme weather events. As the climate continues to change, it is important for fisheries managers to understand the impact these environmental conditions will have on localized fish and invertebrate populations. While previous studies have evaluated the effects of drought conditions on adult fishes, little work has explored the impacts of river discharge on juvenile fishes and invertebrate populations within Mississippi's diverse estuarine environment.


The Mississippi Sound is naturally influenced by six tributaries, however freshwater diversion also poses a considerable threat. The Bonnet Carré Spillway was completed in 1931 to manage the flow of the Mississippi River during major flood events. When opened, the spillway diverts water from the river through Lake Pontchartrain, LA and subsequently into the western Mississippi Sound. These openings cause a rapid influx of freshwater into the estuary, exerting significant impacts on local fish and invertebrate populations. Most notably, spillway openings in 2011 and 2019 resulted in declared fisheries disasters. With peak annual rainfall and river flow fluctuating at extreme levels, the probability of the spillway's annual opening continues to rise.


This study aimed to elucidate the impacts of river discharge and corresponding hydrological changes on recreationally and commercially important fish and invertebrate species within the Mississippi Sound and the adjacent tributaries. Eight target species were selected for analysis to include brown shrimp (Farfantepenaeus aztecus), white shrimp (Litopenaeus setiferus), blue crab (Callinectes spp.), Atlantic Croaker (Micropogonias undulatus), Sand Seatrout (Cynoscion arenarius), Spotted Seatrout (Cynoscion nebulosus), Spot (Leiostomus xanthurus), and Gulf Menhaden (Brevoortia patronus). Multivariate analyses were conducted to assess the impacts of seasonal/annual precipitation, flow rate/river discharge, salinity, and temperature on relative juvenile abundance and year-class strength of each target species over a 15-year time series. The impacts of extreme weather/disaster events on juvenile recruitment were also explored.

The Mississippi Sound is an ecologically and economically important waterbody that stretches from western Alabama to eastern Louisiana. In this system, water clarity is highly dynamic and variable due to seasonal river sediment inflow and engineered diversions. The limitations of traditional point sampling methods in capturing spatial variability are motivating the use of remote sensing for transparency estimation. Water clarity is commonly measured by the Secchi disk depth (Zsd), and indicates light availability in the water and is closely linked to primary productivity, variability in dissolved organic matter, and suspended sediment concentration. For this study, we aim to develop an integrated framework that leverages Sentinel-3 OLCI imagery, in-situ data, and machine learning algorithms to quantify and map the Zsd in the Mississippi Sound. We developed an empirical model for monitoring Zsd based on the multispectral sensor OLCI onboard Sentinel-3. Six campaigns were carried out from July 2023 to June 2024, and surface reflectance and Zsd data were collected. Different machine learning algorithms were tested for Zsd estimation, and results showed that the Random Forest model best fit the data patterns (r-squared = 0.851, bias log = 1.005, and RMSE = 9.785 cm). The model was then applied to three Sentinel-3 OLCI images of the Mississippi Sound and validated with in situ data. The accuracy assessment of the estimated Zsd achieved an r-squared of 0.643, a bias log of 0.93, and an RMSE of 22.65 cm, showing that remote sensing data can accurately estimate water transparency on the Mississippi Sound. Our model can reduce costs and efforts in fieldwork and provide insights into water clarity dynamics along the MS, aiding more effective management and conservation strategies for this critical coastal region.