Understanding the Ways of the Water

The most comprehensive sampling of sediment for texture, mineralogy, and organic and inorganic chemistry within Mobile Bay, the fourth largest estuary in the United States, and Mississippi Sound took place between June 2020 and March 2023. Prior to this work, legacy investigations were limited in scope and outdated in methodology, sample density, and geospatial modeling. This investigation was a cooperative project between the Geological Survey of Alabama and the University of Alabama, Department of Geological Sciences. Alabama's estuaries are economically important for shipping and recreational and commercial fishing and contain vital biological diversity. Understanding the distribution and bioavailability of potentially toxic trace elements and organic compounds in this complex estuary system is therefore of critical importance when considering ecosystem functions and services and restoration planning. The distribution of trace elements in the estuarine environment is controlled by numerous physical, chemical, and biologic processes. Findings from this study improve our understanding of factors that control transportation and deposition of trace elements and organic compounds in estuarine sediments by determining (1) the grain size, mineralogy, and chemical composition of surface sediment samples and (2) the controlling factors through Principal Component Analysis and anthropogenically enhanced trace metal concentrations by implementing normalization of aluminum concentrations. Findings include a decrease over time in clay-sized fractions which deplete these estuaries of an important media for contaminant sequestration. Select trace metals strongly correlate to silt- and clay-sized fractions, iron, aluminum, organic matter content, and adsorption related to vermiculite. Principal Component Analysis statistically validates these findings as well as the value of oxidation reduction potential and conductivity. Phthalates and polycyclic aromatic hydrocarbons were verified as stressing compounds where aquatic thresholds were exceeded.

The most comprehensive sampling for the determination of sediment texture in Mobile Bay and Mississippi Sound took place between June 2020 and March 2024, during a cooperative project between the Geological Survey of Alabama and the University of Alabama, Department of Geological Sciences. Laser granulometry and geographic information system technology were used for sediment particle size classification, and distribution mapping. Prior to this work, legacy investigations were limited by methodology, sample density and the application of geospatial modeling. Alabama's estuaries are exposed to strong hydrodynamic influences. Tropical storms, freshwater inflow, circulation, particulate input, and grain-size all reflect estuarine sediment texture deposition status and trends and are vital to organic and inorganic constituent cycling and are reflected both in geospatial surficial sediment texture trends and in vertical loss. Significant increases in freshwater inflow into Alabama's estuaries also contribute to particulate erosion, transport, and deposition that are commonly associated with tropical storm events and inland precipitation events. Comparisons of sediment texture from this study were made to several legacy investigations that implemented the Shepard schema. Spatial distribution from legacy texture classifications included areas where sand and silt mixed with clay, where clay was dominant or supplemental. Clay content as determined by this study was low; therefore, only restricted areas were designated as clayey silt and sand-silt-clay surficial sediment. This study shows a general trend of texture redistribution and sediment coarsening from clay to silt dominance. Evaluation of skewness and kurtosis analysis results indicates that the Mobile Bay and Mississippi Sound sediment environments are slightly depositional with moderate to little reworking of sediments in this study. Clay composition is extremely important in regarding element and organic contamination cycling and thus should be a consideration regrading restoration planning within Alabama's estuaries.

The Mobile-Tensaw River Delta (MTRD) in Alabama, formed by the confluence of the Alabama and Tombigbee Rivers, is a crucial ecological zone encompassing 960 square miles of braided channels, bayous, lakes, and wetlands. The MTRD is a vital Alabama natural resource, serving as a vital interface between fresh and brackish waters, for fishery productivity, biodiversity, and water quality. The MTRD is Alabama's principal remaining relatively undeveloped region, and in this sense must be regarded as a state asset or trust. It is currently within the jurisdiction of Alabama's Coastal Zone Management program. A study conducted by the Geological Survey of Alabama, through funding from GOMESA, aimed to evaluate sediment quality in the MTRD. The focus of the study was to assess arsenic, cadmium, mercury, and nickel concentrations due to their potential toxic impacts and common occurrence. Sediment samples were collected from 168 sites across five geographic zones between 2019 and 2022. Analysis revealed that these metals frequently exceeded established toxicity thresholds, indicating significant contamination. Arsenic, cadmium, mercury, and nickel surpassed Threshold Effect Limits, Probable Effect Limits, Probable Effect Concentrations, and Severe Effect Levels at multiple sites, particularly in areas influenced by industry, agricultural runoff, and upstream river inputs. These findings underscore the necessity for enhanced monitoring and management strategies to address sediment contamination and protect aquatic ecosystems. Recommendations include implementing comprehensive monitoring programs, fostering multi-stakeholder collaboration, analyzing long-term trends, incorporating emerging contaminants for analysis, increasing public awareness, and analyzing short- and long-term water policy and management. Continued efforts are essential to mitigate risks and maintain the ecological health and sustainability of the MTRD.

Autonomous samplers are the way of the future; they provide scheduling flexibility, cost savings, and access to remote places. They can also be quite a handful.
In 2023, staff of the Mobile Bay National Estuary Program (MBNEP) built a portable autonomous water quality sampling system to augment restoration monitoring efforts. Nicknamed BoCEPhUS - Box of Cool Electronics Phor Understanding Sediments - the system collects in-stream turbidity data, which triggers autonomous collection of water samples at certain thresholds. Collected water samples are filtered, with resultant filters combusted and weighed to determine total suspended solids (TSS). Pairing turbidity readings and TSS allows a calibration curve to be generated, which can estimate how much sediment is transported by a specific waterway. To ensure comparability with existing monitoring protocols, the system methodology was co-opted from Alabama Department of Environmental Management (ADEM) procedures. BoCEPhUS was first deployed during April 2023 to collect post-construction data on a restoration site within the Fish River watershed (Baldwin County, AL). From there, the system was deployed at an additional site within the Magnolia River watershed (Baldwin County, AL) to collect pre-restoration sediment baselines. At the wrap up of the sampling period on July 2nd, 2024, BoCEPhUS had captured 24,335 turbidity readings, collected over 200 samples, and profiled 20 rain events - many of which occurred overnight when conditions were unsafe for a traditional field crew to sample.
Over the course of a year in the field, MBNEP staff adapted BoCePhUS to an array of obstacles and unforeseen circumstances. Despite the challenges, BoCEPhUS still presents significant cost savings over in-person water quality monitoring contractors and collects high-resolution baseline data for sensitive waterways before and after restoration activities occur. This presentation will cover details of the methodology, mechanics, and things to consider in planning for autonomous sampling systems.