Water Quality Observations for Enhanced Understanding and Sustainable Management of Oyster Reefs in Mississippi Sound
The autonomous surface vessel and the multi-rotor unmanned aerial system
Oyster reefs provide substantial ecological value to coastal environments as biodiverse habitats as well as significant economic value to coastal communities as commercial fisheries. Unfortunately, oyster reef acreage as well as the volume and value of commercial oyster harvests in Mississippi waters have declined sharply in recent years, which has been attributed to a range of environmental stressors including impaired water quality. Therefore, we are using field sampling and remote sensing data collected from traditional platforms as well as novel autonomous aerial and surface vehicles to quantify the spatiotemporal variability of water quality at oyster reef sites in Mississippi Sound.
Water quality sampling, Autonomous Surface Vessel (ASV) surveys and Unmanned Aerial Systems (UAS) imaging was conducted from July 26 to 30, 2021 in the western Mississippi Sound proximal to oyster reefs. These data will not only inform the state of the water quality in the region, but also will provide input data for the calibration and validation of UAS and satellite algorithms. The water sampling included collection of water samples and profiles of in situ parameters (temperature, salinity, dissolved oxygen, pH-oxygen reduction potential, photosynthetically available radiation), and remote sensing reflectance measurements. The water samples were collected from 41 locations for suspended particulate matter (SPM), chlorophyll a, cyanobacteria-specific pigment phycocyanin (PC), colored dissolved organic matter (CDOM), absorption, algal toxins, coastal acidification, nutrients, microscopic, bacterial counts, and toxic metal analyses.
The ASV survey provided measurements of Conductivity/salinity, Temperature, pH, Chlorophyll a, Phycocyanin, Phycoerythrin, Colored dissolved organic matter (CDOM), Turbidity at 595 nm, Turbidity at 700 nm, Backscattering at 470 nm, 532 nm, and 650 nm, and Dissolved Oxygen (DO) concentrations collected every second during deployment. During field deployments, all data collected by the ASV are transmitted via cellular uplink to a server in the laboratory at MSU, and the plots and maps of the dataset collected by the ASV are displayed on a website in real time (https://water.geosci.msstate.edu/monitor/). This website is also used to query historical data, generate plots and maps, and/or download the data in multiple formats including Microsoft Excel files or shape files.
Multispectral imagery data were collected with a multi-rotor UAS with 8 cm resolution from a height of 122 m during water sample collection, and remote sensing algorithms will be calibrated and validated by developing quantitative relationships between water quality data and UAS imagery. The algorithms developed will be applied to this multispectral imagery, the imagery collected during the water sampling trips, and a timeseries of satellite data to obtain synoptic information on harmful algal blooms, SPM, CDOM, and other water quality indicators. Based on the in situ, ASV surveys, UAS-derived, and satellite-derived water quality data, the potential impacts of water quality on the oyster population will be determined in the western Mississippi Sound.