Beneath the surface: Spatial and temporal trends in water quality and its impacts on algal community composition in the Albemarle Sound, North Carolina
Description
These files contain data from our research on the interaction between land use, water quality, and algal community composition in the Albemarle Sound, NC. Datasets include data on average water quality across all study sites, water quality data collected over two months for a subset of sites, precipitation in one of the study counties, total algal cell counts, standardized cell counts, standardized algal cell biovolume, and relative biovolume. The two R files contain the code used to analyze these data.
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Field sampling took place in eight NC counties. Six sites in Chowan County were monitored every two weeks, while all other sites were monitored once a month. Water quality data was collected using a Hanna Instruments Combo. Additional water and algal samples were collected and preserved with Lugol’s solution. Weather data was collected from the North Carolina Climate Retrieval and Observations Network of the Southeast Database. Filtered water samples were colorimetrically analyzed for nitrate, phosphate, and ammonia, while unfiltered samples were tested for total phosphorus using a LaMotte Smart 3 colorimeter. Bicarbonate concentration was measured using a LaMotte titration kit. Algal samples from the Chowan sites were enumerated using a microscope. One mL was drawn from each sample, spun down in a centrifuge, and resuspended in distilled water. One tenth mL of sample was analyzed on a Palmer cell. Groups whose genera remained unidentified were included in genus richness and biovolume as a proxy for biomass. All cell counts were standardized to 100 fields of view and 1 mL of original sample. Genus richness was calculated as the total number of genera identified in each sample. Biomass was determined using data from the Nordic Microalgae and Aquatic Protozoa database, phycology data from the Academy of Natural Sciences at Drexel University (included with these data), a diatom biovolume dataset compiled by Leblanc et al. (2012), and other resources. Biomass of unknown groups were calculated based on Hillebrand et al. (1999). Watersheds were delineated using StreamStats. The National Land Cover Database 2016 land cover layer was clipped to each watershed in ArcGIS Pro 2.5.0 to calculate the proportions of land use. Linear modeling was used to assess how nutrient concentrations in the Chowan sites varied over the course of the summer. The models that best fit the data were determined using stepwise AIC model selection. Proportion developed, agricultural, forested, and wetland area in the watershed, antecedent precipitation, date, distance to river mouth (km), and site were included in the modeling for water quality. Antecedent precipitation was determined by averaging the daily precipitation (mm) from the week prior to when the sample was collected. Models selection to assess relationships of land use to nutrient concentration among all sites included proportion developed, agricultural, forested, and wetland area, and distance to river mouth (km). Model selection for genus richness and biomass included nutrient concentrations, precipitation, site name, date, proportion forest, agriculture, wetland, and developed land, distance from river mouth, water temperature, Secchi depth, pH, conductivity, and TDS. Model selection for the percent biomass of cyanobacteria, diatoms, and dinoflagellates included nutrient concentrations, water temperature, site, and conductivity. Statistical analyses were conducted in RStudio version 3.6.2.