By Mika Bishton

Faculty Mentor: Abbie Tomba

Abstract

Agricultural practices and suburban development can contribute to excess nutrients entering freshwater systems and negatively impact biodiversity. Tidal streams, due to high surface area to volume ratios, are more susceptible effects of excess nutrients, thus making them useful water quality indicators for larger watersheds. Macroinvertebrates are good bioindicators of stream health because they are accessible, sensitive to environmental changes, and taxa can be organized based on pollution tolerance. In this study, we compare macroinvertebrate assemblages in Accokeek (AC)and Potomac Creeks (PC) to better understand the relationship between land use , nutrient pollution and macroinvertebrate community structure. Both creeks border the forested Crow’s Nest Nature Preserve but the AC watershed is more suburban upstream whereas the PC watershed is primarily agricultural. Macroinvertebrates were collected at a total of 10 sites (6 AC and 4 PC) during July 2021. At each site, three core sediment samples were taken, sieved, and stored in 90% ethanol. Organisms were identified to the family level except for Oligochaeta. Water quality parameters including temperature, pH, electroconductivity, dissolved oxygen, nitrate and orthophosphate were measured at each site. We found no significant differences between AC and PC for the mean nitrate, orthophosphate, and pH. Potomac Creek had significantly higher dissolved oxygen than Accokeek Creek (p=0.037). There were no significant differences between macroinvertebrate diversity (tTest; p=0.15), richness (p=0.10), and abundance (p=0.51) between AC and PC. Oligochaeta is the dominant species in PC while Chironomidae was most abundant in AC. Overall, we found AC and PC to be healthy streams.