Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)




James Skelton

Committee Member

James Skelton

Committee Member

Harmony Dalgeish

Committee Member

John Swaddle


Anthropogenic activities are the leading cause to biodiversity decline worldwide. It has been well documented that large dams disrupt dispersal and alter local habitat often leading to less diverse aquatic systems. Yet, it is not well known how much more numerous smaller dams impact fish communities in estuary systems where dispersal is a critical part of the ecosystem, or how dams affect variation in species composition across sites (beta diversity). Coastal waterways of Virginia are impounded by hundreds of small dams. Here we used eDNA (environmental DNA) to assess the alpha, beta, and gamma diversity of fish species within the Virginia Peninsula in the lower Chesapeake Bay to compare patterns of diversity between sites with an undammed connection to the estuary to diversity within dammed sites. More than 500 2-Liter samples of water were collected from 35 total sites, 16 undammed creeks and 19 dams. We documented 61 species of fish. We hypothesized that dams cause a local decrease in fish species richness by degrading local habitat and reduce dispersal by creating barriers. Undammed sites had significantly higher alpha diversity by about 10 species per site compared to dammed sites, meaning more species were found in undammed sites. Multivariate analysis showed that dams altered the species composition of fish communities. Furthermore, beta dispersion testing showed that undammed sites had higher beta diversity, meaning undammed sites have higher variability in species from site to site. Dammed sites showed similar species composition when compared to one another. Gamma diversity of these sites across the landscape showed that overall diversity was highest among undammed areas across the peninsula, average of 41 species in dammed sites compared to an average of 58 species in undammed sites. These results suggest that even small dams can disrupt dispersal in estuary networks leading to a loss of biodiversity across the landscape.



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