Theses and Dissertations

ORCID

0009-0004-0028-2711

Advisor

Sandel, Michael

Committee Member

Baker, Beth

Committee Member

Dyer, Jamie

Date of Degree

8-12-2026

Original embargo terms

Immediate Worldwide Access

Document Type

Graduate Thesis - Open Access

Major

Wildlife, Fisheries & Aquaculture

Degree Name

Master of Science (M.S.)

College

College of Forest Resources

Department

Department of Wildlife, Fisheries and Aquaculture

Abstract

River networks organize ecological communities across spatial scales, but whether bacterial communities follow these patterns remains poorly understood. This thesis examined microbial community assembly across three nested spatial scales in a dendritic watershed in east-central Mississippi (USA), asking whether dispersal or environmental selection governs community composition at each scale. At the watershed scale, bacterial diversity increased from headwaters to the river mainstem, consistent with longitudinal diversity accumulation predicted by the River Continuum Concept. At the confluence scale, the composition of post-confluence communities can be predicted as simple mixtures of their tributary inputs, supporting that conservative mixing dominates when unique communities merge. At the reach scale, headwater taxa and wastewater-associated bacteria declined predictably downstream through selective mortality despite continued dispersal. These three scales describe a consistent pattern: microbes readily disperse through the network, but local conditions determine which organisms persist, thereby unifying classical river ecology theories within a single framework.

Sponsorship (Optional)

USDA

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