Date of Award

Spring 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forestry and Environmental Studies

First Advisor

Raymond, Peter

Abstract

Dissolved organic matter (DOM) affects the structure and function of aquatic ecosystems. DOM determines system net heterotrophy or autotrophy, affects light availability and water color, controls the speciation of metals such as iron, and is one of the most reactive carbon pools. DOM quality and source, whether from terrestrial plants and soils or primary production in inland waters, modulates its impact. Here, I characterize DOM cycling in the predominantly forested, temperate Connecticut River watershed. In Chapter 1, I evaluate how commonly used optical indices for DOM source and quality are complicated by the presence of filterable ferric iron in streams and rivers. I test the effectiveness of existing ferric iron correction factors for these indices using size fractionation and demonstrate systematic biases in proxies of DOM quality due to the divergent controls on ferric iron versus DOM. In Chapter 2, I characterize the cycling of two size fractions of dissolved iron in the Connecticut River mainstem. I show that while iron reduction or iron-leaching from plant material drive colloidal iron, DOM quality and amount control soluble iron, likely through complexation. In Chapter 3, I compare dissolved organic carbon (DOC) radiocarbon in the Connecticut River mainstem to atmospheric radiocarbon records to demonstrate how the atmospheric bomb-pulse can be used to estimate the sources of riverine DOC in steady-state river. DOC age in the Connecticut River was driven by flow path depth, ancient carbonate weathering products incorporated into DOC, and the leaching of recently-fixed DOC.

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