Dissertations and Theses

Date of Award

2020

Document Type

Thesis

Department

Earth and Atmospheric Sciences

First Advisor

Maria Tzortziou

Keywords

bioavailability, microbial, wetlands, CDOM, DOC, carbon

Abstract

The Long Island Sound is one of the world's most urbanized estuaries, polluted from excess nutrients which impact the quality of water through increased biological productivity. Dissolved organic matter (DOM) is a sensitive indicator of anthropogenic pollution and nutrient enrichment in coastal waters as well as an important part of the carbon cycle and serves as a primary food source for aquatic food webs. Additionally, the colored portion of DOM (CDOM) impacts coastal optical properties, ocean color, and light attenuation. High levels of CDOM have been shown to inhibit the growth of phytoplankton and limit photosynthesis, damaging the food chain and limiting the production of oxygen in aquatic ecosystems. Bacteria produce and consume DOM, however spatial and temporal dynamics in the microbial availability of DOM derived from different sources in estuarine systems are not well characterized. Because of this, understanding the sources and properties of dissolved organic materials coming into Long Island Sound, and their degradation through microbial processing, is imperative to understanding biogeochemical and ecological processes in coastal urban environments.

We completed 25-day dark incubations of water collected from upriver, marsh, and estuarine sites in different seasons to assess variability in DOM bioavailability across Long Island Sound. Measurements were taken at Days 0 (initial), 2, 5, 9, and 25. DOM optical properties were measured using spectrophotometry (CDOM absorption coefficients and spectral slopes) and spectrofluorometry (FDOM excitation-emission matrices). Dissolved organic carbon (DOC), mass spectrometry (FT-ICR-MS), and microbial count samples were also taken at each measurement point.

Our results emphasize the impact of terrigenous and anthropogenic DOM on estuarine organic matter cycling. Long Island Sound water quality improved with distance from anthropogenic pollution and with ocean mixing, closer to the Atlantic Ocean. The marshes sampled are important carbon sources to the estuary, and DOC was especially bioavailable when exported from terrigenous sources. Microbial degradation decreased CDOM absorption overall. Microbial degradation produced and consumed labile DOM in the first few days of incubations but produced humic-like FDOM afterward. DOC exported from the heavily urbanized Alley Creek system had among the highest rates of microbial degradation, particularly for the visible humic-like CDOM component, suggesting that urbanization may produce more labile DOM, leading to net increases in DOM degradation rates.

Available for download on Wednesday, February 16, 2022

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