Date of Award
5-11-2025
Date Published
June 2025
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Civil and Environmental Engineering
Advisor(s)
Charles Driscoll
Keywords
Adirondack Lakes;Dissolved Organic Carbon (DOC);Dissolved Organic Matter;Recovery from acid deposition;Wetlands
Subject Categories
Civil and Environmental Engineering | Engineering | Environmental Engineering
Abstract
Lakes in Europe and North America have experienced increases in dissolved organic carbon (DOC) concentrations over the past few decades, a phenomenon called “browning”. Dissolved organic matter is a mixture of reduced organic compounds, such as humic and fulvic acids, derived from allochthonous organic matter from the watershed and autochthonous organic matter sources produced within surface waters. The long-term browning of lakes has far-reaching ecological consequences. First, changes in the attenuation of light and heat penetration affect thermal stratification, oxygen concentration gradient, biogeochemical cycling, and primary production in lake systems. Increases in colored dissolved organic matter (CDOM) can shift the absorption of light higher in the water column, enhancing thermal stratification in lakes, while the reduction in light penetration to deeper layers alters the redox status and food web functioning. Research has attributed the increase in dissolved organic carbon concentrations and the browning phenomenon to many factors, including recovery from acid deposition, climatic factors such as increased precipitation and warmer temperatures, and changes in land management practices within lake-watersheds. Due to the spatial and temporal heterogeneity in the key drivers of browning, there is no universally accepted hypothesis. To address this gap, I leveraged a conceptual source-sink model, which outlines the sources of DOC to lake ecosystems and the sinks associated with DOC loss. I analyzed long-term data from 48 Adirondack lakes from the Adirondack Long-term Monitoring (ALTM) program using a combination of trend analysis, Principal Component Analysis (PCA), and stepwise regression analysis to answer two key research questions: What are the drivers of spatial patterns of DOC concentration? What are the temporal patterns, long-term trends, and drivers of DOC change over the study period, and the seasonal patterns of DOC concentration and its change? My results show that spatial patterns in mean dissolved organic carbon (DOC) concentrations across Adirondack lakes can be explained by the source-sink model, with wetlands being the primary source of spatial variability in the supply of dissolved organic matter, while photodegradation through solar radiation is the main sink. Wetlands contribute to DOC through DOC export to lakes, with factors such as precipitation and recovery from acid deposition acting as modulators. On the other hand, the photodegradation process is mainly modulated by retention time, which gives time for DOC processing. Long-term temporal changes in DOC are best explained by variables associated with recovery from acid deposition, such as pH and changes in aluminum speciation. Seasonal analyses further revealed distinct patterns in DOC dynamics, with summer, fall, and winter exhibiting the most consistently increasing trends in DOC. Climatic analyses showed that both mean DOC and its changes were significantly influenced by climate variables, particularly shortwave radiation and precipitation. Correlation analyses confirmed that increasing shortwave radiation supports DOC photodegradation, reducing DOC concentration, while increasing precipitation is positively associated with DOC concentrations. Overall, this work provided new insights into the spatiotemporal patterns of DOC in Adirondack lakes and the drivers of these patterns, consistent with a source-sink model. This work also provides new insights into the seasonality of DOC and its relationship with DOC patterns.
Access
Open Access
Recommended Citation
Bungei, Amos Kiplimo, "Factors Affecting Dissolved Organic Matter Concentrations and its Long-Term Change in Adirondack, NY, Lakes." (2025). Theses - ALL. 940.
https://surface.syr.edu/thesis/940
