Date of Award


Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Christopher S. Cronan

Second Committee Member

Kevin S. Simon

Third Committee Member

Stuart E.G. Findlay


The anthropocene has witnessed nearly a five-fold increase in human population with a disproportionate increase in urban lands housing that population. Much of this population relies on ecosystem services such as clean water provided by ecosystem structure and function. Dissolved organic matter (DOM) is a basal resource fueling the ecosystem function and shaping the ecosystem structure that provides these services. Urbanization, however, may cause a feedback altering the quality of DOM and subsequently degrading the quality of services provided. The objectives of this research were to: i) understand the impact of urbanization on dissolved organic matter composition and quality at regional and global scales; ii) understand how that range in quality may affect ecosystem functions; and iii) relate those measures of DOM composition to metrics of ecosystem health.

These effects were investigated across a gradient of urbanization in the postglacial landscape of southern and central Maine using measurements of DOM composition. As urbanization increased I saw a general decrease in DOM characteristic of wetland and forested land covers and an increase DOM characteristic of microbial sources. DOM from microbial sources was found to degrade faster. This decomposition was driven by increased abundance of lipids, proteins, and carbohydrates, which are common with recent biological production. A meta-analysis of DOM composition data showed that this pattern of increased bioavailable microbial carbon in urban streams also held true at a more global scale. Globally diverse ecoregions from subtropical China, to semi-arid Australia, and to temperate North America showed this increase in microbial DOM in streams affected by urbanization. I found that this change in DOM composition may be useful as an indicator of ecosystem integrity. In our study area increased abundance of microbial DOM corresponded to impaired macroinvertebrate communities. The measurements show that urbanization induces a feedback altering the energetic basis of stream ecosystem structure and function. These results can be understood with the simple message: As goes the composition of DOM from the watershed, so goes the aquatic ecosystem in the watershed.