Quantifying How Coastal Flooding and Stormwater Runoff Drive Spatiotemporal Variability in Carbon and Nutrient Processing in Urban Aquatic Ecosystems

Authors

Matthew A. SmithFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Biology

First Advisor's Name

John Kominoski

First Advisor's Committee Title

committee chair

Second Advisor's Name

Omar Abdul-Aziz

Second Advisor's Committee Title

committee chair

Third Advisor's Name

Evelyn Gaiser

Third Advisor's Committee Title

committee chair

Fourth Advisor's Name

Renè Price

Fourth Advisor's Committee Title

committee chair

Fifth Advisor's Name

Tiffany Troxler

Fifth Advisor's Committee Title

committee chair

Keywords

urban, biogeochemistry, coastal, flooding, carbon, organic matter

Date of Defense

10-21-2021

Abstract

Coastal river networks alter the transport and transformation of dissolved organic carbon (DOC) and dissolved organic matter (DOM), which can vary in concentration and composition across spatiotemporal scales. Given climate-induced shifts in rainfall and tidal variation in low-lying coastal regions, there is an increasing need to quantify effects of flooding on biogeochemical cycling. Specifically, urban flooding is becoming increasingly common due to biophysical alterations to hydrology from urbanization and climate change. Urban ecosystems have been characterized as having a distinct biogeochemistry compared to other systems, largely due to increased frequency and magnitude of riverine and coastal flooding. Consequently, the role of stormwater runoff and tides on DOC, DOM, and nutrient concentration, composition, and biological processing are highly variable. In order to better understand the biogeochemical consequences of urban flooding, it is important to consider the interactions between surface and subsurface environments to hydroclimatic drivers of flood frequency and magnitude. The process of urbanization can significantly alter DOC and DOM regimes by influencing the timing and delivery of fresh versus saltwater to coastal waterways. DOM composition can be quantified using fluorescent DOM (fDOM) properties that indicate relative source in mixed waterways. However, the quantity and composition of DOM varies widely across spatiotemporal scales, particularly in coastal drainages. Further, most research on DOC and DOM in urban aquatic systems to-date has not been done in low-lying coastal areas, despite the majority of the world's cities residing in coastal regions. Thus, quantifying changes in the hydrologic and land use drivers of DOM source and composition change is needed to understand its role in metabolic processing and export to downstream water bodies. This dissertation research examines various biophysical and climatic drivers of runoff and coastal flooding and their relative influences on carbon and nutrient biogeochemical cycling in multiple urban aquatic ecosystems across multiple cities. In Chapter 2, I evaluated how time-variable interactions among water source contributions from freshwater and saltwater influence DOC and nutrient concentrations and DOM composition in urban canals connected to the ocean. Using a combined isotopic-fluorescent DOM (fDOM) tracer approach, we created a Bayesian Monte-Carlo (BMC) mixing model to estimate fractional contributions of marine water, rainwater, stormwater, and groundwater to three coastal canals of Miami, FL. We found that loading of terrestrially sourced DOC and DOM is pulsed to urban canals and shunted downstream and supplemented by microbially sourced DOM during the wet season at high tide. These results provide an important addition of pulsed groundwater contributions to the Pulse-Shunt concept to explain DOM transport versus processing in coastal urban ecosystems. In Chapter 3 of my dissertation, I compared the bioavailability of DOM contributions across urban canals, we found that interactions between stormwater runoff and tidal amplitude increased the bioavailability of DOM and were positively correlated with predominantly humic-like components in the wet season and protein-like components in the dry season. Additionally, increases in recently produced DOM, indicated by tryptophan-like fluorescence, corresponded with elevated concentrations of indicators of human waste (i.e., E. coli, enterococci) from groundwater inputs. These results suggest evidence of an urban priming effect in which labile autochthonous DOM from urban sources can drive microbial processing of DOM in coastal waterways. In Chapter 4, I examined the role of hydrologic and landscape variables on the water column versus whole system nutrient uptake capacity of urban wetlands. Compared to non-urban wetlands, nutrient uptake in the water column represents a significant portion of total uptake, particularly in small urbanized wetlands of short water residence time and supplemented with labile, proteinaceous DOM. Our results suggest that increases in the stoichiometric availability of labile organic carbon can stimulate sequestration of NO3- and SRP in nutrient polluted or nutrient limited urban wetlands. Finally, in Chapter 5 I investigated how urbanization has impacted the spatiotemporal variability of high discharge events in urban and non-urban watersheds across regional climates. In light of the original Pulse-Shunt Concept, I introduce the urban flow-shunt flood-pulse concept to better explain how spatiotemporal synchrony of urban stream discharge occurs following extreme precipitation events across regional climates. Together, this research shows that significant transformation of DOC, DOM, and nutrients occur within urban aquatic systems and such processes are influenced by the source, magnitude, and timing of water contributions to coastal environments.

Identifier

FIDC010467

ORCID

https://orcid.org/0000-0001-8173-3115

Previously Published In

Smith, M. A., Kominoski, J. S., Gaiser, E. E., Price, R. M., & Troxler, T. G. (2021). Stormwater runoff and tidal flooding transform dissolved organic matter composition and increase bioavailability in urban coastal ecosystems. Journal of Geophysical Research: Biogeosciences, 126(7), e2020JG006146.

Recommended Citation

Smith, Matthew A., "Quantifying How Coastal Flooding and Stormwater Runoff Drive Spatiotemporal Variability in Carbon and Nutrient Processing in Urban Aquatic Ecosystems" (2021). FIU Electronic Theses and Dissertations. 4899.
https://digitalcommons.fiu.edu/etd/4899