Resolving Spatial And Temperal Variability in Dissolved Organic Matter Characteristics Within Combined Agricultural and Stormwater Conveyances

Dissolved organic matter (DOM) in the aquatic environment originates from living and decaying organisms and anthropogenic sources. DOM plays a significant role in the availability of dissolved nutrients, sequestration of metals from the environment, and optical properties in aquatic ecosystems, all of which affect aquatic organisms. For example, DOM can change water clarity, introduce stresses from oxygen demand, and ultimately impair aquatic ecosystems. Within urban water systems, significant fluxes of anthropogenic DOM can be contributed to receiving waters with stormwater runoff; however, little is known about the amount, quality, and timing of these contributions. This research is aimed at testing new methods for quantifying the spatial and temporal patterns in the DOM pool within urban waters conveyances that receive stormwater runoff. Tested methods for detecting DOM within the urban water conveyance include in situ fluorescent DOM (fDOM) sensors, excitation-emission matrix (EEM) spectroscopy, and dissolved organic carbon (DOC) analysis. Preliminary results from a season of stromwater sampling efforts within the Northwest Field Canal in Logan City show temporal changes in DOM concentrations, with elevated concentrations from stormwater outfalls that elevate concentrations in the canal during stormwater runoff events. Results also indicate spatial variability of source characteristics within the DOM pool, with stormwater inflows elevating the fraction of allochthonous DOM within the canal. To further characterize spatial and temporal patterns, in situ fluorescence monitoring will be conducted this year at target excitation-emission pairs, paired with the use of a mobile water quality monitoring vessel. The use of targeted excitation-emission sensors will enable the collection high temporal resolution fluorescence data as a surrogate for DOM concentrations that will be used to further characterize the DOM pool. The mobile sensing vessel will provide high spatial resolution data along sections of the canal to capture behavior that would otherwise be unobserved at permanent in situ monitoring sites. This technique is especially advantageous since the DOM pool can change rapidly depending on the chemical composition. Data obtained through these methods will lead to an enhanced understanding of how DOM is processed within aquatic ecosystems. Furthermore, these efforts will assist in quantifying the degree to which spatial and temporal variability of DOM in the conveyance is driven by slow changes over the summer growing season versus sudden inputs from stormwater discharges. This research will contribute to the understanding and management of water resources as water flows through an urban environment. More precisely, quantifying the characteristics and spatial and temporal patterns of DOM will lead to greater understanding of the contributions from input sources and the effects DOM has on urban receiving waters