Description
Urban streams are perhaps the waterways most directly and immediately affected by anthropogenic influences. Concerns over declining water quality have led to increased interest in preserving urban waterways. Quality of dissolved organic matter (DOM) in urban waterways is of particular interest due to the influential role of DOM in the biological functioning of aquatic and terrestrial ecosystems. This thesis is concerned with characterizing changes in water quality in the urban stream Alvarado Creek. Absorbance and fluorescence methods in conjunction with parallel factor analysis (PARAFAC) modeling were used to characterize the quality of DOM in Alvarado Creek. Water quality changes in Alvarado Creek were studied pre and immediately post-restoration, under three regimes: 1) longitudinally, comparing a naturally-lined upstream reach to a concrete-lined downstream reach, 2) seasonally in February 2016, October 2016, and February 2017, and 3) during three storm events. Four unique PARAFAC components were identified, which include two terrestrial humic-like components, one microbial humic-like component (C3), and one tryptophan-like component (C4). Samples in the downstream concrete lined reach had notably higher bacterial numbers and lower nutrient concentrations. Seasonally, higher microbial concentrations occur (high bacterial numbers and tryptophan like fluorescence) during the dry season with lowest base flow. Storm runoff contributes large amounts of bacteria, organic matter, and inorganic matter to Alvarado Creek during the first flush. Optical properties indicate that the composition of DOM during storm events is primarily of terrestrial origin with a high molecular weight. Saturated soils during storm events may also be contributing DOM with high aromaticity. PARAFAC components during storm events were highly variable between storm events and sites in Alvarado Creek. Compared to streams with agricultural, forested, and mixed-use land use types, the urban stream studied here greater variability in DOC concentrations. DOM character of Alvarado Creek is representative of a microbial DOM source (high FI), were consistent with other studies of urban streams, which also found high FI and overall microbial DOM quality. Conclusions regarding water quality response to restoration will require more long-term studies. Additionally, the study of urban streams will provide insight on the composition, transformation, and transportation of organic matter to oceans.
