Date of Award
Doctor of Philosophy (PhD)
Forestry and Environmental Studies
In this research, two studies were conducted to investigate the spatial distribution and seasonal variation of trace metal concentrations and speciation in Connecticut surface waters. In the first part, along with the monthly vertical profile of background biogeochemistry parameters (pH, Temperature, Dissolved oxygen, Major ions, Total dissolved solids, Nutrients, Acid neutralizing capacity, dissolved organic carbon), competitive ligand exchange – adsorptive cathodic stripping voltammetry was used to determine cobalt speciation in Linsley Pond, North Branford. Vitamin B12 (VB12) via enzyme-linked immunosorbent assay (ELISA) was measured in an American stratified lake for the very first time. During summer stratification, the patterns of Co and Mn are similar, very low in surface water, and reach the highest concentration across the redoxcline caused by the bacterial activity of PSB. The different patterns of Co in the hypolimnion between 2017 and 2018 are caused by the formation of CoS. Higher epilimnetic particulate Co is observed in July and August, corresponding to the highest DO and DOC, respectively, indicating that cobalt is closely related to the photosynthesis of phytoplankton, the metabolism of organisms. Total dissolved Co was dominated by its natural organic ligand complex. The measured VB12 ranged from 0.033 – 0.048 nM, comparable to [Co2+] detected in freshwater systems. In the second part, an estuary with self-regulating tide gates (SRTGs) installed was studied about the combination of watershed flood flow and tidal flushing impact at both short and long time scales. The cycling of particle-reactive contaminants represented by the metals was studied over the course of several tidal cycles during both baseflow and storm event conditions. TSS and turbidity were highly correlated at the inlet but not consistently at the tide gates. In contrast, at the tide gates, TSS was dominantly affected by tides unless extreme storms. Cobalt and 7Be budgets over one tidal cycle were determined. Cobalt was mostly in the dissolved form at the tide gates and the inlet, under baseflow conditions. However, particulate Co became the dominant component of total Co at the inlet during storm events, contributed by sediments delivered from the watershed. According to the 7Be mass balance over a tidal cycle, perhaps owing to the large ratio of its watershed to estuary, most of the 7Be (86%) enters the West River estuary from its watershed. Direct atmospheric deposition is a significant but lesser source. In addition to 3% decay in the water column, only 1.5% of 7Be is gained from Long Island Sound via tidal flushing. More than 40% of added 7Be is deposited in sediments within the estuary during a single tidal cycle, meanwhile, Co received from the watershed (ca. 60 g) is approximately equal to the net loss of Co by the tidal exchange. The West River estuary is a tight trap for contaminants that behave like Be, but not for Co or probably other substances that are not strongly particle reactive as well.
Xuan, Zhemin, "Spatial and temporal variability of trace metal concentrations and speciation in Connecticut surface waters" (2021). Yale Graduate School of Arts and Sciences Dissertations. 136.