Date of Award

May 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor(s)

Zunli Lu

Keywords

chloride, climate change, halogens, iodine, road salt, tracers

Subject Categories

Physical Sciences and Mathematics

Abstract

The transport of solutes from their source to natural water systems is a critical control on the chemistry and potability of drinking water supplies. Therefore, developing a thorough understanding not only of contaminant sources, but also of the controls on the movement of solutes through catchments, is essential to providing accurate assessments of how future environmental stressors (e.g. land cover, population growth, and climate change) may affect water resources.

Halogens (specifically, chloride (Cl), bromide (Br), and iodine (I)) occur naturally at low levels in terrestrial aquatic ecosystems, and may also originate from a suite of anthropogenic sources. Due to their largely conservative behavior, and preferential incorporation into mineral crystal lattices during evaporation processes resulting from differences in ionic radii, ratios of Cl/Br are used to identify sources of salinity to freshwater systems. This approach can broadly distinguish endmember sources of salinity (e.g. road salts from basin brines) from one another, although has proven ineffective in distinguishing saline endmembers originating from the same processes (e.g. formation waters of different ages), thus warranting development of alternate approaches.

Elevated levels of Cl are harmful to sensitive biota, threaten riparian ecosystems, and may increase the corrosivity of affected waters. Anthropogenic practices may introduce Cl to drinking water supplies. Present-day controls on the salinization of freshwater systems have been rigorously evaluated. Although, prior to this dissertation, no future predictions of the impacts of continued deicing practices on freshwater salinization had incorporated changes in climate coupled with dynamic population and land use.

Iodinated disinfection by-products (I-DBPs) form when source waters containing halogens and organic matter are disinfected via chloramination during wastewater treatment processes. Despite the emergence of I-DBPs as highly toxic, teratogenic, and potentially carcinogenic agents, controls on the transport of iodine in terrestrial aquatic environments have yet to be fully constrained. As source water iodine is a major source of iodine in the formation of I-DBPs, developing a thorough understanding of the controls on the natural cycling of iodine in paired surface water-groundwater systems is essential to providing accurate assessments for the potential of adverse environmental and health effects following modern wastewater treatment practices. Individual components of the terrestrial aquatic iodine cycle have been studied extensively, although a single study has yet to evaluate variation of total dissolved iodine concentrations at the catchment scale across both time and space.

The purpose of this dissertation research was to evaluate the effects of anthropogenic and hydrogeologic processes on the fate of salinity and halogens at the catchment scale. We focus our efforts in the East and West Branches of the Tioughnioga River Watershed in Upstate New York State (NYS), USA. Spatially and temporally resolved series of major and trace halogens (Cl, Br, and I) were used in combination with graphical, statistical, and numerical approaches to elucidate controls on halogen sources and solute flow paths in headwater catchments with mixed land cover in temperate climates.

Salinity in the Tioughnioga River watershed has been increasing since the late 1930’s. This trend increased precipitously after the completion of a major interstate highway (Interstate-81) in the West Branch catchment area during the 1950’s. We used two independent approaches to characterized sources of Cl to both East and West Branches of the Tioughnioga River over a two-year interval: (1) Cl/Br ratios to graphically separate waters impacted by road salts from other sources of contamination and (2) linear discriminant analysis (LDA) to quantitatively determine the most likely source of contamination to individual water samples. Ratios of Cl/Br suggested that road salt affected waters are present in both branches, but are more prominent in the West Branch, which has a greater percentage of urban land cover. LDA supports the results of Cl/Br in the West Branch and further reveals volumetrically minor contributions of Appalachian Basin Brines to surface waters in the East Branch. Downstream profiles of Cl concentrations in surface waters indicate that sources of pollution are concentrated around urban areas and may impact surface water chemistry year-round. We used a simple mixing model to estimate a residence time of Cl in the watershed of approximately 20 to 30 years, suggesting that stream Cl concentrations may continue to rise for several decades given no change in conditions.

Assessment of the potential future impacts of continued de-icing practices is regularly evaluated using numerical and statistical models. These methods have undoubtedly advanced our understanding of the prolonged effects of de-icing practices on aquatic environments and drinking water quality. Although, these approaches have not incorporated future changes in climate that are projected to impact hydrogeology. To address this deficit, we use an INtegrated CAtchment (INCA) model to simulate Cl concentrations in the Tioughnioga River watershed. We ran the model over a baseline period (1961-1990) and over three future intervals (2010-2039; 2040-2069; 2070-2099) for future climate scenarios from a range of global climate models (GCMs). Model projections suggest that Cl concentrations in the catchment will continue to rise for several decades, before beginning to decline roughly mid-century, with all scenarios resulting in reduced winter snowfall totals and associated salt applications over the course of the 21st century. We attributed the delay in stream response to climate change and continued contribution of Cl from aquifers. By 2100, surface water Cl concentrations will decrease to below 1960’s values. Decreasing trends in average surface water Cl are moderate in catchments dominated by urban lands compared to those in forested catchments.

We evaluate the controls on contributions of iodine to surface water from different sources under variable hydrologic conditions across spatial and temporal scales in the Tioughnioga River watershed. Our findings reveal that iodine varies seasonally with temperature, suggesting a linkage to export of dissolved organic carbon. Iodine may be elevated temporarily during high flow events, resulting from near-stream subsurface storage during dry periods. Based on major ion analysis, LDA, and endmember mixing analysis, under low flow conditions, iodine in surface water likely originates from groundwater. Additionally, our findings illustrate that iodine varies significantly across a catchment, suggesting influence from local hydrologic controls. In addition to atmospheric deposition of iodine in rainwater, additional controls on transport may be linked to weathering of exposed rocks. Thus, we propose that terrestrial iodine fluxes in temperate forested catchments are closely tied to both surface sources and local hydrogeology and thus, suggest that waste water treatment facilities closely monitor source water iodine concentrations and adjust treatment practices accordingly.

This dissertation ultimately contributes to the growing and collective body of knowledge regarding halogen transport and sources in freshwater systems and provides valuable insights to future water resources security.

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