Document Type

Thesis

Date of Award

5-3-2018

Keywords

Earth sciences, C/Q hysteresis, Chloride, INCA, Road salt, Sonde, Streams

Degree Name

Master of Science (MS)

Department

Geological Sciences and Environmental Studies

First Advisor

Dr. Joseph Graney

Subject Heading(s)

Earth sciences; C/Q hysteresis; Chloride; INCA; Road salt; Sonde; Streams; Geochemistry; Geology; Hydrology

Abstract

Chloride contamination of streams and groundwater has become a prevalent issue throughout urbanizing areas in the last half century, particularly in northern latitudes where deicing salts are applied to roadways. This study determined how deicer impacted runoff disperses through sub-urban and urban areas on seasonal and multi-year scales. Chloride concentration changes were then modelled under varying pollutant loading scenarios through an integrated catchment model (INCA-Cl).

Six in-stream conductivity/stage/temperature sondes, recording at 15-minute intervals, were installed within the small (~9.6 km2) Fuler Hollow Creek multi-landuse watershed in Broome County NY and monitored over a 1-year period. Weekly grab samples were taken at each sonde site and analyzed for dissolved cations and anions to help interpret the sensor results. Data from these sensors and local weather stations were used as inputs to the INCA-Cl model. Conductivity and Discharge measurements from stream sondes were used to construct a concentration/discharge hysteresis model of six storm events to determine seasonal variability in stream pollutant source. Results from weekly Fall and Spring stream and groundwater grab samples from 2006–2016 were used in conjunction with the model results to interpret long term trends.

Stream response to storm events was found to be dependent on season as well as amount of impervious surface. In contrast to the urban locations, sub-urban sites did not have an initial increase in total dissolved solids (TDS) before dilution during summer and fall runoff events and had overall smaller TDS increases from winter and spring de-icer flushing events, as well as slower discharge response times. TDS of stream water within the watershed showed increasing concentrations over the 10-year period that cannot be solely accounted for by an increase in impervious surface, thus suggesting an accumulation of deicers in groundwater as well. These observations are consistent with seasonal cation and anion data which suggests baseflow composition retains elevated de-icer levels year-round in parts of the watershed.

Concentration/Discharge (C/Q) hysteresis models indicate groundwater is the dominant pollutant source in non-salting seasons compared to surface water being the dominant source in salting seasons. Response to storm events was also influenced by land use in addition to season. INCA-Cl was able to model seasonal discharge and chloride trends within Fuller Hollow Creek under variable loading conditions throughout the study period. However, chloride increases from individual deicer flushing events could not be accurately replicated with the model. By quantifying and understanding the effects of road salting practices on variable land use areas, better estimates of chloride export and retention can be developed in order to protect salt sensitive freshwater ecosystems.

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