Parts-per-billion levels of cadmium and lead were detected using square-wave anodic stripping voltammetry with a boron-doped diamond electrode. Calibration plots (10-minute deposition time) in KCl and KNO 3 were non-linear at low concentrations (1 ± 5 ppb) due to the deposition mechanism of these metals. The preferred electrolyte for cadmium was KCl, while lead could be measured in either electrolyte. The lowest concentrations included in the linear portion of the calibration plot (5 minute deposition time) for cadmium were 10 ppb and 50 ppb in KCl and KNO 3 , respectively, and 10 ppb for lead in KNO 3 . The presence of either lead or copper suppressed the cadmium stripping peak, but the lead stripping peak was unaffected by cadmium, and enhanced by the addition of copper. A river water sample was analyzed for cadmium and lead, and the cadmium results were confirmed using ICP-AES spectrometry. It was determined electrochemically that a fraction of lead in the river sample was bound by complexing material in the sample.

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Changes in stream temperatures in response to restoration of groundwater discharge and solar heating in a culverted, urban stream A B S T R A C TBoone Creek is a mountainous headwater stream that lies within an urbanized environment in north-western North Carolina. The primary source of thermal pollution in Boone Creek is the urban infrastruc-ture, which affects stream temperatures through (1) heated runoff, which creates temperature surges and (2) the elimination of groundwater-surface water interactions. In this study, we use a Monte Carlo ther-mal mixing model to predict the thermal impact of removing a 700-m-long culvert. Our thermal mixing model balances stream discharge and temperatures with surface-heat exchange parameters and restored baseflow. We calculate the daily-average groundwater discharge velocity at 15 locations in the stream using signal decay in streambed temperatures, and utilize a Monte Carlo implementation of the hetero-geneous baseflow field in the thermal mixing model. We also calculate surface-heat exchange per unit area for conditions upstream and downstream of the existing culvert and utilize those values in the ther-mal mixing model. Our modeled temperatures suggest a decrease in summer stream temperatures down-stream of the culvert that average 1.35 ° C and 1.17 ° C for upstream and downstream surface-heat exchange conditions, respectively. The results of our study have implications for the balance between baseflow and the urban infrastructure in any high-gradient urban stream that experiences similar ther-mal effects.

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The weathering of coal combustion products (CCPs) in a lotic environment was assessed following the Tennessee Valley Authority (Kingston, TN) fly ash release of 2008 into surrounding rivers. Sampled materials included stockpiled ash and sediment collected from 180 to 880 days following the release. Total recoverable concentrations of heavy metals and metalloids in sediment were measured, and percent ash was estimated visually or quantified by particle counts. Arsenic and selenium in sediment were positively correlated with percent ash. For samples collected 180 days after the release, total concentrations of trace elements downstream of the release were greater than reference levels but less than concentrations measured in stockpiled ash. Total concentrations of trace elements remained elevated in ash-laden sediment after almost 2.5 years. A sequential extraction procedure (SEP) was used to speciate selected fractions of arsenic, copper, lead, nickel, and selenium in decreasing order of bioavailability. Concentrations of trace elements in sequentially extracted fractions were one to two orders of magnitude lower than total recoverable trace elements. The bulk of sequentially extractable trace elements was associated with iron-manganese oxides, the least bioavailable fraction of those measured. By 780 days, trace element concentrations in the SEP fractions approached reference concentrations in the more bioavailable water soluble, ion exchangeable, and carbonate-bound fractions. For each trace element, the percentage composition of the bioavailable fractions relative to the total concentration was calculated. These SEP indices were summed and shown to significantly decrease over time. These results document the natural attenuation of leachable trace elements in CCPs in river sediment as a result of the loss of bioavailable trace elements over time.