Stephen C. Peters

The source and transport of arsenic in a bedrock aquifer, New Hampshire, USA

The geographic distribution of elevated groundwater As concentrations in a fractured silicate bedrock aquifer in central New Hampshire correlates with the presence of pegmatites which border late Devonian granites and intrude metasedimentary rocks. As concentrations in the pegmatites averaged 9.6 mg/kg, which is much higher than the associated granites (0.24 mg/kg) and metasedimentary rocks (0.8 mg/kg). As was concentrated in these pegmatites by partial melting of calcareous metapelites and subsequent recrystallization as granites with low As concentrations and pegmatites with high As concentrations. Arsenic behaves similarly to B, which was also concentrated into these late stage fluids. Arsenopyrite (FeAsS) with an oxidation reaction rim of scorodite (FeAsO4·2H2O) was observed in aquifer materials. Elevated As concentrations have been observed to occur in other New England locations in pelitic metasediments intruded by anatectic plutons. It is proposed that pegmatite formation from partial melting of pelitic metasediments may be an important mechanism for concentrating As in crystalline aquifer materials, which can then cause local As enrichment of groundwaters. Groundwater As concentrations ranged from 26 nmol/l to 5300 nmol/l with a median value (210 nmol/l) that is more than 30 times higher than the median for groundwaters from all of New Hampshire (6.5 nmol/l). High chloride concentrations (>1 mmol/l), resulting from road salt contamination of recharge waters, suggest that groundwaters are most likely young ( 670 nmol/l or ∼50 μg/l) have very low Fe concentrations ( 7); samples with low As ( ∼7, Fe oxyhydroxides form rapidly and have a neutral or negative net surface charge that does not readily adsorb As. At pH <∼7, Fe oxyhydroxide formation is slow and depends on dissolved O2 availability, however the resultant Fe oxyhydroxides have a positive net surface charge, and appear to adsorb As readily.

Effects of urbanization on watershed hydrology: The scaling of discharge with drainage area

This study examines the effects of impervious surfaces within urbanized land on the scaling of river discharge with drainage area. Discharge in a river channel grows as drainage basin area increases following the general equation Q = kA c , where Q is river discharge, k is a measure of river base flow, A is upstream drainage area, and c is the scaling power dependency. Land use is a critical variable in the examination of river discharge; discharge has significant geologic and ecologic influences on fluvial systems. Discharge is assumed to scale linearly or nearly linearly with drainage area ( c ∼1), but in spite of its widespread application, the relationship has not been explicitly tested with respect to urbanization. Here we show that in small urban settings the scaling is nonlinear for peak flows. It is proposed that effective water loading occurs through a combination of increased runoff and an increase in the rate of transport to the rivers. These higher discharges in urban rivers have the potential to increase erosion, degrade aquatic habitats, and significantly alter channel forms.

Arsenic in groundwaters in the Northern Appalachian Mountain belt: A review of patterns and processes

Naturally occurring arsenic in the bedrock of the Northern Appalachian Mountain belt was first recognized in the late 19th century. The knowledge of the behavior of arsenic in groundwater in this region has lagged behind nearly a century, with the popular press reporting on local studies in the early 1980s, and most peer-reviewed research articles on regional patterns conducted and written in the late 1990s and early 2000s. Research reports have shown that within this high arsenic region, between 6% and 22% of households using private drinking water wells contain arsenic in excess of 10 microg/L, the United States Environmental Protection Agencys maximum contaminant level. In nearly all reports, arsenic in drinking water was derived from naturally occurring geologic sources, typically arsenopyrite, substituted sulfides such as arsenian pyrite, and nanoscale minerals such as westerveldite. In most studies, arsenic concentrations in groundwater were controlled by pH dependent adsorption to mineral surfaces, most commonly iron oxide minerals. In some cases, reductive dissolution of iron minerals has been shown to increase arsenic concentrations in groundwater, more commonly associated with anthropogenic activities such as landfills. Evidence of nitrate reduction promoting the presence of arsenic(V) and iron(III) minerals in anoxic environments has been shown to occur in surface waters, and in this manuscript we show this process perhaps applies to groundwater. The geologic explanation for the high arsenic region in the Northern Appalachian Mountain belt is most likely the crustal recycling of arsenic as an incompatible element during tectonic activity. Accretion of multiple terranes, in particular Avalonia and the Central Maine Terrane of New England appear to be connected to the presence of high concentrations of arsenic. Continued tectonic activity and recycling of these older terranes may also be responsible for the high arsenic observed in the Triassic rift basins, e.g. the Newark Basin. There are only two well-known cases of anthropogenic contamination of the environment in the northern Appalachian Mountain belt, both of which are industrial sites with surface contamination at that infiltrated the local groundwater.

Nanoscale mineralogy of arsenic in a region of New Hampshire with elevated As-concentrations in the groundwater

Abstract Bedrock samples were examined from a region in south-central New Hampshire in order to understand the factors responsible for elevated As-concentrations (up to 180 ppb) in the groundwater. Although the As is predominantly from natural sources, the precise mineralogy of the As-bearing phases was unknown. As-bearing samples were examined in detail using advanced electron microscopy techniques, including high-angle annular dark field scanning electron microscopy (HAADFSTEM), STEM elemental mapping, and high resolution TEM. Numerous As-bearing minerals were observed, predominantly arsenopyrite (FeAsS) with some westerveldite (FeAs). The arsenopyrite was partially altered to nanocrystalline (~20 nm) magnetite and westerveldite, most likely during hydrothermal circulation of fluids following the emplacement of a nearby granitoid pluton. A reaction rim surrounds the pristine cores of arsenopyrite, with compositionally variable amorphous zones (containing Fe, As, K, and O), a Cu-sulfide, and a uranium-bearing phase, suggesting at least three distinct fluid compositions during alteration. Because the K-Fe-As-oxide is amorphous and the nanocrystalline FeAs has a high surface area per unit mass, the dissolution rate of As-bearing phases during recent low-temperature weathering is increased. The rapid dissolution of the reduced As phase (FeAs), which is unstable under oxidizing conditions, may be an important factor in the elevated As-concentrations in the groundwaters of this region.

Mercury emission from a temperate lake during autumn turnover

Lakes in temperate regions stratify during summer and winter months, creating distinct layers of water differentiated by their physical and chemical characteristics. When lakes mix in autumn and spring, mercury cycling may be affected by the chemical changes that occur during mixing. Sampling was conducted in Lake Lacawac, Eastern Pennsylvania, USA, throughout the autumn of 2007 to characterize changes in emission of gaseous elemental mercury (Hg(0)) from the lake surface and dissolved mercury profiles in the water column during mixing. Water chemistry and weather parameters were also measured, including dissolved organic carbon (DOC), iron, and solar radiation which have been shown to interact with mercury species. Results indicate that emission of Hg(0) from the lake to the atmosphere during turnover was controlled both by solar radiation and by surface water mercury concentration. As autumn turnover progressed through the months of October and November, higher mercury concentration water from the hypolimnion mixed with epilimnetic water, increasing mercury concentration in epilimnetic waters. Dissolved absorbance was significantly correlated with mercury concentrations and with iron, but DOC concentrations were essentially constant throughout the study period and did not exhibit a relationship with either dissolved mercury concentrations or emission rates. Positive correlations between dissolved mercury and iron and manganese also suggest a role for these elements in mercury transport within the lake, but iron and manganese did not demonstrate a relationship with emission rates. This research indicates that consideration of seasonal processes in lakes is important when evaluating mercury cycling in aquatic systems.

The occurrence and dominant controls on arsenic in the Newark and Gettysburg Basins.

Elevated arsenic (As) concentrations in groundwater and rocks have been found in crystalline and sedimentary aquifers from New England to Pennsylvania, USA. The arsenic geochemistry and water-rock interactions of the Northern Appalachian Mountains and the Newark Basin have been researched at length, however, little is known about arsenic in the Gettysburg Basin. Both the Newark and Gettysburg Basins were formed during the breakup of Pangea, sediment deposition occurred during the Triassic and lithologies are of similar depositional environment. We compile and review the work done in the Newark Basin and collect new samples in the Gettysburg Basin for comparison. The Gettysburg Basin has 18%-39% of rock samples with arsenic concentrations greater than the crustal average of 2 mg/kg, while the Newark Basin has 73% to 95% of rock samples above the crustal average. The strongest controls on arsenic in rocks of the Gettysburg Basin are the relationship between arsenic and iron and silicon concentrations while the strongest controls in the Newark Basin are the relationship between arsenic and iron and organic carbon concentrations. The groundwater arsenic concentrations follow similarly with 8-39% of water samples from the Gettysburg Basin above 10 μg/L and 24-54% of water samples from the Newark Basin above 10 μg/L. The strongest controls on arsenic in water of the Gettysburg Basin are pH, alkalinity and silicon, while the strongest controls in the Newark Basin are pH and alkalinity.

Assessing changes in microbial respiration, bacterial growth efficiency, and bacterial production with nutrient addition to batch cultures

Dissolved organic carbon (DOC) provides an important source of energy in lotic systems that can regulate food chain dynamics. It is thought that inorganic nutrient addition to stream culture samples will increase microbial respiration and bacterial growth efficiency (BGE). Nutrient limitation may prevent microbial communities from reaching their full potential in terms of biomass and efficiency, which could limit organisms at higher trophic levels. This study utilized batch cultures to assess changes across a variety of water quality and nutrient parameters in an effort to assess the role of inorganic nutrient addition in regulating microbial activity in headwater streams. Treatments of phosphorus addition (+ P) and nitrogen plus phosphorus addition (+ N + P) were used to assess changes in microbial activity in samples collected from forested and agricultural headwater streams. Phosphorus limitation was observed only at a single site, suggesting that a secondary limiting nutrient (e.g. nitrogen) may affect microbial activity at the other sites. Combined phosphorous and nitrogen additions demonstrated that nitrogen did limit microbial respiration at many of the study sites. BGE was highly variable and did not seem to be controlled by inorganic nutrient concentration. We did observe increased carbon production with nutrient addition at some of the study sites. The results of this study indicate that small streams could export more carbon through respiration rather than by incorporating available DOC into biomass.

Lead zirconium titanate alternatives for nanoactuators

This paper describes the use of commercially available ceramic capacitors as an alternative for lead-containing and relatively expensive lead zirconate titanate (PZT)- based nanoactuators. A PZT actuator is compared with actuators made from both X5R- and Y5V-type ceramic dielectric capacitors using white light interferometry and a spectrometer. This work is useful because these capacitors can provide an economical nanomotion capability to research laboratories or industrial products. Measuring the displacement of the capacitors is also useful when designing electronic products to ensure undesired operation is not caused by the piezoelectric motion. Additionally, unlike the PZT material, the alternative ceramic materials do not contain lead, which is needed for full compliance with the Restriction on Hazardous Substances (RoHS) initiative.

Effects of urbanization on watershed hydrology: The scaling of discharge with drainage area: COMMENT AND REPLY REPLY

We thank Criss and Winston (2007) for their interest in and analysis of our manuscript on the interaction between discharge and drainage area. We feel that their points help strengthen the conclusions of our original article ([Galster et al., 2006][1]). ‘k’ Values : Criss and Winston begin by