Hydrologic Control on Arsenic Cycling at the Groundwater-Surface Water Interface of a Tidal Channel.

Historical industrial activities have resulted in soil contamination at sites globally. Many of these sites are located along coastlines, making them vulnerable to hydrologic and biogeochemical alterations due to climate change and sea-level rise. However, the impact of hydrologic dynamics on contaminant mobility in tidal environments has not been well studied. Here, we collected data from pressure transducers in wells, multi-level redox sensors, and porewater samplers at an As-contaminated site adjacent to a freshwater tidal channel. Results indicate that sharp redox gradients exist and that redox conditions vary on tidal to seasonal timescales due to sub-daily water level fluctuations in the channel and seasonal groundwater-surface water interactions. The As and Fe2+ concentrations decreased during seasonal periods of net discharge to the channel. The seasonal changes were greater than tidal variations in both Eh and As concentrations, indicating that impacts of the seasonal mechanism are stronger than those of sub-daily water table fluctuations. A conceptual model describing tidal and seasonal hydro-biogeochemical coupling is presented. These findings have broad implications for understanding the impacts of sea-level rise on the mobility of natural and anthropogenic coastal solutes.

Metal accumulation capacity in indigenous Alaska vegetation growing on military training lands.

Permafrost thawing could increase soil contaminant mobilization in the environment. Our objective was to quantify metal accumulation capacities for plant species and functional groups common to Alaskan military training ranges where elevated soil metal concentrations were likely to occur. Plant species across multiple military training range sites were collected. Metal content in shoots and roots was compared to soil metal concentrations to calculate bioconcentration and translocation factors. On average, grasses accumulated greater concentrations of Cr, Cu, Ni, Pb, Sb, and Zn relative to forbs or shrubs, and bioconcentrated greater concentrations of Ni and Pb. Shrubs bioconcentrated greater concentrations of Sb. Translocation to shoots was greatest among the forbs. Three native plants were identified as candidate species for use in metal phytostabilization applications. Elymus macrourus, a grass, bioconcentrated substantial concentrations of Cu, Pb, and Zn in roots with low translocation to shoots. Elaeagnus commutata, a shrub, bioconcentrated the greatest amounts of Sb, Ni, and Cr, with a low translocation factor. Solidago decumbens bioconcentrated the greatest amount of Sb among the forbs and translocated the least amount of metals. A combination of forb, shrub, and grass will likely enhance phytostabilization of heavy metals in interior Alaska soils through increased functional group diversity.

Initial Survey of Microplastics in Bottom Sediments from United States Waterways.

Given the reported extent of microplastics in the aquatic environment, environmentally relevant exposure information for sediments dredged by the US Army Corps of Engineers will lend context to the risks posed by this contaminant during dredging. We measured the occurrence, abundance, and polymer composition of microplastics in sediments collected from nine dredged waterways and two non-dredged reference areas. The number of particles in sediment samples ranged from 162 to 6110 particles/kg dry wt., with a mean of 1636 particles/kg dry wt. Fragments were the most prevalent shape observed among the 11 study sites (100% frequency of occurrence), followed by fibers (81%), spheres (75%), foams (38%) and films (34%). Based on analyses of chemical composition of the particles using Fourier transform infrared spectroscopy, polyethylene:propylene was the most common polymer type observed. Consistent with results presented by other investigators, microplastic concentrations and polymer types in bottom sediments in this study were also aligned with the most widely used plastics worldwide.

Sea Level Rise Induced Arsenic Release from Historically Contaminated Coastal Soils.

Climate change-induced perturbations in the hydrologic regime are expected to impact biogeochemical processes, including contaminant mobility and cycling. Elevated levels of geogenic and anthropogenic arsenic are found along many coasts around the world, most notably in south and southeast Asia but also in the United States, particularly along the Mid-Atlantic coast. The mechanism by and the extent to which arsenic may be released in contaminated coastal soils due to sea level rise are unknown. Here we show a series of data from a coastal arsenic-contaminated soil exposed to sea and river waters in biogeochemical microcosm reactors across field-validated redox conditions. We find that reducing conditions lead to arsenic release from historically contaminated coastal soils through reductive dissolution of arsenic-bearing mineral oxides in both sea and river water inundations, with less arsenic release from seawater scenarios than river water due to inhibition of oxide dissolution. For the first time, we systematically display gradation of solid phase soil-arsenic speciation across defined redox windows from reducing to oxidizing conditions in natural waters by combining biogeochemical microcosm experiments and X-ray absorption spectroscopy. Our results demonstrate the threat of sea level rise stands to impact arsenic release from contaminated coastal soils by changing redox conditions.

Sea-level rise and arsenic-rich soils: A toxic relationship.

In the United States, dangerously high arsenic (As) levels have been found in drinking water wells in more than 25 states, potentially exposing 2.1 million people to drinking water high in As; a known carcinogen. The anticipated sea-level rise (SLR) is expected to alter soil biogeochemical and hydrological conditions, potentially impacting their ability to sequester As. In our study of coastal Wilmington, DE, an area projected to experience a 1 -meter SLR by 2100, we examined the spatial distribution, speciation, and release possibilities of As due to SLR. To understand the complex dynamics at play, we employed a comprehensive approach, including bulk and micro X-ray absorption spectroscopy measurements, hydrological pattern evaluation, and macroscopic stirred-flow experiments. Our results suggest that introducing reducing and saline conditions can increase As release in both river water and seawater inundation scenarios, most likely due to ionic competition and the dissolution of As-bearing Fe/Mn oxides. Regardless of the salinity source, the released As concentrations consistently exceeded the EPA threshold for drinking water. Our results provide valuable insights for developing appropriate remedial and management strategies for this site and numerous others facing similar environmental challenges. ENVIRONMENTAL IMPLICATION: With nearly two hundred million individuals living within coastal flood plains and with two million square kilometers of land and one trillion dollars' worth of assets lying less than 1 m above current sea level, sea-level rise (SLR) is one of the significant socio-economic threats associated with global warming. Arsenic is a prevalent contaminant in coastal areas impacted by industrial activities, many of which are susceptible to being impacted by SLR. This study examines SLR's impact on arsenic fate and speciation in a densely populated coastline in Wilmington, DE, expecting 1 meter of SLR by 2100.

Organic contaminant sorption parameters should only be compared across a consistent system of linear functions.

Modeling contaminant sorption data using a linear model is very common; however, the rationale for whether the y-intercept should be constrained or not remains a subject of debate. This article justifies constraining the y-intercept in the linear model to zero. By doing so, one imposes consistency on the system of linear equations, allowing for direct comparison of the sorption coefficients.

Assessing atmospheric nitrogen losses with photoacoustic infrared spectroscopy: Polymer coated urea.

Although N is beneficial and essential for life, it is also a common atmospheric pollutant as nitrous oxide (N2O) and ammonia (NH3)-contributed largely from N fertilization. Polymer-coated urea (PCU) fertilizer is a promising controlled release fertilizer that provides improved N-release timing. Glasshouse studies were conducted to compare N2O and NH3 emissions from PCU and uncoated urea to an untreated control utilizing a non-static, non-flow-through chamber in conjunction with photoacoustic infrared spectroscopy (PAIRS) for gas collection and analysis. Three short-term 20-Day Studies with sand, sandy loam, and loam soils and a full-term 45-Day Study with loam soil were completed. Volatilization of NH3 was reduced by 72% and 22% in the sandy loam and loam soils, respectively, in two of the short-term studies and by 14% in the loam in the full-term study. Evolution of N2O was reduced by 42% and 63% in the sandy loam and loam soils of the short-term studies and by 99% in the loam soil of the full-term study. No differences were observed in the sand soil. Overall, PCU decreased gaseous losses of N following fertilization while providing a steady supply of N to the plant. Higher temporal resolution was observed with the PAIRS instrumentation as compared to what is typically reported and, as such, we recommend PAIRS analysis as a viable method for studying N gas emissions.

Polymer Coated Urea in Turfgrass Maintains Vigor and Mitigates Nitrogen's Environmental Impacts.

Polymer coated urea (PCU) is a N fertilizer which, when added to moist soil, uses temperature-controlled diffusion to regulate N release in matching plant demand and mitigate environmental losses. Uncoated urea and PCU were compared for their effects on gaseous (N2O and NH3) and aqueous (NO3(-)) N environmental losses in cool season turfgrass over the entire PCU N-release period. Field studies were conducted on established turfgrass sites with mixtures of Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.) in sand and loam soils. Each study compared 0 kg N ha(-1) (control) to 200 kg N ha(-1) applied as either urea or PCU (Duration 45CR®). Application of urea resulted in 127-476% more evolution of measured N2O into the atmosphere, whereas PCU was similar to background emission levels from the control. Compared to urea, PCU reduced NH3 emissions by 41-49% and N2O emissions by 45-73%, while improving growth and verdure compared to the control. Differences in leachate NO3(-) among urea, PCU and control were inconclusive. This improvement in N management to ameliorate atmospheric losses of N using PCU will contribute to conserving natural resources and mitigating environmental impacts of N fertilization in turfgrass.