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Pesticide volatilization and deposition with precipitation is widely documented and has been connected to adverse ecological impact. Here we describe a 3-yr study of current use and legacy pesticides in event-based rain samples within a 123-ha agricultural watershed. Crops in farm fields were documented quarterly with data used to estimate target compound use. The median number of pesticide detections in samples was 6. The fungicide, chlorothalonil which was used most intensively was detected in nearly all samples. It had the highest mean and peak concentrations with total deposition ≈ 0.1% of the estimated amount applied. The insecticide endosulfan also had relatively high use with behavior mirroring chlorothalonil. There was strong seasonal variation in concentration and depositional dynamics with the highest values measured during growing seasons. Similar behavior was observed with other compounds detected in rain samples with a general decrease in deposition and mean concentrations as use decreased. Comparison of measured concentrations to values associated with toxic impact on aquatic organisms indicated that chlorothalonil, endosulfan, chlorpyrifos, malathion and atrazine may contribute to adverse impact. The number of samples exceeding risk endpoints ranged from 1 to 77%. The highest value was for endosulfan; however its on-going phase-out is expected to reduce risks. Another finding was that the wet deposition of the herbicide, metolachlor exceeded measured runoff rates in the watershed by 5-fold. The study has demonstrated that localized pesticide wet deposition may present ecological risks and that volatilization and wet deposition is an important pesticide transport pathway at the local scale. Findings point to the need to include wet deposition in assessments of pesticide ecological risk and environmental fate. [ABSTRACT FROM AUTHOR]

Abstract: Transportation infrastructure affects the structure of ecosystems, the dynamics of ecosystem function, and has direct effects on ecosystem components, including their species composition. Clearly, the construction of transport lines results in the direct destruction and removal of existing ecosystems, and the reconfiguration of local landforms. However, transportation systems, and more specifically, roads, have a wide variety of primary, or direct, ecological effects as well as secondary, or indirect, ecological effects on the landscapes that they penetrate. The effects of roads can be measured in both abiotic and biotic components of terrestrial and aquatic ecosystems. The nature of road systems as network structures renders vast areas of the landscape as road-affected, with small patches of isolated habitat remaining beyond the ecological influence of roads. The increasing attention of scientists to the unintended ecological effects of roads has resulted in the emergence of the science of “Road Ecology,” marked with the publication of a multi-authored volume, Road Ecology: Science and Solutions, in 2003. [Copyright &y& Elsevier]

Abstract: The energy density and forces required to separate nanoropes into individual nanotubes was examined by studying both the dilatation separation of arrays and the peeling of a pair of single wall carbon nanotubes. The cohesive energy per unit length was determined from the universal graphitic potential. The magnitude of the peeling force for a pair of tubes configured in a double cantilever beam was calculated over a range of peeling lengths using a cohesive zone model, and compared to predictions from linear elastic fracture mechanics. The results of the analysis reveal that a linear elastic fracture model that incorporates an inherent initial crack length yields a reasonable estimation of the peeling force–deformation response. The energy of separation for the dilatation mechanism was shown to be a strong function of the array size with twice the energy density necessary to separate an array of three CNT as compared to separation of a large array. Estimates of the energy of peeling separation of 0.30 nJ/m is in good agreement with previous work. [Copyright &y& Elsevier]

Dissolved organic matter (DOM) represents an essential component of the carbon cycle and controls biogeochemical and ecological processes in aquatic systems. The composition and reactivity of DOM are determined by the spatial distribution of its sources and its residence time in a watershed. While the effects of agricultural land cover on DOM quality have been reported across spatial and temporal scales, the influence of riparian land cover on stream DOM composition has received little attention. Furthermore, the combined effects of riparian land cover and streamflow rates on DOM composition require investigation. To this end, a multi-year (2016–2018) DOM characterization study was conducted using bi-weekly water samples collected from seven sub-watersheds nested within the Little River Experimental Watershed (LREW) near Tifton, Georgia, USA. DOM optical properties were determined to assess compositional variations using UV–Vis and excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor (PARAFAC) analysis. PARAFAC analysis indicated that DOM in the LREW was dominated by three humic-like fluorescing components of terrestrial, microbial, and anthropogenic origin and a protein-like component. DOM composition was influenced by riparian land cover and hydrology, and shifted towards recently produced, low molecular weight DOM with low aromaticity as the percentage of agricultural land within riparian wetlands increased. During periods of high discharge and high baseflow, the DOM pool was dominated by recalcitrant and terrestrial-derived material but shifted towards protein-like and microbial-derived with increasing cropland in the riparian area. The results of this two-year study indicate that the replacement of forested riparian buffers with agricultural land can result in altered DOM composition which may affect carbon cycling and downstream water quality in agricultural watersheds. Unlabelled Image • The optical properties of DOM in agricultural streams were assessed. • DOM composition was influenced by riparian land cover and hydrology. • Agricultural land increases fresh DOM of low molecular weight and low aromaticity. • Microbial-derived DOM dominates during periods of low discharge and baseflow. [ABSTRACT FROM AUTHOR]

Second generation biofuels, such as perennial grasses, have potential to provide biofuel feedstock while growing on degraded land with minimal inputs. Perennial grasses have been reported to sequester large amounts of soil organic carbon (SOC) in the Midwestern United States (USA). However, there has been little work on biofuel and carbon sequestration potential of perennial grasses in the Southeastern US. Biofuel productivity for dryland Miscanthus × gigantus and irrigated maize in Georgia, USA were quantified using eddy covariance observations of evapotranspiration (ET) and net ecosystem exchange (NEE) of carbon. Miscanthus biomass yield was 15.54 Mg ha−1 in 2015 and 11.80 Mg ha−1 in 2016, while maize produced 30.20 Mg ha−1 of biomass in 2016. Carbon budgets indicated that both miscanthus and maize fields lost carbon over the experiment. The miscanthus field lost 5 Mg C ha−1 in both 2015 and 2016 while the maize field lost 1.37 Mg C ha−1 for the single year of study. Eddy covariance measurement indicated that for 2016 the miscanthus crop evapotranspired 598 mm and harvest water use efficiencies ranged from 6.95 to 13.84 kg C ha−1 mm−1. Maize evapotranspired 659 mm with a harvest water use efficiency of 19.12 kg C ha−1 mm−1. While biomass yields and gross primary production were relatively high, high ecosystem respiration rates resulted in a loss of ecosystem carbon. Relatively low biomass production, low water use efficiency and high respiration for Miscanthus × gigantus in this experiment suggest that this strain of miscanthus may not be well-suited for dryland production under the environmental conditions found in South Georgia USA. • Dryland Miscanthus × gigantus yield was 12–15 Mg ha−1 in the southeastern USA. • Carbon budgets indicated that both miscanthus and maize fields lost carbon. • Miscanthus water use efficiency was comparable to maize when not under drought stress. [ABSTRACT FROM AUTHOR]