Impact of an Extreme Storm Event on River Corridor Bank Erosion and Phosphorus Mobilization in a Mountainous Watershed in the Northeastern United States

Movement of sediment, and associated phosphorus, from stream banks to freshwater lakes is predicted to increase with greater frequency of extreme precipitation events. This higher phosphorus load may accelerate harmful algal blooms in affected water bodies, such as Lake Champlain in Vermont, New York, and Québec. In the Mad River, a subwatershed in central Vermont\u27s Lake Champlain Basin, extreme flooding from Tropical Storm Irene in 2011 caused extensive erosion. We measured stream channel change along the main stem between 2008 and 2011 by digitizing available prestorm and poststorm aerial imagery. Soils were sampled post Irene at six active stream erosion sites, using an experimental design to measure differences in soil texture and phosphorus both with depth (90 cm) and distance from the stream. In addition to total phosphorus (TP), we determined bioavailable (soil test) phosphorus (STP) and the degree of phosphorus saturation (DPS). The six sites represented a 0.87-km length of stream bank that contributed an estimated 17.6 × 10 3 Mg of sediment and 15.8 Mg of TP, roughly the same as average annual watershed export estimates. At four sites, the STP and DPS were low and suggested little potential for short-term phosphorus release. At two agricultural sites where the lateral extent of erosion was high, imagery showed a clear loss of well-established riparian buffer. Present-day near-stream soils were elevated in STP and DPS. An increase in these extreme events will clearly increase sediment loads. There will also be increasing concentration of sediment phosphorus if stream banks continue to erode into actively managed agricultural fields

Cyclic Peptides as Non-carboxyl-terminal Ligands of Syntrophin PDZ Domains

Syntrophins, a family of intracellular peripheral membrane proteins of the dystrophin-associated protein complex (DAPC), each contain a single PDZ domain. Syntrophin PDZ domains bind C-terminal peptide sequences with the consensus R/K-E-S/T-X-V-COOH, an interaction that mediates association of skeletal muscle sodium channels with the DAPC. Here, we have isolated cyclic peptide ligands for syntrophin PDZ domains from a library of combinatorial peptides displayed at the N terminus of protein III of bacteriophage M13. Affinity selection from a library of X10C peptides yielded ligands with the consensus X-(R/K)-E-T-C-L/M-A-G-X-Psi-C, where Psi represents any hydrophobic amino acid. These peptides contain residues (underlined) similar to the C-terminal consensus sequence for binding to syntrophin PDZ domains and bind to the same site on syntrophin PDZ domains as C-terminal peptides, but do not bind to other closely related PDZ domains. PDZ binding is dependent on the formation of an intramolecular disulfide bond in the peptides, since treatment with dithiothreitol, or substitution of either of the two cysteines with alanines, eliminated this activity. Furthermore, amino acid replacements revealed that most residues in the phage-selected peptides are required for binding. Our results define a new mode of binding to PDZ domains and suggest that proteins containing similar conformationally constrained sequences may be ligands for PDZ domains

Modeling sediment mobilization using a distributed hydrological model coupled with a bank stability model

In addition to surface erosion, stream bank erosion and failure contributes significant sediment and sediment-bound nutrients to receiving waters during high flow events. However, distributed and mechanistic simulation of stream bank sediment contribution to sediment loads in a watershed has not been achieved. Here we present a full coupling of existing distributed watershed and bank stability models and apply the resulting model to the Mad River in central Vermont. We fully coupled the Bank Stability and Toe Erosion Model (BSTEM) with the Distributed Hydrology Soil Vegetation Model (DHSVM) to allow the simulation of stream bank erosion and potential failure in a spatially explicit environment. We demonstrate the model\u27s ability to simulate the impacts of unstable streams on sediment mobilization and transport within a watershed and discuss the model\u27s capability to simulate watershed sediment loading under climate change. The calibrated model simulates total suspended sediment loads and reproduces variability in suspended sediment concentrations at watershed and subbasin outlets. In addition, characteristics such as land use and road-to-stream ratio of subbasins are shown to impact the relative proportions of sediment mobilized by overland erosion, erosion of roads, and stream bank erosion and failure in the subbasins and watershed. This coupled model will advance mechanistic simulation of suspended sediment mobilization and transport from watersheds, which will be particularly valuable for investigating the potential impacts of climate and land use changes, as well as extreme events

Long-Term Groundwater Monitoring Results at Large, Sudden Denatured Ethanol Releases

Hundreds of groundwater samples were collected at E95 (95% ethanol, 5% gasoline) train derailment spills in Balaton and Cambria, Minnesota and South Hutchinson, Kansas. Most samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX), ethanol, methane, acetate, terminal electron acceptors, and field parameters. At each site, maximum groundwater ethanol concentrations at percent levels were restricted to the release area and downgradient ethanol transport was not detected. A shallow, anaerobic groundwater zone characterized by the absence of dissolved oxygen, low nitrate (less than 1 mg N/L), high Fe+2, and high dissolved methane (more than 10,000 μg/L) and BTEX formed and spread downgradient from each release area. BTEX appeared to be persistent. Methane appeared to be generated within the capillary fringe and very shallow groundwater and migrate laterally. Methane’s high oxygen demand promotes anaerobic conditions within the shallow groundwater. Estimated and measured methane soil gas concentrations exceeded the lower explosive limit. Long-term monitoring at South Hutchinson and Cambria using 1 to 5-foot (0.3 to 1.5 m) well screens straddling the capillary fringe and the shallow water table effectively demonstrated the presence of high ethanol (~1%) and benzene (more than 250 μg/L) concentrations 5 years after the release. The wells appear impacted by long-term ethanol inputs from the vadose zone where ethanol has persisted for years after the initial release. Toxicity, volatile fatty acids, excess hydrogen production, and/or exudate coatings could be responsible for ethanol’s preservation. High acetate and hydrogen concentrations at South Hutchinson indicated that fermentation was actively occurring in the very shallow groundwater and/or in the lower capillary fringe. Shortscreened (1 to 5 feet; 0.3 to 1.5 m) nested wells were pivotal to improving our understanding of ethanol’s behavior