Shallow slope failures due to erosion are common occurrences along roadways. The use of deep-rooted vegetative covers is a potential solution to stabilize newly constructed slopes or repair shallow landslides. This study compared species that may provide slope stabilization for sites in the Piedmont region of the southeastern USA. Six species were tested on experimental plots under natural rainfall conditions, and vegetation health and establishment were monitored. Two methods were used to measure surface erosion, measurement of total suspended solids in collected runoff and erosion pins. While measurement uncertainty was high for both methods, differences were evident between species in the spatial distribution of surface erosion that was related to the quality of vegetation establishment. For three species that established well, soil cores were collected to measure root biomass at depths up to 40 cm. Vetiver grass (Vetiveria zizaniodies) had substantially higher mean root biomass (3.75 kg/m3) than juniper shrubs (Juniperus chinensis; 0.45 kg/m3) and fescue grass (Lolium arundinaceum; 1.28 kg/m3), with the most pronounced difference in the deepest soil layers. Seeding with turf grass such as fescue is a common practice for erosion control in the region but replacing this with vetiver on steep slopes may help prevent shallow landslides due to the additional root reinforcement. Additional work is needed to measure the magnitude of the strength gain.
<p>Wetland environments are well documented to contain unique hydrogeomorphic subsystems that benefit from nutrient and temperature regimes provided by upwelling groundwater sources. Matrix seepage and preferential flow can both serve as groundwater inputs that control carbon-cycling within these environments. Recent work in a northern boreal peatland of Maine illuminates parallel dynamics to other wetland environments, with matrix seepage and preferential flow pathways (PFPs) identified and quantified proximal to peatland pools. PFPs around the peatland pools have been interpreted as peat pipes, known to transport nutrients within the peat matrix. Thermal signatures surrounding the peatland pool sources were mapped using point temperature measurements, handheld thermal imagery, and airborne thermal infrared mapping. Electrical geophysical methods were deployed to image the structure and stratigraphy of the underlying mineral sediments to delineate the source of focused upwelling around the peatland pools. Ground-penetrating radar (GPR) surveys show discontinuities in the impermeable glacio-marine clay controlling the hydrogeomorphic development of the peatlands studied. These mineral soil discontinuities in the GPR surveys, interpreted to be regional glacial esker deposits, are located proximal to the overlying peatland pools. Electromagnetic induction surveys were deployed to map the bulk electrical conductivity structures associated with the near-surface geology beneath the peatland pools. Point specific conductance measurements were taken at identified zones of thermal anomalies to further validate contrasts between peat pore water and mineral soil groundwater in the peatlands. Water samples were collected at the seepage sites and analyzed for iron and manganese trace elements to support the hypothesis that upwelling occurs from permeable glacial esker deposits. Focused groundwater inputs into peatlands may define a key hydrogeomorphic development process for peatland pool systems and the surrounding ecology. Further, these inputs could have implications for carbon-cycling, building on the established regional relationship between groundwater flow and carbon transport. Illuminating the focused groundwater flowpaths and interpreting their hydrogeologic origins may serve as a basis for future carbon-cycling exploration within peatlands at novel, fine-scales.</p>
<p>The hydrology of northern peatlands is increasingly recognized to be influenced by groundwater flow between peat and underlying mineral sediments. These hydrologic fluxes have been measured in peatlands of central and northern Maine where peatlands formed in depressions within the complex landscape left after the last glacial ice retreat. Although most of these peatlands formed on top of a low permeability confining glaciomarine clay, surface digital elevation maps and subsurface geophysical datasets (ground penetrating radar, electromagnetic and resistivity imaging) indicate that, in places, they are often in hydrogeological contact with eskers (glacial outwash deposits) and possibly even directly in contact with bedrock. Hydrogeological datasets, including direct hydraulic head observations and indirect observations of seepage fluxes, support the case that these points of hydrogeological contact exert a profound influence on the surface hydrology, including pool formation, and ecology of these peatland systems. The unique properties of peat, including the formation of pipe structures, result in highly focused discharges of mineralized water as evidenced from temperature sensing and aqueous geochemistry data (specific conductance, dissolved iron, dissolved manganese). These pipe networks may exert a control on carbon cycling in peatlands via the delivery of nutrients, or possibly by serving as conduits for the release of free phase gas stored in the deep peat. Preliminary observations using gas traps lend support to this hypothesis.</p>
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