Effects of block shape and inclination on the stability of melange bimrocks

Bulletin of Engineering Geology and the Environment - A wide range of heterogeneous geological units composed of strong rock blocks enclosed in a bonded matrix of fine texture exists worldwide....     

Quantifying the impacts of stratification and nutrient loading on hypoxia in the northern Gulf of Mexico

Stratification and nutrient loading are two primary factors leading to hypoxia in coastal systems. However, where these factors are temporally correlated, it can be difficult to isolate and quantify their individual impacts. This study provides a novel solution to this problem by determining the effect of stratification based on its spatial relationship with bottom-water dissolved oxygen (BWDO) concentration using a geostatistical regression. Ten years (1998-2007) of midsummer Gulf of Mexico BWDO measurements are modeled using stratification metrics along with trends based on spatial coordinates and bathymetry, which together explain 27-61% of the spatial variability in BWDO for individual years. Because stratification effects explain only a portion of the year-to-year variability in mean BWDO; the remaining variability is explained by other factors, with May nitrate plus nitrite river concentration the most important. Overall, 82% of the year-to-year variability in mean BWDO is explained. The results suggest that while both stratification and nutrients play important roles in determining the annual extent of midsummer hypoxia, reducing nutrient inputs alone will substantially reduce the average extent.     

St. Clair-Detroit River system: Phosphorus mass balance and implications for Lake Erie load reduction,monitoring, and climate change

To support the 2012 Great Lakes Water Quality Agreement on reducing Lake Erie's phosphorus inputs, we integrated US and Canadian data to update and extend total phosphorus (TP) loads into and out of the St. Clair-Detroit River System for 1998–2016. The most significant changes were decreased loads from Lake Huron caused by mussel-induced oligotrophication of the lake, and decreased loads from upgraded Great Lakes Water Authority sewage treatment facilities in Detroit. By comparing Lake St. Clair inputs and outputs, we demonstrated that on average the lake retains 20% of its TP inputs. We also identified for the first time that loads from resuspended Lake Huron sediment were likely not always detected in US and Canadian monitoring programs due to mismatches in sampling and resuspension event frequencies, substantially underestimating the load. This additional load increased over time due to climate-induced decreases in Lake Huron ice cover and increases in winter storm frequencies. Given this more complete load inventory, we estimated that to reach a 40% reduction in the Detroit River TP load to Lake Erie, accounting for the missed load, point and non-point sources other than that coming from Lake Huron and the atmosphere would have to be reduced by at least 50%. We also discuss the implications of discontinuous monitoring efforts.     

Phytoplankton community composition of Saginaw Bay,Lake Huron,during the zebra mussel (Dreissena polymorpha) invasion: A multivariate analysis

The colonization of the zebra mussel (Dreissena polymorpha) in Saginaw Bay dramatically altered the phytoplankton community composition resulting in exclusion of light sensitive species and dominance of species with oligotrophic preferences and light resistance. In 1990, the NOAA Great Lakes Environmental Research Laboratory initiated a 7-year survey program to monitor changes in the lower food web of Saginaw Bay, where zebra mussels became established in the fall of 1991. To investigate shifts in the phytoplankton community composition over the 7-year period from 1990 to 1996 we searched for clusters of similar composition using multivariate principal component analysis (PCA) on proportions of 22 taxonomic groupings of the total phytoplankton density (cells per milliliter). We then used an agglomerative hierarchical clustering analysis of the PCA scores. We identified five characteristic phytoplankton communities in configurations that allowed recognizing four distinct periods in Saginaw Bay linked to the zebra mussel invasion. Significant changes were indicative of increased water clarity and eutrophic conditions being replaced by more oligotrophic conditions as clusters dominated by light sensitive species, such as the cyanobacteria Oscillatoria redekii, became immediately rare and clusters dominated by diatoms such as Cyclotella spp. became common. Microcystis spp., a light tolerant cyanobacteria not grazed by zebra mussel, dominated assemblages after 1994. The shifts in phytoplankton composition confirm that zebra mussels effects on phytoplankton communities are mediated by both direct (filtration) and indirect (nutrient cycling) mechanisms and also suggests that increased light penetration is an important mechanism behind some changes.     

Numerical Study of Scale Effects on the Stiffness Modulus of Rock Masses

The purpose of this paper is to contribute to the study of scale effects on the stiffness modulus of discontinuous rock masses from a mechanical point of view. The study has been conducted on the basis of the observation that the length and density of the natural discontinuities (cracks) in rock masses increase with the volume of the mass. Compressive tests on specimens containing open and closed flat cracks have been simulated through a numerical procedure that is based on the displacement discontinuity method and the fictitious stress method. Cracks have been generated, through a random process, with dips in the 0°–180° range. Both open and closed cracks have been considered. The numerical results obtained for specimens containing open cracks are found to approach the values obtained through an analytical solution. Then, the numerical method has been applied to the study of scale effects on the stiffness modulus of specimens with closed cracks. The numerical results show a decrease in the stiffness modulus with an increase in the size of the rock volume.     

Thermal treatment stabilization processes in SnO2 thinfilms catalyzed with Au and Pt

We examined the thermal treatment stabilization processes in SnO ₂-based thin films for gas-sensing applications in order to understand their influence on structural properties and possible relations with functional behavior of the sensors. The films of SnO₂ were deposited by magnetron sputtering, following the rules of the rheothaxial growth and thermal oxidation (RGTO) technique and annealed in humid synthetic air at 600°C. Afterward, a thin overlayer of gold or platinum was deposited on the oxidized films. The samples were characterized soon after catalyzer deposition and after one-hour aging process at 400°C, in order to evaluate stabilization process influence as a function of catalyzer. X-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM) demonstrated that a short aging affects the microstructure of gold-catalyzed samples, while it does not influence platinum catalyzed ones. The results of the microstructural characterization were confirmed by electrical measurements of gas-sensitivity: the short-aging influences the stability of gas-sensing parameters only in gold-catalyzed samples     

Incidental oligotrophication of North American Great Lakes

Phytoplankton production is an important factor in determining both ecosystem stability and the provision of ecosystem goods and services. The expansive and economically important North American Great Lakes are subjected to multiple stressors and understanding their responses to those stresses is important for understanding system-wide ecological controls. Here we show gradual increases in spring silica concentration (an indicator of decreasing growth of the dominant diatoms) in all basins of Lakes Michigan and Huron (USA and Canadian waters) between 1983 and 2008. These changes indicate the lakes have undergone gradual oligotrophication coincident with and anticipated by nutrient management implementation. Slow declines in seasonal drawdown of silica (proxy for seasonal phytoplankton production) also occurred, until recent years, when lake-wide responses were punctuated by abrupt decreases, putting them in the range of oligotrophic Lake Superior. The timing of these dramatic production drops is coincident with expansion of populations of invasive dreissenid mussels, particularly quagga mussels, in each basin. The combined effect of nutrient mitigation and invasive species expansion demonstrates the challenges facing large-scale ecosystems and suggest the need for new management regimes for large ecosystems.     

A simple 1-dimensional,climate based dissolved oxygen model for the central basin of Lake Erie

A linked 1-dimensional thermal-dissolved oxygen model was developed and applied in the central basin of Lake Erie. The model was used to quantify the relative contribution of meteorological forcings versus the decomposition of hypolimnetic organic carbon on dissolved oxygen. The model computes daily vertical profiles of temperature, mixing, and dissolved oxygen for the period 1987–2005. Model calibration resulted in good agreement with observations of the thermal structure and oxygen concentrations throughout the period of study. The only calibration parameter, water column oxygen demand (WCOD), varied significantly across years. No significant relationships were found between these rates and the thermal properties; however, there was a significant correlation with soluble reactive phosphorus loading. These results indicate that climate variability alone, expressed as changes in thermal structure, does not account for the inter-annual variation in hypoxia. Rather, variation in the production of organic matter is a dominant driver, and this appears to have been responsive to changes in phosphorus loads.     

Detroit River phosphorus loads: Anatomy of a binational watershed

As a result of increased harmful algal blooms and hypoxia in Lake Erie, the US and Canada revised their phosphorus loading targets under the 2012 Great Lakes Water Quality Agreement. The focus of this paper is the Detroit River and its watershed, a source of 25% of the total phosphorus (TP) load to Lake Erie. Its load declined 37% since 1998, due chiefly to improvements at the regional Great Lakes Water Authority Water Resource Recovery Facility (WRRF) in Detroit and phosphorus sequestered by zebra and quagga mussels in Lake Huron. In addition to the 54% of the load from Lake Huron, nonpoint sources contribute 57% of the TP load and 50% of the dissolved reactive phosphorus load, with the remaining balance from point sources. After Lake Huron, the largest source is the WRRF, which has already reduced its load by over 40%. Currently, loads from Lake Huron and further reductions from the WRRF are not part of the reduction strategy, therefore remaining watershed sources will need to decline by 72% to meet the Water Quality Agreement target - a daunting challenge. Because other urban sources are very small, most of the reduction would have to come from agriculturally-dominated lands. The most effective way to reduce those loads is to apply combinations of practices like cover crops, buffer strips, wetlands, and applying fertilizer below the soil surface on the lands with the highest phosphorus losses. However, our simulations suggest even extensive conservation on those lands may not be enough.