STUDIES ON THE DISTRIBUTION AND PHYSIOLOGY OF LEAD IN PLANTS

The studies reported herein cover two main areas of research. The distribution of lead through the plant has been monitored using histochemical and quantitative techniques, and physiological responses of the plant to lead contamination have been examined. In seeds the testa prevents lead contamination of the embryo prior to germination. In seedlings root-applied lead is capable of essentially unrestricted movement through the plant, although anomalies in distribution exist. The metal is sequestered during its passage through the plant, and the endodermis offers a partial barrier to lead movement, restricting contamination of the aerial parts of the plant. In cotyledon leaves local accumulations may occur, causing necrotic lesions. Subcellular lead contamination again diminishes with distance from the root, but extensive exposure causes heavy contamination of cell walls, increasing wall fragility. Lead deposits occur in association with several cell organelles, but the primary response of plant cells to lead contamination lies in the formation of vesicles, apparently from the endoplasmic reticulum. These fuse into vacuoles and may totally disrupt cell ultrastructure. Lead distributions observed have been verified by X-ray microanalysis. Responses to lead pollution occur in numerous physiological processes, but the most obvious effect lies in the reduction of plant growth. In the root this is at least partially attributable to reduced cell division, but in the stem growth inhibition results primarily from interferences in cell elongation. This inhibition of elongation arises from lead-induced cell wall changes which increase wall rigidity. At high supply levels lead also influences water uptake, possibly via changes in membrane permeability. Endogenous IAA levels increase in response to lead contamination, and may partly alleviate the toxic effects of lead. The metal also promotes changes in chlorophyll synthesis, membrane permeability, ion uptake, water stress and respiration. Possible reactions and interactions involved in these responses are discussed

Hydrological heterogeneity and the plant colonization of recently deglaciated terrain

Climate change accelerates glacier retreat, leading to extensive exposure of sediment to light and ecological succession. Succession has traditionally been studied as a chronosequence, where vegetation development is directly correlated with time since glacier retreat or distance from the retreating glacier margin. More recent work has challenged this model, arguing that succession seems to be mainly influenced by heterogeneous conditions at the local scale. The aim of this study was to identify the factors influencing the local-scale establishment of plant communities following glacier recession. Vascular plants and their cover were inventoried in 100 plots (1 m2) for a thirty-year-old alluvial plain in front of the Otemma glacier (Swiss Alps). Depth to water table, distance to the glacial main river and to the nearest channel, sediment size, moss, lichen, and biological soil crust cover were measured. Results showed that proglacial margins develop hydrological heterogeneity over a small scale, reflected in the four observed plant communities. These range from the dry Sempervivum-dominated community, on gravel-rich sediments with a deep water table, to the Trifolium-dominated community, close to secondary channels, with the highest plant cover and species richness and incorporating grassland species. Heterogeneity in water availability exerted a critical control on vegetation development

EchoBoat and HYPACK: user guide v 1.0

Technical manual for deploying the Seafloor Echo Boat and processing associated data using Hypack

Towards a hydrogeomorphological understanding of proglacial catchments: an assessment of groundwater storage and release in an Alpine catchment

Proglacial margins form when glaciers retreat and create zones with distinctive ecological, geomorphological and hydrological properties in Alpine environments. There is extensive literature on the geomorphology and sediment transport in such areas as well as on glacial hydrology, but there is much less research into the specific hydrological behavior of the landforms that develop after glacier retreat in and close to proglacial margins. Recent reviews have highlighted the presence of groundwater stores even in such rapidly draining environments. Here, we describe the hydrological functioning of different superficial landforms within and around the proglacial margin of the Otemma glacier, a temperate Alpine glacier in the Swiss Alps; we characterize the timing and amount of the transmission of different water sources (rain, snowmelt, ice melt) to the landforms and between them, and we compare the relationship between these processes and the catchment-scale discharge. The latter is based upon a recession-analysis-based framework. In quantifying the relative groundwater storage volumes of different superficial landforms, we show that steep zones only store water on the timescale of days, while flatter areas maintain baseflow on the order of several weeks. These landforms themselves fail to explain the catchment-scale recession patterns; our results point towards the presence of an unidentified storage compartment on the order of 40 mm, which releases water during the cold months. We suggest attributing this missing storage to deeper bedrock flowpaths. Finally, the key insights gained here into the interplay of different landforms as well as the proposed analysis framework are readily transferable to other similar proglacial margins and should contribute to a better understanding of the future hydrogeological behavior of such catchments.</p

Interactions between subgrid-scale resolution, feature representation and grid-scale resolution in flood inundation modelling

Numerical modelling of flood inundation over large and complex floodplains often requires mesh resolutions coarser than the structural features (e.g. buildings) that are known to influence the inundation process. Recent research has shown that this mismatch is not well represented by conventional roughness treatments but that finer scale features can be represented through porositybased sub grid scale treatments. This paper develops this work by testing the interactions between feature representation, sub grid scale resolution and mesh resolution. It uses as the basis for this testing a 2D diffusion-based flood inundation model which is applied to a 2004 flood event in a topologically-complex upland floodplain in northern England. Results showed serious degradation of model predictions without explicit representation of features like walls. Inclusion of such features through raising mesh cell elevations where intersected by a feature resulted in a major improvement in model predictions in terms of reduced inundation extent. To make such treatments physically realistic, and notably so that the full potential for floodplain storage is included, it was shown that a sub grid scale treatment also needed to be included. The effects of this combined treatment was the recovery of more plausible floodplain friction values as well as a sensitivity to friction that allows for more effective representation of floodplain friction effects such as vegetation