Hydrogeologic controls on peatland development in the Malloryville Wetland, New York (USA)

The Malloryville Wetland Complex, a small kettle-hole peatland, contains a diversity of peatland types. The wetland has a ‘rich’ side that contains wetland vegetation associated with solute-rich, near-neutral pH (minerotrophic) water, and a ‘poor’ side containing vegetation that grows in solute-poor and acidic (ombrotrophic) water. Vertical head gradients at piezometer clusters located in the rich side clearly show that groundwater is moving upwards towards the land surface, consistent with the vegetation types and surface water quality. In contrast, vertical head gradients also show that groundwater is moving upward in the poor side even though the vegetation and surface water chemistry are not minerotrophic. An incipient raised bog in the center of the poor side is the only site where groundwater moves consistently downward.

A peat core collected at the bog center shows that the bog site was initially covered by minerotrophic vegetation, typically found in groundwater discharge zones, which was later replaced by ombrotrophic bog vegetation. Theoretical computer simulation experiments of the bog hydrogeologic setting through time suggest that the direction of vertical groundwater flow at the bog site permanently changed from up to down when a water table mound developed under a convex-shaped fen peat mound that probably formed because of differential peat accumulation. Ombrotrophic conditions and bog vegetation probably began when the fen water table mound grew sufficiently large enough to divert the upward movement of regional groundwater. The transition from rich to poor environments probably occurred when the wetland water table was substantially below the elevation of the surrounding regional water table.     

Reconstruction of the ice winter severity since 1701 in the Western Baltic

This reconstruction of the ice winter severity in the Western Baltic is based for the period 1878-1993 on the accumulated areal ice volume along the German Baltic coast with observations from 13 coastal stations; for the period 1701-1877 it is based on the accumulated areal ice volume divided into 7 classes (ice winter severity types). The various types of data consulted in the latter case provided ice data of good spatial and temporal resolution.Speerschneider's compilation of data relating to ice conditions in Danish Baltic waters was found to be a valuable source of information. Using a classification table for the periods 1907-1943 and 1947-1992, five of the seven ice winter types have been derived with certainty as they are characterized by typical stages of maximum ice cover throughout the Western Baltic.The Gaussian lowpass-filtered time series of the ice winter index numerals with a 20 year cutoff period shows four periods of varying ice winter severity over a secular range: 1701-1720: slightly increased ice winter severity with regard to the mean of the 1701-1993 time series; this period can be assigned to the end of a cooling phase during Little Ice Age which in central Europe peaked in the second half of the 17th c. 1721-1760: ice winter severity is clearly reduced in this period. 1761-1860: ice winter severity is clearly increased (maximum occurs around 1800) towards the end of the Little Ice Age, associated with increased variability of ice production. 1861-1993: the present-day ice winter regime when three short intervals with increased ice winter severity (the 1890s, 1940s and 1980s) and a period of greatly reduced ice winter severity (between 1900 and the mid-1920s) stand out.     

High-resolution sea ice in long-term global ocean GCM integrations

The resolution of the sea-ice component of a coarse-resolution global ocean general circulation model (GCM) has been enhanced to about 22 km in the Southern Ocean. The ocean GCM is designed for long-term integrations suitable for investigations of the deep-ocean equilibrium response to changes in southern hemisphere high-latitude processes. The space and time scales of the high-resolution sea-ice component are commensurate with those of the resolution of satellite passive-microwave sea-ice data. This provides the opportunity for a rigorous evaluation of simulated sea-ice characteristics. It is found that the satellite-derived continuous high ice concentration of the interior winter ice pack can only be captured when vertical oceanic mixing is modified in a way that less local, intermittent convection occurs. Furthermore, the width and the variability of the coastal polynyas around the Antarctic continent and its ice shelves are best captured when some form of ice-shelf melting is accounted for. The width of the wintertime ice edge is reasonably reproduced, while its variability remains underestimated, closely following the coarse-grid pattern of the ocean model due to its high dependence on ocean temperature. Additional variability besides daily winds, e.g. in form of idealized tidal currents, improves the temporal and spatial ice-edge variability, while leads in the interior ice pack become more abundant, more in line with the fine-scale satellite-derived texture. The coast- or ice-shelf line is described on the fine grid based on satellite passive-microwave data. This method requires parts of a coarse coastal ocean grid cell to be covered by an inert layer of “fast ice” or “ice shelf”. Reasonable long-term global deep-ocean properties can only be achieved when these areas are not inert, i.e. are exposed to heat flux and ice growth, or when the vertical mixing parameterization allows for excessive open-ocean convection. The model area exposed to cold high-latitude atmospheric conditions thus being most decisive for a realistic representation of the long-term deep-ocean properties, suggests that high-latitude coastlines are definitely in need of being represented at high resolution, including ice sheets and their effects on the heat and freshwater flux for the ocean.     

Dynamic sliding of tetrahedral wedge: The role of interface friction

The role of interface friction is studied by slow direct shear tests and rapid shaking table experiments in the context of dynamic slope stability analysis in three dimensions. We propose an analytical solution for dynamic, single and double face sliding and use it to validate 3D‐DDA. Single face results are compared with Newmark's solution and double face results are compared with shaking table experiments performed on a concrete tetrahedral wedge model, the interface friction of which is determined by constant velocity and velocity stepping, direct shear tests. A very good agreement between Newmark's method on one hand and our 3D analytical solution and 3D‐DDA on the other is observed for single plane sliding with 3D‐DDA exhibiting high sensitivity to the choice of numerical penalty value. The results of constant and variable velocity direct shear tests reveal that the tested concrete interface exhibits velocity weakening. This is confirmed by shaking table experiments where friction degradation upon multiple cycles of shaking culminated in wedge run out. The measured shaking table results are fitted with our 3D analytical solution to obtain a remarkable linear logarithmic relationship between friction coefficient and sliding velocity that remains valid for five orders of magnitude of sliding velocity. We conclude that the velocity‐dependent friction across rock discontinuities should be integrated into dynamic rock slope analysis to obtain realistic results when strong ground motions are considered. Copyright © 2011 John Wiley & Sons, Ltd.     

A three-dimensional numerical groundwater flow model to assess the feasibility of managed aquifer recharge in the Tamne River basin of Ghana

Hydrogeology Journal - Increasing population growth and global climatic changes threaten water security in semiarid regions such as Northern Ghana. The Tamnean Plutonic Suite aquifer is the main...     

Issues associated with the distinction between climatic and tectonic controls on Permian alluvial fan deposits from the Kotzen and Barnim Basins (North German Basin)

Facies analysis focussing on coarse-grained sediments has been carried out on more than 2500 m of drill cores from seven wells from southern margins of the North German Basin (NGB). The NGB forms a central element of the Southern Permian Basin (SPB). The wells exposed conglomerates and sandstones of the Rotliegend Grüneberg and Parchim Formations deposited in the Kotzen Basin and the Barnim Basin.17 lithofacies types have been grouped into six lithofacies associations. The studied successions are dominated by fluid gravity flow deposits (hyperconcentrated flows and stream flows) of alluvial fan and alluvial plain systems. Maximum particle size/bed thickness plots (MPS/BTh) support the interpretation as fluid gravity flow deposits. The MPS and BTh data have also been used to differentiate coarsening–thickening and fining–thinning trends of the fan systems.The dominance of water-rich mass flow processes together with sedimentary structures such as dewatering structures and outwashed tops suggests the presence of wet-type fans and plains under semi-humid to semi-arid seasonal climates in the central SPB. The investigated sediments show variation in clast composition subsequent to deep erosion processes on basin margins and changes of source areas. Synsedimentary normal faults and clastic dykes have been interpreted as indicators of tectonic activity of grabens itself and its frames. On a larger scale, then evolution from a half-graben to a graben is apparent for the Tuchen Sub-basin at least. The progradational/retrogradational cycles of the studied alluvial fan systems document combined local tectonic movements and influences of climatic changes. However, our data did not allow for a clear distinction between climatic and tectonic signals. Furthermore, a one-to-one correlation of fan cycles with depositional trends in the NGB basin centre would appear to be oversimplistic.     

Environmental conservation and the production of new territories: the example of French départements

Very important initiatives have been taken and policies have been adopted in the European Union to protect areas of great importance for threatened species and habitats. Protected areas differ broadly in terms of category, natural conditions and administrative organisation, from international initiative such as Biosphere Reserves, European ones with Natura 2000 network until the institution of national and regional protected areas. In France, the administrative subdivisions known as “départements” were created with the French Revolution in the end of the eighteenth century; in 1985 an original and autonomous procedure to establish special protected areas, called “Sensitive Natural Spaces” (SNS) was devolved to them. The scope of this paper is to present an overview of these devolved powers which enable French départements to create protected areas and to levy a departmental tax on sensitive natural spaces (DTSNS). We statistically studied some parameters by multivariate methods in order to explain the choices of this policy by the départements. The huge variations in the way these powers are implemented prove the development of new environmental territories.     

Eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.) in the Chesapeake Bay Region of Mid-Atlantic Coast of the USA: Challenges in Conservation and Restoration

Decreases in seagrass abundance reported from numerous locations around the world suggest that seagrass are facing a global crisis. Declining water quality has been identified as the leading cause for most losses. Increased public awareness is leading to expanded efforts for conservation and restoration. Here, we report on abundance patterns and environmental issues facing eelgrass (Zostera marina), the dominant seagrass species in the Chesapeake Bay region in the mid-Atlantic coast of the USA, and describe efforts to promote its protection and restoration. Eelgrass beds in Chesapeake Bay and Chincoteague Bay, which had started to recover from earlier diebacks, have shown a downward trend in the last 5–10 years, while eelgrass beds in the Virginia coastal bays have substantially increased in abundance during this same time period. Declining water quality appears to be the primary reason for the decreased abundance, but a recent baywide dieback in 2005 was associated with higher than usual summer water temperatures along with poor water clarity. The success of eelgrass in the Virginia coastal bays has been attributed, in part, to slightly cooler water due to their proximity to the Atlantic Ocean. A number of policies and regulations have been adopted in this region since 1983 aimed at protecting and restoring both habitat and water quality. Eelgrass abundance is now one of the criteria for assessing attainment of water clarity goals in this region. Numerous transplant projects have been aimed at restoring eelgrass but most have not succeeded beyond 1 to 2 years. A notable exception is the large-scale restoration effort in the Virginia coastal bays, where seeds distributed beginning in 2001 has initiated an expanding recovery process. Our research on eelgrass abundance patterns in the Chesapeake Bay region and the processes contributing to these patterns have provided a scientific background for management strategies for the protection and restoration of eelgrass and insights into the causes of success and failure of restoration efforts that may have applications to other seagrass systems.