Quantifying the Effects of Small-Scale Heterogeneities on Flow and Transport in Undisturbed Cores from the Hanford Formation

Accelerated migration of contaminants in the vadose zone has been observed beneath tank farms at the U.S. Department of Energy’s Hanford Reservation, Richland, WA. This paper focuses on quantifying hydrologic processes that control the fate and transport of contaminants in the unsaturated sediments beneath the Hanford tank farms. The experimental approach involved the use of field relevant, long-term unsaturated nonreactive transport experiments in undisturbed sediments from the Hanford Formation. Undisturbed sediment cores were collected from a laminated fine-grained sand unit within the Hanford Formation in both the vertical direction (flow cross bedding) and the horizontal direction (flow bedding parallel). Laboratory-scale saturated and unsaturated flow experiments were conducted using multiple nonreactive tracers to investigate hydrologic processes controlling the vertical and lateral spread of contaminants. The nonreactive tracers differ in their free-water molecular diffusion coefficients, thus providing a quantitative measure of diffusional processes and the presence of immobile water. Asymmetric breakthrough curves (BTCs) and coelution of tracers were observed during saturated flow in both horizontal and vertical cores, indicating advection enhanced solute dispersion with no accompanying immobile water. Unsaturated tracer transport in the vertical and horizontal cores resulted in earlier breakthrough, asymmetric BTCs, and differential breakthrough of tracers where the elution of piperazine-1-4-bis(2-ethanesulfonic acid) (PIPES) preceded that of pentafluorobenzoic acid (PFBA), which preceded that of Br−. These results suggest that physical nonequilibrium processes (PNE) such as preferential finger flow coupled with immobile water may control the unsaturated movement of contaminants in the Hanford Formation

Variability in the freshwater balance of northern Marguerite Bay, Antarctic Peninsula: results from δ18O

We investigate the seasonal variability in freshwater inputs to the Marguerite Bay region (Western Antarctic Peninsula) using a time series of oxygen isotopes in seawater from samples collected in the upper mixed layer of the ocean during 2002 and 2003. We find that meteoric water, mostly in the form of glacial ice melt, is the dominant freshwater source, accounting for up to 5% of the near-surface ocean during the austral summer. Sea ice melt accounts for a much smaller percentage, even during the summer (maximum around 1%). The seasonality in meteoric water input to the ocean (around 2% of the near-surface ocean) is not dissimilar to that of sea ice melt (around 2% in 2002 and 1% in 2003), contradicting the assumption that sea ice processes dominate the seasonal evolution of the physical ocean environment close to the Antarctic continent. Three full-depth profiles of oxygen isotopes collected in successive Decembers (2001, 2002 and 2003) indicate that around 4 m of meteoric water is present in the water column at this time of year, and around 1 m of sea ice formed from this same water column. The predominance of glacial melt is significant, since it is known to be an important factor in the operation of the ecosystem, for example by providing a source of nutrients and modifying the physical environment to control the spatial extent and magnitude of phytoplankton blooms. The Western Antarctic Peninsula is undergoing a very rapid change in climate, with increasing ocean and air temperatures, retreating glaciers and increases in precipitation associated with changes in atmospheric circulation. As climate change continues, we expect meteoric water inputs to the adjacent ocean to rise further. Sea ice in this sector of the Antarctic has shown a climatic decrease, thus we expect a reduction in oceanic sea ice melt fractions if this change continues. Continued monitoring of the oceanic freshwater budget at the western Peninsula is needed to track these changes as they occur, and to better understand their ecological consequences

Geostatistical classification for remote sensing: an introduction

Traditional spectral classification of remotely sensed images applied on a pixel-by-pixel basis ignores the potentially useful spatial information between the values of proximate pixels. For some 30 years the spatial information inherent in remotely sensed images has been employed, albeit by a limited number of researchers, to enhance spectral classification. This has been achieved primarily by filtering the original imagery to (i) derive texture ‘wavebands’ for subsequent use in classification or (ii) smooth the imagery prior to (or after) classification. Recently, the variogram has been used to represent formally the spatial dependence in remotely sensed images and used in texture classification in place of simple variance filters. However, the variogram has also been employed in soil survey as a smoothing function for unsupervised classification. In this review paper, various methods of incorporating spatial information into the classification of remotely sensed images are considered. The focus of the paper is on the variogram in classification both as a measure of texture and as a guide to choice of smoothing function. In the latter case, the paper focuses on the technique developed for soil survey and considers the modification that would be necessary for the remote sensing case. <br/