Tidal along-shore groundwater flow in a coastal aquifer

Cross-shore interactions between the ocean and a coastal aquifer have been studied extensively, whereas the corresponding along-shore case has seldom been examined. This paper presents a numerical model that simulates two-dimensional groundwater flow averaged over the thickness of a coastal aquifer. The model is used to examine the essential features of tide-induced, along-shore effects on an aquifer adjacent to a cross-shore river. The results show that the tide, which fluctuates the water level in the river, induces groundwater table fluctuations and oscillating flows in the along-shore direction. This occurs even at locations much further inland than tidal cross-shore fluctuations can propagate. However, the magnitude of along-shore water table fluctuations and flow velocity at a given cross-shore distance decreases with the distance from the river in the same manner as cross-shore tidal fluctuations. The along-shore groundwater flow, together with the cross-shore flow, forms horizontal circulation and increases mixing of solute in the aquifer. Over a tidal period, a large amount of water exchange occurs at the river-aquifer and ocean-aquifer interfaces, leading to increased transfer of chemicals between the three water bodies. These results have implications for the management of waste discharge in estuaries and coastal aquifers.     

Laboratory Evaluations of the Thermal Degradation Properties of Toxic Organic Materials in Sewage Sludge

Laboratory thermal decomposition studies were performed to evaluate potential emissions from sewage sludge incinerators. Precisely controlled thermal decomposition experiments were conducted on sludge spiked with mixtures of hazardous organic compounds, on mixtures of pure compounds without sludge, and on unspiked sludge. Experiments were conducted in nitrogen and air atmospheres with gas phase reaction times of 2.0 seconds over the temperature range 300°C-1000°C.

It was found that sludge inhibited the decomposition of moderately stable spiked contaminants but accelerated the decomposition of the most stable components. This effect was attributed to radical scavengers produced by the sludge matrix at lower temperatures which then decomposed at higher temperatures. A multiple hearth simulation study suggested that most of the organic material present In the sludge matrix is vaporized within the upper hearths that are held at lower temperatures and may consequently escape from such incinerators undestroyed. A number of stable byproducts resulted from the sludge decomposition that may be of environmental concern.     

Observations Less than the Analytical Limit of Detection: A New Approach

Abstract

Solutions are given for plume rise assuming a power-law wind speed profile in a stably stratified layer for point and finite sources with initial vertical momentum and buoyancy. For a constant wind speed, these solutions simplify to the conventional plume rise equations in a stable atmosphere. In a shear layer, the point of maximum rise occurs further downwind and is slightly lower compared with the plume rise with a constant wind speed equal to the wind speed at the top of the stack. If the predictions with shear are compared with predictions for an equivalent average wind speed over the depth of the plume, the plume rise with shear is higher than plume rise with an equivalent average wind speed.     

Structuring sustainability science

It is urgent in science and society to address climate change and other sustainability challenges such as biodiversity loss, deforestation, depletion of marine fish stocks, global ill-health, land degradation, land use change and water scarcity. Sustainability science (SS) is an attempt to bridge the natural and social sciences for seeking creative solutions to these complex challenges. In this article, we propose a research agenda that advances the methodological and theoretical understanding of what SS can be, how it can be pursued and what it can contribute. The key focus is on knowledge structuring. For that purpose, we designed a generic research platform organised as a three-dimensional matrix comprising three components: core themes (scientific understanding, sustainability goals, sustainability pathways); cross-cutting critical and problem-solving approaches; and any combination of the sustainability challenges above. As an example, we insert four sustainability challenges into the matrix (biodiversity loss, climate change, land use changes, water scarcity). Based on the matrix with the four challenges, we discuss three issues for advancing theory and methodology in SS: how new synergies across natural and social sciences can be created; how integrated theories for understanding and responding to complex sustainability issues can be developed; and how theories and concepts in economics, gender studies, geography, political science and sociology can be applied in SS. The generic research platform serves to structure and create new knowledge in SS and is a tool for exploring any set of sustainability challenges. The combined critical and problem-solving approach is essential.     

Macrofaunal recolonisation following the intertidal placement of fine-grained dredged material

Dredged material is increasingly being regarded as a potential resource, and one of its many uses is to create and/or improve intertidal habitats (i.e. beneficial use). However, uncertainties over the longer-term environmental consequences of such schemes have, to date, limited the practice to small-scale applications in UK waters. This paper studies the macrofaunal recolonisation of fine-grained dredged material recharged concurrently at four adjacent recharge areas along the south-east coast of the UK in order to facilitate predictions regarding the recolonisation of comparable schemes and, thereby, to promote effective environmental management. During the 2-year study period, the four recharge areas were distinctly different in terms of their environmental characteristics, primarily wave exposure and bed level. These conditions resulted in different macrofaunal recolonisation rates and community structures. While the low-level, wave-sheltered area experienced rapid recolonisation, the process was delayed until 12 months post-recharge at the relatively wave-exposed areas. Bed level differences resulted in distinctly different communities in wave-sheltered areas but not under wave-exposed conditions. While we are unable to separate the effects of individual environmental variables on recolonisation, these results provide general conclusions as to the importance of environmental conditions on resulting macrofaunal communities.     

"It's not that simple": A collaborative comparison of sea ice environments, their uses, observed changes, and adaptations in Barrow, Alaska, USA, and Clyde River, Nunavut, Canada

The Arctic environment, including sea ice, is changing. The impacts of these changes to Inuit and I?upiat ways of life vary from place to place, yet there are common themes as well. The study reported here involved an exchange of hunters, Elders, and others from Barrow, Alaska, USA, and Clyde River, Nunavut, Canada, as members of a larger research team that also included visiting scientists. Although the physical environments of Barrow and Clyde River are strikingly different, the uses of the marine environment by residents, including sea ice, had many common elements. In both locations, too, extensive changes have been observed in recent years, forcing local residents to respond in a variety of ways. Although generally in agreement or complementary to one another, scientific and indigenous knowledge of sea ice often reflect different perspectives and emphases. Making generalizations about impacts and responses is challenging and should therefore be approached with caution. Technology provides some potential assistance in adapting to changing sea ice, but by itself, it is insufficient and can sometimes have undesirable consequences. Reliable knowledge that can be applied under changing conditions is essential. Collaborative research and firsthand experience are critical to generating such new knowledge.     

Habitat-specific variation and performance trade-offs in shell armature of New Zealand mudsnails

Studies documenting phenotypic variation among populations show that ecological performance in one activity is sometimes traded off against another. Identifying environment-specific costs and benefits associated with performance trade-offs is fundamental to knowing how conflicting selection pressures shape phenotype-environment matching in populations. We studied phenotypic variation in shell armature (spininess) of the New Zealand mudsnail, Potamopyrgus antipodarum (Gray), and explored how this variability relates to performance trade-offs between flow resistance and predator deterrence. Smooth- and spiny-shell morphotypes exist in populations in New Zealand streams and lakes, but the patterns and correlates of spatial variation of these phenotypes, and the possible hydrodynamical constraints and antipredatory benefits associated with spiny shell armature, are unknown. Samples from 11 rivers and nine lakes on the South Island showed that, on average, nearly 70% of snails in streams were smooth-shelled, whereas >80% of snails in lakes were spiny, suggesting dissimilar selective pressures between habitats. A laboratory flume experiment revealed that spines collected seston (i.e., suspended algae) at current speeds <40 cm/s, making spiny morphs more prone to flow-induced dislodgment than smooth morphs. However, a fish feeding experiment showed that one benefit of spines on shells was a decrease in predation risk from the common bully (Gobiomorphus cotidianus), a widespread predator of mudsnails in both streams and lakes. All snails egested by bullies were dead, further suggesting that these fishes may exert strong lethal effects on mudsnail populations in nature. Spine expression in lakes also appeared to be temperature related. We conclude that functional trade-offs between risk of flow-induced dislodgment and risk of fish predation affect shell armature frequencies of Potamopyrgus in freshwater habitats.     

Effects of residues from municipal solid waste landfill on corn yield and heavy metal content

The effects of residues from municipal solid waste landfill, Khon Kaen Municipality, Thailand, on corn (Zea mays L.) yield and heavy metal content were studied. Field experiments with randomized complete block design with five treatments (0, 20, 40, 60 and 80% v/v of residues and soil) and four replications were carried out. Corn yield and heavy metal contents in corn grain were analyzed. Corn yield increased by 50, 72, 85 and 71% at 20, 40, 60 and 80% treatments as compared to the control, respectively. All heavy metals content, except cadmium, nickel and zinc, in corn grain were not significantly different from the control. Arsenic, cadmium and zinc in corn grain were strongly positively correlated with concentrations in soil. The heavy metal content in corn grain was within regulated limits for human consumption.