Prediction of bioconcentration factors under non-equilibrium conditions

With the bioconcentration of lipophilic compounds by aquatic organisms when equilibrium between water and biota is attained, the logarithm of the bioconcentration factor has a direct linear relationship with the logarithm of the octanol/water partition coefficient. In practice, however, equilibrium may not be reached, particularly for more lipophilic compounds. It is shown theoretically, and confirmed by use of published experimental results on fish, that a different direct linear relationship also exists between the logarithms of the bioconcentration factor and the partition coefficient for compounds not achieving equilibrium after a specific exposure time. Thus, non-equilibrium bioconcentration factors can be predicted from their partition coefficients. The constants in the non-equilibrium linear equation are related to those from the relationships between equilibrium bioconcentration factors and the partition coefficients, and between the first-order clearance rate constants and the partition coefficients.     

Variations in mortality of a coral-reef fish: links with predator abundance

The mortality rates of a pomacentrid Acanthochromis polyacanthus were examined in relation to the abundance of large predatory fish (>200 mm total length, TL) at two spatial scales. Survivorship was negatively related to patterns of predator abundance at a large spatial scale (hundreds of metres) over 3 yr, but not at a small spatial scale (tens of metres) over 2 yr. On the large scale, mortality was consistently greater (14 to 30%) in locations where there were greater numbers of predators, and lower in locations where predators occurred in smaller numbers. Among these locations, spatial differences in rank abundance of surviving juveniles were primarily due to mortality, whereas temporal differences in rank abundance were primarily due to initial juvenile abundance. These data suggest that impacts of large predatory fish were likely to have been greater in space than time and at the large spatial scale than the small spatial scale.     

Population differences in nerve resistance to paralytic shellfish toxins in softshell clam, <Emphasis Type="Italic">Mya arenaria</Emphasis>, associated with sodium channel mutations

The softshell clam, Mya arenaria, is a commercially important bivalve with wide latitudinal distribution in North America. Populations of clams with a history of repeated exposure to toxic Alexandrium spp. have developed a natural resistance to the paralytic shellfish toxins (PSTs) produced by these algae. An association between PST resistance in individual clams and a single mutation in the saxitoxin (STX) binding region of the α-subunit of the voltage-gated sodium (Na⁺) channel gene was previously identified. Here we establish that more than one mutation associated with nerve resistance to STX occurred at this locus. Both cDNA from mRNA and genomic DNA sequences from individual clams are identical demonstrating that both alleles are expressed simultaneously. In addition, one resistant allele per individual is sufficient to confer neural resistance to STX even though heterozygous individuals show an intermediate level of resistance to STX in in vitro nerve trunk assays.     

A preliminary risk assessment of trace elements accumulated in fish to the Indo-Pacific Humpback dolphin (Sousa chinensis) in the northwestern waters of Hong Kong

In order to assess the potential risks associated with consumption of contaminated prey items to the Indo-Pacific Humpback dolphin (Sousa chinensis), fish species (Collichthys lucida, Pseudosciaena crocea, Johnius sp., Thryssa sp., Mugil sp. and Trichiurus sp.) representing the main food items of the dolphin were collected from the northwestern waters of Hong Kong, including the Sha Chau and Lung Kwu Chau Marine Park, which form the main habitat of the dolphin in Hong Kong. Within these waters, there are several potential sources of pollution including significant inputs from the Pearl River catchment, several major sewage outfalls and a series of mud pits that receive contaminated dredged sediments. Concentrations of thirteen trace elements (Ag, As, Cd, Co, Cr, Cs, Cu, Hg, Mn, Ni, Se, V, and Zn) in the fish tissue were analyzed by inductively coupled plasma mass spectrometer (ICP-MS). An assessment of the risks of adverse effects on the dolphin due to consumption of tainted fish was undertaken using two toxic reference benchmarks, namely the reference dose (RfD) and toxicity reference value (TRV). The risk quotient (RQ) calculated for each element showed that the risks from consumption of fish were generally low and within safe limits. The risks associated with arsenic, cadmium and mercury were, however, elevated. The highest calculated RQ was associated with total arsenic; however, the majority of arsenic in marine organisms tends to be in the non-toxic organic form, and the actual risk to the dolphin due to this metalloid is likely to be lower.     

Comparison of adsorption models in reservoir simulation of enhanced coalbed methane recovery and CO2 sequestration in coal

Coalbed methane is an important resource of energy. Meanwhile CO₂ sequestration in coal is a potential management option for greenhouse gas emissions. An attractive aspect to this process is that CO₂ is adsorbed to the coal, reducing the risk of CO₂ migration to the surface. Another aspect to this is that the injected CO₂ could displace adsorbed methane leading to enhanced coalbed methane recovery. Therefore, in order to understand gas migration within the reservoir, mixed-gas adsorption models are required. Moreover, coal reservoir permeability will be significantly affected by adsorption-induced coal swelling during CO₂ injection. Coal swelling is directly related to reservoir pressure and gas content which is calculated by adsorption models in reservoir simulation. Various models have been studied to describe the pure- and mixed-gas adsorption on coal. Nevertheless, only the Langmuir and Extended Langmuir models are usually applied in coal reservoir simulations. This paper presents simulation work using several approaches to representing gas adsorption, implemented into the coal seam gas reservoir simulator SIMED II. The adsorption models are the Extended Langmuir model (ELM), the Ideal Adsorbed Solution (IAS) model and the Two-Dimensional Equation of State (2D EOS). The simulations based on one Australian and one American coal sample demonstrated that (1) the Ideal Adsorbed Solution model, in conjunction with Langmuir model as single-component isotherm, shows similar simulation results as the ELM for both coals, with the IAS model representing the experimental adsorption data more accurately than the ELM for one coal and identically with the ELM for the other coal; (2) simulation results using the 2D EOS, however, are significantly different to the ELM or IAS model for both coal samples. The magnitude of the difference is also dependent on coal swelling and the well operating conditions, such as injection pressure.     

Simulated fate and transport of metolachlor in the unsaturated zone, Maryland, USA

An unsaturated-zone transport model was used to examine the transport and fate of metolachlor applied to an agricultural site in Maryland, USA. The study site was instrumented to collect data on soil-water content, soil-water potential, ground water levels, major ions, pesticides, and nutrients from the unsaturated zone during 2002-2004. The data set was enhanced with site-specific information describing weather, soils, and agricultural practices. The Root Zone Water Quality Model was used to simulate physical, chemical, and biological processes occurring in the unsaturated zone. Model calibration to bromide tracer concentrations indicated flow occurred through the soil matrix. Simulated recharge rates were within the measured range of values. The pesticide transport model was calibrated to the intensive data collection period (2002-2004), and the calibrated model was then used to simulate the period 1984 through 2004 to examine the impact of sustained agricultural management practices on the concentrations of metolachlor and its degradates at the study site. Simulation results indicated that metolachlor degrades rapidly in the root zone but that the degradates are transported to depth in measurable quantities. Simulations indicated that degradate transport is strongly related to the duration of sustained use of metolachlor and the extent of biodegradation.     

Uptake and clearance of diesel alkanes from sediments by the Great Barrier Reef gastropod Strombus luhuanus

Sediments from the reef flat at Heron Island, Great Barrier Reef, were treated with known amounts of diesel and the uptake and clearance characteristics of the diesel n-alkanes by the gastropod Strombus luhuanus, in the field and aquaria, were measured. In each case, the uptake curve was unusual in that the concentration, expressed in terms of wet weight, reached a maxima within 24 h and then declined to relatively low levels. The maximum concentrations reached were below that in the sediments. Within the range investigated, the alkanes exhibited a substantial decline in the uptake rate-constant with increasing carbon number, tricosane exhibiting approximately 25% of the uptake rate-constant of dodecane. On the other hand, persistence, measured as the half-life, showed an increase with carbon number. Dodecane had a half life of 0.6 d and octadecane one of 2.2 d.     

Complexity in the relationship between matrix composition and inter-patch distance in fragmented habitats

The connectivity of fragmented landscapes is a function of the physical distance between suitable habitats and the characteristics of the habitat through which the animal is moving, i.e. the matrix. Experimental manipulations done to explain how spatial arrangement and composition of habitats affects biota remain scarce, particularly in marine systems. Holdfasts of the common kelp, Ecklonia radiata, are discrete units of habitat for small invertebrates (e.g. amphipods, isopods, molluscs, annelids) that can be isolated from other holdfasts by habitat, which may be less suitable (e.g. other species of algae or relatively bare space). We compared assemblages, which colonised defaunated holdfasts in experimentally created small-scale landscapes where patches of habitat (holdfasts) were distant versus close together and which had Sargassum spp. versus relatively bare space in the matrix. We also compared colonisation across matrices of crushed fucoid algae to assess whether the structural or chemical nature of algae in the matrix had the most influence on the colonisation. Assemblages in defaunted holdfasts differed between those that were close to and those that were distant from undisturbed holdfasts, where the matrix was devoid of vegetation. Where Sargassum spp. was present in the matrix, however, this difference disappeared and was possibly due to the chemical, rather than structural, characteristics of the fucoid matrix. The extent to which matrix habitat is a barrier to movement of invertebrates among holdfasts thus depends on not only how extensive it is but what type of habitat it contains. As within terrestrial systems, the nature of the matrix is also likely to be a fundamental component of the connectivity within marine systems.     

Origins and consequences of global and local stressors: incorporating climatic and non-climatic phenomena that buffer or accelerate ecological change

With research into the ecological effects of climatic change intensifying over the past decade, there has been an effort to increase the scale of experiments from a focus on individual organisms to incorporate the effects of the structure and functioning of entire ecosystems. As the scale of investigation becomes increasingly broad, however, the number of seemingly contradictory outcomes also increases. In reality, however, change or persistence of ecological patterns represents interplay of processes across diverse scales of space and time. At one extreme, non-climatic influences can dominate local and short-term processes that protect systems against change or accelerate change. Here, we draw on case studies that demonstrate such contrasting situations, presenting examples where local conditions can either ameliorate or exacerbate the predicted effects of climate change. By incorporating examples of stressors that originate and manifest at different spatial scales, we also attempt to refine some of the efforts surrounding research into the effects of climate change.