Use of an exchange method to estimate the association and dissociation rate constants of cadmium complexes formed with low-molecular-weight organic acids commonly exuded by plant roots

Organic acids released from plant roots can form complexes with cadmium (Cd) in the soil solution and influence metal bioavailability not only due to the nature and concentration of the complexes but also due to their lability. The lability of a complex influences its ability to buffer changes in the concentration of free ions (Cd); it depends on the association (, m mol s) and dissociation (, s) rate constants. A resin exchange method was used to estimate and (m mol s), which is the conditional estimate of depending on the calcium (Ca) concentration in solution. The constants were estimated for oxalate, citrate, and malate, three low-molecular-weight organic acids commonly exuded by plant roots and expected to strongly influence Cd uptake by plants. For all three organic acids, the and estimates were around 2.5 10 m mol s and 1.3 × 10 s, respectively. Based on the literature, these values indicate that the Cd- low-molecular-weight organic acids complexes formed between Cd and low-molecular-weight organic acids may be less labile than complexes formed with soil soluble organic matter but more labile than those formed with aminopolycarboxylic chelates.     

Economic Impacts of Changes in Fish Population Dynamics: The Role of the Fishermen’s Harvesting Strategies

Using a bioeconomic model of the cod (Gadus morhua) and capelin (Mallotus villosus) fisheries of the Barents Sea, this study assesses the role of the fishermen’s behavior in reducing or intensifying the effects on the stocks caused by altered population dynamics. The analysis focuses on the economic development of the fisheries employing a coupled stock size–hydrography-based fishing strategy, which attempts to maximize returns from fishing over a given number of fishing periods. Results show that if the fishing strategy is based on a short optimization period of only two fishing periods, changes in population dynamics have a direct influence on the returns from fishing due to the strong pressure on the stocks applied by the fisheries. If the strategy is based on a longer optimization period, fishing activities may be deferred to allow for stock regrowth, which improves the economic performance of the fisheries. However, in that case, the relationship between population dynamics and fishing activities becomes less clear, as even a reduction of the carrying capacities of the two species allows for an increase in the amount of fish landed without causing a stock collapse due to an increased efficiency of fleet utilization. The simulations indicate that management considerations and the time horizon of the fishing strategy dominate the influence of altered population dynamics on the development of the stocks considered in the model.     

Who are our informal recyclers? An inquiry to uncover crisis and potential in Victoria,Canada

What is considered garbage embodies a recoverable economic value, and environmental cost if not recycled. Throughout the world, the often marginalised and impoverished population earns a living through informal recycling. This is also true for Victoria, British Columbia, one of the most affluent cities in Canada. This paper discusses results of a participatory socio-economic survey involving informal recyclers in Victoria, BC to determine their livelihood determinants. The findings reveal that “binning” is an important survival strategy to generate income. A new waste-management model that considers the social and environmental context is needed. Inclusive public policies can respond to the livelihood concerns outlined in this paper by facilitating access to recyclable materials, devising occupational safety improvements and educating about alternative strategies for resource recovery. This model can contribute to the overall sustainability of the community by reducing the waste of resources and people, empowering marginalised populations and reducing the environmental impacts of natural resource use and waste disposal.     

Rapid Assessment of Organic Pollution in a West-central Mexican River Using a Family-level Biotic Index

The cost-effectiveness of rapid assessment approaches make their adaptation for use in developing countries appealing, but biological assessment methods need to be validated before use in new geographic areas. The authors tested the suitability of a family-level biotic index for use in a river in west-central Mexico that receives organic point-source pollution from untreated municipal sewage and sugar-cane processing. The biotic index was highly correlated to dissolved oxygen, and could detect different levels of pollution. Information from rapid assessment biomonitoring was used successfully by local natural resource managers to help bring about improvements in water resource management.