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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. 相似文献
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Peter Michael Link Uwe A. Schneider Richard S. J. Tol 《Environmental Modeling and Assessment》2011,16(4):413-429
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. 相似文献
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Lisa J. Henne Daniel W. Schneider Luis M. Martinez 《Journal of Environmental Planning and Management》2002,45(5):613-632
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. 相似文献
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