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Elevated major ions (or salinity) are recognised as being a key contributor to the toxicity of many mine waste waters but the complex interactions between the major ions and large inter-species variability in response to salinity, make it difficult to relate toxicity to causal factors. This study aimed to determine if the toxicity of a typical saline seepage water was solely due to its major ion constituents; and determine which major ions were the leading contributors to the toxicity. Standardised toxicity tests using two tropical freshwater species Chlorella sp. (alga) and Moinodaphnia macleayi (cladoceran) were used to compare the toxicity of 1) mine and synthetic seepage water; 2) key major ions (e.g. Na, Cl, SO4 and HCO3); 3) synthetic seepage water that were modified by excluding key major ions. For Chlorella sp., the toxicity of the seepage water was not solely due to its major ion concentrations because there were differences in effects caused by the mine seepage and synthetic seepage. However, for M. macleayi this hypothesis was supported because similar effects caused by mine seepage and synthetic seepage. Sulfate was identified as a major ion that could predict the toxicity of the synthetic waters, which might be expected as it was the dominant major ion in the seepage water. However, sulfate was not the primary cause of toxicity in the seepage water and electrical conductivity was a better predictor of effects. Ultimately, the results show that specific major ions do not clearly drive the toxicity of saline seepage waters and the effects are probably due to the electrical conductivity of the mine waste waters.

Elevated major ions (or salinity) are recognised as being a key contributor to the toxicity of many mine waste waters but the complex interactions between the major ions and large inter-species variability in response to salinity, make it difficult to relate toxicity to causal factors. This study aimed to determine if the toxicity of a typical saline seepage water was solely due to its major ion constituents; and determine which major ions were the leading contributors to the toxicity. Standardised toxicity tests using two tropical freshwater species Chlorella sp. (alga) and Moinodaphnia macleayi (cladoceran) were used to compare the toxicity of 1) mine and synthetic seepage water; 2) key major ions (e.g. Na, Cl, SO4 and HCO3); 3) synthetic seepage water that were modified by excluding key major ions. For Chlorella sp., the toxicity of the seepage water was not solely due to its major ion concentrations because there were differences in effects caused by the mine seepage and synthetic seepage. However, for M. macleayi this hypothesis was supported because similar effects caused by mine seepage and synthetic seepage. Sulfate was identified as a major ion that could predict the toxicity of the synthetic waters, which might be expected as it was the dominant major ion in the seepage water. However, sulfate was not the primary cause of toxicity in the seepage water and electrical conductivity was a better predictor of effects. Ultimately, the results show that specific major ions do not clearly drive the toxicity of saline seepage waters and the effects are probably due to the electrical conductivity of the mine waste waters.

Chronic toxicity tests were conducted to assess the effect of Cu, Cr and Pb on Moinodaphnia macleayi and Ceriodaphnia dubia -two cladoceran species from the Argentinian Fluvial Littoral Zone (AFLZ)- and Daphnia magna -an holarctic species-. The specimens were exposed to three concentrations of each metal. As endpoints, the number of living and dead organisms, molts, neonates released, and the age of first reproduction were recorded. Chronic assays showed that Cu significantly affected the analyzed life history traits in the three species. The lowest Pb and Cr concentrations did not affect survival, molting or fecundity in D. magna. Conversely, in M. macleayi and C. dubia, survival, molting and fecundity showed highly significant differences in all the concentrations tested compared to control assay. The present study stresses the importance of using biological parameters as bioindicators, as well as the study species from the Southern Hemisphere to assess metal pollution.

Life table response experiments (LTRE) were performed to investigate effects of food supply on density-dependent effects on life history and population responses of the tropical cladoceran Moinodaphnia macleayi to cadmium. Its short life cycle and relatively constant age-specific birth and mortality rates allowed population growth rates (λ) to be accurately estimated from short life table experiments and by using a simplified two-stage demographic model. Decomposition and regression analyses of λ showed that density-dependent effects on population responses to cadmium were modified by food availability through density-dependent effects on mortality and reproductive rate. At moderate food levels (1.8 µg C/mL of Chorella vulgaris) and low densities (<125 animals/L), the effects of cadmium on λ decreased with increasing population density, due to antagonistic effects between the contributions of age at first reproduction and daily reproduction on λ. At high densities (>125 animals/L), the negative effects of cadmium on daily reproduction rates increased with density; hence density promoted the negative effects of cadmium on λ. At low food levels (0.4 (µg C/mL of Chorella vulgaris), increasing population density reduced juvenile survival, increasing food per head. Thus adverse effects of cadmium on reproduction, which had the greatest contribution to λ, were buffered by increasing population density. Regression analysis performed on population responses across increasing population density levels and cadmium concentrations showed that at high densities and low food levels ecological compensation will prevent populations at the steady-state equilibrium size from being driven to extinction by toxicity effects at the individual level. Alternatively, at low densities, when food availability is not limiting, exposure to toxic substances can increase extinction probability. These results indicate that risk assessment procedures based on demographic analysis performed at low densities and high food levels may overestimate the ecological risk posed by toxic substances.

A study of the cladoceran community in three rice fields at Nakhon Si Thammarat was carried out from June to September 2007. A total of 21 taxa of Cladocera was recorded. Of these, nine belong to the family Chydoridae, three are from the Macrothricidae, two each from the families Bosminidae, Daphniidae, Moinidae, and Sididae, and one species from the family Ilyocryptidae. The primary species of these three areas were Moinodaphnia macleayi, Diaphanosoma excisum, and Bosminopsis deitersi, and these were also the most frequently found taxa. The dominant species changed throughout a crop cycle: during the seedling stage, B. deitersi (27.91%); during the growing period, Macrothrix triserialis (30.05%); and in the harvesting period, D. excism (35.40%). Nitrogen, nitrite, and phosphate were shown to play a major role in establishing the distribution of the cladoceran community over a crop cycle. Une étude de la communauté des Cladocères dans trois rizières à Nakhon Si Thammarat a été menée de juin à septembre 2007. Au total, 21 taxons de Cladocères ont été identifié. Parmi ceux-ci, neuf appartiennent à la famille des Chydoridae, trois à la famille des Macrothricidae, deux à chacune des familles Bosminidae, Daphniidae, Moinidae et Sididae et une espèce à la famille des Ilyocryptidae. Les espèces typiques de ces trois régions sont Moinodaphnia macleayi, Diaphanosoma excisum et Bosminopsis deitersi, et ce sont aussi les taxons les plus fréquemment trouvés. Les espèces dominantes changeaient au cours d'un cycle de récolte: au cours du repiquage, l'espèce dominante était B. deitersi (27,91%); pendant la phase de croissance, Macrothrix triserialis (30,05%); et dans la période de récolte D. excisum (35,40%). L'azote, les nitrites et les phosphates sont démontrés comme jouant un rôle majeur en déterminant la répartition de la communauté des Cladocères au cours du cycle de culture.

The acute salinity tolerance of three tropical freshwater cladoceran species, M. macleayi, C. rigaudii and D. brachyurum was determined. The existence of these species represented new records for Trinidad and Tobago, a tropical Caribbean island. It has a large oil based industry, in which, the primary effluent (saline produced water) is discharged directly into many freshwater systems. Cladoceran species are used routinely in temperate regions, to assess the impacts of chemicals and effluents in freshwater systems. However, relatively few studies have assessed the salinity tolerance of these organisms. Test organisms were assayed using seven salinity treatments (0, 1, 3, 5, 10, 15, 20, 25[per thousand]) prepared by volumetrically mixing natural filtered seawater with dilution water. C. rigaudii had a 48 h LC50 of 1.6[per thousand], M. macleayi 1.5[per thousand] and D. brachyurum <1[per thousand]. The CSmax (critical salinity maximum) for C. rigaudii and M. macleayi was 3[per thousand] after 48 h, compared to 1[per thousand] for D. brachyurum. There was no salinity value at which there was 100% survival. The resulting salinity response curve was a straight line which indicated that each species was intolerant of salt. Consequently, any of these can be considered as a representative freshwater organism for toxicity testing in Trinidad and Tobago.