An assessment of the chronic toxicity of the synthetic pyrethroid, fenvalerate, to Daphnia galeata mendotae, using life tables

The effects of chronic exposure to fenvalerate, a synthetic pyrethroid insecticide, on the cladoceran Daphnia galeata mendotae were evaluated under laboratory conditions. The daphnids were exposed for their entire life cycle to concentrations ranging from 0.005 to 0.1 microg fenvalerate litre(-1). The parameters used to determined toxicity were survival, time to first reproduction, reproductive frequency, number of young per brood, cumulative brood size, intrinsic rate of natural increase (r(m)), generation time (T) and net reproductive rate (R(0)). A concentration of 0.005 microg fenvalerate litre(-1) resulted in an increase in longevity but a decrease in production of young. Higher concentrations caused a decrease in survival. Studies of shorter duration than the complete life cycle of the organisms would not have detected toxicity at such low levels. The intrinsic rate of natural increase, r(m), was not affected by fenvalerate until concentration reached 0.05 microg litre(-1) and r(m) decreased to 0.113 from 0.238. A concentration of 0.01 microg litre(-1) caused the net reproductive rate, R(0), and the generation time, T, to decrease to 73.2 offspring per female and 17.3 days from 125.9 offspring per female and 20.3 days, respectively.     

Predicting the biological condition of streams: use of geospatial indicators of natural and anthropogenic characteristics of watersheds

We developed and evaluated empirical models to predict biological condition of wadeable streams in a large portion of the eastern USA, with the ultimate goal of prediction for unsampled basins. Previous work had classified (i.e., altered vs. unaltered) the biological condition of 920 streams based on a biological assessment of macroinvertebrate assemblages. Predictor variables were limited to widely available geospatial data, which included land cover, topography, climate, soils, societal infrastructure, and potential hydrologic modification. We compared the accuracy of predictions of biological condition class based on models with continuous and binary responses. We also evaluated the relative importance of specific groups and individual predictor variables, as well as the relationships between the most important predictors and biological condition. Prediction accuracy and the relative importance of predictor variables were different for two subregions for which models were created. Predictive accuracy in the highlands region improved by including predictors that represented both natural and human activities. Riparian land cover and road-stream intersections were the most important predictors. In contrast, predictive accuracy in the lowlands region was best for models limited to predictors representing natural factors, including basin topography and soil properties. Partial dependence plots revealed complex and nonlinear relationships between specific predictors and the probability of biological alteration. We demonstrate a potential application of the model by predicting biological condition in 552 unsampled basins across an ecoregion in southeastern Wisconsin (USA). Estimates of the likelihood of biological condition of unsampled streams could be a valuable tool for screening large numbers of basins to focus targeted monitoring of potentially unaltered or altered stream segments.     

Land User Participation in Developing a Computerised Decision Support System for Combating Desertification

Combating desertification in natural rangelands has recently become a priority in large parts of southern Africa. Rangeland managers, farmers, scientists, conservationists and land users have been applying a variety of restoration technologies to address this problem. Bush encroachment, as part of the desertification process, involves the natural replacement of the herbaceous plant cover by undesirable problem woody species. The active and passive restoration technologies that are applied, are mainly based on indigenous knowledge and include the chemical, mechanical or manual reclamation of unproductive rangelands, as well as the combating of woody and alien species encroachment. Indigenous practices and knowledge play a major role in the effectiveness and success rate of these technologies. This project faces the challenge of bringing together both local and scientific knowledge in a single user-friendly, computerised Decision Support System (DSS) which is directly accessible by land users to support them in the process of decision making, concerning the combating of desertification. Case studies from central and northern Namibia were used to combine qualitative and quantitative data to develop this Decision Support System. The DSS currently consists of two databases and an expert system, which evaluates the results of land users’ management practices, and provides easily accessible information and advice for participants in the system, based on the incorporated data. The DSS is also linked to national and international web sites and databases to offer a wider range of information on technologies concerning agricultural and conservation practices.     

IMPACTS OF VISITORS ON SOIL AND VEGETATION OF THE RECREATIONAL AREA “NACIMIENTO DEL RÍO MUNDO” (CASTILLA-LA MANCHA, SPAIN)

This study examines the effects of recreational use on the soil and vegetation at a site of ecological importance (Nacimiento del Río Mundo, Albacete, Spain). The most visited sites showed increased soil compaction of approximately 50%, bare ground increase to 61 ± 10% and a decrease in richness (from 25 ± 2 to 15 ± 2 species), diversity (from 4.0 ± 0.1 to 2.7 ± 0.4) and stratification of plant species (from 80 ± 11 to 21 ± 4%). The most visited sites had 90% less plant species as compared to the least visited. Intense use was associated with the presence of nitrophilous plant and vegetal species with a morphology adapted to heavy trampling. The recreational areas showed a distribution pattern of impact radiating outwards from the most used and degraded point. At the most visited point, Los Chorros (the spring of the river), the impact radiated outwards for about 20 m. A pilot experiment examining the effects of one-year restriction to visitors for access to a formerly impacted area showed a plant cover increase by anthropic and not by native species of 57 percent units.     

Modeling rhizofiltration: heavy-metal uptake by plant roots

The discovery of phytoaccumulation potential of plant species has led to its application for remediation of heavy-metal-contaminated soil and wastewater, which is termed as phytoextraction/rhizofiltration. For prediction, analysis, planning and cost-effective design of such systems, mathematical models not only are used as a screening tool but also provide optimal parameters like harvesting time, irrigation schedule, etc. Several laboratory and field scale studies have been carried out in the past, and mathematical expressions have been developed by various researchers for different phenomena like metal adsorption in soil, plant root growth with time, moisture and metal uptake by plant root, moisture movement in unsaturated zone, soil moisture relationship, etc. The complete design of any such phytoremediation program would require the knowledge of behavior of heavy-metal movement in soil, water and plant root system. In this paper, a model for simulating heavy-metal dynamics in soil, water and plant root system is developed and discussed. The governing non-linear partial differential equation is solved numerically by implicit finite difference method using Picard's iterative technique, and the formulation has been illustrated using a characteristic example. The source code is written in MATLAB.     

Evaluation of groundwater quality and its suitability for drinking and agricultural use in Thanjavur city, Tamil Nadu, India

As groundwater is a vital source of water for domestic and agricultural activities in Thanjavur city due to lack of surface water resources, groundwater quality and its suitability for drinking and agricultural usage were evaluated. In this study, 102 groundwater samples were collected from dug wells and bore wells during March 2008 and analyzed for pH, electrical conductivity, temperature, major ions, and nitrate. Results suggest that, in 90% of groundwater samples, sodium and chloride are predominant cation and anion, respectively, and NaCl and CaMgCl are major water types in the study area. The groundwater quality in the study site is impaired by surface contamination sources, mineral dissolution, ion exchange, and evaporation. Nitrate, chloride, and sulfate concentrations strongly express the impact of surface contamination sources such as agricultural and domestic activities, on groundwater quality, and 13% of samples have elevated nitrate content (>45 mg/l as NO₃). PHREEQC code and Gibbs plots were employed to evaluate the contribution of mineral dissolution and suggest that mineral dissolution, especially carbonate minerals, regulates water chemistry. Groundwater suitability for drinking usage was evaluated by the World Health Organization and Indian standards and suggests that 34% of samples are not suitable for drinking. Integrated groundwater suitability map for drinking purposes was created using drinking water standards based on a concept that if the groundwater sample exceeds any one of the standards, it is not suitable for drinking. This map illustrates that wells in zones 1, 2, 3, and 4 are not fit for drinking purpose. Likewise, irrigational suitability of groundwater in the study region was evaluated, and results suggest that 20% samples are not fit for irrigation. Groundwater suitability map for irrigation was also produced based on salinity and sodium hazards and denotes that wells mostly situated in zones 2 and 3 are not suitable for irrigation. Both integrated suitability maps for drinking and irrigation usage provide overall scenario about the groundwater quality in the study area. Finally, the study concluded that groundwater quality is impaired by man-made activities, and proper management plan is necessary to protect valuable groundwater resources in Thanjavur city.     

Estimating Trophic State Proportions of a Regional Lake Population: Are Larger Samples Always Better?

During the summers of 1991–1994, the Environmental Monitoringand Assessment Program (EMAP) sampled 344 lakes throughout thenortheastern United States using a proportional stratified sampling design based on lake size. Approximately one-quarter ofthe 344 lakes were sampled each year (4 years) for totalphosphorus to determine the proportion (and associated95% confidence intervals) of the northeast lake population 1ha (11,076 ± 1,699 lakes) that was in oligotrophic,mesotrophic, eutrophic, or heupereutropic (4 classes) conditionaccording to the total phosphorus criteria of the North AmericaLake Manegement Society. Estimates for the second, third, andfourth yr were developed as cumulative of the previous yrsamples and the current yr samples for the northeast as a wholeand for each of its three ecoregions (4 regions). New confidence intervals were computed for each cumulative yrcondition estimate. This produced a total (4 years × 4classes × 4 regions) of 64 cumulative yr tropic conditionestimates. Confidence intervals for 21% of these estimates didnot shorten with increased sample size. This phenomena raisedquestions about the accuracy of estimates based on cumulativesampling procedures. We explain why and how the phenomenon comesabout with both straight random and proportional randomsampling. Further, we present an example of the effects thisphenomenon has on lake tropic state condition estimates in thenortheastern United States.