Contamination of drinking water resources in the Mekong delta floodplains: arsenic and other trace metals pose serious health risks to population

This study presents a transnational groundwater survey of the 62,000 km(2) Mekong delta floodplain (Southern Vietnam and bordering Cambodia) and assesses human health risks associated with elevated concentrations of dissolved toxic elements. The lower Mekong delta generally features saline groundwater. However, where groundwater salinity is <1 g L(-)(1) Total Dissolved Solids (TDS), the rural population started exploiting shallow groundwater as drinking water in replacement of microbially contaminated surface water. In groundwater used as drinking water, arsenic concentrations ranged from 0.1-1340 microg L(-)(1), with 37% of the studied wells exceeding the WHO guidelines of 10 microg L(-)(1) arsenic. In addition, 50% exceeded the manganese WHO guideline of 0.4 mg L(-)(1), with concentrations being particularly high in Vietnam (range 1.0-34 mg L(-)(1)). Other elements of (minor) concern are Ba, Cd, Ni, Se, Pb and U. Our measurements imply that groundwater contamination is of geogenic origin and caused by natural anoxic conditions in the aquifers. Chronic arsenic poisoning is the most serious health risk for the ~2 million people drinking this groundwater without treatment, followed by malfunction in children's development through excessive manganese uptake. Government agencies, water specialists and scientists must get aware of the serious situation. Mitigation measures are urgently needed to protect the unaware people from such health problems.     

A proposed coast-wide reference monitoring system for evaluating wetland restoration trajectories in Louisiana

Wetland restoration efforts conducted in Louisiana under the Coastal Wetlands Planning, Protection and Restoration Act require monitoring the effectiveness of individual projects as well as monitoring the cumulative effects of all projects in restoring, creating, enhancing, and protecting the coastal landscape. The effectiveness of the traditional paired-reference monitoring approach in Louisiana has been limited because of difficulty in finding comparable reference sites. A multiple reference approach is proposed that uses aspects of hydrogeomorphic functional assessments and probabilistic sampling. This approach includes a suite of sites that encompass the range of ecological condition for each stratum, with projects placed on a continuum of conditions found for that stratum. Trajectories in reference sites through time are then compared with project trajectories through time. Plant community zonation complicated selection of indicators, strata, and sample size. The approach proposed could serve as a model for evaluating wetland ecosystems.     

Water management strategies against toxic Microcystis blooms in the Dutch delta.

To prevent flooding of the Dutch delta, former estuaries have been impounded by the building of dams and sluices. Some of these water bodies, however, experience major ecological problems. One of the problem areas is the former Volkerak estuary that was turned into a freshwater lake in 1987. From the early 1990s onward, toxic Microcystis blooms dominate the phytoplankton of the lake every summer. Two management strategies have been suggested to suppress these harmful algal blooms: flushing the lake with fresh water or reintroducing saline water into the lake. This study aims at an advance assessment of these strategies through the development of a mechanistic model of the population dynamics of Microcystis. To calibrate the model, we monitored the benthic and pelagic Microcystis populations in the lake during two years. Field samples of Microcystis were incubated in the laboratory to estimate growth and mortality rates as functions of light, temperature, and salinity. Recruitment and sedimentation rates were measured in the lake, using traps, to quantify benthic-pelagic coupling of the Microcystis populations. The model predicts that flushing with fresh water will suppress Microcystis blooms when the current flushing rate is sufficiently increased. Furthermore, the inlet of saline water will suppress Microcystis blooms for salinities exceeding 14 g/L. Both management options are technically feasible. Our study illustrates that quantitative ecological knowledge can be a helpful tool guiding large-scale water management.