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Aquatic ecosystems are used for extensive rice-shrimp culture where the available water alternates seasonally between fresh and saline. Poor water quality has been implicated as a risk factor for shrimp survival; however, links between shrimp, water quality and their main food source, the natural aquatic biota inhabiting these ponds, are less well understood. We examined the aquatic biota and water quality of three ponds over an entire year in the Mekong Delta, Vietnam, where the growing season for the marine shrimp Penaeus monodon has been extended into the wet season, when waters freshen. The survival (30–41%) and total areal biomass (350–531 kg ha−1) of shrimp was constrained by poor water quality, with water temperatures, salinity and dissolved oxygen concentrations falling outside known optimal ranges for several weeks. Declines in dissolved oxygen concentration were matched by declines in both shrimp growth rates and lipid content, the latter being indicative of nutritional condition. Furthermore, as the dry season transitioned into the wet, shifts in the taxonomic composition of phytoplankton and zooplankton were accompanied by declines in the biomass of benthic algae, an important basal food source in these systems. Densities of the benthic invertebrates directly consumed by shrimp also varied substantially throughout the year. Overall, our findings suggest that the survival, condition and growth of shrimp in extensive rice-shrimp ecosystems will be constrained when poor water quality and alternating high and low salinity negatively affect the physiology, growth and composition of the natural aquatic biota. Changes in management practices, such as restricting shrimp inhabiting ponds to the dry season, may help to address these issues and improve the sustainable productivity and overall condition of these important aquatic ecosystems. Unlabelled Image • Shrimp growing is extending into the wet season in extensive rice-shrimp ponds. • Salinity, water temperature, dissolved oxygen were often suboptimal for shrimp. • Aquatic food sources declined, compositions shifted with dry-wet season transition • Shrimp survival below 50%; growth and lipid declined with dissolved oxygen • Shrimp growth, condition, survival constrained by conditions from changing salinity [ABSTRACT FROM AUTHOR]

Adaptation to drought is particularly challenging on remote island atolls, such as those found in the Republic of the Marshall Islands (RMI), a nation of 58,000 populating 29 low-lying coral atolls spread over >2 million km2. Exposure to consecutive atmospheric hazards, such as meteorological floods and droughts diminish scarce water resources and erode the resilience of island communities. Drought impact mitigation measures must supply emergency drinking water to stricken communities, while simultaneously conserving natural sources in order to reduce their vulnerability to subsequent events. Household surveys (n = 298) and focus group discussions (n = 16) in eight RMI communities revealed that 86% of households have experienced drought and 88% reported using multiple water sources to meet normal household needs. With no surface water and a thin freshwater lens (FWL), rainwater collected from rooftops is the most common household water source. The traditional use of carved hollows in the base of coconut trees to collect rainwater ("Mammaks") appears to have been displaced by large rainwater tanks. However, rationing of rainwater for consumption only during drought was widely reported, with private wells supporting non-consumptive uses. Reverse osmosis (RO) desalination units have provided relief during drought emergencies but concerns have been raised around dependency, maintenance challenges, and loss of traditional water practices. Most notably, RO use has the potential to change the anthroposhpere by adversely affecting the FWL; 86% of RO units were installed at island-centre where excessive pumping can cause upconing, making the FWL brackish. Balancing the introduction of desalination technology to mitigate water shortages with maintenance of traditional water conservation practices to preserve the quantity and quality of the FWL is a promising strategy on island atolls that requires further investigation. Unlabelled Image • Small island states are among the most vulnerable to drought and climate change. • Cycling of multiple household water sources increases resilience to drought. • Austere usage behaviors conserve rainwater for drinking during drought. • Emergency water created using reverse osmosis presents a hazard to groundwater. [ABSTRACT FROM AUTHOR]

It is a substantial challenge to quantify the benefits which ecosystems provide to water supply at scales large enough to support policy making. This study tested the hypothesis that vegetation could reduce riverbank erosion, and therefore contribute to reducing turbidity and the cost of water supply, during a large magnitude flood along a 62 km riparian corridor where land cover differed substantially from natural conditions. Several lines of evidence were used to establish the benefits that vegetation provided to reducing eleven riverbank erosion processes over 1688 observations. The data and analyses confirmed that vegetation significantly reduced the magnitude of the riverbank erosion process which was the largest contributor to total erosion volume. For this process, a 1% increase in canopy cover of trees higher than five metres reduced erosion magnitude by between 2 and 3%. Results also indicate that riverbank erosion was likely to be affected by direct changes to the riparian corridor which influenced longitudinal coarse sediment connectivity. When comparing the impact of these direct changes on a relative basis, sand and gravel extraction was likely to be the dominant contributor to changed erosion rates. The locations where erosion rates had substantially increased were of limited spatial extent and in general substantial change in river form had not occurred. This suggests that the trajectory of river condition and increasing turbidity are potentially reversible if the drivers of river degradation are addressed through an ecosystem restoration policy. Unlabelled Image • 1% increase in vegetation canopy cover reduced riverbank erosion by between 2 and 3% • Changes to longitudinal coarse sediment connectivity also affected riverbank erosion • Both drivers need to be addressed for effective ecosystem restoration [ABSTRACT FROM AUTHOR]