Management actions to mitigate the occurrence of pharmaceuticals in river networks in a global change context.

Human consumption of pharmaceuticals leads to high concentrations of pharmaceuticals in wastewater, which is usually not or insufficiently collected and treated before release into freshwater ecosystems. There, pharmaceuticals may pose a threat to aquatic biota. Unfortunately, occurrence data of pharmaceuticals in freshwaters at the global scale is scarce and unevenly distributed, thus preventing the identification of hotspots, the prediction of the impact of Global Change (particularly streamflow and population changes) on their occurrence, and the design of appropriate mitigation actions. Here, we use diclofenac (DCL) as a typical pharmaceutical contaminant, and a global model of DCL chemical fate based on wastewater sanitation, population density and hydrology to estimate current concentrations in the river network, the impact of future changes in runoff and population, and potential mitigation actions in line with the Sustainable Development Goals. Our model is calibrated against measurements available in the literature. We estimate that 2.74 ± 0.63% of global river network length has DCL concentrations exceeding the proposed EU Watch list limit (100 ng L-1). Furthermore, many rivers downstream from highly populated areas show values beyond 1000 ng L-1, particularly those associated to megacities in Asia lacking sufficient wastewater treatment. This situation will worsen with Global Change, as streamflow changes and human population growth will increase the proportion of the river network above 100 ng L-1 up to 3.10 ± 0.72%. Given this background, we assessed feasible source and end-of-pipe mitigation actions, including per capita consumption reduction through eco-directed sustainable prescribing (EDSP), the implementation of the United Nations Sustainable Development Goal (SDG) 6 of halving the proportion of population without access to safely managed sanitation services, and improvement of wastewater treatment plants up to the Swiss standards. Among the considered end-of-pipe mitigation actions, implementation of SDG 6 was the most effective, reducing the proportion of the river network above 100 ng L-1 down to 2.95 ± 0.68%. However, EDSP brought this proportion down to 2.80 ± 0.64%. Overall, our findings indicate that the sole implementation of technological improvements will be insufficient to prevent the expected increase in pharmaceuticals concentration, and that technological solution need to be combined with source mitigation actions.

Humans reshape wetlands: Unveiling the last 100 years of morphological changes of the Mara Wetland, Tanzania.

The Lower Mara River and Wetland, Tanzania, is an important ecosystem and unique water resource for a vast semi-arid area. The river, an affluent of Lake Victoria, and the wetland are experiencing morphological and vegetation changes resulting in channel avulsions and wetland expansion. This study analyses the changes over the last 100 years and investigates natural and anthropogenic behaviors to explain the increase of the Mara Wetland area. We collated historical topographic maps and satellite images. We conducted two field surveys in low and high flow condition with an unmanned aerial vehicle, a sonar and an ADCP. We mapped selected areas as well as the bed topography in some stretches of the river, measured discharges, and collected river bed and suspended sediment samples. The analysis of the sediments shows that the wetland system, dominated by papyrus sp., is very efficient in trapping sediment, releasing clear water to the Lake Victoria. The historical reconstruction using topographic maps, satellite images and a multivariable analysis including hydrology and land cover, shows that 4 major avulsions occurred in the last 70 years due to a combination of natural behaviors, hydrological fluctuations and anthropogenic factors such as basin deforestation, farming and grazing along the river banks and in the wetland. Each avulsion led to substantial expansion of the wetland. Combined, they increased the wetland area by a factor of 3.6. Describing the Lower Mara River dynamic behavior, this work provides relevant information for sustainable future water and sediment management in order to preserve wetland habitats and natural resources.