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Doñana's water quality, in danger due to intensive agriculture and a poor residual water treatment

Irene Paredes, researcher of the study

Eutrophication is a major cause of wetland degradation worldwide. In recent decades, reductions in nutrient inputs have led to improvements in water quality in many rivers and lakes in central and northern Europe, but long-term trends are less clear in southern Europe. The Doñana Biological Station conducted the first comprehensive study of water quality in Doñana, one of the most important wetland complexes in Europe and the Mediterranean region.

The core area of Doñana is a large shallow, seasonal marsh (UNESCO World Heritage Site—WHS) that floods during rainy, cool winter months, then dries out during the summer. The marsh is fed by three main streams whose catchments are within a Biosphere Reserve but are impacted by greenhouses (for cultivating fruit, irrigated with groundwater), poorly treated urban wastewaters and tourism.

From 2013 to 2016, the research team monitored nutrient and phytoplankton chlorophyll-a (chla) concentrations in surface waters of the Doñana marsh and the three main streams. They quantified changes in greenhouse cover since 1995 using satellite images. Nutrient concentrations in streams were consistently higher than in the marsh, particularly in the Partido and Rocina streams that regularly reached concentrations equivalent to a "bad physico-chemical status" under the EU Water Framework Directive (WFD), and whose catchments suffered a fivefold expansion of greenhouses from 1995 to 2016.

The Partido was the most polluted stream, and the most affected by wastewater effluents, and had particularly high concentrations of NH4+ and NO2? across seasons. Patterns in chla concentrations were less consistent, but streams generally had higher concentrations than the marsh. Nutrient concentrations in spot samples within the marsh largely depended on a combination of evaporation (as revealed by higher stable isotope ?2H values in the water column) and spatial processes (concentrations increase close to stream entry points, where conductivity is lower).

Anthropogenic nutrient pollution in entry streams is a serious problem in Doñana, with extensive stretches too toxic for fish. Reinforcement of policies aimed at reducing nutrient inputs to Doñana are urgently required to meet the biodiversity conservation and environmental objectives for the WHS and WFD, respectively. Paradoxically, the marsh is currently relied upon to purify the water entering from streams.



Paredes, I., Ramírez, F., Aragonés, D., Bravo, M.A., G. Forero, M., Green, A.J. (2021). Ongoing anthropogenic eutrophication of the catchment area threatens the Doñana World Heritage Site (South-west Spain). Wetlands Ecology and Management.

Read the full press release (Spanish)

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Combined effects of global change on bumblebees

Combined effects of global change on bumblebees

The decline in bee populations has recently attracted much attention from researchers, conservationists and the general public, with insect-mediated pollination being a key process for terrestrial ecosystems as well as for crop production. The conclusions of different studies suggest that this decline is the result of pressures from different drivers of global change such as habitat destruction, pesticide use and climate warming. However, there is increasing evidence that these pressures do not act in isolation, and may have complex interactive effects beyond the sum of their individual effects. The interactive effect on bumblebee colonies of three of these global change pressures was explored: climate change, exposure to pesticides, and landscape transformation, through a series of field experiments that simulate these global change drivers independently and in combination. In this work, the joint effect of these stressors on the reproductive capacity of the colonies is analysed. The results show that bumblebees have larger reproductive success at high temperatures, but only when there are abundant floral resources. In addition, exposure to pesticides was observed to produce a decrease in the number of males. Furthermore, the size of both queens and workers increased at high temperatures but the size of queens decreased with increased floral resources. Interestingly, bumblebees increased the investment in wax and silk used to protect queen cocoons from high temperatures, and need to actively ventilate the colonies using workers that fan their wings at the colony entrance. These two mechanisms may cushion the negative impacts of high temperatures by either better insulating the colony or reducing heat excess. However, these kinds of responses may be only affordable when resources are not limiting. This experiment suggests that the interaction between different stressors may not be additive and that the mechanisms to cushion some of the impacts may not be enough when multiple stressors act simultaneously. informacion[at] Zaragoza-Trella et al (2020) Interactions among global change pressures act in a non-additive way on bumblebee individuals and colonies. Functional Ecol DOI 10.1111/1365-2435.13703