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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.

informacion[at]ebd.csic.es

Referencia: 

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. https://doi.org/10.1007/s11273-020-09766-5

Read the full press release (Spanish)


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Low levels of chemical anthropogenic pollution may threaten amphibians by impairing predator recognition

Low levels of chemical anthropogenic pollution may threaten amphibians by impairing predator recognition

Recent studies suggest that direct mortality and physiological effects caused by pollutants are major contributing factors to global amphibian decline. This study shows how sublethal concentrations of pollutants can disrupt the ability of amphibian larvae to recognize their natural predators, hence increasing the risk of predation in the populations. This indirect effect is indeed much more important since very low amounts of pollutants are ubiquitous, and environmental efforts are mostly directed towards preventing lethal spills. Researches have compared the swimming activity of tadpoles of the western spadefoot toad, Pelobates cultripes, in the presence and absence of water-borne chemical cues from a common predator –nymphs of the dragonfly Anax imperator–, at different concentrations of two contaminants present in natural waters: humic acid and ammonium nitrate. Tadpoles reduced swimming activity in response to predator cues in the absence of pollutants, whereas they remained unresponsive to these cues when either humic acid or ammonium nitrate was added to the water, even at low concentrations. Alteration of the natural chemical environment of aquatic systems by pollutants may represent a serious threat for amphibian populations. informacion[at]ebd.csic.es Polo-Cavia et el (2016) Low levels of chemical anthropogenic pollution may threaten amphibians by impairing predator recognition Aquat Toxicol 172: 30-35 doi:10.1016/j.aquatox.2015.12.019


http://www.sciencedirect.com/science/article/pii/S0166445X1530134X