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Human Pressure and Its Effects on Water Quality and Biota in the Llobregat River

Abstract:

The Llobregat River has severely been impacted by anthropogenic pressures since long time ago. The mid and lower Llobregat basin holds an important concentration of industries, agricultural activities, and urban areas, with high associated water demand and wastewater discharge. Salt mine activities, hydropower water diversion, and flow regime alteration by dams affect both the Llobregat headwaters and middle reaches. These impacts have historically caused the degradation of riparian biological communities and the loss of habitats along the river. The high amount of information available on water quality and biological community composition allows establishing a suitable monitoring program aimed to improve its ecological status. Some measures have been applied to mitigate the impacts, and Llobregat’s biological quality status has progressively improved. The biological communities, mainly diatoms and macroinvertebrates, have recovered even those inhabiting the river mouth, but mostly during wet periods. However, some anthropogenic pressures still remain and Llobregat’s biological status is not completely restored. The high amount of small weirs and hydropower water diversion along the Llobregat and Cardener Rivers, together with flow regime regulation by dams, riparian degradation, and point nutrient discharges (from water sewage plants) and salt debris due to mine activities, result in a poor biological quality status in the mid and lower Llobregat River. Fish fauna is the most altered community, with a high number of nonnative species present. The occurrence of some priority substances and emergent pollutants (e.g., endocrine disruptors, heavy metals, pesticides, flame retardants, drugs, and pharmaceuticals), even at low concentrations, further alter the biological quality. The changes in the biological community structure in the middle part of the river can be detected by using biomarkers, and these should additionally be considered as biological monitoring tools necessary for an integral ecological status diagnosis.