Land-use effects on stream ecosystems: do metals from mining run-off return to land by emergence and dispersion of aquatic insects? A stable isotopes approach

Abstract

Anthropic activities cause the increase of pollutants concentrations in the environment. These can interfere in energy and nutrient flow and, consequently, endanger aquatic and terrestrial ecosystems. Metal pollutants have been caused great concern due to their environmental persistence, toxicity and incorporation capacity in food webs. Mining is an important economic activity in the world, but result in large amounts of waste, especially the concentrations of metals in the aquatic ecosystems. Aquatic invertebrates are used for evaluating ecological impacts in streams facing metal contamination. They have a key role in the energy transference in freshwater and terrestrial systems and can contribute substantially to the diet of riparian predators. In this way, emerging insects from polluted streams can act as pollutant conveyors from water to land. The use of stable isotopes can be a useful tool to understand how the metals ecosystems moves along the food chain. By comparing the isotopic composition and the metal concentration in organisms, it is possible to find if the contaminant has been biomagnified or biodispersed along the food chain. The objective of this study is to investigate if insects inhabiting streams contaminated by heavy metals from mines accumulate and disperse these metals to land. We will select streams in five pristine areas and five polluted areas. These are located near the city of Coimbra in the central region of Portugal. We will sample (i) the aquatic invertebrates with hand-nets, (ii) the emerging insects by using floating traps and (iii) terrestrial predators (riparian spiders) by hand or plastic flasks. We will identify and classify the organisms in taxonomic (family or genus) and feeding groups. We will also sample the potential food sources and the physical-chemical parameters of water. The polluted streams will be compared with reference streams to study the bioaccumulation, biomagnification and biodispersion processes. We want to understand the relationship between trophic position and the concentration of the metals in contaminated stream to understand whether metals increase, decrease or if there is no change in the consumers as we go up in the food chain. We also aim to understand how the emerging insects disperse metals in the aquatic-terrestrial interface through predation of these emerging insects. Therefore, the emerging aquatic insects are important to link the freshwater and terrestrial environments, so it is important understand you role in the dispersal of pollutants to others environments. (AU)