Conservation ecology of headwater streams: a case study from the Pyrenees
- Autores: Alejandro López de Sancha
- Directores de la Tesis: Anna Vila Gispert (dir. tes.), Helena Guasch i Padró (codir. tes.)
- Lectura: En la Universitat de Girona ( España ) en 2022
- Idioma: inglés
- Tribunal Calificador de la Tesis: Daniel Oro de Ribas (presid.), Dani Boix (secret.), Marta Muñoz Frigola (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología del Agua por la Universidad de Girona
- Materias:
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- Resumen
Pyrenean headwater streams are singular ecosystems, with particular and sensitive abiotic characteristics in a seasonal pattern, that sustain a unique biodiversity especially sensitive to environmental change. Because of this, their ecosystem structure and function are highly threatened by many anthropogenic stressors such as the precipitation decrease and water warming promoted by climate change, damming, and metal pollution derived from mining and other human activities. An integrative assessment of these impacts by using multiple bioindicators at the same time, with both a structural and functional approach, can fill the current knowledge gap for the correct evaluation of the vulnerability of headwater streams to those stressors. This kind of streams are fundamental for the ecological integrity of whole river networks, but there is still a need of more knowledge to propose adequate management actions. Pyrenean headwater streams are a great example to appraise these topics as they are threatened by climate change and many of them are affected by damming and metal pollution. Even more, the projected evolution of water demand on this mountain range, during the current century, estimates large uncertainties in water supply, which stresses the need for adaptation strategies. In this context, a practical research aim is needed in order to properly manage and conserve these threatened ecosystems.
Considering these needs, this thesis has selected as a case study a Pyrenean headwater stream that presents a hydroelectric dam and that receives the runoff of other tributaries draining from an old antimony mine. In this study case, it was assessed i) how seasonality, damming and different precipitation regimes modulate the abiotic conditions and the biofilm and macroinvertebrate communities of these ecosystems, ii) how the macroinvertebrate community assemblage can act as a bioindicator for the anthropogenic impacts on the ecosystem structure and function of these ecosystems, iii) the use of macroinvertebrates as prey for vertebrate predators of these streams in the current changing context, and iv) the impacts of metal pollution and damming on the Pyrenean brook newt (Calotriton asper).
In Chapter 1, during a two years span, it was determined, through the analysis of the biofilm and macroinvertebrate communities of a Pyrenean headwater stream, the response of the variables linked to the structure of those communities to seasonality, the presence of a dam, different precipitation regimes, and to metal pollution. The structural metrics analysed followed a strong seasonal pattern that was altered by damming and reduction in the precipitations, due to the water flow reduction and temperature increase that they implied. This promoted an algal and macroinvertebrate biomass increase at expenses of their biodiversity, a situation that is expected to worsen in the current climate change context. The water flow reduction during the dry precipitation regime increased the concentration of metals and metalloids in the stream, but their presence downstream of the dam was lower due to the water diversion that it implied. These results suggest that the maintenance of a sufficient ecological flow in dam-impounded streams is needed in order to overcome the analysed impacts in the current climate change context. Moreover, they highlight the need of more field studies to assess how multiple anthropogenic stressors interact and threaten the ecosystem integrity of headwater streams.
In Chapter 2, the macroinvertebrate community of the stream was used as a bioindicator for the analysis of the alteration of ecosystem. The effects of seasonality, damming and different precipitation regimes were assessed on multiple ecosystemic functions indirectly calculated using taxonomic data of the macroinvertebrate community. The water flow reduction caused by damming and a decrease in precipitations promoted the autotrophy of the stream, altering the normal seasonal pattern that structures the macroinvertebrate assemblage, decreasing its biodiversity and disrupting the proportion of feeding roles. This structural change translated into an impact on the ecosystem functioning of the stream, as it caused an alteration of the direction of the trophic chain. The intensification of bottom-up trophic processes through the autotrophy promotion reduced the strength of top-down processes, decreasing the predator abundance.
In Chapter 3, we analysed the diet overlap between three vertebrate insectivorous species emblematic of Pyrenean headwater streams: Galemys pyrenaicus, Neomys fodiens and Cinclus cinclus. This diet overlap implied a trophic competition situation in which the Pyrenean desman G. pyrenaicus specialized on energetically profitable and highly available rheophile prey due to its physiologic and morphologic adaptations that allow it to capture aquatic prey more efficiently, while avoiding terrestrial individuals. This makes this species highly vulnerable to a decrease in food availability and to anthropogenic stressors that reduce the habitat quality. The obtained results show the importance of the habitat, indicating the need to maintain enough riffle sections in the stream to provide of enough quality habitat and prey to the Pyrenean desman that would allow it to effectively use its adaptations. In this regard, it is considered that the flow reduction and connectivity loss that damming causes is a serious threat for the conservation of this species, which needs of a higher awareness. In this study it was also determined that diet analyses are effective in the assessment of the food resource requirements of endangered species such as the Pyrenean desman, but they need to consider the ecology of the prey that it feeds on in order to extract reliable conclusions in prey electivity analyses.
In Chapter 4, a new population of the endangered Pyrenean brook newt, Calotriton asper, was described, and the impacts of damming and metal and metalloid pollution on it were assessed. Density of individuals, body sizes and chytridiomycosis prevalence were compared between subpopulations at each side of the dam. It was determined that metal pollution caused a decrease in both the density of individuals and the body size of the upstream subpopulation. No individuals affected by chytridiomycosis were found in this stream despite being only 8 Km apart from an infected population. More research is needed on the impacts of metals and metalloids and damming on C. asper in order to manage small populations in headwater streams affected by these anthropogenic threats, improving their conservation.
The results obtained in this thesis provide, in a conservation context, new information about the interactive impacts of climate change, damming and metal pollution on the ecosystem structure and function of the aquatic communities in headwater streams. It was observed that a reduction in precipitations had a synergistic impact with damming through the reduction of the water flow, which promoted the autotrophy of the stream and reduced its biodiversity, altering its ecosystem functioning. These results provide scientific evidence for the proposal of effective management actions for these ecosystems, such as the maintenance of an environmental flow, especially when considering additional local threats to each headwater stream such as metal pollution. The consequences of these interactive threats are especially relevant for key headwater species. On one hand, the availability of basal resources can be impaired, increasing the competition for certain preys on higher trophic levels, displacing species such as the endangered Pyrenean desman (Galemys pyrenaicus). On the other hand, the interaction of damming and metal pollution can severely affect the health and distribution of populations of sensitive species such as the Pyrenean brook newt (Calotriton asper). This thesis highlights the fact that integrative approaches, including trophic interactions, are useful to understand the effects of anthropogenic impacts on the biodiversity of headwater streams and to propose effective management and conservation actions.
