Publication
Cumulative and interactive effects of drought and chemical contamination on aquatic macroinvertebrate communities
| Summary: | Water is recognised as an essential natural resource, providing key ecosystem services for humans and being a vital support for aquatic life. However, freshwater biodiversity is declining due to conflicts with human activities. In this scope, capable monitoring tools and assessment frameworks are needed to adequately support the conservation of freshwater ecosystems and, in the European case, to comply with the goals of the EU Water Framework Directive (WFD). This need is heightened under climate change, which exacerbates and confounds other key stressors (e.g. chemical pollutants). Rivers from the Mediterranean region are particularly vulnerable to water scarcity and intermittency, which are constitutive (in dryer areas) but have also been increasing in frequency or intensity in the last decades. Stemming from this, the main aim of this Thesis was to assess the effects of water scarcity in aquatic communities across a climatic and water availability gradient, and how this is reflected in the overall ecological status of freshwaters, using benthic macroinvertebrates as a sensitive proxy. To do so, this work intended to understand how various environmental datasets (climatic, hydromorphological and physicochemical) shape macroinvertebrate communities – structurally and functionally – and explain the ecological variation between regions. Also, this study reflects on the accuracy of the WFD bioassessment scheme to evaluate the effects of multiple stressors, including water scarcity, and identifies directions for the improvement of the current toolbox. Prompted by the issues raised by the scientific community involving the ecological evaluation of freshwaters, we initially developed a reflection on how the WFD bioassessment is performed and how it can be improved to face current challenges imposed to riverine communities, including those driven by climate change. Despite the irrefutable importance of the WFD in the evaluation of freshwater ecosystems in Europe, its standard assessment scheme should be re-assessed and new avenues should be explored towards higher effectiveness. This was done by exploring the existing literature on the WFD bioassessment scheme for rivers and reviewing improvements that have been suggested by the scientific community. Following that, a conceptual scheme for an improved bioassessment was built, consisting of a tiered approach of increasing complexity and spatial resolution that includes expert judgement in all decision phases. A chapter of this Thesis is devoted to this retrospective and prospective assessment. Given the current scenario of global climate change and the increasing occurrence of extreme phenomena, we conducted a survey on benthic macroinvertebrate communities and ecological status of a set of small streams from three Portuguese regions (Regions C, N and S) featuring distinct climatic and water availability scenarios. Within each region, sampling sites were chosen in locations that are prone to suffer intermittency periods. The sampling period was preceded by an unusually long drought period in 2017, with different degrees of severity according to the region. Sampling of macroinvertebrate communities took place in the Spring of 2018 (in the aftermath of the 2017 extreme drought) and 2019 (when precipitation was closer to the norm). Data from this extensive field and laboratory work delivered three chapters included in this Thesis. Through the comparison of the communities of the regions in one single year (2019), environmental and biotic gradients among regions were clearly identified. Region C was found to be the wettest and S was the driest, with Region N occupying an intermediate position. Also, there was overall higher ecological quality in Region C than in Regions N and S. This data highlighted the shared influence of the three environmental components (climate, hydromorphology and physicochemistry) in the modulation of macroinvertebrate community structure. Then, we compared the communities and their bioindicator value between 2018 and 2019. Despite the background differences, data showed consistent environmental and ecological gradients in both years and, once again, the separation between Region C (wettest) and S (driest) and the intermediate position of Region N. Region C remained the one with overall better ecological quality. The absence of marked differences between years with different water availability history suggested that macroinvertebrates may present some degree of adaption or resilience to stressful flow fluctuations; alternatively, this may translate incomplete recovery of these communities from the 2017 impacts. Finally, a trait-based approach was applied to the biological dataset of the three regions in both years, in an effort to understand if the previously detected regional differences translated into distinct functional features of the macroinvertebrate communities. Functional richness was higher in Region C (the less affect by water scarcity), opposing Region S (with more intermittency), indicating coherence between taxonomical and functional approaches. Importantly, loss of functional diversity was noticed in water-stressed regions, but long term data are missing to assess whether this reflects local adaptation of macroinvertebrate communities to constitutive ecosystem features or rather reflects drought effects. |
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| Main Authors: | Santos, Joana Isabel Marques dos |
| Subject: | Freshwater ecosystems Macroinvertebrate communities Ecological status Mediterranean streams Water scarcity Environmental gradient Functional traits |
| Year: | 2023 |
| Country: | Portugal |
| Document type: | doctoral thesis |
| Access type: | embargoed access |
| Associated institution: | Universidade de Aveiro |
| Language: | English |
| Origin: | RIA - Repositório Institucional da Universidade de Aveiro |
| Summary: | Water is recognised as an essential natural resource, providing key ecosystem services for humans and being a vital support for aquatic life. However, freshwater biodiversity is declining due to conflicts with human activities. In this scope, capable monitoring tools and assessment frameworks are needed to adequately support the conservation of freshwater ecosystems and, in the European case, to comply with the goals of the EU Water Framework Directive (WFD). This need is heightened under climate change, which exacerbates and confounds other key stressors (e.g. chemical pollutants). Rivers from the Mediterranean region are particularly vulnerable to water scarcity and intermittency, which are constitutive (in dryer areas) but have also been increasing in frequency or intensity in the last decades. Stemming from this, the main aim of this Thesis was to assess the effects of water scarcity in aquatic communities across a climatic and water availability gradient, and how this is reflected in the overall ecological status of freshwaters, using benthic macroinvertebrates as a sensitive proxy. To do so, this work intended to understand how various environmental datasets (climatic, hydromorphological and physicochemical) shape macroinvertebrate communities – structurally and functionally – and explain the ecological variation between regions. Also, this study reflects on the accuracy of the WFD bioassessment scheme to evaluate the effects of multiple stressors, including water scarcity, and identifies directions for the improvement of the current toolbox. Prompted by the issues raised by the scientific community involving the ecological evaluation of freshwaters, we initially developed a reflection on how the WFD bioassessment is performed and how it can be improved to face current challenges imposed to riverine communities, including those driven by climate change. Despite the irrefutable importance of the WFD in the evaluation of freshwater ecosystems in Europe, its standard assessment scheme should be re-assessed and new avenues should be explored towards higher effectiveness. This was done by exploring the existing literature on the WFD bioassessment scheme for rivers and reviewing improvements that have been suggested by the scientific community. Following that, a conceptual scheme for an improved bioassessment was built, consisting of a tiered approach of increasing complexity and spatial resolution that includes expert judgement in all decision phases. A chapter of this Thesis is devoted to this retrospective and prospective assessment. Given the current scenario of global climate change and the increasing occurrence of extreme phenomena, we conducted a survey on benthic macroinvertebrate communities and ecological status of a set of small streams from three Portuguese regions (Regions C, N and S) featuring distinct climatic and water availability scenarios. Within each region, sampling sites were chosen in locations that are prone to suffer intermittency periods. The sampling period was preceded by an unusually long drought period in 2017, with different degrees of severity according to the region. Sampling of macroinvertebrate communities took place in the Spring of 2018 (in the aftermath of the 2017 extreme drought) and 2019 (when precipitation was closer to the norm). Data from this extensive field and laboratory work delivered three chapters included in this Thesis. Through the comparison of the communities of the regions in one single year (2019), environmental and biotic gradients among regions were clearly identified. Region C was found to be the wettest and S was the driest, with Region N occupying an intermediate position. Also, there was overall higher ecological quality in Region C than in Regions N and S. This data highlighted the shared influence of the three environmental components (climate, hydromorphology and physicochemistry) in the modulation of macroinvertebrate community structure. Then, we compared the communities and their bioindicator value between 2018 and 2019. Despite the background differences, data showed consistent environmental and ecological gradients in both years and, once again, the separation between Region C (wettest) and S (driest) and the intermediate position of Region N. Region C remained the one with overall better ecological quality. The absence of marked differences between years with different water availability history suggested that macroinvertebrates may present some degree of adaption or resilience to stressful flow fluctuations; alternatively, this may translate incomplete recovery of these communities from the 2017 impacts. Finally, a trait-based approach was applied to the biological dataset of the three regions in both years, in an effort to understand if the previously detected regional differences translated into distinct functional features of the macroinvertebrate communities. Functional richness was higher in Region C (the less affect by water scarcity), opposing Region S (with more intermittency), indicating coherence between taxonomical and functional approaches. Importantly, loss of functional diversity was noticed in water-stressed regions, but long term data are missing to assess whether this reflects local adaptation of macroinvertebrate communities to constitutive ecosystem features or rather reflects drought effects. |
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