The influence of river regulation on the affinity for nature and perceptions of local populations.

Rivers are powerful systems supporting human civilization, but despite the enormous dependence on rivers by humans, this does not stop them to assault rivers in the most varied ways. Such dependency determines the establishment of strong river flow-human relationships, and river degradation the prompting of health and non-tangible complications for humans. This work assesses how river regulation, interacting with sociodemographic characteristics, influences the affinity for nature and the perception of humans regarding its effects on river systems. Increased affinity for nature and clearer perceptions about the effects of river regulation improve emotive connection with nature and promote pro-environmental concerns towards a more sustainable water management. Two case studies were selected with different river regulation types (run-of-river and storage reservoir). In each one, the affinity for nature and social perceptions were assessed via telephone-assisted questionnaire surveys carried out in 2020 using 402 randomly selected numbers of local human communities living in its influence areas. Results showed that despite river regulation, communities remain connected to the river system with well-established flow-human relationships. Nonetheless, these relationships have changed due to socioeconomic and cultural changes over time. Significant differences were found in educational attainment and age regarding the affinity for nature. On the other hand, gender differs significantly regarding both the affinity for nature and how the river regulation affect perception, highlighting a gender gap motivated by social and cultural customs passed throughout generations. The lower education level of women and less frequent use of the river acts as a barrier to their perception of river ecosystems and the regulation effects. The affinity for nature and the perception of ecosystems changes by local populations were also significantly different according to the river regulation type, where residents near the run-of-river dam present less affinity for nature. Notwithstanding, the perceptions of local communities were in general in accordance with the scientific knowledge on rivers' condition. Finally, this work highlights the necessity for education through schools, local communities, municipalities and families, providing conditions for dedication and time to nature and promoting environmental knowledge through direct experience.

River ecosystem endangerment from climate change-driven regulated flow regimes.

Major threats of freshwater systems are river damming and habitat degradation, further amplified by climate change, another major driver of biodiversity loss. This study aims to understand the effects of climate change, and its repercussions on hydropower production, on the instream biota of a regulated river. Particularly, it aims to ascertain how mesohabitat availability downstream of hydropower plants changes due to modified flow regimes driven by climate change; how mesohabitat changes will influence the instream biota; and if instream biota changes will be similar within and between biological groups. We used a mesohabitat-level ecohydraulic approach with four biological elements - macrophytes, macroalgae, diatoms and macroinvertebrates - to encompass a holistic ecosystem perspective of the river system. The ecological preferences of the biological groups for specific mesohabitats were established by field survey. The mesohabitat availability in three expected climate change-driven flow regime scenarios was determined by hydrodynamic modeling. The biota abundance/cover was computed for the mesohabitat indicator species of each biological group. Results show that climate-changed flow regimes are characterized by a significant water shortage during summer months already for 2050. Accordingly, the regulated rivers' hydraulics are expected to change towards more homogeneous flow conditions where run habitats should prevail. As a result, the biological elements are expected to face abundance/cover modifications ranging from decreases of 76% up to 67% increase, depending on the biological element and indicator taxa. Diatoms seem to endure the greatest range of modifications while macrophytes the slightest (15% decrease to 38% increase). The greatest modifications would occur on decreasing abundance/cover responses. Such underlies an important risk to fluvial biodiversity in the future, indicting climate change as a significant threat to the fluvial system in regulated rivers.

Influence of river regulation and instream habitat on invertebrate assemblage' structure and function.

Dams modify geomorphology, water quantity, quality and timing of stream flows affecting ecosystem functioning and aquatic biota. In this study, we addressed the structural and functional macroinvertebrate community alterations in different instream mesohabitats of two Portuguese rivers impaired by dams. We sampled macroinvertebrates in riffles, runs and pools of river sites downstream of the dams (i.e. regulated; n = 24) and in sites without the influence of the dams (i.e. unregulated; n = 7), assessing a total of 64 mesohabitats, following late spring-early summer regular flows. We found a distinct taxonomic structure and trait composition of macroinvertebrate assemblages between regulated and unregulated flow sites, and also between mesohabitats in which the differences were more evident. When analysing each mesohabitat individually, the effect of flow regulation was detected only in run-type mesohabitats for both taxonomic and trait composition, leading us to infer that a selective macroinvertebrate assessment on run mesohabitats would be a valuable contribution to detect regulated flow effects on ecosystems impaired by dams. Additionally, there is evidence that respiration and locomotion traits could be effective tools to identify damming flow alterations. This study supports that the quality assessments of rivers impacted by dams could benefit from a sampling approach focused on run mesohabitats and the detection of some key traits, which would improve assessment accuracy.

Multi-biologic group analysis for an ecosystem response to longitudinal river regulation gradients.

This work assesses the effects of river regulation on the diversity of different instream and riparian biological communities along a relieve gradient of disturbance in regulated rivers. Two case studies in Portugal were used, with different river regulation typology (downstream of run-of-river and reservoir dams), where regulated and free-flowing river stretches were surveyed for riparian vegetation, macrophytes, bryophytes, macroalgae, diatoms and macroinvertebrates. The assessment of the regulation effects on biological communities was approached by both biological and functional diversity analysis. Results of this investigation endorse river regulation as a major factor differentiating fluvial biological communities through an artificial environmental filtering that governs species assemblages by accentuating species traits related to river regulation tolerance. Communities' response to regulation gradient seem to be similar and insensitive to river regulation typology. Biological communities respond to this regulation gradient with different sensibilities and rates of response, with riparian vegetation and macroinvertebrates being the most responsive to river regulation and its gradient. Richness appears to be the best indicator for general fluvial ecological quality facing river regulation. Nevertheless, there are high correlations between the biological and functional diversity indices of different biological groups, which denotes biological connections indicative of a cascade of effects leading to an indirect influence of river regulation even on non-responsive facets of communities' biological and functional diversities. These results highlight the necessary holistic perspective of the fluvial system when assessing the effects of river regulation and the proposal of restoration measures.

Streamflow regulation effects in the Mediterranean rivers: How far and to what extent are aquatic and riparian communities affected?

Dam-induced disruption of the natural continuum of rivers has manifold consequences on fluvial ecosystems, but how distinct plant groups and plant adaptive strategies can mediate the regulation effects is largely unexplored. In this work, we focused on how different plant groups (macrophytes, bryophytes, and riparian woody vegetation) respond to hydrological alterations along the river and across the riparian zone downstream of dams. We specifically aimed to determine the degree of regulation [DOR] and distance from dam [DFD], where river regulation no longer significantly affects plant communities in two case studies - a run-of-river dam and a reservoir in Portugal. We collected data on plant species cover in 7 unregulated and 24 regulated sites in June-July 2019. We performed a cluster and ordination analysis to derive guilds using flow-responsive traits and applied linear models to predict guild alterations along the gradient of DOR and DFD. We established three macrophytes, six bryophytes, and five riparian guilds. Our results showed that the vegetation response to regulation was plant group-reliant and guild-specific. Overall, plant responses were expressed by changes in plant cover, and not by guilds' loss. We observed (1) an increase of the guild cover of macrophytes and a decrease in bryophytes cover with increasing regulation gradient and diverse responses for riparian guilds; (2) an encroachment of riparian vegetation guilds into the channel downstream of the storage reservoir and expansion outwards downstream of the run-of-river dam; (3) a higher number of significant alterations for reservoir sites compared with run-of-river sites. Finally, for particular guilds, we determined specific DOR and DFD from which guild covers became significantly indistinct from respective guild cover in unregulated circumstances. Understanding the communities' responses to diverse regulation types and the extent that different plant adaptations may counter regulation effects can be vital for optimizing river restoration projects.

Field data on Vegetation Structure and Effects of Human Use of the Dambos Ecosystem in Northern Mozambique.

The data content of this paper is related to the original research article entitled "Vegetation Structure and Effects of Human Use of the Dambo Ecosystem in Northern Mozambique" that was published in the Global Ecology and Conservation. Woody and grass vegetation was inventoried in the dambos wetlands of the Niassa National Reserve (NNR), the largest Protected Area (PA) in Mozambique and the third largest in Africa. The six dambos assessed were selected through Google Earth, MODIS satellite images and exploratory field visits. The selected dambos were surveyed using a two-stage systematic sampling procedure in which woody vegetation was inventoried by means of transects, and the grass was inventoried using quadratic sub-plots laid down within the transects. The woody vegetation survey included the identification of all individuals to the species level, measurement of total height and diameter at breast height (DBH). The grass vegetation survey consisted of measurement of the total height and species identification within sub-plots. Woody vegetation data in this article includes also estimation of total richness, absolute and relative abundance, dominance, frequency, species volume and successional stage of each species in the vertical structure. Estimation of richness and absolute dominance is also presented for the grass vegetation.

Factors related to fish kill events in Mediterranean reservoirs.

Fish kills are widespread visible events perceived by the civil society as a major cause for concern about water quality and ecosystem health. Investigations conducted so far have linked fish kills to multiple factors, but extensive studies examining quantitatively the likelihood of fish kills are missing. In the present study, factors related to fish kills in 67 Mediterranean reservoirs located in the Iberian Peninsula were investigated. Moreover, the variation in the likelihood of fish kills with the foreseen consequences of anthropogenically driven climate change upon temperature and precipitation was assessed. During the 23-year period studied (1995-2017) the number of fish kills per reservoir varied from 0 to 3 and happened mostly in Southern reservoirs and during the warmest months, particularly in June. Twelve explanatory variables showed significant differences between reservoirs with and without fish die-offs. Reservoir depth, surface area oxygen and chlorophyll a concentrations were the variables that, together, best discriminated between reservoirs with and without fish kills, explaining 67.2% of the total variation in the occurrence of fish die-offs. The variables retained in the mortality model explained unique parts of that variation, but a considerable amount of the explained variation was shared by all the variables. The number of fish kill events appears to be rising during the examined period and the projection made indicated an increase in the likelihood of fish kills towards the end of the 21st century, particularly for the RCP8.5 emission scenario, with the prevalence of fish kills reaching 0.865 in Southern reservoirs. In the future, oligotrophication is likely the only strategy to consistently reduce fish kills in Mediterranean reservoirs.

Flow Management to Control Excessive Growth of Macrophytes - An Assessment Based on Habitat Suitability Modeling.

Mediterranean rivers in intensive agricultural watersheds usually display outgrowths of macrophytes - notably alien species - due to a combination of high concentrations of nutrients in the water runoff and low flows resulting from water abstraction for irrigation. Standard mechanical and chemical control is used to mitigate the problems associated with excessive growth of plant biomass: mainly less drainage capacity and higher flood risk. However, such control measures are cost and labor-intensive and do not present long-term efficiency. Although the high sensitivity of aquatic vegetation to instream hydraulic conditions is well known, management approaches based on flow management remain relatively unexplored. The aim of our study was therefore to apply physical habitat simulation techniques promoted by the Instream Flow Incremental Method (IFIM) to aquatic macrophytes - the first time it has been applied in this context - in order to model shifts in habitat suitability under different flow scenarios in the Sorraia river in central Portugal. We used this approach to test whether the risk of invasion and channel encroachment by nuisance species can be controlled by setting minimum annual flows. We used 960 randomly distributed survey points to analyze the habitat suitability for the most important aquatic species (including the invasive Brazilian milfoil Myriophyllum aquaticum, Sparganium erectum, and Potamogeton crispus) in regard to the physical parameters 'flow velocity,' 'water depth,' and 'substrate size'. We chose the lowest discharge period of the year in order to assess the hydraulic conditions while disturbances were at a low-point, thus allowing aquatic vegetation establishment and subsistence. We then used the two-dimensional hydraulic River2D software to model the potential habitat availability for different flow conditions based on the site-specific habitat suitability index for each physical parameter and species. Our results show that the growth and distribution of macrophytes in the hydrologically stable vegetation period is primarily a function of the local physical instream condition. Using site-specific preference curves and a two-dimensional hydraulic model, it was possible to determine minimum annual flows that might prevent the excessive growth and channel encroachment caused by Myriophyllum aquaticum.

The Role of River Morphodynamic Disturbance and Groundwater Hydrology As Driving Factors of Riparian Landscape Patterns in Mediterranean Rivers.

Fluvial disturbances, especially floods and droughts, are the main drivers of the successional patterns of riparian vegetation. Those disturbances control the riparian landscape dynamics through the direct interaction between flow and vegetation. The main aim of this work is to investigate the specific paths by which fluvial disturbances, distributed by its components of groundwater hydrology (grndh) and morphodynamic disturbance (mrphd), drive riparian landscape patterns as characterized by the location (position in the river corridor) and shape (physical form of the patch) of vegetation patches in Mediterranean rivers. Specifically, this work assesses how the different components of fluvial disturbances affect these features in general and particularly in each succession phase of riparian vegetation. grndh and mrphd were defined by time and intensity weighted indexes calculated, respectively, from the mean annual water table elevations and the annual maximum instantaneous discharge shear stresses of the previous decade. The interactions between riparian landscape features and fluvial disturbances were assessed by confirmatory factor analysis using structural equation modeling. Two hypothetical models for patch location and shape were conceptualized and tested against empirical data collected from 220 patches at four different study sites. Both models were successfully fitted, meaning that they adequately depicted the relationships between the variables. Furthermore, the models achieved a good adjustment for the observed data, based on the evaluation of several approximate fit indexes. The patch location model explained approximately 80% of the patch location variability, demonstrating that the location of the riparian patches is primarily driven by grndh, while the mrphd had very little effect on this feature. In a multigroup analysis regarding the succession phases of riparian vegetation, the fitted model explained more than 68% of the variance of the data, confirming the results of the general model. The patch shape model explained nearly 13% of the patch shape variability, in which the disturbances came to have less influence on driving this feature. However, grndh continues to be the primary driver of riparian vegetation between the two disturbance factors, despite the proportional increase of the mrphd effect to approximately a third of the grndh effect.

Modeling the evolution of riparian woodlands facing climate change in three European rivers with contrasting flow regimes.

Global circulation models forecasts indicate a future temperature and rainfall pattern modification worldwide. Such phenomena will become particularly evident in Europe where climate modifications could be more severe than the average change at the global level. As such, river flow regimes are expected to change, with resultant impacts on aquatic and riparian ecosystems. Riparian woodlands are among the most endangered ecosystems on earth and provide vital services to interconnected ecosystems and human societies. However, they have not been the object of many studies designed to spatially and temporally quantify how these ecosystems will react to climate change-induced flow regimes. Our goal was to assess the effects of climate-changed flow regimes on the existing riparian vegetation of three different European flow regimes. Cases studies were selected in the light of the most common watershed alimentation modes occurring across European regions, with the objective of appraising expected alterations in the riparian elements of fluvial systems due to climate change. Riparian vegetation modeling was performed using the CASiMiR-vegetation model, which bases its computation on the fluvial disturbance of the riparian patch mosaic. Modeling results show that riparian woodlands may undergo not only at least moderate changes for all flow regimes, but also some dramatic adjustments in specific areas of particular vegetation development stages. There are circumstances in which complete annihilation is feasible. Pluvial flow regimes, like the ones in southern European rivers, are those likely to experience more pronounced changes. Furthermore, regardless of the flow regime, younger and more water-dependent individuals are expected to be the most affected by climate change.