Mediterranean-climate Rivers Research Articles

Microplastic concentration, distribution and dynamics along one of the largest Mediterranean-climate rivers: A whole watershed approach.

Microplastics (MPs) have been recognized as one of the most ubiquitous environmental pollutants globally. They have been found in all ecosystems studied to date, threatening biological diversity, ecosystem functioning and human health. The present study aimed to elucidate the environmental and anthropogenic drivers of MP dynamics in the whole catchment of the Biobío river, one of the largest rivers in South America. MP concentration and characteristics were analysed in 18 sites subjected to different sources of pollution and other human-related impacts. The sampling sites were classified in relation to altitudinal zones (highland, midland and lowland) and ecosystem types (fluvial and reservoir), and different water and territorial environmental variables were further collated and considered for analysis. Seven types of microplastic polymers were identified in the samples analysed, with a catchment mean (±SE) MP concentration of 22 ± 0.4 particles m−3, and MP presence being significantly higher in lowlands (26 ± 2 particle m−3) and in reservoirs (42 ± 14 particle m−3). The most abundant type of MP was fragments (84%), with a mean concentration of 37 ± 6 particles m−3. Overall, MP concentrations were low compared to those found in other studies, with a strong influence of human population size.

Biotic indices of hydrological variability as tools to inform dynamic ecological status assessments in river ecosystems

River biomonitoring uses biotic indices that assess human-induced degradation, including pollution, by comparison with type-specific static biological reference conditions. However, index scores that indicate pollution may reflect biological responses to natural hydrological variability associated with low flows and drying, leading biomonitoring schemes to misclassify sites as degraded. To address this, dynamic, site-specific adjustments of static biological reference conditions have been proposed, but current biomonitoring tools cannot facilitate implementation of these adjustments. We analyzed 329 samples from mediterranean-climate rivers in Greece, to evaluate the use of six stressor-specific macroinvertebrate-based indices of hydrological variability (CEFI, DEHLI, ELF, LIFE, LIFENZ, MIS-index) as tools to facilitate dynamic adjustments of static biological reference conditions. We examined macroinvertebrate assemblage responses to physicochemical and land use drivers in relation to each sample's hydrological conditions, as assessed by the six indices. We evaluated index performance beyond the region of development by exploring correlations among indices, including correlations with the region-specific Greek ELF index, for which 100% of taxa were represented. We also examined the influence of inorganic nutrient pollution on index performance by comparing index scores from samples with and without nutrient pollution. Season, water temperature, agricultural land use and nutrient pollution were major drivers of macroinvertebrate assemblage composition. Indices were positively correlated but correlation strength varied considerably, driven primarily by taxonomic representation (the proportion of sampled taxa included in each index's calculation), and potentially also by differences in river types, taxonomic resolution and sampling strategies. All indices identified site-specific hydrological conditions both in the presence and absence of nutrient pollution. We recommend the development of region-specific biotic indices of hydrological variability, or regional adaptation of existing indices, to represent 100% of the regional taxa pool and thus to enable acceptable performance beyond their region of development. Such indices could inform dynamic adaptation of static biological reference conditions by assessing site-specific hydrological conditions based on a macroinvertebrate assemblage, without the collection of additional, abiotic field data. Application of our proposed approach could prevent misclassification of ecological status, thus avoiding time-demanding and costly mismanagement of rivers and streams.

Invasibility of Mediterranean-climate rivers by non-native fish: the importance of environmental drivers and human pressures.

Invasive species are regarded as a biological pressure to natural aquatic communities. Understanding the factors promoting successful invasions is of great conceptual and practical importance. From a practical point of view, it should help to prevent future invasions and to mitigate the effects of recent invaders through early detection and prioritization of management measures. This study aims to identify the environmental determinants of fish invasions in Mediterranean-climate rivers and evaluate the relative importance of natural and human drivers. Fish communities were sampled in 182 undisturbed and 198 disturbed sites by human activities, belonging to 12 river types defined for continental Portugal within the implementation of the European Union's Water Framework Directive. Pumpkinseed sunfish, Lepomis gibbosus (L.), and mosquitofish, Gambusia holbrooki (Girard), were the most abundant non-native species (NNS) in the southern river types whereas the Iberian gudgeon, Gobio lozanoi Doadrio and Madeira, was the dominant NNS in the north/centre. Small northern mountain streams showed null or low frequency of occurrence and abundance of NNS, while southern lowland river types with medium and large drainage areas presented the highest values. The occurrence of NNS was significantly lower in undisturbed sites and the highest density of NNS was associated with high human pressure. Results from variance partitioning showed that natural environmental factors determine the distribution of the most abundant NNS while the increase in their abundance and success is explained mainly by human-induced disturbance factors. This study stresses the high vulnerability of the warm water lowland river types to non-native fish invasions, which is amplified by human-induced degradation.

Pollution in mediterranean-climate rivers

This review examines information generated over the past decade on the pollution of rivers in regions with a mediterranean-type climate (med-climate). Pollution has clearly increased in the last 100 years and is correlated with the development of industry, agriculture and human population. Important efforts have been made in some med-climate countries in order to characterise the chemical status of rivers. In addition, the number of chemical substances detectable in mediterranean-climate rivers (med-rivers), as well as the limits of detection, have improved from the development of better analytical methods. New substances detected in rivers are gaining attention. We discuss available knowledge regarding real and potential effects of pollutants on the biota and ecosystems in med-rivers, taking into account natural environmental characteristics of these rivers. The extreme seasonal conditions in med-rivers add to the potential risk because these characteristics can enhance pollutant effects. Efforts and policies to prevent or reduce pollution effects on med-rivers are linked to the knowledge about pollution pressures associated with the degree of economic development. Aquatic communities in med-rivers are more sensitive to pollutants because they are exposed to strong natural and human stressors.

Disturbance and the role of refuges in mediterranean climate streams

Refuges protect plant and animal populations from disturbance. Knowledge of refuges from disturbance in mediterranean climate rivers (med-rivers) has increased the last decade. We review disturbance processes and their relationship to refuges in streams in mediterranean climate regions (med-regions). Med-river fauna show high endemicity and their populations are often exposed to disturbance; hence the critical importance of refuges during (both seasonal and supraseasonal) disturbances. Disturbance pressures are increasing in med-regions, in particular from climatic change, salinisation, sedimentation, water extraction, hydropower generation, supraseasonal drought, and wildfire. Med-rivers show annual cycles of constrained precipitation and predictable seasonal drying, causing the biota to depend on seasonal refuges, in particular, those that are spatially predictable. This creates a spatial and temporal mosaic of inundation that determines habitat extent and refuge function. Refuges of sufficient size and duration to maintain populations, such as perennially flowing reaches, sustain biodiversity and may harbour relict populations, particularly during increasing aridification, where little other suitable habitat remains in landscapes. Therefore, disturbances that threaten perennial flows potentially cascade disproportionately to reduce regional scale biodiversity in med-regions. Conservation approaches for med-river systems need to conserve both refuges and refuge connectivity, reduce the impact of anthropogenic disturbances and sustain predictable, seasonal flow patterns.

Restoring mediterranean-climate rivers

Mediterranean-climate rivers (med-rivers) have highly variable flow regimes, with large, periodic floods shaping the (often-braided) channels, which is different from stable humid-climate rivers, whose form may be dominated by the 1.5-year flood. There is a fundamental challenge in attempting to “restore” such variable, ever-changing, dynamic river systems, and the most effective restoration strategy is to set aside a channel migration zone within which the river can flood, erode, deposit, and migrate, without conflicting with human uses. An apparent cultural preference for stable channels has resulted in attempts to build idealized meandering channels, but these are likely to wash out during large, episodic floods typical of med-rivers. Med-rivers are more extensively dammed than their humid-climate counterparts, so downstream reaches are commonly deprived of high flows, which carry sediments, modify channel morphology, and maintain habitat complexity. Restoration of the entire pre-dam hydrograph without losing the benefits of the dam is impossible, but restoration of specific components of the natural hydrograph (to which native species are adapted) can restore some ecosystem components (such as native fish species) in med-rivers.

Water management in mediterranean river basins: a comparison of management frameworks, physical impacts, and ecological responses

Rivers in mediterranean climates have been extensively modified by water management infrastructure and practices, yet patterns of development and consequent effects on freshwater ecosystems have not been compared across multiple regions. To evaluate the influence of water management on mediterranean-climate rivers, we compare the historic progression of management policies, institutions, and ecosystem impacts in the Sacramento River (California, USA), Ebro River (Spain), and Biobio River (Chile) basins. There are broad similarities in patterns of ecosystem alterations related to the extensive development of dams and water management infrastructure in the three study basins. Flow regimes have been altered by the reduction of winter peak flows and increased summer baseflows. There are also common patterns of disturbance from sediment transport alteration, water quality degradation, and declines in freshwater biodiversity. Current approaches are inadequate for addressing the formidable water management challenges in California, Spain, and Chile, yet the dramatic evolution of water policies and institutions over the past 150 years suggests that further adaptation is possible. Advances toward integrated and sustainable water management models are likely to occur through incremental change, driven by growing awareness of climate change effects and public demands for water-use efficiency and improved environmental quality.

New records of Trichoptera in reference Mediterranean-climate rivers of the Iberian Peninsula and north of Africa: taxonomical, faunistical and ecological aspects

Trichoptera is a very rich order in the Western Mediterranean, but knowledge of caddisflies in the Iberian Peninsula and northern Africa is still not complete. We present records of caddisflies collected in 114 sites of the Mediterranean climate region of the Iberian Peninsula and the western Rif. We also provide notes on ecological aspects and taxonomical remarks on some species. Atotal of 86 species were identified and 8 species extended their distribution range. Considering the four differentiated geological regions in the western Mediterranean Basin during the Tertiary, 60 species were collected in the Iberian plate region, 29 in the Transition, 30 in the Betic and 18 in the Rif. Local richness was not significantly different between the four regions but significant differences were found among several river ecotypes within regions. Temporary sites had lower local richness than other ecotypes in all regions except in the Rif, whereas headwaters had similar richness in any region regardless of their geology. The Rif region had the lowest Trichoptera richness, which is not only the result of the scarcity of faunistic studies in the area but also of the high frequency of temporary rivers and the isolation of the area. Our results suggest that conservation measures addressed to preserve the biodiversity of the Western Mediterranean should be enforced, especially in the Rif region.

Ecological profiles of caddisfly larvae in Mediterranean streams: implications for bioassessment methods

Caddisflies are a well represented group with high species diversity in Mediterranean climate rivers. Although they are widely used in water quality assessment, little is known of the ecological profiles of families or species. We present a simple score for ecological profiles which measures intolerance to water quality. The ecological profiles of caddisflies are diverse and the degree of tolerance at the family level is related to species diversity and the tolerance of individual species to water quality. Comparisons with the scores used in the biotic index IBMWP show general agreement between the degree of intolerance of a family and its score in the IBMWP, with few exceptions. Studies on tolerance are required to elucidate the autecology of taxa, and to develop biological indices, especially in areas with high species diversity.