The frequency and spatial extent of non-flow periods in streams is growing in many regions worldwide. Consequently, many perennial streams are abruptly becoming intermittent, with unknown consequences for their structure and functioning. We conducted a laboratory mesocosm experiment to compare the resistance and resilience to drying of perennial and intermittent streams. Therefore, we collected stones from 10 perennial and 10 intermittent streams during the flowing phase, placed them in open recirculating mesocosms under standardized conditions, and exposed them to a complete flowing-drying-rewetting cycle. During the experiment, we followed changes in epilithic biofilm structure (bacteria and fungi composition, algal biomass, pigment composition) and functioning (community metabolism, nutrient uptake). Our results show generally higher resistance and resilience to drying in biofilms from intermittent streams. Nonetheless, the response was complex, with inconsistencies among the measured variables. Overall, our results indicate that biofilms from perennial streams are less adapted to drying-rewetting cycles than biofilms from intermittent streams, which has relevant implications for stream ecosystems in many temperate climate regions.

Environmental conditions drive both the biodiversity and functioning of aquatic ecosystems. Change to these conditions may translate into biodiversity changes, affecting their associated ecosystem functions and, ultimately their relationship (BEF). In temporary streams, drying shapes community biodiversity and functioning of organisms including photoautotrophs, many of which are desiccation-sensitive and disappear during dry periods; others have adaptations to tolerate desiccation. Despite the close relationship between biodiversity and ecosystem functioning, the nature and strength of BEF relationships are poorly understood, especially in temporary streams. To address this knowledge gap, we selected 32 permanent and temporary streams across the NE Iberian Peninsula, characterised their hydrological regimes, and calculated metrics to summarise temporal components of the dry periods. Stream biofilms were analysed for their physiology (active chlorophyll), biodiversity (calculated from photoautotrophic composition) and functioning (primary production). Permanent and temporary stream biofilms showed differences at both functional and structural level. We then developed a structural equation model to characterise causal relationships between environmental conditions, biofilm composition and functioning. Photoautotrophic physiology and diversity changed in response to the dry duration, and both contributed equally to functional responses. Beyond the predictable positive contribution of active chlorophyll to primary production, the positive relationship between photoautotrophic diversity and its functioning highlights the key role of community diversity to maintain autochthonous production. Biodiversity has an intrinsic value but, understanding how key ecosystem processes are affected by changes in biodiversity will inform river ecosystem management in the face of ongoing climate change.

Ecological status classification based on benthic macroinvertebrates is performed through comparison between observed and reference conditions. To prevent major shortcomings deriving from natural biological variability, reference conditions are established in accordance to river typologies. However, river flow and local hydraulic features are changing over time and constantly modify the occurrence of lentic and lotic habitat features introducing influential natural variations which bypass river types definition. To reduce systematic bias in ecological assessments, site-specific tuning of reference conditions related to the ratio of lentic to lotic habitats might be required. We performed a piecewise spline regression analysis to investigate the response of macroinvertebrate metrics to the lentic-lotic character. Nineteen metrics from assessment systems of South European countries were tested on predominantly temporary river reaches in Sardinia, Italy. A significant response of most metrics to the ratio of lentic-lotic habitats was observed with a parabolic or a decreasing lotic to lentic trend. Best correlations were observed for richness, score-based metrics, ovoviviparous taxa and multi-metric indices. Potential impact on ecological status assessment was tested for the STAR_ICM index, formally used in Italy for classification and in Europe for the Water Framework Directive intercalibration process. Better ecological status was obtained after adjusting the bias caused by the ratio of lentic to lotic habitat features. Results prove the importance of including lentic-lotic information in the definition of reference conditions. Failing to include this aspect might hamper the understanding of biological responses to pressures and/or provide a largely biased classification of ecological status in many circumstances.

Non-Pollen Palynomorphs (NPPs) includes a large group of fungi, algae and invertebrates remains. Their abundance, diversity and resistance to degradation allow their use in palaeoenvironmental reconstructions. Here we describe NPPs (45 taxa) from the sedimentary core of Lagoa do Caldeirão (Corvo Island, Azores). The successional NPPs assemblages track changes from a pristine ecosystem to an area severely altered by human activities over the last two millennia. The first assemblage includes an abundance of megascleres of Racekiela and a set of aquatic fungal species associated with littoral plant communities (Clasterosporium, Vargamyces). This is followed by an increase in Hyphomycetes conidia from decaying wood, Kretzschmaria deusta (forest pathogen) and Glomus, which is derived from a forested landscape that is disturbed by soil erosion and herbivore, this fungi assemblage points to the significant transformation of the landscape from a forest to open grass. This landscape transformation began before the arrival of the Portuguese (1450 AD) and was dramatically amplified in the following centuries. The most recent assemblage is dominated by coprophilous fungi (Podospora, Cercophora) from pasture-livestock faeces and a substantial increase in planktonic algae (Lacunastrum, Desmodesmus and Closterium) which are associated with nutrient enrichment. The use of NPPs will improve palaeoenvironmental reconstructions, although further studies of modern analogues are required to understand better the specific habitats related to different taxa.

Remote oceanic islands are compared to natural laboratories of evolution, providing model systems for testing evolutionary, ecological, and biogeographic theories. Island ecosystems are usually hotspots of biodiversity, with legacies of recent human impact, offering an ideal scenario to trace the first human impacts and their fragile ecosystems' effects and resilience. Lake sediments constitute natural archives of past environmental changes. Their analysis allows access to various information indicating early human activities and their impacts on these ecosystems and their ecological shifts. Here we present the onset and evolution of human disturbance on Azores aquatic ecosystems revealed through multi-proxy characterization of lake sedimentary archives.
Our results show that first human impacts on lake ecosystems and their watersheds on the Azores vary in time7space. They present clear evidence of initial human impact predating the official Portuguese colonization in 1432CE. These first impacts had few ecological repercussions and were extended over time. During this period, landscapes were modified by burning practices and prepared for agricultural purposes, leading to soil erosion. This initial human disturbance only affected lakes' catchment and often predates the first detectable response in aquatic systems by several decades. The most intense human impact phase started with the official Portuguese colonization. Human practices such as species introduction and increase of farming activities led to rapid shift state changes, such as acidification and eutrophication. Changes in ecosystem structure or function depend on lake characteristics and human activities conducted in the catchment.
This research is funded by FCT (DL57/2016/ICETA/EEC2018/25; PTDC/CTA-AMB/28511/2017), and (CGL2010-15767, CGL2013-40608-R, CGL2016-75281-C2)

The assessment of reference conditions is a key requirement of Water Framework Directive (WFD). In the absence of long-term data, pre-human impact conditions can be assessed through paleoecological data. Diatoms, well-known for their high sensitivity to changes in the aquatic environment, are widely used to define those conditions in lakes and evaluate the degree of deviation to determine the ecological status. To assess the reference conditions of the lakes of the Azores we calculated the dissimilarity between diatom assemblages in sediment samples of six lakes from two types (shallow type: Caldeirão, Caveiro and Peixinho; deep type: Rasa, Lomba and Funda) dated before human arrival to the Archipelago (900-1000 y BP). We also compare diatom assemblages between pre-human and modern samples in each lake to determine the degree of change in ecological conditions. Our results revealed a high dissimilarity between diatom assemblages in pre-human samples and the absence of a common reference community for all lakes or in each lake type. Our results strongly support the existence of site-specific reference conditions, mainly determined by lakes morphology, hydrology and ontogeny. The differences in the lakes characteristics and ontogeny resulting in different reference conditions suggest that the baseline conditions for ecological status assessment should be considered individually (i.e., site-specific). Modern assemblages show significant deviation from pre-human states and don't fulfil the environmental goals of the WFD, requiring restoration measures.