Understanding the ecological effects of climate change on freshwater ecosystem dynamics requires assessment of the influence of other large-scale processes. However, few studies allow such assessments over decadal timescales. Here, we examined how variation in annual weather patterns associated with the North Atlantic Oscillation (NAO) over four decades affected synchrony and stability in a metacommunity of stream invertebrates across contrasting headwater streams in central Wales (UK). Prolonged warmer and wetter conditions during positive NAO winters synchronised variations in population and community composition among and within streams thereby reducing stability across levels of organisation. This climatically-mediated synchronisation occurred in all streams irrespective of acid-base status and land use, but was weaker where invertebrate communities were more functionally diverse. Wavelet modelling indicated that variation in the NAO explained up to 50% of overall synchrony in species abundances at a timescale of 6-8 years. However, the synchronising effect of the NAO varied across species groups, with cold-adapted species showing high sensitivity to climate variation. The NAO had no effects on spatial synchrony in hydrochemistry, instead appearing to affect ecological dynamics through local variations in temperature, precipitation and discharge.
Our findings illustrate how large-scale climatic fluctuations generated over the North Atlantic can affect population persistence and dynamics in continental freshwater ecosystems in ways that transcend local catchment character. The analyses also suggest that protecting and restoring functional diversity in stream communities can increase their stability in the face of warmer, wetter conditions that are analogues of ongoing climate change.

Droughts are significant hydrological and environmental hazards that threaten the ecological status and functioning of streams. Low flow together with increased water temperature leads to a cascade of hydrochemical processes that can impair water quality and threaten a wide range of ecosystem services including clean water supply, nutrient retention, and biodiversity. In the face of the current climate crisis, nutrient release from river sediments may become the dominant factor controlling the biogeochemistry and water quality of lotic ecosystems. Our study aims at analysing the mechanisms and drivers of nutrient remobilisation from stream sediments via a combination of laboratory experiments and event-based water quality monitoring. We further aim at estimating the significance of this remobilisation potential for water management under different low flow and environmental conditions. First results from temperature simulation experiments in the lab show a clear relationship between increased PO4-P release from the sediments and warming, albeit in dependence of the phosphorus loading of the sediments. In contrast, sediment respiration declined with increasing temperature. The patterns were less clear for organic carbon and the different species of dissolved inorganic nitrogen. Further experiments will look into the role of dissolved oxygen, heterotrophic and autotrophic microbial activities, and sediment composition on the nutrient remobilisation potential under warming.

Climate change has been shown to affect the physical and chemical component of stream ecosystems both directly (e.g. via changes in flow regime) and indirectly (e.g. via changes in frequency and intensity of catchment forest fires). Effects on stream biota are less well known, but long-term sampling in bioassessment programs (e.g. RIVPACS in the UK) may reveal climate-change driven changes in the benthic community. In Canada, the Canadian Aquatic Bioassessment Network (CABIN) program has gathered data on the monitoring of 100s of reference (i.e. low exposure to local human activity) streams in British Columbia for 25 years, with several sites sampled more than three times over periods of more than six years. We measured temporal change in the composition of the benthic community at these sites by looking at changes over time in the sites as a whole and the trajectory of individual, repeatedly sampled sites. This was compared to the 10x10km resolution climate change projection model created from archival temperature and precipitation data by Environment & Climate Change Canada. At some sites, there is evidence of systematic community change over time that is related to climate change. At others, variability through time does not track changes in the climate. We will look at some of the factors that may help explain these different answers to the question of if and how much climate change affects stream ecosystems.

Like the rest of the world, the UK is facing an unprecedented climate change crisis. This is likely to affect the quality of its standing waters. Here, we present some of the evidence required to evaluate climate-related risks to our standing waters and to inform adaptation strategies that will safeguard their integrity, biodiversity and sustainable use. Focusing on Scotland’s standing waters, we have combined information from the literature, expert opinion and monitoring data, and used statistical analyses and visualisation (mainly mapping), to explore potential changes in climate change stressors to 2080. We have found that the water temperature of 97% of Scottish lochs increased between 2015 and 2019, and that most (88%) had warmed by 0.25°C to 1.0°C per year over that period. A small number (9%) of lochs had increased by 1.1°C to 1.3°C per year over that period. Using newly available climate change projections, we found that average April to September water temperatures in Scottish standing waters would probably rise by about 3°C by 2080, and that extreme drought events were likely to become more common. Our results suggest that by 2080, algal blooms are likely to become more prevalent in response to warming, lower flushing rates, and mismatches in the seasonal timing of algal communities and their zooplankton grazers. We provide evidence that climate change risk assessments are needed, urgently, for all standing waters to inform an evidence based, whole system approach to the sustainable management of lakes and reservoirs before it is too late.

Shallow freshwater ecosystems are experiencing increasingly frequent blooms of macroalgae (blanket weed) which can cause surface proliferations that can negatively impact aquatic ecosystem functions and aesthetics. The current extent, cause and consequences of these prolific blooms are largely unknown. Understanding what triggers these blooms is therefore critical for the future management of fresh waters. Routine limnological monitoring over an 18-month period was carried out at Clumber Lake, a shallow water body within the National Trust property of Clumber Park, Nottinghamshire, UK, that has had nuisance macroalgal blooms over recent decades. We found that Clumber Lake receives highly nutrient-rich waters from the River Poulter; bioassay experiments confirmed that the vast biomass of macroalgae growing in the lake was unlikely to be nutrient limited at any point of the year. Using mesocosm experiments we investigated the effects of light intensity, photoperiod and water temperature on the growth and surface bloom formation of macroalgal blooms. Longer daylengths with higher light intensities triggered bloom formation and increased algal growth rates. We also identified a thermal optimum between 16-22 °C for algae to form surface blooms, whilst the highest growth rate of algae on the sediment occurred at 14°C. With the increasing impact of climate change on freshwater ecosystems, data from these projects will help predict the occurrence of surface blooms of macroalgae and assess which waterbodies could be under threat of blanket weed blooms in the future, with the aim of informing effective management responses.

Knowing about ecological niche properties has a great utility for examining the mechanisms which differentiate species across space and time. Range restricted species such as freshwater fishes from southwestern Europe may be particularly important for evaluating the ability of species to cope with global changes. Here we examined Luciobarbus bocagei, L. comizo and L. microcephalus, barbels which occur in the western region of the Iberian Peninsula. L. bocagei and L. comizo are partially sympatric in the Tagus basin, while L. microcephalus distribution is nested within the southern distributional range of L. comizo. We built Species Distribution Models to predict species current and future distributions. Forecasts were projected to the current distributional ranges, as well as beyond them. We further evaluate niche properties, including niche as breath and overlap. Overall, models performed excellently regarding predictive accuracy and discriminatory ability. Ecological niche properties revealed that the three Luciobarbus species have relatively broad niche breadth and high overlap. Finally we discuss the species ability to adapt to future environments, the accuracy of using such species as biotic indicators, and the risks translocating such species into new areas.