There is widespread evidence for the warming of lake surface waters across the globe and the impacts of increased thermal stratification on deep water oxygen decline during the summer. These changes in the oxygen regimes of lakes have potentially severe consequences for nutrient cycling in enriched systems, with the positive feedback effects of increased internal nutrient cycling exacerbating water quality problems and delaying ecological recovery. Here we present long term data analysis from the temperate English Lake District collected as part of the UK-SCAPE Cumbrian Lakes Monitoring Platform. Long-term increases in surface temperature and stratification metrics are positively correlated with measures of oxygen decline and the duration of anoxia in a productive lake. Changes in anoxia are subsequently associated with an increase in late summer phosphorus and reduced nitrogen concentrations. These changes are indicative of increased internal nutrient supply from lake bed sediments and consequent impacts on phytoplankton biomass. These climate induced changes pose critical challenges to our ability to effectively manage lake water quality in a warmer world.

Many waterbodies are characterised by high turbidity levels due to the presence of algae or suspended fine inorganic sediment in the water column. In many locations, large populations of bivalves have been observed to act as ecosystem engineers, actively filtering the water they inhabit by extracting fine organic and inorganic particles from the water column. As such, when population densities are high, bivalves may have a significant influence on turbidity levels potentially resulting in major changes to the water clarity of the aquatic systems they inhabit. With water temperatures predicted to increase in the future due to climate change, filter feeding effects may be enhanced as metabolic activity increases. This paper examines the filtering activity of small and large Asian clams, Corbicula fluminea, on turbidity levels at different temperatures (10-25°C) in a series of controlled experiments. Filter-feeding activity of C. fluminea reduced turbidity levels significantly compared to control treatments (no C. fluminea) with the fine sediments bound together within their pseudo-faeces. This binding of fine sediment may lead to a reduction in the subsequent resuspension of fine sediments. There was a strong association between the size of the individual clam and the reduction in turbidity over time. The results also clearly indicated that as water temperature increased, turbidity levels were reduced more rapidly than at lower temperatures. The wider implications of the filter-feeding activity of C. fluminea populations will be considered in relation to wider habitat characteristics and how this may change under future warmer conditions.

Aquatic ecosystems around the world are currently warming with unprecedented rates since observations started, but warming occurs highly variable among ecoregions. So far, mountain rivers were expected to experience attenuated warming due to cold water input from snow or ice. But since air temperatures in mountain areas are increasing faster than the global average, these cold rivers are expected to warm accordingly. In this presentation we summarize warming dynamics in different river types in the European Alps by comparing results from different studies. We compared the warming rates of different river types (low-order vs. high order) during the last decades and assessed longitudinal and daily temperature dynamics along rivers draining small catchments in high altitudes, leading to the following findings: a) large Alpine streams warmed size-dependent during the last decades (with average rates between +0.24 and +0.44 °C decade-1), warmed also during winter, and exhibited increases in extreme water temperatures and lengthening of warm phases, b) high-altitude rivers are warming only during summer but at higher rates (around +0.25 year-1), and c) smallest rivers at high altitudes show very high daily and longitudinally temperature dynamics with changes up to 2°C during same days or +2°C per 100 m. This presentation demonstrates substantial warmings of mountain rivers with size- and season-dependent rates (also evidencing phenological shifts) and river-type-specific sensibilities to rising air temperatures. Given the dominant role of water temperature for ecological processes and functioning in aquatic habitats, this presentation adds to the understanding of climate change affects in mountain rivers.

Ecosystems can be allies to confront anthropogenic climate change created by the huge amount of Greenhouse Gases (GHG) emissions by human activities. The biogeochemical cycles of Earth’s ecosystems are modified by climate change but also by other anthropogenic impacts, such as land use changes. Here we present a multiscale workflow aiming to fix the relative importance of ecological processes and that of anthropogenic pressures and impacts, and the interconnections among scales at the proper level. This approach starts from measuring (and collecting from other available data sources) the rates of significant biogeochemical processes mediating GHG exchanges between different wetland’s types representative sites and the atmosphere under different conditions, then assayed under experimentally controlled conditions. These data serve to calibrate C-cycle and GHG-exchange models to see how driving factors (e.g. temperature, hydrological patterns, meteorology, salinity, land use changes, etc.) can affect C and GHG fluxes. Multilevel models integrate C-cycle, hydrology and climate, allowing to forecast how human actions and future climate can influence C and GHG fluxes under different management/restoration/policy/climate-change scenarios. These models can be extrapolated when applying the conditions generated by climate change models, but also be related with the conservation/ecological status obtained from land uses and their changes (LULUC) applying novel methods, such as the LUPLES2 method: Land Uses – Pressure Level – Ecological Status – Ecosystem services. This work was supported by projects CLIMAWET-CONS (PID2019-104742RB-I00), funded by AEI (Spanish Government), and Wetlands4Climate (LIFE19 CCM/ES/001235), funded by the EU-LIFE programme, and has inspired the new EU Horizon project Restore4Cs.

The Llyn Brianne project in central Wales began in 1981 as an investigation of the role of land use and acid deposition in the acidification of upland streams. In over 40 years of continuous investigations that have followed, as well as providing one of the longest contemporary records of recovery from acidification, the research has diversified to appraise the influence of global warming, effects of the NAO, land use change and climate change adaptation on stream organisms and ecosystem processes. Centred on 14 replicate streams with contrasting land use and hydrochemistry, and now featuring unique stream mesocosms, the project is now one of the longest catchment-scale ecological projects in the world. In this presentation, I review some of the seminal results arising from the work of many students and ecologists who have worked at the Observatory.

The impacts of global change on hydrological patterns in the Mediterranean region are already significant, with decreased streamflow, reduced stream network connectivity, and increased stressors like groundwater demand and nutrient concentration. We used the Onyar River basin in NE Spain to better understand the chain of effects from global change, including land use changes, water withdrawal, and climate change, on hydrological patterns, water quality, and primary producer biomass. We used a hydrological model to simulate river flow and compared the results to hydrochemical data and ecological observations of algal biomass at 23 sampling points. Our model showed that water flow in the river network is progressively decreasing due to climate change (i.e., increased evapotranspiration) and anthropogenic pressures (i.e., increased water abstraction and land use changes). These changes were also reflected in water chemistry, with increases in nutrient concentrations, particularly nitrogen forms. The intense exploitation of the alluvial and deep sedimentary aquifers in the lower basin areas contributed to water flow interruption in extensive parts of the river network. Following on this network disconnection and nutrient loads increase, algal biomass shows significant spatial and temporal variations, and the higher occurrence of large algal growths. These findings highlight the challenges that climate change and human overuse of water resources directly affect water quality and ecological integrity, which require of appropriate management strategies to make compatible the preservation of ecosystems and sustainable resource exploitation.