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This study highlights how Chinese economic development detrimentally impacted water quality in recent decades and how this has been improved by enormous investment in environmental remediation funded by the Chinese government. To our knowledge, this study is the first to describe the variability of surface water quality in inland waters in China, the affecting drivers behind the changes, and how the government-financed conservation actions have impacted water quality. Water quality was found to be poorest in the North and the Northeast China Plain where there is greater coverage of developed land (cities + cropland), a higher gross domestic product (GDP), and higher population density. There are significant positive relationships between the concentration of the annual mean chemical oxygen demand (COD) and the percentage of developed land use (cities + cropland), GDP, and population density in the individual watersheds (p < 0.001). During the past decade, following Chinese government-financed investments in environmental restoration and reforestation, the water quality of Chinese inland waters has improved markedly, which is particularly evident from the significant and exponentially decreasing GDP-normalized COD and ammonium (NH4+-N) concentrations. It is evident that the increasing GDP in China over the past decade did not occur at the continued expense of its inland water ecosystems. This offers hope for the future, also for other industrializing countries, that with appropriate environmental investments a high GDP can be reached and maintained, while simultaneously preserving inland aquatic ecosystems, particularly through management of sewage discharge.

As the largest renewable electricity source, hydropower represents an alternative to fossil fuels to achieve a low-carbon future. However, increasing evidence suggests that hydropower reservoirs are an important source of biogenic greenhouse gases (GHGs), albeit with large uncertainties. Combining spatially resolved assessments of GHG fluxes and hydroelectric capacity databases, we assessed that global GHG emissions from reservoirs is 0.38 Pg CO2 eq.yr−1, accounting for 1.0% of global anthropogenic emissions. The median carbon intensity for hydropower is ∼63.0 kg CO2eq. MWh−1, which is lower than that for fossil fuels, but higher than that for other renewable energy sources. High carbon intensity is mostly linked to shallow (water storage depth <20 m) and eutrophic reservoirs. Furthermore, we found that the reservoir carbon intensity (CI) value would be markedly increased to 131.5 kg CO2eq. MWh−1 when considering the dams under construction and planning. A low-carbon future will benefit from optimal dam planning and management measures, i.e., applying sludge removal treatments, thereby reducing the proportion of shallow reservoirs and anthropogenic pollution.

Microplastics are small (&lt;5 mm) plastic particles of varying shapes and polymer types that are now widespread global contaminants of marine and freshwater ecosystems. Various estimates suggest that several trillions of microplastic particles are present in our global oceanic system, and that these are readily ingested by a wide range of marine and freshwater species across feeding modes and ecological niches. Here, we present some of the key and pressing issues associated with these globally important contaminants from a microbiological perspective. We discuss the potential mechanisms of pathogen attachment to plastic surfaces. We then describe the ability of pathogens (both human and animal) to form biofilms on microplastics, as well as dispersal of these bacteria, which might lead to their uptake into aquatic species ingesting microplastic particles. Finally, we discuss the role of a changing oceanic system on the potential of microplastic-associated pathogens to cause various disease outcomes using numerous case studies. We set out some key and imperative research questions regarding this globally important issue and present a methodological framework to study how and why plastic-associated pathogens should be addressed.

Across the world, lakes deliver irreplaceable services to both nature and so-ciety, but anthropogenic activities, such as nutrient pollution and climate change, have deteriorated lake ecosystems with impacts projected to con-tinue in the future. However, in an effort to halt and reverse this degradation, management and restoration of lakes are increasing. Submerged macro-phytes and fish play a key role in the stability and state of shallow lake eco-systems, but their influence varies with climate and water temperature. Pro-cess-based lake ecosystem models have proven capable of supporting lake management by reproducing lake ecosystem dynamics and are used for forecasts and predictions, but today few models factor in the varying influ-ence of macrophytes and fish when modelling shallow lake ecosystems in subtropical and tropical climates or lakes affected by climate change. This thesis aimed to test, improve and apply the state-of-the-art lake ecosystem model GOTM-WET, with focus on macrophytes and fish, to assess how shallow lake ecosystems respond to different restoration methods in a temperate and tropical climate. GOTM-WET consists of the 1-dimensional, hydrodynamic model GOTM (General Ocean Turbulence Model) and the ecosystem model WET (Water Ecosystems Tool) coupled together by the Framework for Aquat-ic Biogeochemical Models. Before application of the lake model, an effective approach to analyse lake ecosystem models with two global sensitivity methods was developed and applied to test the influence of model parame-ters on water quality and food web variables in different temperate lakes. Be-sides informing the following case studies in this thesis on lake model behav-iour and parameter sensitivity, the sensitivity analysis also highlighted the in-fluence of macrophytes and fish on most water quality and food web varia-bles on the shallowest lake analysed. Then, the lake ecosystem model was applied to the temperate shallow Lake Arreskov in Denmark. The model was challenged in reproducing the frequent shifts in ecosystem states from a tur-bid, phytoplankton-dominated state to a clear-water, macrophyte-dominated state and vice versa after a restoration effort including external nutrient load reduction and removal of plankti- and benthivorous fish. How-ever, overall, the observed seasonal dynamics of water quality parameters were reproduced with the single-model ensemble approach and improve-ments were obtained in simulating algae surface blooms compared to previ-ous model efforts on the same lake. To model the fish community, including omni-benthivorous fish that are commonly observed in tropical lakes, a model for adaptive fish foraging behaviour was developed and implemented into the lake ecosystem model. The model ensemble with the fish-adapted lake model reproduced shifts in ecosystem state from phytoplankton-dominated to macrophyte-dominated primary production and simulated changes in fish community composition and diet in tropical shallow Huizhou West Lake in China after a restoration initiative including external nutrient load reductions and several biomanipulation methods. In conclusion, this thesis has has again emphasised the importance of including macrophytes and fish in shallow lake ecosystem models and has improved the lake modelling of food web and ecosystem dynamics in warmer climates. This contribution and the continued research and application of lake ecosystems models worldwide will make lake ecosystem models an increasingly powerful tool to support lake man-agement and regulation with preserving and restoring shallow lakes against the current and future global changes.

Marine algae have emerged as an alternative feedstock for the production of a number of renewable fuels, including biogas. In addition to energy potential, other characteristics make them attractive as an energy source, including their ability to absorb carbon dioxide (CO2), higher productivity rates than land-based crops and the lack of water use or land competition. For Ireland, biofuels from marine algae can play an important role by reducing imports of fossil fuels as well as providing the necessary energy in rural communities. In this study, five potential seaweed species common in Irish waters, Saccorhiza polyschides, Ulva sp., Laminaria digitata, Fucus serratus and Saccharina latissima, were co-digested individually with bovine slurry. Batch reactors of 120ml and 1000ml were set up and incubated at 35 degrees C to investigate their suitability for production of biogas. Digesters fed with S. latissima produced the maximum methane yield (335 ml g volatile solids(-1) (g(VS)(-1) followed by S. polyschides with 255 ml g(VS)(-1). L. digitata produced 246ml g(VS)(-1) and the lowest yields were from the green seaweed Ulva sp. 191ml g(VS)(-1). The methane and CO2 percentages ranged between 50-72% and 10-45%, respectively. The results demonstrated that the seaweed species investigated are good feedstocks candidates for the production of biogas and methane as a source of energy. Their use on a large-scale process will require further investigation to increase yields and reduce production costs.

European seas are experiencing rapid development. The anthropogenic demand for marine resources and space exerts the need for novel concepts for sustainable resource exploitation and smart space allocation. Multi-Use (MU) is an emerging concept to overcome spatial claims and support Blue Growth, however its actual potentials and current status of implementation in different sea basins is to a large extent unexplored. An analytical framework using a mixed method approach is proposed for the identification and analysis of MU potentialities in eight EU countries of the Euro-Mediterranean sea basin. The paper addresses opportunities and challenges of ten existing and potential MU combinations driven by three maritime sectors: tourism, renewable energy and Oil & Gas industry. Opportunities and challenges for MU development were presented in terms of drivers, added values, barriers and impacts. Results show that highest potential for MU development are related to tourism-driven MU combinations (e.g. pescatourism), but also emerging MU potentials exist related to Floating Offshore Wind energy and aquaculture (Gulf of Lion) and the re-use of Oil & Gas decommissioned platforms (Northern-Central Adriatic Sea). Findings were discussed for their geospatial distribution and their policy, socio-economic, technical and environmental boundary conditions. Recommendations on actions to foster MU development in the Euro-Mediterranean sea space are provided.

We studied the microbial functional diversity, biochemical activity, heavy metals (HM) availability and soil toxicity of Cd, Pb and Zn contaminated soils, kept under grassland or short rotation coppice (SRC) to attenuate the risks associated with HM contamination and restore the soil ecological functions. Soil microbial functional diversity was analyzed by the GeoChip, a functional gene microarray containing probes for genes involved in nutrient cycling, metal resistance and stress response. Soil under SRC showed a higher abundance of microbial genes involved in C, N, P and S cycles and resistance to various HM, higher microbial biomass, respiration and enzyme activity rates, and lower HM availability than the grassland soil. The linkages between functional genes of soil microbial communities and soil chemical properties, HM availability and biochemical activity were also investigated. Soil toxicity and N, P and Pb availability were important factors in shaping the microbial functional diversity, as determined by CCA. We concluded that in HM contaminated soils the microbial functional diversity was positively influenced by SRC management through the reduction of HM availability and soil toxicity increase of nutrient cycling. The presented results can be important in predicting the long term environmental sustainability of plant-based soil remediation.