Agricultural practices have gained intensity over recent decades, which has resulted in enrichment of surface and ground waters. Contamination from livestock wastes; land fill site leachate, road runoff and detergents in wastewater have all contributed to environmental water quality issues and enrichment. Constructed wetlands (CWs) have been increasingly utilised as a method by which nutrient pressures on ecosystems, in the form of nitrogen (N)-containing and phosphorus (P)-containing compounds can be alleviated. This thesis focuses on three main research areas; hybridised floating CWs (FCW) for algal bloom mitigation in standing water bodies combining algaecide release from organic matter with conventional FCW design, installation of CWs on North Wales conservation sites to prevent enrichment and CW system optimisation for calcium (Ca) mobility maintenance. The process of eutrophication, subsequent algal bloom formation and senescence can have significant negative impacts on the condition and health of a water body. In this study FCW design combined existing technology for N and P removal via rhizosphere processing and plant uptake with the release of anti-algal phenolic compounds from organic matter added to the rhizosphere. These methods were combined in order to assess their potential for enhanced organic matrix material degradation and phenolic release by the inclusion of macrophytes capable of oxygenating the rhizosphere. Combination of these mechanisms resulted in increased algal bloom control. However, control systems lacking wetland macrophytes resulted in an algal density 10 to 20-fold greater than planted systems. However, the research proved that by not adding plants to the organic matter in a FCW, algal growth was significantly accelerated. As part of the study three CWs were installed on the Llyn and Anglesey Fens project conservation sites in North Wales. Sites of special scientific interest (SSSI), special areas for conservation (SAC) and national nature reserves (NNR) make up the fen conservation sites featured in the project. Here, localised enrichment from surface and ground water inputs has driven plant species assemblage changes within the fen basins. This process has been attributed to the influx of N and P which has led to the invasion of more competitive wetland macrophyte species. CWs located at the site margin were employed to treat eutrophic water flowing into the site. On completion of the systems, average nutrient pollutant removal was estimated over a 14 month period of operation. Total N removed as a result of the CW installations was approximately equivalent to 1.2 tonnes of inorganic fertilizer. This N would otherwise have continued to enter into the conservation sites. Further investigation was undertaken into the use of CWs with respect to the conservation targets of the Llyn and Anglesey Fens project. SSSI classification has been applied to the sites on Anglesey due to the presence of Ca-rich, oligotrophic water chemistry supporting a unique vegetation community. Conventionally, CWs for N removal by denitrification require anaerobic conditions in order for N removal to occur. These conditions also result in the precipitation of Ca within the wetland in the form of Ca carbonates. This is undesirable as Ca is required for the development of the rare fen vegetation communities. Experiments were undertaken to examine the potential for Ca mobility maintenance and the prevention of Ca loss due to carbonate flocculation. The potential of dissolved organic carbon (DOC) and phenolic compounds produced in the system to preserve Ca in a dissolved form was investigated. Existing research into the role of DOC in affecting Iron (II) mobility motivated this investigation. Preliminary investigations found that Ca formed an association with with low molecular weight (LMW) (typically <1000 Dalton (Da)) DOC. Ca was also observed to associate with DOC of low phenolic content. These findings were used to inform mesocosm experimental design and hypotheses. A mesocosm experiment incorporating three treatments was set up in order to assess the impact on Ca mobility of phenolic concentration and DOC molecular weight. Two CW types and two wetland macrophyte species were compared. The experiment showed that horizontal subsurface flow (HSSF) systems reduced total Ca by 28% on average, whilst Iris pseudacorus showed a similar result. However, total calcium was reduced by 38% in the Phragmites australis mesocosms. Contradictory to preliminary investigations, greater concentrations of phenolics correlated with increased total Ca. DOC was also characterised in the CW mesocosms using UV-Vis spectral slope ratios. Significant variation in DOC character was observed between plant species. These findings motivated further analysis into the quantification and characterisation of DOC produced as root exudate from the wetland macrophytes. Furthermore, this research also addresses targets as set out by the Llyn and Anglesey fens project with concern to reducing DOC inputs. Iris pseudacorus was observed to produce 55% less or 1.59mg DOC/g biomass less DOC than Phragmites. In addition, this species produced lower MW DOC with higher phenolic content, therefore promoting chelation and solubility maintenance of Ca. The findings of this research can now be applied to further CWs on the Llyn and Anglesey conservation sites. This research will also be used to inform management best practice at future CW locations where calcium maintenance is required.