The epilimnion is the surface layer of a lake typically characterised as well mixed and is decoupled from the metalimnion due to a steep change in density. The concept of the epilimnion (and, more widely, the three-layered structure of a stratified lake) is fundamental in limnology, and calculating the depth of the epilimnion is essential to understanding many physical and ecological lake processes. Despite the ubiquity of the term, however, there is no objective or generic approach for defining the epilimnion, and a diverse number of approaches prevail in the literature. Given the increasing availability of water temperature and density profile data from lakes with a high spatio-temporal resolution, automated calculations, using such data, are particularly common, and they have vast potential for use with evolving long-term globally measured and modelled datasets. However, multi-site and multi-year studies, including those related to future climate impacts, require robust and automated algorithms for epilimnion depth estimation. In this study, we undertook a comprehensive comparison of commonly used epilimnion depth estimation methods, using a combined 17-year dataset, with over 4700 daily temperature profiles from two European lakes. Overall, we found a very large degree of variability in the estimated epilimnion depth across all methods and thresholds investigated and for both lakes. These differences, manifesting over high-frequency data, led to fundamentally different understandings of the epilimnion depth. In addition, estimations of the epilimnion depth were highly sensitive to small changes in the threshold value, complex thermal water column structures, and vertical data resolution. These results call into question the custom of arbitrary method selection and the potential problems this may cause for studies interested in estimating the ecological processes occurring within the epilimnion, multi-lake comparisons, or long-term time series analysis. We also identified important systematic differences between methods, which demonstrated how and why methods diverged. These results may provide rationale for future studies to select an appropriate epilimnion definition in light of their particular purpose and with awareness of the limitations of individual methods. While there is no prescribed rationale for selecting a particular method, the method which defined the epilimnion depth as the shallowest depth, where the density was 0.1 kg m⁻³ more than the surface density, may be particularly useful as a generic method.

Undertaking integrated and sustainable water resources management (ISWRM) and providing socially acceptable solutions with scientifically solid bases is a dynamic and challenging process. Two basic pillars–umbrellas can be identified in the literature: stakeholder engagement and analysis; and integrated monitoring–modelling in the form of a decision support system (DSS) that can assess, evaluate and rank the management options. This study presents a framework that can be used as a good-practice example of successful stakeholder engagement (public engagement and collaboration with local communities towards shared visions) and an integrated DSS for ISWRM (including characterisation at catchment and local scales, programmes of measures and their evaluation): the Framework for Integrated Land and Landscape Management (FILLM), developed by an Irish multi-disciplinary and multi-stakeholder platform, the Water Forum. The fundamental theoretical principles and practical aspects of the FILLM are analysed. A step-by-step guide is proposed for its application, bridging the above pillars, using examples, reviewing methods and software, and analysing challenges and trends. It can help both socio-economic and environmental scientists (modellers) understand each other’s roles and find reviews of useful tools and methods for their work. This work can be a reference point for future ISWRM and environment management and can contribute to holistic education on such topics.

Internationally, water management is moving from the traditional top-down approach to more integrated initiatives focussing on community-led action. With inadequacies in previous engagement initiatives undertaken through the first cycle of River Basin Management Planning for the EU Water Framework Directive (WFD), the Republic of Ireland has only recently embraced this bottom-up approach. The attempted introduction of national charging for domestic water use in 2015 has resulted in significant public disquiet and protest movements against the national government. In April 2015 we undertook a survey of current opinion on water management and community engagement initiatives in the Republic of Ireland and the United Kingdom. A total of 520 survey responses identified that although freshwater bodies are important in peoples’ lives, respondents were typically unaware of global initiatives such as Integrated Water Resources Management and Integrated Catchment Management. Overall, 81% of respondents did not feel included in decisions about their water environment despite an overwhelming 95% believing that local communities should have a say in how the water environment is managed. However, only 35.1% of respondents stated that they would be willing to attend local water management engagement initiatives. Rather than supporting individual gain, respondents identified social gains for the local community as avenues for increasing local involvement in water initiatives. In the Republic of Ireland, a water engagement initiative that implements the national framework local delivery model should be developed and implemented. This would 1) contribute to the second round of WFD River Basin Management Planning; 2) facilitate stronger connections between local communities and their water environment; and 3) foster bottom-up initiatives that empower communities regarding local water management issues.

The River Basin Management Plan (RBMP) is an essential component of the European Union Water Framework Directive that details an integrated approach required to protect, improve and sustainably manage water resources. RBMP were intended to be produced for the periods 2009–2015, 2016–2021 and 2022–2027. However, after two years of delays in the development processes, the Republic of Ireland produced its first RBMP in 2010. The second RBMP cycle was also implemented in 2018 and is expected to run until the end of 2021 to give way to the third RBMP, whose consultation processes have been ongoing since December 2019. This paper contributes to the forthcoming RBMP by assessing stakeholders’ perspectives on the second RBMP through a desk-based review and by conducting interviews with nine institutions (14 interviewees). The qualitatively analysed interviews reveal a broad spectrum of actors associated with water management and governance in the Republic of Ireland through a three-tier governance structure that has been delivered (with amendment) through the first two RBMPs. Organisations such as the An Fóram Uisce|The Water Forum, the Environmental Protection Agency, the Local Authority Waters, and the Agricultural Sustainability Support and Advisory Programme have responsibilities designated in the RBMPs to deliver improved water quality, integrated catchment management, community engagement and awareness-raising. Trust has also been building up among these organisations and other agencies in the water sector. Despite these responsibilities and progress made, the interviews identified communication lapses, ineffective collaboration and coordination among stakeholders and late implementation to be hampering the successful delivery of the second RBMP, in addition to significant pressures acting on water bodies from agricultural activities and urban wastewater treatment. Towards the third RBMP, the paper concludes that optimised water sector finance, enhanced and well-resourced communications, and improved stakeholder collaboration are needed to foster effective and efficient water services delivery and quality. More so, given the cross-cutting impact of the Sustainable Development Goals on water resources and the interconnected relations among the goals, the paper further recommends the integration of the SDGs in the various plans of actions and a co-benefits approach to derive the triple benefits from biodiversity, climate change initiatives and water quality measures.

Source protection is part of a multi-solution approach for the provision of safe drinking water. In the Republic of Ireland, community-led Group Water Schemes (GWS) provide treated drinking water to approximately 69,000 rural households. Between 2009 and 2019, preliminary source protection assessments were undertaken for 70 GWS abstracting from surface water sources to provide physical catchment characterisation and untreated and treated water quality analysis. Catchment areas upstream of abstraction points varied in size, with 51.5% being less than 5 km² and only 10.7% being larger than 100 km². The majority (91%) of assessed GWS serve a population of less than 3000 people, and 94% supply less than 1500 m³ per day. Exceedances of the EU Drinking Water Regulations were recorded for 27 parameters, with the greatest number of exceedances due to total trihalomethanes followed by microbial contamination. The most frequent recommendation for improving GWS drinking water quality was associated with managing livestock access to local water bodies. Improving stakeholder engagement represented 38% of all recommendations made. Drinking water source protection measures and catchment-scale actions can be an additional model to assist in the delivery of Integrated Catchment Management and river basin management planning in the Republic of Ireland. For the GWS sector, challenges lie in securing resources to improve both source water and drinking water quality to deliver integrated catchment management plans for source protection.