EPA - Ireland's Environment, An Integrated Assessment - 2020

Chapter 7: Water Quality Topic Box 7.4 The 2018 Drought The impact of the drought in 2018 on river flows and lake water levels was severe, particularly in July, but it was neither as prolonged a national phenomenon as the 1975-1976 drought nor as severe as the 1995 drought in the Midlands and Western regions. The dry weather resulted in a large soil moisture deficit, and almost two-thirds of all rivers fell below their 95th percentile flow (i.e. very low flow conditions). The main impact was on the provision of drinking water, and restrictions on water use were in place for several weeks between July and September. Inland Fisheries Ireland reported an increase in fish kills during 2018 (EPA, 2019a), and the low flows may have both directly and indirectly contributed to this rise by increasing the vulnerability of fish to pollution events (i.e. increased water temperature, depressed oxygen concentration). Low flow levels encountered in the Owenbrin river, Co. Mayo, during the summer of 2018. Our lake, reservoir and groundwater levels were buffered by the elevated precipitation and snow melt early in 2018, and, although their levels dropped, they did not fall to the same critical levels observed in approximately half of the rivers in the country. By November 2018, river flow and lake, reservoir and groundwater levels had returned to ‘normal’, except for a few lakes in the Midland region. Overall, the drought highlighted the vulnerability of certain water supplies in Ireland, because when these water supplies were first built, they were designed to cater for a smaller population and therefore supply lower volumes of water. This vulnerability may be magnified by the impacts of climate change and highlights the need for robust water supply and water resource management to ensure a safe and secure water supply in the future. Invasive Species The introduction of invasive species can also cause damage by displacing native species and affecting the functioning of aquatic ecosystems. In Ireland, the most invasive aquatic species include the zebra mussel ( Dreissena polymorpha ), the Asian clam ( Corbicula fluminea ) and plants such as the curly waterweed ( Lagarisiphon major ) and Nuttall’s waterweed ( Elodea nuttallii ). Other invasive species that occur along rivers such as Japanese knotweed ( Fallopia japonica ) and Himalayan balsam ( Impatiens glandulifera ) can destabilise river banks increasing erosion. Invasive species can also be vectors of disease or a direct cause of disease. For example, crayfish plague (caused by Aphanomyces astaci ), a fungal disease introduced to Europe most probably on American crayfish imported for aquaculture, has devastated river populations of Ireland’s native crayfish species (see Chapter 6). The National Biodiversity Data Centre maintains the National Invasive Species Database, which provides information on the distribution of invasive species. This work aims to facilitate the updating of risk assessments undertaken by Invasive Species Ireland and establishes an early warning system to alert us to new arrivals on the island of Ireland. This is covered further in Chapter 6. 177