Peatlands have been in the Irish landscape since the last Ice Age and form part of our oldest natural heritage; occurring as raised bogs, blanket bogs, and fens. Due to the extensive modification by humans, currently more than 40% of the peatland area does not have its original hydrophytic vegetation—this has been replaced by forest, grassland, or removed through peat extraction.
Draining peatlands causes the water table (WT) to lower, leading to significant changes in peat properties but more critically it enhances the aerobic decomposition of organic matter, resulting in significant emissions of gaseous and fluvial carbon dioxide to the atmosphere, and the degradation of water quality. Altered water runoff regimes are accompanied by changes in the water quality of downstream water bodies, relative to intact peatlands—this is due to leaching of metals, nutrients, dissolved organic carbon, and particulate organic carbon. So far, no studies have been published in Ireland regarding the impact of drainage.
Due to waterlogging, ammonium and nitrate concentrations are typically low in intact peatland waters but significantly higher in the marginal and turf-cutting face-bank areas. Ammonia is produced when organic compounds are decomposed through microbial action; drainage of peat induced ammonia release in discharge water, the fate of which relies on the pH and temperature of the receiving water body. Un-ionised ammonia which remains in water (above pH7.2) is toxic to fish, with increased toxicity with increasing temperature. Alternatively, ammonia is oxidised into ammonium and then nitrite and nitrate through nitrification—this removes dissolved oxygen from the water leading to distress or death of aquatic life. Nitrate can also be quickly transported to oligotrophic waters leading to eutrophication and further water quality problems. No data for nutrient exports have been published from extracted Irish peatlands.
Intensive drainage networks in industrial cutaway peatlands lead to further hydrological changes such as large runoff peaks and increase erosion, leading to siltation and eutrophication of downstream water courses due to high suspended solids. The erosion process has also transformed peat soils from sinks to sources of lead contamination. The impacts of drainage on the peatland-fed riverine biota has been more difficult to establish due to the difficulty of using standard water quality indicators (macroinvertebrates and benthic diatoms) in catchments prone to flash flooding and high seasonal physico-chemical variations.