Impact of agriculture on groundwater in Ireland

Ireland has large water resources. Only 5.3% of developable waters are as yet developed, to supply some 650 I/day/per capita to the population of some 3.37 million people. State of development varies in each of the seven water resources regions. Precipitation is fairly evenly distributed over the year, but the percentage infiltrating to form groundwater varies quite sharply. Some 61% of infiltration occurs in the four winter months November to February, when agricultural activities are low. Only 10% infiltrates in the four summer months, May to August, when agricultural activities are high. In all, annual groundwater amounts to some 24.8 km³, of which 50% is considered to be recoverable. Capital groundwater reserves must be large, but are unquantified. Under these conditions, the impact of agriculture on groundwater quantities is negligible. Of the annual extraction of some 170 × 10⁶m³ of groundwater, some 66 × 10⁶m³/year are used in different agricultural activities. Drainage operations, however, have effects on Irish groundwater. Such lands may overlie impermeable strata or pans, or may receive concealed or visible groundwater discharge. Their drainage will affect the groundwater in various ways. There has been a considerable impact of agriculture on groundwater quality. The effects on the atmosphere and on precipitation are not identifiable. Effects of diffuse infiltration are treated with respect to: (a) application of ground limestone (lime); (b) application of K.N.P. inorganic fertilizer; (c) spreading of organic slurries; (d) development of organic nitrogen in soils, mainly after ploughing of grasslands; and (e) residues from herbicides, fungicides, and pesticides. The infiltration of these substances spread on the land is closely related to the interaction between times of ground-water recharge and times of fertilizer application. Effects of concentrated infiltration are treated under seven sub-heads: (a) infiltration of polluted surface waters; (b) localized farm infiltration; (c) concentrated waste disposal from feedlots; (d) concentrated waste disposal from silage; (e) concentrated waste disposal from agro-industries; (f) disposal through sinkholes and quarries; and (g) disposal by deep well injection. These operations are deliberate, and not related to times of groundwater recharge. They are often into the limestone aquifers, and so doubly dangerous.