Ecosystem Irrigation as a Means of Groundwater Recharge and Water Quality Improvement

Groundwater is used for both public supply and industrial use on a large scale in many parts of the United Kingdom. This occurs mainly in the south-east where the chalk is the principal aquifer, and in central and north-western England where the Triassic aquifers, mainly in the Bunter Sandstone, are drawn upon. As a result of the abstraction of water from the aquifer at rates in excess of natural replenishment, in some areas large volumes of these aquifers have been dewatered. This is particularly true of the Bunter Sandstones of Nottinghamshire which are heavily drawn upon in the Nottingham, Mansfield and Doncaster areas. In other areas the remaining surpluses are small (Downing et al. 1970). More than 590 x 103m3 day-' of water are drawn from the Bunter Sandstone aquifer in the Trent River basin and a large proportion of this is subsequently discharged as effluent to the River Trent either directly or into tributaries. This helps to sustain the river's high minimum flow and thus maintains it as a large, potentially potable resource. The effluent includes sewage, industrial processes wastes and cooling water. The large resources available in the Trent are, therefore, heavily polluted. A research programme was initiated in 1966 by the Water Resources Board to seek the most suitable and economical method of treatment and re-use. The study of artificial recharge of the Bunter Sandstone as a means of re-using polluted water has been one important element in the programme (Satchell & Edworthy 1972), and recharge from a basin and by spray irrigation on the surface, have been studied. The present paper is concerned only with recharge by spray irrigation of natural heathland vegetation over the Bunter Sandstone. Groundwater recharge by spray irrigation requires the application of water in excess of the loss by evaporation so that a surplus is available for infiltration beyond the root zone. This system provides a major benefit since the contaminants of polluted water are removed or inactivated by the soil-vegetation system. Ecological changes during this process were expected to occur and some aspects of these have been studied and are presented in this paper. If the ecological effects of this form of recharge can be predicted and managed then the potential benefits are three-fold: (i) improvement in the quality of the water applied; (ii) recharge of the aquifer; (iii) increased yield of the vegetation by fertilization. Early attempts to use land as an agent for improvement of the quality of water and groundwater recharge differ from the work described here in two respects: vegetation was not included in the system and sewage effluent, rather than polluted river water, was used (McMichael & McKee 1965; McGaughey, Krone & Winneberger 1966).