Land drainage is an essential component of agricultural activity throughout the world. The intent is to increase the production and/or productivity of the land. However, many drainage schemes in Ontario (Snell 1987) and elsewhere (Davis and Froend 1999; La Peyre et al. 2001) have often contributed to the loss of wetland areas. The installation and maintenance of open ditch or closed outlet drainage systems contribute to the alteration of natural environments (Krapu 1996). While the approval of an individual drainage work may appear insignificant, the cumulative impact of these decisions results in significant losses of function, value and wetland area (Hill 1976; Spaling 1995). The interaction of physical, biological and chemical components of a wetland provides a number of functions that include flood protection, erosion control, groundwater recharge and discharge and water purification through the retention of nutrients, sediments and pollutants (Whiteley 1979). The values that wetlands provide to society include maintenance of water quality and quantity, recreation and tourism opportunities and wildlife resources. However, historical studies have demonstrated that despite the natural functions and values of wetlands, southern Ontario has experienced a loss of wetland areas at the expense of improving agricultural land (Snell 1987). To protect against the continued loss of wetland area in Ontario, a referral process has been developed to regulate outlet drainage activities that are pursued under the Drainage Act R.S.O. (1990, c. D. 17).
Responsibility for regulating drainage resides at the provincial level in Canada. Provinces have the statutory control of private property and civil rights, as well as control over natural resources and public lands. The management of wetlands regularly deals with a conflict over private property rights and public rights. The indirect protection of wetlands through various Ontario statutes is one means through which government agencies guide development on private property (Dahme 1988). However, when dealing with wetlands, further protection is extended to wildlife and the maintenance of the ecological integrity of an area. Therefore, lawmakers and government officials have to balance the rights of individual property owners with the interests of the public and other species.
In Ontario, the Drainage Act outlines a referral system for agencies to protect wetland resources against the impacts of municipal outlet drainage. The purpose of this article was to assess the outcome of the mitigation measures recommended for municipal outlet drainage schemes and the impacts on wetland area at the landscape scale. Drainage has been a long-established practice in Zorra Township for over 125 years (Wicklund and Richards 1961). A review of Zorra Township's drainage applications for the period 1978-1997 provides insights into Ontario's municipal outlet decision-making process, the nature of recommended mitigation measures and resulting impacts on wetland area (Figure 1).
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Agricultural drainage research
The conflict between agricultural production and wet]and management is a long-standing research theme (Kettel and Day 1974; Whiteley 1979; Bowers 1983; Turner et al. 1983; Williams and Browne 1987; Morris 1989; Mitchell and Shrubsole 1994). This section provides a brief overview of previous research related to wetland protection and agricultural drainage.
The economic value of drainage works or benefit-cost analysis has often been calculated to determine the utility of drainage projects. In England, both Bowers (1983) and Turner et al. (1983) examined the utility of drainage projects. They concluded that the benefit-cost appraisals that supported drainage projects generally overestimated benefits (Bowers 1983) and that agricultural drainage of wetlands could not be supported on economic grounds (Turner et al. …