Afforestations structure in the context of requirements for biogeochemical barriers in an agricultural catchment

Maria Szyszkiewicz-Golis

Abstrakt


Among many significant environmental problems related to agricultural production, the matter of the first importance is the decrease in water quality. European Community policy has been concerned with this issue for over twenty years. But whilst the initial directives concerned themselves mainly with water for human consumption, more recent directives, suchas those on nitrates from agricultural sources (Directive 91/676/EEC) have placed increased emphasis on the environmental effects of excess nitrogen, in particular eutrophication. In the context of agriculture there are two main objectives of the Nitrate Directive: to reduce water pollution caused by nitrates from agricultural sources and to prevent further pollution of this kind. In order to achieve the objectives, the member states have to identify waters affected by, and those subject to pollution, and designate these areas as Vulnerable Zones. In these areas, as well as promoting crop rotations, soil winter cover or limitations per crop, the Nitrate Directive implements the use of non-fertilised grass strips and hedges along watercourses and ditches to serve as buffer zones (Duer, 2003; Report COM(2002)407). The importance of permanently vegetated land strips in controlling diffuse pollution from agricultural sources has been proved in many studies, most of them concerned with the efficiency of riparian plant buffer zones (Haycock et al.,1977). In addition to these, much has been published on shelterbelts and grasslands functioning as biogeochemical barriers reducing pollutants in ground water in upper parts of drainage areas (Bartoszewicz, 1994b, 2000, 2001; Prusinkiewicz et al., 1996; Ryszkowski et al., 1989, 1996; Szpakowska et al., 1994). Although a great deal has been published on this matter there is still some uncertainty about barrier size requirements for site-specific locations and a need for accepted methods for biogeochemical barrier design. As T.A. Dillaha and S.P. Inamdar pointed out (1997, after Castelle et al., 1994) buffers that are undersized place aquatic resources at risk. On the other hand, buffers that are larger than necessary needlessly deny landowners the use of a portion of their land. The difficulties with establishing rules for designing biogeochemical barriers are related to the complexity of landscape processes, which require evaluations based on different scale analysis of all landscape components. When considering practical aspects of the issue, local scale analyses are of critical importance. As the evaluation of biogeoche- mical barrier requirements is a very complex task, there is a need for a method for practical use in landscape planning. A way for it would be an estimation of the spatial structure of afforestations in subcatchments where surface and groundwater are highly polluted from agricultural sources, which suggests high barriers requirements. The obtained values, of the indexes proposed, can be compared to those in similar landscape types in order to evaluate afforestations requirements there. The aim of this study is to attempt to evaluate the structure of agricultural landscape afforestations and answering the question: what are the main spatial characteristics of suchinsufficient structure in two subcatchments located in two different agricultural landscape types?


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