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CHAPTER 6. TECHNOLOGICAL AND MANAGERIAL ASPECTS OF EUTROPHICATION

6.8. Land Use Control

Proper solutions of the wastewater and solid waste problems are a prerequisite, but not sufficient to ensure a high water quality in an aquatic ecosystems. The application of the solutions mentioned above must be combined with a comprehensive land use plan. Lakes and reservoirs are open and are therefore easily exposed to all types of pollution. The transition areas (i.e., ecotones) between aquatic and terrestrial ecosystems are of utmost importance as they serve as buffer zones. They are able to buffer water level fluctuation and to prevent nutrients, pesticides, and heavy metals to reach the lakes and reservoirs because they are removed by decomposition and uptake processes in the ecotones.

In this context, the lakeshore is considered a filter for undesired releases into the lakes: it protects the lake the way the membrane protects the cells. Lakes with over-exploited shorelines become more vulnerable, particularly to alteration of the lake environment.

The transition zones, mainly the supralittoral and littoral zones, have been shown to remove organic and inorganic material from water that flows through them. This effect is most pronounced for particulate matter, which is removed almost completely in the transition zone, provided that the zone is sufficiently large and kept under natural conditions. The important processes in the transformation zone are illustrated in Figure 6.7. Adsorption of pesticides, heavy metals, phosphorus, organic matter, and nitrogen compounds is indicated in the figure. Further, the figure shows decomposition of pesticides and organic matter, uptake of pesticides, heavy metals, phosphorus and nitrogen compounds by plants, and nitrification and denitrification in the transition zone.

It is possible to conclude that the wetlands at the shoreline of aquatic ecosystems must be conserved, maintained, and protected. However, not only the transition zones or ecotones along the aquatic ecosystems are of importance for the water quality of lakes and reservoirs. The entire watershed influences the water quality, as all ecosystems are open. Intensive agricultural or intensive industrial use of the watershed will inevitably influence the quantity and quality of the drainage water and the ability of the area to cope with the pollutants, i.e., remove them by processes similar to those illustrated in Figure 6.7. Green areas are therefore not only important to recreation of the local population, but also to reduction of the overall effects of the diffuse pollution which is inevitably the result of intensive use of the area. It is significant to plan the land use as a pattern of different applications. The entire spectrum from intensively industrial and/or agricultural use to recreational areas of different types should be represented in the landscape to ensure healthy ecosystem and high sustainability of the area, not only a dull and homogeneous landscape, resulting from an intensive utilization.

Figure 6.7. The processes in the littoral zone (i.e., the wetland, or ecotone, between terrestrial and aquatic ecosystems) are outlined. As seen, pesticides, heavy metals, phosphorus, (toxic) organic matter, and nitrogen compounds may be removed.

Advantages to forming a pattern of many different types of natural and artificial ecosystems in the use of the landscape can be summarized by the following points:

• The green areas will partly remove pollutants originating from intensively used areas. The processes are presented in Figure 6.7. It will result in a reduced impact on all ecosystems.
• Higher diversity in the landscape pattern will inevitably lead to a higher biodiversity.
• Higher diversity of the landscape and of the species composition will not necessary give higher stability of the ecosystems forming the landscape but will give the entire landscape a better ability to meet new and unexpected disturbances, because higher diversity will give a wider spectrum of buffer capacities. In other words, the buffer capacities will not necessarily increase, but the spectrum of buffer capacities will be wider.
• The possibilities of exchange of species among the ecosystems are considerably higher when the distance from one ecosystem to the next is smaller. Therefore, there are more pronounced possibilities for the ecosystems to maintain their functions under changed conditions, which is particularly due to emigration of other species better fitted to the emerging conditions. This is also known from the concept of maintaining "corridors of migration" in the landscape.
• Ecological conditions, including meteorological conditions, in a landscape, are a function of time and space. It means that it is important to consider the heterogeneity in the land use which inevitably will imply that a pattern of different ecosystems will emerge.

It is difficult to give rigorous recommendations on the land use control of a watershed. However, it is important that the watershed encompasses as many different kinds of ecosystems as possible, not only man-made ecosystems as we know from municipalities and agriculture. The application of wetlands between aquatic ecosystems such as lakes, reservoirs and streams, and man-made ecosystems, is under all circumstances compulsory. In the management of landscapes, it should also be considered to apply different types of wetlands as a pattern, to erect plantations or forests, to use fallow land, to erect corridors with trees and bushes, and to preserve the existing natural ecosystems.

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