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CHAPTER 7. MANAGEMENT

7.7. Conclusions and Recommendations

Lake and reservoir environments are dynamic, changing as the economic activities in its surrounds change. Many of the large impoundments were planned when world awareness of environmental issues, especially ecological management of freshwater resources was low. The management structures put in place then reflected the concerns of that era. Now these issues are critical for the well being of humanity. Sates need to ensure functional and durable mechanisms for the management of lakes and reservoirs, mechanisms that are able to respond to ever changing challenges. These include proper institutions, adequate funding for both management and research, stakeholders participation, and functional legal frameworks at both national and international levels.

As the need for energy continues to increase in Latin America, more reservoirs will be built up either by the public or private sector. The introduction of management plans prior to the reservoir construction and operation is an economic and social issue of relevance. The filling phase of reservoirs is the fundamental event that sets up the pattern of succession. It is fundamental to establish a monitoring programme that will follow the changes from the beginning of the impoundment. The management of reservoirs, and specially those in Latin America, is a complex operation that needs permanent input from basic sciences. The knowledge about mechanisms of functioning is thus essential for management. Management includes the recovery and inputs to the construction of new reservoirs in order to optimize multiple uses, prevent eutrophication and deterioration. Adaptive management should be developed for each reservoir or a cascade of reservoirs. Each case is unique. Management has to grow with knowledge and should be adapted to multiple uses along the process of succession. Management needs the contribution of limnologists, engineers, biologists, operational managers, and decision-makers. A certain level of prediction, based on empirical observations and experiments, is necessary for the management of reservoirs in Latin America. Countries like Argentina, Brazil, Chile, and Mexico, are reviewing the status of the regulations and improving them, thus enhancing law enforcement for the management of reservoirs.

As compared with lakes, water reservoirs are more sustainable against the growing biological load. It is explained by the larger share of mineral particles in the balance of sediments, due to the abrasion of the reservoirs' shores. For this reason, the shores' abrasion plays a positive role co-precipitating and burying under bottom sediments man-made pollutants, including the phosphorus compounds. On average, the internal phosphorus load in reservoirs is less than in lakes.

The analysis of the ecological state of the well-studied water reservoirs in Russia demonstrates that, in spite of the considerable phosphorus load, most of the largest reservoirs are mesotrophic with the features of slowly developing eutrophication.

Management of the non-point external nutrients load is complicated due to very large territories of the reservoirs' basins in Russia (10⁴ to 10⁶ km²). To increase the self-purification capacity of the valley reservoirs, an original method is suggested. The reservoir has to be converted into a polysectional water body with one or more WPSs.The method is based on the control of the internal water exchange of those water reservoirs that have the yearly amplitude of the water level over 2 to 3 m.

Any water reservoir has its individual hydrological features that change in accordance with variations of hydrometeorological conditions. For this reason, the design of the optimal location of the intersectional dams is always individual. It should be based on field measurements of the water and compounds balances together with the mathematical modeling of the processes of water exchange and self-purification in the ecosystem of the reconstructed reservoir.

Other examples from the world show the role of institutional and legal frameworks in the management of lakes and reservoirs, especially with respect to eutrophication. Technical know-how alone, without sound institutional support and good governance, is unlikely succeed in sustainable water quality management. At international level shared water resources needs clear conventions in which the participating states' responsibilities and privileges are clear, and where clear protocols for management co-operation and dispute resolution are transparent.

Climate change will affect lake and reservoir hydrology. In the tropics the IPCC scenarios indicate a possible decrease in precipitation and a possible increase in evaporation by up to 40% for 1 to 2°C. These changes will have pronounced effects on the storage of lakes and reservoirs. The African great lakes, for example, have delicate hydrological budgets, with normally less than 10% of watershed run-off appearing as stream flow. A decrease in precipitation and increase in evaporation could convert these lakes into a closed watershed. Where the outflow represents only a small percentage of total inflow, increased evaporation alone could result in an interrupted outflow, as recently shown. The vulnerability of medium seized reservoirs in Southern Africa was shown. Recent reports from Ghana also show that even in the humids tropics the ecological effects would be felt in impacts of increased temperature on lake's stratification. At high temperatures, stable thermoclines form with only a small temperature differences between the hyperlimnion and hypolimnion is less than 1°C (see Lake Victoria in International Lake Environment Committee (ILEC), 1994). In eutrophic conditions, these stable stratification conditions will enhance oxygen depletion, production of hydrogen sulphide, and possibly lead to changes of fish species composition. Algal, as well as macrophyte growth rates will be enhanced. These changes will have significant economic impacts in fisheries and the potable water supply. Therefore they should be considered in the future planning of construction of new reservoirs and in management of the present lakes and reservoirs.

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