Lake restoration and biomanipulation in temperate lakes: relevance for subtropical and tropical lakes

This introductory chapter to the book “Tropical eutrophic lakes: their restoration and management” gives a summary survey of the responses of temperate lakes to increased nutrient loading (the eutrophication process) and during remediation. Chemically and biologically conditioned resistance may cause a delayed response to the nutrient loading reduction and different methods of overcoming this resistance are briefly described. Biological restoration methods (termed “biomanipulation”) are promising new tools. However, a significant difference in biological interactions in temperate versus subtropical-tropical lakes renders it difficult directly to apply the biological restoration methods. These include often higher dominance and abundance of small fish, higher aggregation of fish in vegetation, higher number of fish cohorts per year, higher degree of omnivorous feeding by fish and less piscivory in subtropical and tropical lakes than in temperate lakes. Unfortunately, only little is known about the trophic dynamics and the role of fishes in warm lakes. Since many subtropical and tropical lakes are today heavily eutrophicated, there is a great need for gaining new knowledge of trophic interactions and possible lake restoration methods for these regions. This is amplified by the fact that the eutrophication problem is expected to increase in the near future due to both the economical development and global warming. Eutrophication of lakes During the past centuries, increased urbanization and sewage disposal, regulation of wetlands and streams and more intensive farming practices have increased the nutrient loading to many shallow lakes world-wide, not least in the industrialized part of the world. This has resulted in major changes in the biological structure and dynamics of the lakes and often in a shift from a clear to a turbid state.