1. What do we mean by shallow lakes and why are they important?

Of the world's freshwaters, it is the large lakes, like Geneva, Superior, Baikal, Ness and Biwa, that have attracted the most attention, both of scientists and tourist industries. But they occupy only a small proportion of the world's freshwater area [155]. They have huge volume and grandeur and often spectacular settings, but it is the shallow pools, only a few metres deep, that are much more numerous and are ultimately much more important to both people and wildlife [48] (Fig 1)

Fig 1 Deep lakes in grand settings are important natural resources; but shallow lakes, usually in the lowlands contain higher biodiversity and on them many people depend for survival. Loch Lomond, Scotland, and the Uru-Aymara people of the Lake Titicaca wetlands.

Millions of tropical people depend on shallow lakes, fringed by reeds, papyrus or lilies; they cut reed for building, take fish for daily meals and use the wet fringing sediments in the dry season for growing rice or vegetables. In the industrial world, it is the amenity value, the angling, the flocks of ducks to be fed with bread by children, and perhaps the sight of dragonflies mating on a summer evening, that are important. And for the many who value wildlife, such wetland lakes, the world over, are of immense importance. Their complex ecological structure and high productivity [43,89] support the bulk of the biodiversity associated with freshwaters, from crustaceans only millimetres long to spectacular mammals and birds that come to feed by the pools of undisturbed floodplains

Their usual location on the flatter, farmable lowlands, makes shallow lakes more vulnerable to influences that may diminish the uses and values of the lakes and wetlands. Pollution of a large body of water is easily soluble, at least in technical terms, if not always in political ones, but the restoration of a shallow wetland lake, whose ecological structure has been severely damaged, is more difficult. Progress has been hampered by an assumption that the mechanisms which are important in the functioning of the ecosystems of deep lakes, dominated by a microscopic suspended algal community, the phytoplankton, must also apply directly to shallow lakes. Only in the last twenty years has research on shallow lake systems shown how different are systems normally dominated by large water plants (macrophytes) (Fig 2)