Tundi Agardy, Ph.D.
Introduction
Water makes life possible – no other element is so universally required by living things. The bulk of our bodies is water, and all life on earth depends on it, either for drinking, nurturing eggs and young, or providing living space. Even ocean creatures rely on freshwater; all water is inexorably linked. This essential connection between freshwater and seawater underpins the great array of life in the sea.
Freshwater ecosystems are diverse and valuable in their own right. The number of species supported by freshwater systems far exceeds that which would be expected given the small amount of space they occupy on the planet. For instance, inland wetlands occupy less than 1% of the Earth’s surface, yet support 40% of known fish species1. In fact, it has been estimated that a quarter or more of all vertebrate species live in or near inland waters. Endemism – that is, existence of species that exist nowhere else in the world – is generally high in rivers, streams, and lakes, since physical barriers set the stage for speciation.
Rivers and streams deliver freshwater and other nutrients to estuaries, and to all coastal seas. But the link between rivers and oceans also has a cost - whatever degradation is occurring in freshwater ecosystems inevitably impacts marine life as well. As pressures on aquatic systems mount around the world in response to growing needs for drinking water, irrigation, and energy needs, less and less water is able to reach the world's coasts -- changing the very nature of marine ecosystems, making estuaries more saline and diminishing the extent of ecologically important brackish waters. And as poor land use practices lead to pollution and erosion, run-off and other non-point discharges create a toxic brew of coastal seas downstream. Disappearing coastal wetlands only exacerbate the problem, as the ecosystem service of water filtration that these critical habitats provide are being lost.
Yet, significant hope lies in the multi-stakeholder and international efforts to better manage watersheds, as is occurring in many of the world's great river systems. So, too, does hope lie in the greater awakening of the public to the crucial role that healthy freshwater systems play in supporting the world ocean.
1 Millennium Ecosystem Assessment (MEA). 2005. Ecosystems and Human Well-Being. Ch. 20 Inland Water Systems. Island Press, Washington p561
