Linking freshwater flows and ecosystem services appropriated by people:: The case of the Baltic Sea drainage basin

Humanity's dependence on ecosystem support is "mentally hidden" to large segments of society; it has no price in the market and is seldom accounted for in decision making. Similarly the needs of ecosystems for fresh water for generation of nature's services are largely invisible. Freshwater assessments predominantly have focused on human uses of liquid water in rivers, lakes, and reservoirs. We estimated the spatial appropriation of terrestrial and marine ecosystems-the ecological footprint-of the 85 million inhabitants in the Baltic Sea drainage basin with regard to consumption of food and timber and waste assimilation of nutrients and carbon dioxide. We also estimated the amount of fresh water-the water vapor flow-that the inhabitants depend upon for their appropriation of these ecosystem services. The ecological footprint estimate corresponds to an area as large as 8.5-9.5 times the Baltic Sea and its drainage basin with a per capita ecosystem appropriation of 220,000-250,000 m(2). This large estimate is mainly attributed to carbon sequestering by marine ecosystems and forests. The water vapor flow of the ecological footprint of forests, wetlands, agriculture, and inland water bodies for making the human appropriation of ecosystem services possible is estimated at 1175-2875 km(3) y(-1). Human dependence on water vapor flows for ecosystem services is as great as 54 times the amount of freshwater runoff that is assessed and managed in society. Decision making on an increasingly human-dominated planet will have to address explicitly the critical interdependencies between freshwater flows and the capacity of ecosystems to generate services. We advocate a dynamic ecohydrological landscape-management approach upstream and downstream in watersheds to reduce unintentional impacts, irreversible change, and further loss of freshwater resources, ecosystem. services, and resilience.