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 se gments of society; it has no price in the market and is seldom accounted fo r in decision making. Similarly the needs of ecosystems for fresh water for generation of nature's services are largely invisible. Freshwater assessme nts predominantly have focused on human uses of liquid water in rivers, lak es, and reservoirs. We estimated the spatial appropriation of terrestrial a nd marine ecosystems-the ecological footprint-of the 85 million inhabitants in the Baltic Sea drainage basin with regard to consumption of food and ti mber and waste assimilation of nutrients and carbon dioxide. We also estima ted the amount of fresh water-the water vapor flow-that the inhabitants dep end upon for their appropriation of these ecosystem services. The ecologica l footprint estimate corresponds to an area as large as 8.5-9.5 times the B altic 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 b odies for making the human appropriation of ecosystem services possible is estimated at 1175-2875 km(3) y(-1). Human dependence on water vapor flows f or ecosystem services is as great as 54 times the amount of freshwater runo ff that is assessed and managed in society. Decision making on an increasin gly human-dominated planet will have to address explicitly the critical int erdependencies between freshwater flows and the capacity of ecosystems to g enerate services. We advocate a dynamic ecohydrological landscape-managemen t approach upstream and downstream in watersheds to reduce unintentional im pacts, irreversible change, and further loss of freshwater resources, ecosy stem. services, and resilience.