Publication reviewFreshwaters include groundwater, rivers, lakes, and reservoirs. These ecosystems represent about 7% of earth´s terrestrial surface area.Although aquatic and terrestrial ecosystems appear clearly separate to the human eye, groundwaters, lakes, and rivers are in fact closely connected to terrestrial systems (Magnuson et al. 2006).
Climate, soils, and water-use haracteristics of terrestrial plants affect infiltration of water to groundwater and runoff to surface waters. Terrestrial systems contribute nutrients and organic matter to freshwater systems. Rivers in flood fertilize their valleys.
Terrestrial organisms are eaten by aquatic ones, and vice versa. A natural unit for considering coupled terrestrial and aquatic ecosystems is the watershed. Within a watershed, ecosystems are closely linked through flows of water, dissolved chemicals, including nutrients and organic matter, and movements of organisms.
Thus watersheds are natural units of analysis for freshwater resources.
