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Inland aquatic systems connect headwater systems of streams and ponds to rivers and lakes downstream, transporting sediment, nutrients, biota and contaminants. In this web focus, we present a collection of articles and opinion pieces from Nature Geoscience about inland aquatic systems; the hydrological, chemical and biological functions they provide to ecosystems; their influence on biogeochemical cycles and the threats they face due to human demands and climate change.
Enhanced protection is needed for freshwater bodies in the United States — in particular impermanent streams and wetlands outside floodplains — according to an assessment of their value and vulnerability.
Many of the world's saline lakes have been shrinking due to consumptive water use. The Great Salt Lake, USA, provides an example for how the health of and ecosystem services provided by saline lakes can be sustained.
Lakes are sources of the greenhouse gas methane. A synthesis of measurements of methane emissions reveals that lakes and ponds above 50 °N emit 16.5 Tg methane annually, and emissions may increase by 20 to 50% with longer ice-free seasons.
Glaciers and polar ice sheets store and release a small but important pool of organic carbon. The changing climate is making glaciers an increasingly important driver of carbon dynamics in aquatic ecosystems.
A substantial amount of atmospheric carbon taken up on land is transported laterally from upland terrestrial ecosystems to the ocean. A synthesis of the available literature suggests that human activities have significantly increased soil carbon inputs to inland waters, but have only slightly affected carbon delivery to the open ocean.
Rivers may be efficient environments for metabolizing terrestrial organic carbon that was previously thought to be recalcitrant, owing to pockets that provide geophysical opportunities by retaining material for longer, and to the adaptation of microbial communities, which has enabled them to exploit the energy that escapes upstream ecosystems.