The carbon budget of continents is strongly influenced by overlooked lake littoral zones

In the littoral zone, at the land-water interface of lakes and running waters, the areal productivity of plants rivals that of rain forests, resulting in a potentially very high carbon (C) turnover. While tidal wetlands at the land-ocean interface are now included in global C budgets, littoral zones of inland waters are currently not accounted for. This is remarkable given that the total shoreline of inland waters is more than 20 times longer than that of the global ocean. Here we argue that ignoring littoral C turnover in inland waters potentially results in biased estimates of continental C cycling. By including for the first time the turnover of C fixed by aquatic plants in the littoral, we show that the estimated global C balance of lakes may reverse from a net C source to a net C sink. In addition, a large part of the C outgassed in the pelagic zone might originate from the littoral, implying that previous estimates of terrestrial C inputs to inland waters were too high. We argue that the quantification and modeling of littoral C fluxes is essential to more accurately estimate the feedbacks between the continents and climate.