Contribution of lake littoral zones to the continental carbon budget

Abstract

In the littoral zone, at the land–water interface of lakes, the areal productivity of aquatic vegetation rivals that of rainforests, resulting in a potentially very high carbon (C) turnover. Whereas tidal wetlands at the land–ocean interface are included in global C budgets, lake littoral zones are currently not accounted for, despite the total shoreline of lakes being estimated at four times longer than that of the global ocean. Here we quantify the littoral net atmospheric C sink using mass balance and a model of C export from the littoral to the pelagic zone. We argue that ignoring littoral C turnover in lakes potentially results in biased estimates of continental C cycling. In our global estimate, we show that the estimated global C balance of lakes may reverse from a net C source to a net C sink (that is, net C burial > net C outgassing). In addition, a large part of the C outgassed in the pelagic might originate from the littoral, implying that previous estimates of terrestrial C inputs to inland waters were too high. We argue that quantifying and modelling lake littoral C fluxes are essential to more accurately estimate the feedback between the continents and climate. The land–water interface of lakes is highly vegetated and may reverse the global carbon balance of lakes from a net source to a net sink, according to a mass balance and horizontal transport model quantification of lake littoral zones.