Where Carbon Goes When Water Flows: Carbon Cycling across the Aquatic Continuum

Abstract

The purpose of this review is to highlight progress in unraveling carbon cycling dynamics across the continuum of landscapes, inland waters, coastal oceans, and the atmosphere. Earth systems are intimately interconnected, yet most biogeochemical studies focus on specific components in isolation. The movement of water drives the carbon cycle, and, as such, inland waters provide a critical intersection between terrestrial and marine biospheres. Inland, estuarine, and coastal waters are well studied in regions near centers of human population in the Northern hemisphere. However, many of the world's large river systems and their marine receiving waters remain poorly characterized, particularly in the tropics, which contribute to a disproportionately large fraction of the transformation of terrestrial organic matter to carbon dioxide, and the Arctic, where positive feedback mechanisms are likely to amplify global climate change. There are large gaps in current coverage of environmental observations along the aquatic continuum. For example, tidally-influenced reaches of major rivers and near-shore coastal regions around river plumes are often left out of carbon budgets due to a combination of methodological constraints and poor data coverage. We suggest that closing these gaps could potentially alter global estimates of CO 2 outgassing from surface waters to the atmosphere by several-fold. Finally, in order to identify and constrain/embrace uncertainties in global carbon budget estimations it is important that we further adopt statistical and modeling approaches that have become well-established in the fields of oceanography and paleoclimatology, for example.

A review of CO2 and associated carbon dynamics in headwater streams: A global perspective

“…This is remarkable because its surface area is only 3% of the estimated global river surface area [ Downing et al , ]. Such recent and ever upward revised global numbers are also confirmed by Ward et al [] and outline why quantifications of CO 2 outgassing from rivers and streams is a major unknown factor in global carbon budgets for inland waters.…”

Modeling CO2 emissions from Arctic lakes: Model development and site‐level study

“…Carbon burial in lake sediments is an important carbon sink in the global carbon cycle, on the magnitude larger than carbon burial in ocean sediments [Ward et al, 2017]. But the understanding for carbon burial in the sediments of Arctic lakes is still uncertain [Sobek et al, 2009[Sobek et al, , 2014.…”

Composition and Transformation of Dissolved Organic Matter in the Baltic Sea

“…Although they represent only a small part of the total ocean, about 20% of the marine organic matter production and 80% of organic matter deposition to ocean sediments occurs there (Borges, 2005). Yet, the carbon cycling in coastal waters is still not well understood, partly because the different carbon sources and sinks are highly complex (Gattuso et al, 1998;Ward et al, 2017).…”