TREATISE ON COASTAL AND ESTUARINE SCIENCE- CONTRIBUTORS’ INSTRUCTIONS

Estuaries profoundly transform the large amounts of carbon delivered from rivers before their transfer to the adjacent coastal zone. As a consequence of the complex biogeochemical reworking of allochtonous carbon in the sediments and the water column, CO2 and CH4 are emitted into the atmosphere. We attempt to synthesize available knowledge on biogeochemical cycling of CO2 and CH4 in estuarine environments, with a particular emphasis on the exchange with the atmosphere. Unlike CH4, the global emission of CO2 to the atmosphere from estuaries is significant compared to other components of the global carbon cycle. p0010 Estuaries are dynamic ecosystems that host some of the highest biodiversity and biological production in the world (Bianchi, 2007). At the land–ocean interface, estuaries receive large amounts of dissolved and particulate carbon (C), nitrogen (N), phosphorous (P), and silica from rivers. This riverine material undergoes profound transformations in estuaries before being transferred to the adjacent coastal zone (Wollast, 1983). Since the pioneering studies of Park et al. (1969) and Reeburgh (1969), it is known that estuarine environments emit carbon dioxide (CO2) and methane (CH4) to the atmosphere. Yet, it is only during the last decade that the dynamics of these two potent green-house gases has been investigated in greater depth in estuarine environments. In the present chapter, we summarize the available knowledge on the multiple drivers of biogeochemical cycling of CO2 and CH4 in estuarine environments, with a particular emphasis on the exchange with the atmosphere. s0005 5.04. 1 Estuarine Definitions and Classifications from the Perspective of CO2 and CH4 Dynamics p0015 Estuaries are commonly defined as “semi-enclosed coastal bodies of water that have a free connection with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage” (Pritchard, 1967). This definition, based on salinity, was extended by Perils (1995) AU2 including geomorphological, physical, and biological information, whereby an estuary is defined as “a semi-enclosed coastal body of water that extends to the effective limit of tidal influence, within which sea water entering from one or more free connections with the open sea, or any saline coastal body of water, is significantly diluted with fresh water derived from land drainage, and can sustain euryhaline biological species from either part or the whole of the life cycle. ” This definition allows to set the upstream limit of estuaries to the tidal river and to include within estuaries the intertidal areas. Although from the point of view of, for example, estuarine ecology, coastal management, and legislation, the definitions of Pritchard (1967) and Perillo (1995) might be ambiguous or incomplete (e.g., Elliott and McLusky, 2002), these definitions provide the basis for the analysis of CO2 and CH4 biogeochemistry examined in this chapter. However, there is a need to further classify estuarine systems into different types that are characterized by different physical settings that strongly influence organic carbon dynamics and, ultimately, CO2 and CH4 dynamics. p0020 The first estuarine classifications were based on physiography. Pritchard (1952, 1955) classified estuaries based on physical mixing. Fairbridge (1980) provided a classification ESCO 00504