Environmental and Human Drivers of Carbon Sequestration and Greenhouse Gas Emissions in the Ebro Delta, Spain

Abstract

Coastal and deltaic wetlands are among the most effective ecosystems for climate regulation through carbon sequestration and storage. The Ebro Delta is an example of a landscape that attempts to integrate nature protection with economic development that is threatened by global change. The functionality of Ebro Delta wetlands is deteriorating due to sea-level rise, subsidence, sediment starvation, limited hydrological connectivity and direct impacts caused by human activities (i.e., agriculture). Here we review studies on natural and agricultural wetlands (i.e., rice fields) with a focus on drivers of carbon (C) dynamics. The evidence supports that natural wetlands keep functioning as C sinks despite the impact of anthropogenic activities in the Delta, while rice fields act as net carbon sources to the atmosphere. Rates of C sequestration are mainly related to hydrological connectivity and salinity that modulate metabolic rates. In coastal lagoons (lower connectivity, lower salinity), autochthonous primary productivity is the main C sequestering process, whereas in salt marshes (higher connectivity, higher salinity) with lower metabolic rates, deposition of allochthonous material dominates. We discuss management options that promote C sequestration and greenhouse gas (GHG) emission reduction under a changing climate. Integrated management both at the local level – mainly of rice fields and adjacent wetlands – and at the regional level – the whole river basin and the delta – is essential to enhance fundamental ecosystem services such as carbon sequestration provided by the Ebro Delta, in order to increase its capacity to mitigate climate change.