Tropical wetlands: seasonal hydrologic pulsing, carbon sequestration, and methane emissions

Abstract

This paper summarizes the importance of climate on tropical wetlands. Regional hydrology and carbon dynamics in many of these wetlands could shift with dramatic changes in these major carbon storages if the inter-tropical convergence zone (ITCZ) were to change in its annual patterns. The importance of seasonal pulsing hydrology on many tropical wetlands, which can be caused by watershed activities, orographic features, or monsoonal pulses from the ITCZ, is illustrated by both annual and 30-year patterns of hydrology in the Okavango Delta in southern Africa. Current studies on carbon biogeochemistry in Central America are attempting to determine the rates of carbon sequestration in tropical wetlands compared to temperate wetlands and the effects of hydrologic conditions on methane generation in these wetlands. Using the same field and lab techniques, we estimated that a humid tropical wetland in Costa Rica accumulated 255 g C m -2 year -1 in the past 42 years, 80% more than a similar temperate wetland in Ohio that accumulated 142 g C m -2 year -1 over the same period. Methane emissions averaged 1,080 mg-C m -2 day -1 in a seasonally pulsed wetland in western Costa Rica, a rate higher than methane emission rates measured over the same period from humid tropic wetlands in eastern Costa Rica (120-278 mg-C m -2 day -1 ). Tropical wetlands are often tuned to seasonal pulses of water caused by the seasonal movement of the ITCZ and are the most likely to be have higher fire frequency and changed methane emissions and carbon oxidation if the ITCZ were to change even slightly.

Possible impacts of climate change on wetlands and its biota in the Brazilian Amazon

“…Added to these, the coastal wetlands, such as mangroves, might also be influenced by the rising of sea levels (Mitsch et al, 2010).…”

Ecosystem respiration and its components from a Carex meadow of Poyang Lake during the drawdown period

“…Wetlands cover only about 5e8% of the terrestrial land surface (Mitsch and Gosselink, 2007), but they are estimated to account for 20e30% of the global soil organic carbon pool (Roulet, 2000;Bridgham et al, 2006). High productivity and waterlogged conditions make many wetlands significant carbon sinks .…”

What are the greenhouse gas observing system requirements for reducing fundamental biogeochemical process uncertainty? Amazon wetland CH<sub>4</sub> emissions as a case study

“…CH 4 can be transferred directly into the atmosphere via macrophytes, thus circumventing the aerobic soil layer (Whalen, 2005). Water-body depth (Mitsch et al, 2010), type (Devol et al, 1990) and aquatic macrophyte density (Laanbroek, 2010) can affect the proportion of wetland CH 4 transferred to the atmosphere.…”

“…The successes of GOSAT (Yokota et al, 2009) and OCO-2 (Crisp et al, 2004) open the door to designing a next generation of spaceborne greenhouse gas measurements to test specific hypotheses about the terrestrial biosphere or the oceans. In this paper, we report an observing system design exercise aimed at identifying the observing system needed to increase understanding of a long-standing uncertainty in the global carbon budget, specifically the role of tropical wetlands in the global CH 4 budget (Mitsch et al, 2010;Bloom et al, 2010;Melton et al, 2013). While we focus this analysis on CH 4 , we note that the models and methodology are equally applicable to other gases (such as CO 2 ), as well as other regions or mechanisms.…”