School of Natural and Environmental Sciences

Projects

Trace gases in tropical coastal zones

Overview

We estimated carbon dioxide, methane and nitrous oxide emissions from mangrove surrounding waters along the east coast of India, finding trace gas emissions to be driven by “tidal pumping” of sediment pore waters via tidally-related changes in hydrostatic pressure, consistent with trace gas production during sediment diagenesis. Tidally pumped waters were transported seaward, impacting trace gas concentrations in adjacent coastal waters and contributing to air-sea exchange over a wide area. 

Project description

We estimated carbon dioxide, methane and nitrous oxide emissions from mangrove surrounding waters and adjacent estuaries along the east coast of India (including the two largest Indian river/estuarine systems), directly via the use of flux chambers and indirectly by applying gas exchange relations to measured water and air concentrations.

The region is highly susceptible to anthropogenic destabilization through demographic and industrial pressures that caused a 50% size contraction of mangroves between 1960 and 1990. Consequently, the region has a diversity of mangrove and estuarine sites ranging from pristine to those heavily perturbed.  

We found that trace gas emissions were driven by “tidal pumping” of sediment pore waters due to tidally-related changes in hydrostatic pressure, consistent with trace gas production during sediment diagenesis. The tidally pumped waters were transported seaward, impacting trace gas concentrations in adjacent coastal waters and contributing to air-sea exchange over a wide area.

We concluded that improving our current understanding of mangrove carbon dynamics is important, not only for reducing current uncertainties, but for predicting the system response to large-scale changes such as mangrove replanting and clearance, both of which are becoming increasingly important aspects of mangrove “management” and for which the response through gaseous carbon emissions may not be well anticipated.