Constraining historical accumulation of carbon, nutrient and trace metals in tropical mangrove forests

Abstract

Mangrove forests are highly biodiverse environments and support critical ecological services, including organic carbon sequestration and retention of nutrient and trace metal sorbed to sediments. Along with seagrass and saltmarshes (blue carbon ecosystems), mangrove forest ecosystems have the capacity to accumulate more organic carbon per area unit area per unit time, than terrestrial forests. Yet rates of carbon accumulation vary spatially and temporally between tropical mangrove systems, and the processes controlling carbon sequestration and storage are still poorly resolved. Similarly, variability in the rate of nutrient and metal accumulation in mangrove sediments confound attempts to quantify these ecosystems services. Additionally, anthropogenic activities in coastal areas can impact the ability of mangrove forests to act as a sink for carbon, nitrogen and trace metals. In this thesis I argue that mangrove sediments provide important biogeochemical records that reveal historical trends in carbon, nutrient and trace metal accumulation rates in often highly degraded tropical estuaries. I present dated sediment cores from two critical tropical mangrove forest regions in Brazil and India, so as to quantify the long-term accumulation of carbon, nutrients and trace metals rates in both pristine and degraded mangrove systems. This thesis provides a robust set of data that can identify baselines for environmental monitoring and rehabilitation, and quantify the ecosystem services provided by these critically important systems. This research emphasizes the critical role played by mangrove ecosystems in sequestering carbon and attenuating anthropogenically-derived nutrients and pollutants in poorly-understood tropical estuarine systems. The data provided in this thesis contributes to a better understanding of carbon sequestration in mangrove ecosystems, which is crucial for climate change mitigation strategies and the implementation of carbon offset schemes.