Carbon and nutrient exchange of mangrove forests with the coastal ocean

Abstract

Mangrove forests exchange materials with the coastal ocean through tidal inundation. In this study, we aim to provide an overview of the published data of carbon (C) and nutrient exchange of mangrove forests with the coastal ocean at different spatial scales to assess whether the exchange is correlated with environmental parameters. We collected data on C (dissolved and particulate organic C; DOC and POC) and nutrient exchange (dissolved and particulate nitrogen, N and phosphorus, P) and examined the role of latitude, temperature, precipitation, geomorphological setting, hydrology, dominant mangrove species and forest area in explaining the variability of the exchange. We identified that there are a range of methodologies used to determine material exchange of mangroves with the coastal zone, each methodology providing data on the exchange at different spatial scales. This variability of approaches has limited our understanding of the role of mangroves in the coastal zone. Regardless, we found that mangrove forests export C and nutrients to the coastal zone in the form of litter and POC. We found that precipitation is a major factor influencing the export of C in the form of litter; sites with low annual precipitation and high mean annual temperatures export more C as litter than sites with high precipitation and low temperature. Furthermore, export of POC is higher in zones with low mean annual minimum temperature. Identification of broad-scale trends in DOC and dissolved nutrients was more difficult, as the analysis was limited by scarcity of suitable studies and high variability in experimental approaches. However, tidal amplitude and the concentration of nutrients in the floodwater appears to be important in determining nutrient exchange. The strongest conclusion from our analysis is that mangrove forests are in general sources of C and nutrients in the form of litter and POC and that they are most likely to be exporting C subsidies in dry regions.

Small-scale variability in geomorphological settings influences mangrove-derived organic matter export in a tropical bay

“…The among-site variability observed in Gazi Bay is consistent with the pattern recently described by Adame and Lovelock (2011): mangroves dominated by tidal pumping, like the Kinondo stand, are characterised by bidirectional flows that favour retention of autochthonous material and tight interlinkage between mangroves and adjacent seagrass beds. Higher retention of autochthonous organic matter within a mangrove forest has also been reported in arid mangrove systems in the Arabian Gulf with almost no freshwater input (Walton et al, 2014).…”

“…According to the "environmental setting hypothesis" (Twilley, 1985), geomorphological features and hydrology are the most important abiotic factors affecting the exchange of mangrove material across ecosystem boundaries (Adame and Lovelock, 2011;Lee, 1999). In particular, the combined control of river discharge (magnitude and frequency), tidal amplitude, rainfall, and wave action is reported to influence the exchange of material across boundaries in estuarine mangrove systems.…”

“…Otherwise, low rainfall and freshwater runoff have been related to reduced mangrove outwelling (Walton et al, 2014). Tidal amplitude, frequency and direction (flood vs. ebb tide) influence cross-habitat connectivity in the tropical coastal seascape, through bidirectional movements of water and nekton across wide spatial scales (Adame and Lovelock, 2011).…”

Spatiotemporal Variation in Mangrove Chlorophyll Concentration Using Landsat 8

“…In addition, C removal from the atmosphere has been estimated at around 1,170 ± 127 g·C·m −2 ·year −1 [13]. These figures acquire relevance in the context of climate change mitigation as C sequestration is emerging as a major strategy to reduce atmospheric C. In spite of the array of ecosystem services provided by mangroves, their high productivity, and their role played in C dynamics at the land-ocean interface [14], large areal losses are presently occurring due to deforestation and land use conversion due to both human and natural drivers [15,16].…”

Global patterns of aboveground carbon stock and sequestration in mangroves

“…Given the importance that this function may have to justify mangrove conservation, it becomes necessary to direct efforts to quantify the fluxes and pools of carbon in the different compartments of the ecosystem as well as to understand the factors that control them. In the last 20 years, some reviews have been published addressing the storage and flux of carbon or organic matter in mangrove ecosystems (Twilley et al 1992, Saenger and Snedaker 1993, Chmura et al 2003, Komiyama et al 2008, Kristensen et al 2008, Adame and Lovelock 2011, Alongi 2014, Hutchison et al 2014, which sought to synthesize the results of numerous previously published articles on the subject. Although some of these reviews present surveys of aboveground biomass, none have addressed the factors that influence the aboveground biomass (or carbon stock in this compartment) and the rate of aboveground biomass increment (or carbon sequestration in this compartment), except for Hutchison et al (2014) on the role of climate variables.…”