Modeling Plant-Scale Transient Hydraulics in Hypersaline Mangrove Ecosystems

  • Augustine Nwokoye

Student thesis: Master's Thesis


Mangrove forests are among the most carbon-dense ecosystems worldwide, largely contributing to the global carbon budget. Due to their ability to store a large amount of carbon in their biomass and organic sediment, Mangroves act as natural carbon sinks, significantly mitigating global climate change. Still, mangroves' productivity is a function of many environmental conditions, projected to vary markedly under future climate scenarios. In particular, the amount of carbon they can store in their biomass depends on their response to environmental stress factors, such as increasing temperatures, submersion (hydraulic stress) and salinity (osmotic and ionic stress). As a result, in the world's arid regions, mangroves' potential for carbon sequestration is limited by harsh environmental conditions, resulting in extremely low productivity and soil accretion rates. Dryland mangroves thus represent a unique benchmark for understanding the future of mangrove forests and tidal wetlands in general, under climate change, sea-level rise (SLR) and coastal salinization. In a hyper-arid environment like the UAE, scarce precipitation, hyper-salinity, extraordinary, elevated temperatures, high evapotranspiration rates, and low nutrient inputs (in the absence of river discharge) represent endemic stress factors. These are the same stress factors that humid regions' highly productive mangrove ecosystems are expected to face under future global warming and sea-level rise (SLR). The impacts of salinity on mangrove productivity have been poorly addressed. However, high salinity limits plant growth and its effects on coastal wetlands productivity cannot be dismissed as marginal. Also, in this context, mangroves in arid regions can teach us a big deal about how the mangrove ecosystem will respond to future SLR, seawater intrusion and coastal salinization. In addition, like other forests, mangroves are also affecting the climate on an ecosystem scale. This feedback results from carbon and water exchange between land and the atmosphere (land-atmosphere interactions, L-AI). Understanding L-AI's in tidal regions is key to understanding future climate and its feedback on different biomes. Generally, it's been reported that Mangroves play a significant role in mitigating global climate change due to their ability to capture large amounts of carbon and store them in their biomass and organic sediment. Under future climate scenarios, the productivity of Mangroves will largely depend on their endurance level to a range of environmental conditions. The current study presented the results of an Eddy Covariance monitoring campaign performed in an inter-tidal dwarf Avicennia marina ecosystem in Abu Dhabi, UAE. It explored how salinity affects the transpiration and productivity of the Avicennia marina and the possible feedback this ecosystem has on the local climate. The ecosystems' carbon, water and energy fluxes were estimated, visualized, and compared with results obtained from other experiments. In our study, we found out that the maximum daytime CO2 flux intake, −11.54 µmols −1m−2 , during the study period was observed within November and December, months within the winter period when salinity declined, and air temperature drastically reduced by about 66.79 percent compared to temperatures within July and August when the observation started. During this period, the physiological stress on the mangrove forest was extremely low. Also, we observed that carbon uptake increases (i.e., daytime CO2 fluxes first decreased) with an increasing air temperature and achieved its maximum at an optimal temperature of about 30.5 oC. Beyond this temperature, the mangroves' carbon uptake and respiration increase. Similarly, the daytime CO2 fluxes response curve was significantly influenced by the VPD with an optimum of 2.80 kPa. Additionally, the high carbon assimilation we recorded under high tidal levels justifies that the Avicennia marina mangrove specie is highly resilient and is characterised by its high carbon assimilation rate and water use efficiency (WUE) amidst tidal inundation. Furthermore, the energy fluxes are influenced by varying environmental factors, including VPD, air temperature, tidal inundation, and salinity. For example, more energy is partitioned into latent heat when the sediments are fully inundated during flooding. We recorded higher latent heat fluxes at this level than when the sediments were fully exposed. However, the mangrove forest maintained a lesser transpiration rate at high tidal inundation during this season in November and December, thereby maintaining an increased WUE at high tides. In general, the study provided a better understanding of the possible response of mangroves in the humid regions, albeit more productive than those in the arid areas now, to future environmental conditions.
Date of AwardJul 2022
Original languageAmerican English


  • Eddy Covariance
  • Arid Region
  • Coastal wetlands
  • Avicennia marina
  • CO2 fluxes
  • Salinity
  • Energy Fluxes
  • tidal Inundation.

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