Title: A comparative analysis of mangrove health and carbon storage along porewater electrical conductivity gradients in Lamu, Kenya

Author: Agnes Wanyonyi

Supervising Institution: IHE Delft Institute for Water Education

Year: 2025

 

Abstract:

Lamu is endowed with mangrove biodiversity and has Kenya’s largest continuous acreage of mangroves approximately 33000 hectares which provides critical ecological, socio-economic and climate regulation services. They support biodiversity especially fisheries, stabilize the coastline and act as carbon sinks contributing to climate change mitigation through blue carbon storage. However, these ecosystems are increasingly threatened by multiple stressors due to anthropogenic and natural processes. These includes overexploitation by local communities for timber and other non-wood products, clearing for urban development and mariculture, pollution and rising sea levels. Mangroves are also affected by variations in salinity whose proxy in this study was porewater electrical conductivity and is a significant factor affecting overall mangrove ecosystem health and functioning.
This study assessed mangrove health and soil organic carbon storage along porewater electrical conductivity gradients in Lamu, Kenya. The primary objective was to assess how variations in porewater electrical conductivity influenced mangrove traits expression, biomass, species composition and soil organic carbon stocks across selected mangrove sites. Field data were collected from Kipungani, Kizingo and Matondoni where key mangrove parameters were recorded at plot and tree level. Plot level characteristics included canopy cover and height, sapling density, dieback and species composition, porewater electrical conductivity and soil organic carbon while above and below ground biomass, tree height, diameter at breast height, leaf and root characteristics were taken for mangrove trait characteristics. Multivariate statistical analysis including Principal Component Analysis and correlation tests was performed to examine the relationships between environmental gradients and mangrove ecosystem health indicators. No significant relationships were found between porewater electrical conductivity and mangrove health indicators. There were weak correlations between soil organic carbon and porewater electrical conductivity. Notable correlations were found between soil organic carbon and mangrove traits of different species. Ceriops tagal and Xylocarpus granatum had positive correlation while Avicennia marina had negative correlations. The findings highlighted the complex interactions in the mangrove ecosystem which could have obscured direct linear relationships rather it illustrated mangroves relationship with external factors like organic carbon. Hence, it is recommended that in future studies multiple variables such as sediment characteristic, tidal regimes, human impacts and nutrient dynamics should be considered in such complex ecosystems. Despite the lack of direct significant relationships among the variables, the study contributes to baseline knowledge on mangrove traits responses to environmental variables and soil organic carbon distribution in Kipungani, Kizingo and Matondoni in Lamu. The significant correlations found between mangrove traits with soil organic carbon was beyond the primary objectives of the current study which remains a potential area of research for future studies to further investigate on specific mangrove species and blue carbon potential. It is recommended that for future studies, multiple environmental variables should be considered in longer-term monitoring campaign.

 

Keywords: Mangrove, carbon storage, biodiversity, porewater electrical conductivity, ecosystem, soil organic carbon