Interactions between pH and other physicochemical properties of mangrove sediments: A review

Abstract

Mangrove ecosystem provides a broad array of ecological services including carbon fixation and storage, pollution prevention, water purification and maintaining a high level of biodiversity. However, mangrove systems cannot migrate, these wetlands are now facing a slew of serious threats from climate change and human activities that shrinking mangrove habitats intact, ecosystem structure and its ecological functions. A net loss can be expected in many of these ecosystems. Key physiochemical properties of mangrove sediments such as pH, nutrient contents, and salinity, play important roles in regulating mangrove growth and their ecosystem functions. Different physiochemical properties of mangrove soils can influence each other through microorganism activities or chemical reactions. When changes in one physiochemical factor are accompanied by changes in another, it will adversely affect mangroves and even the entire ecosystem. In order to maintain the carbon fixation and storage functions of mangrove ecosystem, it is an emerging priority to keep the pH of mangrove soil fluctuate in a reasonable range. Mangrove sediments are usually acid-sulphate soils with high sulfur content, and their pH are generally negatively correlated with total sulfur content. Total mass, species, density, distribution, and population structure of mangroves directly affect the soil sulfur content. The oxidation state of the soil, sulfur content, and the speciation and distribution of sulfides are important factors in determining the soil pH. Meanwhile, the pH is also affecting the sulfide minerals in mangrove soil. Moreover, the intake and decomposition of organic matter in mangrove soil is an ongoing process, in which the organic carbon content and its speciation affect soil pH by changing the population structure, growth, and physiological processes of soil bacteria. Concurrently, the balance of soil pH affects the organic carbon content and its speciation in the mangrove soil. There is generally a positive correlation between pH and salinity in hyperhaline mangrove soil; however, whether salinity directly affects or indirectly affects pH changes remains to be further studied. Thus, systematic studies on the destruction, protection and reconstruction of mangroves are urgently needed. In this review, we summarized our current understandings focusing on the pH of mangrove sediments and its interactions with other physical and chemical properties including salinity, sulfur, organic carbon, dissolved oxygen, nitrogen, and phosphorous contents. We also examined the possible impacts on the pH and other physiochemical properties of mangrove sediment from climate change and human activities, such as sea level rise, pollution discharge and mangrove restoration. Moreover, the effects of these changes on structure, functions and ecological services of mangroves ecosystems were evaluated. The research contents and analysis methods reviewed in this article have important reference significance for the carbon storage capacity, restoration and reconstruction of mangroves.