Effects of nutrient limitation, salinity increase, and associated stressors on mangrove forest cover, structure, and zonation across Indian Sundarbans

• Published in: Hydrobiologia 2019-10, Vol.842 (1), p.191-217
• Main Authors: Chowdhury, Rajojit, Sutradhar, Tapan, Begam, Mst. Momtaj, Mukherjee, Chandan, Chatterjee, Kiranmoy, Basak, Sandip Kumar, Ray, Krishna
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Biomedical and Life Sciences; Coastal zone management; Cores; Decomposers; Ecology; Forest degradation; Forests; Freshwater & Marine Ecology; Intrusion; Life Sciences; Mangrove swamps; Mangroves; Microorganisms; Mineral nutrients; Nutrient cycles; Nutrient release; Primary Research Paper; Salinity; Salinity effects; Salinity gradients; Shorelines; Soil; Soil conditions; Soil nutrients; Species; Sulfides; Sulphides; Surveying; Tides; Zonation; Zoology
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1007/s10750-019-04036-9

Anthropogenic coastal activities and natural stressors aggravate degradation of small coastal patches of mangroves, which in turn destroy local resilience of mangrove forests in the Indian Sundarbans, the continuous mangrove habitat that spans between India and Bangladesh. We conducted an analytical survey across 19 shoreline mangrove fringes spanning the Sundarbans, including both healthy and disturbed forests, and evaluated ninety-five 60-cm composite sediment cores across a degradation and salinity gradient from ~ 4 to ~ 12 ppt. Increased salinity and anoxicity greatly inhibited nutrient cycling and release by microbial decomposers, subsequently resulting in nutrient-poor soil as a condition of degradation. Nutrient limitation, salinity rise, anoxicity increase, and sulfide build-up negatively controlled forest structure causing declines of forest coverage from ~ 98 to ~ 11%. In addition, the tide-dominated salinity gradient controlling species zonation was disrupted in disturbed forests with salinity-sensitive species gradually disappearing. An obvious change in species distribution is anticipated while salt-sensitive Heritiera fomes , Xylocarpus spp., and Phoenix paludosa failed to cope with increased salinity, evident by their absence from many forests. Excoecaria agallocha and Avicennia spp. acclimated well and expanded freely into degraded forests across the Sundarbans. Overall, our study strongly establishes salinity intrusion as primary mechanism for mangrove degradation.