Andaman mangrove sediments: source of nutrients and sink of heavy metals

Abstract

Andaman Islands (AI) of India is a biodiversity hotspot of mangroves but biogeochemical dynamics of AI is less understood. We collected sediment samples of four AI mangrove sites and one site without mangroves for nutrients and trace metal analysis. Samples were collected from each site at the inlet of seawater (Zone A) and the other 500m into the mangrove creek (Zone B). Nutrients (sulphate, ammonium, nitrite and nitrate) levels, organic matter (OM) and carbon content were higher at Zone B of mangrove ecosystem due to the higher OM content from mangrove leaf litter decomposition and microbial degradation. Metal (Pb &Cd) content of zones with and without mangroves were similar and Igeo values indicated moderate contamination of mangrove zones of AI due to lack of anthropogenic pollution. Our results suggest mangrove ecosystems of AI are uncontaminated from heavy metals and are source of nutrients to the oligotrophic coastal ecosystems of Andaman Sea.

Seagrass Ecosystems of India as Bioindicators of Trace Elements

“…The concentration of Fe in the sediment were higher on the west coast at Vijayagiri and Ratnagiri of Maharashtra within the H. beccarii meadows (Table 2). However, these Fe values in the sediment of H. beccarii are more than three decades old and this high concentration of Fe in H. beccarii sediment compared to other seagrass ecosystem of India can be due to its presence within close proximity of mangrove sediments, which act as sink of trace elements (Apte et al, 2016;Mishra and Kumar, 2020). Though most of the trace element levels in the sediment of S. isoetifolium, T. hemprichii and C. serrulata meadows of Palk bay have similar levels in their sediment (Govindasamy et al, 2013;Libin Baby et al, 2017;Thangaradjou et al, 2013) the concentration of Cu and Zn are 20-fold lower in the sediment of T. hemprichii meadows (Jagtap and Untawale, 1984).…”

Seagrass ecosystem adjacent to mangroves store higher amount of organic carbon of Andaman and Nicobar Islands, Andaman Sea

“…Thalassia hemprichii is one of the keystone seagrass species of ANI found in the sandy intertidal habitats and amidst coral rubbles up to a depth of 15 m (Jagtap et al, 2003). Thalassia hemprichii is also found associated with other seagrass species such as H. ovalis and C. rotundata or with mangrove ecosystems (Mishra and Mohanraju 2018;Mishra and Apte 2020;Mishra and Kumar 2020). The association of T.…”

Ecological association between seagrass and mangrove ecosystems increases seagrass population longevity in island ecosystem

“…The plastochrome interval (Site 1 (25.49 days/leaf), site 2 (26.8 days/leaf)) in our studies for T. hemprichii were higher, than observed for T. hemprichii population of Philippines coast (9.19 days/leaf) (Rollon et al, 2010). However, when compared to global plastochrome interval of T. hemprichii (10.9-21.9 days/leaf) data of Short and Duarte, (2001), the T. hemprichii population of ANI required more days to produce a single leaf compared to global data, which can be the impact of low nutrient content in the oligotrophic waters of Andaman Sea (Mishra and Kumar, 2019, accepted article) for T. hemprichii population. Secondly our sampling period was in summer season, when more energy is diverted towards T. hemprichii reproductive cycle than plant productivity for T. hemprichii population of Andaman Sea (Tongkok et al, 2018).…”

“…The number of leaves per shoot and the number of leaves produced per year (Table 1) derived from plastochrome interval for site 1 (25.49 days per leaf) was higher compared to site 2 without mangroves, which suggests the T. hemprichii meadows being associated with mangroves have the requisite nutrients and favourable conditions to produce a single leaf within 25.49 days, whereas the site without mangroves is deprived of nutrients as the waters of Andaman Sea are oligotrophic (Mishra and Mohanraju, 2018; Mishra and Kumar, 2019 accepted article) and are under immense pressure from breaking waves. The number of leaves per shoot at site 2 (3.80±0.03) in our studies are similar (3.80) and higher at site 1 (3.98±0.01) to previously observed results of ANI (Savurirajan et al, 2018).…”