Krishnan K P, Fernandes Sheryl Oliveira, Chandan G S, Loka Bharathi P A
National Institute of Oceanography, Dona Paula, Goa, India.
Mar Pollut Bull. 2007 Sep;54(9):1427-33. doi: 10.1016/j.marpolbul.2007.05.023. Epub 2007 Jul 16.
The Mandovi and Chapora are two tropical estuaries lying in close geographic proximity on the west coast of India. Seasonal changes in down core variation of Fe, Mn and Total Organic Carbon (TOC) in the mangrove sediments adjoining these estuaries were studied to assess their influence on some of the representative benthic bacteria belonging to heterotrophic and autotrophic groups. Heterotrophic bacteria (HB) cultured on different nutrient concentrations (0.01%, 0.1% and 25%) together with nitrifiers (NtB; representating autotroph) were chosen to assess the influence of the above-mentioned abiotic parameters on the former. The experimental site located along the Mandovi is under the influence of extensive ferromanganese ore mining, while the control site at Chapora is relatively free from such influences. Geoaccumulation index computed for Mandovi showed that sediments (0-10cm) were 'uncontaminated to moderately contaminated' by Fe during the pre monsoon and monsoon seasons, while in the post monsoon season the 4-10cm fraction was almost completely restored from contamination. Similar computations for Mn showed that in pre monsoon, sediments fell in the 'moderately contaminated' and 'moderately to strongly contaminated' categories, while in the monsoon and post monsoon seasons all the sections were 'Uncontaminated'. The difference observed in correlation between Fe and Mn with the various fractions of heterotrophs and nitrifiers indicated that though these two elements shared a similar chemistry in the environment, microbes involved in biogeochemical processes might prefer them differentially. The relationship between TOC and HB enumerated on 0.01% dilute nutrient agar remained at r=0.50, p<0.05 throughout the year. Hence, it could be apparently linked to their preferred concentration of organic carbon requirement. A relationship of r=0.61, p<0.01 between manganese concentration and heterotrophs recovered on different strengths of nutrient agar is suggestive of their response to the metal enrichment. They could thus contribute towards maintaining the level of Mn at par with reference levels at Chapora. A positive correlation between Mn with NtB (n=10, p<0.05, r=0.58) at the experimental site during the non-monsoon months is suggestive of the latter's contribution to regulation of the metal concentration in the sediment probably through anaerobic nitrification at the expense of manganese. The study therefore supports our hypothesis that both autochthonous autotrophs and heterotrophs work in tandem to mitigate concentration of Mn and related metals in mangrove sediments.
曼多维河和乔波拉河是位于印度西海岸地理位置相近的两个热带河口。研究了这些河口附近红树林沉积物中Fe、Mn和总有机碳（TOC）的垂向变化的季节性变化，以评估它们对一些属于异养和自养群体的代表性底栖细菌的影响。选择在不同营养浓度（0.01%、0.1%和25%）下培养的异养细菌（HB）以及硝化细菌（NtB；代表自养菌）来评估上述非生物参数对前者的影响。位于曼多维河沿岸的实验地点受到广泛的铁锰矿开采的影响，而乔波拉河的对照地点相对不受此类影响。对曼多维河计算的地积累指数表明，在季风前和季风季节，沉积物（0 - 10厘米）中的Fe处于“未受污染到中度污染”状态，而在季风后季节，4 - 10厘米的部分几乎完全从污染中恢复。对Mn的类似计算表明，在季风前，沉积物属于“中度污染”和“中度到重度污染”类别，而在季风和季风后季节，所有剖面均“未受污染”。观察到Fe和Mn与异养菌和硝化细菌的不同组分之间的相关性差异表明，尽管这两种元素在环境中具有相似的化学性质，但参与生物地球化学过程的微生物可能对它们有不同的偏好。全年在0.01%稀释营养琼脂上计数的TOC与HB之间的关系保持在r = 0.50，p < 0.05。因此，这显然可能与它们对有机碳需求的偏好浓度有关。锰浓度与在不同强度营养琼脂上回收的异养菌之间的r = 0.61，p < 0.01的关系表明它们对金属富集的反应。因此，它们可能有助于将Mn的水平维持在与乔波拉河参考水平相当的水平。在非季风月份，实验地点的Mn与NtB之间存在正相关（n = 10，p < 0.05，r = 0.58），这表明后者可能通过以锰为代价的厌氧硝化作用对沉积物中金属浓度的调节做出了贡献。因此，该研究支持了我们的假设，即本地自养菌和异养菌协同作用以减轻红树林沉积物中Mn和相关金属的浓度。
