Browsing by Author "Mishra, Amrit Kumar"
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- Elevated trace elements in sediments and seagrasses at CO2 seepsPublication . Mishra, Amrit Kumar; Santos, Rui; Hall-Spencer, JasonSeagrasses often occur around shallow marine CO2 seeps, allowing assessment of trace metal accumulation. Here, we measured Cd, Cu, Hg, Ni, Pb and Zn levels at six CO2 seeps and six reference sites in the Mediterranean. Some seep sediments had elevated metal concentrations; an extreme example was Cd which was 43x more concentrated at a seep site than its corresponding reference site. Three seeps had metal levels that were predicted to adversely affect marine biota, namely Vulcano (for Hg), Ischia (for Cu) and Paleochori (for Cd and Ni). There were higher-than-sediment levels of Zn and Ni in Posidonia oceanica and of Zn in Cymodocea nodosa, particularly in roots. High levels of Cu were found in Ischia seep sediments, yet seagrass was abundant there, and the plants contained low levels of Cu. Differences in bioavailability and toxicity of trace elements helps explain why seagrasses can be abundant at some CO2 seeps but not at others.
- Global change effects on seagrass ecosystemPublication . Mishra, Amrit Kumar; Santos, RuiLong and short effects of increased CO2 on seagrass carbon metabolism were investigated. Cymodocea nodosa meadows, exposed to long term elevated CO2 at shallow volcanic CO2 seeps off Greece and Italy were investigated using population reconstruction techniques. Growth, morphometry, density, biomass and age structure was affected by high CO2. Above to below ground biomass ratio of C. nodosa were higher at CO2 seeps. C. nodosa population grew faster but longevity of plants was lower at the seeps. The present recruitment (sampled year) of the seagrass was higher near the seeps. Carbon to nitrogen ratios (%DW) in leaves and annual leaf production of C. nodosa were higher at seeps. Elements (Fe and Cd, Cu, Co, Hg, Pb, Mn, Ni and Zn) were analysed from sediments and P. oceanica and C. nodosa compartments from CO2 seeps off Greece and Italy. Sediment Quality Guidelines Quotient pollution index indicated higher element level seeps than reference sites with possibility of moderate to adverse biological impacts. Element concentration in the sediments and seagrass compartments were higher at seeps. Higher accumulation of elements in the seagrass compartments were observed. Net community production (NCP) and community respiration (CR) of intertidal Z. noltii and unvegetated sediment communities were measured under air exposed and CO2 enriched conditions seasonally. Increase in NCP of Z. noltii and sediment community were observed with elevated CO2 concentrations than natural conditions within similar light range. NCP of Z. noltii was higher than sediment community in both summer and winter seasons under CO2 enriched conditions. CR of both communities were less affected under CO2 enriched conditions. Light compensation point of Z. noltii were lower than sediment communities in summer season with elevated CO2 levels. Seasonal community production of Z. noltii were higher than sediment communities. Significant effect of light on NCP was observed from linear regression model.