Iron released from ilmenite mineral sustains a phytoplankton community in microcosms

Abstract

Natural biotic communities from Kalbadevi Bay were monitored in microcosms (1-l glass flasks) to test the hypothesis that iron released from ilmenite through microbial action contributes to proliferation of phytoplankton. Microcosms containing ilmenite had significantly higher phytoplankton growth compared with controls containing no ilmenite or those containing only ferrous sulfate. Phytoplankton cell numbers in the ilmenite-supplemented treatment were 20= higher than in controls. The later stages were marked by the dominance of bottom dwelling Nitzschia spp. and Navicula spp. Iron-preferring Eunotia spp. and Pinnularia spp. were also encountered. Hence, increased phytoplankton biomass may be attributable to the steady release of bioavailable iron. We therefore infer that ilmenite mineral might sustain the phytoplankton community in ilmenite-dominated systems. Increases in density and diversity of phytoplankton over time and significant interrelationship between various parameters in the microcosm containing ilmenite indicate that stimulatory effect of iron released from this mineral could be beneficial to the biota in the system.

An appraisal of biological responses and network of environmental interactions in non-mining and mining impacted coastal waters

“…The similar order in abundance in TC and TVa at 10 8 cells/l in RAT was indicative of higher viability of aerobic bacterial community. This feature has been earlier recorded in the adjoining beach sediments and bay waters (Fernandes 2011). The variation in the nutrient concentrations brought about changes in the relative abundance of diatoms and dinoflagellates.…”

“…This range, especially in the sediments, was comparatively higher than other Indian coastal regions (Alagarsamy 2006). In contrast, the associated mangroves of RAT cover a mere 8.28 sq.km while the total iron is the range of 50-149 mg/g and~10 mg/l in sediment and water, respectively (Table 1; Rokade 2009;Fernandes 2011). Therefore, the total sedimentary iron concentration is 3-4 times higher in GOA than RAT.…”

“…Additionally, the sediments are rich in placer minerals such as ilmenite (FeTiO 3 ) and magnetite (Fe 3 O 4 ) (Siddiquie and Rajamanickham 1979). Bio-available iron released from these minerals is perhaps involved in enhancing regional primary productivity subsequently enhancing the tertiary productivity of the area (Fernandes et al 2011; Department of Fisheries, Government of Maharashtra, India, http://fisheries. adfmaharashtra.in).…”

Environmental Gradient Favours Functionally Diverse Macrobenthic Community in a Placer Rich Tropical Bay

“…Therefore, it may be possible that in Kalbadevi Bay, iron may not be a limiting factor for phytoplankton as it may be continuously leached from ilmenite (FeTiO 3 ). Mats of green algae have been also observed in the sea floor of the bay [34]. This could also explain for the high quality organic matter in the region throughout the year.…”

“…There was no significant seasonal or spatial change in PRT concentration and PRT : CHO ratio. Further, a microcosm study demonstrated the influence of bioavailable iron released from ilmenite by microbial action on the abundance and diversity of phytoplankton [34]. Therefore, it may be possible that in Kalbadevi Bay, iron may not be a limiting factor for phytoplankton as it may be continuously leached from ilmenite (FeTiO 3 ).…”