Joyanto Routh

An environmental record of changes in sedimentary organic matter from Lake Sattal in Kumaun Himalayas, India

Sattal a small mountainous lake in the Kumaun Himalayas has been impacted by various cultural activities in recent years. We explored the effects of human-induced changes in this lake by using various geochemical proxies. Shifts in TOC and N flux, C/N ratio, stable isotopes (delta13C and delta(15)N), n-alkane, and pigment concentrations in sediments indicate a steady increase in primary productivity over the last few decades. The trophic status of the lake has changed from mesotrophic to eutrophic condition. The C/N, CPI, and TAR based ratios in sediments indicate accumulation of algal matter derived primarily from in situ production, with limited input of terrestrial organic matter from the watershed. The low (between 0.1 and 1 per thousand) delta15N values imply N2-fixation by cyanobacteria, and the decrease in delta13C values up-core represent the effect of sewage input and land based runoff, or possible contribution from microbial biomass. The pigments change from non-N2 fixing cyanobacterial species to the N2-fixing community, and are consistent with the proxy-based productivity shifts inferred in the lake. The deeper sediments are affected by post-diagenetic changes causing an increase in delta13C (and possibly delta15N) due to mineralization of organic C and N.

Phosphorus dynamics in shallow eutrophic lakes: an example from Zeekoevlei, South Africa

Zeekoevlei is the largest freshwater lake in South Africa and has been suffering from hyper-eutrophic conditions since last few decades. We have used total P (TP), dissolved phosphate (PO43−), organic P (OP), calcium (Ca) and iron (Fe) bound P fractions to investigate the relevant physical, chemical and biological processes responsible for sedimentation and retention of P and to study phosphorus (P) dynamics in this shallow lake. In addition, redox proxies (V/Cr and Th/U ratios) are used to study the prevailing redox conditions in sediments. Adsorption by CaCO3 and planktonic assimilation of P are found to control P sedimentation in Zeekoevlei. Low concentration of the labile OP fraction in surface sediments restricts the release of P by bacterial remineralisation. Low molar Ca/P and Fe/P ratios indicate low P retention capacity of sediments, and P is most likely released by desorption from wind-induced resuspended sediments and mixing of pore water with the overlying water column.

Cave Geomicrobiology in India: Status and Prospects

The subsurface of the Earth is one of the major habitats and contains a significant proportion of microbial life (Whitman et al., 1998; Ghiorse, 2008; Roussel et al., 2008). However, our overall knowledge about the life forms and biogeochemical processes contained within it is rather scarce, mainly because of the difficulties in approaching this habitat. One relatively easy way to approach this habitat is to investigate karst terrains, which expand over ∼20% of the Earth’s subsurface (Ford and Williams, 2007). Since caves are one of the most prominent features of karst terrain, they may serve as noteworthy entries and virtual “windows” into subsurface habitats (e.g. Engel et al., 2008). It is widely recognized that caves can also host a wide spectrum of fascinating life forms, starting from biofilms harbouring different types of microorganisms to different types of cave-dwelling animals such as snails, worms, spiders, leeches, crickets, cockroaches, scorpions, fishes and bats. Cave geobiology is therefore a fascinating discipline for exploring different basic aspects of the subsurface eco-systems and their interactions with the eco-systems of the surface. Cave geomicrobiology deals specifically with the microorganisms, other life forms and their interactions with minerals and provides us with information about the past geomicrobiological interactions.