Light has received very less attention as a selective factor, probably because the changing vertical light gradient makes light a rather complex factor when compared with the nutrient competition. In our study we modified an analytically tractable model based upon the Beer-Lambert law. The study aimed to predict the outcome of phytoplankton competition for light, on the basis of field measurements. When we considered competition theory, Fragilaria was found to be more competitive than other genera. The overall result shows that the trends flow in the following manner; Fragilaria [ Gomphonema [ Diatoma [ Amphora [ Achnanthes.

Light plays an important role in the life of organisms including the whole diversity of plants ranging from microscopic phytoplankton to giant trees, because it is the sole source of energy which effects the growth dynamics and structure of most aquatic and terrestrial communities. The unidirectional nature of light gives rise to a vertical gradient of light intensity as a function of depth.

The present study was performed to estimate the quality of Suswa river at Raiwala. Test for both, physico-chemical and heavy metals were carried out at different sites of the Suswa river near Raiwala.

The  present  study  deals  with  the  analysis  of physico-chemical  parameters  of the  Song river  at Dehradun,  Uttarakhand during  the  pre-autumn,  autumn  and  post-autumn  months  of 2007.  In  the  present  study  of the  Song  river  its  physico- chemical  characteristics  viz  temperature,  velocity,  total  solids,  total  suspended  solids,  total dissolved  solids,  turbidity,  pH, dissolved  oxygen,  free  CO ,  BOD,  COD,  alkalinity,  chlorides,  sulphate  and identification  of fishes  were  done.  The  data revealed  that  36 species  of fishes  are present  in the  Song river  of Dehradun,  Uttarakhand.

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