This chapter presents a generalized picture of various aspects of assimilation by native biota and underscores the importance of safeguarding the environment from excessive discharge of nutrient-rich effluents, even though they are non-toxic. It reveals the findings of mesocosm experiments, conducted to evaluate the assimilation potential of water column biota (bacteria, phytoplankton, and zooplankton). Bulk water quantities from coastal locations, characterized by intense tourist activity, were brought to set up mesocosms during pre-monsoon, monsoon, and post-monsoon periods. Six different conditions - with organic nutrients (urea), inorganic nutrients (nitrate, phosphate), and toxic responses of biotic components to altered situations. Several relevant parameters were monitored through the three seasons. Results of the study suggest that the native biota cannot utilize nutrients beyond certain limits even in a non-toxic, unpolluted condition. Also, toxic chemicals are far more deleterious in combination than individually