(i) Nutrients are supplied to the water body from domestic drainage as well as from water run off from agricultural
fields with a cumulative rate, which is assumed to be a constant.
(ii) The algal population density is wholly dependent on cumulative concentration of nutrients.
(iii) The detritus in the water body is formed by the death of algae (phytoplankton), which is transformed
into nutrients by remineralization process using dissolved oxygen.
(iv) The level of dissolved oxygen in water body increases by air, water interaction at the water surface with a
constant rate as well as by photosynthesis/respiration by algae. Its concentration is depleted by its utilization
by detritus in formation of nutrients, the amount of which is assumed to be proportional to the
concentration of dissolved oxygen.