ABSTRACT
ABSTRACT Eutrophication of aquatic systems is often caused by human activities. Here we shall discuss eutrophication and its effects in a shallow freshwater lake caused by purely natural factors involving aquatic birds. Excessive phosphate input into the Kokilamedu Lake via bird droppings led to eutrophication and associated bottom hypoxia and fish kill. Nutrient chemistry of the lake, characterized by low N : P ratio, facilitated the development of a dense chlorophyceandominated phytoplankton standing stock. To analyze the influence of eutrophic conditions on periphyton, the development of periphyton in the Kokilamedu Lake was compared with that in another nearby freshwater reservoir. Parameters such as periphyton thickness, algal density, biomass, chlorophyll a, viable bacterial count, species composition and succession pattern of microalgae were compared. The
results showed that periphyton thickness, algal density, species diversity, biomass, chlorophyll a and bacterial density were significantly different in the two lakes. Species composition as well as succession pattern of microalgae also varied between the two stations. In the Kokilamedu Lake, diatoms dominated the periphyton community throughout the study period; Chlorophyceae and Cyanobacteria were present in lesser numbers. In contrast, in the reservoir, the initial stage (upto three days) was dominated by Chlorophyceae, followed by domination by Bacillariophyceae and finally by Cyanobacteria. Nutrient characteristics of the bulk water influence periphyton development and species composition in the two environments. This chapter also discusses possible strategies for restoration of the lake. It is emphasized that management strategies must concentrate on stoppage of external nutrient loading via bird droppings and internal loading via sediment leaching.
