Still Water (Lentic)
The classification of still water environments is a gradient from lakes to ponds to bogs to swamps and marshes. To understand the biology of lakes, one must understand the influences on aquatic life by light, temperature, oxygen and nutrients. The interaction of these factors influences the abundance, distribution and diversity of most lakes.
The energy source of lake ecosystem is sunlight. The depth to which light can penetrate is limited by the turbidity of the water and the absorption of the light rays. On this basis, lakes can be divided into two basic layers, the trophogenic zone, roughly corresponding to the epilimnion in which photosynthesis dominates, and the second and lower tropholytic zone where decomposition is most active. This zone is about the same as the hypolimnion.
The boundary between the two zones is the compensation depth, the depth at which photosynthesis balances respiration and beyond which light penetration is so low that it is no longer effective. Generally, the compensation depth occurs where light intensity is about 100 foot/candles or approximately 1% of full noon sunlight incident to the surface.
The region of photosynthetic activity can be divided into two subzones. First is the littoral or shallow water zone where light penetrates to the bottom. Rooted plants such as water lilies, rushes and sedges occupy the area. Beyond this is the limnetic or open water zone that extends to the depth of effective light penetration. It is inhabited by plant and animal plankton and the nekton or free swimming organisms such as fish.
Common to both tropholytic and trophogenic zones is the benthic or bottom region. The organisms that inhabit the benthic zone are collectively known as the benthos. Although these areas are named and often described separately, all are closely dependent on one another in nutrient cycles and energy flow.