Science of Water : Concepts and Applications

160 The Science of Water: Concepts and Applications
Decomposers make up the fi nal biotic part. They include aquatic bacteria and fungi, which are
distributed throughout the pond.
As stated earlier, an ecosystem is a cyclic mechanism. From a functional viewpoint, an
ecosystem can be analyzed in terms of several factors. The factors important in this study include
the biogeochemical cycles and energy and food chains.
BIOGEOCHEMICAL CYCLES
Several chemicals are essential to life and follow predictable cycles through nature. In these natural
cycles or biogeochemical cycles, the chemicals are converted from one form to another as they
progress through the environment. The water/wastewater operator should be aware of those cycles
dealing with the nutrients (e.g., carbon, nitrogen, and sulfur) because they have a major impact on
the performance of the plant and may require changes in operation at various times of the year to
keep them functioning properly; this is especially the case in wastewater treatment. The microbiology
of each cycle deals with the biotransformation and subsequent biological removal of these
nutrients in wastewater treatment plants.
√ Note: Smith (1974) categorizes biogeochemical cycles into two types, the gaseous and the sedimentary.
Gaseous cycles include the carbon and nitrogen cycles. The main sink of nutrients in
the gaseous cycle is the atmosphere and the ocean. Sedimentary cycles include the sulfur cycle.
The main sink for sedimentary cycles is soil and rocks of the Earth’s crust.
CARBON CYCLE
Producers (rooted plants)
Producers (phytoplankton)
Primary consumers (zooplankton)
Sediment
Sun
Secondary consumer (fish)
Tertiary consumer (turtle)
Dissolved
chemicals
FIGURE 6.3 Major components of a freshwater pond ecosystem.
Freshwater pond
Decomposers (bacteria and fungi)
Carbon, which is an essential ingredient of all living things, is the basic building block of the large
organic molecules necessary for life. Carbon is cycled into food chains from the atmosphere, as
shown in Figure 6.4.
From Figure 6.4 it can be seen that green plants obtain carbon dioxide (CO 2 ) from the air and
through photosynthesis, which is described by Asimov (1989) as the “most important chemical