Microorganisms and Water Quality

Abstract

Phytoplankton and bacteria have a greater effect on water quality than do other aquatic microorganisms. Phytoplankton are the main primary producers while bacteria are responsible for the majority of organic matter decomposition and nutrient recycling. An overview of microbial growth, photosynthesis, and respiration is provided, and methods for measuring primary production and respiration in water bodies are discussed. The combined physiological activities of producer and decomposer organisms in water bodies cause pH and dissolved oxygen concentration to increase and carbon dioxide concentration to decrease in daytime, while the opposite occurs during nighttime. In unstratified water bodies, aerobic conditions usually exist in the water column and at the sediment-water interface. Nevertheless, sediment typically is anaerobic at depths greater than a few centimeters in oligotrophic water bodies or greater than a few millimeters in eutrophic water bodies. In anaerobic sediment (or water), the metabolic activity of chemotrophic bacteria is important in decomposing organic compounds resulting from fermentation. Although chemotrophic bacteria are beneficial in assuring more complete decomposition of organic matter, toxic metabolic wastes—particularly nitrite and hydrogen sulfide—produced by these microorganisms can enter the water column. Blue-green algae—often called cyanobacteria—tend to dominate phytoplankton communities in eutrophic waters. Blue-green algae can cause surface scums and shallow thermal stratification, be toxic to other algae and aquatic animals, or produce taste and odor problems in public water supplies.