Water, though it may appear clear, is a complex environment teeming with microscopic life. These tiny living things, known as water microorganisms, are found in virtually all water bodies across the planet, including oceans, rivers, lakes, and groundwater. They play important roles within aquatic environments, influencing processes that maintain ecosystem balance.
Types and Habitats
Water microorganisms encompass diverse forms, including bacteria, viruses, protozoa, algae, and fungi. Bacteria are single-celled organisms that lack a membrane-bound nucleus. Viruses are non-cellular infectious agents that reproduce inside the living cells of host organisms. Protozoa are single-celled eukaryotic organisms, some motile, forming the base of many food webs, providing nutrients for other organisms.
Algae are plant-like eukaryotes that contain chlorophyll and perform photosynthesis, ranging from microscopic unicellular forms to multicellular structures. Fungi are eukaryotic organisms with rigid cell walls, which can be unicellular (like yeasts) or multicellular (like molds). Unlike algae, fungi do not contain chlorophyll and absorb dissolved nutrients from their environment. These microorganisms thrive in various aquatic environments, including freshwater bodies like lakes, rivers, and ponds, as well as saltwater environments such as oceans and estuaries. They are also present in groundwater and in treated drinking water systems, though their presence in the latter is minimal and carefully controlled.
Roles in Aquatic Ecosystems
Microorganisms perform many functions in aquatic environments. They act as decomposers, breaking down organic matter from dead plants and animals. This process recycles nutrients, such as phosphorus and nitrogen, back into the ecosystem, making them available for new plant growth.
These organisms are also involved in nutrient cycling, including the nitrogen, carbon, and sulfur cycles. Nitrogen-fixing bacteria convert atmospheric nitrogen into forms usable by other organisms, while nitrifying bacteria oxidize ammonium to nitrate. Photosynthetic microorganisms, such as algae and cyanobacteria, are primary producers that convert sunlight and nutrients into organic matter, forming the base of aquatic food webs and providing energy for larger organisms. Their photosynthetic activity also contributes to oxygen production, helping to maintain dissolved oxygen levels in water bodies.
Impact on Human Health and Water Quality
Water microorganisms can significantly impact human well-being and water usability. Waterborne pathogens are microorganisms that can cause illness if ingested. Common pathogenic bacteria include Escherichia coli (E. coli), which can cause diarrheal disease, and Salmonella, which can lead to salmonellosis or typhoid fever. Other bacterial pathogens like Campylobacter jejuni can cause gastroenteritis.
Viruses such as Norovirus and Hepatitis A are also transmitted through contaminated water, causing acute gastroenteritis and infectious hepatitis, respectively. Protozoa like Giardia lamblia and Cryptosporidium parvum are common causes of waterborne diseases, leading to gastrointestinal illnesses such as giardiasis and cryptosporidiosis.
Beyond direct health impacts, microorganisms can degrade water quality in other ways. Excessive growth of algae or cyanobacteria, known as algal blooms, can cause visual pollution, produce unpleasant tastes and odors, and deplete oxygen levels in the water, harming fish and other aquatic life. Some cyanobacteria can also produce toxins, such as microcystin, which can be harmful to animals and humans if ingested. Biofilms, resilient microbial layers formed by bacteria and fungi, can attach to surfaces like pipes in water distribution systems. These slimy layers can restrict water flow, contribute to pipe corrosion, and harbor pathogens, compromising water quality and potentially leading to health risks. Biofilms can also alter water characteristics, causing changes in taste, odor, and appearance.
Managing Microorganisms in Water
Various methods are employed to control and manage microorganisms in water, especially for human consumption. Drinking water treatment typically involves several steps to ensure water safety. Coagulation and flocculation help bind small particles, forming larger flocs that settle out during sedimentation. Filtration through materials like sand, gravel, or charcoal physically removes germs, including parasites, bacteria, and viruses.
Following filtration, disinfection methods are used to kill or inactivate any remaining pathogens. Common disinfection techniques include chlorination, which adds chlorine, chloramine, or chlorine dioxide to the water. Ultraviolet (UV) light disinfection uses short-wavelength UV-C light to destroy the nucleic acids of microorganisms. Ozonation involves infusing water with ozone, a powerful oxidizing agent that destroys microorganisms and degrades organic pollutants.
Microorganisms are also utilized in wastewater treatment plants to break down pollutants. Aerobic bacteria, such as Pseudomonas, Nitrosomonas, and Nitrobacter, consume organic matter in the presence of oxygen, converting harmful waste into safer by-products like carbon dioxide, water, and nitrogen. Anaerobic bacteria, like methanogens, break down complex organic compounds in the absence of oxygen, producing biogas and reducing sludge volume. These biological processes reduce the biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of wastewater, leading to cleaner effluent.
Preventing contamination and ongoing monitoring are also important. Protecting source water from pollution, ensuring proper sanitation practices, and routine monitoring of water quality help detect and prevent microbial contamination. Microbial source tracking (MST) techniques, which analyze genetic material in fecal bacteria, can identify the specific sources of contamination, enabling targeted corrective actions to improve water quality.