7 public questions tagged with this topic.
Cyanobacterial colonies are generally surrounded by a gelatinous sheath and often form blooms in polluted water bodies. Cyanobacteria may be unicellular, colonial or filamentous.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Bacteria - Structure and Economic Importance
Eutrophication is enrichment of water with nutrients, especially phosphorus in many fresh waters and nitrogen in many coastal systems. The added nutrients remove a growth limitation on phytoplankton or cyanobacteria, allowing rapid population increase that appears as an algal bloom. Dense blooms reduce water clarity and shade submerged vegetation. When algal cells die, bacteria decompose the organic matter and consume dissolved oxygen; stratified bottom waters may then become hypoxic or anoxic. Fish kills, loss of oxygen-sensitive species, toxin-producing cyanobacteria, unpleasant odours, and altered food webs may follow. Nutrient enrichment can initially increase biomass or the abundance of a few species, but it does not reliably boost biodiversity and often reduces it through dominance and oxygen stress. Clear water and higher oxygen are therefore opposite to the common late consequences. Natural eutrophication occurs slowly as basins age, whereas fertilizer, manure, sewage, and urban runoff can accelerate it dramatically. The bloom is the immediate visible response because nutrient supply raises photosynthetic growth before decomposition generates oxygen depletion.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3
Synthetic estrogens such as 17alpha-ethinylestradiol can feminise fish by binding estrogen receptors and altering gene expression during gonadal development and adult reproduction. Effects include male vitellogenin production, intersex tissue, reduced sperm production, female-biased phenotypes, and population decline. Testosterone is androgenic rather than estrogenic, while mercury and PCBs have important toxic effects but are not the clearest specific answer. Trophic transfer can occur when predators consume contaminated prey, although evidence for consistent biomagnification of particle numbers remains system-dependent. Standardised sampling and contamination controls are essential because airborne fibres can enter samples during collection and laboratory processing. Particle size, shape, polymer type, weathering state, and associated chemicals all influence uptake and biological response, so microplastics are not a uniform toxicant. Laboratory effects must be interpreted alongside environmentally realistic concentrations, while field detection demonstrates exposure but does not alone prove causation. Prevention requires reducing unnecessary plastic use, improving collection and recycling, controlling lost fishing gear, and limiting releases of fibres and tyre-wear particles.
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology
Many pharmaceuticals are consumed, incompletely metabolised, and excreted in urine or faeces. Sewer systems carry the parent compounds and active metabolites to treatment plants, where conventional processes may not remove them completely; treated effluent or untreated sewage then reaches rivers and lakes. Improper disposal can add to this route. Aerosols, fertilisers, and forest runoff are not the dominant general pathway. Because conventional polymers persist, fragmentation redistributes plastic into smaller pieces rather than removing its mass from the ecosystem. Trophic transfer can occur when predators consume contaminated prey, although evidence for consistent biomagnification of particle numbers remains system-dependent. Standardised sampling and contamination controls are essential because airborne fibres can enter samples during collection and laboratory processing. Particle size, shape, polymer type, weathering state, and associated chemicals all influence uptake and biological response, so microplastics are not a uniform toxicant. Laboratory effects must be interpreted alongside environmentally realistic concentrations, while field detection demonstrates exposure but does not alone prove causation.
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology
Excess nitrogen and phosphorus stimulate eutrophication by removing nutrient limitation on algae and cyanobacteria. Dense blooms reduce light penetration, and their eventual decomposition raises microbial oxygen demand, producing hypoxia or anoxia that can kill fish and benthic animals. Some cyanobacteria also release toxins. Mercury, lead, and cadmium are hazardous metals, but they do not drive the nutrient-enrichment process that defines eutrophication. Aquatic effects depend on chemical form, persistence, solubility, dose, and the capacity of organisms to metabolise or excrete the substance. Catchment processes connect land use with rivers, lakes, estuaries, and coastal waters, so prevention at the source is usually more effective than downstream treatment. Ecological assessment distinguishes hazard from risk: a substance may be intrinsically harmful, but realised impact also requires sufficient environmental exposure. Sensitive developmental stages may respond at concentrations that cause little immediate adult mortality, making reproduction and recruitment essential endpoints. Monitoring should include appropriate controls, spatial replication, temporal variation, and validated analytical methods before broad conclusions are drawn.
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology
Fertiliser runoff is a non-point source because nutrients leave many dispersed fields through rainfall, overland flow, erosion, and subsurface drainage rather than through one readily identified discharge pipe. Its loading varies with land use, weather, soil, and farm management. A sewage outlet or industrial effluent pipe is a point source whose location can be mapped and monitored directly. Community-level consequences can emerge when physiological injury changes survival, reproduction, species interactions, or the flow of energy through food webs. Aquatic effects depend on chemical form, persistence, solubility, dose, and the capacity of organisms to metabolise or excrete the substance. Catchment processes connect land use with rivers, lakes, estuaries, and coastal waters, so prevention at the source is usually more effective than downstream treatment. Ecological assessment distinguishes hazard from risk: a substance may be intrinsically harmful, but realised impact also requires sufficient environmental exposure. Sensitive developmental stages may respond at concentrations that cause little immediate adult mortality, making reproduction and recruitment essential endpoints.
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology
High nitrate in drinking water can cause infant methaemoglobinaemia, commonly called blue baby syndrome. Gut microbes reduce nitrate to nitrite, which oxidises haemoglobin iron from the ferrous to ferric state, producing methaemoglobin that cannot bind oxygen effectively. Infants are particularly susceptible because of gastrointestinal and enzymatic features. Minamata and Itai-itai diseases involve mercury and cadmium, respectively, while cholera is an infection. Sensitive developmental stages may respond at concentrations that cause little immediate adult mortality, making reproduction and recruitment essential endpoints. Monitoring should include appropriate controls, spatial replication, temporal variation, and validated analytical methods before broad conclusions are drawn. Community-level consequences can emerge when physiological injury changes survival, reproduction, species interactions, or the flow of energy through food webs. Aquatic effects depend on chemical form, persistence, solubility, dose, and the capacity of organisms to metabolise or excrete the substance. Catchment processes connect land use with rivers, lakes, estuaries, and coastal waters, so prevention at the source is usually more effective than downstream treatment.
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology
