Correct Option
Effluents are liquid waste discharges originating from industrial processes, municipal sewage systems, and agricultural runoff. These discharges introduce a variety of pollutants, including organic matter, inorganic salts, heavy metals, nutrients (such as nitrates and phosphates), and thermal pollution, directly into water bodies. This leads to significant alterations in physico-chemical characteristics such as pH, dissolved oxygen (DO) levels, biochemical oxygen demand (BOD), chemical oxygen demand (COD), electrical conductivity, turbidity, and temperature. Such alterations degrade water quality and adversely affect aquatic ecosystems.
Incorrect Options
- Aquatic macrophytes are macroscopic aquatic plants. While they contribute to nutrient cycling, oxygen production, and habitat provision, they do not fundamentally alter the overall physico-chemical characteristics of water sources under normal conditions. Their excessive growth, often a consequence of nutrient enrichment from other sources, can lead to secondary changes like diurnal dissolved oxygen fluctuations, but they are not the primary cause of direct physico-chemical alteration of the water source itself.
- Aquatic fungi are decomposers within aquatic ecosystems, playing a role in breaking down organic matter and nutrient cycling. However, similar to macrophytes, they do not directly introduce substances that fundamentally change the bulk physico-chemical properties of water sources in the manner that effluents do. Their proliferation is often a response to, rather than a primary cause of, significant physico-chemical changes.
- Evapotranspiration is the process by which water is transferred from the land to the atmosphere through evaporation from surfaces and transpiration from plants. This process primarily involves the movement of water vapor and does not introduce pollutants or chemical substances into the water source. Therefore, it does not directly alter the physico-chemical characteristics of the remaining water in the source.