Water Pollution Indicators: Signs Of Aquatic Distress

Water quality is a fundamental factor for human development, as it directly affects human well-being and health, industrial and domestic use, and the natural environment. Water pollution refers to the contamination of water by toxic elements and harmful chemical agents, which alter the natural state of water, including its physical, chemical, and biological properties. There are several indicators of water pollution, including dissolved oxygen, turbidity, pH, bioindicators, nitrate chemicals, and water temperature. These indicators provide data that gives important information on pollution and changes in patterns of standard behaviour.

Temperature

Water temperature can be defined as a measurement of the average thermal energy of a substance. This thermal energy is the kinetic energy of the water's atoms and molecules, and it can be transferred between substances as heat. Heat transfer, from sources such as the air, sunlight, or another water source, can cause fluctuations in water temperature throughout the day and between seasons.

Groundwater, streams, and rivers can alter the temperature of the receiving body of water. For example, if a spring or groundwater source is colder than the river it flows into, the river will become cooler. Similarly, glacial-fed streams will keep conjoining rivers cooler near the source compared to further downstream.

Man-made influences can also significantly impact water temperature. Thermal pollution, which is any discharge that dramatically alters the temperature of a natural water source, is a primary concern. This can include municipal and industrial effluents, runoff from impervious surfaces like parking lots, and deforestation. Deforestation removes the shading that vegetation provides, allowing sunlit water to absorb more heat and altering the natural temperature cycle and habitats.

Water temperature directly affects aquatic organisms and their habitats. It influences the metabolic rates, biological activity, and chosen habitats of various aquatic life. Some organisms, like certain aquatic plants, thrive in warmer temperatures, while some fish species, such as trout or salmon, prefer colder streams. The reproductive stage, particularly spawning and embryo development, is the most temperature-sensitive period for fish. Deviations from the optimal temperature range for a given species can increase stress levels and even lead to death.

Dissolved oxygen

Oxygen is essential for the survival and growth of aquatic organisms, including fish, invertebrates, bacteria, and plants. These organisms use oxygen in respiration, with some obtaining oxygen for respiration through their gills, and others requiring DO for respiration when there is no light for photosynthesis. The amount of DO needed varies from creature to creature. For example, bottom feeders, crabs, oysters, and worms need minimal amounts of oxygen (1-6 mg/L), while shallow-water fish need higher levels (4-15 mg/L).

The presence of excess organic material in lakes and rivers can cause eutrophic conditions, which is an oxygen-deficient state that can lead to a water body's death. This can occur due to pollution from fertilizer runoff or poorly treated wastewater. Algal blooms, which are common in eutrophic lakes, can initially boost DO levels, but as more algae means more plant respiration, drawing on DO, and the subsequent decomposition by bacteria, the available oxygen is rapidly depleted.

Water temperature also affects DO concentrations in a river or water body. Cold water can hold more dissolved oxygen than warm water. Consequently, DO concentrations are usually higher in winter than in summer.

pH

The pH of water is an important factor in determining water quality. It can be affected by pollution, which can cause harm to animals and plants living in the water. For example, water contaminated by coal mining activities can have a pH of 2, which is highly acidic and detrimental to aquatic life. Conversely, high pH levels can also be problematic, as they can affect the taste of water, cause deposits to form on pipes and appliances, and reduce the effectiveness of chlorine disinfection.

Fluctuations in pH can be caused by various factors, including pollution and environmental changes. Acid rain, resulting from the reaction of water with nitrogen and sulfur oxides, is a well-known example of how human activities can influence the pH of water. Other sources of pH variation include point source pollution, which can increase or decrease pH depending on the specific chemicals involved, and natural processes such as intense photosynthesis, which typically lead to diurnal increases in pH.

The optimal pH range for most aquatic organisms is between 6.5 and 8. Deviations from this range can cause physiological stress, reduced reproduction, decreased growth, disease, and even death. Even small changes in pH can significantly impact the community composition of streams, as certain species are adapted to specific pH levels. This, in turn, can lead to a decrease in biological diversity.

While pH is a critical indicator of water quality, it is not the only factor that determines it. Other indicators, such as dissolved oxygen, turbidity, and total suspended solids, also play a significant role in assessing the overall health of a water body.

Total dissolved solids

TDS is important because it affects water taste, appearance, and safety. High TDS levels can make water taste bad, leading to a salty or bitter flavour. It can also harm plants and animals and, in some cases, be toxic to humans. For example, very high TDS levels can cause gastrointestinal irritation. Water with a TDS above 1000 mg/L may taste unpleasant, discouraging adequate hydration. Additionally, extremely low TDS water lacks essential minerals and may not effectively quench thirst.

TDS levels are also important in agriculture and aquaculture. In hydroponics and aquaculture, TDS is monitored to create a water quality environment favourable for organism productivity. For freshwater oysters, trouts, and other high-value seafood, mimicking the TDS and pH levels of each species' native environment maximises productivity and economic returns. In hydroponic uses, TDS is considered one of the best indices of nutrient availability for aquatic plants.

TDS is typically measured in ppm (parts per million), which indicates the number of milligrams of dissolved solids per litre of water. The World Health Organization, the Safe Drinking Water Foundation in Canada, and the United States Environmental Protection Agency (EPA) have all established guidelines for TDS levels in drinking water, ranging from 500 mg/L to 2,900 mg/L, depending on the context and location. While TDS itself may not be a direct health hazard, it can indicate the presence of harmful contaminants such as iron, manganese, sulfate, bromide, and arsenic.

Conductivity

It is important to test the parameters of temperature, salinity, and conductivity together because they can affect water quality. As salinity and temperature increase, conductivity also increases, which can have a negative effect on the quality of water.

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