Water Pollution Indicators: What To Look For

Water quality is a critical indicator of ecosystem health, and monitoring it is essential to identify potential environmental issues. Water quality is described by various indicators, including physical, chemical, and biological properties. Physico-chemical indicators, such as water temperature, dissolved oxygen, pH, salinity, and nutrients, provide information on the cause of any problems. Biological indicators, on the other hand, give a direct measure of the health of the flora and fauna in the ecosystem. For example, chlorophyll-a is used as a biological indicator in estuaries to measure the density of phytoplankton populations. In addition, habitat indicators, such as the width and continuity of riparian habitats, are important to include in monitoring programs as factors other than water quality, like habitat degradation, can influence aquatic ecosystem health. Furthermore, chemical indicators, such as oxidation-reduction potential and electrical conductivity, are used to detect pollution in aquatic ecosystems. These indicators help assess the suitability of water for human consumption, industrial use, and maintaining the natural environment.

Dissolved oxygen levels

Dissolved oxygen (DO) is a critical factor in assessing water quality. It refers to the level of free, non-compound oxygen present in water or other liquids. It is essential for aquatic life, including fish, invertebrates, bacteria, and plants, which use oxygen for respiration. The amount of dissolved oxygen needed varies from organism to organism. For instance, bottom feeders, crabs, oysters, and worms require minimal amounts of oxygen (1-6 mg/L), while shallow-water fish need higher levels (4-15 mg/L).

DO levels in water bodies can fluctuate naturally due to various factors. For example, running water, such as a swift-moving stream, dissolves more oxygen than the still water of a pond or lake. Water temperature also plays a significant role, as colder water can hold higher DO levels than warmer water. Additionally, altitude influences DO levels, with water at lower altitudes having a higher capacity to hold dissolved oxygen compared to water at higher altitudes.

Human activities can also impact DO levels in aquatic ecosystems. Pollution from fertilizer runoff or poorly treated wastewater can lead to excessive nutrient levels, promoting algae blooms. While algae initially boost dissolved oxygen levels, their respiration and subsequent bacterial decomposition deplete the oxygen available, creating an anoxic environment where many organisms cannot survive. This phenomenon is known as eutrophication and is commonly observed in lakes.

Low DO levels, or hypoxia, can have detrimental effects on aquatic life. Some sensitive species may move away, experience health issues, or even die due to insufficient oxygen. Gasping fish may indicate a lack of DO. Additionally, changes in aquatic community structure can occur, with species intolerant of low DO, such as certain mayflies, stoneflies, caddisflies, and beetles, being replaced by tolerant worms and fly larvae.

DO measurement is crucial for monitoring water quality and ensuring optimal conditions for various applications, including wastewater treatment and aquaculture. It is a direct indicator of an aquatic resource's ability to support aquatic life and plays a vital role in groundwater quality by supporting bacteria that break down pollutants.

Water temperature

Additionally, water temperature impacts ammonia levels, photosynthesis rates, and the sensitivity of aquatic organisms to pollution. Due to changes in external environmental conditions, water temperatures naturally fluctuate throughout the day and between seasons. These fluctuations influence the species that can live and thrive in a particular body of water, as certain species have specific temperature requirements. Therefore, water temperature is a critical factor in determining the composition and diversity of aquatic life in a given ecosystem.

Salinity

The effects of salinity on water quality include:

• Increased salinity can lead to higher concentrations of metals in water, such as radium, and can cause radioactive materials to become more concentrated in groundwater and surface water.
• Excess salinity can occur in areas with high evaporation rates and can be made worse by repeated water usage for irrigation or water withdrawals, road de-icers, mining, oil and gas drilling, and wastewater discharges.
• Salinity can be a stressor for aquatic organisms as fluctuating levels can affect those adapted to prevailing salinity concentrations.
• Salinity influences the types of plants and animals that live in different parts of an estuary. Less salt-tolerant organisms are found upstream, while more tolerant organisms are found closer to the ocean.
• Salinity can make water undrinkable, increase water treatment costs, and harm freshwater fish and wildlife.

To manage salinity, affected jurisdictions have developed salinity management plans or strategies with identified objectives and priority areas for rehabilitation. These plans aim to ensure that salt concentration and load targets are met, and water quality remains fit for purpose.

Turbidity

Water test kits are available to test for turbidity, and other factors such as temperature, pH, and dissolved oxygen. These tests can be performed by teachers and water-science enthusiasts to build public awareness and involvement in protecting water resources.

Biological indicators

In freshwater, biological indicators include various measures of macroinvertebrate or fish diversity, benthic algal growth, and benthic oxygen demand. For estuaries, chlorophyll-a, which measures phytoplankton population density, is the only commonly used biological indicator. In coastal embayments, seagrass condition and the condition of fringing coral reefs are sometimes used as biological indicators.

Other biological indicators include bacteria such as Escherichia coli and Enterococci, which are used to detect and estimate the level of pollution in different ecosystems. Insects can also be used as biological indicators, as their populations can be affected by changes in the environment, such as water stress in reforestation areas. Ants, in particular, are very sensitive to environmental changes and play a key role in the recovery of degraded ecosystems.

Zooplankton and phytoplankton are also important biological indicators of water pollution. They are microscopic animals that exist near the surface of aquatic ecosystems and feed on phytoplankton, marine snow, and bacterial planktons. Their movements depend on tides and currents, and they are influenced by weather fluctuations. Plankton is also used as an indicator of lake conditions, particularly when there are high concentrations of phosphorus and nitrogen, which can indicate poor water quality.

Frequently asked questions