Water Pollution Measurement: Understanding The Standard Units

Water quality is measured through various methods and technologies, which help determine the level of water pollution. Water quality measurements are crucial as they provide evidence of ecosystem health and indicate if water is usable, consumable, and swimmable. There are several factors that determine water quality, including turbidity, pH, temperature, dissolved oxygen, and conductivity. Turbidity, which measures the amount of light that can pass through the water, is a key indicator of potential pollution and degradation. The presence of solids in the water, such as suspended particles and total suspended solids (TSS), can impact water clarity and photosynthetically active radiation (PAR), affecting the health of the aquatic ecosystem. pH levels are also important as they can influence the toxicity of certain substances, such as ammonia, to plants and aquatic animals. Temperature plays a role in the metabolic rate of aquatic life and their sensitivity to pollution, parasites, and diseases. Dissolved oxygen (DO) measures the amount of oxygen available to flora and fauna, while conductivity indicates the water's ability to conduct electricity, revealing the presence of dissolved substances. These parameters are measured using specialized equipment and sensors, such as thermometers, pH sensors, dissolved oxygen sensors, and conductivity loggers. By monitoring and assessing these factors, researchers and environmentalists can gain insights into the health of water bodies and develop strategies to ensure clean and healthy aquatic ecosystems.

Turbidity

The propensity of particles to scatter a light beam focused on them is considered a meaningful measure of turbidity in water. Turbidity measured this way uses an instrument called a nephelometer with the detector set up to the side of the light beam. The units of turbidity from a calibrated nephelometer can be either Nephelometric Turbidity Unit (NTU) or Formazin Nephelometric Units (FNU), depending on the standard method used. The NTU is mostly used in the U.S., while the FNU is more widely used in Europe.

There are several practical ways of checking water quality, the most direct being some measure of attenuation (reduction in strength) of light as it passes through a sample column of water. The Jackson Candle method, which is not often used as it is not compliant with international standards, is the inverse measure of the length of a column of water needed to completely obscure a candle flame viewed through it. The more water needed (the longer the water column), the clearer the water.

The Secchi disk is often lowered into a water body to measure the depth until it is no longer visible. This is also a measure of the cloudiness of the water.

pH

Water with a pH below 6 or 6.5 is generally considered to have low pH and is addressed as a potential cause of effects on aquatic life. A sudden increase in pH can cause a change in the chemical state of pollutants such as copper and ammonia, increasing their solubility, transport, and bioavailability. This can, in turn, increase the exposure of aquatic plants and animals to toxic metals and nutrients. For example, ammonia at a high pH is toxic to plants and aquatic animals.

Sources of acidic deposition, or acid rain, include power plants, industrial sources, and internal combustion engines. Acid rain is formed when sulfur and nitrogen oxides are emitted into the atmosphere and transformed into H2SO4 and HNO3. Acid rain can also occur due to extremely high levels of CO2. When deposited into freshwater systems, these gases increase SO42-, NO3-, and H+, which can decrease the pH of the water. Streams and lakes with relatively low buffering capacity or low flow are particularly susceptible to low pH from acidic deposition.

The pH of water can also be influenced by natural processes. For example, the process of photosynthesis by algae and plants uses hydrogen, increasing pH levels, while respiration and decomposition can lower pH. Additionally, coloured or chromophoric dissolved organic matter (CDOM) occurs naturally in water bodies and can decrease pH as it decomposes and releases tannin, an organic pollutant.

Measuring the pH of water is an important aspect of water quality monitoring, as it can serve as an indicator of contamination. Municipal water suppliers often test the pH of their water to monitor for pollutants. By understanding the relationship between pH and other water quality parameters, environmentalists can assess the conditions of unmonitored water bodies and identify human activities that contribute to pollution.

Temperature

Water temperature is typically measured using one of three scales: Celsius, Fahrenheit, or Kelvin. The Celsius and Fahrenheit scales measure temperature in degrees, while the Kelvin scale uses the unit "kelvin," which is the same magnitude as a Celsius degree. Water temperature is generally reported in degrees Celsius due to its universal use. The Fahrenheit and Celsius scales are defined by the temperatures at which water freezes and boils. In contrast, the Kelvin scale is based on the theoretical point of absolute zero.

Several instruments are employed to obtain temperature readings at different depths, times, and locations. These include thermometers, thermistors, thermocouples, and digital temperature sensors.

Thermal pollution, which is any discharge that significantly alters the temperature of a natural water source, can have detrimental effects on water quality. This type of pollution commonly originates from municipal or industrial effluents, with warmer temperatures negatively impacting water quality. Thermal pollution can lead to reduced dissolved oxygen levels, fish kills, and the introduction of invasive species. Additionally, runoff from impervious surfaces, such as parking lots, can contribute to thermal pollution by transferring heat to nearby streams or rivers.

Water temperature is a critical parameter in water quality assessment, influencing various ecological processes and the health of aquatic ecosystems.

Dissolved oxygen

Water quality is determined by measuring various characteristics such as turbidity, pH, colour, and dissolved oxygen. Dissolved oxygen (DO) refers to the level of free, non-compound oxygen present in water or other liquids. It is a critical factor in assessing water quality because it influences the organisms living within a body of water. DO is a measure of the amount of oxygen available to flora and fauna and is reported as percent saturation or mg/L.

The presence of adequate DO in surface water is essential for all forms of aquatic life. Oxygen enters a stream from the atmosphere and groundwater discharge. Groundwater discharge significantly contributes to oxygen levels in streams where groundwater is a large component of streamflow, such as in areas of glacial deposits. Photosynthesis is the primary process affecting the dissolved-oxygen/temperature relation. Water clarity, sunlight strength, and duration impact the rate of photosynthesis.

The actual rate of oxygen consumption in a stream is influenced by several factors, including temperature, pH, the presence of certain microorganisms, and the type of organic and inorganic material in the water. High temperatures reduce the solubility of oxygen in water, with warm water holding less DO than cold water. Additionally, high nutrient levels can lead to excessive plant growth, resulting in decreased DO due to increased respiration and decomposition. Sediments can also impact DO levels by preventing oxygen from permeating interstitial areas.

Oxygen depletion in water bodies can have severe consequences for aquatic life. When oxygen concentrations fall below 2 mg/L, the water is defined as hypoxic, leading to the death of many organisms unable to escape, creating what is known as a "dead zone." For instance, a dead zone forms seasonally in the northern Gulf of America when subsurface waters become depleted in dissolved oxygen, unable to support most life.

DO levels in water can be measured using field and lab meters, and the results are reported as percent saturation or mg/L. Monitoring DO concentrations over a 24-hour period can help identify diurnal patterns and provide valuable information about DO depletion.

Conductivity

Each body of water tends to have a relatively constant range of conductivity that, once established, can be used as a baseline for comparison with regular conductivity measurements. Significant changes in conductivity could indicate that a discharge or some other source of pollution has entered the body of water.

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