Through Water Chemistry Monitoring, Volunteer Monitors test the physical and chemical characteristics of water to identify pollution sources and long-term trends in water quality. Six variables (listed below) are measured with a customized test kit and results can be compared with water quality standards that define conditions for healthy waterbodies.
Air and Water Temperature
Temperature affects the physical and chemical properties of water, which can influence the feeding, reproduction, and metabolic rates of aquatic organisms.
Aquatic organisms, like fish, have different tolerances to changes in temperature:
| Temperature guild | Species | Optimum range °C | Upper lethal limit °C |
| Coldwater | Rainbow trout | 13 – 21 | 24 – 28 |
| Coolwater | Yellow perch | 19 – 21 | 21 – 30 |
| Warmwater | Channel catfish | 21 – 27 | 30 – 35 |
| Tropical | Blue tilapia | 23 – 30 | 29 – 39 |
There are many natural and human factors that can affect water temperature, including: change in the season, groundwater, springs, shading by vegetation, clearing of the riparian zone, industrial and power plants, and runoff from heated surfaces.
pH
pH is a measure of how acidic or basic a solution is.
Low pH levels reduce the solubility of calcium carbonate inhibiting shell growth in aquatic organisms. Fish struggle to reproduce, become susceptible to fungal infections and other physical damage, and if pH drops below 4.0 is deadly. Amphibians are vulnerable to low pH, probably because their skin is sensitive to pollutants. Streams draining forests and marshes are often slightly acidic due to the presence of acids produced by decaying vegetation in the soil.
High pH levels in water can damage gills and skin of aquatic organisms, cause inability to dispose metabolic waste, and cause death at levels over 10.0. Since photosynthesis occurs only when light is present, the highest pH in waterbodies with dense algae often occurs in the late afternoon. A shift of pH in either direction from neutral may indicate the presence of a pollutant in the stream.
Total Hardness
Hardness is related to the amount of calcium and magnesium are in water. Calcium and magnesium help support animal and plant life. Plants use calcium to develop cell walls and magnesium for photosynthesis, and animals use calcium for shells and bones.
Aquatic organisms can tolerate a broad range of hardness. Most of them live in waters with total hardness between 15 and 200 mg/L.
High hardness levels may indicate the influence of human activity in the area. Drainage from mines can contribute calcium, magnesium, iron, manganese, and other ions. This can increase the hardness of a stream. Industrial processes may also produce significant amounts of calcium and manganese, and effluents from wastewater treatment plants discharged to streams. Hard waters usually have a high pH.
Total Alkalinity
Alkalinity is a measure of the buffering capacity of water. Water with low alkalinity is susceptible to rapid changes in pH and is therefore less stable for aquatic life.
Limestone is a natural source of both hardness and alkalinity. The chemical name for limestone is calcium carbonate (CaCO3) or magnesium carbonate (MgCO3). The carbonate (CO3) and bicarbonate (HCO3) ions in dissolved limestone are a natural source of alkalinity.
In areas with no industrial impacts, total hardness and total alkalinity values tend to be very similar.
Waterbodies with little to no alkalinity have less capacity to neutralize acids and because of this, pH can drop below the optimal range for aquatic life (between 6.5 and 8.5), acidifying the water. Changes in pH increase toxicity of certain chemicals, cause harm, stress, and death to fish and other aquatic life.
High alkalinity may indicate runoff from lawns where owners apply limestone to raise the soil’s pH and improve lawn growth. Excessive limestone reaching streams may greatly increase water pH, and reach dangerous levels for aquatic life. A sudden change in pH of 1.5 unit or higher in water could kill about 50 percent of the fish in the water.
Dissolved Oxygen
Just like humans, aquatic plants and animals need oxygen to survive. Dissolved oxygen is the amount of oxygen available to aquatic life in water.
Oxygen can enter a waterbody physically through riffles, waterfalls, and other disturbance at the water’s surface and biologically through photosynthesis of aquatic plants.
Low dissolved oxygen levels in streams may be because a) the water is too warm; b) there are too many bacteria and a high biological oxygen demand; or c) excessive algae growth (caused by excess nutrients) which when it dies and decompose, consumes DO. Extended low DO levels may result in fish kills and loss of other aquatic life like caddisfly, and stonefly nymphs.
Turbidity
Turbidity is a measurement of water clarity.
High turbidity indicates soil erosion, runoff, discharges, stirred sediments or algal blooms. It can increase water temperatures and decrease dissolved oxygen levels, inhibit photosynthesis by blocking sunlight, and choke aquatic organisms. Sediments can carry bacteria, protozoa, nutrients (ex. Nitrates and phosphorus), pesticide, mercury, lead and other materials, and cover streambed gravel in which aquatic life lay eggs, killing those eggs.
Secchi Disk Depth
Secchi disk depth is used as an indicator of water quality related trophic status and is an indirect measurement of chlorophyll concentration, oxygen depletion rate and fish yield. Secchi depth is recommended to be measured on a weekly basis.
Low Secchi Depth values mean the water has less clarity (is more turbid) indicating pollution. Watershed development and poor land use practices cause increases in erosion, organic matter, and nutrients, all of which cause increases in algae growth. Nitrogen and phosphorus entering a stream provide more food available for algae, so algal concentrations increase, the water becomes less transparent (cloudier) and the Secchi Disk Depth decreases.
Salinity (coastal only)
Salinity is measured in waterbodies where brackish water or saltwater is present. AWW Volunteers use a refractometer to measure salinity, which is the concentration of dissolved salts in water (expressed in parts per thousand, ppt).
Salinity impacts various physical and chemical properties of water, such as density and ability to support aquatic life.
