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Water Quality Monitoring Parameters Listed and Explained
In compiling this list of water quality measures and explanations, material has been sourced from mostly Australian sources and also through Google which is a good source of basic knowledge. Not all of the material available internationally is relevant to Australian conditions, for example salinity in our offshore waters can reach 55ppt, rather than the 35ppt quoted for waters in the northern hemisphere.
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Therefore this information is provided as a basis for your understanding of water quality parameters, rather than a definitive scientific guide; if you wish a deeper explanation I would encourage you to undertake further research.
Water temperature – This is a measure of the hotness or coldness of water, which is termed a measure of the kinetic energy the water possess at that point in time. Water temperature is particularly relevant when we consider the habitat it provides for the many animals who choose to make it home. For example colder water holds more dissolved oxygen than warm water and can support a greater biodiversity in some climates. Very warm water kills macroinvertebrates. Other factors which impact water temperature include: the time of year; water depth; overhanging vegetation; time of day and speed of flow of the water.
pH – This is the measure of how acidic or alkaline water is. The range of measurements varies between 0 and 14, with the neutral point at 7. Therefore 0 – 7 is acidic and 7- 14 alkaline. pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water.
In terms of relevance to us, our drinking water can range in pH from 6.5 to 8.5, being more friendly to our bodies if it is more alkaline than acidic. By contrast livestock are reportedly able to tolerate acidity as low as 5.5. It is significant to note that spring water is best for us since it contains essential minerals we need, however filters will usually remove the beneficial minerals along with the contaminants.
Oxidation Reduction Potential (ORP) – This is a measure of the ability of a body of water to attack and break down contaminants such as pollution, and decaying plants and animals. ORP is a direct measure of the oxygen available in the water to undertake this vital work; the higher the value of the reading the more oxygen available to do the work required.
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The optimal reading of ORP in really healthy water is anything in excess of 600mV, which is a much greater measurement than ORP readings of around 200mV which we commonly record.
At the opposite end of the scale there can be a negative reading which implies that the water at that point in time is not as healthy as it could be and is therefore heavily contaminated; thankfully we record very few negative readings.
Conductivity – This is ability of water to conduct an electrical current, measured in mS/m , which in turn is determined by the amount of dissolved minerals, salts and other chemicals. The higher the amount of dissolved substances the higher the conductivity reading, especially in salt water.
Note that all such dissolved substances are impurities in the water, therefore the conductivity reading is significant one when assessing the health of a stream.
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High conductivity in water for human or animal consumption can cause health problems, and can also damage household plumbing due to chemical aggregation and consequent deterioration.
In water quality terms a reading of less than 1000mS/cm is considered safe; our local readings are always less than this figure, usually ranging from 200 – 400 mS/cm.
Turbidity – This is measure of the amount of suspended matter in water. Turbidity is caused by particle held in suspension in the water making is appear clouded or discoloured. Any amount of noticeable turbidity in water indicates pollution of some type, be it sediment, organic and inorganic matter, algae and other organisms.
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In drinking water, turbidity is less than 1NTU; across our sampling sites the readings will vary from 0 in Guanaba Creek up to 200NTU in locations at Waterhen Lake at Oxenford. It must be said however that readings in Waterhen Lake several years ago were up to 1000NTU, therefore significant improvement has occurred in those waters.
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Following flooding, it is common in the Coomera River to experience readings up to 100NTU, hence the need to contain sediment from excavations, housing lot construction, and roadworks so that it does not end up in the Coomera River and Broadwater and smother mangroves, weed beds and seagrasses.
Dissolved Oxygen (DO) – This is a measure of how much oxygen is dissolved in a given body of water and indicates the amount of oxygen available to the animals and plants choosing to live in that water.
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The lower the level of dissolved oxygen the poorer the water quality, and the less likely it is to host large number of vertebrate and invertebrate animals such as macroinvertebrates and fish.
Levels of dissolved oxygen are determined by such factors as wind which increases levels of surface oxygen; photosynthesis of plants which also increases dissolved oxygen; water temperature and rate of stream flow.
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Levels of dissolved oxygen most supportive of life are more than 6mg/L, which is a low reading for a fast flowing stream which can enjoy levels up to 14mg/L. It is no surprise therefore that the higher scoring macroinvertebrates live in the fastest flowing streams.
In still or stagnant waters levels of dissolved oxygen may vary between 1 and 3 mg/L – too low to support most macroinvertebrates and fish.
Total Dissolved Solids ( TDS) - This is a measure of the total amount of material dissolved in the water, both organic and inorganic, which is composed of soluble metals, mineral and salts, and ions, and organic matter. In short, everything soluble apart from H2O molecules.
It is interesting to note that water can be classified by reference to the level of total dissolved solids as follows:
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In fresh water the TDS is less than 1000ppm
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In brackish water the TDS ranges 1000 to 10000ppm and
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In salt water the TDS ranges 10000 to 35000 ppm
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In terms of human consumption, a high level of TDS indicates the presence of toxic minerals and can taste salty, bitter and/or metallic.
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In our streams the TDs is generally lower than 300ppm.
Salinity – This is the measure of dissolved salts in water; these dissolved salts can consist of sodium, potassium, calcium, magnesium, chloride, sulphate, bicarbonate, carbonate and nitrate.
Australian standards for salinity in drinking water generally limit salinity to 20mg/L , although levels can be as high as 500mg/L without affecting human health.
When levels of salinity exceed 180mg/L the water develops a salty taste which most people find distasteful.
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In the freshwaters we sample, salinity is always less than 1mg/L, therefore salinity is never a problem.
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By way of contrast the estuarine sections of the Coomera River can be as high as 40mg/L, a marked difference.
Conclusion
Water quality measures involve an interplay of a variety of differing parameters, all of which are relevant to a lesser or greater degree. The most significant are arguably dissolved oxygen, conductivity and pH, yet all have their part to play. Our role as citizens and water consumers is to ensure that our catchments are as pristine as can be managed, given the high rate of urban development. The most damaging of all environmental factors is vegetative clearing and sedimentation: if we plant more native trees and vegetation, and conduct ourselves as responsible environmental stewards, we are off to a good start.
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Steven Gill 4th April, 2023