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Understanding the Dip

Understanding the Dip Results

The Dip kit gives values for 6 different water quality measures that are important to maintaining the healthy ecosystem habitats. Once the tests are completed the results are recorded on the Dip postcard and returned with the kit supplies to the City of Surrey.

The City of Surrey follows the Provincial water quality guidelines. Read to learn more about the properties of water that are suitable for fish to live in!

Turbidity

Turbidity is a measurement of how clear, or opaque, the water is. Turbid water occurs when there are higher levels of suspended soil, clay, silt, organic/inorganic matter and microscopic organisms in the water. Turbid water is different than dark coloured water as dark coloured water can still be clear. High levels of turbidity in Surrey’s streams could indicate a greater amount of soil entering a storm drain and could be caused by a construction site nearby. High turbidity in streams also occurs during rain events. In urban streams, the lower the turbidity the better the water quality for aquatic species. If a high value over the background level is recorded in a stream sample where a pollution source can be identified then it triggers further investigation with sample collection for analysis at a lab facility.

Measurements in the Take the Dip kits record measurements as JTU units as a visual determination is used for when the checked circle inside (this is a ‘secchi disk’ tool) is no longer visible.

Temperature

Salmon, trout and other aquatic species are very sensitive to temperature changes in the water. The temperature must stay within a certain range for them to be able to survive. The preferable temperature range for Pacific Northwestern streams is 4 to 18 degrees Celcius. Temperature also affects other things in an aquatic habitat as well, such as the amount of dissolved oxygen the water can hold (the warmer the water the less dissolved oxygen).

Nutrients (Nitrate/Nitrite)

Nutrients are common chemicals found in products that make things grow (like fertilizers) or wastes (like sewer discharges and animal waste). If there are too many nutrients in a waterway it can cause too much growth of algae that will then die off when the nutrients are used up. When this plant material decays it causes higher turbidity, lower the dissolved oxygen in the water and cause bad smells which makes it difficult for aquatic species to live in.
Nitrate and nitrite can also be directly toxic to fish populations as they may affect the ability of the organism to utilize the dissolved oxygen in the water. The B.C. guidelines to protect freshwater aquatic life is 3.0 mg/L for nitrate and 0.06 mg/L for nitrite.

pH

pH is a measurement of how acidic or basic the water is. The range for pH is 0 for very acidic to 14 for very basic, with a pH of 7 being neutral. Most aquatic species thrive in water that has a pH range from 6.5 to 8. Should the pH values vary outside of this range or change quickly from one end of the scale to the other, it can cause stress to the aquatic species in the water. In areas with air pollution concerns, the rainwater may become more acidic as the rain encounters atmospheric gases as it falls to the ground. The rainwater becomes weak sulphuric and nitric acids as the rain absorbs concentrations of sulphur and nitrogen oxides and can bring the pH level down to 4.

Dissolved Oxygen

All aquatic species need dissolved oxygen (DO) to live. It is measured either as parts per million (ppm) or an equivalent unit of milligrams per litre (mg/L). The streams and creeks with consistently high levels of DO support a wide diversity of life. There are many factors that can affect the level of DO in a waterway with some of these factors being natural and some not. A natural factor that can lower the DO in a stream is temperature – the higher the temperature of the water, the less DO the water can hold. For example, water at 28 degrees Celsius can hold 8 ppm of DO and water at 8 degrees Celsius can hold 12 ppm of DO. Some other factors that can affect the amount of DO in the water are nutrient levels and organic matter. When these breakdown in waterways it can consume dissolved oxygen in the water leaving less available for aquatic species. To maintain aquatic life in all the life cycle stages of a fish the dissolved oxygen levels should be higher than 5 mg/L.

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