Real-time water quality monitoring

Stratification is a measure of the distribution of water into surface and deeper layers.

Water quality can vary with depth in sheltered estuaries. Layers of water can form due to differences in salinity, temperature and oxygen. This layering or stratification has an important influence on how estuaries process nutrients and organic matter from the catchment.

Dissolved oxygen is the amount of oxygen in the water.

Aquatic animals need oxygen to breathe. Cooler water with, low salinity water carries more oxygen and warmer more saline water carries less oxygen. Oxygen levels vary throughout the day and night and are a common indicator for algal blooms.

Oxygen levels can be naturally low in deeper water due to the higher demand for oxygen when organic matter like algae, plankton and land-based organic matter decomposes. Under these low oxygen conditions, sediments at the bottom release nutrients in a form that can be easily taken up by plants and animals.

The temperature, or how cool or warm water is during the day and night, has an impact on aquatic life in an estuary.

Measuring temperature is important. Aquatic plants and animals can only survive within a particular temperature range and changes in temperature can have direct impacts on oxygen levels in the water and how microbes and aquatic animals use up that oxygen. Higher temperatures often correlate with lower oxygen levels and can contribute to toxic algal blooms.

Turbidity is a measure of how clear or murky water is. Turbidity is related to the amount of material is suspended in water.

Water clarity or murkiness determines how deep light can penetrate the water. High turbidity levels can result from suspended sediments and high levels of microscopic algae. This can restrict the amount of light available for aquatic plants like seagrasses and impact a lagoon’s ecological health. Seagrasses are particularly susceptible to murky water, which can limit their growth and in severe cases reduce their range across an estuary or result in complete loss.

Salinity represents how much salt is present in the water.

In intermittently open and closed lakes and lagoons (ICOLLS) salinity can vary depending on the entrance channel and the amount of water running off the surrounding catchment.

The salinity of an ICOLL with an open entrance can be almost as salty as ocean water. When an ICOLL entrance has been closed for an extended time, salinity can reduce because freshwater fills the lagoon after rain and the closed entrance prevents sea water from flowing in. When salty ocean water is introduced, usually from waves, it will sink to the bottom because it is heavier than the fresh lagoon water. This results in stratification of the water into different layers.

pH is a measure of how acidic the water is.

pH is important because it affects how nutrients (phosphorous, nitrogen and carbon) and heavy metals dissolve and are made available to aquatic plants and animals. A pH reading less than 7 indicates acidity whereas pH greater than 7 indicates alkaline.

The pH of ocean water is around 8 and rarely changes. The pH of coastal lagoons is usually between 6 and 8. Variations in pH in coastal lagoons are influenced by the mixing of freshwater and ocean water, and increases and decreases in oxygen as aquatic plants and algae photosynthesise and make oxygen, and animals respire and use up oxygen. Changes in pH can also indicate a pollution event or the exposure of naturally occurring acid sulphate soils.

Chlorophyll a is a green pigment found in plants. Plants use chlorophyll to absorb sunlight, and covert it into sugars and energy during photosynthesis.

In water samples, chlorophyll a is used to measure the amount of microalgae or phytoplankton present. It can also indicate excess nutrients and poor water quality. Chlorophyll a levels fluctuate and are often higher after rainfall when more nutrients have washed into the water, or during summer when it is warmer and there is more light available. An increase in nutrients in a lagoon can cause microalgae to grow out of control and create algal blooms.

Phycocyanin is an indicator of potentially toxic blue-green algae or cyanobacteria.

Blue green algae are found naturally in all types of water and understanding the levels of these microorganisms is important. When water is nutrient-rich, or levels of phosphorus and nitrogen increase, blue-green algae can multiply quickly and create blooms that spread across the water’s surface. These algal blooms block sunlight and use oxygen that aquatic plants and animals need to survive. They also produce harmful toxins that can make people and animals sick.

Coloured dissolved organic matter is a measure of the amount of organic matter in the water.

Coloured dissolved organic matter contributes to murkiness of water and indicates nutrient availability and ecosystem productivity. Different freshwater sources such as runoff, groundwater and swamp water have distinct signatures of organic matter concentrations, which helps us understand the influence these freshwater sources have on an estuary.