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Box & Whisker Plots

(with outliers removed)

 

The graphs below show the Dissolved Oxygen and Available Phosphates data across the Bellinger and Kalang catchments July 2017 to June 2020. We update these graphs every 12 months. 

Bellingen Riverwatch data results supports the findings from the Bellinger and Kalang River Eco Health Report Card (2011) and the Bellinger River Health Plan (2010) and tells us that there are elevated nutrient levels in the river, particularly phosphate, and low Dissolved Oxygen levels. Phosphorus is a naturally occurring nutrient that originates from plant and animal matter, and is applied as fertilizer to increase plant growth in agriculture. Dissolved oxygen is a measure of the availability of oxygen to aquatic life. The amount of oxygen in the water regulates the distribution, activity, movement, and behavior of all aquatic animals.

From Bellingen Riverwatch data to date, we can see elevated Available Phosphate levels presenting in the Upper Bellinger River, Upper Kalang River, Upper Never Never River and Rosewood River. Low Dissolved Oxygen levels are presenting at sites in the Upper Bellinger River, on the Rosewood River and Spicketts Creek, and at all of our testing sites on the Kalang River and Never Never River. In the Bellinger and Kalang River Eco Health Report Card (2011), the Bellinger River received a B- mark, and the Kalang River received a C+ mark.


Available Phosphate

Phosphates are the essential plant and animal nutrient that occurs naturally in very low levels in Australian soils. The ANZECC Water Quality Trigger Values for Available Phosphates for moderately disturbed ecosystems for Lowland Rivers is 0.02mg/L.

Frequent occurrence of Available Phosphate results above 0.02mg/L could be harmful to aquatic ecosystems and increases the likelihood of impacts on waterways such as an abundance of algae and aquatic weeds which out-compete native plants; waterways choked with vegetation; increased biochemical oxygen demand; reduced dissolved oxygen; reduced plant and animal diversity; blue-green algal blooms; and eutrophication.

Possible causes of results outside these values include sewage, sediments erosion, faeces from feedlots, dairies and pets, phosphate-based detergents, decaying plant material, fertilisers and industrial waste and natural geological sources.

Scientists from the NSW Department of Planning, Industry & Environment (DPIE) are carrying out a comprehensive bi-annual water quality and macro-invertebrate surveys which will help identify the causes of elevated phosphate and nitrate levels.

Bellingen Riverwatch Available Phosphate Data

 


Dissolved Oxygen

The ANZECC Water Quality Values for Dissolved Oxygen for moderately disturbed ecosystems for Lowland Rivers (less than 150m elevation) is between 85% and 110% saturation.

Results outside the guidelines could be harmful to ecosystems. Dissolved Oxygen levels below 85% is a threat to aquatic life and the macroinvertebrates that our turtles love to eat. Potential impacts outside ANZECC trigger values include lack of oxygen to support aquatic plant and animal life and fish kills. Monitoring Dissolved Oxygen levels is very important as the Bellingen River Snapping Turtle (BRST) is able to supplement its oxygen uptake through cloacal (bum) breathing, reducing its need to come to the water surface to breathe.

Possible causes of results outside these values include stagnant water, organic waste such as sewage, fertiliser run-off and plant material in the waterway. Micro-organisms use the oxygen as they break down the organic matter.

Bellingen Riverwatch Dissolved Oxygen Data

How to read our Historical Data Graphs

Box and Whisker Plot

We have used a box and whisker plot to represent the complete data set from July 2017 to present. This plot style is commonly used to show key parameters regarding data sets. The maximum and minimum are represented via the whiskers and the box is showing average data and the median.

Average To Date Data
We now highlight on our graphs and maps (red dots) the sites where their to-date average (mean) does not meet the guidelines of a healthy river.

Outliers 

To improve legibility of our data, we have removed outliers. Outliers have been removed by determining the midpoint in the upper and lower quartiles, to define the upper and lower bounds of the data. Data outside these bounds has been removed to create the graphs below. 

Available Phosphates Coloured Bands 
To aid interpretation of the Available Phosphates results, we have scored the parameters against Water Quality Guidelines to indicate how far the results lie outside of the guidelines:
  • Excellent = below 0.02mg/L 
  • Very Good = between 0.02-0.25 mg/L
  • Fair = between 0.025-0.03 mg/L
  • Poor = between 0.03-0.035 mg/L
  • Very poor = above 0.035 mg/L
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