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Climate Detectives Projects 2023-2024

Project title: From pollution to fish population

College Hagelstein   Sint-Katelijne-Waver   Belgium

Research question

How does water quality influence the population size of different species of fish in Flanders?

Summary of the project

We are three students, Jesse, Dien, and Xander, from College Hagelstein, embarking on a study to examine the impact of water quality on the fish population in two Flemish rivers (Dijle and Grote Nete). To investigate this issue, we initiated our research by assessing the water quality. This involved measuring various parameters such as the levels of oxygen, nitrogen, ammonium, phosphorus content, pH, and water temperature. It’s important to note that in Flanders, our rivers are not very clean as you can see in the graph obtained from the Flemish Environment Agency. They have been heavily polluted due to various discharges and dumping. This graph illustrates a clear correlation: a greater variety of macroinvertebrates in the watercourse signifies improved biological water quality. Furthermore, it’s evident from recent trends depicted in the graph that water quality has been on the rise, which can likely be attributed to the implementation of more stringent environmental regulations.
Our fieldwork involved fishing expeditions in the grote Nete and Dijle rivers. We employed two telescopic fixed rods and two standard rods, baiting our hooks with worms, staples that are commonly attractive to a variety of fish species. The number and species of fish we captured during these sessions were carefully recorded to establish a comparison between the fish count and the water quality. While fishing in the Dijle, we selected a location with minimal water flow. To attract the fish, we introduced a mixture of boiled potatoes seasoned with fish food (Mondial-f bio mix) into the water. Employing two telescopic rods with fixed lines and using fly larvae as bait. In the Nete, due to stronger currents, we opted for one telescopic rod with a fixed line and two casting rods. Utilizing the same method of baiting with seasoned potatoes and worms.

Main results and Conclusions

How does water quality influence the population size of different species of fish in Flanders?

We have measured the water quality of the Dijle River. Our findings are as follows :
– ammonium levels were 0.7 mg/L
– oxygen content was at 10 mg/L
– nitrite levels were 3 mg/L
– nitrate levels were 0.3mg/L
– and phosphate levels were 1 mg/L.
– the pH was around 7
During our three-hour fishing session in the Dijle, we successfully captured a total of 51 fish. Our haul included a diverse range of species, prominently featuring two breams—one tipping the scales at 1 kilogram and the other close to 800 grams. Additionally, we caught two whitefish, each weighing approximately 300 grams. The majority of our catch consisted of 47 small gobies, showcasing their prevalence in the river. The accompanying photographs illustrate the diversity of our catch: the images display our larger bream and one of the gobies.
In our recent water quality assessment of the Grote Nete, we recorded the following measurements:
– The level of nitrate were at 1 mg/L,
– The level of ammonium was undetectable at 0 mg/L.
– The level of phosphate was 0.7 mg/L.
– nitrite was 0.2 mg/L.
– the level of oxygen was 10 mg/L.
– the pH was 6.5
Over a three-hour fishing session in the Grote Nete, we successfully caught six larger fish, including a notably large eel. The river appeared quite murky, with significant amounts of sand and mud in circulation. This may have affected the visibility for the fish, potentially influencing their behaviour.

What’s Next? Actions to make a difference and help lessen the problem

In the chart enclosed, water quality parameters from the Dijle and Grote Nete rivers is compared against the maximum concentrations for a water body to be considered clean. The dark green bars represent the threshold for clean water standards—levels below this are generally acceptable, whereas levels above indicate potential concerns.
For parameters like nitrate, oxygen (8mg/L is the average and more is not considered particularly bad), and pH, both the Dijle and Grote Nete measurements are within the acceptable range, suggesting that the water quality is generally good in these respects. However, for parameters such as phosphate and ammonium, where the measurements exceed the dark green bars, there’s a clear indication of pollution.
Particularly for the Grote Nete, the phosphate levels are significantly above the standard, which is a serious issue as elevated phosphate can lead to eutrophication, causing algae blooms that deplete the water of oxygen and harm aquatic life. Similarly, any detection of ammonium above clean water standards can suggest organic pollution and is also harmful to fish and other wildlife.
These findings are concerning so it’s imperative that we address the sources of these contaminants to preserve the ecological balance of our rivers and the health of the organisms that inhabit them. Stopping the dumping of waste and runoff into these waters is a critical step towards achieving cleaner, healthier river systems.

Projects are created by the teams and they take the full responsibility of the shared data.
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