Pipes, Pollutants and the Pulse of the river - The impact of stormwater on macroinvertebrate biodiversity in the Rönne river

Abstract

Stormwater pollution is known to alter river water quality, but its impacts on aquatic biodiversity remain poorly understood. This study investigates the effects of stormwater runoff on water quality and benthic macroinvertebrate communities in the Rönne å river, southern Sweden. A field-based study was conducted in rural and urban river sections, comparing pipe discharge sites with nearby reference sites unaffected by stormwater. Water samples were analysed for heavy metals, nutrients, conductivity, turbidity, and pH, while macroinvertebrate diversity was assessed using Average Score per Taxon (ASPT), family richness, and abundance. The effects of treatment (pipe/control) on pollutant concentrations and the combined effects of location (urban/rural) and treatment on biodiversity indices were examined. Results indicate elevated concentrations of certain pollutants at pipe sites, although these differences were not statistically significant after correction for multiple testing. Biodiversity indices also showed no significant differences between treatments; however, ASPT scores were significantly lower and macroinvertebrate abundance was higher in urban and downstream sections of the river. These findings suggest that stormwater runoff may contribute to increased pollutant levels and influence macroinvertebrate community dynamics. The study highlights the potential role of cumulative downstream effects on macroinvertebrate abundance and resilience rather than direct impacts from stormwater alone. Further research, including sediment analysis, a complementary lab setup, studies across multiple rivers, and the consideration of additional environmental variables, is recommended to gain a deeper understanding of the long-term effects of stormwater runoff on aquatic biodiversity.

Popular Abstract

How Can Innocent Raindrops Affect River Life?

Imagine it’s a rainy summer day, the first rain after two weeks of warm sunshine. You walk outside and see raindrops falling on the street, with the water flowing into drains and eventually making its way to the river through pipes. You might think that rainwater is clean, helpful for nature, and good for plants. But could these innocent raindrops be doing harm to the animals living in the river?

Rivers have changed over the years because of human activities like building cities, turning forests into farms, and altering the natural flow of water. Today, instead of flowing naturally through side streams, stormwater often runs through pipes directly into rivers. Along the way, rainwater picks up all kinds of pollutants. For example, fertilizers from farms or tiny bits of tire rubber from roads can end up in the rainwater. These pollutants can include harmful metals like zinc and nutrients like phosphorus and nitrogen. The first rain after a dry period, known as the first flush, is especially harmful because it mobilizes most of these pollutants. When these pollutants build up in rivers, they can harm animals especially small creatures called macroinvertebrates, like mussels, mosquito larvae, and dragonfly larvae, that live on the riverbed.

Some macroinvertebrate species, like mayflies and stoneflies, are very sensitive to pollution and disappear when pollutant levels are too high. Others, like worms and mosquito larvae, are more resistant and thrive in polluted waters. Because of this, macroinvertebrates are considered a good indicator of pollution levels in rivers.

This project looks at how stormwater runoff, which comes from cities and farmland, affects the pollution levels in a river and the macroinvertebrates that live in them. In April and May 2024, data was collected by canoeing along the Rönne river in southern-Sweden to collect data. After the first flush, water samples were taken from stormwater pipes and from reference areas a few meters upstream, away from the influence of the stormwater. Additionally, samples were collected of macroinvertebrates from the riverbed. In the laboratory, water samples were analyzed for concentrations of heavy metals and nutrients, and macroinvertebrate species were identified under a stereomicroscope.

The results showed slightly higher pollutant levels near the stormwater pipes compared to reference areas. However, no clear impact of stormwater on the diversity of macroinvertebrates were observed. Interestingly, downstream urban sections of the river showed a higher abundance of pollutant-resistant species, potentially linked to the accumulation of pollutants transported from upstream areas.

In conclusion, this project shows that stormwater runoff can increase pollution in rivers, though the direct effects on river animals remain unclear. The findings of this project can help water managers to identify areas where efforts should be focused to reduce pollutants. For example, they can implement solutions like rain gardens, green roofs, or wetlands in the most polluted places to filter out pollutants before rainwater reaches the river.

So next time you see raindrops disappearing down the drain, remember they may not be as clean as it looks.

Masters Degree project in Biology, 45 credits, Department of Biology, Lund university.
Advisor: Maria von Post and Per Carlsson
Department of Biology and Ängelholm municipality

• author: van Klinken, Elsa
• supervisor: Maria von Post; Per Carlsson
• organization: Degree Projects in Biology
• course: BION02 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9185145
• date added to LUP: 2025-02-13 13:27:44
• date last changed: 2025-02-13 13:27:44