How does the water chemistry in runoff water from stormwater pipes affect periphyton in Rönne Å?

Sammanfattning

Stormwater is runoff water from snow or rain events that enters a recipient shortly after the precipitations has reached the ground. Stormwater can contain heavy metals and nutrients depending on the type and size of the catchment area as well as the intensity and regularity of the precipitation. In high amounts, the pollutants can inhibit algal growth and have a negative effect in algal diversity. However, previous research is inconsistent regarding these negative effects of pollution in rivers and more research is needed on the topic. This study investigates if the algal growth or diversity is influenced by the stormwater entering the Swedish river Rönne Å. The study focuses on assessing the quantity of chosen heavy metals and nutrients coming from the stormwater pipes and if these explain differences in algal growth or diversity in different parts of the river. It also investigates if there are differences between the urban or rural part of the river regarding the constituents of the stormwater and the algal growth and diversity. The elements, lead (Pb), cadmium (Cd), copper (Cu), chromium (Cr), mercury (Hg), nickel (Ni), zinc (Zn), total nitrogen (N) and total phosphorus (P), were chosen based on findings in previous studies and available resources. The study found no difference in algal growth, algal diversity or in metal and nutrient concentration between the rural or urban areas. Further, there was no difference in algal growth, algal diversity or in metal and nutrient concentration between water sampled from underneath stormwater pipes and water from upstream reference points. Copper, nickel and zinc positively correlated with the algal growth. The observed correlation does not necessarily demonstrate causative effects. The metal concentrations in the river were mostly below the limits for good water quality and the concentrations. At these concentrations, metals do not have a negative effect on algal growth or diversity but are beneficial resources for algae. The study is a pilot study and the methods and findings can be used for future research to further refine and build up on.