Assessing the Impact of Combined Sewer Overflow on the Habitat of Lampetra planeri: A Case Study in Flanders, Belgium

Sammanfattning

Lampetra planeri or Brook Lamprey is an aquatic fish-like species, characterized by its lack of jaws and long eel-like morphology. The species is usually found in small streams with gravel or sandy riverbeds and has seen a strong population decline during the last few decades. The primary goal of this thesis was to investigate if combined sewer overflows prevent the further spread of the Lampetra planeri in Flanders through habitat deterioration. The secondary goal was the development of a GIS methodology which could be used for similar ecological issues in the future. Eight watercourses in Belgium were selected for the analysis. Segments from each watercourse were enriched with a modelled water pollution score and the presence or absence of Lampetra planeri, sourced from existing fish survey data. The pollution score was calculated based on the presence and location of combined sewer overflows in the watercourse while taking into account the effects of dilution over distance and river flow. A Chi-square test of independence and Fisher's exact test were performed and showed a statistically significant relationship between the presence of combined sewer overflows and the presence of Lampetra planeri. However, several considerations must be addressed when interpreting these findings. Variations in the composition of combined sewer overflow discharges as well as the frequency of overflow events were not taken into account. Additional factors that could potentially influence the presence/absence of Lampetra planeri, such as the occurrence of migration barriers, morphological river quality and landuse on the riverbanks, were not included in the analysis. However, the methodology has a modular structure and allows for other factors to be included in future research.