In the City of Helsinki and Helsinki University joint project, the presence of fecal contamination and possible contamination sources were investigated on the Marjaniemi bathing site in Helsinki. Bathing water samples were collected weekly during the summer 2024.
The results of this study show that the quality of bathing water in Marjaniemi was mainly good. However, GenBac3 gene marker, indicating fecal contamination from warm-blooded animals, was detected from every studied bathing water sample. In microbial source tracking investigations, also bird fecal marker GFD was often detected from the bathing water. This was expected, as birds live and forage in areas close to the Marjaniemi beach. Human specific gene marker HF183 was also detected in the bathing water.
Stormwater drains located on the beach and nearby were identified as a likely fecal contamination source, especially after heavy rain. High numbers of E. coli bacteria, intestinal enterococci, and GenBac3 gene marker were detected from stormwater drains. Also bird, dog, and human specific gene markers were detected from the drains. GenBac3 gene marker was detected in higher numbers after heavy rain from the Mustapuro stream flowing to the sea close to the Marjaniemi beach. Heavy rains can cause runoffs and transport microbes from land to the stream. The fecal contamination from the stream can also affect the bathing water quality in Marjaniemi beach.
Noroviruses were not detected in the bathing water. The detected Campylobacter numbers were low. Campylobacter can cause a health hazard for bathers, when their number in water is high and the bather swallows water while swimming.
The source tracking of fecal contamination provides essential insights for the development of further targeted strategies to improve the bathing water quality. This study suggests that overflow from stormwater drains should be prevented through better design, placement, and maintenance of the drains in proximity of bathing areas. Also, the bird and dog feces should be removed from the beach and nearby more efficiently.
Research report provided to the City of Helsinki Environment and Permits Sub-committee is available on the committee web page (hel.fi) (in Finnish).
Further information:
Annastiina Rytkönen
Doctoral researcher
University of Helsinki
Phone: 0294158213
annastiina.rytkonen@helsinki.fi
Tarja Pitkänen
Associate Professor
University of Helsinki
Phone: 0504285746