Browsing by Author "Strömgård, Simon"

Multiple factors determine diversity of diatoms in running waters. Diversity is a complex concept and made up by different components. Diversity can be divided into alpha, beta and gamma diversity. These different types of diversity are regulated by factors operating on a large geographic scale and by local environmental factors. Studies concentrating on diversity patterns of diatoms have become more common in the last 10 years. Especially beta diversity has gotten an increasing interest. Despite the increasing interest in the subject, the driving mechanisms are still not fully understood in aquatic ecosystems. The aim of this theses is to investigate which factors affect alfa and beta diversity in 10 streams in southern Finland. The influence of habitat heterogeneity on beta diversity is also investigated. In addition, the aim is to examine which local environmental factors structure the variation in species composition. The study area covers a 115 km wide area to minimize the effect of large scale factors on species composition. The material consists of environmental data and diatom data from 49 study sites. Land use data used in the study is derived from CORINE Land Cover 2012 data set. All samples were collected during a two-week period (30.7.2014–11.8.2014). Statistical methods used were linear models, generalized linear models (GLM), distance based redundancy analysis (db-RDA) and test for homogeneity of multivariate dispersions (PERMDISP). Water conductivity and light conditions at the study sites were strong environmental factors determining diatom alpha diversity. Habitat heterogeneity showed only a marginally significant positive relationship to beta diversity but a clear trend was visible in the data. The db-RDA results showed that different environmental factors accounted for the variation in species composition. Conductivity, light, water color, water temperature and stream width were important factors explaining variation in species composition. These results suggest that there is a possible connection between habitat heterogeneity and beta diversity. Further research in the subject should be done to determine if there is a significant relationship. The local environmental factors are important for structuring species composition. Possible anthropogenic stress factors influencing stream ecosystems can affect patterns of beta diversity and should be emphasizes in coming research.