Vedenlaadun arvioiminen piilevien avulla Hämeenlinnan Alajärveen laskevissa ojissa ja puroissa

Diatom communities are known to indicate differences in water quality. In this study, the water quality in ditches and brooks of the drainage basin of Lake Alajärvi in Hämeenlinna was researched with the help of diatom analyses and water chemistry analyses. For the examination of the diatom material, we used chemical properties of water and physical properties of the river beds along with indexes reflecting contamination and eutrophication. The ecological information was obtained by classifying the diatoms on the basis of organic loading (saprobia) and nutrient loading (trophia). Omnidia database was used in this study. The diatom and water samples were collected in the summer of 2013 and the data was simultaneously documented in field observation forms. Linear regression models and multivariate models, including general linear models and redundancy analysis, were used as statistical analyses. On average, based on the organic pollution index (IPS) the quality of water was in a good state (16.03). According to the TDI index which reflects nutritiousness, water quality was on average oligo-mesotrophic (7.39). More eutrophication occurred in brooks and ditches where there were two observation sites. Based on the GDI gender-related index, water quality was on average satisfactory (14.4). In ecological classification, diatom communities indicated oligo-eutrophic or eutrophic level water quality. As regards to saprobia, on most obser-vation sites the diatom communities indicated mesosaprobia. There were no observations of loading sources with water quality deteriorating chemistry except for field fertilization. In brook and ditch waters of marsh, forest, and field areas, clear concentration differences between the different observation sites could be observed. The average concentration value of total phosphorus was eutrophic, i.e. rich in nutrients (44,54 µg/l). The average concentration value of total nitrogen was 1028,5 µg/l, i.e. mesotrophic. Total phosphorus and total nitrogen concentrations were higher on the field areas due to fertilization. The average pH value of the waters was 6.2. The pH value of water ranged from 4,05 to 7,34. The term acidification can be used when the pH value falls below level 6.0. On five observation sites, the pH value was below 6. Conductivity of the waters on the observation sites was on average 74,45 mS/m which indicated salts coming from the drainage basin. Conductivity varied between 33.4 and 196.1 mS/m. Due to fertilization, the values were higher on the field areas. The average color value was 251.90 mg Pt/l. The color value on the observation sites varied between 30 and 700 mg Pt/l, i.e. there were great differences in color values. In brooks and ditches where there were two observation sites, the color value in upstream was lower. High color values indicated humus content levels of water due to waters running from the marsh areas. Of the observation sites, two had low humus content and four humus content. The other observation sites had high humus content due to waters running from the marshlands. As a result of GLM models, total phosphorus and nitrogen, shading and pH were the environmental variables that had the greatest effect on the number of species in diatom communities. As a result of the redundancy analysis, depth and color value of water were the most statistically significant factors affecting diatom communities. Unexpectedly, other water chemical variables were not statistically significant in redundancy analysis. On the basis of the results, there was no contamination that called for measures in the water quality of the research area. The diatoms indicated differences in water quality well. According to the plans, the present forms of land use of Alajärvi drainage basin will not be changed in a way that would cause deterioration of water quality.