Comparative study of monitoring South-Finnish rivers and streams using macroinvertebrate and benthic diatom community structure

In southern Finland, most of the rivers are turbid and suffer from eutrophication and leaching of suspended solids from diffuse sources. We first related benthic diatom and macroinvertebrate structure to environmental factors using direct ordination. Second, benthic diatoms and macroinvertebrates were simultaneously sampled in several South-Finnish rivers and streams to compare two monitoring methods. The study sites constituted of some large, moderately nutrient rich rivers and some smaller, less eutrophic streams situated on the south coast of Finland. Diatom species distribution was most affected by conductivity, total P and latitude. Species distribution of macroinvertebrates was mostly related to channel width, conductivity and pH. For diatoms, separation of community structure between sampling stations was clear, but corresponding macroinvertebrate communities were more similar to each other. Correlation between diatom and macroinvertebrate pollution indices was rather low and insignificant (r = 0.28). As a whole, variation of macroinvertebrate index values (CV = 4.7%) among replicate samples was slightly lower than for diatom index (CV = 6.0%). On the contrary, community similarity between the replicate samples was slightly lower among macroinvertebrates (r = 0.770) due probably to their larger local scale spatial variation, sampling of more habitats and lower density compared to diatoms (r = 0.874). In conclusion, multiple pressures affecting the river ecosystems at different spatial and temporal scales should lead to choosing more than one biological monitoring method with clearly identifiable responses.