Satu Maaria Karjalainen

Freshwater diatoms as environmental indicators: evaluating the effects of eutrophication using species morphology and biological indices

Anthropogenic eutrophication is a major form of perturbation in freshwaters, and several approaches aim to recognise its effects on lake ecosystems. We compared the responses of diatom species morphology, diversity indices and diatom indices to total phosphorus, total nitrogen and distance from a point stressor causing eutrophication in a large lake. We specifically examined the degree to which extent nutrients and distance to the stressor affect variation in the values of various biological indices and diatom valve size. In addition, special attention was given to the adequate repetition of diatom valve width measurements in the context of environmental assessment. Our results showed that diatom valve width was a better indicator of nutrient concentrations than any of the diatom and diversity indices examined. However, the results varied between the two study transects, suggesting that the diatom-based variables not only respond to nutrients but also to other environmental factors (e.g. shoreline morphology). We also found that when using the method based on diatom morphology, one should measure more valves than has been originally suggested to provide a more reliable picture of response to eutrophication. We argue that diatom morphology could be considered as an additional environmental assessment tool, because it may complement the information provided by the traditional diatom indices. Diatom valve width may also be more sensitive to early phases of the eutrophication process and its effects on freshwater ecosystems than various diatom indices that were developed in regional contexts with wide ranges in nutrient levels.

Disentangling the responses of boreal stream assemblages to low stressor levels of diffuse pollution and altered channel morphology.

Non-point diffuse pollution from land use and alteration of hydromorphology are among the most detrimental stressors to stream ecosystems. We explored the independent and interactive effects of morphological channel alteration (channelization for water transport of timber) and diffuse pollution on species richness and community structure of four organism groups in boreal streams: diatoms, macrophytes, macroinvertebrates, and fish. Furthermore, the effect of these stressors on stream condition was evaluated by Ecological Quality Ratios (EQR) from the national Water Framework Directive (WFD) assessment system. We grouped 91 study sites into four groups that were impacted by either diffuse pollution or hydromorphological alteration, by both stressors, or by neither one. Macroinvertebrate richness was reduced by diffuse pollution, whereas other biological groups were unaltered. Hydromorphological modification had no effect on taxon richness of any of the assemblages. Community structure of all groups was significantly affected by diffuse pollution but not by hydromorphology. Similarly, EQRs indicated negative response by diatoms, macroinvertebrates and fish to diffuse pollution, but not to hydromorphological alteration. Agricultural diffuse pollution thus affected species identities and abundances rather than taxonomic richness. Our results suggest that channelization of boreal streams for timber transport has not altered hydromorphological conditions sufficiently to have a strong impact on stream biota, whereas even moderate nutrient enrichment may be ecologically harmful. Controlling diffuse pollution and associated land use stressors should be prioritized over restoration of in-stream habitat structure to improve the ecological condition of boreal streams.

Metacommunity structuring in a highly-connected aquatic system: effects of dispersal, abiotic environment and grazing pressure on microalgal guilds

Abstract Associating a deconstructive approach with metacommunity ecology brings insights into how biological communities are structured. We examined the effects of dispersal, habitat conditions, and grazing pressure on ecological guilds (i.e., deconstructed entire communities by guilds) of freshwater microalgae. The combination of focus on efficient passive dispersers, an extensive sampling survey, large numbers of abiotic explanatory variables, information on grazing pressure, and characteristics (i.e., high connectivity and areal extent) of the study area enabled us to model roles of various metacommunity processes for guild structure and diversity within guilds. We found that water chemistry, physical habitat, and spatial variables all accounted for rather small amounts of variation in the guild structures. Diversity within each guild generally showed clear spatial patterns independent of local environmental conditions. Wave action and slope of the study sites also affected diversity. Grazing had clear effects on some aspects of diversity. Importantly, the guilds showed significant spatial patterns, suggesting that mass effects occurred at different intensities in our highly-connected study system. The intensity of dispersal was partly related to different dispersal potentials among the guilds. Different traits associated with ecological guilds may hence be associated with dispersal processes detected in systems with high connectivity among sites.

Redundancy in the ecological assessment of lakes: Are phytoplankton, macrophytes and phytobenthos all necessary?

Although the Water Framework Directive specifies that macrophytes and phytobenthos should be used for the ecological assessment of lakes and rivers, practice varies widely throughout the EU. Most countries have separate methods for macrophytes and phytobenthos in rivers; however, the situation is very different for lakes. Here, 16 countries do not have dedicated phytobenthos methods, some include filamentous algae within macrophyte survey methods whilst others use diatoms as proxies for phytobenthos. The most widely-cited justification for not having a dedicated phytobenthos method is redundancy, i.e. that macrophyte and phytoplankton assessments alone are sufficient to detect nutrient impacts. Evidence from those European Union Member States that have dedicated phytobenthos methods supports this for high level overviews of lake condition and classification; however, there are a number of situations where phytobenthos may contribute valuable information for the management of lakes.

Bacterial metacommunity organization in a highly connected aquatic system

The spatial structure and underlying assembly mechanisms of bacterial communities have been studied widely across aquatic systems, focusing primarily on isolated sites, such as different lakes, ponds and streams. Here, our main aim was to determine the underlying mechanisms for bacterial biofilm assembly within a large, highly connected lake system in Northern Finland using associative methods based on taxonomic and phylogenetic alpha- and beta-diversity and a large number of abiotic and biotic variables. Furthermore, null model approaches were used to quantify the relative importance of different community assembly processes. We found that spatial variation in bacterial communities within the lake was structured by different assembly processes, including stochasticity, species sorting and potentially even dispersal limitation. Species sorting by abiotic environmental conditions explained more of the taxonomic and particularly phylogenetic turnover in community composition compared with that by biotic variables. Finally, we observed clear differences in alpha diversity (species richness and phylogenetic diversity), which were to a stronger extent determined by abiotic compared with biotic factors, but also by dispersal effects. In summary, our study shows that the biodiversity of bacterial biofilm communities within a lake ecosystem is driven by within-habitat gradients in abiotic conditions and by stochastic and deterministic dispersal processes.

Long-term purification efficiency of a wetland constructed to treat runoff from peat extraction

ABSTRACT Peat extraction increases the phosphorus, nitrogen, organic matter, suspended solids, and iron concentrations in runoff, resulting in negative effects on downstream water bodies. Wetlands are commonly used as natural cost-effective solutions to mitigate these negative effects. This study analyzed changes in the quality of runoff water from peat extraction areas and the long-term efficiency of constructed wetlands. The results indicate that the quality of runoff water changed after the initial drainage and during peat extraction. Nitrogen leached at high concentrations in the early stages of peat extraction following drainage, whereas the leaching of iron and phosphorus increased after peat extraction from deeper layers. Comparison of water quality and impurities retained immediately after treatment wetland construction and 14 years later showed that the treatment wetland remained functional, with good retention capacity, over a long period.

Environmental filtering and spatial effects on metacommunity organisation differ among littoral macroinvertebrate groups deconstructed by biological traits

We examined spatial and environmental effects on the deconstructed assemblages of littoral macroinvertebrates within a large lake. We deconstructed assemblages by three biological trait groups: body size, dispersal mode and oviposition behaviour. We expected that spatial effects on assemblage structuring decrease and environmental effects increase with increasing body size. We also expected stronger environmental filtering and weaker spatial effect on the assemblages of flying species compared with assemblages of non-flying species. Stronger effect of environmental filtering was expected on the assemblages with species attaching eggs compared with assemblages of species with free eggs. We used redundancy analysis with variation partitioning to examine spatial and environmental effects on the deconstructed assemblages. As expected, the importance of environmental filtering increased and that of spatial effects decreased with increasing body size. Opposite to our expectations, assemblages of non-flying species were more affected by environmental conditions compared to assemblages of flying species. Concurring with our expectations, the importance of environmental filtering was higher in structuring assemblages of species attaching eggs than in structuring those with freely laid eggs. The amount of unexplained variation was higher for assemblages with small-sized to medium-sized species, flying species and species with free eggs than those with large-sized species, non-flying species and species with attached eggs. Our observations of decreasing spatial and increasing environmental effects with increasing body size of assemblages deviated from the results of previous studies. These results suggest differing metacommunity dynamics between within-lake and among-lake levels and between studies covering contrasting taxonomic groups and body size ranges.

Do different facets of littoral macroinvertebrate diversity show congruent patterns in a large lake system

Modern biodiversity research focuses on multiple diversity facets because different indices may describe different ecological and environmental processes, as well as the effects of varied disturbances of natural and anthropogenic origins. We investigated littoral macroinvertebrate diversity in a large boreal lake system and specifically explored congruence of indices within and between the three diversity facets: species diversity, functional diversity and taxonomic distinctness. First, we found that the indices of taxonomic distinctness were the most sensitive indicators of eutrophication. Second, we observed that most correlations between the indices within the same diversity facet, and between the indices of functional and species diversity, were relatively strong. However, the indices of taxonomic distinctness (Δ+ and Λ+) were weakly associated with other metrics of diversity, emphasising the importance of taxonomic distinctness as a complementary dimension of biodiversity. Therefore, our observations support the importance to examine multiple facets for mapping biodiversity or for assessing the effects of anthropogenic disturbances on biological communities.

Different species trait groups of stream diatoms show divergent responses to spatial and environmental factors in a subarctic drainage basin

Understanding the drivers of community structure is an important topic in ecology. We examined whether different species trait groups of stream diatoms (ecological guilds and specialization groups) show divergent responses to spatial and environmental factors in a subarctic drainage basin. We used local- and catchment-scale environmental and spatial variables in redundancy analysis and variation partitioning to examine community structuring. Local and catchment conditions and spatial variables affected diatom community structure with different relative importance. Local-scale environmental variables explained most of the variation in the low-profile and motile guilds, whereas local and spatial variables explained the same amount of the variation in the high-profile guild. The variations in the planktic guild and the specialist species were best explained by spatial variables, and catchment variables explained most variation only in generalist species. Our study showed that diatom communities in subarctic streams are a result of both environmental filtering and spatial processes. Our findings also suggested that dividing whole community into different groups by species traits can increase understanding of metacommunity organization.