Heikki Hämäläinen

Correspondence between regional delineations and spatial patterns in macroinvertebrate assemblages of boreal headwater streams

Geographical stratification may provide a useful framework for stream management programs, yet most studies testing the utility of such stratifications have been conducted in temperate regions. We studied the correspondence between regional delineations (5 ecoregions, 11 subecoregions), environmental characteristics, and benthic macroinvertebrate assemblages in 156 boreal headwater streams in Finland, using a combination of principal components analysis, nonmetric multidimensional scaling, and discriminant function analysis (DFA). Both stream characteristics and macroinvertebrate assemblage structure showed a closer correspondence to ecoregions than to subecoregions, a pattern partly attributable to the smaller number of classes at the ecoregion level. Based on environmental variables, DFA classified correctly 84.0% of the streams by ecoregion and 74.4% by subecoregion. For macroinvertebrate assemblages, 64.7% of the streams were correctly classified at the ecoregion, and 51.9% at the subecoregion level. Arctic-alpine and north boreal ecoregions supported the most distinct benthic assemblages. There were significant differences among ecoregions in mean species number, with lowest species richness in the middle boreal and highest in the south boreal streams. However, no clear latitudinal gradients in local species richness were detected. Relative abundances of functional-feeding groups also exhibited regional differences. Shredders dominated the middle boreal brown-water streams, whereas scrapers attained their highest abundances in the arctic-alpine and north boreal clear-water streams. Despite some congruence among ecoregions and macroinvertebrate assemblages, regional delineations alone do not provide a suitable background for stream biomonitoring programs. A combination of regional delineations and local characteristics probably provides a better framework for the classification of boreal headwater streams, and for the prediction of their benthic fauna.

DEFINING MACROINVERTEBRATE ASSEMBLAGE TYPES OF HEADWATER STREAMS: IMPLICATIONS FOR BIOASSESSMENT AND CONSERVATION

We used data from 235 boreal headwater streams in Finland to examine whether macroinvertebrate assemblages constitute clearly definable types, and how well biologically defined assemblage types can be predicted using environmental variables. Two- way indicator species analysis produced 10 assemblage types, which differed significantly from each other (multiresponse permutation procedure, MRPP). However, based on MRPP and nonmetric multidimensional scaling, there was wide variation among sites within each assemblage type, and high degrees of overlap among assemblage types. Such continuous variation was also evidenced by the low number of effective indicator taxa (indicator value method) for each assemblage type. Furthermore, discriminant function analysis based on environmental variables showed a moderate yet variable prediction success (59.6% of sites correctly predicted; range 0-96% per group). Canonical correspondence analysis indicated that variation in assemblage structure was primarily related to latitude and water chemistry, especially pH and water color. The absence of discrete macroinvertebrate assemblage types in boreal headwater streams may stem from a number of reasons: (1) macroinvertebrate taxa inhabiting boreal streams tend to exhibit individualistic, taxon-specific responses to environmental gradients, (2) they have wide environmental tolerances and geographic dis- tributions, and (3) boreal streams are characterized by frequent, unpredictable disturbances. Our results suggest that local filters in headwater streams are relatively weak, resulting in poorly distinguishable assemblage types. By contrast, the major latitudinal gradients in macroinvertebrate assemblage structure suggest that regional-scale filters, e.g., temperature, exert strong control over taxon distributions in headwater streams. We suggest that a tiered approach combining regional stratification and subsequent prediction of assemblage struc- ture could provide a suitable framework for the bioassessment and conservation of boreal headwater streams.

Littoral species diversity and biomass: concordance among organismal groups and the effects of environmental variables

Abstract.Biomass and species diversity (richness and evenness) of littoral organisms were explored in 27 sites in three basins of the large Lake Saimaa system in eastern Finland. The basins differed in degree of nutrient loading and trophic status. Six organismal groups, i.e., phytoplankton, periphyton, macrophytes, crustacean zooplankton, benthic macroinvertebrates and fish were studied. Factors affecting the biomass and diversity of these groups were explored by multiple stepwise regression analysis. The biomass of different groups was explained by the same variables, mainly nutrients, while diversity was associated with different environmental factors among the studied groups. The biomass of periphyton, phytoplankton, zooplankton, and fish correlated significantly with each other. There was also an apparent association between the biomass of macrophytes and that of benthic invertebrates. However, no significant correlations were found among the diversity of the studied groups. In accordance with previous studies, our results did not support the existence of species-rich hotspots or the possibility of using any surrogate taxon to reveal overall biodiversity. Thus, for conservation planning, biological surveys should include extensive collection of taxonomic groups and organisms at all trophic levels.

Natural variation of profundal macroinvertebrate communities in boreal lakes is related to lake morphometry: implications for bioassessment

Modern biological assessment of aquatic systems is often based on the reference condition approach, which requires characterization of biota in undisturbed conditions. For this approach, it is essential to recognize the origins and degree of natural variation in communities. We used data from 55 minimally disturbed Finnish lake basins to investigate the natural variation of profundal macroinvertebrate community composition in relation to environmental factors. Partial canonical correspondence analysis showed that most (68% combined, 39% uniquely) of the total explained compositional variation (29%) was correlated with environmental variables insensitive to human activities, especially lake morphometry. In contrast, the unique contributions of geographical location and variables influenced by human activities (dissolved oxygen and total phosphorus) were substantially smaller (5.5% and 22%, respectively). All of the explained variation (38%–64%) of three widely used community metrics was also correlated wit...

Assessing stream condition using macroinvertebrates and macrophytes: concordance of community responses to human impact

Freshwater bioassessment is typically based on well known taxonomic groups, such as fish and macroinvertebrates, while less studied groups are frequently excluded from bioassessment programs. We examined the community variation of stream macroinvertebrates and macrophytes (mainly aquatic bryophytes) in near-pristine reference sites and sites impacted by agriculture, forestry, or in-stream habitat alteration in western and central Finland. We specifically examined whether these taxonomic groups exhibited concordant variation in community structure and whether they could be used as surrogates for each other in stream bioassessment. The effects of human disturbance on taxonomic composition and community structure were investigated using canonical correspondence analysis and RIVPACS-type predictive models. The community concordance between macroinvertebrates and macrophytes was higher when test sites were included, suggesting that environmental degradation may increase community concordance between different biotic groups. However, despite increased concordance, macroinvertebrates and macrophytes responded to different stressors. The sensitivity of the two groups to human disturbance also differed markedly. The macroinvertebrate model determined 13 (with P t = 0+ as the threshold for species inclusion) and 12 (with P t = 0.4) out of 35 test sites as altered, whereas the macrophyte model detected impairment for only 7 sites (both probability levels), likely because of the low species richness of macrophytes in our study streams. Low richness of macrophytes may thus hinder their use in bioassessment based on taxonomic completeness, suggesting that measures that do not rely solely on species loss might perform better in at least high-gradient boreal streams.

A Priori Typology-Based Prediction of Benthic Macroinvertebrate Fauna for Ecological Classification of Rivers

We evaluated a simple bioassessment method based on a priori river typology to predict benthic macroinvertebrate fauna in riffle sites of rivers in the absence of human influence. Our approach predicted taxon lists specific to four river types differing in catchment area with a method analogous to the site-specific RIVPACS-type models. The reference sites grouped in accordance with their type in NMS ordination, indicating that the typology efficiently accounted for natural variation in macroinvertebrate assemblages. Compared with a null model, typology greatly increased the precision of prediction and sensitivity to detect human impairment and strengthened the correlation of the ratio of observed-to-expected number of predicted taxa (O/E) with the measured stressor variables. The performance of the typology-based approach was equal to that of a RIVPACS-type predictive model that we developed. Exclusion of rarest taxa with low occurrence probabilities improved the performance of both approaches by all criteria. With an increasing inclusion threshold of occurrence probability, especially the predictive model sensitivity first increased but then decreased. Many common taxa with intermediate type-specific occurrence probabilities were consistently missing from impacted sites, a result suggesting that these taxa may be especially important in detecting human disturbances. We conclude that if a typology-based approach such as that suggested by the European Union’s Water Framework Directive is required, the O/E ratio of type-specific taxa can be a useful metric for assessment of the status of riffle macroinvertebrate communities. Successful application of the approach, however, requires biologically meaningful river types with a sufficient pool of reference sites for each type.

The response of benthic macroinvertebrates to whole-lake biomanipulation

The response of a benthic macroinvertebrate assemblage to whole-lake biomanipulation was studied in a small Finnish mesotrophic lake. From 1993 to 1997, over 200 kg ha−1 of fish, mainly roach (Rutilus rutilus (L.)) and bream (Abramis brama (L.)) were caught and the fish biomass was reduced by nearly 80%. The biomass and density of benthic invertebrates were investigated during the years of fish removal and for the following three years. The decrease in benthivorous fish stock led to a higher biomass and density of all major groups of benthic invertebrates during the early years of fish removal. Non-biting midges (Chironomidae), water mites (Hydrachnellae), mayfly nymphs (Ephemeroptera), sphaeriid clams (Bivalvia: Sphaeridae) and biting midges (Ceratopogonidae) seemed to respond most profoundly to changes in fish biomass. The biomass of most invertebrate groups correlated negatively with the catch-per-unit-effort (CPUE). The total biomass and density of invertebrates had strong negative correlations with the CPUE (r= -0.85, p = 0.016, r = -0.84, p = 0.019, respectively), but they did not correlate significantly with total phosphorus, chlorophyll a, or temperature. However, the variation in total biomass that was not explained by the CPUE, was significantly associated with total phosphorus.The fish stock recovered to almost its initial level within three years after fish removal had been discontinued. As an apparent response to increased predation pressure, the biomasses of many invertebrate groups decreased again in the years 1999–2000. The strong relationship between macrozoobenthos and fish populations in the studied lake is likely to be a consequence of the open and sparsely vegetated bottom, which offers minimal shelter to invertebrate prey. An additional factor behind the recent low biomass levels may be changes in primary production. Phosphorus and chlorophyll a concentrations started to decrease markedly after three years of fishing and they have remained at a low level.

Predicting the stream macroinvertebrate fauna across regional scales: influence of geographical extent on model performance

Abstract Predictive modeling is used increasingly often in freshwater bioassessment. These models are routinely applied across broad geographical areas, yet the influence of spatial extent on model performance has not been assessed directly. We examined the influence of changing geographical extent on the performance of River InVertebrate Prediction and Classification System (RIVPACS)–type predictive models of benthic macroinvertebrates in boreal headwater streams representative of reference conditions. Separate models were constructed for 2 hierarchical extents: within ecoregions (middle boreal and north boreal) and across ecoregions. We assessed the accuracy and precision of the models using root mean squared error (RMSE) of the observed/expected (O/E) ratio of the number of predicted taxa. We compared the RMSE of the within-ecoregion models to that of the across-ecoregions models. We tested the models using 2 thresholds for probability of species occurrence (Pt): Pt = 0+ (all predicted taxa) and Pt = 0.5 (only common taxa). We also assessed the importance of catchment vs local habitat variables as predictors of macroinvertebrate fauna. Within the 2 ecoregions, region-specific models performed better than the across-ecoregions model with Pt = 0+, but the difference in performance of models with different regional extents decreased when Pt = 0.5. Catchment area and stream slope were the only consistently significant predictor variables, but overall, only minor differences were found in the relative importance of catchment vs local attributes. Models with Pt = 0.5 performed better than those with Pt = 0+; this result suggests that models based only on common taxa might perform more consistently than models based on all taxa in the assessment of headwater streams. However, the expected number of taxa would then become very low (mean: 8.0–12.6 with Pt = 0.5), which might impede detection of human impact. Alternative approaches that do not rely solely on taxon occurrences but also incorporate aspects of assemblage composition might be needed for assessment of headwater streams.

Estimation of Acidity in Streams by Means of Benthic Invertebrates: Evaluation of Two Methods

The distribution of benthic invertebrates was studied in relation to stream acidity. The object was to evaluate use of invertebrates in assessing stream acidity. Of two methods applied, the first is tolerance limit (TL) method based on presence/absence of indicator species. The second method is weighted averaging based on species optima and tolerances, which were estimated by maximum likelihood (ML) and weighted averaging (WA) methods, assuming unimodal relationship between relative abundance of invertebrate taxa and the stream pH.

Comparison of sampling methods and habitat types for detecting impacts on lake littoral macroinvertebrate assemblages along a gradient of human disturbance.

We explored environmental variables structuring littoral macroinvertebrate communities in a large lake basin along a gradient of nutrient enrichment. Furthermore, we evaluated sensitivity and cost-effi ciency of different sampling schemes (i.e. combinations of three habitat types and a number of standard sampling methods) to detect changes in macroinvertebrate communities along this anthropogenic disturbance gradient. Partial canonical ordination analysis showed that habitat characteristics accounted for a major part (56 % uniquely) of the explained variation in the species composition of invertebrate communities. When different mesohabitats were examined separately, assemblage variation of stony bottoms was most strongly associated with human-induced changes in water chemistry (51 % of the explained variation). In sandy and vegetated habitats, shore morphometry and habitat characteristics were more infl uential factors. The most time-consuming phases of sample processing were sorting and identifi cation, whilst the time-costs of fi eld sampling were relatively low. The duration of sample treatment was positively correlated with the numbers of individuals counted and taxa identifi ed. Additionally, processing time was associated with habitat type, samples from stony bottoms being the least laborious. Kick-net sampling on stony shores was the most cost-effi cient sampling scheme with low costs and highest sensitivity to detect anthropogenic impacts.