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In the present study, we developed a new Swedish phosphorus diatom index (PDISE) to improve the poor fit of existing indices to match the needs of water managers to detect and mitigate eutrophication. We took advantage of a large amount of data (820 Swedish stream sites) collected in recent years. During our work, we found an unexpected bimodal response of the diatom assemblages to phosphorus. The taxa clustered either into an assemblage with a low or with a high site-specific averaged TP optimum (a calculated value comprised of the diatom taxa-specific optima). We could not find a characteristic diatom assemblage for sites with intermediate site-specific averaged TP optima. To our knowledge, this bimodal community response has not been shown earlier. The PDISE correlated more strongly than the currently used TDI to changes in TP concentrations. Thus, the PDISE should replace the TDI in the Swedish standard method. The modeled TP optima (expressed as categories) were different compared to the TDI for most of the taxa included in the index, indicating that the realized niche for these morphotaxa was different between Sweden and the UK where the TDI was developed originally. With a r2 of 0.68, the correlation of the PDISE to TP is among the highest reported for other diatom nutrient indices globally; thus, we believe that it might be worth to test it for other bioregions with similar geography and climate. [ABSTRACT FROM AUTHOR]

With the current loss of biodiversity and threats to freshwater ecosystems, it is crucial to identify hot-spots of biodiversity and on which spatial scale they can be resolved. Conservation and management of these important ecosystems needs insight into whether most of the regional biodiversity (i.e. γ-diversity) can be found locally (i.e. high α-diversity) or whether it is distributed across the region (i.e. high β-diversity). Biodiversity patterns of benthic macroinvertebrates and diatoms were studied in 30 headwater streams in five Swedish catchments by comparing the relative contribution of α- and β-diversity to γ-diversity between two levels of stream habitat hierarchy (catchment and region level). The relationship between species community structure and local environmental factors was also assessed. Our results show that both α- and β-diversity made a significant contribution to γ-diversity. β-diversity remained relatively constant between the two levels of habitat hierarchy even though local environmental control of the biota decreased from the catchment to the region level. To capture most of headwater γ-diversity, management should therefore target sites that are locally diverse, but at the same time select sites so that β-diversity is maximized. As environmental control of the biota peaked at the catchment level, the conservation of headwater stream diversity is likely to be most effective when management targets environmental conditions across multiple local sites within relatively small catchments. [ABSTRACT FROM AUTHOR]

The European Union (EU) member states have agreed on the Water Framework Directive. The vision is that all European waters will achieve ''good'' ecological status. Each member state has agreed to meet these commitments. In Sweden, the Environmental Protection Agency regulates the methods used for classification of the ecological status of inland and coastal waters. The aim of this study was to evaluate how these criteria (using diatoms, benthic fauna, fish, water chemistry, hydromorphology) principally affect the classification of two typical forest streams. Forestland constitutes approximately 70% of the Swedish land area and forestry is the dominating human impact on many waters. Particular attention was paid to evaluate how the classification may vary with catchment size and between years. The results indicate that there is an obvious risk that many Swedish forest streams will not achieve ''good'' ecological status. The classification outcome may vary between years and regarding fish status; it also seems to depend on stream size. [ABSTRACT FROM AUTHOR]

1. The aim of this study was to estimate patchiness in biomass and in the internal nutrient status of benthic algae on hard substrata (epilithon) in Lake Erken, Sweden, over different levels of distance, depth and time. Knowledge of the sources and scale of patchiness should enable more precise estimation of epilithic biomass and nutrient status for the entire lake. We focused on the horizontal scale, about which little is known. 2. We sampled epilithon by SCUBA diving and used a hierarchical sampling design with different horizontal scales (cm, dm, 10 m, km) which were nested in two temporal scales (within and between seasons). We also compared two successive years and three sampling depths (0, 1 and 4 m). Biomass was measured as particulate carbon and chlorophyll a (Chl a ) and internal nutrient status as carbon : nitrogen : phosphorus (C : N : P) ratios and as specific alkaline phosphatase activity (APA). 3. Horizontal variation accounted for 60–80 and 7–70% of the total variation in biomass and in nutrient status, respectively, at all depths and during both years. Both small and large scales accounted for significant variation. We also found variation with time and depth. Biomass increased in autumn after a summer minimum, and the within-season variation was very high. The lowest biomass was found at 0 m depth. Both N and P limitation occurred, being higher in 1996 than in 1997 and decreased with depth. 4. As a consequence, any sampling design must address variation with distance, depth and time when estimating biomass or nutrient limitation of benthic algae for an entire lake. Based on this analysis, we calculated an optimal sampling design for detecting change in the epilithic biomass of Lake Erken between different sampling days. It is important to repeat the sampling as often as possible, but also the large scales (10 m and km) and the dm scale should be replicated. Using our calculations as an example, and after a pilot study, an optimal... [ABSTRACT FROM AUTHOR]

• Water chemistry and climatic factors were inferred from diatom assemblages. • The models were calibrated with Swedish data and inferred for Finland. • The predictive performance of all calibration models in Sweden were good or moderate. • The predictive performances of the cross-regional models were low. Ongoing climatic change and anthropogenic pressure highlight the importance of reliable assessment of the ecological status of freshwaters. Bioindicators are used widely in ecological assessments as biotic assemblages reflect the environmental conditions in current ecosystems. However, the robustness of bioindicators relies on the transferability of indices and models outside the regions they were derived from. We tested the reliability of stream diatom assemblages as indicators of water chemistry and climatic factors in a cross-regional assessment by developing a predictive model with diatom assemblage data from Sweden and using it to model stream conditions in Finland. The inference models and predictions were performed using the Boosted Regression Trees (BRT) method, separately in species and genus levels. The predictive performance of the calibration models in Sweden were good or moderate for both water chemistry and climatic variables, both at species and genus levels. The most important climatic (growing degree days, r2 = 0.57) and water chemistry variables (pH, r2 = 0.65; and total phosphorus (TP), r2 = 0.52) could be inferred from diatom assemblages relatively well. However, predictive performances of the cross-regional models were low (r2 ≤ 0.13). Nevertheless, water chemistry variables, conductivity (r2 = 0.13) and TP (r2 = 0.12), were predicted the best. The most important diatom indicators for climatic and environmental variables varied between Sweden and Finland. The study showed that diatom assemblages can be robust indicators of water chemistry and climatic variables within the region where the inference models are calibrated. However, their indicator ability may be weak between regions. The reason for the low transferability of the diatom inference models may stem from between-region differences in species realized niches, species pools and/or ecosystems, local adaptation or species identification. Hence, models should only be used with caution in geographical contexts other than the one where they were developed. The calibration data should cover as large geographical area as possible to give reliable predictions when applied in smaller regions. [ABSTRACT FROM AUTHOR]

Pesticides are frequently detected in surface waters, sometimes at levels exceeding ecotoxicological guidelines. We screened for almost 100 pesticides in 32 streams from intense agricultural areas in Southern Sweden, in concert with water chemistry parameters. In addition, we investigated the communities of benthic macroinvertebrates, biofilm nematodes and algae and calculated multiple bioassessment metrics. The number of pesticides found in each stream ranged between 2 and 52, but the sum of Toxic Units (ΣTU) for the mixtures was generally low, and exceeded the European Uniform Principles only in a single sample for algae and in 2% of the samples for Daphnia. Only nematode communities were significantly correlated with the ΣTU, potentially due to their higher pesticide exposure in biofilms. Diatom metrics showed that most streams were impacted by eutrophication and macroinvertebrate metrics showed good status in most streams, whereas the SPEAR pesticides (SPEcies At Risk) index, specifically designed to indicate pesticide effects, showed that about half of the samples were at risk. Interestingly, SPEAR pesticides was not correlated to ΣTU Daphnia, and this discrepancy suggests that redefining the boundaries for quality classes might be necessary for this index. Moreover, SPEAR pesticides was positively correlated with the commonly used macroinvertebrate index ASPT, although disparate results were found for several streams. We argue that this questions the scaling of both metrics and the specificity of their responses. We discuss that the overall good/moderate status of the streams, despite the intense agriculture in the catchments, can be due to the fact that i) a sampling strategy with repeated grab samples did not capture peak pesticide concentrations, thus underestimating acute exposure, ii) pesticide run-off indeed was low, due to measures such as buffer strips, and iii) the nutrient-rich conditions and high sediment loads counteracted pesticide toxicity. We conclude that agricultural land use was the overriding stressor in the investigated streams, including strong effects of nutrients, less apparent effects of pesticides and likely impact of hydromorphological alterations (not specifically addressed in this study). Image 1 • 32 agricultural streams in Sweden were screened for pesticides. • Between 2-52 pesticides were found per stream, albeit mostly at low concentrations. • Biological indices showed generally good-moderate status of the streams. • Nematode species composition was correlated to pesticide toxic units for Daphnia. • Diatom genus composition was affected by eutrophication, not pesticides. [ABSTRACT FROM AUTHOR]