1. The effect of nutrient enrichment on structural (invertebrate indices) and functional (leaf-litter breakdown rates) characteristics of stream integrity was studied in nine boreal streams. 2. The results showed predicted changes in biotic indices and leaf-litter breakdown along a complex (principal component) nutrient gradient. Biotic indices were better correlated with nutrient effects than leaf-litter breakdown. 3. Fungal biomass and invertebrate densities in the litter bags were positively correlated with leaf-litter breakdown, and both were also positively related to the nutrient gradient. 4. Invertebrate community composition influenced breakdown rate. High breakdown rates at one site were associated with the high abundance of the detritivore Asellus aquaticus. 5. This study lends support to the importance of invertebrate and fungi as mediators of leaf-litter decomposition. However, our study also shows that study design (length of incubation) can confound the interpretation of nutrient-induced effects on decomposition.

Carbon and nitrogen stable isotopes are frequently used to study energy sources and food web structure in ecosystems, and more recently, to study the effects of anthropogenic stress on aquatic ecosystems. We investigated the effect of nutrient enrichment on d 13 C and d 15 N in fine (FPOM), coarse (CPOM) particulate organic matter, periphyton, invertebrates and fish in nine boreal streams in south-central Sweden. In addition, we analysed the diet of benthic consumers using stable isotope data. Increases in d 15 N of periphyton (R 2 = 0.88), CPOM (0.78), invertebrates (0.92) and fish (0.89) were related to nutrient enrichment. In contrast, d 13 C signatures did not change along the nutrient gradient. Our results show that d 15 N has potential as a sensitive indicator of nutrient enrichment in boreal streams. Carbon and nitrogen isotopes failed to elucidate putative diets of selected aquatic consumers. Indeed, comparison of low-and high-impact sites showed that d 13 C of many consumers were found outside the ranges of basal resource d 13 C. Moreover, ranges of basal resource d 13 C and d 15 N overlapped at both low and high sites, making discrimination between the importance of allochthonous and autochthonous production difficult. Our findings show that a fractionation rate of 3.4% is not always be appropriate to assess trophic interactions, suggesting that more studies are needed on fractionation rates along gradients of impairment.

Th e Tarland Catchment Initiative is a partnership venture between researchers, land managers, regulators, and the local community. Its aims are to improve water quality, promote biodiversity, and increase awareness of catchment management. In this study, the eff ects of buff er strip installations and remediation of a large septic tank effl uent were appraised by water physicochemistry (suspended solids, NO 3 , NH 4 , soluble reactive P) and stream macroinvertebrate indices used by the Scottish Environmental Protection Agency. It was done during before and after interventions over an 8-yr period using a paired catchment approach. Because macroinvertebrate indices were previously shown to respond negatively to suspended solid concentrations in the study area, the installation of buff er strips along the headwaters was expected to improve macroinvertebrate scores. Although water quality (soluble reactive P, NH 4 ) improved downstream of the septic tank effl uent after remediation, there was no detectable change in macroinvertebrate scores. Buff er strip installations in the headwaters had no measurable eff ects (beyond possible weak trends) on water quality or macroinvertebrate scores. Either the buff er strips have so far been ineff ective or ineff ectiveness of assessment methods and sampling frequency and time lags in recovery prevent us detecting reliable eff ects. To explain and appreciate these constraints on measuring stream recovery, continuous capacity building with land managers and other stakeholders is essential; otherwise, the feasibility of undertaking suffi cient management interventions is likely to be compromised and projects deemed unsuccessful.

Two vegetation-monitoring methods were compared: subplot frequency analysis (SF) and visual estimation of percentage cover (VE). Two independent observers collected data from two semi-natural, species-rich grasslands on three different occasions during the growth-season. During the last data collection period, survey times were also recorded. The two different data sets from the two methods were compared using partial Redundancy Analyses. The purpose of the comparison was to identify the method that explains most of the relevant variation in biodiversity-monitoring (inter- and intra-site variation), and the variation irrelevant when evaluating data (systematic inter-observer variation and variation due to phenological changes). Compared with VE data, more variation in SF data could be explained by spatial variables, while less variation depended on the observer and time of year surveyed. SF also found more species per plot but took on average five times longer to complete than VE. In conclusion, the different methods are suitable for different purposes: SF is more suitable for purposes demanding high accuracy and high precision, such as long-term biodiversity-monitoring when the identification of small changes has high priority, while VE might be more suitable for a one-time mapping of a large area.