Quantifying plant biomass and related processes such as element allocation is a major challenge at the scale of entire riparian zones. We applied sub-decimetre-resolution (5 cm) remote sensing using an unmanned aircraft system (UAS) in combination with field sampling to quantify riparian vegetation biomass at three locations (320-m river stretches) along a mining-impacted boreal river and estimated the amounts of Cd, Cu, and Zn stored in the dominant species. A species-level vegetation map was derived from visual interpretation of aerial images acquired using the UAS and field sampling to determine species composition and cover. Herbaceous and shrub biomass and metal contents were assessed by combining the vegetation maps with field sampling results. Riparian zone productivity decreased from 9.5 to 5.4 t ha-1 with increasing distance from the source of contamination, and the total amount of vegetation-bound Cd and Zn decreased from 24 to 0.4 and 3,488 to 211 g, respectively. Most Cu was stored at the central location. Biomass and metal contents indicated large variation between species. Salix spp. comprised only 17% of the total dominant-species biomass but contained 95% of all Cd and 65% of all Zn. In contrast, Carex rostrata/vesicaria comprised 64% of the total dominant-species biomass and contained 63% of all Cu and 25% of all Zn. Our study demonstrates the applicability of UAS for monitoring entire riparian zones. The method offers great potential for accurately assessing nutrient and trace element cycling in the riparian zone and for planning potential phytoremediation measures in polluted areas

The efficiency of biogeochemical mapping for identifying acid sulphate soils (AS soils) was studied by sampling and analysing water, transplanted aquatic moss (Fontinalis antipyretica) and leaves of the vascular plant Calamagrostis purpurea at two sites in a stream in northern Sweden with AS soils in its drainage area. One upstream sampling station (Mårtsmarken) was situated in an area dominated by till, and a downstream station (Persraningen) was situated in an area where AS soils are common. Metal contents in F. antipyretica and C. purpurea at these sites were compared to those in water (both unfiltered samples, and samples subjected to 0.22 μm membrane filtration and 1 kDa ultrafiltration to obtain data on metal speciation and its effects on uptake). Oxidation of sulphides with associated increases in acidity and release of metals were clearly reflected by differences in the water samples. At Persraningen the pH was lower than at Mårtsmarken, and the unfiltered concentrations of Al, Ca, Cd, Co, Cu, K, Mg, Mn, Ni, P, S, Sr, Y and Zn were higher. At the upstream station, Mårtsmarken, the suspended fraction was an important carrier of Fe and P, and the colloidal concentrations were higher than or similar to the dissolved concentrations for all determined elements except Na and K. At Persraningen the low pH resulted in changes of speciation, so that the dissolved concentrations were higher than the colloidal concentrations for most elements. For Al, As, Cr, Cu, Pb and Y, the dissolved and colloidal concentrations were similar. For Fe, the colloidal concentration was usually higher than the dissolved concentration, and suspended Fe was detected. Aluminium, Cr, Cu, Fe and Y concentrations were significantly higher in Fontinalis antipyretica at Persraningen than at Mårtsmarken. In addition, concentrations of Al and Fe in C. purpurea were significantly higher at Persraningen. Our results highlight the potential of biogeochemical mapping for predicting the occurrence of AS soils. A limitation is the strong pH dependence of the uptake of metals in the aquatic mosses resulting in that only a few of the elements typically occurring at high concentrations in waters draining AS soils are enriched in the macrophytes. A combination of maps showing both absolute concentrations and elemental ratios would be useful for this, including not only ratios of previously suggested utility (e.g. Y:Pb and Ni:Pb), but also others, such as Y:Ca, Al:Ca, Cu:Ca, Y:Mg, Al:Mg and Cu:Mg. © 2014 AAG/The Geological Society of London.

QuestionsDo high-resolution (sub-decimetre) aerial images taken with unmanned aircraft systems (UASs) allow a human interpreter to recognize aquatic plant species? Can UAS images be used to (1) produce vegetation maps at the species level; and (2) estimate species abundance? LocationOne river and two lake test sites in northern Sweden, middle boreal sub-zone. MethodsAt one lake and at the river site we evaluated accuracy with which aquatic plant species can be identified on printouts of UAS images (scale 1:800, resolution 5.6 cm). As assessment units we used homogeneous vegetation patches, referred to as vegetation stands of one or more species. The accuracy assessment included calibration and validation based on field controls. At the river site, we produced a digital vegetation map based on an UAS orthoimage (geometrically corrected image mosaic) and the results of the species identification evaluation. We applied visual image interpretation and manual mapping. At one of the lake sites, we assessed the abundance (four-grade scale) of the dominating Phragmites australis and produced a cover map. ResultsWe identified the species composition of vegetation stands at the lake and the river site with an overall accuracy of 95.1% and 80.4%, respectively. It was feasible to produce a digital vegetation map, albeit with a slight reduction in detail compared to the species identification step. At the site for abundance assessment, P. australis covered 20% of the total lake surface area, and 70% of the covered area had cover ≤25%. ConclusionsThe tested UAS facilitates lake and river vegetation identification and mapping at the species level, as well as abundance estimates

An analytical method allowing multi-element characterization by external calibration, osmium (Os) concentration determination by isotope dilution (ID) and 187Os/188Os isotope abundance ratio measurement from a single sample preparation was developed. The method consists of microwave-assisted, closed-vessel acid digestion of small (0.01-0.4 g dry weight) biological samples spiked with Os solution enriched in a 190Os isotope followed by concentration and Os isotope ratio measurements using double-focusing, sector field inductively coupled plasma mass-spectrometry (ICP-SFMS) operated with methane addition to the plasma and solution nebulization (SN) sample introduction. For samples with Os content below 500 pg, complementary analysis using gas-phase introduction (GPI) on the remaining sample digests was performed. The use of disposable plastic lab ware for sample digestion and analysis by SN ICP-SFMS circumvents Os carry-over effects and improves the sample throughput and cost-efficiency of the method. For a 0.1 g dried sample, Os method limits of detection (MLODs) of 2 pg g -1 and 0.2 pg g-1 were obtained using SN or GPI, respectively. Long-term reproducibility of 187Os/188Os isotope abundance ratio measurements using the GPI approach was better than 1.5% RSD for our in-house control sample (moose kidney) with an Os concentration of approximately 5 pg g-1. Os data for several commercially available reference materials of biological or plant origin (not certified for Os) are presented. The method was used in the large scale bio-monitoring of free-living bank voles from an area affected by anthropogenic Os emissions.

Many northern lakes are regulated to enhance hydropower production and flood protection. This bears hydromorphological pressures which are important factors causing lowered ecological status. Water level fluctuation triggers erosion on the shoreline and, depending on fluctuation range, also affects species composition or disappearance of sensitive aquatic macrophytes. We developed a water leveldrawdown index (WIc) for Nordic lakes using macrophytedata from 73 lakes with varying water level fluctuation in Finland, Norway and Sweden. The index is based on the ratio between sensitive and tolerant macrophyte species. The sensitive and tolerant species are identified based on a percentile approach, analysing the presence or absence of species along the winter drawdown range. The index correlates well with winter drawdown in Finnish and Norwegian lakes with strongest correlations with winter drawdown in storage lakes (lakes regulated for hydroelectric power and with a considerable winter drawdown). The WIcindex is applicable in low alkalinity, oligotrophic and ice-covered lakes, and is suggested to be a useful tool to identify and designate heavily modified water bodies in Nordic lakes according to the European Water Framework Directive.

The question of the limiting nutrient(s) for production of phytoplankton and macrophytes was explored in two contrasting freshwater systems receiving N- and P-rich mine effluents from the Boliden and Kiruna mine sites, northern Sweden. For both sites, total N (TN), total P (TP) and TN:TP mass ratios in water, sediment and macrophytes were used to examine (1) spatial variations within the systems, (2) differences between the systems and (3) seasonal variations. The TN concentration from the discharge point at the Kiruna site was about seven times higher than at the Boliden discharge point, while the TP concentration was 10 times lower than in the discharge point at the Boliden site. The majority of the studied lakes showed elevated biomass of phytoplankton, with maximum values found in Lake Bruträsket (Boliden). Mining activities have affected the nutrient regime of the two recipients by contributing to elevated TN and TP concentrations and TN:TP mass ratios as well as elevated production of phytoplankton and macrophytes compared to the reference sites. Depending on the NH4 concentration in the effluent at the Boliden site, water column TN:TP mass ratios shifted from being >22, indicating P-deficiency, to between 9 and 22, indicating a transition from N- to P-deficiency (co-limitation). However, water column TN:TP mass ratios at the Kiruna site always indicated P-deficiency, while TN:TP mass ratios of macrophytes indicate that both sites may vary from N- to P-limitation. The study suggests that for the design of efficient monitoring programmes and remediation measures, it is important to consider the major N and P species in water, phytoplankton, sediment and macrophytes.

Uncertainty is an important factor in ecological assessment, and has important implications for the ecological classification and management of lakes. However, our knowledge of the effects of uncertainty in the assessment of different ecological indicators is limited. Here, we used data from a standardized campaign of aquatic plant surveys, in 28 lakes from 10 European countries, to assess variation in macrophyte metrics across a set of nested spatial scales: countries, lakes, sampling stations, replicate transects, and replicate samples at two depth-zones. Metrics investigated in each transect included taxa richness, maximum depth of colonisation and two indicators of trophic status: Ellenberg’s N and a metric based on phosphorus trophic status. Metrics were found to have a slightly stronger relationship to pressures when they were calculated on abundance data compared to presence/absence data. Eutrophication metrics based on helophytes were found not to be useful in assessing the effects of nutrient pressure. These metrics were also found to vary with the depth of sampling, with shallower taxa representing higher trophic status. This study demonstrates the complex spatial variability in macrophyte communities, the effect of this variability on the metrics, and theimplications to water managers, especially in relation to survey design.

Four metal speciation and fractionation techniques – DGT (diffusive gradients in thin films), 1-kDa ultrafiltration, 0.22-µm membrane filtration and aquatic moss – were simultaneously applied to a small, contaminated freshwater stream in northern Sweden to investigate differences and similarities between the methods regarding trace metal speciation and their dependence on geochemical water properties. The investigated metals comprise Al, Cd, Co, Cu, Fe, Mn, Ni, and Zn. The normal DGT devices with Chelex cation exchanger were used. Shoots from the aquatic moss Fontinalis antipyretica L ex Hedw. were collected in a non-polluted brook and transplanted to the sampling site for exposure. It was evident that 0.22-µm membrane filtration, 1-kDa ultrafiltration and DGT generally measured different metal fractions where <1-kDa ultrafiltered concentrations were lower than DGT labile concentrations which in turn were lower than <0.22-µm concentrations. The differences between DGT and <1-kDa concentrations indicate the occurrence of labile colloids discriminated by ultrafiltration. Strong correlations between DGT and <1 kDa concentrations were found for Al, Cu, Cd, Co and Zn. Despite a rigorous sample cleaning, retention of particulate matter on the moss samples was revealed by a significant correlation between metal concentrations in moss and particulate Fe. Generally, elevated trace metal concentrations were found in moss exposed at the sampling site compared to reference moss from the non-polluted brook. No significant correlations were found between DGT-labile concentrations and moss concentrations.

This paper presents a biogeochemical model developed for a clarification pond receiving ammonium nitrogen rich discharge water from the Boliden concentration plant located in northern Sweden. Present knowledge about nitrogen (N) transformations in lakes is compiled in a dynamic model that calculates concentrations of the six N species (state variables) ammonium-N (Nam), nitrate-N (Nox), dissolved organic N in water (Norg), N in phytoplankton (Npp), in macrophytes (Nmp) and in sediment (Nsed). It also simulates the rate of 16 N transformation processes occurring in the water column and sediment as well as water–sediment and water–atmosphere interactions. The model was programmed in the software Powersim using 2008 data, whilst validation was performed using data from 2006 to 2007. The sensitivity analysis showed that the state variables are most sensitive to changes in the coefficients related to the temperature dependence of the transformation processes. A six-year simulation of Nam showed stable behaviour over time. The calibrated model rendered coefficients of determination (R2) of 0.93, 0.79 and 0.86 for Nam, Nox and Norg, respectively. Performance measures quantitatively expressing the deviation between modelled and measured data resulted in values close to zero, indicating a stable model structure. The simulated denitrification rate was on average five times higher than the ammonia volatilisation rate and about three times higher than the permanent burial of Nsed and, hence, the most important process for the permanent removal of N. The model can be used to simulate possible measures to reduce the nitrogen load and, after some modification and recalibration, it can be applied at other mine sites affected by N rich effluents.