Occurrence of the odours geosmin and 2-methylisoborneol (MIB) in freshwater environments indicates that odour-producing organisms are commonly occurring. In the present study, we assumed actinomycetes to be a major source of the odours. Seasonal concentrations of odours and abundance of Actinobacteria, which includes actinomycetes and other G+ and high GC bacteria, were determined in one oligotrophic and two eutrophic freshwater streams, as well as in aquacultures connected to these streams, in Denmark. Concentrations of geosmin and MIB ranged from 2 to 9 ng l(-1) and were lowest in the winter. Passage of stream water in the aquacultures increased the amount of geosmin and MIB by up to 55% and 110%, respectively. Densities of actinobacteria were determined by fluorescence in situ hybridization with catalyzed reporter deposition (CARD-FISH) technique and were found to make up from 4 to 38 x 10(7) cells l(-1), corresponding to 3-9% of the total bacterial populations. The lowest densities of actinobacteria occurred in the winter. Filamentous bacteria targeted by the FISH probe made up about 2.7-38% (average was 22%) of the actinobacteria and were expected to be actinomycetes. Combined microautoradiography and CARD-FISH demonstrated that 10-38% (incorporation of 3H-thymidine) and 41-65% (incorporation of 3H-leucine) of the actinobacteria were metabolically active. The proportion of active actinobacteria increased up to 2-fold during passage of stream water in the aquacultures, and up to 98% of the cells became active. Sequencing of 16S rRNA genes in 8 bacterial isolates with typical actinomycete morphology from the streams and ponds demonstrated that most of them belonged to the genus Streptomyces. The isolated actinomycetes produced geosmin at rates from 0.1 to 35 aggeosmin bacterium(-1)h(-1). MIB was produced at similar rates in 5 isolates, whereas no MIB was produced by three of the isolates. Addition of the odours to stream water demonstrated that indigenous stream bacteria were capable of reducing the odours, and that enrichment with LB medium stimulated the degradation. Our study shows that bacterial communities in freshwater include geosmin- and MIB-producing actinobacteria. However, the mechanisms controlling production as well as degradation of the odours in natural waters appear complex and require further research.
During the 20th century Idefjord was considered one of the most polluted marine areas in Scandinavia. For decades it received high discharges from paper/pulp industry, which made it anoxic and extremely polluted by heavy metals and organic contaminants. Today the fjord is close to fulfil a complete pollution-recovery cycle, which is recorded in its sediment archives. Here we report results from five sediment cores studied for TC, C/N, heavy metals and benthic foraminifera. All of the cores have laminations deposited during 1940-1980s and indicative of long-lasting anoxia; high TC and heavy metal content, poor foraminiferal faunas and lack of macrofauna. The upper part of the cores deposited since 1980s shows a gradual pollutant decrease and partial foraminiferal recovery. The majority of foraminiferal species in Idefjord are agglutinated opportunistic and stress-tolerant taxa, which to some extent tolerate hypoxia and are early colonisers of previously disturbed environments. The current study demonstrates a value of benthic foraminiferal stratigraphy as a useful tool in understanding processes driving environmental degradation and recovery of coastal ecosystems.
There is a great deal of interest to determine the state and variations of water quality parameters in the lower Athabasca River (LAR) ecosystem, northern Alberta, Canada, due to industrial developments in the region. As a cold region river, the annual cycle of ice cover formation and breakup play a key role in water quality transformation and transportation processes. An integrated deterministic numerical modelling framework is developed and applied for long-term and detailed simulation of the state and variation (spatial and temporal) of major water quality constituents both in open-water and ice covered conditions in the lower Athabasca River (LAR). The framework is based on the a 1D and a 2D hydrodynamic and water quality models externally coupled with the 1D river ice process models to account for the cold season effects. The models are calibrated/validated using available measured data and applied for simulation of dissolved oxygen (DO) and nutrients (i.e., nitrogen and phosphorus). The results show the effect of winter ice cover on reducing the DO concentration, and a fluctuating temporal trend for DO and nutrients during summer periods with substantial differences in concentration between the main channel and flood plains. This numerical frame work can be the basis for future water quality scenario-based studies in the LAR.
A study was undertaken to test the effects of molybdenum (Mo) and phosphorus (P) amendments on biological nitrogen (N) fixation (BNF) by boreal forest moss-associated cyanobacteria. Feather moss (Pleurozium schreberi) samples were collected on five sites, on two dates and at different roadside distances (0-100m) corresponding to an assumed gradient of reactive N deposition. Potential BNF of Mo and P amended moss samples was measured using the acetylene reduction assay. Total N, P and heavy metal concentrations of mosses collected at 0 and 100m from roadsides were also measured. Likewise, the needles from Norway spruce trees (Picea abies) at different roadside distances were collected in late summer and analyzed for total N, P and heavy metals. There was a significant increase in BNF with roadside distance on 7-of-10 individual Site×Date combinations. We found no clear evidence of an N gradient across roadside distances. Elemental analyses of feather moss and Norway spruce needle tissues suggested decreasing deposition of heavy metals (Mo-Co-Cr-Ni-V-Pb-Ag-Cu) as well as P with increasing distance from the roadside. The effects of Mo and P amendments on BNF were infrequent and inconsistent across roadside distances and across sites. One particular site, however, displayed greater concentrations of heavy metals near the roadside, as well as a steeper P fertility gradient with roadside distance, than the other sites. Here, BNF increased with roadside distance only when moss samples were amended with P. Also at this site, BNF across all roadside distances was higher when mosses were amended with both Mo and P, suggesting a co-limitation of these two nutrients in controlling BNF. In summary, our study showed a potential for car emissions to increase heavy metals and P along roadsides and underscored the putative roles of these anthropogenic pollutants on BNF in northern latitudes.
It is proposed that carbon (C) sequestration in response to reactive nitrogen (Nr ) deposition in boreal forests accounts for a large portion of the terrestrial sink for anthropogenic CO2 emissions. While studies have helped clarify the magnitude by which Nr deposition enhances C sequestration by forest vegetation, there remains a paucity of long-term experimental studies evaluating how soil C pools respond. We conducted a long-term experiment, maintained since 1996, consisting of three N addition levels (0, 12.5, and 50 kg N ha(-1) yr(-1) ) in the boreal zone of northern Sweden to understand how atmospheric Nr deposition affects soil C accumulation, soil microbial communities, and soil respiration. We hypothesized that soil C sequestration will increase, and soil microbial biomass and soil respiration will decrease, with disproportionately large changes expected compared to low levels of N addition. Our data showed that the low N addition treatment caused a non-significant increase in the organic horizon C pool of ~15% and a significant increase of ~30% in response to the high N treatment relative to the control. The relationship between C sequestration and N addition in the organic horizon was linear, with a slope of 10 kg C kg(-1) N. We also found a concomitant decrease in total microbial and fungal biomasses and a ~11% reduction in soil respiration in response to the high N treatment. Our data complement previous data from the same study system describing aboveground C sequestration, indicating a total ecosystem sequestration rate of 26 kg C kg(-1) N. These estimates are far lower than suggested by some previous modeling studies, and thus will help improve and validate current modeling efforts aimed at separating the effect of multiple global change factors on the C balance of the boreal region.
Mosses dominate many northern ecosystems and their presence is integral to soil thermal and hydrological regimes which, in turn, dictate important ecological processes. Drivers, such as climate change and increasing herbivore pressure, affect the moss layer thus, assessment of the functional role of mosses in determining soil characteristics is essential. Field manipulations conducted in high arctic Spitsbergen (78 degrees N), creating shallow (3 cm), intermediate (6 cm) and deep (12 cm) moss layers over the soil surface, had an immediate impact on soil temperature in terms of both average temperatures and amplitude of fluctuations. In soil under deep moss, temperature was substantially lower and organic layer thaw occurred 4 weeks later than in other treatment plots; the growing season for vascular plants was thereby reduced by 40%. Soil moisture was also reduced under deep moss, reflecting the influence of local heterogeneity in moss depth, over and above the landscape-scale topographic control of soil moisture. Data from field and laboratory experiments show that moss-mediated effects on the soil environment influenced microbial biomass and activity, resulting in warmer and wetter soil under thinner moss layers containing more plant-available nitrogen. In arctic ecosystems, which are limited by soil temperature, growing season length and nutrient availability, spatial and temporal variation in the depth of the moss layer has significant repercussions for ecosystem function. Evidence from our mesic tundra site shows that any disturbance causing reduction in the depth of the moss layer will alleviate temperature and moisture constraints and therefore profoundly influence a wide range of ecosystem processes, including nutrient cycling and energy transfer.
Mosses collected decades ago and stored in herbaria are often used to assess historical nitrogen deposition. This method is effectively based on the assumption that tissue N concentration remains constant during storage. The present study raises serious doubt about the generality of that assumption. We measured tissue N and C concentrations as well as d15N, d13C, Pb and Mg in herbarium and present day samples of seven bryophyte species from six sites across Denmark. While an increase in nitrogen deposition during the last century is well-documented for the study site, we surprisingly found foliar N concentration to be higher in historical samples than in modern samples. Based on d15N values and Pb concentration, we find nitrogen contamination of herbarium specimens during storage to be the most likely cause, possibly in combination with dilution though growth and/or decomposition during storage. We suggest ways to assess contamination and recommend caution to be taken when using herbarium specimens to assess historical pollution if exposure during storage cannot be ruled out.
The Baltic Sea is one of the most eutrophied water bodies in northern Europe and more than 50% of its total anthropogenic waterborne phosphorus (P) and nitrogen (N) loads derive from agricultural sources. Sweden is the second largest contributor of waterborne N and the third largest contributor of waterborne P to the Baltic Sea. Horse farms now occupy almost 10% of Swedish agricultural land, but are not well investigated with regard to their environmental impact. In this study, potential P, N and carbon (C) leaching losses were measured from two representative horse paddock topsoils (0-20 cm; a clay and a loamy sand) following simulated rainfall events in the laboratory. Results showed that the leachate concentrations and net release of P, N and dissolved organic C (DOC) from paddock topsoils were highest in feeding and excretion areas and considerably higher from the loamy sand than the clay paddock topsoil. Leaching losses of dissolved reactive P (DRP) were significantly (p
Sludge treatment reed bed (STRB) systems combine dewatering, stabilisation and long-term storage of sludge. The main objective of this study was to investigate how substance concentrations change in the sludge residue during treatment and to conduct substance flow analyses covering the flow of substances in an STRB system over a 12-year treatment period, followed by three months' post-treatment in a stockpile area (SPA). Samples of sludge, reject water and sludge residue of different ages were collected at two Danish STRB system facilities and analysed for content of relevant substances. Concentrations of carbon and nitrogen in the sludge residue residing in an STRB system changed as a function of treatment time, mainly due to mineralisation; only a negligible part was lost to reject water. Considering metals and phosphorus, the main share was accumulated in the sludge residue; only minor fractions were lost to mineralisation or reject water. Post-treatment in an SPA resulted in an increase in dry matter content from 24% to 32%. After treatment, the concentrations of heavy metals (lead, cadmium, nickel, zinc, copper and chromium) in the sludge residue met the threshold values stated by the Danish Environmental Protection Agency and the EU.
Anthropogenically enhanced atmospheric sulphur (S) and nitrogen (N) deposition has acidified and eutrophied forest ecosystems worldwide. However, both S and N mechanisms have an impact on microbial communities and the consequences for microbially driven soil functioning differ. We conducted a two-forest stand (Norway spruce and European beech) field experiment involving acidification (sulphuric acid addition) and N (ammonium nitrate) loading and their combination. For 4 years, we monitored separate responses of soil microbial communities to the treatments and investigated the relationship to changes in the activity of extracellular enzymes. We observed that acidification selected for acidotolerant and oligotrophic taxa of Acidobacteria and Actinobacteria decreased bacterial community richness and diversity in both stands in parallel, disregarding their original dissimilarities in soil chemistry and composition of microbial communities. The shifts in bacterial community influenced the stoichiometry and magnitude of enzymatic activity. The bacterial response to experimental N addition was much weaker, likely due to historically enhanced N availability. Fungi were not influenced by any treatment during 4-year manipulation. We suggest that in the onset of acidification when fungi remain irresponsive, bacterial reaction might govern the changes in soil enzymatic activity.