Arctic Catchment Research Articles

Antecedent controls on rainfall runoff response and sediment transport in a high arctic catchment

In the High Arctic, late summer rainfall events have the potential to increase discharge and transport substantial amounts of sediment. Past studies have not considered the role of antecedent soil moisture with respect to rainfall‐runoff response, particularly in the context of changing climate. We investigate these processes through multiple major rainfall events and the associated discharge and suspended sediment response, measured in a small watershed at ape ounty, elville sland, unavut. Fluvial and sedimentological responses to two major rainfall events on 9 ul. and 23 ul., 2012, totaling 35.4 and 10.6 mm, respectively, resulted in negligible responses in discharge and suspended sediment mobilization. The magnitude and intensity of these events were not unusual in this region, but the lack of response was substantial when compared with past events of similar magnitudes. The two‐week antecedent period leading up to the 9 ul. rainfall was characterized by exceptional temperatures and high solar radiation, decreasing soil moisture and increasing infiltration potential, all of which substantially diminished the runoff and resultant suspended sediment transport. These results demonstrate that antecedent catchment conditions may substantially attenuate suspended sediment transport responses to multiple major rainfall events and decrease runoff ratios and characterization of these conditions is necessary to accurately model catchment response.

Seasonal fluxes and age of particulate organic carbon exported from Arctic catchments impacted by localized permafrost slope disturbances

Projected warming is expected to alter the Arctic permafrost regime with potential impacts on hydrological fluxes of particulate organic carbon (POC) and sediment. Previous work has focused on large Arctic basins and revealed the important contribution of old carbon in river POC, but little is known about POC fluxes from smaller coastal watersheds, particularly where widespread postglacial raised marine sediments represent a potential source of old soil carbon that could be mobilized by permafrost disturbance. To evaluate these processes, the characteristics of POC, particulate nitrogen (PN) and suspended sediment transport from paired small coastal Arctic watersheds subject to recent permafrost disturbance were investigated at the Cape Bounty Arctic Watershed Observatory (CBAWO) in the Canadian High Arctic. Approximately 2% of the total suspended sediment load from both watersheds was composed of POC and the majority of the sediment and POC fluxes occurred during the spring snowmelt period. Radiocarbon analysis of POC indicates recent permafrost disturbances deliver substantially older POC to the aquatic system. Localized permafrost slope disturbances have a measurable influence on downstream POC age and dominate (estimated up to 78% of POC) sediment fluxes during summer baseflow. The elevation of disturbances and Holocene emergence data show limited age sensitivity of POC to the location of disturbance and suggest slope failures are likely to deliver carbon with a relatively similar age range to the aquatic system, regardless of landscape location.

Catchment-scale dissolved carbon concentrations and export estimates across six subarctic streams in northern Sweden

Abstract. Climatic change is currently enhancing permafrost thawing and the flow of water through the landscape in subarctic and arctic catchments, with major consequences for the carbon export to aquatic ecosystems. We studied stream water carbon export in several tundra-dominated catchments in northern Sweden. There were clear seasonal differences in both dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations. The highest DOC concentrations occurred during the spring freshet while the highest DIC concentrations were always observed during winter baseflow conditions for the six catchments considered in this study. Long-term trends for the period 1982 to 2010 for one of the streams showed that DIC concentrations has increased by 9% during the 28 yr of measurement while no clear trend was found for DOC. Similar increasing trends were also found for conductivity, Ca and Mg. When trends were discretized into individual months, we found a significant linear increase in DIC concentrations with time for September, November and December. In these subarctic catchments, the annual mass of C exported as DIC was in the same order of magnitude as DOC; the average proportion of DIC to the total dissolved C exported was 61% for the six streams. Furthermore, there was a direct relationship between total runoff and annual dissolved carbon fluxes for these six catchments. These relationships were more prevalent for annual DIC exports than annual DOC exports in this region. Our results also highlight that both DOC and DIC can be important in high-latitude ecosystems. This is particularly relevant in environments where thawing permafrost and changes to subsurface ice due to global warming can influence stream water fluxes of C. The large proportion of stream water DIC flux also has implications on regional C budgets and needs to be considered in order to understand climate-induced feedback mechanisms across the landscape.

Changes in dynamics and runoff from the High Arctic glacial catchment of Waldemarbreen, Svalbard

Since 1997, the runoff from the High Arctic catchment of Waldemarbreen has been recorded continuously at the gauging station located in northwest Spitsbergen, Svalbard. The analysis of the changes in dynamics and runoff from the glacial (polar) catchment of Waldemarbreen was made. One of the aims of this study was to try to determine how changes in the degree of the glaciation of the catchment influence the volume of the river discharge and runoff. This was found to be directly dependent on the percent glacier cover of the catchment and its changes. Changing the area and the volume of the glacier reduces the rate of the discharge, even when the intensity of melting does not change. Glaciological investigations of Waldemarbreen were taken between 1996 and 2009. The average ablation of Waldemarbreen varied from 64 to 137cm w.e. during this time, while the average winter balance of this glacier was 50cm w.e. During the summer season the mean discharge of the Waldemar River at the point which closed the glacier catchment in the years 1997–2009 was 1.0m3s−1 (541mm). The average proportion of ablation within the runoff was 55%, and ranged from 30 to 77% during individual seasons. This study also examines selected elements which play some role in the dynamics of the glacial catchment of Waldemarbreen, for example icings or a moraine-dammed lake. It is the first such analysis for this region of Svalbard.

Accumulation, storage and release of atmospheric mercury in a glaciated Arctic catchment, Baffin Island, Canada

Part of the mercury (Hg) entering Arctic ecosystems is believed to be delivered from the atmosphere in snow but this source is difficult to quantify due to limited spatial coverage of Hg data in snow. Here we evaluate the atmospheric deposition, storage and release of total Hg (THg) and monomethyl mercury (MeHg) on Penny ice cap, Baffin Island. This is the first such study in the Baffin region. THg levels in snow and firn (mean=0.61ngL−1) are comparable to those on High Arctic glaciers but MeHg levels are noticeably higher (mean=0.11ngL−1). We find little evidence of springtime enhancement of Hg deposition in snow attributable to atmospheric mercury depletion events. Estimated accumulation rates of THg and MeHg in firn are ∼0.33 and 0.03μgm−2a−1, higher than on High Arctic glaciers, possibly due to higher precipitation on southern Baffin Island. The estimated net annual release of THg by glacial snow and ice melt is small (THg: 1.86kg; MeHg: 0.18kg). In the study area, geogenic Hg contributions from sediment-loaded glacial meltwater could be as large or larger than those from melting ice. MeHg levels are very low in meltwater-fed streams and lakes (⩽0.01ngL−1), suggesting that MeHg is released early in the snowmelt season and/or quickly removed from meltwater by various processes. Summer melt and percolation on Penny ice cap remobilise Hg in firn after deposition, and this imposes resolution limits of at least 3years on depositional trends inferred from ice cores.

Distribution of polar membrane lipids in permafrost soils and sediments of a small high Arctic catchment

The distribution of bacteriohopanepolyols (BHPs) and intact polar membrane lipids (IPLs) was studied in different soil profiles and in fluvial and marine sediments along the pathway of transport in a small catchment in the high Arctic at Ny-Ålesund, Svalbard (79°N, 12°E). Both groups of cellular membrane lipids have been used as biomarkers for determining major microbial groups and biogeochemical processes in natural environments. Little is known about their distribution and usefulness as environmental markers in the Arctic. In this study, we show that both membrane lipid groups are variably distributed in the drainage area of the Brøggerbreen Glacier, with highest abundance and diversity in the organic mat overlying the mineral soils, as well as in mossy surface soil. The BHP and IPL composition and abundance both indicate a larger community of phototrophic bacteria in the organic mats and fluvial sediments. The greater diversity and abundance of BHPs relative to IPLs in sub-soils, including probable markers for cyanobacteria, suggest a greater resistance to degradation. In contrast, IPL concentration decreased strongly with soil depth, pointing to their rapid degradation. Bacterial IPLs are thus thought to reflect more reliably the biomass of viable phototrophic bacteria. The high concentrations of proposed soil marker BHPs, adenosylhopane and related structures vs. published results and their relative increase with soil depth suggest better preservation and more effective accumulation of the compounds at low temperature.

Glacier ecosystem response to episodic nitrogen enrichment in Svalbard, European High Arctic

We describe the climatology, hydrology and biogeochemistry of an extreme nitrogen deposition event that occurred in the highly glacierised environment of the European High Arctic during June 1999. Meteorological analysis, three-dimensional air mass trajectories and a 3D transport model show that blocking high pressures over Scandinavia and the rapid advection of western European pollution toward Svalbard were sufficient to cause the most concentrated (1.15 ppm NO3–N and 1.20 ppm NH4–N), high magnitude (total 26 mm and up to 2.4 mm h−1 at 30 m above sea level) nitrogen deposition event on record in this sensitive, high Arctic environment (78.91° N, 11.93° E). Since the event occurred when much of the catchment remained frozen or under snow cover, microbial utilisation of nitrogen within snowpacks and perennially unfrozen subglacial sediments, rather than soils, were mostly responsible for reducing N export. The rainfall event occurred long before the annual subglacial outburst flood and so prolonged (ca. 10 day) water storage at the glacier bed further enhanced the microbial assimilation. When the subglacial outburst eventually occurred, high runoff and concentrations of NO3 − (but not NH4 +) returned in the downstream rivers. Assimilation accounted for between 53 and 72% of the total inorganic nitrogen deposited during the event, but the annual NO3 − and NH4 + runoff yields were still enhanced by up to 5 and 40 times respectively. Episodic atmospheric inputs of reactive nitrogen can therefore directly influence the biogeochemical functioning of High Arctic catchments, even when microbial activity takes place beneath a glacier at a time when terrestrial soil ecosystems remain frozen and unresponsive.

Suspended and solute transport in a small glaciated catchment Bertram River, Central Spitsbergen, in 2005–2006

The paper presents data on hydrochemistry and suspended sediment dynamics from a small glaciated catchment in Svalbard. Such catchments, formerly omitted and neglected in investigations of polar and high-mountain geo-ecosystems, have become an important subject of environmental research in recent years. High sensitivity to global warming, relative ease of taking measurements, the variety of locations, and further possibilities of modelling, make the catchments important sites for studying glaciological, hydrological and geomorphological processes. Hydrochemical data from seasonal observations and complementary 24-hour measurements, together with detailed geomorphological mapping of river channels and their surroundings, served as a basis for scientific description of the conditioning of seasonal and diurnal variations in suspended and solute matter transport in a small High Arctic catchment. Bertram River is distinguished by a system of waterfalls which divides the 4.9 km2 catchment in two parts: an upper glaciated part located on mountainous plateau, and a lower part where an abraided plain has been formed within the bottom of the Ebba River valley. On the basis of observations it is concluded that a particular role in the conditioning of glaciofluvial transport was played by an extreme weather event in the form of föhn-type wind, observed in the decline of ablation season and also by waterfalls which diversified the fluvial activity.

Hydroclimatic and channel snowpack controls over suspended sediment and grain size transport in a High Arctic catchment

AbstractTemporal variability in suspended sediment delivery processes was studied during three seasons in a 7·9 km2 catchment at Cape Bounty, Melville Island, Nunavut in the Canadian High Arctic. Discharge was controlled primarily by the magnitude of snowmelt, with limited inputs from ground ice melt and precipitation. Years with greater snowpack non‐linearly increased sediment yield and resulted in seasonal counter‐clockwise hysteresis, while a year with low snowpack resulted in reduced sediment yield and clockwise hysteresis, and indicates that sediment was increasingly available after the onset of streamflow. In addition to the event‐scale hysteresis observed during the nival discharge peak, diurnal clockwise hysteresis was observed during all three seasons and suggests daily exhaustion of sediment supplies. These results indicate that the channel snowpack plays a primary role over sediment accessibility during the nival discharge peak. Similarly, grain size analysis of suspended material in the river showed that the coarsest mean grain size was transported during the early phase of peak nival discharge and indicates that isolated sources of coarse material were being accessed by high velocity flow. Snowpack is present through the peak nival period and conditions sediment availability by isolating channel sediments from high‐energy flow. These results indicate sediment delivery characteristics in small High Arctic catchments reflect complex interactions with channel snowpack and disproportionate responses to flow conditions that differ from glacial and temperate settings. Copyright © 2008 John Wiley & Sons, Ltd.

The impact of a shrinking cryosphere on the form of arctic alluvial channels

AbstractA shrinking cryosphere has important implications for the geomorphology of alluvial channels in arctic catchments because ice and permafrost alter the driving and resisting forces responsible for shaping local channel cross sections. For example, bedfast ice in shallow channels can suppress bedload transport during snowmelt events causing a reduction in the frequency of geomorphically effective flows, while cap ice in deeper channels can alter stream hydraulics. The impact of these local controls on catchment‐scale geomorphic patterns, however, is less certain. A case study of one arctic river in northern Alaska, USA, reveals hydraulic geometry anomalies that can be reasonably explained by the influence of ice and permafrost on local channel form. However, there is a critical lack of data from rivers wholly contained in the continuous permafrost zone preventing comprehensive understanding of how arctic rivers might respond in a shrinking cryosphere. Copyright © 2008 John Wiley & Sons, Ltd.

Bacterial responses in activity and community composition to photo-oxidation of dissolved organic matter from soil and surface waters

To better understand how photo-oxidation of dissolved organic matter (DOM) affects microbial activity and DOM processing along hydrological flow paths in an arctic catchment, we conducted experiments measuring responses in bacterial production (BP) to sunlight-exposed DOM from up-slope sources, including soil, stream, and lake water. Overall, sunlight exposure significantly reduced specific ultra-violet absorbance and dissolved organic carbon concentrations and increased phenolic concentrations; these changes were more pronounced in soil than in surface waters. Sunlight-exposed DOM reduced BP in common inoculum bioassay experiments at short time scales (hours), but the magnitude of the effect differed among DOM sources and was related to phenolic content; effects were more negative on DOM sources with high phenolic contents. In contrast, longer contact times (weeks) between bacteria and photo-oxidized soil, stream, and lake water DOM enhanced, did not change, and reduced BP, respectively. In these longer-term experiments, sunlight-exposed DOM had a greater positive effect on lake than stream BP, and caused shifts in bacterial community composition (based on denaturing gradient gel electrophoresis of bacterial-specific 16S rDNA). Changes in bacterial community composition were greater in response to sunlight-exposed DOM from soils than from the stream. Our findings suggest that overall impacts of DOM photo-oxidation in aquatic environments depends on DOM source, and that contrasting effects of photo-oxidized DOM at varying time scales may be partly due to shifts in the bacterial community composition to groups better able to consume photoproducts or tolerate harmful radicals.

Identifying Differences in Carbon Exchange among Arctic Ecosystem Types

Our objective was to determine how varied is the response of C cycling to temperature and irradiance in tundra vegetation. We used a large chamber to measure C exchange at 23 locations within a small arctic catchment in Alaska during summer 2003 and 2004. At each location, we determined light response curves of C exchange using shade cloths, twice during a growing season. We used data to fit a simple photosynthesis-irradiance, respiration-temperature model, with four parameters. We used a maximum likelihood technique to determine the acceptable parameter space for each light curve, given measurement uncertainty. We then explored which sites and time periods had parameter sets in common—an indication of functional similarity. We found that seven distinct parameter sets were required to explain observed C flux responses to temperature and light variation at all sites and time periods. The variation in estimated maximum photosynthetic rate (Pmax) was strongly correlated with measurements of site leaf area index (LAI). The behavior of tussock tundra sites, the dominant vegetation of arctic tundra, could largely be described with a single parameter set, with a Pmax of 9.7 μmol m−2 s−1. Tussock tundra sites had, correspondingly, similar LAI (mean = 0.66). Non-tussock sites (for example, sedge and shrub tundras) had larger spatial and temporal variations in both C dynamic parameters (Pmax varying from 9.7–25.7 μmol m−2 s−1) and LAI (0.6–2.0). There were no clear relationships between dominant non-tussock vegetation types and a particular parameter set. Our results suggest that C dynamics of the acidic tussock tundra slopes and hilltops in northern Alaska are relatively simply described during the peak growing season. However, the foot-slopes and water tracks have more variable patterns of LAI and C exchange, not simply related to the dominant vegetation type.

Spatial–temporal variability in solar radiation during spring snowmelt

Much of the spring landscape of arctic regions is dominated by a patchy snow cover with implications for both spring melt runoff and atmospheric fluxes. In addition to a variable end-of-winter snowpack, spatial differences in snowmelt energy terms play an important role in the development of this patchy snow cover. This paper focuses specifically on the influence of solar radiation on snowmelt by using a model to simulate the small-scale variability of solar radiation incident on the ground surface due to topographic influences over a small arctic catchment. The model only requires a digital elevation model (DEM) and measured global radiation. Despite the relatively low relief (average slope 3°) of the study area, the results showed solar radiation differences of up to 10% of the area-wide mean over the melt period. This would result in differences in snowmelt amounts of up to 50 mm, a value similar in magnitude to the overall mean end-of-winter snow water equivalent in the study region. An analysis of the effects of changing model scale showed that the simulated variability decreased substantially for larger grid sizes. The results show that the small-scale variability of solar radiation contributes greatly to the mosaic patterns in melting snow covers of arctic regions, affects the timing and amount of meltwater release and influences the surface energy balance of these areas considerably.

Modelling the spatial–temporal variability of spring snowmelt in an arctic catchment

Arctic spring landscapes are usually characterized by a mosaic of coexisting snow-covered and bare ground patches. This phenomenon has major implications for hydrological processes, including meltwater production and runoff. Furthermore, as indicated by aircraft observations, it affects land-surface–atmosphere exchanges, leading to a high degree of variability in surface energy terms during melt. The heterogeneity and related differences when certain parts of the landscape become snow free also affects the length of the growing season and the carbon cycle. Small-scale variability in arctic snowmelt is addressed here by combining a spatially distributed end-of-winter snow cover with simulations of variable snowmelt energy balance factors for the small arctic catchment of Trail Valley Creek (63 km2). Throughout the winter, snow in arctic tundra basins is redistributed by frequent blowing snow events. Areas of above- or below-average end-of-winter snow water equivalents were determined from land-cover classifications, topography, land-cover-based snow surveys, and distributed surface wind-field simulations. Topographic influences on major snowmelt energy balance factors (solar radiation and turbulent fluxes of sensible and latent heat) were modelled on a small-scale (40 m) basis. A spatially variable complete snowmelt energy balance was subsequently computed and applied to the distributed snow cover, allowing the simulation of the progress of melt throughout the basin. The emerging patterns compared very well visually to snow cover observations from satellite images and aerial photographs. Results show the relative importance of variable end-of-winter snow cover, spatially distributed melt energy fluxes, and local advection processes for the development of a patchy snow cover. This illustrates that the consideration of these processes is crucial for an accurate determination of snow-covered areas, as well as the location, timing, and amount of meltwater release from arctic catchments, and should, therefore, be included in hydrological models. Furthermore, the study shows the need for a subgrid parameterization of these factors in the land surface schemes of larger scale climate models. Copyright © 2005 John Wiley & Sons, Ltd.

Modelling spatially distributed snowmelt and meltwater runoff in a small Arctic catchment with a hydrology land‐surface scheme (WATCLASS)

The fully distributed hydrology land‐surface scheme WATCLASS is used to simulate spring snowmelt runoff in a small Arctic basin, Trail Valley Creek, dominated by open tundra and shrub tundra vegetation. The model calculates snowmelt rates from a full surface energy balance, and a three‐layer soil model is used to simulate the infiltration into and the exchange of heat and moisture within the ground. The generated meltwater is delivered to the stream channel network by overland flow, interflow, and baseflow and subsequently routed out of the catchment. Subgrid spatial variability is handled by the model through the use of grouped response units (GRUs). The GRUs in WATCLASS are chosen according to vegetation land cover. Five spring snowmelt periods with a variety of initial end‐of‐winter snow cover and melt conditions were simulated and compared with observed runoff data. In a second step, the model's ability to simulate spatially variable snow covered area (SCA) within the basin was tested by comparing model predictions to remotely sensed SCA. WATCLASS was able to predict runoff volumes (on average within 15% over five years of modelling) as well as timing of snowmelt and meltwater runoff for open tundra fairly accurately. However, the model underestimated melt in the energetically more complex shrub tundra areas of the basin. Furthermore, the observed high spatial variability of the SCA at a 1‐km resolution was not captured well by the model. Several recommendations are made to improve model performance in Arctic basins, including a more realistic implementation of the gradual deepening of the thawed layer during the spring, and the use of topographic information in the definition of land cover classes for the GRU approach.

Climatic Controls on Streamflow and Suspended Sediment Transport in Three Large Middle Arctic Catchments, Boothia Peninsula, Nunavut, Canada

Streamflow, suspended sediment transport, and meteorological variables were measured during two field seasons in order to determine the climatic controls on daily discharge and suspended sediment load for three large middle arctic catchments. Substantive suspended sediment transfer only occurred during the short-lived nival peak, and the duration of the peak appears to be broadly scaled with interannual catchment snow water equivalence (SWE). Thermal energy was critical in generating streamflow and suspended sediment transfer, but only until watershed snowpack had been exhausted. Thus, total annual suspended sediment load in this environment is ultimately a function of total discharge through SWE rather than melt energy. Specific sediment yields were some of the lowest recorded in the arctic, ranging between 0.2 and 1.9 t km−2·a−1. This study demonstrates the sensitivity middle arctic watersheds to both winter snowpack and spring thermal conditions and provides a basis for understanding the hydrological impact of future climate changes.

Lake-catchment interactions with climate in the low Arctic of southern West Greenland

Arctic hydrology plays a central role in the earth’s heat balance and ocean circulation (Vörösmarty et al. 2001). Future changes associated with human influence on the climate system are also predicted to cause major changes in the energy and hydrologic mass balance of Arctic catchments. Climate change will likely affect permafrost and snowmelt, which dominate Arctic hydrology and control the chemistry of surface runoff (and hence streams and lakes) as water percolates through the active layer. However, the controls and dynamic impact of snowmelt are poorly understood, because this critical timeframe is often missed by sampling programmes. In the Søndre Strømfjord area only the broadest aspects of hydrologic variability have so far been documented (Hasholt & Søgaard 1976).

Snow drift losses from an Arctic catchment on Spitsbergen: an additional process in the water balance

Blowing snow is a process, which can be observed during the entire winter season in Arctic catchments. On Spitsbergen at 78° North, the ground is bare of tall vegetation and the snow is easily moved by the wind. During frequent storms, large masses of snow are relocated from erosion to deposition areas. In this study, the mass of snow, transported out of an Arctic valley to the open sea is estimated via direct measurements and model calculations. The study area is a valley on Spitsbergen in the high Arctic. The valley is approximately 4 km wide and 10 km long and ends in a fjord arm. The wind direction in the valley is very uniform. During the winter season, the wind is blowing out of the valley 80% of the time. There is one permanent automatic weather station located in the valley. In addition, three automatic weather stations were installed in the valley during a study period of 2 months in February and March 2000. These stations measure, in addition to wind speed and direction, the snow drift flux with acoustic snow drift sensors. The results of the study period are related to those of the permanent station to quantify the accumulated snow mass passing from the valley to the open sea for the entire season. The results show that the transport snow mass equals 0.2% of the annual precipitation in the catchment. Thus, the losses due to snow drift to the open sea are of little importance to the valleys water balance.

Acoustic snowdrift measurements: experiences from the FlowCapt instrument

Three acoustic FlowCapt™ (IAV Engineering) drifting snow instruments were deployed during the 1999 and 2000 field season on Spitsbergen, Norway. Three different experiments were carried out to test the instruments for their use in snowdrift research. The data from the three instruments were compared during a study of drifting snow within an Arctic catchment and around a building. The principle of the instruments is based on the acoustic signal, generated by the mechanical impact of drifting snow particles on a vertical tube. Microphones inside the tube transmit the signal to a frequency analyser. By Fourier transformation, the signal can be divided into the high frequencies of the impacting snow particles and the low frequencies, resulting from the loosening wake eddies behind the tube. In this way, both snow drift flux and wind speed can be measured simultaneously. Results from the three experiments show that the instruments are useful tools to study drifting snow in remote areas. A reliable indication of the occurrence and strength of drifting snow events can be determined even if the absolute accuracy is difficult to quantify.

Sulphur isotope composition of stream water, moss and humus from eight arctic catchments in the Kola Peninsula region (NW Russia, N Finland, NE Norway)

In summer 1994, stream water, moss and humus samples were collected for sulphur isotopic analysis from eight catchments located in the western Kola Peninsula region, where several industrial centres emit high loads of SO2 and other elements to the atmosphere. Three potential sources of sulphur and their isotopic signatures were identified: (1) marine (δ34S +20 to +21‰ CDT), (2) anthropogenic emissions (<+10‰), and (3) geogenic (variable δ34S, mostly <+10‰). Averaged per catchment, the sulphur isotopic composition varies between +6.0 and +16.3‰ for stream water sulphate, +6.0 and +8.4‰ for moss sulphur, and +5.2 and +12.2‰ for humus sulphur. The δ34S composition of stream water from the more remote catchments is quite variable, reflecting several natural (geogenic) sources, but it becomes restricted to the range +8 to +10‰ near the pollution sources. A plot of δ34S vs. 1:SO4 in stream water suggests that sulphate originating from the smelters has a δ34S value ≈+9.5‰, and is a dominant source. Sulphur isotope values for moss and humus are consistent with the deduced composition for the emitted sulphur, though for humus a component of geogenic sulphur incorporated via vegetation uptake may play a role. Further isotopic characterisation of atmospheric emissions, together with environmental samples, is needed to better understand sulphur sources and sinks in the area.