Arctic Watersheds Research Articles

An Incidence of Multi-Year Sediment Storage on Channel Snowpack in the Canadian High Arctic

During June 2005, we identified the presence of sediment buried within multi-year channel snowpack of a small river located near Cape Bounty, Melville Island, Nunavut (74°55' N, 109°35' W). Photographic evidence indicates that the sediment was deposited during the 2003 season by the initial meltwater flowing on the snowpack, which was dammed by snow upstream of a channel constriction. The resulting pond covered a minimum area of 180 m2 and contained an estimated minimum 27 Mg of sediment. Suspended sediment measurements during the 2003 season indicate that deposition on the snowpack at this location represented 49%–65% of the sediment transport prior to the ponding and emplacement of the sediment on the snow, and approximately 20% of the measured sediment flux for the entire season. Multi-year snow accumulations immediately downstream exhibited similar sediment deposition on snow, but no evidence of multi-year sediment storage was present. By contrast, a similar stream in an adjacent watershed channelized rapidly, with minimal sediment deposition on the snow, and delivered a large pulse of sediment to the downstream lake. These results provide quantitative evidence for the magnitude of sediment storage on snowpack and point to the unique role that snow plays in the fluvial geomorphology of High Arctic watersheds.

Synoptically forced hydroclimatology of major Arctic watersheds in general circulation models; Part 2: Eurasian watersheds

AbstractA synoptic climatology of daily sea level pressure patterns over Eurasia has been created and used to assess simulations of regional circulation and hydroclimatology from fourteen general circulation models (GCMs). The quality of simulated circulation varies considerably among both individual models and seasons, with summer and winter showing the best agreement with reanalysis data. Close examination of five select models reveals a tendency for GCMs to either over‐ or under‐emphasize the strength and persistence of the winter storm track over Eurasia, with an overemphasized track resulting in better agreement with reanalyses on annual time‐scales. Although pronounced, these biases have relatively little impact on the hydroclimatology of the Ob, Yenisey, and Lena watersheds. Instead, large‐scale precipitation biases appear to be primarily the result of systematic errors in simulated precipitation processes, perhaps related to relevant parameterization schemes. Finally, an effort was made to identify and characterize 20th century precipitation trends related to greenhouse gas induced climate change, by decomposing precipitation time series on the basis of variability in circulation and the mean intensity of precipitation events. Results suggest the influence of anthropogenic climate change over the past forty years is masked by natural variability. Copyright © 2008 Royal Meteorological Society

Synoptically forced hydroclimatology of major Arctic watersheds in general circulation models; Part 1: the Mackenzie River Basin

AbstractThe ability of 14 general circulation models (GCMs) to realistically simulate weather patterns and precipitation regimes affecting the Mackenzie River Basin has been assessed. Applying the method of self‐organizing maps to daily data from the model ensemble and the 40‐year reanalysis project of the ECWMF (ERA‐40), a regional synoptic climatology of sea level pressure was developed and used to analyse the model output. GCM performance, as compared with ERA‐40, varies significantly between models and seasons, but is generally best during the summer and winter. In‐depth examination of a five‐model subset reveals biases in the placement of the Pacific storm track, which may be related to misrepresentations of the Beaufort High. Biases in Mackenzie Basin precipitation are only weakly connected to these circulation errors, and are, instead, primarily the result of inaccurate representations of basin‐scale precipitation regimes. In particular, models allow excessive orographic precipitation along the west coast of North America to intrude into the Mackenzie Basin. These results suggest that projections of the Mackenzie's response to climate change could benefit from climate downscaling studies. Copyright © 2008 Royal Meteorological Society

Seasonal dynamics of dissolved nitrogen exports from two High Arctic watersheds, Melville Island, Canada

This study examines the magnitude and seasonal patterns of dissolved N export during the 2006 melt season from two small watersheds on Melville Island, in the Canadian High Arctic. The dominant N species was dissolved organic nitrogen (DON), comprising >80% of the seasonal nitrogen flux from both rivers. The total DON and dissolved inorganic nitrogen (DIN, NH4++NO3−) yields from the catchments were similar (183 and 204 kg DON, and 46–42 kg DIN): however, on a per unit area basis the West catchment had greater yields of both DON and DIN. There were also differences in the temporal patterns and concentrations of the N species between the catchments, which may be a function of inter-catchment differences in vegetation cover. Low end-of-season DIN concentrations in the West river suggest there is strong biogeochemical retention of inorganic N in this catchment during the growing season relative to the East catchment, where stream NO3− concentrations increase through July. A decrease in DOC:DON ratios in the East river at the end of season also indicates a change in the composition of dissolved organic matter in this river that is not evident in the West river. The results illustrate that there can be large differences in the processes controlling nitrogen between two adjacent and similar catchments.

A multimodel simulation of pan‐Arctic hydrology

We compare the performance of five land surface models (Chameleon Surface Model (CHASM), Noah, Community Land Model (CLM), Variable Infiltration Capacity Model (VIC), European Centre for Medium Range Weather Forecasts (ECMWF)), in the simulation of hydrological processes across the terrestrial Arctic drainage system for the period 1980–2001. The models represent a wide range of model physics, particularly with respect to high‐latitude processes, and are forced with surface meteorology derived from the ERA‐40 reanalysis. Models offer great potential for enlightenment regarding large‐scale hydrology in this poorly observed region; thus our objective is to assess the ability of the models to capture various aspects of pan‐Arctic hydrology as well as identify those features that contain the largest uncertainty. Results reveal up to a 30% difference in annual partitioning of precipitation between evaporation and runoff with major Arctic watersheds such as the Lena. Capturing the correct base flow of the large rivers is a consistent problem. The model hydrographs are often out of phase, peaking too early in comparison to observations. However, allowing for a large uptake in soil moisture as well as moisture movement during frozen periods alleviates this discrepancy. A negative correlation exists between models and observations for annual runoff time series over the Yenesi basin, apparently mostly because of inconsistencies in the input data. Compared to station data, all models produce similar errors in snow water equivalent; yet they differ widely in their snow regimes in terms of snowfall quantity, estimated snow depths, and most importantly, sublimation rates. Additionally, model albedo is consistently higher than observations in the presence of snow. No single model is the best or worst performing when compared to a range of observations.

Hydroclimate controls over seasonal sediment yield in two adjacent High Arctic watersheds

AbstractInterannual variations in seasonal sediment transfer in two High Arctic non‐glacial watersheds were evaluated through three summers of field observations (2003–2005). Total seasonal discharge, controlled by initial watershed snow water equivalence (SWE) was the most important factor in total seasonal suspended sediment transfer. Secondary factors included melt energy, snow distribution and sediment supply. The largest pre‐melt SWE of the three years studied (2004) generated the largest seasonal runoff and disproportionately greater suspended sediment yield than the other years. In contrast, 2003 and 2005 had similar SWE and total runoff, but reduced runoff intensity resulted in lower suspended sediment concentrations and lower total suspended sediment yield in 2005. Lower air temperatures at the beginning of the snowmelt period in 2003 prolonged the melt period and increased meltwater storage within the snowpack. Subsequently, peak discharge and instantaneous suspended sediment concentrations were more intense than in the otherwise warmer 2005 season. The results for this study will aid in model development for sediment yield estimation from cold regions and will contribute to the interpretation of paleoenvironmental records obtained from sedimentary deposits in lakes. Copyright © 2007 John Wiley & Sons, Ltd.

Fluvial sediment flux to the Arctic Ocean

The paper presents an overview of recent publications on the fluvial suspended sediment flux to the Arctic Ocean. The total suspended matter exported from the Russian territory is 102 × 10 6 t/year and from the Canadian Arctic is 125 × 10 6 t/year. The total suspended matter (TSM) flux to the Arctic (227 × 10 6 t/year) is very low, only about 1% of the global flux. Mean concentrations of suspended matter and specific sediment discharge are approximately one order of magnitude lower than the global concentration. An analysis of the trends in the sediment loads based on records of up to 62 years in length shows decreases (Yenisey), increases (Kolyma) and stability (Ob). Among the reasons for the very low concentrations and fluxes of suspended sediment in the Arctic rivers are thin weathering crusts on the Arctic watersheds, low precipitation, extensive permafrost, low temperatures for most of the year, large areas of swamps and lakes and a low level of human activity. A stochastic sediment transport model by Morehead et al. [Morehead, M.D., Syvitski, J.P., Hutton, E.W., Peckham, S.D., 2003. Modeling the temporal variability in the flux of sediment from ungauged river basins. Glob. Planet. Change 39, 95–110] is applied to the Arctic rivers to estimate the sediment load increase should the surface temperature of the drainage basin increase. For every 2 °C of warming a 30% increase in the sediment flux could result and for each 20% increase in water discharge, a 10% increase in sediment load could follow. Based on this model, an increase of the sediment flux of six largest arctic rivers (Yenisey, Lena, Ob, Pechora, Kolyma and Severnaya Dvina) is predicted to range from 30% to 122% by 2100.

Ecosystem and human health assessment to define environmental management strategies: The case of long-term human impacts on an Arctic lake

There are rich deposits of mineral and fossil natural resources in the Arctic, which make this region very attractive for extracting industries. Their operations have immediate and vast consequences for ecological systems, which are particularly vulnerable in this region. We are developing a management strategy for Arctic watersheds impacted by industrial production. The case study is Lake Imandra watershed (Murmansk oblast, Russia) that has exceptionally high levels of economic development and large numbers of people living there. We track the impacts of toxic pollution on ecosystem health and then — human health. Three periods are identified: (a) natural, pre-industrial state; (b) disturbed, under rapid economic development; and (c) partial recovery, during recent economic meltdown. The ecosystem is shown to transform into a qualitatively new state, which is still different from the original natural state, even after toxic loadings have substantially decreased. Fish disease where analyzed to produce and integral evaluation of ecosystem health. Accumulation of heavy metals in fish is correlated with etiology of many diseases. Dose–effect relationships are between integral water quality indices and ecosystem health indicators clearly demonstrates that existing water quality standards adopted in Russia are inadequate for Arctic regions. Health was also poor for people drinking water from the Lake. Transport of heavy metals from drinking water, into human organs, and their effect on liver and kidney diseases shows the close connection between ecosystem and human health. A management system is outlined that is based on feedback from indices of ecosystem and human health and control over economic production and/or the amount of toxic loading produced. We argue that prospects for implementation of such a system are quite bleak at this time, and that more likely we will see a continued depopulation of these Northern regions.

Northern High-Latitude Precipitation as Depicted by Atmospheric Reanalyses and Satellite Retrievals

Abstract Monthly precipitation based on forecasts from the new 40-yr ECMWF Re-Analysis (ERA-40) is evaluated for the north polar region (the region north of 45°N), the terrestrial Arctic drainage, and its four major watersheds: the Ob, Yenisey, Lena, and Mackenzie basins. Corresponding evaluations are performed for precipitation from the NCEP–NCAR reanalysis, the earlier 15-yr ERA (ERA-15), and satellite-derived estimates from the Global Precipitation Climatology Project (GPCP). Evaluations rely on an improved gridded dataset of precipitation derived from monthly gauge data during the period 1979–93. The available number of gauges has declined since 1993, making it difficult to perform evaluations for later years. ERA-40 depicts monthly precipitation much better than NCEP–NCAR. This is with respect to both lower mean biases and higher squared correlations between modeled and observed grid-cell time series. Squared correlations between monthly time series of ERA-40 and observed precipitation, averaged over the four major Arctic watersheds, typically range from 0.60 to 0.90. Performance over the central Arctic Ocean is poor in winter and spring, but improves in summer and autumn when precipitation amounts are higher. While the overall performance of ERA-40 is better than NCEP–NCAR, it offers no obvious improvement over ERA-15. In some respects, ERA-15 performs slightly better in summer. This lack of improvement may relate to difficulties in assimilating satellite radiances. All of the reanalyses provide better depictions of monthly precipitation than do the GPCP satellite retrievals. This applies to both land areas and the Arctic Ocean. There is no clear improvement in the GPCP estimates after 1987 when the Television Infrared Observational Satellite (TIROS) Operational Vertical Sounder (TOVS) data began to be used. The GPCP estimates are best in summer.

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.

Compatibility analysis of precipitation and runoff trends over the large Siberian watersheds

The consistency of long‐term yearly precipitation and runoff trends over the largest Arctic watersheds (Ob, Yenisei and Lena Rivers) is examined. Three gridded precipitation datasets (Climatic Research Unit, University of Delaware, NCEP) are used for comparative analyses with runoff data collected at basin outlets. The results generally demonstrate inconsistency in long‐term changes of basin precipitation and runoff. The Yenisei River runoff increases significantly, while precipitation data show mostly negative trends. The Ob River does not show any significant trend either in precipitation or runoff. Positive trend in the Lena River runoff is accompanied by a weak precipitation increase; however, the precipitation increase is not strong enough to support the observed runoff change. The inconsistency identified in basin precipitation and runoff trends suggests uncertainty in both the quality of basin precipitation and runoff datasets, as well as the perceived hydrologic factors impacting runoff change.

Increasing river discharge in the Eurasian Arctic: Consideration of dams, permafrost thaw, and fires as potential agents of change

Discharge from Eurasian rivers to the Arctic Ocean has increased significantly in recent decades, but the reason for this trend remains unclear. Increased net atmospheric moisture transport from lower to higher latitudes in a warming climate has been identified as one potential mechanism. However, uncertainty associated with estimates of precipitation in the Arctic makes it difficult to confirm whether or not this mechanism is responsible for the change in discharge. Three alternative mechanisms are dam construction and operation, permafrost thaw, and increasing forest fires. Here we evaluate the potential influence of these three mechanisms on changes in discharge from the six largest Eurasian Arctic rivers (Yenisey, Ob', Lena, Kolyma, Pechora, and Severnaya Dvina) between 1936 and 1999. Comprehensive discharge records made it possible to evaluate the influence of dams directly. Data on permafrost thaw and fires in the watersheds of the Eurasian Arctic rivers are more limited. We therefore use a combination of data and modeling scenarios to explore the potential of these two mechanisms as drivers of increasing discharge. Dams have dramatically altered the seasonality of discharge but are not responsible for increases in annual values. Both thawing of permafrost and increased fires may have contributed to changes in discharge, but neither can be considered a major driver. Cumulative thaw depths required to produce the observed increases in discharge are unreasonable: Even if all of the water from thawing permafrost were converted to discharge, a minimum of 4 m thawed evenly across the combined permafrost area of the six major Eurasian Arctic watersheds would have been required. Similarly, sensitivity analysis shows that the increases in fires that would have been necessary to drive the changes in discharge are unrealistic. Of the potential drivers considered here, increasing northward transport of moisture as a result of global warming remains the most viable explanation for the observed increases in Eurasian Arctic river discharge.

Characterization of high arctic stream diatom assemblages from Cornwallis Island, Nunavut, Canada

Distinct diatom assemblages often characterize stream habitats, providing the potential to reconstruct past precipitation, snowmelt, and streamflow levels in high arctic watersheds by analyzing fossil assemblages preserved in downstream lake sediments. Diatom assemblages were studied from seven streams and two rivers surrounding Lake Sophia, Cornwallis Island, Nunavut, Canada (75°06' N, 93°36' W). A total of 64 diatom taxa were identified from epilithic and epiphytic assemblages in these lotic habitats. Of these, certain diatom taxa exhibited clear microhabitat preferences. Hannaea arcus (Ehrenberg) Patrick, Achnanthes minutissima (Kützing) Hustedt, Achnanthes petersenii Hustedt, and Meridion circulare (Greville) Agardh were the most common taxa on epilithic substrates, and as a group made up 61–95% of the diatom epilithon. Achnanthes taxa (mainly A. petersenii and A. minutissima) were the dominant taxa in moss habitats, representing between 45 and 73% of the diatom epiphyton. The relative abundance of H. arcus in epilithic habitats was negatively correlated with water temperature (r2= 0.71, n = 8). Hannaea arcus was found in greater abundances in cool, fast-flowing streams. This apparent correlation may more closely reflect current speed, which is inversely correlated to temperature in these streams. When these streams discharge into lake basins, the characteristic stream diatoms H. arcus and M. circulare are deposited in lakes. These diatom taxa have the potential to infer past streamflows using paleolimnological techniques.Key words: diatoms, arctic, stream, rheophilous, Lake Sophia, Hannaea arcus.

Degradation as a Loss Mechanism in the Fate of α-Hexachlorocyclohexane in Arctic Watersheds

Water extracts of samples collected from Amituk Lake in July--August, 1994 and samples collected at Char and Meretta Lakes in July 1997 were analyzed for enantiomers and concentrations of {alpha}-HCH to estimate the extent of biodegradation in watersheds in the Canadian High Arctic. (+)/({minus})-{alpha}-HCH enantiomer ratios (ERs) in three streams entering Amituk Lake ranged from racemic values of 1.01 in snow to 0.36 in meltwater. Lower ERs were promoted by warmer temperatures and increased contact with stream substrates during low streamflows, especially biologically productive substrates. Most {alpha}-HCH degradation occurred during peak runoff when ERs were 0.95--0.80, rather than later in summer when ERs reached their minimum. Approximately 7% of {alpha}-HCH in the Amituk Lake basin was enantioselectively degraded prior to entering the lake. ERs within Amituk Lake are controlled by meltwater inputs rather than within lake degradation and clearly illustrate the riverine-like nature of high arctic lakes. Differences in lake {alpha}-HCH inventory from end of summer 1993 to spring 1994 indicate that from 33 to 61% of {alpha}-HCH within the lake may have been lost via nonenantioselective microbial degradation at a rate ranging from 0.48 to 1.13 y{sup {minus}1}.

Application of Oxygen-18 Tracer Techniques to Arctic Hydrological Processes

The [delta][sup 18]O value of streamflow at Imnavait Creek, Alaska, shifted dramatically from [minus]30.3[per thousand] on 14 May, the first day of streamflow in 1990, to [minus]22.5[per thousand] on 22 May, at the end of the snowmelt. Nevertheless, independent hydrological measurements of snow redistribution by wind, snow ablation, snow and soil mixture content, and snowmelt runoff indicate there cannot be significant mixing of meltwater with underlying ice-rich soils. An alternative explanation is that isotopic fractionation during the phase change from solid to liquid dominates the isotopic variation in streamflow during snowmelt and prevents a straightforward application of [sup 18]O as a conservative hydrological tracer. By contrast, under dry antecedent conditions in late summer, [sup 18]O appeared to be a suitable tracer following rain contributions to streamflow. Streamflow increased as a result of rainfall, but stream isotopic composition did not change until at least two hours after streamflow increased, implicating a wave, or piston-like mechanism for forcing [open quotes]old[close quotes] water into the stream channel. Analyses of the stable hydrogen and oxygen isotope composition of various hydrological components within the watershed indicate the importance of evaporation as a dominant factor in the hydrological cycle; soil moisture, alteration as a result ofmore » evaporation. The analyses indicate that caution would be advised for any application of stable isotopes to hydrological studies in arctic watersheds. Proportions of snowmelt mixing with underlying soil water may be subject to overestimation because isotopic fractionation as snow melts can be similar in direction and magnitude to the isotopic mixing of snowmelt an soil waters. 40 refs., 7 figs., 1 tab.« less

Cation export from Alaskan arctic watersheds

Cation export from Alaskan arctic watersheds