Isotopic constraints on water balance of tundra lakes and watersheds affected by permafrost degradation, Mackenzie Delta region, Northwest Territories, Canada.

Widespread permafrost degradation in Canada's western Arctic has led to formation of shoreline retrogressive thaw slumps (SRTS), a process influential in modifying water and biogeochemical balances of tundra lakes. To investigate hydrological effects of SRTS, water sampling campaigns were conducted in 2004, 2005, and 2008 for paired lakes (undisturbed vs SRTS) in the upland region adjacent to the Mackenzie Delta, Northwest Territories, Canada. An isotope mass balance model to estimate evaporation/inflow, precipitation/inflow, water yield, and runoff ratio was developed incorporating seasonal evaporative drawdown effects and a mixing model to simulate gradients in marine-continental atmospheric moisture.

Molecular profiling of naphthenic acids in technical mixtures and oil sands process-affected water using polar reversed-phase liquid chromatography-mass spectrometry.

In this work, a reversed-phase ultra-HPLC (UHPLC) ultrahigh resolution MS (UHRMS) method was evaluated for the comprehensive profiling of NAs containing two O atoms in each molecule (O2NAs; general formula C H O , where n is the number of carbon atoms and z represents hydrogen deficiency). Using a polar cyanopropyl-bonded phase column and negative-ion electrospray ionization mass spectrometric detection at 120,000 FWHM (m/z 400), 187 and 226 O2NA species were found in two naphthenic acid technical mixtures, and 424 and 198 species with molecular formulas corresponding to O2NAs were found in two oil sands process-affected water samples (one from a surface mining operation and the other from a steam-assisted gravity drainage operation), respectively. To our knowledge, these are the highest numbers of molecular compositions of O2NAs that have been profiled thus far in environmental samples.

Jasechko et al. reply.

replying to A. M. J.

Terrestrial water fluxes dominated by transpiration.

Renewable fresh water over continents has input from precipitation and losses to the atmosphere through evaporation and transpiration. Global-scale estimates of transpiration from climate models are poorly constrained owing to large uncertainties in stomatal conductance and the lack of catchment-scale measurements required for model calibration, resulting in a range of predictions spanning 20 to 65 per cent of total terrestrial evapotranspiration (14,000 to 41,000 km(3) per year) (refs 1, 2, 3, 4, 5). Here we use the distinct isotope effects of transpiration and evaporation to show that transpiration is by far the largest water flux from Earth's continents, representing 80 to 90 per cent of terrestrial evapotranspiration.

Evaporative isotope enrichment as a constraint on reach water balance along a dryland river.

Deuterium and oxygen-18 enrichment in river water during its transit across dryland region is found to occur systematically along evaporation lines with slopes of close to 4 in (2)H-(18)O space, largely consistent with trends predicted by the Craig-Gordon model for an open-water dominated evaporating system. This, in combination with reach balance assessments and derived runoff ratios, strongly suggests that the enrichment signal and its variability in the Barwon-Darling river, Southeastern Australia is acquired during the process of evaporation from the river channel itself, as enhanced by the presence of abundant weirs, dams and other storages, rather than reflecting inherited enrichment signals from soil water evaporation in the watershed. Using a steady-state isotope mass balance analysis based on monthly (18)O and (2)H, we use the isotopic evolution of river water to re-construct a perspective of net exchange between the river and its contributing area along eight reaches of the river during a drought period from July 2002 to December 2003, including the duration of a minor flow event.

Climate change effects on hydroecology of arctic freshwater ecosystems.

In general, the arctic freshwater-terrestrial system will warm more rapidly than the global average, particularly during the autumn and winter season. The decline or loss of many cryospheric components and a shift from a nival to an increasingly pluvial system will produce numerous physical effects on freshwater ecosystems. Of particular note will be reductions in the dominance of the spring freshet and changes in the intensity of river-ice breakup.

Historical changes in arctic freshwater ecosystems.

Various types of ecosystem-based climate proxies have been used to assess past arctic change. Although lotic records are relatively poor because of the constant reworking of riverine material, high-quality lentic data have been assembled back to the end of the Pleistocene and deglaciation of the circumpolar Arctic. In general, climatic variations in the Holocene, partly due to changes in the shrinking effect of glacier coverage, produced significant temporal and spatial variations in arctic hydrology and freshwater ecosystems.