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A portable Wavelength Scanned-Cavity Ring-Down Spectrometer (Picarro L2120) fitted with a diffusion sampler (DS-CRDS) was used for the first time to continuously measure δ18O and δ2H of stream water. The experiment took place during a storm event in a wet tropical agricultural catchment in north-eastern Australia. At a temporal resolution of one minute, the DS-CRDS measured 2160 δ18O and δ2H values continuously over a period of 36 h with a precision of ±0.08 and 0.5‰ for δ18O and δ2H, respectively. Four main advantages in using high temporal resolution stream δ18O and δ2H data during a storm event are highlighted from this study. First, they enabled us to separate components of the hydrograph, which was not possible using high temporal resolution electrical conductivity data that represented changes in solute transfers during the storm event rather than physical hydrological processes. The results from the hydrograph separation confirm fast groundwater contribution to the stream, with the first 5 h of increases in stream discharge comprising over 70% pre-event water. Second, the high temporal resolution stream δ18O and δ2H data allowed us to detect a short-lived reversal in stream isotopic values (δ18O increase by 0.4‰ over 9 min), which was observed immediately after the heavy rainfall period. Third, δ18O values were used to calculate a time lag of 20 min between the physical and chemical stream responses during the storm event. Finally, the hydrograph separation highlights the role of event waters in the runoff transfers of herbicides and nutrients from this heavily cultivated catchment to the Great Barrier Reef. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The differences between δ 18 O and δ 2 H in throughfall and open rainfall were studied for a selected typhoon event in a watershed within the Taihu Lake drainage basin, eastern China. In this event, the isotopic composition of precipitation exhibited a strong temporal variation. Comparison results show that an isotopic composition difference existed not only between gross rainfall and average incremental rainfall, but also between different calculation methods used to derive average. The differences between incremental precipitation and throughfall isotopic composition were observed in this study. Considering the temporal variation in rainfall and throughfall during this typhoon event, the incremental value can have an effect on hydrograph separation more accurately in evaluating the importance of 'new' water. In addition, isotopic fluctuations of surface water and groundwater differed from those of rainfall and throughfall throughout the event.

During landfall of extratropical cyclones between 2005 and 2011, nearly 1400 precipitation samples were collected at intervals of 30-min time resolution with novel automated collectors at four NOAA sites in northern California [Alta (ATA), Bodega Bay (BBY), Cazadero (CZD) and Shasta Dam (STD)] during 43 events. Substantial decreases were commonly followed hours later by substantial increases in hydrogen isotopic composition (δ2HVSMOW where VSMOW is Vienna Standard Mean Ocean Water) and oxygen isotopic composition (δ18OVSMOW) of precipitation. These variations likely occur as pre-cold frontal precipitation generation transitions from marine vapour masses having low rainout to cold cloud layers having much higher rainout (with concomitant brightband signatures measured by an S-band profiling radar and lower δ2HVSMOW values of precipitation), and finally to shallower, warmer precipitating clouds having lower rainout (with non-brightband signatures and higher δ2HVSMOW values of precipitation), in accord with 'seeder–feeder' precipitation. Of 82 intervals identified, a remarkable 100.5 ‰ decrease in δ2HVSMOW value was observed for a 21 January 2010 event at BBY. Of the 61 intervals identified with increases in δ2HVSMOW values as precipitation transitioned to shallower, warmer clouds having substantially less rainout (the feeder part of the seeder–feeder mechanism), a remarkable increase in δ2HVSMOW value of precipitation of 82.3 ‰ was observed for a 10 February 2007 event at CZD. All CZD and ATA events having δ2HVSMOW values of precipitation below −105 ‰ were atmospheric rivers (ARs), and of the 13 events having δ2HVSMOW values of precipitation below −80 ‰, 77 % were ARs. Cloud echo-top heights (a proxy for atmospheric temperature) were available for 23 events. The mean echo-top height is greater for higher rainout periods than that for lower rainout periods in 22 of the 23 events. The lowest δ2HVSMOW of precipitation of 28 CZD events was −137.9 ‰ on 16 February 2009 during an AR with cold precipitating clouds and very high rainout with tops >6.5 km altitude. An altitude effect of −2.5 ‰ per 100 m was measured from BBY and CZD δ2HVSMOW data and of −1.8 ‰ per 100 m for CZD and ATA δ2HVSMOW data. We present a new approach to categorise rainfall intervals using δ2HVSMOW values of precipitation and rainfall rates. We term this approach the algorithmic-isotopic categorisation of rainfall, and we were able to identify higher rainout and/or lower rainout periods during all events in this study. We conclude that algorithmic-isotopic categorisation of rainfall can enable users to distinguish between tropospheric vapour masses having relatively high rainout (typically with brightband rain and that commonly are ARs) and vapour masses having lower rainout (commonly with non-brightband rain). [ABSTRACT FROM AUTHOR]

Epps, Thomas H., Daniel R. Hitchcock, Anand D. Jayakaran, Drake R. Loflin, Thomas M. Williams, and Devendra M. Amatya, 2012. Characterization of Storm Flow Dynamics of Headwater Streams in the South Carolina Lower Coastal Plain. Journal of the American Water Resources Association (JAWRA) 1-14. DOI: 10.1111/jawr.12000 Abstract: Hydrologic monitoring was conducted in two first-order lower coastal plain watersheds in South Carolina, United States, a region with increasing growth and land use change. Storm events over a three-year period were analyzed for direct runoff coefficients (ROC) and the total storm response (TSR) as percent rainfall. ROC calculations utilized an empirical hydrograph separation method that partitioned total streamflow into sustained base flow and direct runoff components. ROC ratios ranged from 0 to 0.32 on the Upper Debidue Creek (UDC) watershed and 0 to 0.57 on Watershed 80 (WS80); TSR results ranged from 0 to 0.93 at UDC and 0.01 to 0.74 at WS80. Variability in event runoff generation was attributed to seasonal trends in water table elevation fluctuation as regulated by evapotranspiration. Groundwater elevation breakpoints for each watershed were identified based on antecedent water table elevation, streamflow, ROCs, and TSRs. These thresholds represent the groundwater elevation above which event runoff generation increased sharply in response to rainfall. For effective coastal land use decision making, baseline watershed hydrology must be understood to serve as a benchmark for management goals, based on both seasonal and event-based surface and groundwater interactions. [ABSTRACT FROM AUTHOR]

Runoff components of the Zastler catchment (18 x 4 km2, southern Black Forest, Germany) were analysed with hydrograph separations using stable oxygen isotopes and dissolved silica. It was shown that event water and components with low silica contributed only smallamounts to total runoff. In addition, comparison of the two-component hydrograph separations showed that the low-silica components are generated by both event water and pre-event water fractions, depending on the state of the system. A modified three-component hydrograph separation method was introduced using dissolved silica and 18O. During storm events an interaction of three runoff components having distinct silica concentrations could be shown. Based on the geological and geomorphological genesis of the study site, it was appropriate to assign (i) the low silica component to the riparian zones and impermeable areas, (ii) the medium silica component to the periglacial debris cover and (iii) the high silica component to the crystallinedetritus and crystalline hard rock. Exact quantification of the runoff components remained difficult. However, runoff components with medium silica concentrations reacted very sensitively and intensely. Thecontribution of this component to total runoff is comparatively large. This shows the important role of the periglacial debris to runoff generation of the study site and emphasizes the importance of runoff generation processes occurring in this reservoir. [ABSTRACT FROM AUTHOR]

Permafrost thaw in peatlands has the potential to alter catchment export of dissolved organic carbon (DOC) and thus influence downstream aquatic C cycling. Subarctic peatlands are often mosaics of different peatland types, where permafrost conditions regulate the hydrological setting of each type. We show that hydrological setting is key to observed differences in magnitude, timing, and chemical composition of DOC export between permafrost and nonpermafrost peatland types, and that these differences influence the export of DOC of larger catchments even when peatlands are minor catchment components. In many aspects, DOC export from a studied peatland permafrost plateau was similar to that of a forested upland catchment. Similarities included low annual export (2-3 g C m(-2) ) dominated by the snow melt period (~70%), and how substantial DOC export following storms required wet antecedent conditions. Conversely, nonpermafrost fens had higher DOC export (7 g C m(-2) ), resulting from sustained hydrological connectivity during summer. Chemical composition of catchment DOC export arose from the mixing of highly aromatic DOC from organic soils from permafrost plateau soil water and upland forest surface horizons with nonaromatic DOC from mineral soil groundwater, but was further modulated by fens. Increasing aromaticity from fen inflow to outlet was substantial and depended on both water residence time and water temperature. The role of fens as catchment biogeochemical hotspots was further emphasized by their capacity for sulfate retention. As a result of fen characteristics, a 4% fen cover in a mixed catchment was responsible for 34% higher DOC export, 50% higher DOC concentrations and ~10% higher DOC aromaticity at the catchment outlet during summer compared to a nonpeatland upland catchment. Expansion of fens due to thaw thus has potential to influence landscape C cycling by increasing fen capacity to act as biogeochemical hotspots, amplifying aquatic C cycling, and increasing catchment DOC export., (© 2014 John Wiley & Sons Ltd.)