Thermochron iButtons incorporate the latest in digital technology, making them smaller, less expensive, durable and potentially more reliable than many other temperature logging devices. The objective of this study was to test the accuracy of an inexpensive air temperature measurement system, composed of a Thermochron iButton and radiation shield. Sixty-one iButtons were subjected to a sequence of two water baths (0°C and 24·9°C) to assess the absolute accuracy of the sensors. Five solar radiation shields were tested in a greenhouse setting to evaluate the reduction in radiative heating. Significant differences (p < 0·05) were detected between instruments subsequent to both water-bath treatment analyses. The accuracy of the sensors was well within the manufacturer's stated specification of ±1·0°C with a collective temperature variance of ±0·21°C. Temperature responses generated by the Thermochron iButtons in different radiation shields were consistent, but varied significantly (p < 0·05) from 28 to 44°C based on diurnal temperature ranges. Results indicate that the Thermochron iButton is an accurate, inexpensive alternative to more expensive temperature datalogging systems, and is well suited for obtaining quality spatially distributed data for hydrologic and water quality investigations.

Forests modify snow processes and affect snow water storage as well as snow disappearance timing. However, forest influences on snow accumulation and ablation vary with climate and topography and are therefore subject to temporal and spatial variability. We utilize multiple years of snow observations from across the Pacific Northwest, United States, to assess forest-snow interactions in the relatively warm winter conditions characteristic of maritime and transitional maritime-continental climates. We (a) quantify the difference in snow magnitude and disappearance timing between forests and open areas and (b) assess how forest modifications of snow accumulation and ablation combine to determine whether snow disappears later in the forest or in the open. We find that snow disappearance timing at 12 (out of 14) sites ranges from synchronous in the forest and open to snow persisting up to 13 weeks longer in the open relative to a forested area.By analyzing accumulation and ablation rates up to the day when snow first disappears from the forest, we find that the difference between accumulation rates in the open and forest is larger than the difference between ablation rates. Thus, canopy snow interception and subsequent loss, rather than ablation, set up longer snow duration in the open. However, at two relatively windy sites (hourly average wind speeds up to 8 and 17 m/s), differential snow disappearance timing is reversed: Snow persists 2-5 weeks longer in the forest. At the windiest sites, accumulation rates in the forest and open are similar. Ablation rates are higher in the open, but the difference between ablation rates in the forest and open at these sites is approximately equivalent to the difference at less windy sites. Thus, longer snow retention in the forest at the windiest sites is controlled by depositional differences rather than by reduced ablation rates. These findings suggest that improved quantification of forest effects on snow accumulation processes is needed to accurately predict the effect of forest management or natural disturbance on snow water resources.

Isotopic composition of snow cover and streamflow was determined in a snowdominated, forested watershed to quantify the spatial variability and processes that alter stable isotope (oxygen-18, 18 O and deuterium, 2 H) composition under different forest canopy conditions (clear-cut, partial-cut (thinned), and unimpacted forest). Snow sampling was carried out on 4 days in late winter and early spring 2006. Meteorological data, precipitation, and streamflow were continuously monitored during the study. Isotope analyses of precipitation samples were conducted weekly through the 2005-2006 snow season. Values of d 18 O varied between −22·0 and −9·5‰ , and d 2 H varied between −170 and −76‰ . Isotope concentrations from snowpack samples varied between −17·5 and −13·8‰ for d 18 O, and between −129 and −102‰ for d 2 H. These ranges reflect differences in precipitation, accumulation, sublimation, and melting of the snow cover. Streamflow samples were collected during the snowmelt season from two locations every alternate day from the beginning of April until the end of May. Streamflow and snow from a partial-cut and an uncut forest were enriched in the heavy isotopes ( 18 O and 2 H) relative to streamflow and snow from a clear-cut forest.Based on the low water contents of the snowpack under dense canopies, we infer that the isotope enrichment resulted primarily from sublimation of snow intercepted by the canopy, with more enrichment in denser canopies. There was no significant correlation between snowpack isotope concentration and altitude. Results indicate that variations in canopy structure can alter snow isotope composition. This finding will provide a useful index of snowpack sublimation, and thus, improved parameterization of distributed hydrological models.

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