Many floods of record in cold regions are produced b_y s_n9w ablation. Accurate prediction of snowmelt runoff events by using computer models hinges upon an accurate understanding of the hydrologic role of frozen soils. This paper discusses the redistribution of soil moisture that takes place during the development of seasonal frost in a silty loam soil and the infiltration characteristics of this seasonally frozen soil. Depending upon the total (water and ice) soil moisture conditions near the ground surface, a wide range of infiltration rates can exist. This disparity in the infiltration rate results in considerable variation in the amount of snowmelt runoff. BASIC PROCESSES
Nanoengineered hydrogels offer the potential to design shear-thinning bioinks for three-dimensional (3D) bioprinting. Here, we have synthesized colloidal bioinks composed of disk-shaped two-dimensional (2D) nanosilicates (Laponite) and poly(ethylene glycol) (PEG). The addition of Laponite reinforces the PEG network and increases viscosity, storage modulus, and network stability. PEG-Laponite hydrogels display shear-thinning and self-recovery characteristics due to rapid internal phase rearrangement. As a result, a range of complex patterns can be printed using PEG-Laponite bioinks. The 3D bioprinted structure has similar mechanical properties compared to the as-casted structure. In addition, encapsulated cells within the PEG-Laponite bioink show high viability after bioprinting. Overall, this study introduces a new class of PEG-Laponite colloidal inks for bioprinting and cell delivery.
Topp and Davis [this issue] are disturbed because we introduced the concept of capacitance into our presentation about time domain refiectometry (TDR). We [Stein and Kane, 1983]. preceded our discussion on TDR with some introductory paragraphs about capacitance because we felt that capacitance is a more widely known concept than dielectric constant and because we felt that there are some analogies between the two subjects that lead to a better understanding of the concept of measuring dielectric properties.In response to the comment of Topp and Davis about the geometry of capacitors and probes for TDR, we did not intend to imply in our introductory section that they must have the same configuration. In the first case, we are talking strictly about capacitors. In the second instance, we discuss measuring dielectric properties.There has been concern expressed by Topp and Davis and others about the design of what we call our 300-ohm TV wire system. As is stated in the paper, it was only used for 1 year because we noted many of the limitations of this system as expressed by others. However, at the time we received funds for this instrumentation, we had very little time to experiment with various configurations in the laboratory if we were going to collect field data during that winter and following snowmelt period. Since we wanted to specifically monitor snowmelt infiltration into seasonally frozen soils, we went ahead and installed the probes using the 300-ohm TV wire. However, we continued to examine other designs in the laboratory and soon developed the present design that we have used extensively in all types of soils. The lengthy exploration of Topp and Davis into limitations of our first system is an excellent, detailed description of why we abandoned this sytem after the first field year. REFERENCES Stein, J., and D. L. Kane, Monitoring the unfrozen water content of soil and snow using time domain refiectrometry, Water Resour.
More than half of the annual acidic deposition to Canada's boreal forests is released during spring snowmelt. To evaluate the impact of this acidity upon the aquatic environment, the sources and hydrologic pathways must be defined. Two environmental tracers, oxygen 18 and silica, were used to meet this objective for spring snowmelt at Lac Lafiamme. Stream water could be partitioned into four distinct waters based upon event and flow path; however, similar division for lake water was not possible due to inconsistencies between tracer contents in the lake water. In terms of the major source of acidity, snow meltwater, stream water had an average meltwater content of 70% while near-shore lake water ranged from greater than 70% at spring melt commencement to less than 45% at the end. These high amounts of meltwater represent a severe hazard for the potential occurrence of "acid shock" of nearshore spawning grounds. INTRODUCTION The acidification of lakes is greatly affected by spring snowmelt, which represents the major hydrological event for many watersheds in northern latitudes [Bottomley et al., 1986; Gjessing and Johannessen, 1987; Roberge and Plamondon, 1987]. Chemical fractionation within the melting snowpack also contributes to the acidic "shock" of spring meltwaters; 50 to 80% of the solutes contained within the snowpack will be released upon melt of the first third of the snowpack [Gjessing and Johannessen, 1987; Davis et al., 1987]. The amount of acidity that eventually reaches the stream or lake waters, however, is dependent upon dilution by preevent groundwaters and upon the flow pathways. Meltwaters are altered by chemical reactions within the organicmineral matrix and delayed in arrival by the path length and permeability of the flow system [Bottomley et al., 1985; Anderson and Bowser, 1986; Hooper and Shoemaker, 1987]. Thus a definition of the relative amounts of preevent groundwaters and the flow paths taken by the meltwaters is essential for the evaluation of the acidification potential of a watershed. The amount of groundwater in streams is, in part, dependent upon the amount of event water (precipitation and/or meltwater) that infiltrates into the soil. The infiltration of snowmelt waters is controlled by ice layers at the snow-soil interface, soil properties (hydraulic conductivity, porosity), and the height of the water table. For forested watersheds with deep snowpacks, much of the initial meltwater will infiltrate if concrete ice or basal snow ice layers are absent [Price and Hendrie, 1983; Bottomley et al., 1986; Roberge and Plamondon, 1987]. High soil moisture contents (resulting from rainfall in autumn or snowmelt in midwinter) can result in the reduction of infiltration rates and the occurrence of large amounts of surface runoff in the spring snowmelt season [Kane and Stein, 1983; Price and Hendrie, 1983]. As melt proceeds, the water table rises toward the soil surface, resulting in increased groundwater discharge, interflow (lateral flow within the top soil horizons), and surface runoff [R...
The calibration of time domain reflectometry, previously established for an organic soil of 0.422 Mg•m−3 bulk density, was established for peat blocks with bulk densities ranging from 0.06 to 0.25 Mg•m−3. An empirical relationship between the volumetric water content and the measured apparent dielectric constant was established in the laboratory. This relationship can be used to estimate volumetric water content between 0.21 and 0.95 cm3•cm−3 with a standard deviation of 0.03 cm3•cm−3. The large variations observed during the calibration were mainly attributed to the size and heterogeneousness of peat samples. When water tables in the field were high, standard deviation decreased to 0.02 cm3•cm−3, which agrees very well with other time domain reflectometry experiments.
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