Spring Thaw Period Research Articles

The character and bioactivity of dissolved organic matter at thaw and in the spring runoff waters of the arctic tundra North Slope, Alaska

The brief spring thaw period in the arctic is an important time when carbon is transferred from terrestrial to aquatic systems as melting snow and soil waters run off into the streams, lakes, and ocean. Measurements were made of the quantity and quality of dissolved organic carbon (DOC) in thawing soil and runoff waters in the foothills region of the Kuparuk River basin of arctic Alaska, during the thaw of May 1996. Incubations were performed using DOC and soil cores at the time of thaw from the surface layers of two major tundra types of the region, nonacidic and acidic tundra. Results indicated that there are major changes in both the quantity and quality of DOC as soil waters thaw and move to the streams and lakes. DOC concentrations were found to be reduced up to 90% as soil waters thawed and became free‐flowing soil waters with leachates from thawed soil cores averaging 116 mg DOC/L at thaw and soil waters averaging 20 mg DOC/L. Stream and inlet to Toolik Lake DOC concentrations averaged 12 and 10 mg DOC/L respectively indicating further dilution of DOC. Quality differences elucidated by XAD‐8/4 resin fractionation of DOC were observed for waters at various points in the ecosystem. The hydrophilic neutral fraction (HIN) accounted for 71% of the DOC in waters of thawing soil cores, but was only 23% in flowing waters of soils, and 9–20% in stream waters. A 14 day 4°C incubation of DOC from thawing soil core waters reduced DOC an average of 39%, with 80% of that reduction occurring in the HIN fraction. Soil waters and stream waters were similar in DOC fraction composition, and fulvic acid fractions were dominant. Initial 14 day DOC respiration rates with high HIN waters were 10 mg CO2‐C/g DOC/d, and reduced to 1.2–1.7 mg CO2‐C/g DOC/d after 34 days incubation. Respiration rates of thawed cores ranged from 0.12 to 0.06 and 0.03 mg CO2‐C/g C/d for nonacidic and acidic cores, respectively.

Simulation of freeze‐thaw cycles in a general circulation model land surface scheme

Using observed meteorological data collected from four sites in the former Soviet Union, a land surface scheme designed for use in climate models was integrated for 6 years. Using observed available soil moisture and freezing front data, the model simulation of freeze‐thaw cycles over the 6 years for each station was validated. The model was able to simulate the general characteristics of the seasonal freeze‐thaw cycles for all stations for all years. There were problems in the simulation of the spring period by Best Approximation of Surface Exchanges (BASE): the model simulated excess accumulation of liquid soil moisture in spring and failed to match the observed timing of total freeze and total thaw. Most problems could be linked to the parameterization of hydraulic conductivity, and when this was modified, the model was able to simulate the available soil moisture more accurately. Moreover, it was shown that the inclusion of a frozen soil parameterization is necessary in order to capture the broad seasonal cycle of soil moisture and that the impact of not accounting for frozen soil can extend beyond the spring thaw period. To improve the simulations further, it may be necessary to model the effects of cryoturbation (including macropores), freezing fronts, ice‐lensing and other periglacial processes. Given the spatial resolution of climate models, the vertical resolution of land surface schemes (1–5 layers), and the lack of suitable observed data, even if these processes could be parameterized, the quality of the simulations are unlikely to increase enough to warrant the additional computational expense.

Nitrous oxide emissions from agricultural fields during winter and spring thaw as affected by management practices

Highest rates of N2O emissions from fertilized as well as natural ecosystems have often been measured at spring thaw. But, it is not clear if management practices have an effect on winter and spring thaw emissions, or if measurements conducted over several years would reveal different emission patterns depending on winter conditions. In this study, we present N2O fluxes obtained using the flux-gradient approach over four winter and spring thaw periods, spanning from 1993 to 1996, at two locations in Ontario, Canada. Several agricultural fields (bare soil, barley, soybean, canola, grass, corn) subjected to various management practices (manure and nitrogen fertilizer addition, alfalfa ploughing, fallowing) were monitored. Nitrous oxide emissions from these fields from January to April over four years ranged between 0 and 4.8 kg N ha-1. These thaw emissions are substantial and should be considered in the nitrous oxide budgets in regions where thaw periods occur. Our study indicates that agricultural management can play a role in mitigating these emissions. Our data show that fallowing, manure application and alfalfa incorporation in the fall lead to high spring emissions, while the presence of plants (as in the case of alfalfa or grass) can result in negligible emissions during thaw. This presents an opportunity for mitigation of N2O emissions through the use of over-wintering cover crops.

Reducing Damage to Low-Volume Roads by Using Trucks with Reduced Tire Pressures

Heavy-volume highways in seasonal frost areas are designed to resist the effects of spring thaw. However, timber access roads, county roads, and other low-volume roads with thin bituminous surfaces can be quite susceptible to pavement damage during midwinter- and spring-thaw periods. To reduce damage to low-volume roads, towns, cities, and states typically either post reductions in allowable load or completely prohibit hauling during damage-susceptible periods. Associated economic impact can be significant. To evaluate the effects of tire pressure on cumulative road damage, a mechanistic pavement design procedure developed by the U.S. Army Corps of Engineers for use in seasonal frost areas was used on a matrix of tire pressures, low-volume pavement cross sections, and environmental conditions. A series of computer simulations showed ( a) trucks operating with conventional tire pressures can cause excessive damage, particularly in the form of cracking, to low-volume roads with thin bituminous surfaces during relatively short thaw periods; ( b) pavement damage could be reduced substantially by restricting hauling to trucks operating with reduced tire pressures; and ( c) there are “threshold” tire pressures under which only minimal damage occurs, even during critical spring thaw. These results could influence guidelines for hauling restrictions and, in turn, associated economics.

Seasonal Soil Strength by Spectral Analysis of Surface Waves

Spectral analysis of surface waves (SASW) is a nondestructive test technique that can be used to determine profiles of surface-wave–velocity-versus-depth. In this work, the technique is used to determine the wave-velocity profile at a selected site at several different days during the spring thaw periods of 1989 and 1990. The test technique uses standard procedures using two accelerometers connected to a spectral analyzer. Results from each test are processed using a desktop computer and programs developed specifically for analysis of the data. Over 200 tests are done on 20 different days, and results are summarized in the paper. Specific results indicate that the SASW technique has excellent potential for detecting time-varying changes in soil properties. In particular, the results indicate that wave velocities at a given depth tend to start high (frozen soil), decreasee to a low value (thawed wet soil), then increase (thawed dry soil) as the spring thaw period progresses. In addition, results show a good correlation between calculated thaw depth and thaw depth estimated from SASW techniques.

Nitrate and chloride distribution and balance under continuous potato cropping

A study was conducted between 1977 and 1982 to determine N losses from sandy loam soil under continuous potato cropping in Southern Ontario, Canada. A monthly climatic water budget was used to evaluate the timing and amount of soil drainage in relation to changes in the distribution of NO 3 −-N and Cl − in the soil profile. Significant temporal variations in NO 3 −-N and Cl − concentration were associated with percolation. The presence of concentration peaks below 183 cm, adjacent to a shallow water-table aquifer underlying the field, indicated definite leaching patterns. Ground water in the aquifer and in springs located down-gradient from the field had NO 3 −-N concentrations > 10 mg l −1. Little leaching occurred during the summer, but considerable amounts of NO 3 −-N and Cl − were lost during major episodes of soil drainage in autumn before freeze-up and in the early spring thaw period. The similar pattern of NO 3 −-N and Cl − concentration in the 0–3-m soil profile suggested that denitrification was not an important N-loss mechanism. This conclusion was supported by laboratory incubations of soil samples which showed that 8–20% of the initial NO 3 −-N was denitrified over a 14-day period in samples from 0–15-cm depth, whereas soils from greater depths exhibited very low denitrification potentials. Mass balance data for 1979–1982 indicated that annual N losses from the 0–183-cm soil profile ranged between 78 and 220 kg ha −1 under potato crops which received annual fertilizer applications of 160–210 kg N ha −1. Above-normal precipitation in late summer and autumn may have increased the rates of NO 3 −-N leaching into the shallow aquifer during the study period.

Retention and release of chemical species by a Northern Michigan snowpack

Snowcore and water samples were collected during the 1981 to 82 winter at two independent sites in Northern Michigan; the Little Pigeon River and McNearney Lake. Acidic and basic species were determined in all samples. Examination of the concentration vs depth profiles of snow cores showed that all species were stable in the snowpack until the spring thaw period. During the thaw, 50 to 70% of the stored acids were released during the first 20% of the snowmelt. However, rainfall during the melt period contributed as much acidity to the environment as the snowmelt. Study of runoff showed that only 30% of the nitrate originally present in the snowpack appeared in the Little Pigeon River. Therefore, H2SO4 dominated the runoff acidity at the Little Pigeon River. Both nitrate and sulfate were responsible for the slight acidification of McNearney Lake during the snowmelt period.

Northern Michigan snowpack—a study of acid stability and release

Weekly samples of wet deposition, dry deposition, and the snowpack were collected during the 1981–1982 winter at the University of Michigan Biological Station which is located near Pellston, Michigan. All the major acidic and basic species were determined. Comparison of the cumulative wet deposition acid loading to the snowpack loading as well as an examination of concentration vs depth profiles showed that all species were stable in the snowpack until the spring thaw period. During the spring thaw, approximately 50% of the acids were contained in the first 20 % of the snowmelt. Rainfall during the thaw period deposited as much nitrate and acid and more than double the amount of sulfate as was released from the snowpack. It was also concluded that dry deposition to snow at this location was not significant.

Colonization of decomposing deciduous leaf litter by Testacea (Protozoa, Rhizopoda): Species succession, abundance, and biomass.

The colonization of leaf litter by testate amoebae in a cool temperate deciduous forest was studied over the first 60 months of decomposition. No colonization of fresh leaf litter by Testacea was recorded before the first spring thaw period. Colonization of aspen and balsam leaves was similar in terms of species and numbers of species, with the balsam litter being colonized by slightly fewer species. In the aspen litter bags, all the L-layer species were present after 18 months, and all the species recorded in all soil layers were found after 60 months. The proportion of species which constructed their tests from platelets rather than sediment was 70% of the total number of species for the first 36 months of colonization of both litter types. After 60 months, seven species comprised 70% of the total numbers of Testacea but only 33-38% of the total biomass. Significant, positive correlation existed between the dry weight loss of leaf litter and the total number of active Testacea, the total number of living Testacea, and the total number of species present. The prime limitations to testacean colonization of decomposing leaf litter appeared to be substrate quality, food supply and/or availability of test-building materials.