Fall Freeze Research Articles

Dense brine formation in Arctic coastal regions

In the past 2 years, winter field programs have been conducted along the northeast coast of the Chukchi Sea to study the formation and fate of very cold and salty water produced during fall freeze up and lead refreezing processes. These programs, headed by Lon E. Hachmeister of Envirosphere Company, Bellevue, Wash., and James R. Payne of Science Applications International Corporation, La Jolla, Calif., have been funded by the National Oceanic and Atmospheric Administration Outer Continental Shelf Environmental Assessment Program (NOAA/OCSEAP) to better understand physical processes in arctic coastal regions in regard to potential impact bv oil and gas development.

Field Study of the Fate of Fall‐Applied 15N‐Labelled Fertilizers in Three Alberta Soils1

AbstractFall application of N fertilizers is often less effective than spring application in increasing yields of cereal crops in portions of the Prairie Provinces of Canada. This paper reports on five field experiments (and involving three soils) using 15N‐labelled fertilizers to determine the amounts of mineral N lost over the winter by denitrification, leaching, and immobilization. The labelled N fertilizers were applied at 112 kg N ha−1in October in 1974–1975 experiments and in December in 1975–1976 experiments. The plots were sampled to a depth of 120 or 150 cm in late May. In the two 1974–1975 experiments (Malmo sicl soil), KNO3 and urea were mixed into the 0 to 12 cm depth of soil, and (NH4)2SO4 was placed in a band. Recovery of the labelled fertilizer N found in the total soil N was lowest for KNO3 (60 %), next for urea (71 %), the highest for (NH4)2SO4 (84%). The addition of 50 mm of water to the soil, which reduced the soil moisture tension of the 0 to 15 cm depth to less than 33 KPa on fall freezing, decreased the recoveries of KNO3 and urea in the total soil N to 26 and 54%, respectively. There was no leaching below the 60 cm depth. For the three fertilizers, from a 10th to a third of applied N was immobilized. In the three 1975–1976 experiments, the three soil types were, Demay 1, Malmo sicl, and Falun 1. The fertilizers were placed in bands 5 cm deep into the frozen soil. There was little loss of the labelled N from the total soil N for (NH4)2SO4, but very large losses for KNO3. As in the experiments from 1974–1975, the experiments for 1975–1976 showed no 15N below 60 cm depth for KNO3, and below 30 cm depth for (NH4)2SO4. The percent of applied N which became immobilized range from 7 to 49%, with the highest value for (NH4)3SO4 on a Malmo sicl soil. In summary, substantial losses of late fall‐applied l5N‐labelled fertilizers occurred over the winter, with field experiments that were started in 2 different years. These losses from the soil averaged 67% for KNO3 (five experiments, range of 40 to 87%), 38% for urea (two experiments, range of 29 to 46%), and 10% for (NH4)2SO4 (five experiments, range of 1 to 18%). The overwinter loss of fall‐ or winterapplied N was not through leaching, but through denitrification which apparently took place in early spring. The amount of immobilization of the labelled fertilizers varied from experiment to experiment.

Estimating minimum temperature and climatological freeze risk in hilly terrain

Differences between weather station and on-farm minimum temperatures in hilly terrain were related to general weather parameters, using stepwise multiple linear regression and correlation techniques. Opacity (cloud cover) and wind speed were the most significant parameters, explaining up to 79% of the variation in night-time temperature differences between base station and field sites 20–40 km away. Considering dew point depression, days since 0.25 cm rainfall, absolute minimum temperature, cloud base height, opacity as quadratic and an exponential relationship did not improve the regression estimates significantly. Standard error of estimates ranged from 0.8°C for sites on hilltops to 2.3°C for valley bottoms. In independent data tests using 19 cases, the average minimum temperature difference between the base station and a high risk site was estimated within 0.4°C of the measured value. Significance of the regression relationships increased proportionally with distance down the slopes. Base station-site minimum temperature differences on relatively clear calm nights averaged near 1°C on hilltops, 2° to 3°C midway down slopes and 5° to 6°C in the hollows. Regression equations developed from short-term temperature measurements at more than 50 sites were used to estimate daily site minimum temperatures for a 21-year period. Spring and fall freeze probabilities for critical temperatures of 32°, 30° and 28°F (0.0°, −1.1° and −2.2°C) were then calculated for each site using standard climatological techniques. Estimated average freeze dates in hollows were up to 34 days later in spring and 39 days earlier in fall than on hilltops. Average dates of spring and fall freeze occurrences were delayed and advanced respectively about 6 days for each degree (C) drop in critical temperature. In independent data tests the average spring and fall ground frost dates at the base station were estimated within 2 days of measured values, using similar techniques. Minimum temperatures measured by traverses on a clear, calm night were highly correlated with estimated frost dates ( R = 0.99).

Litter decomposition in a cool temperate deciduous forest

Amounts of autumn tree leaf litter fall, understory litter input, tree leaf litter nutrient input, and rates of dry weight loss in decomposing leaf litter were estimated in an aspen woodland (Populus tremuloides Michx. – P. balsamifera L.) site in the Rocky Mountains in southwestern Alberta. Tree leaf litter input amounted to 250 g m−2 and comprised 3.7% of the total organic matter in the ecosystem (1.92 × 105 kg ha−1). The ratio of the weight of aspen leaf fall to balsam leaf fall was about 6:1. The tree leaf litter input and the total litter input figures were similar to those for other Northern Hemisphere aspen forests. The understory litter input in the study plots was measured as 99 g m−2. The importance by weight of some of the nutrients returned to the soil via tree leaf litter fall was Ca > N > K > Mg > P > Zn > Fe > Mn > Na > Cu. The total weight of these nutrients returned to the soil was 116 kg ha−1, with N, Ca, and K comprising 89% and Mg and P comprising 9.8% of the total.The dry weight loss of decomposing aspen and balsam leaves was measured at 1-, 5-, 8-, 12-, 18-, 24-, and 30-month intervals by using 3-mm-mesh litter bags, and at 12-, 24-, 36-, 48-, and 60-month intervals by using 10-mm-mesh bags. Litter-bag mesh size was of little consequence to the rate of dry weight loss for the first 12 months, but subsequent dry weight loss was greater in the 3-mm-mesh bags, which maintained higher, more representative, moisture conditions than did the 10-mm-mesh bags. However, tethered leaves lost 1.7 times more weight over the first 12 months of decomposition than did confined litter. The decay rate decline with time and with the depth of the litter bag in the litter layers, with maximum dry weight loss occurring over the period encompassing the fall freeze, winter, and the spring thaw and runoff. Leaf litter placed on north-facing slopes was characterized by significantly slower decay rates than that on south-facing slopes.The dry weight loss for aspen leaf litter was 26.2 ± 2.0% after 12 months. 40.0 ± 1.6% after 30 months, and 58.7% after 60 months (by regression): for balsam litter it was 21.2 ± 1.9% after 12 months, 37.4 ± 1.7% after 30 months, and 47.9% after 60 months (by regression). The highly leachable component of leaf litter was estimated at 23.1% for aspen and 21.4% for balsam. The time required for 99% decomposition was calculated as about 24 years for aspen and about 27 years for balsam, which gives average annual decay rates of 3.2% for aspen and 2.9% for balsam. The decay rate for Populus leaf litter was lower than that for aspen in Alaska and appeared to fit the range for deciduous leaf litter from some forested IBP Tundra Biome sites.

End of Squaring as an Economic Indicator of Approximate Time to End Insecticidal Treatments for Boll Weevil Control1

Under various field conditions in North Carolina, cotton planted in mid-April started squaring in mid-June, stopped squaring in mid-August or earlier, and did not produce bolls which failed to open prior to the first fall freeze. Square infestation by Authonomus grandis Boheman was reduced and the yield of cotton was economically increased by insecticidal treatments applied at approximately 5-day intervals from the time the square infestation in July reached 10% until the end of squaring. After the end of squaring, additional treatments applied at approximately 5-day intervals did not reduce the adult boll weevil population or increase the yield of cotton. Hence, from the economic standpoint of cotton production, the end of squaring (less than I square per linear ft of row) indicated the approximate time to end insecticidal treatments for boll weevil control.

Stimulation of Leaf Abscission of Woody Plants by Potassium Iodide and Alanine1

Abstract Nurserymen often wish to dig plants prior to natwl leaf abscission. Plants for some areas could be shipped for fall planting if digging could be done early enough. In other areas an extended digging period would lessen harvest pressure or make better use of labor. Early digging would also de crease danger of losses from early fall freezes. Some plants (i.e. Weigela) retain their leaves extremely late in the season

Pollen Analyses of Surface Materials from the Southern San Juan Mountains, Colorado

Information about modern pollen deposition is needed to interpret fluctuations in the postglacial pollen record in mountain regions. Thirty-five samples of surficial water-laid sediment and moss were collected in the vicinity of Durango and Silverton, Colorado, from sites ranging between 6850 and 12,600 feet above sea level. The regional differences in pollen concentration are not clearly shown when, as is the common practice, the pollen taxa are expressed as percentages of the total pollen at each site. Various site factors can obscure existing trends. Pollen concentrations in surface samples are most easily compared by examining ratios determined by the frequencies of only two pollen types in the sample. The effect of other pollen is thus excluded. Three ratios are examined utilizing combinations of pine (Pinus), spruce (Picea), oak (Quercus), and sage-brush or wormwood (Artemisia) pollen. These taxa are easily identified and comprise the bulk of the pollen in the samples. The ratios Picea/Pinus, Artemisia/Quercus, and Pinus/Quercus exhibit linear trends when plotted against elevation on semilogarithmic paper; their relations to elevation can be approximated by exponential functions. Several factors affect the value of a ratio. For example, the Picea/Pinus ratio depends upon: (1) elevation (and the control that the moisture and temperature regime exerts on vegetation); (2) density of the surrounding forests; (3) size of the basin in which the pollen accumulates; and (4) statistical variation associated with random counting errors. The highest values of Artemisia pollen, released late in the flowering season, were found in sediments of cirque lakes above timber line. The cirque lakes remain frozen until midsummer, overflow with meltwater until late in the pollination season, and then become standing bodies of water until the fall freeze. The cirque lake sediments are deficient in early-season pollen. The logarithm of certain pollen ratios may be correlated with elevation because environmental factors associated with elevation control the distribution of the plants in mountain regions. If the elevations of the vegetation zones varied in the past because of different climatic conditions, the ratios of the taxa at any one site would be expected to change and indicate an “apparent elevation” different from the present. Study of the apparent changes in elevation of a site in the Animas Valley region, based on variations in the pollen ratios of its post-glacial sediments, may provide evidence of past climate fluctuation.

CLIMATOLOGICAL ANALYSIS OF FREEZE DATA FOR IOWA

A set of freeze thresholds is defined which replaces the loosely defined element “killing frost.” Freeze series are tested and found to be random. This makes it possible to fit frequency distributions. It is hypothesized that these distributions are normal and a test of significance verifies this. A hypothesis that the variance parameter is constant over Iowa is tested and found to be true. It is shown that spring and fall freeze are independent and this results in a simple form of freeze-free period distribution. The calculation of probabilities of freeze and freeze-free season are explained.

Some Effects of the First Fall Freeze

Some Effects of the First Fall Freeze