Years Of Low Precipitation Research Articles

Physical and chemical properties of the Sulphur Mountain thermal springs, Banff National Park, and implications for endangered snails

Nine thermal springs, in three groups, occur along the flank of Sulphur Mountain in Banff National Park. The principal recharge zone is suggested to be above 2000 m elevation on Mount Rundle, circulation depths are estimated to be 3.2 ± 0.6 km, and discharge is focused along the Sulphur Mountain Thrust. Springs show constant temperature and total dissolved solids load throughout the winter, whereas both drop in association with spring snowmelt. The degree and timing of temperature drops are a function of elevation, with the highest springs showing the earliest and most significant temperature drop. The highest elevation springs also show the greatest seasonal variability in water chemistry. Unusual seasonal flow stoppages of these springs are related to extreme low precipitation years. The biogeochemistry of the thermal springs and population fluctuations of the endemic and endangered Banff springs snail (Physella johnsoni) are strongly related to seasonal variability in flow rates. Changes in redox conditions associated with an influx of shallow groundwater during spring snowmelt negatively impact the microbial community that forms a principal food supply for the snail.

Perspective: Evolution of flower color in the desert annual Linanthus parryae: Wright revisited.

Linanthus parryae, a diminutive desert annual with white or blue flowers, has been the focus of a long-standing debate among evolutionary biologists. At issue is whether the flower color polymorphism in this species is the product of random genetic drift, as Sewall Wright argued, or of natural selection, as proposed by Carl Epling and his colleagues. Our long-term studies of three polymorphic populations in the Mojave Desert demonstrate that flower color is subject to selection that varies in both time and space in its direction and magnitude. For all sites taken together, blue-flowered plants produced more seeds than white-flowered plants in years of relatively low seed production, whereas white-flowered plants had higher fitness in years of high seed production. Evidence of selection on flower color was found in two of the three study sites. Differences in fitness between the color morphs were sometimes large, with selection coefficients as high as 0.60 in some years. Our longest period of observations was at Pearblossom site 1, where plants reached appreciable densities in seven of the 11 years of study. Here we found significant differences in the seed production of the color morphs in six years, with three years of blue advantage and three years of white advantage. For all sites taken together, total spring precipitation (March and April) was positively correlated with both absolute and relative seed production of the color morphs. At Pearblossom site 1, blue-flowered plants typically had a fitness advantage in years of low spring precipitation, whereas white-flowered plants had a fitness advantage in years of high spring precipitation. This temporal variation in selection may contribute to the maintenance of the flower-color polymorphism at Pearblossom site 1, whereas gene flow from neighboring populations is proposed as the principal factor maintaining the polymorphism at the other study sites. We found no significant differences between the color morphs in pollinator visitation rate or in their carbon isotope ratio, a measure of water-use efficiency. Although the mechanism of selection remains elusive, our results refute Wright's conclusion that the flower color polymorphism in L. parryae is an example of isolation by distance, a key component of his shifting balance theory of evolution.

PERSPECTIVE: EVOLUTION OF FLOWER COLOR IN THE DESERT ANNUAL LINANTHUS PARRYAE: WRIGHT REVISITED

Linanthus parryae, a diminutive desert annual with white or blue flowers, has been the focus of a long-standing debate among evolutionary biologists. At issue is whether the flower color polymorphism in this species is the product of random genetic drift, as Sewall Wright argued, or of natural selection, as proposed by Carl Epling and his colleagues. Our long-term studies of three polymorphic populations in the Mojave Desert demonstrate that flower color is subject to selection that varies in both time and space in its direction and magnitude. For all sites taken together, blue-flowered plants produced more seeds than white-flowered plants in years of relatively low seed production, whereas white-flowered plants had higher fitness in years of high seed production. Evidence of selection on flower color was found in two of the three study sites. Differences in fitness between the color morphs were sometimes large, with selection coefficients as high as 0.60 in some years. Our longest period of observations was at Pearblossom site 1, where plants reached appreciable densities in seven of the 11 years of study. Here we found significant differences in the seed production of the color morphs in six years, with three years of blue advantage and three years of white advantage. For all sites taken together, total spring precipitation (March and April) was positively correlated with both absolute and relative seed production of the color morphs. At Pearblossom site 1, blue-flowered plants typically had a fitness advantage in years of low spring precipitation, whereas white-flowered plants had a fitness advantage in years of high spring precipitation. This temporal variation in selection may contribute to the maintenance of the flower-color polymorphism at Pearblossom site 1, whereas gene flow from neighboring populations is proposed as the principal factor maintaining the polymorphism at the other study sites. We found no significant differences between the color morphs in pollinator visitation rate or in their carbon isotope ratio, a measure of water-use efficiency. Although the mechanism of selection remains elusive, our results refute Wright's conclusion that the flower color polymorphism in L. parryae is an example of isolation by distance, a key component of his shifting balance theory of evolution.Corresponding Editor: C. Eckert

Competition intensity as a function of resource availability in a semiarid ecosystem.

Two field experiments were conducted using three dominant perennial species of the Chihuahuan Desert: Hilaria mutica (a tussock grass), Larrea tridentata (a microphyllous shrub) and Opuntia rastrera (a flat-stemmed succulent cactus). Two hypotheses concerning competition in arid plant communities were tested. (1) Marked resource partitioning with no interspecific competition could be expected since the three species belong to different life-forms, and that plant growth in deserts is basically limited by harsh environmental conditions. (2) Alternatively, resource scarcity (particularly water) will result in strong plant competition. In a 1-year removal experiment, water status and plant growth of the three species were monitored in twelve 10 m × 10 m plots randomized in three blocks and assigned to the following treatments: (a) removal of all species, except H. mutica; (b) removal of all species, except L. tridentata; (c) removal of all species, except O. rastrera, and (d) control without any manipulation. In a watering experiment, under two neighbourhood conditions (growing isolated or in associations of plants of the three species in plots of 20 m2), the water status of the three species and the growth of H.mutica and L.tridentata were studied for 32 days after an irrigation equivalent to 30 mm of rain, similar to a strong storm event at the site. In the removal experiment, where plants were free to capture water, no evidence of competition was observed. However, during the watering experiment, in which water was forced into the soil, competitive effects were observed. Associated individuals of L. tridentata had lower xylem water potentials and osmotic potentials (OPs) and produced shorter twigs and less leaves and nodes. Although less pronounced, neighbours also had a negative effect on the OP in O. rastrera. According to these results, the intensity of the interspecific competition for water seems to depend on the level of resource availability in the soil. Thus, the validity of the two hypotheses tested in this study also depends on the level of resources. Competition could be absent or very low in years of low precipitation, as in the year of this study (173 mm against a 25-year average of 264 mm). However, when soil water availability is high, e.g. following heavy rain, the negative interactions between species could be more intense.

Habitat Selection and Survival of Mule Deer: Tradeoffs Associated with Migration

We examined tradeoffs related to migration in a population of mule deer ( Odocoileus hemionus ) in southern California from 1989 to 1991. All male deer that we radiocollared were migratory, whereas females exhibited a mixed strategy with both migrant and resident individuals. Increased movements of deer were associated with decreased temperatures and increased weekly precipitation. No differences within seasons in the sizes of home ranges occurred for either migrant or resident deer. The size of home ranges of deer, however, was smaller in summer than in winter. Sizes of home ranges were associated positively with proximity to human development and to the amount of avoided (use was less than availability) habitat in the home range. Deer avoided human developments in all seasons. Further, males and resident females used areas farther from water in summer than expected by chance, whereas migratory females selected areas nearer to water. In summer, migratory females selected meadows, riparian habitats, and pine forests, whereas resident females avoided riparian habitats and used pine forests less than did migratory females. Migratory males used habitats in a way similar to migratory females, although they avoided meadows and riparian areas. Clear tradeoffs existed for deer in montane southern California about whether they migrated. Migratory females were farther from human disturbance and used habitats of high quality more often than did nonmigratory conspecifics. Nonetheless, deer were at increased risk of predation during migration and, in years of low precipitation (low snow), had higher rates of mortality than did resident deer. Thus, in areas with extremely variable precipitation and snow cover, a mixed strategy for migration can be maintained in populations of mule deer.

Dynamics of Inorganic Particles in Headwater Streams: Linkages with Invertebrates

Export of particulate inorganic matter (PIM) from three headwater streams was studied from 1985 to 1991 at Coweeta Hydrologic Laboratory. The study encompassed years of extreme high and low precipitation. During three years of the study, the stream draining Catchment 54 (C 54) received seasonal treatments of an insecticide. This treatment greatly reduced abundance biomass and secondary production of most invertebrate taxa. Streams draining Catchments 53 and 55 (C 53 and C 55) served as reference streams. During treatment, concentration of PIM in C 54 decreased significantly from pretreatment levels for both instantaneous (grab) and continuous samples, while those of reference streams either increased or did not exhibit significant change. Maximum PIM concentrations, measured during rising hydrographs of storms, were over 2× greater in the reference streams than in C 54. During treatment of C 54, export of PIM per unit maximum discharge (L/s) during sampling intervals (∼2 wks) decreased significantly compared with that of reference streams. Annual PIM export in reference streams displayed a strong (p < 0.002) exponential relationship with annual discharge, whereas that of the treated stream did not (p > 0.05). High discharges during post-treatment years (1989-1991) resulted in increased concentration and export of PIM in all streams. However, PIM concentrations in C 54 remained lower than those of the two reference streams. Invertebrate manipulation apparently reduced PIM export from C 54 by at least two mechanisms. First, the rate of particle generation by feeding activities was reduced. Second, invertebrate manipulation reduced rates of leaf litter processing, which resulted in increased storage of leaf litter and enhanced retention of particles. Comparisons of predicted versus measured export suggest that invertebrate manipulation in C 54 reduced PIM export by ∼76%, or 550 (relative to C 53R) to >1000 kg (relative to C 55) over the 6-yr treatment and post-treatment period. These comparisons exceed those made previously for the impact of invertebrate manipulation on FPOM export and provide another example of the link between animal communities and ecosystem processes. This study also provides evidence that stored leaf material, like that of woody debris, augments retention of inorganic particles in small headwater streams.

Response of Headwater Lakes to Varying Atmospheric Deposition in North-Central Ontario, 1979–85

Between 1976 and 1985, loadings of SO42− to the Algoma district (north-central Ontario) varied from a low of 47 (1980) to a high of 84 meq∙m−2 (1978) and was low in years of low annual precipitation. The mean and median lake concentrations of H+ and SO42− in 54 lakes declined between 1979 and 1982 following the period of lowest annual deposition and declined further between 1982 and 1985. Overall, mean lake pH increased 0.35 unit between 1979 and 1982 and an additional 0.07 unit over the next 3 yr. Lake concentrations in the Turkey Lakes watershed exhibited a similar trend. Two lakes without fish in 1979 and with pH's &lt; 5.5 developed white sucker (Catostomus commersoni) populations by 1986 with ages indicating that survival began after 1980. This apparent invasion from downstream populations probably occurred when lake pH's neared 5.5. Although a direct link has not been established, these lakes appear to be extremely responsive to changes in atmospheric deposition. The "recovery" of water quality clearly extends beyond that locally documented at Sudbury, Ontario, yet it remains to be determined to what degree the responses relate to differences in continental deposition and/or responses within the watershed.

Infiltration and runoff in wheat fields in the semi-arid region of Israel

The efficiency of application of different amounts of phosphogypsum (PG) (and the methods of application) in runoff control was tested for 3 years in small field-plots using a portable rainfall simulator and in runoff plots (Wischmeier plots) located in commercial wheat fields. Five t/ha of phosphogypsum spread over the soil surface after sowing the wheat was found to be the most efficient method of application, generally. In loessial soils with ESP's of 3–4 the amounts of runoff in the PG-treated plots were only 15–30% of that of the control. The wheat yield was increased by 25% in the two low-precipitation years. The marginal return for each m 3 of water was 2 kg of wheat grain. In the high-precipitation year (150% of the average) the wheat yields in the control and PG-treated plots were the same although runoff was reduced considerably.

Minchinia nelsoni (MSX) infections in the James River seed-oyster area and their expulsion in spring

Spread of a new oyster disease caused by Minchinia nelsoni (MSX) in lower Chesapeake Bay in 1959–1960 threatened Virginia's James River seed area. Infections appeared in the lower half of the seed area in 1960 and 1961, but few oysters died from the disease and infections were eliminated by oysters in April-May the following spring. Distribution of the disease in controlled broadly by low salinities that inhibit development of infections and allow oysters to discharge plasmodia. Penetrations of the seed area occurred in dry and wet years, but mortalities occurred only in 1964 and 1980, both years of low precipitation. Little mortality was caused by transplanting infected seed oysters to other rivers because only low-salinity grounds were planted after 1959–1960 when severe mortalities occurred in areas of high salinities. In most years, infections were minimal in the seed area and other estuaries where salinities do not exceed 15–20‰ in late summer and fall. Salinities <10‰ prevailed in most of the seed area when oysters expelled the pathogen in early spring.

Discussion on ‘Threshold Slopes in south Wales’ by W. C. Rouse &amp; Y. I. Farhan

The authors present an interesting account of the role of rapid mass movements in the slope morphology of South Wales. They attribute much of the slope form to mass movements during periglacial conditions, with more recent movements only superficially modifying that form. A similar conclusion regarding the role of periglacial conditions was made for colluvial masses in the Appalachian Plateau province of the United States (Gray et al . 1978, D'Appolonia et al . 1967, Philbrick 1961). However, large-scale movement of the type previously assigned to periglacial conditions recently occurred in a colluvial mass in that region, indicating that such movements may not be strictly related to past climatic conditions. Detailed study indicated that movements may have been triggered by a period of abnormally high precipitation that was preceded by at least 30 years of low precipitation (Gray &amp; Gardner 1977). Large-scale movements are thought to occur infrequently and long intervals may occur where only smaller scale, superficial mass movements occur, such as those now observed in South Wales. Intervals between large-scale movements are marked by continued build-up of colluvium and decreased equilibrium in portions of the larger mass. Eventually, some triggering mechanism (e.g. high precipitation) initiates large-scale movements that continue until the mass reaches equilibrium. We suggest that a similar mechanism should be investigated for slope development in South Wales. This possibility seems to be supported by the authors' statement that ‘rapid mass movements may be on the increase’.

Effect of Rate and Date of Seeding Shoshoni Winter Wheat on Soil Moisture Depletion1

AbstractSome growers in southeastern Wyoming plant winter wheat (Triticum aestivum L.) 2 weeks earlier than the recommended planting date, a procedure that utilizes more moisture than necessary for stand establishment. This experiment was designed to determine the extent to which high rates and early planting of winter wheat depleted soil moisture.‘Shoshoni’ winter wheat was planted at seeding rates of 17, 34, 50, and 67 kg/ha on four seeding dates, August 19, August 26, September 4, and September 11, 1965. In mid‐August, November, April, and after harvest soil moisture was measured to a depth of 122 cm using the neutron probe. Moisture depletion during the fall, winter, and spring growing periods was calculated.During stand establishment, the wheat planted August 19 depleted soil moisture significantly more than wheat planted September 4 and 11, and the wheat seeded at the rates of 34, 50, and 67 kg/ha depleted soil moisture significantly more than that at the 17 kg/ha rate.Kernel protein content of wheat harvested from planting dates August 19, August 26, September 4, and September 11 was 12.2, 13.3, 13.2, and 14.2% respectively. There were no significant differences in grain yield attributed to planting dates or rates.During the test period adequate spring moisture was received. During years of low spring precipitation, conservation of moisture by planting on the recommended date or later could be important.

Changes in Arctic Eriophorum Tussock Communities Following Fire

The arctic cottongrass (Eriophorum vaginatum ssp. spissum) tussock community is susceptible to fire even though it has a relatively small aboveground standing crop and the peaty substrate is wet even in years of low precipitation. While burns can be severe enough to kill all aboveground plant parts, differential protection is provided new shoots by tussocks bases, moss mats, and peat. Plant succession following fire was unique in that no new species invaded the area. Growth came principally from root stocks protected by the organic surface. Cottongrass and Carex spp. were the first to show regrowth following a June fire at one site. The role of cottongrass seedlings in colonizing these tussock communities was minor, because few seedlings older than 1 year were found on any of the sites. Epilobium angustifolium ssp.angustifolium and some Calamagrostis canadensis ssp. canadensis originated from seed although most plants of the latter species had long vigorous rootstocks. These plants occurred as minor components in the undisturbed community and increased when fire destroyed the competing species. The charred organic surface, being very dark, absorbed more short wave energy and the active layer depth increased by 35 to 50% in June and as much as 25% by late autumn. The same thermal regime was found in burns several years old. This warmer soil mass, over a longer period of time, was conducive to better growing conditions. Annual plant production had almost recovered after two growing seasons, and nutrient content of the plants was higher in the burned area. This may be due to the greater soil mass available for root exploration, to nutrient release by fire, and to greater microbial activity in the warmer soils. If other tundra communities respond to fire in a similar manner as cottongrass tussock communities, fires may act as a rejuvenating factor, as they do in other biomes