Natural Temporal Variability Research Articles

Natural temporal variability of atmospheric acoustic absorption coefficients

Since acoustic absorption coefficients depend upon environmental temperature and humidity, they vary in response to chaning atmospheric conditions on a variety of time scales. This natural temporal variability is often neglected in outdoor noise assessment work, where averaged meteorological data are used to estimate absorption. In this study the authors assess the validity of calculating absorption coefficients from meteorological data which have been averaged on various time scales. The results indicate that the use of annual mean meteorological data can result in frequency-dependent r.m.s. errors ranging from 20 to 50%. Seasonal averaging can result in r.m.s. errors of 20 to 30%. Even daily averages may be unsatisfactory: for some of the cases presented absorption changes by 200% during the course of a single day.

Zoobenthic variability associated with a flood and drought in the Hawkesbury estuary, New South Wales: Some consequences for environmental monitoring

Changes in the Hawkesbury zoobenthos associated with a major flood and drought are described and comparisons made in the patterns of change among estuarine reaches and among sites within reaches. The consequences for environmental monitoring and management are discussed. Replicate grab samples were taken from four sites in each of the lower, middle and upper reaches. Reductions in the mean number of species per grab (S) following the flood were significant only in the lower reaches and at one site in the middle reaches. Increases in S accompanied the drought in all reaches but intra-reach variation in temporal patterns occurred in both S and in the most abundant species found. Thus, major weather events are associated with temporal changes whose patterns differ on both small and large spatial scales. Consequently, the results from fixed-factor sampling designs, which are widely used, may be unrepresentative of other areas. Unfortunately, the alternative approach of stratified random sampling will probably be both prohibitively expensive and difficult to implement in the complex estuarine benthic habitat. Further, short-term studies will probably be grossly unrepresentative of natural temporal variation. Attempts to reduce expenses by using only one or two abundant species as characterising communities or as indicators of physicochemical conditions may be unreliable because of variation in both time and space in dominant species and the lack of pollution-response knowledge for local species.

Evaluation of in situ Enclosures for Larval Fish Studies

Two in situ enclosure designs intended for use in larval fish studies were evaluated for their capability to reproduce and track the physical properties of the surrounding water and to maintain the behavioral characteristics of enclosed organisms. The enclosures, which were constructed of porous material, allowed near instantaneous response to natural variations in temperature, salinity, and dissolved oxygen at all depths. Phytoplankton biomass inside the enclosures was less variable than that observed outside and its size composition was related to the porosity of the material used. Particle sinking rates inside the enclosures were much lower than those previously reported for plastic bags, suggesting a higher degree of turbulence in our enclosures. Newly hatched larval capelin (Mallotus villosus) and Zooplankton stocked into the enclosures exhibited diel migration of amplitude similar to that observed in the field. Zooplankton were more homogeneously distributed than fish larvae although heterogeneity decreased at night for both taxa. Low cost, ease of handling, environmental reproducibility, and quality of replication provided by the enclosures make them particularly appropriate for replicated experimental studies of the interactions between larval fishes, their predators, and prey.

Differential temperature sensitivity of two cladoceran species to resource variation during a blue-green algal bloom

The sensitivity of life-table parameters of two cladoceran zooplankton to slight, natural variations in temperature was determined during the onset of a midsummer blue-green algal bloom in a large turbid reservoir (Lake Texoma, Oklahoma, Texas). Prior to the onset of blue-green algae, cohorts of Ceriodaphnia lacustris incubated at ambient epilimnion temperatures (27–30 °C) had higher individual somatic and population growth rates, an earlier age at first reproduction, and shorter life-spans than cohorts incubated at a constant 25 °C. As blue-green algae became abundant, Ceriodaphnia growth rates were reduced more dramatically at ambient temperatures than at 25 °C, suggesting that a temperature–resource interaction was important to determination of somatic growth rate, age of first reproduction, and population growth rate. Ceriodaphnia populations declined in Lake Texoma as blue-green algae became abundant. Diaphanosoma leuchtenbergianum, which was abundant throughout the period of blue-green algal dominance, did not show the temperature–resource interaction found for Ceriodaphnia. Temperature–resource interactions have been hypothesized to determine seasonal change in zooplankton community structure; this study provides experimental evidence of demographic consequences in natural populations of one kind of common temperature–resource interaction.

Long-term changes in some benthic species in the Firth of Clyde, with particular reference to Tellina tenuis da Costa

SynopisPresent knowledge of long-term changes in benthic species in the Firth of Clyde is reviewed.Recent work on the annual variations in seasonal cycles of the sand-dwelling bivalve Tellina tenuis da Costa shows some correlations with natural and man-made variations in seawater temperature. Between 1973 and 1984 inclusive good settlements of young occurred on the two beaches examined in the autumns of years when higher mean seawater temperatures occurred in June and July. The implications are discussed in relation to cycles of climatic change. In general, settlements at Hunterston, a thermally enriched area, were considerably greater than at Kames Bay, a site affected only by natural temperature changes. However, T. tenuis at Kames Bay grew to much larger maximum sizes than at Hunterston, except in 1979, when Hunterston animals were larger. The possible interactions of food availability and the modifying effects of heated discharges are discussed.Earlier results by Dr A. C. Stephen between 1926 and 1951 are reassessed in the light of present knowledge.

Number of kernels in wheat crops and the influence of solar radiation and temperature

SUMMARYThe number of kernels per m2 (K) in well managed and watered wheat crops was studied using results of experiments in Mexico and Australia in which short spring wheat cultivars were subjected to independent variation in radiation, largely via artificial shading, and in temperature. Also crops subjected to differences in weather (year), sowing date and location within Mexico, revealed responses to the natural and simultaneous variation which occurs in radiation and temperature. Responses in K were interpreted in terms of spike dry weight at anthesis (g/m2) and number of kernels per unit of spike weight.K was linearly and most closely related to incident solar radiation in the 30 days or so preceding anthesis, herein termed the spike growth period; for the cultivar Yecora 70 with full ground cover the slope was 19 kernels/MJ. This response seemed largely due to a linear response of crop growth rate to intercepted solar radiation. The proportion of dry weight increase partitioned to the spike increased somewhat with reduced radiation. Also increasing temperature in the range 14–22 °C during this period reduced K (slope approximately 4% per CC at 15 °C). The cause appeared to be lower spike dry weight due to accelerated development. The number of kernels per unit spike weight at anthesis was little affected by radiation or temperature, and averaged 78±2/g for the cultivar Yecora 70.With natural variation in radiation and temperature, K was closely and linearly correlated with the ratio of mean daily incident or intercepted radiation to mean temperature above 4·5 °C in the 30 days preceding anthesis. As this ratio, termed the photothermal quotient, increased from 0·5 to 2·0 MJ/m2/day/degree, K increased from 70 to 196 × 102/m2. These responses of K to weather, sowing date and location were closely associated with variation in spike dry weight.It was concluded that the ratio of solar radiation to temperature could be very useful for estimating K in wheat crop models. Also the analysis of K determination in terms of spike dry weight appeared promising, and suggests that wheat physiologists should place greater emphasis on the growth period immediately before anthesis.

An Application of Ecological Modelling: Impact of Thermal Effluent on a Smallmouth Bass Population

Abstract We report on a 20-year integrated field, laboratory, and simulation study of the impact of thermal effluent from a nuclear power plant on the smallmouth bass Micropterus dolomieui population in Baie du Dore, Lake Huron. A quantitative model was constructed to forecast the range of likely effects of the plant on the population. The model was based on the findings of 50 years of basic research on smallmouth bass ecology in Ontario and on 15 years of environmental and biological data collected at Baie du Dore before the power plant became operational. The model embodies detailed descriptions of both the natural variation in water temperature at Baie du Dore, and the mechanisms whereby variations in temperature generate variations in cohort strength. Five years of monitoring data, collected after the plant became operational, were used to evaluate the forecasts of the model. Observed effects on timing of spawning and individual growth were generally within the range defined by the forecasts. The ther...

Phytoplankton in marine surface microlayers

Surface microlayer phytoplankton populations were monitored to assess natural temporal and spatial variability. Microlayer samples (collected using glass plates) were compared with reference bulkwater samples over hourly, diel, and seasonal time periods on spatial scales of ~0.5 to 20 km. Microlayers were consistently depleted in chlorophyll a relative to bulkwaters in diurnal samples. Depletions had no seasonal patterns and were not influenced by dissolved nutrients or organic materials or by varying wave states. A diel pattern, with nocturnal enrichments, indicated photoinhibition of microlayer microbiota. Exceptions to these patterns occurred in naturally slicked surfaces which generally had large chlorophyll a enrichments. Disparate descriptions of microlayer phytoplankton populations in previous work probably resulted from (1) use of different sampling methods, (2) geographic variations in bulkwater phytoplankton biomass, (3) low numbers of samples, and (4) uncertain identification or definition of slick conditions.

Evolution of single characters in the Jurassic ammonite Kosmoceras

The classic biometrical study of phyletic evolution in Kosmoceras (Brinkmann 1929) is evaluated using unpublished raw data provided by Professor Brinkmann. Most morphological characters show statistically significant changes over time yet it is difficult to provide an unequivocal biological interpretation for these changes. In a few cases, runs tests indicate that evolution was nonrandom in the sense that fewer reversals in the direction of evolution occurred than would be predicted from a null hypothesis based on a random walk. These cases suggest persistence of natural selection regimes for fairly long periods of time. In other cases, and with other kinds of testing, the random walk model cannot be rejected although failure to reject the hypothesis does not justify its acceptance! Thus, the contribution of random factors (either genetic drift or selection in a randomly changing environment) cannot be assessed with confidence. It is problematical also whether the Kosmoceras series represent significant evolution by phyletic gradualism or just the natural temporal variation that characterizes stasis (sensu Eldredge and Gould 1972).

Determination of heat transfer coefficients in steam turbines

A method for the determination of heat transfer coefficients is described which is particularly suited for measurements inside steam turbine cylinders and buckets. The heat transfer coefficients are derived from the temperature frequency characteristics of the walls. Correlations are made between the time-dependent fluid temperature and the corresponding signal received by a detector just below the wall's surface. The natural stochastic temperature variation within a steam turbine can be used as test signal. Measurements in a 2 Megawatt steam turbine demonstrate, that the signal's power density is sufficiently high and the attenuation low within the important frequency range of 1/s ⩽ ω⩽ 10/s. The experimental verification of the method in a steam tunnel showed good results.

Photosynthetic Acclimation to Temperature in the Desert Shrub, Larrea divaricata

The response of photosynthetic electron transport and light-harvesting efficiency to high temperatures was studied in the desert shrub Larrea divaricata Cav. Plants were grown at day/night temperatures of 20/15, 32/25, or 45/33 C in rough approximation of natural seasonal temperature variations. The process of acclimation to high temperatures involves an enhancement of the stability of the interactions between the light-harvesting pigments and the photosystem reaction centers. As temperature is increased, the heat-induced dissociation of these complexes results in a decrease in the quantum yield of electron transport at limiting light intensity, followed by a loss of electron transport activity at rate-saturating light intensity. The decreased quantum yield can be attributed to a block of excitation energy transfer from chlorophyll b to chlorophyll a, and changes in the distribution of the excitation energy between photosystems II and I. The block of excitation energy transfer is characterized by a loss of the effectiveness of 480 nm light (absorbed primarily by chlorophyll b) to drive protochemical processes, as well as fluorescence emission by chlorophyll b.

Natural stream temperature variations in a catchment

In order to establish water temperature criteria or limits for reaches of streams downstream from thermal discharges, a knowledge of the natural water temperature is necessary. To overcome the situation where no historical records are available, a simple method of predicting natural water temperatures in a catchment is presented. The only data required for computation are the site altitude and the air temperature at a station in the catchment or the natural water temperature in an upstream reach or other tributary in the catchment. The time scale of the predicted water temperature is a function of the frequency of measurement of the independent variables.

Reproductive Response of Geese to a Cool Environment

Geese kept at 4.5° C. trended toward greater fertility than geese housed but subjected to natural temperature variations. This trend became highly significant after April 3.

One‐week summer program at MIT

A special one‐week summer program on Engineering Aspects of Heat Disposal from Power Generation will be held at the MIT Parsons Laboratory for Water Resources and Hydrodynamics June 28–July 2, 1971. This special summer program is designed for engineers, ecologists, educators, members of the utility industry, and regulatory agencies who are concerned with the problem of heat disposal associated with fossil and nuclear power generation. Emphasis will be placed on the use of predictive techniques in assessing the feasibility of alternative methods of heat disposal. Topics will include: once‐through cooling processes in lakes, rivers, estuaries, and the ocean; natural temperature variations, cooling ponds, cooling towers, beneficial uses, management models, and the impact of thermal pollution control standards. The program is under the direction of Donald R.F. Harleman.

TEMPERATURE CHANGE AND GAS EXCHANGE IN NOVA SCOTIA AND GEORGIA SALT‐MARSH MUDS1

Variations in oxygen uptake with variations in temperature were measured on undisturbed salt‐marsh muds taken from Georgia, the Bay of Fundy, and the eastern shore of Nova Scotia. Mud temperatures were measured in the marsh. Natural temperature variations were about twice as great in Georgia as in Nova Scotia. Q10 values for respiration determined in any one season varied from 1 to 4, tending to be lower in southern marshes and marshes located nearer low water level. In all marshes, seasonal changes of mud respiration were correlated with changes in energy supply and with temperature. Considering periods of days or weeks rather than months, the southern mud organisms show more stability under conditions of changing temperature than the northern ones. This may be due to better stirring by large animals and the absence of freezing in the south.