Energy Budget Method Research Articles

Hydrogeologic Controls on the Groundwater Interactions with an Acidic Lake in Karst Terrain, Lake Barco, Florida

Transient groundwater interactions and lake stage were simulated for Lake Barco, an acidic seepage lake in the mantled karst of north central Florida. Karst subsidence features affected groundwater flow patterns in the basin and groundwater fluxes to and from the lake. Subsidence features peripheral to the lake intercepted potential groundwater inflow and increased leakage from the shallow perimeter of the lake bed. Simulated groundwater fluxes were checked against net groundwater flow derived from a detailed lake hydrologic budget with short‐term lake evaporation computed by the energy budget method. Discrepancies between modeled and budget‐derived net groundwater flows indicated that the model underestimated groundwater inflow, possibly contributed to by transient water table mounding near the lake. Recharge from rainfall reduced lake leakage by 10 to 15 times more than it increased groundwater inflow. As a result of the karst setting, the contributing groundwater basin to the lake was 2.4 ha for simulated average rainfall conditions, compared to the topographically derived drainage basin area of 81 ha. Short groundwater inflow path lines and rapid travel times limit the contribution of acid‐neutralizing solutes from the basin, making Lake Barco susceptible to increased acidification by acid rain.

A community model of ciliateTetrahymena and bacteriaE. coli: Part I. Individual-based models ofTetrahymena andE. coli populations

The dynamics of a microbial community consisting of a eucaryotic ciliateTetrahymena pyriformis and procaryoticEscherichia coli in a batch culture is explored by employing an individual-based approach. In this portion of the article, Part I, population models are presented. Because both models are individual-based, models of individual organisms are developed prior to construction of the population models. The individual models use an energy budget method in which growth depends on energy gain from feeding and energy sinks such as maintenance and reproduction. These models are not limited by simplifying assumptions about constant yield, constant energy sinks and Monod growth kinetics as are traditional models of microbal organisms. Population models are generated from individual models by creating distinct individual types and assigning to each type the number of real individuals they represent. A population is a compilation of individual types that vary in a phase of cell cycle and physiological parameters such as filtering rate for ciliates and maximum anabolic rate for bacteria. An advantage of the developed models is that they realistically describe the growth of the individual cells feeding on resource which varies in density and composition. Part II, the core of the project, integrates models into a dynamic microbial community and provides model analysis based upon available data.

A community model of ciliate Tetrahymena and bacteria E. coli: Part I. Individual-based models of Tetrahymena and E. coli populations

The dynamics of a microbial community consisting of a eucaryotic ciliate Tetrahymena pyriformis and procaryotic Escherichia coli in a batch culture is explored by employing an individual-based approach. In this portion of the article, Part I, population models are presented. Because both models are individual-based, models of individual organisms are developed prior to construction of the population models. The individual models use an energy budget method in which growth depends on energy gain from feeding and energy sinks such as maintenance and reproduction. These models are not limited by simplifying assumptions about constant yield, constant energy sinks and Monod growth kinetics as are traditional models of microbal organisms. Population models are generated from individual models by creating distinct individual types and assigning to each type the number of real individuals they represent. A population is a compilation of individual types that vary in a phase of cell cycle and physiological parameters such as filtering rate for ciliates and maximum anabolic rate for bacteria. An advantage of the developed models is that they realistically describe the growth of the individual cells feeding on resource which varies in density and composition. Part II, the core of the project, integrates models into a dynamic microbial community and provides model analysis based upon available data.

Comparison of areally averaged turbulent fluxes over non-homogeneous terrain: Results from the EFEDA-field experiment

In June 1991 the EFEDA-field experiment (ECHIVAL Field Experiment in a Desertification-Threatened Area) was carried out in the Spanish province Castilla-La Mancha, to improve the understanding of the interactions between the soil, the vegetation and the atmosphere. Here results of energy balance studies at the Barrax site are given, one of the three intensively studied experimental sites within Castilla-La Mancha. This area is characterized by a large fraction of irrigated fields (40%) while the remaining 60% was fallow land at the end of June 1991. The energy balances over these two characteristic land-use classes totally differ. While for the irrigated fields the evapotranspiration is dominant, for the non-irrigated fields the sensible and the soil heat fluxes dominate and the latent heat flux is nearly negligible. In order to achieve areally averaged turbulent fluxes, surface, SODAR and aircraft data have been used. Comparing the surface fluxes from all three facilities, it can be found that: The sensible heat flux estimation from SODAR (Σw-method) gives reliable results when a calibration of Σw is done with another independent system (e.g. aircraft). Aircraft measurements in conjunction with energy budget methods yield surface fluxes of sensible heat, which are about 20% lower than the areally averaged values calculated by the surface measurements. The areally averaged latent heat fluxes from aircraft and surface measurements agree better than the sensible heat fluxes.

Estimation of the atmospheric surface layer parameters and comparison with SODAR observations

Similarity relationships for the atmospheric surface layer are used to estimate wind and turbulence parameters and are compared against the data from a three-axis monostatic SODAR. The daytime surface heat flux is estimated using energy budget method which takes as input the routinely measured wind, temperature and cloud cover. Heat flux is also derived from SODAR mixing height and the vertical velocity variance during daytime convective conditions. Data for a period of five clear sky days were collected for the present study. The energy budget is tuned using the SODAR inferred heat flux values by adjusting the Bowen ratio which gives better agreement when set to 0.5. Computed values of the vertical velocity variances agree fairly well with those computed using similarity relation during convective conditions while during nighttimes SODAR overestimates them. Similarly, the wind profile computed using flux-profile relations from 50 m up to 250 m height shows closer agreement with the SODAR observation during daytime conditions. However, direct measurements of the flux using in situ sensors are required for better evaluation of the SODAR inference scheme.

Sensitivity of Reservoir-Yield Estimates to Model Time Step Surface-Moisture Fluxes

Determining the yield from a storage reservoir typically requires estimating the contribution to storage by precipitation and the loss of water by free-surface evaporation over time, among other factors. Due to the difficulty in estimating reservoir evaporation by accepted energy budget methods, it is useful to determine the sensitivity of estimated reservoir yield to both factors. First, an experiment comparing storage-yield curves generated by a daily, monthly, and annual time-step mass-balance reservoir model is performed. The monthly time-step model's estimated yield is slightly larger than that estimated using a daily time-step model, and the error becomes smaller as the storage capacity gets larger. In a second experiment, comparisons are made for yield estimates using different combinations of precipitation and potential evaporation time series and/or mean monthly values. Assuming that the best reservoir yield is determined using a year-round, open-water, potential-evaporation time series, fixed av...

Evaluation of 11 Equations for Determining Evaporation for a Small Lake in the North Central United States

Eleven equations for calculating evaporation were compared with evaporation determined by the energy budget method for Williams Lake, Minnesota. Data were obtained from instruments on a raft, on land near the lake, and at a weather station 60 km south of the lake. The comparisons were based on monthly values for the open‐water periods of 5 years, a total of 22 months. A modified DeBruin‐Keijman, Priestley‐Taylor, and a modified Penman equation resulted in monthly evaporation values that agreed most closely with energy budget values. To use these equations, net radiation, air temperature, wind speed, and relative humidity need to be measured near the lake. In addition, thermal surveys need to be made to determine change in heat stored in the lake. If data from distant climate stations are the only data available, and they include solar radiation, the Jensen‐Haise and Makkink equations resulted in monthly evaporation values that agreed reasonably well with energy budget values.

Effects of Unilateral Eyestalk Ablation on Growth in Juvenile Blue Crabs Portunus pelagicus(L.) (Crustacea: Decapoda: Portunidae)

The effects of unilateral eyestalk ablation on growth in Portunus pelagicus were investigated using the physiological energy budget method and checked by means of actual growth performance and body condition indices. Unilateral eyestalk ablation significantly increased absorption efficiency and dry meat yield (% of dry weight) by 12.3% and 332%, respectively. It also accelerated molting by 3.4 days. The physiological mechanisms of growth enhancement are increased absorption efficiency and possi­bly also increased feeding rate and decreased energetic loss to carapace. The increased absorption efficiency, standard ammonia excretion rate, and low O:N ratio in ablated crabs indicate the need to determine optimal lipid and protein levels in the diet. Dry meat yield is suggested as a better gauge than whole wet weight for assessing growth response to eyestalk ablation since the reducing effect of ablation on carapace size tends to mask its weight gain enhancement effect.

Comparison of energy-budget evaporation losses from two morphometrically different Florida seepage lakes

Evaporation was computed by the energy-budget method for two north Florida lakes with similar surface areas but different depths, for the period May 1989 to December 1990. Lake Barco, in north-central Florida, is shallow, with an average depth of 3 m; Lake Five-O, in the Florida panhandle, is considerably deeper, with an average depth of 9.5 m. As a result, the thermal regime and seasonal evaporation rates of the lakes are different. Evaporation from the shallower lake was higher than that from the deeper lake in the winter and spring. In the late summer and autumn, however, the situation is reversed. Evaporation from the shallow lake is directly related to the amount of incoming shortwave radiation because of its limited ability to store energy. The lag in evaporation at the deeper lake is a function of the greater amount of heat that it seasonally stores and releases. The difference in annual evaporation between Lake Barco (151 cm year −1) and Lake Five-O (128 cm year −1) is related to differences in regional climatic conditions between the two sites. Additionally, higher than normal evaporation rates at the two lakes are probably related to drought conditions experienced in north Florida during 1990, which resulted in higher temperatures and more incoming radiation. Monthly evaporation at Lake Barco could usually be estimated within 10% of the energy-budget evaporation using a constant pan coefficient. This lake may be representative of other shallow lakes that do not store considerable heat. Monthly evaporation at Lake Five-O, however, could not be estimated accurately by using an annual pan coefficient because of the large seasonal influence of change in stored heat. Monthly mass-transfer evaporation compared well with energy-budget evaporation at Lake Barco, but did not compare well at Lake Five-O. These errors may also be associated with changes in heat storage. Thus, the thermal regime of the lake must be considered to estimate accurately the seasonal evaporation rates from a deep lake.

Energy transports by ocean and atmosphere based on an entropy extremum principle. Part II: Two-dimensional transports

The maximum entropy production (MEP) principle used in Part J has been extended to separate the two-dimensional required energy transports determined from Nimbus 7 satellite net radiation measurements into atmospheric and oceanic components. In terms of the meridional component of the ocean transport vectors, results show northward ocean transports throughout the entire Atlantic ocean from southern hemisphere high latitudes to northern hemisphere polar regions, southward transports throughout the entire Indian Ocean, and poleward transports separated at approximately 10°S in the Pacific Ocean. The ocean transport patterns are consistent with well-known features concerning heat transport within the three ocean basins. However, uncertainty remains in the magnitudes of the transports. Because of the large remaining discrepancies between published estimates based on direct measurements and indirect estimates derived from energy budget methods, assessing the accuracy of the magnitudes is difficult, although there is evidence that the limited model resolution leads to synergistic biases in the North Atlantic and North Pacific. In terms of the crossmeridional energy transport component, results suggest that most of the net energy transfer in the tropics takes place within the ocean. In the southern hemisphere high latitudes, the Pacific and Indian Oceans export heat cross-meridionally to the Atlantic Ocean through the passages below Cape Horn and the Cape of Good Hope, although the magnitudes of these inter-ocean heat exchanges are small. Another important aspect of the southern hemisphere results is that poleward transports are dominated by the atmospheric component with strong zonal asymmetry. By contrast, in the northern hemisphere, atmospheric transports over the ocean are generally weaker than the corresponding southern hemisphere terms, indicating that the northern hemisphere oceans are relatively more effective in transferring heat poleward. Finally, poleward atmospheric transports over the continental areas exceed those over the ocean at equivalent latitudes as a result of the generally greater energy deficits over the land areas.

Evaluation of the Energy Budget Method of determining evaporation at Williams Lake, Minnesota, using alternative instrumentation and study approaches

Best estimates of evaporation at Williams Lake, north central Minnesota, were determined by the energy budget method using optimum sensors and optimum placement of sensors. These best estimates are compared with estimates derived from using substitute data to determine the effect of using less accurate sensors, simpler methods, or remotely measured data. Calculations were made for approximately biweekly periods during five open water seasons. For most of the data substitutions that affected the Bowen ratio, new values of evaporation differed little from best estimates. The three data substitution methods that caused the largest deviations from the best evaporation estimates were (1) using changes in the daily average surface water temperature as an indicator of the lake heat storage term, (2) using shortwave radiation, air temperature, and atmospheric vapor pressure data from a site 110 km away, and (3) using an analog surface water temperature probe. Recalculations based on these data substitutions resulted in differences from the best estimates as much as 89%, 21%, and 10%, respectively. The data substitution method that provided evaporation values that most closely matched the best estimates was measurement of the lake heat storage term at one location in the lake, rather than at 16 locations. Evaporation values resulting from this substitution method usually were within 2% of the best estimates.

Evaporation from Lake Kinneret: 1. Eddy correlation system measurements and energy budget estimates

Evaporation rates over Lake Kinneret were directly and continuously measured by means of the eddy correlation system (ECS) for the relatively long periods of 20 and 44 days at the beginning and end of the summer (first and second periods), respectively. Results clearly show that wind speed and stability of thermal stratification over the water surface strongly affect evaporation from the lake. Consequently, large differences in measured daily evaporation rates were apparent during both periods. Evaporation rates, estimated by the energy budget method (EBM) were compared with the corresponding values measured directly by the ECS. Large differences were found between the estimated hourly evaporation rates and the measured ones, in both the values and the timing of maximal rates. In addition, the EBM calculated negative nocturnal evaporation rates, while the ECS measured positive values. Differences between estimated and measured evaporation rates monitored on a daily basis were also noted. The differences were larger for the first period, characterized by sharav events denoting climatic instability. High evaporation rates resulting from strong winds were not depicted by EBM estimates. The distributions of hourly evaporation rates over a 24 hour period or of the daily rates over an entire period as estimated by the EBM were very similar to those of net radiation, while corresponding distributions resulting from ECS measurements were very similar to those of wind speed. The daily average evaporation rate for the first period, calculated by the EBM, was smaller than the corresponding value resulting from ECS measurements. When applied on a hourly basis, the EBM gave a much more similar estimate. For the second period, there were no significant differences between the daily average based on the computed values (for both daily and hourly intervals) and the corresponding average based on the measured ones.

Energy budget comparison of snowmelt rates in a deciduous forest and an open site

Daily snowmelt rates at a leafless deciduous forest site were 40–85% of those at an open site. Reduced snowmelt rates were caused by a difference in meteorological conditions at the forested site. Solar radiation, net radiation and wind speed were especially reduced in the forest, and relationships between them at the two sites were represented by linear functions. Snowmelt rates at the two sites could be predicted by an energy budget method, and net radiation was the major component in the snowmelt energy at both sites. Differences between snowmelt rates at the two sites were due to net radiation differences over many days, but dependency on net radiation at both sites was reduced under particular meteorological conditions. Parameteric analysis under fixed meteorological conditions indicates that this dependency is changed by wind speed, temperature and humidity, because wind speed is reduced in the forest and decrease of turbulent heat exchange in the forest will be notable under strong wind conditions.

Energy budget comparison of snowmelt rates in a deciduous forest and an open site

Daily snowmelt rates at a leafless deciduous forest site were 40–85% of those at an open site. Reduced snowmelt rates were caused by a difference in meteorological conditions at the forested site. Solar radiation, net radiation and wind speed were especially reduced in the forest, and relationships between them at the two sites were represented by linear functions. Snowmelt rates at the two sites could be predicted by an energy budget method, and net radiation was the major component in the snowmelt energy at both sites. Differences between snowmelt rates at the two sites were due to net radiation differences over many days, but dependency on net radiation at both sites was reduced under particular meteorological conditions. Parameteric analysis under fixed meteorological conditions indicates that this dependency is changed by wind speed, temperature and humidity, because wind speed is reduced in the forest and decrease of turbulent heat exchange in the forest will be notable under strong wind conditions.

Regional surface fluxes under nonuniform soil moisture conditions during drying

The fifth intensive field campaign of FIFE (First ISLSCP Field Experiment (International Satellite Land Surface Climatology Project)) was conducted in northeastern Kansas during late summer 1989, in order to study the dry down of a surface with prairie vegetation prior to senescence and dormancy. As precipitation became sparse and rare, the surface developed nonuniform features at the scales of the rainfall events. Nevertheless, lower boundary layer measurements used together with remotely sensed surface temperatures on the basis of Monin‐Obukhov similarity allowed the estimation of the flux of sensible heat for a region with characteristic dimensions of 104 m. In contrast, under these conditions it was difficult to aggregate an array of local flux measurements into a true regional mean. On account of the same problem in the aggregation of local measurements of net radiation and ground heat flux, the reliability of the estimation of regional evaporation by the energy budget method was hard to assess.

Energy budget evaporation from Williams Lake: A closed lake in north central Minnesota

Evaporation from Williams Lake, computed by the energy budget method for the five open‐water seasons of 1982–1986, varied from a maximum seasonal rate of 0.282 cm/d in 1983 to a minimum seasonal rate of 0.219 cm/d in 1982. The pattern of monthly values of evaporation is not consistent from year to year. The normally expected pattern of low evaporation values in May, followed by increasing values in June to maximum values in July is true for only 3 of the 5 years. Comparison of annual evaporation calculated by the energy budget and mass transfer methods indicates that energy budget values varied from 13% greater to 11% less than mass transfer values. Furthermore, there is no seasonal bias in the pattern. Large differences exist in the magnitude of energy fluxes to and from Williams Lake. By far the greatest energy fluxes, having magnitudes of hundreds of watts per square meter, are incoming solar radiation, incoming atmospheric radiation, and outgoing long‐wave radiation emitted by the lake water. The least energy fluxes are related to advection, which generally have magnitudes less than 5 W m−2.

A Method for Controlling the Feeding Behaviour of Aquatic Birds: Heart Rate and Oxygen Consumption During Dives of Different Duration

ABSTRACT Tufted ducks, Aythya fuligula, were trained to dive for different durations in shallow tanks using a computer-controlled system of lights. The birds were rewarded with food for a correct response, i.e. performing a dive of the required duration. When dive durations (td) elicited by the system were longer than the durations required, the extra time was spent feeding. As the required duration was increased, so the time spent feeding decreased, and the required and actual dive durations approached equality. This occurred at approximately 40 s, although some birds did perform dives of up to 45 s. Heart rate (FH) and oxygen consumption () were measured from the birds during voluntary diving using an implanted radiotransmitter and respirometry, respectively. The oxygen consumption during submersion decreased with increasing mean td, and may reflect a reduction in aerobic metabolism as a dive progressed, possibly as a result of reduced buoyancy or through a gradual switch to anaerobic metabolism. Over a total dive cycle (the time spent submerged plus that spent on the surface between dives), FH proved to be a very good predictor of , with an error of only +7.9%. This compares favourably with other methods used to determine the energy expenditures of animals, e.g. the doubly labelled water and the time energy budget methods, and shows that the electronic acquisition of fH could be a useful tool for estimating the energy usage of free-living, aquatic birds.

Atmospheric surface layer characteristics with MONTBLEX data

Data obtained from the 30m high MONTBLEX tower installed at the Indian Institute of Technology, Kharagpur are described. Data on wind speed and direction, temperature and humidity were recorded during the first week of July 1989 at six levels on the tower. They indicate some of the atmospheric surface layer characteristics. Using two levels of tower data involving wind speed and temperature a profile method was used for computing the surface fluxes of heat and momentum. A method for calculating the surface roughness length using the data was also used to obtain the vertical windspeed profile. The computed wind profile was compared with observations, while the surface roughness length was compared with values obtained by a least square fit. The computed surface fluxes were compared with theoretical values obtained by an energy budget method which uses only wind data at one level. The agreement was reasonably good.

A comparison of short-term measurements of lake evaporation using eddy correlation and energy budget methods

Concurrent short-term measurements of evaporation from a shallow lake, using eddy correlation and energy budget methods, indicate that sensible and latent heat flux between lake and atmosphere, and energy storage in the lake, may vary considerably across the lake. Measuring net radiation with a net radiometer on the lake appeared to be more accurate than measuring incoming radiation nearby and modeling outgoing radiation. Short-term agreement between the two evaporation measurements was obtained by using an energy storage term that was weighted to account for the area-of-influence of the eddy correlation sensors. Relatively short bursts of evaporation were indicated by the eddy correlation sensors shortly after midnight on two of three occasions.

Regional Surface Fluxes From Remotely Sensed Skin Temperature and Lower Boundary Layer Measurements

During First International Satellite Land Surface Climatology Project Field Experiment in north‐eastern Kansas, surface temperature was measured by infrared radiation thermometers at some 12 stations spread over the 15 × 15 km experimental area. These data, together with wind and temperature profiles in the unstable atmospheric boundary layer measured by means of radiosondes, were analyzed within the framework of Monin‐Obukhov similarity. The radiometric scalar roughness corresponding to the radiometric surface temperature was found to increase as the season progressed; for the spring campaign the mean value was zoh,r = 4.56 × 10−7 m and for the fall zoh, r = 1.01 × 10 −2 m. The radiometric scalar roughness could also be expressed as a function of solar elevation and to a lesser extent, of canopy height or leaf area index. For an elevation range 10° ≤ α ≤ 75° the regression equation is zoh,r = exp [−0.735 ‐ 3.61 tan (α)]. With this function good agreement (r = 0.87) was obtained between the profile‐derived regional surface flux of sensible heat and the mean flux measured independently at ground‐based stations under unstable conditions. Similarly, regional values of evaporation, obtained by means of the energy budget method from these sensible heat flux estimates, were in good agreement (r = 0.96).