Energy Budget Components Research Articles

Role Of Energy Budget Components On Snow Ablation From A Mid-Latitude Prairie Snowpack

This work considers what aspects of the surface energy budget were most important for the development of rapid snow melt during the spring of 1997 in the Red River Valley of North Dakota and Minnesota. The rapid snow melt of an exceptionally large snowpack that season led to catastrophic flooding. We use this event as a case study in order to better understand what meteorological forcings are most important with regard to rapid melting of a large winter snowpack in a mid-latitude prairie region. The SNTHERM model was used as a means to estimate snow melt flux and energy budget components. It was found that the net radiation balance was the dominant factor in snow melt throughout the winter months until late March, but ablation rates were small due to the extremely low temperatures. As warm air masses began to traverse the region in late March, the snow melt flux began to increase significantly due to the influences of sensible and latent heat fluxes on the surface of the snowpack. After the passing of a strong late-season blizzard, temperature and humidity increased rapidly with a corresponding increase in wind speed. The sensible heat flux then dominated as temperatures rose well above freezing, melting off the snowpack extremely quickly.

Continental heat gain in the global climate system

Recent estimates have shown the heat gained by the ocean, atmosphere, and cryosphere as 18.2 · 1022 J, 6.6 · 1021 J, and 8.1 · 1021 J, respectively over the past half‐century. However, the heat gain of the lithosphere via a heat flux across the solid surface of the continents (29% of the Earth's surface) has not been addressed. Here we calculate that component of Earth's changing energy budget, using ground‐surface temperature reconstructions for the continents. In the last half‐century there was an average flux of 39.1 mW m−2 across the land surface into the subsurface, leading to 9.1 · 1021 J absorbed by the ground. The heat inputs during the last half‐century into all the major components of the climate system — atmosphere, ocean, cryosphere, lithosphere‐reinforce the conclusion that the warming during the interval has been global.

A high standard metabolic rate constrains juvenile growth

The allocation of energy to various components of an individual's energy budget is often viewed as a competitive process. As such, a tradeoff may exist between production (growth) and maintenance metabolism. One view of a potential tradeoff, termed "the principle of allocation", suggests that individuals with lower maintenance metabolic expenditures may have higher growth rates. To determine whether such a tradeoff exists, I analyzed the relationship between growth rate and maintenance metabolism of 225 juvenile snapping turtles housed in the laboratory. I measured growth from hatching to 6 months of age, and then measured oxygen consumption and calculated standard metabolic rate. Mean growth rate was 0.19 g d(-) and mean standard metabolic rate (SMR) was 1.41 kJ d(-). Maintenance metabolism and growth were negatively correlated after both were adjusted for body mass. The results support the "principle of allocation" theory: individuals with higher standard metabolic rates tended to have low growth rates.

Radiation and energy budget components over cropped surface and bare soil during LASPEX-97

Radiation and energy budget components over cropped surface and bare soil during LASPEX-97

A constrained algorithm for retrieval of stratocumulus cloud properties using solar radiation, microwave radiometer, and millimeter cloud radar data

Nonprecipitating liquid phase clouds of the planetary boundary layer are important components of the Earth's energy budget. Modern remote sensors are able to probe these clouds with increasing precision and detail, and extensive boundary layer cloud data sets are being generated at multiple sites around the world. In this paper we integrate several recent cloud property retrieval algorithms targeted at boundary layer stratocumulus clouds into a single framework that returns the vertical profile of microphysical properties. The new algorithm guarantees consistency among the radar reflectivity profile, the microwave radiometer‐derived liquid water path, and the surface solar flux transmission ratio. We demonstrate a 0.9 μm rootmean‐square difference and 0.89 correlation coefficient when results from the new approach are compared to aircraft‐observed volume mean cloud droplet radii. An additional stratocumulus case study observed at an Atmospheric Radiation Measurement site is briefly described.

The Influence of the Inclusion of Soil Freezing on Simulations by a Soil–Vegetation–Atmosphere Transfer Scheme

The interactions between the soil, biosphere, and atmosphere (ISBA) land surface parameterization scheme has been modified to include soil ice. The liquid water equivalent volumetric ice content is modeled using two reservoirs within the soil: a thin surface layer that directly affects the surface energy balance, and a deep soil layer. The freezing/drying, wetting/thawing analogy is used, and a description of the modifications to the ISBA force–restore scheme, in particular to the hydrological and thermal transfer coefficients, is presented. In addition, the ISBA surface/vegetation scheme is coupled to a multilayer explicit diffusion soil heat and mass transfer model in order to investigate the accuracy of the force–restore formalism soil freezing parameterization as compared with a higher-order scheme. An example of the influence of the inclusion of soil freezing in ISBA on predicted surface and soil temperatures and surface fluxes is examined using prescribed atmospheric forcing from a micrometeorological case study that includes freeze–thaw cycles. Surface temperature prediction is improved in comparison with the observed values, especially at night, primarily from the release of latent heat as the soil freezes. There is an improvement in the overall surface flux prediction, although for some specific periods there is increased error in the prediction of various components of the surface energy budget. Last, the simplified force–restore approach is found to produce surface flux and temperature predictions consistent with the higher-resolution model on typical numerical weather prediction model timescales (on the order of several days to two weeks) for this particular site.

The energy budget of captive Siberian hamsters, Phodopus sungorus, exposed to photoperiod changes: mass loss is caused by a voluntary decrease in food intake.

Unlike most nonhibernating small mammals, Siberian hamsters (Phodopus sungorus) undergo a pronounced mass loss, almost exclusively as white adipose tissues, in response to a switch from long- to short-photoperiod exposure. This mass loss can be caused by an increase in the rate of energy expenditure, a decrease in the rate of energy intake, or a decrease in assimilation efficiency. In order to determine how they relate to photoperiod-induced mass loss, we measured these energy budget components every 2 wk on 12 captive Siberian hamsters exposed to 8 wk of long photoperiod followed by 12 wk of short photoperiod. Body mass decreased shortly after short-photoperiod exposure. This was accompanied by an immediate decrease in the rate of energy intake and, after a 2-wk delay, by a decrease in the rate of energy expenditure. The overall cumulative decrease in energy intake (376 kJ) could account for the mass loss (249 kJ) observed during short-photoperiod exposure. Regression analyses indicated that only the rate of energy intake was significantly related to the rate of mass change. Therefore, we conclude that photoperiod-induced mass loss in Siberian hamsters is caused by a decrease in the rate of food intake, rather than by changes in energy expenditure or in assimilation efficiency.

Determination of surface heating by convective cloud systems in the central equatorial Pacific from surface and satellite measurements

The heating of the ocean surface by longwave radiation from convective clouds has been estimated using measurements from the Central Equatorial Pacific Experiment (CEPEX). The ratio of the surface longwave cloud forcing to the cloud radiative forcing on the total atmospheric column is parameterized by the ƒ factor. The ƒ factor is a measure of the partitioning of the cloud radiative effect between the surface and the troposphere. Estimates of the ƒ factor have been obtained by combining simultaneous observations from ship, aircraft, and satellite instruments. The cloud forcing near the ocean surface is determined from radiometers on board the National Oceanic and Atmospheric Administration P‐3 aircraft and the R/V John Vickers. The longwave cloud forcing at the top of the atmosphere has been estimated from data obtained from the Japanese Geostationary Meteorological Satellite GMS 4. A new method for estimating longwave fluxes from satellite narrowband radiances is described. The method is based upon calibrating the satellite radiances against narrowband and broadband infrared measurements from the high‐altitude NASA ER‐2 aircraft. The average value of ƒ derived from the surface and satellite observations of convective clouds is 0.15±0.02. The area‐mean top‐of‐atmosphere longwave forcing by convective clouds in the region 10°S–10°N, 160°E–160°W is 40 W/m2 during CEPEX. These results indicate that the surface longwave forcing by convective clouds was approximately 5 W/m2 in the central equatorial Pacific and that this forcing is the smallest radiative component of the surface energy budget.

Measuring and modelling the seasonal climatic regime of a temperate wooded wetland

This paper documents the performance of the organic soil version of the Canadian Land Surface Scheme (CLASS) in modelling the hydrology and energy balance of the Beverly Swamp, Southern Ontario. The hydrometeorological dataset used to assess model performance begins in the autumn of 1983 and spans 33 months, presenting the first multi‐year characterization of the area. The Beverly Swamp receives approximately 900 mm of precipitation per year, of which one third is lost to net runoff, and the remainder to evaporation. Vertical drainage at this site is impeded, due to the presence of a marl layer below the highly decomposed peat soil, at approximately 1‐m depth. This mixed‐forest wetland is unique among surfaces used for CLASS testing to date. Within CLASS, vertical drainage at the bottom of the soil profile is set to zero to represent the marl subsurface boundary. Preliminary runs have shown that after each melt period this produced ponded water on site which persisted from year to year. The inclusion of a simple lateral drainage function in CLASS simulated actual measured lateral surface flow, and effectively reproduced seasonal differences in water table position. Comparisons between measured and modelled diurnally averaged energy budget components taken from two summers indicate that there is a marked tendency for CLASS to underestimate latent heat flux (QE) by 29% of the observed values, the major cause of this disagreement being due to systematic error. Concurrent with this error is an overestimation of the magnitude of soil heat storage (QG), by a factor of seven, wherein the error is dominantly systematic. Modifications made to the canopy resistance parametrization, based on site measurements, resulted in improved model estimates of QE, reducing the underestimation to 12% of observed values, and changing the major cause of error from systematic to unsystematic in nature. The improvement in QE corresponded with a change in the prediction of sensible heat flux (QH). A tendency to overestimate QH by 20% of the observed values changed to an underestimation of QH by 14%, the error being unsystematic in each case. The modifications resulted in no significant change to either the magnitude or the nature of the error for QG. Modelled daily average temperatures for the third soil layer versus temperature measured at 1‐m depth (the centre of the layer) indicated that modelled values had more extreme minima and maxima, although some of this discrepancy could be attributable to the heterogeneous nature of the soil column, and the unavoidable use of point versus layer average temperatures. Discrepancies also exist between measured and modelled snow mass duration and the timing of melt for three consecutive winters. This suggests that further tests of CLASS, using winter season data, must be conducted before it can be determined if the model is able to correctly simulate snow accumulation and melt. Wintertime total albedo at this site was also poorly modelled during the fall and winter periods. Further test runs determined that this overestimation in total albedo was not contributing significantly to the lower modelled soil temperatures or to the persistence of the winter snowpack. The correspondence between modelled and observed data, particularly given the complexity of the canopy and surface at this study site, is adequate but suggests that further code testing and development initiatives should be directed towards improving the simulation of latent and soil heat fluxes, shortwave reflectivity, winter snowpack dynamics and surface and subsurface moisture transfers, which are especially important in wetland environments.

Growth parameters of deep-water decapod crustaceans in the Northwestern Mediterranean Sea: a comparative approach

Relative and absolute growth were studied in 17 species of deep-water decapod crustaceans, spanning nine families of six different infra-orders, in the Northwestern Mediterranean Sea. The overall maximum abundance of these species lay between 200 m and 750 m (i.e. upper- and mid-slope species). Relative and absolute growth rates were compared by contrasting the slopes of the size–weight relationships for the different species and calculating the von Bertalanffy growth-equation parameters asymptotic length (L ∞ ) and growth rate (k). The size–weight relationships differed significantly as function of the species' life habits. The results revealed a significant decrease in weight relative to size in mesopelagic species (which carry out diel vertical migrations), an almost isometric relationship between size and weight in the less mobile nektobenthic species, and a significant increase in weight relative to size in strictly benthic species. The mean allometric coefficient for each group increased significantly from mesopelagic to benthic species. However, no general trend was observed in the growth-performance index, Φ (an index used to compare absolute growth rates between species, as a function of habit and depth of maximum abundance for all species combined), suggesting that the deep-water decapod crustaceans studied have similar absolute growth rates. Nevertheless, comparison of growth-parameter and growth-performance index values within families did reveal differences. Mesopelagic species of the families Sergestoidae and Pasiphaeidae showed slightly increased growth rates with increasing depth of distribution. Nektobenthic species of the genus Plesionika followed a trend opposite to that shown by mesopelagic species, with a higher growth rate for the shallowest-dwelling species (P. heterocarpus) than the deepest-dwelling species (P. acanthonotus). Taking growth as one of the major components of an organism's energy budget, the growth rates for the decapod crustacean species in this study were significantly lower than those reported in the literature for shallow-water penaeid crustacean species (which are distributed in higher-temperature habitats than deep-water Mediterranean crustaceans) and higher than those reported for mesopelagic myctophid fish species. Hence, the well-defined growth trends shown by deep-water decapod crustacean species in the Northwestern Mediterranean Sea, compared to the less well-defined trends in the other taxa, is discussed in the framework of the overall dynamics of their ecosystem.

An evaluation of NCEP Eta model predictions of surface energy budget and cloud properties by comparison with measured ARM data

Time‐series output from the Eta forecast model of the National Weather Service's National Centers for Environmental Prediction was evaluated by comparison with measured values for a location in Oklahoma. The measured data were drawn from the archives of the Department of Energy's Atmospheric Radiation Measurement program for the southern Great Plains site. Surface energy budget components and cloud indicators were examined for the first half of 1997. Overall, the Eta surface energy budget was found to be nearly balanced, as intended by the model physics, except for one instance when light snowfall occurred in the spring. Despite this balance, an average 50 W m−2 excess in incoming solar radiation was found. Approximately half of this excess was attributed to deficient extinction of shortwave radiation by water vapor and aerosols in the model, while the remainder appeared to be due to cloud treatment errors. The excess shortwave flux was offset by a smaller negative bias in the downwelling infrared flux and the use of slightly high albedos, in addition to errors of lesser magnitude in the latent and sensible heat fluxes. The upwelling infrared flux and ground heat flux were closer to measured values. Ambiguity in the definition of a cloud as well as measurement limitations hindered the analysis of cloud prediction. However, a rough cloud comparison indicated that the Eta model has more difficulty predicting convection than the movement of large storm systems. In addition, cirrus clouds were predicted too frequently in the winter, while low and midlevel clouds were often missed in the spring. This study demonstrates that single‐point time‐series data can be used effectively both to ascertain the quality of model output and to investigate the treatment of individual physical processes within models.

A study on the partition of net radiation into heat fluxes on a dry asphalt surface

Variation of the energy budget components of a dry asphalt surface over an annual cycle is discussed based on the analysis of data collected from a micrometeorological road station near Vienna, in Austria. Net radiation ( R N) and ground heat flux ( G) are directly measured. Sensible heat flux ( H) for dry surface conditions is estimated as a residual of the surface energy balance. Throughout the year, ground heat flux is found to be of larger magnitude than that of the sensible heat flux. The partitioning of net radiation into ground and sensible heat fluxes are studied. Variation of G (and H) with R N showed hysteresis loop behaviour with anti-clockwise cycle (clockwise for H) during cooler periods and clockwise cycle (anti-clockwise for H) during warm periods. The coefficients of time-dependent Camuffo and Bernadi formulations relating the net radiation with the heat fluxes are estimated for different periods of the year.

Behavioral thermoregulation in the intertidal fish Girella laevifrons (kyphosidae): The effect of starvation

One of the key factors that determine an animal's distribution and abundance is environmental temperature. This factor affects all the components of an organism's energy budget and fitness. In this study, we tested the effect of water temperature and starvation on patterns of space use in the intertidal fish Girella laevifrons. We postulated that starved animals would select cold temperatures as a mechanism of energy conservation while fed animals would prefer higher temperatures as a mechanism to facilitate digestive processes. In a thermal gradient tank, fishes, irrespective of treatment (fed and starved), actively selected temperatures between 15 and 18°C. Starvation did not affect temperature selection, although it did alter the time and number of visits to thermal gradient extremes. Starved fishes stayed longer in, and visited the warmer temperatures of the gradient more frequently. In contrast, fed fishes stayed longer in, and visited cold temperatures more frequently. We discuss the ecological consequences of temperature selection and the possible relationship between water temperature, food selection and digestive processes.

Measurement of energy budget components during the International Rice Experiment (IREX) in Japan

A field study was conducted to measure the fluxes of energy budget components above a rice canopy in Okayama, Japan, from 5 to 16 August 1996. During this period, the canopy height was, on average, 0.72 m and the leaf area index was about 3.1. The study site was approximately 300 m × 300 m, and was surrounded by similar rice fields. Our footprint analysis indicated that > 90% of the measured flux (at a height of 2.2 m above the ground) was expected from within the nearest 300 m of upwind area. The closure of the energy budget was examined to ensure the data quality. Owing to poor thermal conductivity of the heat transducers, soil heat fluxes were corrected for the difference in the thermal conductivities of the paddy soil and the transducer. Eddy covariance fluxes were corrected for the effects of line averaging and the sensor separation. Latent heat flux was further corrected for the density fluctuations. The magnitudes of the total corrections were not small and amounted to up to 20% of the raw flux values. With these corrections the surface energy budget of a rice stand was closed within 1% under drained conditions and 5% under flooded conditions. The daily evapotranspiration (ET) rate was near the potential rate of open water evaporation and ranged from 4.2 to 5.8 mm d -1 . In terms of changes in crop water use with irrigation, no difference in ET rates was found between the drained and flooded conditions.

Measurement of energy budget components during the International Rice Experiment (IREX) in Japan

Measurement of energy budget components during the International Rice Experiment (IREX) in Japan

Comparison of Four Different Stomatal Resistance Schemes Using FIFE Data. Part II: Analysis of Terrestrial Biospheric–Atmospheric Interactions

Stomatal resistance (Rs) forms a pivotal component of the surface energy budget and of the terrestrial biosphere–atmosphere interactions. Using a statistical–graphical technique, the Rs-related interactions between different atmospheric and physiological variables are resolved explicitly from observations made during the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE). A similar analysis was undertaken for the Rs parameterization schemes, as used in the present models. Three physiological schemes (the Ball–Woodrow–Berry, Kim and Verma, and Jacobs) and one operational Jarvis-type scheme were evaluated in terms of their ability to replicate the terrestrial biosphere–atmosphere interactions. It was found that all of the Rs parameterization schemes have similar qualitative behavior for routine meteorological applications (without carbon assimilation). Compared to the observations, there was no significant difference found in employing either the relative humidity or the vapor pressure deficit as the humidity descriptor in the analysis. Overall, the relative humidity–based interactions were more linear than the vapor pressure deficit and hence could be considered more convenient in the scaling exercises. It was found that with high photosynthesis rates, all of the schemes had similar behavior. It was found with low assimilation rates, however, that the discrepancies and nonlinearity in the interactions, as well as the uncertainties, were exaggerated. Introduction of CO2 into the analysis created a different dimension to the problem. It was found that for CO2-based studies, the outcome had high uncertainty, as the interactions were nonlinear and the schemes could not converge onto a single interpretive scenario. This study highlights the secondary or indirect effects, and the interactions are crucial prior to evaluation of the climate and terrestrial biosphere–related changes even in the boundary layer perspective. Overall, it was found that direct and indirect effects could lead the system convergence toward different scenarios and have to be explicitly considered for atmospheric applications at all scales.

Modelling the thermal climate in city canyons

This paper presents an approach to the numerical modelling of the wind and thermal climates, as well as the energy budgets of city canyons. The model involves the coupling of three sub-models: (a) a surface energy budget model, (b) a windfield model, based on the k–ϵ turbulence model, and (c) a scalar dispersion model. In its current formulation, the model is two-dimensional, for clear sky conditions, for dry surfaces, and is most appropriate for conditions in which forced convection dominates over buoyancy effects. The model is capable of simulating the components of the wind; spatial patterns of canyon energy budget components; subsurface and air temperature; as controlled by location, date (i.e. solar path), weather conditions in the overlying air mass, canyon geometry and orientation, surface radiative and aerodynamic properties, substrate thermal properties, and, building interior climate.

Correlates of seasonal changes in metabolism in Atlantic harbour seals (Phoca vitulina concolor)

This study tested the hypothesis that seasonal variation in resting metabolic rate (RMR) was more closely related to changes in total energy use than to energy intake. It also quantified the extent to which variation in metabolism contributed to changes in total energy expenditure. RMR, gross energy intake, and body mass and composition were measured in six captive Atlantic harbour seals (Phoca vitulina concolor) over 16 months. Gross energy intake during the year (across all seals) averaged 25.4 ± 4.1 MJ/d (mean ± SD). The energy used by the seals Eused a composite measure of energy expenditure from ingested energy and tissue catabolism) averaged 19.2 ± 3.4 MJ/d. RMR averaged 11.2 ± 1.5 MJ/d during the year, while mass-corrected metabolism declined with age. The seals displayed significant changes in both absolute and mass-corrected metabolism during the year. Overall, Eused was a stronger predictor of changes in metabolism than either gross energy intake or body mass. Mass-corrected metabolic rate was more closely related to Eused than was absolute metabolism. Energy changes in metabolism during the year (range = 6.9 ± 1.9 MJ/d) were minor compared with those in Eused (27.8 ± 7.3 MJ/d). These results suggest that seasonal changes in metabolism were a response to, or facilitated by, concurrent changes in Eused but were not the cause of variation in Eused. Rather, variation in both RMR and Eused was the result of changes in other bioenergetic components of the seals' energy budget, such as activity.

THE CLIMATE OF THE KALAHARI TRANSECT

SUMMARY The climate of the Kalahari Transect is defined by the nature of the general circulation of the atmosphere over Africa south of the equator and the regional circulation variations that determine local weather. Individual synoptic systems and the transport of moisture into the region by converging and diverging airstreams in both summer and winter govern conditions favouring or inhibiting the major rainfall-producing process of convective precipitation. The climate is illustrated by the spatial variation of moisture, rainfall, temperature, evaporation and other fields. It is shown that the climate of the transect varies from the subtropical in the south to the tropical in the north with characteristic gradients of most parameters between the two regions in both summer and winter. The Kalahari Transect is a multi-disciplinary regional project having as its aim the advancement of the understanding of the effects of human and climatically induced global change over a large area of southern Africa. It has a near-unique advantage of being a study where the underlying regional geology, comprising Kalahari sand, is uniform over a considerable range of latitude. This offers the prospect of reducing the uncertainties associated with regional manifestations of global change. Climate and climatic change remain major determinants of all facets of the Kalahari Transect study. In this paper, the nature of the regional climate of the transect and how it may change in the future are discussed. The Kalahari Transect has a latitudinal extent from 14°S to 28°S and a longitudinal equivalent from 21°E to 28°E. The delimited area covers much of central southern Africa, ranging from shrubland and grassy desert in the south to evergreen dense woodland in the north. The whole region is dominated by the southern hemisphere descending limb of the Hadley cell of the general atmospheric circulation, the southern part of the transect more so than the northern part. This means that anticyclonic circulation patterns are the dominant circulation type for most of the year. The attendant atmospheric conditions are characterised by subsiding, stable air masses, hazy lower tropospheric conditions and generally cloud-free skies. South of the Tropic of Capricorn disturbances in the mid-latitude westerlies assume an increasingly important role in determining rainfall, whereas to the north seasonal migrations of the Inter-Tropical Convergence Zone (ITCZ) become the major determinant of the annual rainfall cycle. Over the whole region cumulus convective activity, enhanced by atmospheric disturbances associated with negative pressure departures and suppressed by those with positive departures, is the major determinant of rainfall, which everywhere exhibits a strong seasonal cycle with a summer maximum. In general, it is difficult to acquire a dense coverage of continuous, long-period, modern meteorological records for Africa south of the Sahara. The same is true of the region covered by the Kalahari transect. Good general descriptions of the climate of the region are provided in the atlases of Jackson (1961) and Thompson (1965). The reviews of Torrance (1972), Schulze (1972, 1984). Hastenrath (1984) and Tyson (1986) provide additional and more up-to-date material. These sources and others have been used to compile a climatology of the Kalahari transect region. After a brief summary of the regional atmospheric circulation, the main parameters to be considered are rainfall, cloud cover, energy budget components, temperature, atmospheric moisture, evaporation and potential evapotranspiration. The summary of the transect climate concludes with estimates of possible future regional conditions that may follow from global greenhouse warming.

A seasonal energy budget for zebra mussels (Dreissena polymorpha) in western Lake Erie

We constructed a balanced energy budget for zebra mussels (Dreissena polymorpha) from the western basin of Lake Erie during the active growth and reproductive season (May-October). We measured metabolic costs (oxygen consumption and ammonia excretion), body mass change, and feces production weekly and marked mussels to quantify shell growth. Costs of reproduction were measured by inducing spawning four times using serotonin and collecting gametes. After conversion to calories, all energy budget components were combined with published length-frequency distributions and mussel densities to estimate population consumption. We estimated that individual zebra mussel consumption averaged 3.16 cal ·day-1 (1 cal = 4.1868 J). Metabolic costs account for >90% of energy consumption. Mussels <15 mm increased in body mass whereas mussels >15 mm allocated energy to reproduction in lieu of somatic growth. Our estimates of population consumption were sensitive to mussel size distribution, with the most abundant size-class responsible for the greatest proportion of population consumption. Based on published estimates for primary production in western Lake Erie, our energy budget estimated that zebra mussels (10 000 - 50 000 mussels ·m-2) potentially consume an equivalent of 10-50% of summer primary production.