Experiments on mixing and dissipation in internal solitary waves over two triangular obstacles

A series of laboratory experiments was undertaken in a stratified two-layer fluid to investigate the energetics of the interaction between an internal solitary wave (ISW) and triangular obstacles, as well as to determine the partitioning of ISW energy and its subsequent dynamics. The ISW energy was dissipated as a result of internal breaking and turbulent mixing induced by wave instability. Tests involving different combinations of triangular obstacles in various heights and intervals and ISW of different amplitudes were performed. The wave features resulting from the interaction of an ISW and double obstacles were found to differ from those of single obstacle. The incident energy of an ISW was either reflecting back from the obstacles, dissipated through turbulent mixing, or transmitted over the double obstacles. Reduction in wave energy increased as the intervals between obstacles reduced. For two obstacles in different heights, energy dissipation was greater in the case with a higher obstacle ahead of a lower one. However, the overall performance was dependent on the relative height of the obstacles, relative water depth of the upper and bottom layer, in addition to the intervals between the obstacles.     

Laboratory experiments on waveform inversion of an internal solitary wave over a slope-shelf

Internal solitary waves (ISWs) have been detected in many parts of the world oceans, particularly over slope-shelf topography, on which signature of waveform inversion has been identified. The effects of these waves on engineering operations and ecological process have also been reported in the literature. This article reports the results of a series of numerical modeling and laboratory experiments on waveform evolution of a depression ISW in a nearly stratified two-layer fluid system, in which specific water depth ratios above the horizontal plateau of the trapezoidal obstacle were arranged to facilitate the occurrence of waveform inversion. Classifications of waveform instability (no instability, shear instability and overturning with breaking) on the slope are confirmed in the present laboratory study. Numerical results for waveform variation are also found in fair agreement with the laboratory measurements for cases without waveform inversion and minor internal breaking. Moreover, laboratory results revealed that the depth ratio of the stratified two-layer fluid above the plateau and the magnitude of the incident ISW were the two most important factors for promoting waveform inversion beyond a turning point, in addition to the requirement of a sufficient distance from the shoulder of the trapezoidal obstacle. These factors also influenced the outcome of the shoaling process, energy dissipation, internal wave breaking and turbulent mixing on the front slope, as well as the likelihood of waveform inversion on the horizontal plateau. Contrary to the common perception, it was also observed, at least from the results of the present laboratory experiments, that not all the incident ISWs of depression would produce waveform inversion on the plateau, where the upper layer was physical greater than the bottom layer, unless moderate incident wave was provided. The outcome might also be attributed to the limited distance from the shoulder onto the plateau in the present laboratory setup. However, once waveform inversion occurred on the plateau, it was found, among others, that: (1) the amplitude of the transmitted leading crest and trough might be as low as 30 and 20%, respectively, to the amplitude of the incident wave in depression; (2) the characteristic wavelength of the transmitted leading trough doubled while that of the crest was asymptotically one-half of the incident wavelength, despite the wide range variation in the depth ratios above the plateau; and (3) the transmitted potential wave energy of the leading crest contained 30% of the incident energy. Based on the results of present laboratory experiments, the range for the non-dimensional parameter α, which indicates the effect of nonlinearity and the promotion of waveform inversion on horizontal plateau, will be proposed.     

Using discriminant analysis to determine the breaking criterion for an ISW propagating over a ridge

This study aims to develop methods that are capable of deciding the breaking criterion for an internal solitary wave (ISW) propagating over a submarine ridge. Laboratory experiments were conducted in a wave tank to measure ISWs propagating over a submarine ridge. The results suggest that the ISW-ridge interaction can be grouped according to three degrees of magnitude based on the blockage parameter ζ and the degree of blocking B. For classification reasons, we first present an alternative decision model for evaluating the interaction of ISWs with an underwater ridge in a two-layer system. This approach is based on a multivariate statistical method and discriminant analysis. Information obtained from the eigenvalues is used to combine different ratio measures which are defined according to every single input and output. The discriminant model effectively classifies units into distinct predefined groups. An experimental simulation is conducted to demonstrate the practical implementation of the ISW-ridge interaction. The results of the method applied in this example are statistically significant, demonstrating the effectiveness of the ISW-ridge interaction classification method.     

The generation of internal waves by tidal flow over continental shelf/slope topography

Experiments were performed to investigate the generation of internal waves induced by a barotropic tidal flow over continental shelf/slope topography in a two-layer stratified fluid. The interaction of the barotropic tide with the continental slope resulted in the formation of both linear and nonlinear waveforms, ranging from a linear wave of depression to a highly nonlinear internal bolus. The type of wave response was strongly dependent on the tidal forcing intensity and the position of the density interface relative to the shelf depth. Based on the values of the internal Froude number and the layer depth ratio, we delineate four distinct generation regimes, each with a distinct wave response.     

Terrigenous Inputs and Accumulation of Trace Metals in the Southeastern Taiwan Strait

Abstract

Terrigenous inputs and sedimentary fluxes of trace metals were studied to understand the metal sources, transport and sinks in the southeastern Taiwan Strait. the major terrigenous metals come from seven major rivers in the southwestern Taiwan, even though significant fractions of most metals were retained in estuaries. the net fluxes of river borne metals contributed from 65% (Pb) to 92% (Fe, Zn) of total inputs. the remainder was attributed to marine sewage discharges (0.6–6.9%) and atmospheric inputs (5.3–31.5%). Sedimentary fluxes of trace metals were spatially variable as a result of derivation from site-specific sedimentation rates and metal distributions in sediments. in spite of imbalance between sources and sinks of trace metals, an accumulation of metals in the sediment of southeastern Taiwan Strait was found for sites close to Taiwan Island. Surface enrichment of metals in near-shore sediments beginning around 1976 was coincident with a time of industrial boom in Taiwan. the metal enrichment hierarchy was found as (Cd, Pb < Cu < Zn < Mn, Fe).     

Depth zonation and metabolic adaptation in Dover sole,Microstomus pacificus,and other deep-living flatfishes: factors that affect the sole

Flatfishes of Monterey Bay, central California, undergo species replacements with increasing depth along a transect from 100 m on the continental shelf down to a depth of 1400 m on the continental slope. The Dover sole, Microstomus pacificus, differs from the other local flatfish species by undergoing an extensive ontogenetic vertical migration, occupying all depth zones at different life stages, and having its maximum spawning biomass in the oxygen minimum zone between 600 and 1000 m. Size-activity relationships and depth-activity relationships for the glycolytic enzyme lactate dehydrogenase (LDH) and for two enzymes associated with aerobic metabolism, malate dehydrogenase and citrate synthase (CS), were examined in white-muscle tissue of shallow-living, deep-living and ontogenetically-migrating species. Scaling coefficients (b) for weight-specific enzyme activity (log activity)=a+b (log wet weight), varied in sign as well as magnitude for fishes living at different depths. In the shallow-living California halibut Paralichthys californicus, LDH scaled positively (0.39) and CS scaled negatively (-0.15) with size, a pattern observed previously for most shallow-water fish species. The permanently deep-living species, the deepsea sole Embassichthys bathybius, differed in that both LDH and CS scaled strongly negative (-2.0 and-1.5, respectively). For the ontogenetically migrating Dover sole Microstomus pacificus, there was a shelf-slope transition. For the shelf specimens (200 m), LDH scaled positive (0.11) and CS negative (-0.29) and for the slope specimens (400 m), LDH scaled negative (-0.65) and CS strongly negative (-0.63). Rex sole, Glyptocephalus zachirus, showed a similar shelf-slope transition. Intraspecific depth-enzyme activity differences were not incremental, but changed abruptly between the continental shelf stations (100 to 200 m) and the continental slope (400 to 1400 m). Based on comparisons with laboratory-maintained individuals, the decline in the metabolic capacity of the white muscle of Dover sole is a phenotypic response to the low food and oxygen conditions of the continental slope. Contrary to expectation, anaerobic capacity (LDH activity) decreased in response to low oxygen conditions, suggesting that in a permanently hypoxic environment such as the oxygen minimum zone the metabolic strategy may be to not incur an oxygen debt that would be difficult to pay back.     

Modelling the motion of an internal solitary wave over a bottom ridge in a stratified fluid

A series of laboratory experiments has been carried out to investigate the passage of an internal solitary wave of depression over a bottom ridge, in a two-layer fluid system for which the upper and lower layer is linearly-stratified and homogeneous respectively. Density, velocity and vorticity fields induced by the wave propagation over the ridge have been measured simultaneously at three locations, namely upstream, downstream and over the ridge crest, for a wide range of model parameters. Results are presented to show that wave breaking may occur for a sufficiently large wave amplitude and a strong ridge blockage factor, with accompanying mixing and overturning. Density field data are presented (i) to illustrate the overturning and mixing processes that accompany the wave breaking and (ii) to quantify the degree of mixing in terms of the wave and ridge parameters. For weak encounters, good agreement is obtained between the laboratory experimental results (velocity and vorticity fields induced by the wave propagation) and the predictions of a recently-developed fully nonlinear theory. Discrepancies between theory and experiment are discussed for cases in which breaking and mixing occur.     

Spatial structure of internal Poincaré waves in Lake Michigan

In this paper we examine the characteristics of near-inertial internal Poincaré waves in Lake Michigan (USA) as discerned from field experiments and hydrodynamic simulations. The focus is on the determination of the lateral and vertical structure of the waves. Observations of near-inertial internal wave properties are presented from two field experiments in southern Lake Michigan conducted during the years 2009 and 2010 at Michigan City (IN, USA) and Muskegon (MI, USA), respectively. Spectra of thermocline displacements and baroclinic velocities show that kinetic and potential baroclinic energy is dominated by near-inertial internal Poincaré waves. Vertical structure discerned from empirical orthogonal function analysis shows that this energy is predominantly vertical mode 1. Idealized hydrodynamic simulations using stratifications from early summer (June), mid-summer (July) and fall (September) identify the basin-scale internal Poincaré wave structure as a combination of single- and two-basin cells, similar to those identified in Lake Erie by Schwab, with near-surface velocities largest in the center of the northern and southern basins. Near-inertial bottom kinetic energy is seen to have roughly constant magnitude over large swathes across the basin, with higher magnitude in the shallower areas like the Mid-lake Plateau, as compared with the deep northern and southern basins. The near-bottom near-inertial kinetic energy when mapped appears similar to the bottom topography map. The wave-induced vertical shear across thermocline is concentrated along the longitudinal axis of the lake basin, and both near-bottom velocities and thermocline shear are reasonably explained by a simple conceptual model of the expected transverse variability.     

Quantifying the effect of wind on internal wave resonance in Lake Villarrica,Chile

Lake Villarrica, located in south central Chile, has a maximum depth of 167 m and a maximum fetch of about 20 km. The lake is monomictic, with a seasonal thermocline located at a depth of approximately 20 m. Field data show the presence of basin-scale internal waves that are forced by daily winds and affected by Coriolis acceleration. A modal linear and non-linear analysis of internal waves has been used, assuming a two-layer system. The numerical simulations show good agreement with the internal wave field observations. The obtained modes were used to study the energy dissipation within the system, which is necessary to control the amplitude growth. Field data and numerical simulations identify (1) the occurrence of a horizontal mode 1 Kelvin wave, with a period of about a day that coincides with the frequency of daily winds, suggesting that this mode of the Kelvin waves is in a resonant state (subject to damping and controlled by frictional effects in the field) and (2) the presence of higher-frequency internal waves, which are excited by non-linear interactions between basin-scale internal waves. The non-linear simulation indicates that only 10 % of the dissipation rate of the Kelvin wave is because of bottom friction, while the rest 90 % represents the energy that is radiated from the Kelvin wave to other modes. Also, this study shows that modes with periods between 5 and 8 h are excited by non-linear interactions between the fundamental Kelvin wave and horizontal Poincaré-type waves. A laboratory study of the resonant interaction between a periodic forcing and the internal wave field response has also been performed, confirming the resonance for the horizontal mode 1 Kelvin wave.     

Far-field vortex structures in mountain wakes

Laboratory experiments on scaled mountain wakes have provided the first demonstration that indicates the existence of two distinct mechanisms for the formation of the long-lived vortex structures that have been frequently observed in satellite imagery. In a series of laboratory experiments the well-known von Kármán vortex shedding mechanism has been observed at low values of Froude number (corresponding to low speed flow and strong stratification). At high Froude numbers the initial highly turbulent wake evolves into a vortex pattern similar to the far-wake dipole eddies previously observed in laboratory studies of submerged stratified wakes. In satellite imagery vortex structures have been observed to persist for hundreds of kilometers. In the present laboratory experiments far-wake dipole eddies were observed to persist for at least 200 diameters downstream, which corresponds to ~4,000?km when scaled to actual mountains. When generated at multiple sites along a continental mountain chain, these eddy structures could play a significant role in the development and variability of multi-scale weather and climate patterns.     

On the fine structure of the thermal bar front

The thermal bar—a hydrodynamic phenomenon, arising in natural basins due to successive changes of the water temperature across the temperature of maximum density (T_m, which is close to 4°C)—has been studied in laboratory experiments and by numerical simulations. The experiments were performed in a rectangular tank with an inclined bottom, filled with water with initial temperature T₀ < T_m and then heated at the surface. During the heating a basin-wide circulation develops, consisting of down-slope cascades in regions where T < T_m, a subsurface off-shore jet in the region where T > T_m, and a compensating flow at intermediate depths towards the shallow part of the tank, supplying both off-shore flows with waters from deeper regions. Analysis of the water temperature and density fields as well as the currents has revealed that the location of the convergence zone of the surface current (when formed) does not coincide with that of the Tm-isotherm. The thermal bar front is typically understood as a convergence zone near the 4°C-isotherm, formed due to the effect of cabbeling. Our experiments demonstrate, however, that the front is associated with the leading edge of the subsurface current. The increasing distance between the 4°C-isotherm and the subsurface jet has been recorded in the laboratory experiments. Numerical simulation results corroborate the laboratory experiments. A scaling analysis predicts the speed of propagation of this frontal zone to be U ~ [g × Δρ/ρ × H]^1/2, where H is the depth (increasing with time) of the upper thermo-active layer, ρ₀ a reference density, and Δρ is the characteristic horizontal density difference across the front. A combined analysis of laboratory, field and numerical data has corroborated this law.     

Industrial solid waste flow analysis of eco-industrial parks: implications for sustainable waste management in China

Sustainable waste management in the industrial ecology perspective brings enormous challenges to the existing methodology of waste analysis at the industrial park (IP) scale. In this study, a four-step method was proposed for industrial solid waste (ISW) flow analysis of eco-industrial parks (EIPs) and applied to two IPs in eastern China. According to a park-wide census of 619 industrial enterprises and 105 questionnaires by a survey from 2006 to 2008, the results indicated that: 1) at the enterprise scale, more than 60% of enterprises were small-ISW-generation enterprises which encountered great difficulties on effective waste management; 2) at the IP scale, though the two IPs have set up their own environmental management systems and passed the ISO 14001 certification, the efficiencies of the ISW management systems have yet to be improved in the industrial ecology perspective; and 3) at the regional scale, more than 97% of ISW flowed within the provincial region, indicating that the provincial governments prevented the wastes from flowing into their own “back yard”. Effective waste management should be placed in a broader perspective. Approaches to sustainable waste management may include wastes exchange, efficient waste and information flow, virtual EIP, waste minimization clubs and regionalization of waste management.     

Tsunami generation by submarine landslides: comparison of physical and numerical models

An idealised two-dimensional laboratory model of tsunamis generated by submarine landslides is described. The experimental configuration corresponds to the benchmark configuration suggested by other researchers in the international tsunami community. It comprises a semi-elliptical rigid landslide with a height to length ratio of 0.052 sliding down a 15° slope. The initial landslide submergence and specific gravity are varied, the second of which primarily determines the initial landslide acceleration. In these experiments the landslide motion is generally well approximated as consisting of two periods of constant acceleration. The first phase of positive acceleration finishes as the landslide reaches the base of the slope, while the second period of a slower deceleration continues until the landslide comes to rest along the horizontal base of the tank. A novel experimental technique, which utilises laser-induced fluorescence (LIF), is employed to measure the free surface displacement over the entire space and time domains. This enables the wave potential energy field to be computed directly and provides a vivid picture of the wave generation and development process. Particle tracking velocimetry provides detailed information on the landslide motion and also some data on the sub-surface velocity field. Experimental runs require multiple repeats (typically 35–50) of the same setup in order to capture the entire wave field with the desired resolution. Thus high level experimental repeatability is required, and this is demonstrated. A range of parameters relevant to hazard management are presented and discussed. Maximum crest and trough amplitudes of the offshore propagating waves are shown to be approximately proportional to the initial landslide acceleration and somewhat less strongly dependent on the initial landslide submergence. The maximum wave run-up experienced at the shoreline is shown to depend almost linearly on the magnitude of a high deceleration that occurs for a short period when the landslide nears the toe of the slope. The initial submergence and initial acceleration do not directly determine the maximum wave run-up, although for these experiments they impact indirectly on the magnitude of the deceleration. The efficiency of the energy transfer from the landslide potential energy to the wave field potential energy reaches values of up to 6% and is found to be strongly dependent on the initial submergence. However because of the link between the landslide mass and its acceleration, this efficiency is almost completely independent of the initial acceleration. The results from a numerical model based on linear, inviscid and irrotational wave theory, and solved with the boundary element method, are compared with the data from the experimental program. The numerical model accurately produces the generated sequence of wave crests and troughs, but slightly overpredicts their phase speed by between 2 and 4%. For all other parameters the numerical model predictions are within 25% of the experimental values, although this includes both under- and overprediction for the range of independent parameters covered.     

δ13C and fatty acid composition of mesopelagic fishes in the South China Sea and their influence factors

Study of the ecology of mesopelagic fishes is central for assessing the active biological pump in the ocean, especially in the mesopelagic layers. The use of δ¹³C and fatty acid analysis can help to analysis the ecology of mesopelagic fishes. Here, we analysed the fatty acid composition of mesopelagic fishes from the continental northern slope of the South China Sea (NSSCS) and compared with nearshore SCS fishes and mesopelagic fishes collected from the Southern Ocean. The mesopelagic fishes had unusually high lipids, which resulted in Δδ¹³C values exceeding 1‰, more than the enrichment factor in the food web. The mesopelagic fishes had higher C18:1n-9/C18:1n-7 and C20:1n-9/ C18:1n-7 ratios compared with other fishes in the SCS, which confirmed that plankton were their main dietary source. The mesopelagic fishes from SCS and Southern Ocean had different ratios of C20:5n-3/C22:6n-3 (EPA/DHA), suggesting geographical locations and diet sources had obvious influence on their fatty acid composition. The SCS mesopelagic fishes had higher C20:4n-6/C22:6n-3 (ARA/DHA) and C20:4n-6/C20:5n-3 (ARA/EPA) ratios than mesopelagic fishes in the Southern Ocean, indicating the influence of physical factors on fatty acid composition. Thus, future studies of the fatty acids in mesopelagic fishes should consider both dietary sources and physical environments.     

台湾海峡水域的β—葡萄糖苷酶活性

本研究分别在1997年8月10日至8月19日,1998年2月20日至3月7日,对台湾海峡进行现场调查研究,在九个断面20个站位取得水文、化学和生物学综合参数,研究该海域β－葡萄糖苷酶活性（βGlcA),细菌生物量及生产力的时空动态,主要结果如下①夏季台湾海峡南部各站位βGlcA的值为1．94mmol/L^-1h^-1,变化幅度大于（0．31－8．1nmol/L^-1h^-1;冬季海峡北部βGlcA平均值为0．86nmol/L^-1h^-1,变化幅度大（0．34－1．89nmol/L^-1h^-1)远小于夏季。②以碳的转化量表示,夏冬两季的βGlcA分别为0．14μgL6-1h^-1和0．062μgL6-1h^-1,分别高于这两个季节的细菌生产力。③从离岸到近岸,细菌胞外酶活性升高。④该海域胞牙酶活性与细菌的二次生产力的相关性不够明显。⑤βGlcA的剖面分布及周日变化与细菌生产力的相关性不很明显。⑥表层水游离态的细菌的βGlcA,在整个海区的分布特征与该水层的总βGlcA分布特征相似。     

Growth and damping of interfacial waves on a diffuse interface

The resonant interaction of surface and internal waves produces a nonlinear mechanism for energy transfer among wave components in oceans, lakes, and estuaries. In many field situations, the stratification may be well approximated by a two-layer fluid with a diffuse interface. The growth and damping rates of sub-harmonic interfacial waves generated by a surface wave through a three-wave resonant interaction are measured in the laboratory. These measurements are compared with theoretical predictions. A diffuse interface reduces the damping rate and increases the growth rate. The predicted growth rate provides excellent comparison with the laboratory measurements. The inclusion of the effects of a diffuse interface significantly improve the comparison.     

Movements and wintering areas of breeding age Thick-billed Murre <Emphasis Type="Italic">Uria lomvia</Emphasis> from two colonies in Nunavut,Canada

The non-breeding movements of marine birds were poorly known until recently, but this information is essential to understanding the risk to different geographical populations from events on the wintering grounds. We tracked the migration routes and wintering areas of Thick-billed Murre Uria lomvia from two breeding colonies in eastern Canada: Coats Island in northern Hudson Bay and The Minarets, Baffin Island, during the period August 2007–May 2008 using geolocation loggers. Birds from The Minarets moved south rapidly post-breeding and wintered principally off Newfoundland and southern Labrador, or between Newfoundland and southern Greenland, remaining south of 55°N until at least the spring equinox. Those from Coats Island remained in Hudson Bay until at least mid-November, after which they moved rapidly through Hudson Strait to winter in southern Davis Strait and the northern Labrador Sea, mostly north of 55°N. Many individuals stayed throughout the winter in areas of heavy ice cover. Adults from the two colonies appear to be completely segregated in winter and those from Coats Island probably did not enter the area of the winter hunt in Newfoundland. Unexpectedly, some birds from The Minarets wintered in waters beyond the continental slope and outside the distribution of pack ice, demonstrating that particular individuals can be wholly pelagic throughout the winter. Coats Island birds returned through Hudson Strait as soon as open water areas became available in spring. Their sojourn in Hudson Bay coincided very closely with the occurrence of areas with <90% ice cover. In spite of the relatively large error in positions obtained from geolocation loggers, our results demonstrated the value of these devices by uncovering a number of previously unknown aspects of Thick-billed Murre non-breeding ecology in the Northwest Atlantic. Comparison of the non-breeding ecology based on SST experienced in winter show that the winter niche is broader than hitherto assumed, demonstrating that separate populations may experience different selection in the face of climate change.     

Physical and numerical modelling of tsunami generation by a moving obstacle at the bottom boundary

This paper presents a study of the waves generated by a solid block landslide moving along a horizontal boundary. The landslide was controlled using a mechanical system in a series of physical experiments, and laser-induced fluorescence measurements resolved both spatial and temporal variations in the free surface elevation. During its constant-velocity motion, the landslide transferred energy into ‘trapped’ offshore-propagating waves within a narrow frequency band. The wave trapping is demonstrated by investigating the wave dispersion characteristics using a two-dimensional Fourier Transform. The first of the trailing waves broke at Froude numbers greater than or equal to 0.625. The parametric dependence of the largest-amplitude waves and the potential energy within the wave field are discussed. The experimental results were compared to the predictions of an incompressible Navier–Stokes solver with and without turbulence models. The numerical model under-predicted the measured wave amplitudes, although it accurately predicted the measured wave phasing. The turbulent model more accurately predicted the shapes of the trailing waves. Both experimental and numerical results confirmed that investigations into wave generation by submerged objects moving at constant velocity should also consider the initial acceleration of the object, as this affects the overall evolution of the wave field. The applicability of the horizontal-boundary results to more realistic field scenarios is discussed.     

The potential of current legal structures to support Aboriginal and Torres Strait Islander interests in the Australian bush food industry

There are complex connections between Australia’s native plants and first peoples, the Aboriginal and Torres Strait Islander peoples. The maintenance of these connections is central to Aboriginal and Torres Strait Islander culture and well-being and the tangible realisation of Australian policy commitments. Diverse cultural connections combine with other motivations to underpin an array of Aboriginal and Torres Strait Islander interests in the commercial development of traditional plant foods (‘bush foods’). Despite nation-wide policy support for these interests, there is no national legal framework to support them. This fortifies the popular call for a new (sui generis) law that transforms the interests of Aboriginal and Torres Strait Islander peoples into enforceable legal rights. It is unclear the extent to which a single sui generis law might help Aboriginal and Torres Strait Islander peoples realise their diverse interests in the development of gourmet bush food products and new bush food varieties. It is also unlikely that Australia will implement such a law in the near future. This paper offers a preliminary study of the capacity of current legal structures to support some key Aboriginal and Torres Strait Islander interests that might arise in these two development contexts. The study can inform the future development of practical legal strategies to support the diverse interests of Aboriginal and Torres Strait Islander peoples in the bush food industry.