Tracer Storage Research Articles

Long‐Distance/Time Surf‐Zone Tracer Evolution Affected by Inner‐Shelf Tracer Retention and Recirculation

AbstractThe evolution of a surf‐zone released tracer ( Liter over 4 hr) was observed for h. Surf‐zone tracer was transported alongshore (y) with relatively steady mean speed vSZ ≈ 0.18 m s−1, consistent with obliquely incident wave forcing. Maximum in situ surf‐zone tracer concentration decayed exponentially with 1.6 km alongshore e‐folding length scale, that is, 2.5 hr advective time scale. Surf‐zone tracer time‐series evolved downstream of the release from a top‐hat structure for y ≤ 1 km to increasingly skewed farther downstream. Within km of the northward propagating tracer front, inner‐shelf tracer was confined to onshore of (surf‐zone width LSZ ≈ 100 m) and was alongshore patchy. A coupled surf‐zone/inner‐shelf tracer advection‐diffusion‐exchange box model reproduces the observed surf‐zone downstream max concentration decay and temporal skewness, with surf‐zone flushing time h. A weaker inner‐shelf unidirectional‐exchange rate kIS ≈ kSZ/2 indicates reduced horizontal mixing outside the surf‐zone. Surf‐zone temporal skewness is linked to inner‐shelf tracer storage, differential surf‐zone/inner‐shelf advection, and recirculation, that is, non‐asymptotic shear dispersion. On the inner‐shelf (), tracer vertical structure differed in the morning versus afternoon suggesting internal tide and solar forced thermal modulation. Model parameters representing surf‐zone processes are well constrained by existing observations and scales. However, the many overlapping inner‐shelf processes make a single process based generalization of inner‐shelf cross‐shore exchange rate (i.e., kIS) and alongshore transport difficult.

Forest succession, soil carbon accumulation, and rapid nitrogen storage in poorly remineralized soil organic matter

Substantial nitrogen (N) retention by temperate terrestrial ecosystems results from the rapid storage of newly deposited N in stable soil organic matter. Yet, we poorly understand the ecosystem properties that regulate the kinetics of this process. We applied mineral 15N to temperate hardwood forest soils to test the hypothesis that N stabilization is faster owing to greater stocks of soil carbon (C) in late‐successional than in young forests. Within 26 minutes of addition, about 30% of tracer N was stored in stable form in organic‐horizon soil with a median residence time of >29 years. About 5–10% of tracer N was stored in a soluble organic form. An additional 30% of tracer N was recovered within hours from organic‐horizon soils in a remineralizable (labile) form, apparently derived from microbial biomass. Over the following year, tracer N storage in stable and soluble organic pools remained constant while recovery from labile and microbial pools declined. Tracer storage was greater in older forests with larger soil C pools, supporting our hypothesis that the accumulation of soil C with forest succession promotes ecosystem N retention. Rapid storage of stable soil N in the O horizon may create a source for chronic dissolved organic N losses from watersheds.

Magnetic tracing of fine-sediment over pool-riffle morphology

Field studies documenting fine-sediment (<2mm) transport in gravel-bed rivers are rare. For the first time in a fluvial environment, a technique that enhances the magnetic susceptibility of sand is used to trace its longitudinal dispersion and storage. This paper describes the methodology behind the artificial magnetic enhancement of iron-stained sand, and presents the results from sand tracing exercises conducted on two gravel-bed channels with pool-riffle morphology; one unregulated and sinuous in nature (site A), the other regulated and straight (site B), both situated on the River Rede Northumberland, UK. Two tonnes of magnetically enhanced tracer sand was introduced to site A and four tonnes to site B, to provide information on fine-sediment storage dynamics, interaction of fines with the stream bed, and rates of movement, expressed as virtual velocity (Vi). Sand transport pathways appeared to differ between the reaches; for site A, sand storage was found on bars and riffle margins with no storage or signs of transport through pools, and in contrast pool storage of tracer was a key feature shown at site B. Topographic forcing may cause differences in sediment sorting at site A; topographic highs tend to have low sand transport rates with sand grains becoming congested in these areas, whereas topographic lows show higher transport rates resulting in greater dispersion. Supply limitation of sand on the falling limb of the hydrograph may also become an issue in the topographic lows at this site. Hydrograph differences between the regulated and unregulated reaches could also play a role; however this could not be quantified in this study. There was no evidence of sand infiltration into the bed at site A; however marginal evidence for infiltration into the near-surface (0–15cm) substrate voids was found at site B. The general lack of evidence for significant infiltration may reflect limited availability of void space in substrate framework gravels. Tracer sand was transported over the bed surface, with little vertical interaction with the substrate, despite periods of gravel mobilisation at site A. Vi over the study duration for site A was 2.28mday−1, and 0.28mday−1 for site B. These values are greater than those calculated using existing predictive equations developed from gravel tracer data, possibly reflecting differences in the mode of transport between bedload and saltation load.

Free Fatty Acid Storage in Human Visceral and Subcutaneous Adipose Tissue

OBJECTIVEBecause direct adipose tissue free fatty acid (FFA) storage may contribute to body fat distribution, we measured FFA (palmitate) storage rates and fatty acid (FA) storage enzymes/proteins in omental and abdominal subcutaneous fat.RESEARCH DESIGN AND METHODSElective surgery patients received a bolus of [1-14C]palmitate followed by omental and abdominal subcutaneous fat biopsies to measure direct FFA storage. Long chain acyl-CoA synthetase (ACS) and diacylglycerol acyltransferase activities, CD36, fatty acid-binding protein, and fatty acid transport protein 1 were measured.RESULTSPalmitate tracer storage (dpm/g adipose lipid) and calculated palmitate storage rates were greater in omental than abdominal subcutaneous fat in women (1.2 ± 0.8 vs. 0.7 ± 0.4 μmol ⋅ kg adipose lipid−1 ⋅ min−1, P = 0.005) and men (0.7 ± 0.2 vs. 0.2 ± 0.1, P < 0.001), and both were greater in women than men (P < 0.0001). Abdominal subcutaneous adipose tissue palmitate storage rates correlated with ACS activity (women: r = 0.66, P = 0.001; men: r = 0.70, P = 0.007); in men, CD36 was also independently related to palmitate storage rates. The content/activity of FA storage enzymes/proteins in omental fat was dramatically lower in those with more visceral fat. In women, only omental palmitate storage rates were correlated (r = 0.54, P = 0.03) with ACS activity.CONCLUSIONSSome adipocyte FA storage factors correlate with direct FFA storage, but sex differences in this process in visceral fat do not account for sex differences in visceral fatness. The reduced storage proteins in those with greater visceral fat suggest that the storage factors we measured are not a predominant cause of visceral adipose tissue accumulation.

Postabsorptive VLDL‐TG Fatty Acid Storage in Adipose Tissue in Lean and Obese Women

Adipose tissue lipoprotein lipase (LPL) is a necessary enzyme for storage of very-low-density lipoprotein-triglyceride (VLDL-TG), but whether it is a rate-determining step is unknown. To test this hypothesis we included 10 upper-body obese (UBO), 11 lower-body obese (LBO), and 8 lean women. We infused ex vivo-labeled VLDL-(14)C-TG and then performed adipose tissue biopsies to understand the relationship between VLDL-TG storage and LPL activity in femoral and upper-body subcutaneous fat. Both fractional tracer storage and rate of storage of the VLDL-TG tracer were evaluated. VLDL-TG storage was also examined as a function of regional adipose tissue blood flow (ATBF), insulin, VLDL-TG turnover, regional fat mass, fat-free mass (FFM), and fat cell size. LPL activity per adipocyte was significantly greater in obese than lean women but not significantly different per gram lipid. Both VLDL-TG fractional tracer storage per kg lipid and VLDL-TG storage rate per kg lipid were similar in abdominal and femoral fat in all three groups and were not significantly different between groups. Multiple regression analysis identified FFM and femoral fat mass as significant independent predictors of VLDL-TG fractional tracer storage and insulin as a significant predictor of VLDL-TG fatty acid storage rate. LPL activity, ATBF, and VLDL-TG turnover did not predict VLDL-TG storage. We conclude that lower FFM and greater plasma insulin are associated with greater VLDL-TG deposition in abdominal subcutaneous and femoral fat. Greater femoral fat mass signals greater femoral VLDL-TG storage. We suggest that the differences in VLDL-TG storage in abdominal and femoral fat that occur with progressive obesity are regulated through mechanisms other than LPL activity.

Plasma NEFA storage in adipose tissue in the postprandial state: sex-related and regional differences.

We recently reported that a small fraction of circulating NEFA is stored through direct uptake in subcutaneous fat in postabsorptive humans in vivo and that this pathway may favour lower-body fat distribution in women. Here, we examined sex-related and regional differences in storage of plasma NEFA in subcutaneous adipose tissue during postprandial conditions. At 1 h after lunch, men and women of normal weight received an intravenous bolus of approximately 1.66 MBq [1-(14)C]oleate followed by timed subcutaneous fat biopsies. The preceding breakfast was either a normal- or high-fat meal; the high-fat breakfast was used to create postprandial oleate concentrations in the postabsorptive range. Storage of the NEFA tracer in adipose tissue (dpm/g lipid) was greater in women; in both sexes abdominal fat stored tracer more avidly than femoral fat. A greater fraction of the administered tracer was stored in whole body subcutaneous fat of women than in that of men (27 +/- 3 vs 8 +/- 1%, respectively, p < 0.0001). No significant differences in tracer storage were observed between participants consuming the high- vs normal-fat breakfast. Postprandial NEFA storage in subcutaneous fat through direct uptake accounts for approximately 25% of NEFA disposal in women, but for <10% in men in a wide range of circulating NEFA concentrations. It is greater in the upper- than lower-body subcutaneous fat, favouring upper-body fat accumulation in both sexes.

Plasma Free Fatty Acid Storage in Subcutaneous and Visceral Adipose Tissue in Postabsorptive Women

We assessed the direct (VLDL-triglycerides [VLDL-TG] independent) storage of circulating free fatty acids (FFAs) in visceral and subcutaneous fat in postabsorptive women. Twelve women (BMI 29.6 +/- 6.6 kg/m(2)) received an identical, intravenous bolus dose of [1-(14)C]oleate followed by timed subcutaneous fat biopsies (abdominal and femoral) and then omental fat biopsy during tubal ligation surgery. Regional fat masses were assessed by combining dual-energy X-ray absorptiometry and computed tomography scanning. Separately, we assessed the fraction of FFA tracer entering VLDL-TG over the time representing the delay in collecting omental fat. Site-specific fat specific activity (SA) (dpm/g lipid) decreased as a function of fat mass in both upper-body subcutaneous (UBSQ) and visceral fat depots. These patterns are consistent with dilution of a relatively fixed amount of FFA tracer within progressively greater amounts of fat. Interestingly, femoral SA did not vary as a function of lower-body subcutaneous (LBSQ) fat mass. [1-(14)C]oleate storage per million LBSQ adipocytes was positively associated with LBSQ fat mass, but no significant relationships were observed in UBSQ or visceral fat depot. The fraction of [1-(14)C]oleate stored in UBSQ, LBSQ, and visceral fat was 6.7 +/- 3.2, 4.9 +/- 3.4, and 1.0 +/- 0.3%, respectively. Only approximately 4% of the tracer traversed VLDL-TG over 9.5 h. The increase in FFA tracer storage per adipocyte as a function of LBSQ fat mass implies that LBSQ adipocytes, in contrast to UBSQ and omental adipocytes, store more FFA in women with greater adiposity. The direct FFA storage pathway might play a role in favoring lower-body fat accumulation in women.

Effects of mesoscale eddies on global ocean distributions of CFC-11, CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, and Δ&amp;lt;sup&amp;gt;14&amp;lt;/sup&amp;gt;C

Abstract. Global-scale tracer simulations are typically made at coarse resolution without explicitly modelling eddies. Here we ask what role do eddies play in ocean uptake, storage, and meridional transport of transient tracers. We made global anthropogenic transient-tracer simulations in coarse-resolution (2°cosφ×2°, ORCA2) and eddy-permitting (½°cosφ×½°, ORCA05) versions of the ocean general circulation model OPA9. Our focus is on surface-to-intermediate waters of the southern extratropics where air-sea tracer fluxes, tracer storage, and meridional tracer transport are largest. Eddies have little effect on global and regional bomb Δ14C uptake and storage. Yet for anthropogenic CO2 and CFC-11, refining the horizontal resolution reduced southern extratropical uptake by 25% and 28%, respectively. There is a similar decrease in corresponding inventories, which yields better agreement with observations. With higher resolution, eddies strengthen upper ocean vertical stratification and reduce excessive ventilation of intermediate waters by 20% between 60° S and 40° S. By weakening the residual circulation, i.e., the sum of Eulerian mean flow and the opposed eddy-induced flow, eddies reduce the supply of tracer-impoverished deep waters to the surface near the Antarctic divergence, thus reducing the air-sea tracer flux. Thus in the eddy permitting model, surface waters in that region have more time to equilibrate with the atmosphere before they are transported northward and subducted. As a result, the eddy permitting model's inventories of CFC-11 and anthropogenic CO2 are lower in that region because mixed-layer concentrations of both tracers equilibrate with the atmosphere on relatively short time scales (15 days and 6 months, respectively); conversely, bomb Δ14C's air-sea equilibration time of 6 years is so slow that, even in the eddy permitting model, there is little time for surface concentrations to equilibrate with the atmosphere, i.e., before surface waters are subducted.

Models of tracer breakthrough and permeability in simple fractured porous media

Abstract Tailing and bimodal behaviour of tracer breakthrough curves from tracer tests conducted in fractured porous media are commonly presented as ‘deviations’ from the Fickian model for homogeneous porous media. Tailing is mainly attributed to: (1) tracer storage brought about by diffusion between mobile and static regions of fluid; (2) a concentration of flow towards the wider (aperture) and, thus, more permeable fracture zones; and (3) the high variance in fracture conductivity and consequent mixing of tracer. Bi- (or multi-) modality has been attributed to solute following a few highly permeable flow paths. Systematic numerical simulations of flow and transport in geometrically simple fractured porous media were conducted using a 2D finite difference flow code and a particle tracking transport model. As a simplification only advective dispersion was considered. The modelling study produced a large variety of tracer breakthrough curves, including two patterns commonly seen in field data — the backward tailed uni-modal type and the Gaussian type. The study demonstrates that different types of breakthrough might be characteristic of particular sets of conceptual models for heterogeneities and, as such, may provide a useful pointer in the application and interpretation of tracer tests.

Analysis of constructed treatment wetland hydraulics with the transient storage model OTIS

The model one-dimensional transport with inflow and storage (OTIS) was calibrated to results from tracer experiments conducted in the Orlando Easterly Wetland in order to quantify short-circuiting of the treatment volume and temporary storage of tracer in isolated, low-flow regions. OTIS was found to fit experimental data very well for both steady and unsteady flow conditions. The model calibrations indicate the presence of three different hydraulic ‘zones’ of the wetland. The first zone is the actively flowing main channel; the second, a temporary storage zone where water and constituents are exchanged with the main flow channel; and the third, completely isolated, ‘dead’ water. The uncertainty of storage zone parameters was determined to be low due to the experimental Damköhler number that quantifies intra-zone mass transfer processes. The appropriateness of the use of a one-dimensional model for treatment wetlands is also addressed.

Longitudinal dispersion in natural channels: 3. An aggregated dead zone model applied to the River Severn, U.K.

Abstract. An Aggregated Dead Zone (ADZ) model is presented for longitudinal dispersion of tracer in river channels, in which the channel cross-section is divided into two parallel regions: the bulk flow and dead zone storage. Tracer particles in the bulk flow are assumed to obey plug-flow advection at the discharge velocity U without any mixing effects. The dispersive properties of the model are completely embodied in the residence time for tracer storage in the dead zone. The model provides an excellent description and prediction of empirical concentration-time distributions, for times t &lt; x/U. Its physical realism is demonstrated by using it to describe the evolution of a tracer cloud in the River Severn, U.K., and by comparing it with a more complex model which incorporates the additional effects of shear flow dispersion within the bulk flow. The ADZ model is a potentially useful tool for practical prediction of dispersion in natural channels. Keywords: Channels; dispersion; dead zones; tracers; River Severn

Longitudinal dispersion in natural channels: 2. The roles of shear flow dispersion and dead zones in the River Severn, U.K.

Abstract. The classical one-dimensional advection-diffusion equation (ADE) gives an inadequate description of tracer cloud evolution in the River Severn, U.K. A solute transport model incorporating the effects of tracer storage in dead zones is presented in which the channel is conceived as being divided into two parallel regions. The bulk flow region occurs in the central part. Its longitudinal dispersive properties are described by the ADE. Adjacent to this, an additional cross-sectional area is defined in which tracer can be stored temporarily in regions of slowly moving water called dead zones. Exchange between the two regions follows a first order rate equation. Applying the model to the River Severn shows that a dispersing cloud’s evolution occurs in two distinct stages with a rapid transitional phase. Initially, shear-dispersion is dominant while the tracer particles mix fully over the bulk flow. Once this has occurred, dead zone storage accounts well for the non-Fickian evolution of the cloud. After the transitional phase the dead zone storage mechanism clearly dominates over shear-dispersion. Overall, the combined shear flow dispersion – dead zone model (D-DZM) provides a much better, physically consistent description of the tracer cloud’s evolution than the simple classical ADE approach can do alone. Keywords: Channels; dispersion; dead zones; tracers; River Severn

Sensitive Human Thyrotropin Immunoradiometric Assay Set Up by the Identification and Minimization of Nonspecific Bindings

An immunoradiometric assay (IRMA) of human thyrotropin (hTSH), based on magnetic solid phase separation, was studied especially in terms of its nonspecific bindings (B0) which were identified as a product of the interaction between an altered form of radioiodinated anti-hTSH monoclonal antibody (125l-mAB) and the uncoupled magnetizable cellulose particle (matrix). Preincubation with the same matrix, solid phase saturation with milk proteins, tracer storage at 4°C and serum addition during incubation were found to be particularly effective in preventing their formation. These findings were used to reproducibly decrease nonspecific bindings to values < 0.1% (or < 70 cpm), thus increasing the signal-to-noise ratio (B60/B0) up to values of 300-500. This way hTSH radioassays were obtained with functional sensitivities of about 0.05 mlU/L and analytical sensitivities of the order of 0.02 mlU/L. Such sensitivities, and, more importantly, a general improvement in assay performance, were obtained in a highly reproducible manner and all over the useful tracer life.

Interactions of solutes and streambed sediment: 1. An experimental analysis of cation and anion transport in a mountain stream

An experimental injection was performed to study the transport of stream water solutes under conditions of significant interaction with streambed sediments in a mountain pool‐and‐riffle stream. Experiments were conducted in Little Lost Man Creek, Humboldt County, California, in a period of low flow duringwhich only a part of the bank‐full channel held active surface flow. The injection of chloride and several trace cations lasted 20 days. In this report we discuss the results of the first 24 hours of the injection and survey the results of the first 10 days. Solute‐streambed interactions of two types were observed. First, the physical transport of the conservative tracer, chloride, was affected by intergravel flow and stagnant watt, zones created by the bed relief. Second, the transport of the cations (strontium, potassium, and lithium) was appreciably modified by sorption onto streambed sediment. In the stream the readily observable consequence of the solute‐streambed interactions was an attenuation of the dissolved concentration of each of the tracers. The attenuation in the stream channel occurred concurrently with the storage of tracers in the streambed via both physical and chemical processes. All tracers were subsequently present in shallow wells dug several meters from the wetted part of the channel. Sediment samples collected approximately 3 weeks after the start of the injection contained increased concentrations of the injected cations.

Macromolecular transport in the spiral prominence.

Transport of macromolecules in the spiral prominence of the guinea pig was studied after perilymphatic and intravenous horseradish peroxidase (HRP) injection. HRP was taken up by the spiral prominence epithelium from the perilymphatic space and in a much higher degree from the endolymphatic space. A highly endocytic activity was shown by the stroma cells surrounding the spiral prominence vessel. HRP particles were stored in the cytoplasm within vesicles and vacuoles of different sizes and different contrasts. The mode of tracer storage in the spiral prominence epithelium and in the stroma cells from the morphological point of view suggests lysosomal digestion. HRP was transported from the perilymphatic space into the spiral prominence vessel lumen by means of vesicular transport through the vessel wall, while transport of the tracer from the vessel lumen into the perilymphatic space after intravenous injection was not observed.

Improved radioimmunoassay for human TSH

This study concerns the optimization of the human TSH (h-TSH) radio-immunoassay with special emphasis on reducing the heterogeneity of the 125I h-TSH tracer. Enzymatic iodination of h-TSH with glucose oxidase/lactoperoxidase was shown to be superior to either low or high dose chloramine-T procedures, producing a high specific activity reagent (70–150 μCi/μg) with minimal evidence of damage. Tracer purification procedures not only affected initial immunoactivity but also storage stability and heterogeneity of the resulting 125I h-TSH. Tracers purified by combining concanavalin A-Sepharose adsorption and high resolution gel filtration (Sephadex G100), produced significantly lower ( p < 0.001) serum h-TSH measurements than were observed in less purified tracer materials. Concanavalin A-Sepharose adsorption yield of the 125I h-TSH iodination products closely correlated with the yield ( r = 0.85, p < 0.001) and immunoactivity ( r = 0.90, p < 0.001) of the tracer produced, thus making this an ideal method for initial tracer purification. Storage of tracer adsorbed to a solid support (concanavalin A-Sepharose) reduced technical manipulations without compromising tracer performance. Loss of specific activity was minimized by storage at −70°C. The assay developed using these technical approaches showed a sensitivity limit of 0.005 ± 0.001 (S.E.M.) μU/tube; 50% displacement at 0.18 ± 0.08 (S.E.M.) μU/tube and complete delineation between euthyroid ( n = 49 2.44 ± 0.18 (S.E.M.) mU/1, range 1.00–6.08) and hyperthyroid.( n = 62 0.34 ± 0.02 (S.E.M.) mU/1, range 0.10–0.85), serum h-TSH levels.