Characterizing bioavailable phosphorus concentrations in an agricultural stream during hydrologic and streambed disturbances

In freshwater ecosystems, phosphorus (P) is often considered a growth-limiting nutrient. The use of fertilizers on agricultural fields has led to runoff-driven increases in P availability in streams, and the subsequent eutrophication of downstream ecosystems. Isolated storms and periodic streambed dredging are examples of two common disturbances that contribute dissolved and particulate P to agricultural streams, which can be quantified as soluble reactive P (SRP) using the molybdate-blue method on filtered water samples, or total P (TP) measured using digestions on unfiltered water reflecting all forms of P. While SRP is often considered an approximation of bioavailable P (BAP), research has shown that this is not always the case. Current methods used to estimate BAP do not account for the role of biology (e.g., NaOH extractions) or require specialized platforms (e.g., algal bioassays). Here, in addition to routine analysis of SRP and TP, we used a novel yeast-based bioassay with unfiltered sample water to estimate BAP concentrations during two storms (top 80% and?>?95% flow quantiles), and downstream of a reach where management-associated dredging disturbed the streambed. We found that the BAP concentrations were often greater than SRP, suggesting that SRP is not fully representative of P bioavailability. The SRP concentrations were similarly elevated during the two storms, but remained consistently low during streambed disturbance. In contrast, turbidity and TP were elevated during all events. The BAP concentrations were significantly related to turbidity during all disturbance events, but with TP only during storms. The novel yeast assay suggests that BAP export can exceed SRP, particularly when streams are not in equilibrium, such as the rising limb of storms or during active dredging.

     

Quantifying Burial,the Transport of Matter from the Lake Biosphere to the Geosphere

Burial is one of the most fundamental processes in contexts of massbalance calculations for substances (such as nutrients, organics, metals and radionuclides) in lakes. Substances can leave a lake by two processes, outflow, i.e., the transport to a downstream system, and burial, i.e., the transport by sedimentation from the lake biosphere to the geosphere. This work gives for the first time, to there best of the author's knowledge, a review on the factors and processes regulating burial and presents a general model for burial. This approach accounts for bottom dynamic conditions (i.e., where areas of fine sediment erosion, transport and accumulation prevail), sedimentation, bioturbation, mineralisation, and the depth and age of the bioactive sediment layer. This approach has been critically tested with very good results for radiocesium, radiostrontium, many metals, calcium from liming and phosphorus, but it has not been presented before in a comprehensive way. This model for burial is meant to be used in massbalance models based on ordinary differential equations (i.e., box models) in contexts where burial is not a target y‐variable but a necessary model variable (an x‐variable). This means that there are also specific demands on this approach, e.g., it must be based on readily accessible driving variables so that it is not too difficult to use the model in practice within the context of an overall lake model. The factors influencing burial, e.g., the deposition of materials and the depth of the bioactive sediment layer, are also needed in calculations of sediment concentrations and to determine amounts of substances or pollutants in sediments. To carry out such calculations, one also needs information on sediment bulk density, water content and organic content. This paper also presents new empirical models for such calculations to be used in the new model for burial.     

Integrative Analysis of the Physical Transport Network into Australia

Effective biosecurity is necessary to protect nations and their citizens from a variety of threats, including emerging infectious diseases, agricultural or environmental pests and pathogens, and illegal wildlife trade. The physical pathways by which these threats are transported internationally, predominantly shipping and air traffic, have undergone significant growth and changes in spatial distributions in recent decades. An understanding of the specific pathways and donor-traffic hotspots created by this integrated physical transport network is vital for the development of effective biosecurity strategies into the future. In this study, we analysed the physical transport network into Australia over the period 1999–2012. Seaborne and air traffic were weighted to calculate a “weighted cumulative impact” score for each source region worldwide, each year. High risk source regions, and those source regions that underwent substantial changes in risk over the study period, were determined. An overall risk ranking was calculated by integrating across all possible weighting combinations. The source regions having greatest overall physical connectedness with Australia were Singapore, which is a global transport hub, and the North Island of New Zealand, a close regional trading partner with Australia. Both those regions with large amounts of traffic across multiple vectors (e.g., Hong Kong), and those with high levels of traffic of only one type (e.g., Bali, Indonesia with respect to passenger flights), were represented among high risk source regions. These data provide a baseline model for the transport of individuals and commodities against which the effectiveness of biosecurity controls may be assessed, and are a valuable tool in the development of future biosecurity policy.     

腐殖质呼吸作用及其生态学意义

腐殖质呼吸是厌氧环境中普遍存在的一种微生物呼吸代谢模式.自1996年发现以来,日益成为生态学与环境科学领域的研究热点.在厌氧条件下,一些微生物能以腐殖质作为唯一电子受体,氧化环境中的有机质或者甲苯等环境有毒物质,产生CO2,参与碳循环;同时,腐殖质呼吸作用产生的还原态腐殖质可以还原环境中的一些氧化态物质,如Fe(III)、Mn(IV)、Cr(VI)、U(VI) 、硝基芳香化合物和多卤代污染物.因此,腐殖质呼吸能够影响环境中C、N、Fe、Mn以及一些痕量金属元素的生物地球化学循环,并且能够促进重金属以及有机污染物的脱毒,在水体自净、污染土壤原位修复、污水处理等方面具有积极作用.     

Transported material in a small river with multiple impoundments

SUMMARY.

• 1 The transport of particulate material in a multiply-impounded southern African river was studied from source to mouth over a period of 2 years during base flow conditions.
• 2 More than 95% of the dissolved and particulate material in transport was ultra fine (<80 μm). We conclude that too much emphasis has been placed on coarse material (>1 mm) in theories of river ecosystem functioning.
• 3 The ratio of CPOM:FPOM (1000–4000:250–1000 μm) in transport decreased with increasing stream order as a result of inputs of FPOM from pollution sources and from plankton blooms discharged from reservoirs.
• 4 The downstream effects of impoundment depended largely on the type of release and the quality of the inflowing water: surface-releasing reservoirs in the clean, upper reaches of the river had the least effect on transported material. A polluted surface-release impoundment in the mid-reaches of the river converted the particle size spectrum of the river from small (<80 μm) to large (250–1000 μm). Bottom-released water carried high concentrations (36–190 g m³) of small (<5 μm) and largely inorganic (86–93%) material.
• 5 The distance required for zooplankton densities to reduce by 95% was between 4 and 8 km downstream of an impoundment, except below a polluted impoundment where zooplankton densities took 32–35 km to reduce by 95%.
• 6 Most of the downstream changes in transported organic matter in the Buffalo River are due to inflows of agricultural and urban effluent. These disturbances to the river cause greater perturbations than do the impoundments.

     

Probabilistic settling in the Local Exchange Model of turbulent particle transport

The Local Exchange Model (LEM) is a stochastic diffusion model of particle transport in turbulent flowing water. It was developed mainly for application to particles of near-neutral buoyancy that are strongly influenced by turbulent eddies. Turbulence can rapidly transfer such particles to the bed, where settlement can then occur by, for example, sticking to biofilms (e.g., fine particulate organic matter, or FPOM) or attaching to the substrate behaviorally (e.g., benthic invertebrates). Previous papers on the LEM have addressed the problems of how long (time) and far (distance) a suspended particle will be transported before hitting the bed for the first time. These are the hitting-time and hitting-distance problems, respectively. Hitting distances predicted by the LEM for FPOM in natural streams tend to be much shorter than the distances at which most particles actually settle, suggesting that particles usually do not settle the first time they hit the bed. The present paper extends the LEM so it can address probabilistic settling, where a particle encountering the bed can either remain there for a positive length of time (i.e., settle) or immediately reflect back into the water column, each with positive probability. Previous results for the LEM are generalized by deducing a single set of equations governing the probability distribution and moments of a broad class of quantities that accumulate during particle trajectories terminated by hitting or settling on the bed (e.g., transport time, transport distance, cumulative energy expenditure during transport). Key properties of the settling-time and settling-distance distributions are studied numerically and compared with the observed FPOM settling-distance distribution for a natural stream. Some remaining limitations of the LEM and possible means of overcoming them are discussed.     

Effects of experimental playbacks on availability for detection during point counts

Point counts are the most commonly used technique for surveying passerines during the breeding season. Several methods for estimating probabilities of detection during point count surveys have been developed. These methods have focused primarily on accounting for the influence of environmental factors (e.g., weather and noise) on detectability, however, the probability that birds are available for detection (e.g., sings or moves) during point counts has received less attention. We used sequential point counts to determine the effect of playback of the mobbing calls of Black‐capped Chickadees (Poecile atricapillus) and the flight calls of Red‐tailed Hawks (Buteo jamaicensis) on availability for detection (e.g., singing or moving) during point‐count surveys. We conducted 180 point counts over a 2‐yr period in central – east central Minnesota to evaluate the possible effect of playbacks on observed density, overall species richness, minute of first detection, and distance of first detection. We also used removal models to quantify the magnitude of changes in detectability and direction of response to playbacks for 10 focal species. Playback of the mobbing calls of Black‐capped Chickadees increased observed density and decreased the average distance of detection and time of first detection, whereas playback of the flight calls of a Red‐tailed Hawk resulted in a decrease in observed density and species richness, and an increased time of first detection. Playback treatment was a covariate in all best performing models for the 10 species analyzed, but the magnitude and direction of response to playbacks were species specific. The importance of playback type in detectability models indicates that the calls of heterospecifics can influence species availability for detection. As such, researchers using playback methods should seek to quantify species‐specific responses in detection probability and consider how component detection probabilities could influence survey outcomes.     

Cutters,carriers and transport chains: Distance-dependent foraging strategies in the grass-cutting ant <Emphasis Type="Italic">Atta vollenweideri</Emphasis>

Summary Most studies on leaf-cutting ant foraging examined forest species that harvest dicot leaves. We investigated division of labor and task partitioning during foraging in the grass-cutting ant Atta vollenweideri. Workers of this species harvest grass fragments and transport them to the nest for distances up to 150 m along well-established trunk trails. We recorded the behavior of foraging ants while cutting and monitored the transport of individually-marked fragments from the cutting site until they reached the nest. A. vollenweideri foragers showed division of labor between cutting and carrying, with larger workers cutting the fragments, and smaller ones transporting them. This division was less marked when plants were located very close to the nest and no physical trail was present, i.e., the cutter often transported its own fragment back to the nest. On long foraging trails, the transport of fragments was a partitioned task, i.e., workers formed transport chains composed of 2 to 5 carriers. This sequential load transport occurred more often on long than on short trails. The first carriers in a transport chain covered only short distances before dropping their fragments, and they were observed to turn back and revisit the patch. The last carriers covered the longest distance. The probability of dropping the carried fragment on the trail was independent of both worker and fragment size, and there was no particular location on the trail for dropping, i.e., fragments were not cached. Transport time of fragments transported by a chain was longer than for those transported by single workers all the way to the nest, i.e., sequential transport did not save foraging time. Two hypotheses concerning the possible adaptive value of transport chains are discussed. The first one argues that sequential transport may lead to an increased material transport rate compared to individual transport. The second one considers sequential transport as a way to enhance the information flow among foragers, thus leading to a quicker build-up of workers at particular harvesting places. It is suggested that rather than increasing the gross transport rate of material, transport via chains may favor the transfer of information about the kind of resource being actually harvested.Received 19 December 2002; revised 14 March 2003; accepted 19 March 2003     

Electrophoretic Analysis of Axonally Transported Proteins in Toad Retinal Ganglion Cells

As a preliminary step to studying changes in axonal transport in regenerating neurons, we have analyzed the composition and organization of polypeptides normally axonally transported in a neuronal system capable of regeneration, i.e., the retinal ganglion cells of the toad, Bufo marinus. We labeled proteins synthesized in the retina with 35S-methionine and subsequently used one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis to analyze labeled, transported proteins in tissues containing segments of the axons (the optic nerve, optic tract, and optic tecta) of the retinal ganglion cells. The transported polypeptides could be divided into five groups according to their apparent transport velocities. Many of the polypeptides of each group were electrophoretically similar to polypeptides of corresponding groups previously described in rabbit and guinea pig retinal ganglion cells, and in some cases, additional properties of the polypeptides indicated that the transported materials of the two vertebrate classes were homologous. These results serve two purposes. First they establish the retinal ganglion cells of the toad Bufo marinus as a model system in which changes in gene expression related to regeneration may be studied. Second they show that the organization and many aspects of the composition of axonal transport in retinal ganglion cells have been conserved in animals as unrelated as amphibians, and mammals.     

Use of fluorescent sphingolipid analogs to study lipid transport along the endocytic pathway

Sphingolipids (SLs) are concentrated at the plasma membrane where they play important roles in cell-cell communication, host-pathogen interactions, and cell signaling events. Our laboratory has used fluorescent SL analogs and SL-binding toxins to elucidate mechanisms by which SLs are internalized by endocytosis and subsequently sorted and transported to various intracellular compartments. These studies have relied on the use of temperature shift protocols, co-localization studies with compartment-specific markers, selective biochemical treatments that inhibit specific endocytic mechanisms, and the expression of dominant negative proteins (e.g., rabs) that block specific steps in transport. These methods are presented here so that they can be utilized by others for the study of endocytic trafficking of lipids and other molecules.     

Chemical factors that influence nucleocytoplasmic transport: a fluorescence photobleaching study

The technique of fluorescence redistribution after photobleaching was used to measure the translocation rate of fluorescein-labeled dextrans across the nuclear pore complex in isolated rat liver nuclei. A transport assay system was established that could monitor the effect of biologically active molecules, e.g., ATP, GTP, cAMP on the translocation process. The results show that ATP, phosphoinositides, RNA, and insulin can enhance transport rates from 195 to 432%. It was further demonstrated that concanavalin A, but not wheat germ or soybean agglutinin, can block dextran transport completely. The effectors of dextran transport are similar to substances demonstrated to effect the efflux of RNA from isolated nuclei. A model for translocation through the nuclear pore is now presented that incorporates data from protein influx and RNA efflux experiments into a single pathway controlled by ATP.     

Nitrification rates in the lower river Rhine as a monitor for ecological recovery

The rate of in situ nitrification was tested as an indicator of the toxicological quality of the river Rhine. Concentration changes of ammonium ions over 85 to 133 km long reaches of three river branches downstream of the densely populated Ruhr-area (F.R.G.) were calculated from a data base for the period 1972 to 1986. Concentrations of ammonium in the river exceeded values of 1 mg N/l in winter. Because of the very high input of ammonium, bacterial nitrification dominated over other nitrogen processes. Relative rates of nitrification in the three river branches were proportional to the water temperature for the individual years. Nitrification rates in the river increased by a factor of ca. 4 during the period of 1972 to 1986. Toxic substances, whose concentrations decreased in the same period of time, were proposed as inhibitors of in situ nitrification rather than e.g. a low oxygen saturation of the water. The improvement of the conditions in the river, indicated by the in situ rate of nitrification, was also documented by data on macrofauna and fish populations.     

El Nino effects on hydrogen ion concentration of a California reservoir

Hydrogen ion concentration, [H⁺], of discharge water from Pardee reservoir in the central Sierra Nevada, California was greater than expected in years of El Nino occurrence over the period 1954–86. This pattern is in addition to the general increase in [H⁺] over the same period attributed to acidic atmospheric deposition. Monthly means of [H⁺] also show differences between El Nino and non-El Nino years. Total annual runoff does not seem to be a controlling factor; the source and timing of storms are probably more important. Storms are usually from the west or northwest, but during El Nino years tropical-like storms from a more-southerly direction appear to carry acidic pollutants to the central Sierra Nevada.     

Centrifuge Modeling of Cadmium Migration in Saturated and Unsaturated Soils

Researchers recently have come to recognize that geotechnical centrifuge can provide a powerful experimental tool for investigating the flow and transport of inorganic contaminants in soils. Inert, non-adsorptive inorganic compounds (e.g., sodium ions) rather than adsorptive heavy metals are often used as the chemical for the investigation of pollutant transport behavior in most centrifuge modeling. To overcome the shortcomings of this approach, centrifuge tests for the study of one-dimensional pollutant migration in both saturated and unsaturated soils were designed using an adsorptive pollutant (i.e., cadmium) and conducted at two centrifugal accelerations. In this study, the concentration profile of adsorptive cadmium along the depth of soil, the moisture content varying with the soil depth and the transport behavior of the cadmium in soils were investigated. The centrifuge results show that the cadmium concentration profiles are found to be similar for the centrifuge models performed at 15 g and 20 g and the one-dimensional moisture movement in the unsaturated soil can be reproducible. The validity of centrifuge modeling of adsorptive pollutants might be affected by the g-level that, in turn, determines the centrifuge testing time and affects the sorption equilibrium.     

Biomonitoring of air pollution as exemplified by recent IAEA programs

Biomonitoring is an appropriate tool for assessing the levels of atmospheric pollution, having several advantages compared with the use of direct measurements of contaminants (e.g., in airborne particulate matter, atmospheric deposition, precipitation), related primarily to the permanent and common occurrence of the chosen organisms in the field, the ease of sampling, and trace element accumulation. Furthermore, biomonitors may provide a measure of integrated exposure over an extended period of time and are present in remote areas and no expensive technical equipment is involved in collecting them. They accumulate contaminants over the exposure time and concentrate them, thus facilitating analytical measurements. Based on largescale biomonitoring surveys, polluted areas can be identified, and by applying appropriate statistical tools, information can be obtained on the type of pollution sources and on the transboundary transport of atmospheric pollutants. The International Atomic Energy Agency is including the research on biomonitors in its projects on health-related environmental studies. Biomonitoring activities from several coordinated research projects on air pollution are presented, and results from an international workshop are discussed. In addition, activities in supporting improvement quality in the participating laboratories are outlined.     

One axon,many kinesins: What's the logic?

A large number of membrane-bounded organelles, protein complexes, and mRNAs are transported along microtubules to different locations within the neuronal axon. Axonal transport in the anterograde direction is carried out by members of a superfamily of specialized motor proteins, the kinesins. All kinesins contain a conserved motor domain that hydrolyses ATP to generate movement along microtubules. Regions outside the motor domain are responsible for cargo binding and regulation of motor activity. Present in a soluble, inactive form in the cytoplasm, kinesins are activated upon cargo binding. Selective targeting of different types of kinesin motors to specific cargoes is directed by amino acid sequences situated in their variable tails. Cargo proteins with specific function at their destination, bind directly to specific kinesins for transport. Whereas most kinesins move to microtubule plus-ends, a small number of them move to microtubule minus-ends, and may participate in retrograde axonal transport. Axonal transport by kinesins has a logic: Fully assembled, multisubunit, functional complexes (e.g., ion channel complexes, signaling complexes, RNA-protein complexes) are transported to their destination by kinesin motors that interact transiently (i.e., during transport only) with one of the complexes' subunits.     

Nutrient transport systems in brain: 40 years of progress

In the last 40 years, especially with the application of new neurochemical and molecular biologic techniques, there has been an explosive progress in understanding how nutrients are transported across the blood–brain barrier and choroid plexus into brain and CSF, and how nutrient homeostasis in brain is achieved. In most cases, there are separate transporters, or in a few cases, systems that transport related substances (e.g., biotin, lipoic, and pantothenic acids). This review focuses on three crucial nutrients (glucose, ascorbic acid, and folates) for which there is substantial new information including ‘knock down’ and ‘knockout’ models in mice and/or humans. The overall objective is to show that this new knowledge leads not just to a more thorough understanding (e.g., of ‘why’ questions like: why do neurons require up to 10 mM ascorbic acid intracellulary?); but in some cases leads to clinically important predictions that allow treatment of heretofore devastating neurologic disorders.     

Fast axonal transport in motor nerve regeneration.

This report describes the fast transport of [3H]-leucine-labeled proteins in regenerating rat sciatic motor nerves. A normal rate of fast transport (383 +/- 33 mm/day) was present in the regenerating sprouts, as well as in the central stumps. The rapidly transported proteins passed the level of axotomy without impediment, and accumulated in the endings of the regenerating sprouts, as shown by electron microscope autoradiography. In addition, transported proteins accumulated in terminal neuromas. The relative amount of protein-incorporated radioactivity in the crest of transport in the regenerating nerves was increased compared to control nerves. These results are interpreted to suggest that the mechanism of fast transport is the same in regenerating nerves was increased compared to control nerves. These results are interpreted to suggest that the mechanism of fast transport is the same in regenerating sprouts as in normal axons; during regeneration fast transport appears to add newly synthesized materials to the growing tip.     

Environmental pollutants and skin cancer

We are increasingly exposed to environmental pollution. Pollutants can be inhaled, ingested or come into contact with the skin depending on the form in which they occur. On metabolization, activation, or accumulation, pollutants can become extremely toxic for the vital organs and this is often related to a strong genotoxic effect. Since the skin acts as a barrier between the organism and the environment, it is frequently directly exposed to pollution. It is very often degraded by polluting agents and acts as an inlet toward other tissues. Numerous studies in man recognize and demonstrate the carcinogenic power of certain pollutants in the digestive and respiratory tracts. The "pollutants" that react most specifically with the skin are: ultraviolet radiation, polycyclic aromatic hydrocarbons (e.g., benzo[a]pyrene), volatile organic compounds (e.g., benzene), heavy metals, and ozone. Ultraviolet radiation, a "physical" pollutant, has been described as being the factor responsible for most skin cancers in man. The genotoxicity of UV light is well documented (type of lesion or mutation, etc.) and its carcinogenic effect is clearly demonstratedin vivo in man. A few epidemiological studies describe the carcinogenicity of certain pollutants such as arsenic or lead on the skin. However, most of the evidence for the role of pollutants in skin cancers comes fromin vivo animal studies or fromin vitro studies (e.g., PAHs). In this report, different studies are presented to illustrate the research strategies developed to investigate the mechanism of action of "chemical" pollutants and their potential role in human skin pathology. All the study models and the associated techniques of investigation are tools for a better understanding and thus more efficient prevention of the deleterious effects caused by the environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

River runoff reconstructions from novel spectral luminescence scanning of massive coral skeletons

Inshore massive corals often display bright luminescent lines that have been linked to river flood plumes into coastal catchments and hence have the potential to provide a long-term record of hinterland precipitation. Coral luminescence is thought to result from the incorporation of soil-derived humic acids transported to the reef during major flood events. Corals far from terrestrial sources generally only exhibit dull relatively broad luminescence bands, which are attributed to seasonal changes in coral density. We therefore tested the hypothesis that spectral ratios rather than conventional luminescence intensity provide a quantitative proxy record of river runoff without the confounding effects of seasonal density changes. For this purpose, we have developed a new, rapid spectral luminescence scanning (SLS) technique that splits emission intensities into red, green and blue domains (RGB) for entire cores with an unprecedented linear resolution of 71.4 μm. Since humic acids have longer emission wavelength than the coral aragonite, normalisation of spectral emissions should yield a sensitive optical humic acid/aragonite ratio for humic acid runoff, i.e., G/B ratio. Indeed, G/B ratios rather than intensities are well correlated with Ba/Ca, a geochemical coral proxy for sediment runoff, and with rainfall data, as exemplified for coral records from Madagascar. Coral cores also display recent declining trends in luminescence intensity, which are also reported in corals elsewhere. Such trends appear to be associated with a modern decline in skeletal densities. By contrast, G/B spectral ratios not only mark the impact of individual cyclones but also imply that humic acid runoff increased in Madagascar over the past few decades while coral skeletal densities decreased. Consequently, the SLS technique deconvolves the long-term interplay between humic acid incorporation and coral density that have confounded earlier attempts to use luminescence intensities as a proxy for river runoff.