Uptake and transfer of14C-simetryne through the laboratory freshwater food chain

This paper deals with the bioconcentration of¹⁴C-simetryne from water by aquatic test organisms: green algae—Monoraphidium minutum, rotifers—Brachionus rubens, daphnids—Daphnia magna, and fish—Brachydanio rerio. The chemical was bioconcentrated rapidly in all test species during the first 48 hours of experiment. The BCF values (bioconcentration factor) from all uptake studies show that simetryne has higher accumulation in algae than in rotifers, daphnids and zebra fish. The logarithm of the n-octanol/water partition coefficient of simetryne measured as 2.06±0.05 was correlated with the BCFs in the organisms as based on the lipid contents. ¹⁴C-simetryne uptake via the food-chain amounted to only 22% to 42% of the bioconcentration from water. Clearance of¹⁴C-derived residues from fish was rapid with a half-life of 2.1 days. This project is a part of a cooperation program between the Institute of Hydrobiology, Academia Sinica, Wuhan, and the Institut fur Okologische Chemie, GSF, F. R. Germany, and is supported by the Natural Science Foundation of Academia Sinica.     

Bank‐toe processes in incised channels: the role of apparent cohesion in the entrainment of failed bank materials

Numerous processes may instigate bank retreat and the consequent collection of failed cohesive materials at the bank toe. Cohesion between the failed material and the substrate can provide additional strength to resist direct fluvial entrainment. Failed, cohesive material can act as a form of natural bank‐toe protection by consuming and diverting flow energy that may otherwise be used to further scour the basal zone of incising channels. Investigations in Goodwin Creek, Mississippi, have revealed the existence of apparent cohesion between failed, cohesive blocks and their underlying surface. The method used to assess this cohesion involved a pulley system mounted on a tripod and supporting a load cell. Mean and maximum apparent‐cohesion values of 1·08 kPa and 2·65 kPa, respectively, were measured in this way, identifying a source that bonds blocks to the underlying surface. Cohesion values and types vary spatially and temporally. Tensiometric tests beneath blocks suggest that cohesion resulting from matric suction alone may be as much as 3·5 kPa in summer and 1·8 kPa in winter. Apparent cohesion is believed to have been sufficient to help prevent removal of the largest blocks by a peak flow of 66·4m³/s on 23 September 1997. Maximum excess shear stress required to entrain a D₇₅ block can be augmented by as much as 97% by the presence of apparent cohesion at the block–substrate interface when compared with a condition with zero apparent cohesion at the block underside. Given these findings, it is no longer sufficient to estimate block entrainment in the basal area from block size or bed roughness alone, as in a Shields‐type approach. Copyright © 2001 John Wiley & Sons, Ltd.     

A graduate student experience with Professor Donald V. Helmberger

A year after the passing of Don Helmberger,it is remarkable how memories of interactions with him over my entire professional career continue to spark affection...     

Hydrological influences on hyporheic water quality: implications for salmon egg survival

The spatial and temporal variability of groundwater–surface‐water (GW–SW) interactions was investigated in an intensively utilized salmon spawning riffle. Hydrochemical tracers, were used along with high‐resolution hydraulic head and temperature data to assess hyporheic dynamics. Surface and subsurface hydrochemistry were monitored at three locations where salmon spawning had been observed in previous years. Temperature and hydraulic head were monitored in three nests of three piezometers located to characterize the head, the run and the tail‐out of the riffle feature. Hydrochemical gradients between surface and subsurface water indicated increasing GW influence with depth into the hyporheic zone. Surface water was characterized by high dissolved oxygen (DO) concentrations, low alkalinity and conductivity. Hyporheic water was generally characterized by high levels of alkalinity and conductivity indicative of longer residence times, and low DO, indicative of reducing conditions. Hydrochemical and temperature gradients varied spatially over the riffle in response to changes in local GW–SW interactions at the depths investigated. Groundwater inputs dominated the head and tail of the riffle. The influence of SW increased in the area of accelerating flow and decreasing water depth through the run of the riffle. Temporal GW–SW interactions also varied in response to changing hydrological conditions. Gross changes in hyporheic hydrochemistry were observed at the weekly scale in response to changing flow conditions and surface water inputs to the hyporheic zone. During low flows, caused by freezing or dry weather, hyporheic hydrochemistry was dominated by GW inputs. During higher flows hyporheic hydrochemistry indicated that SW contributions increased. In addition, high‐resolution hydraulic head data indicated that rapid changes in GW–SW interactions occurred during hydrological events. The spatial, and possibly the temporal, variability of GW–SW interactions had a marked effect on the survival of salmon ova. It is concluded that hyporheic dynamics and their effect on stream ecology should be given increased consideration by fisheries and water resource managers. Copyright © 2004 John Wiley & Sons, Ltd.     

RING CURRENT DYNAMICS DURING THE 13–18 JULY 2000 STORM PERIOD

We study the development of the terrestrial ring current during the time interval of 13–18 July, 2000, which consisted of two small to moderate geomagnetic storms followed by a great storm with indices Dst=−300 nT and Kp=9. This period of intense geomagnetic activity was caused by three interplanetary coronal mass ejecta (ICME) each driving interplanetary shocks, the last shock being very strong and reaching Earth at ∼ 14 UT on 15 July. We note that (a) the sheath region behind the third shock was characterized by B _z fluctuations of ∼35 nT peak-to-peak amplitude, and (b) the ICME contained a negative to positive B _z variation extending for about 1 day, with a ∼ 6-hour long negative phase and a minimum B _z of about −55 nT. Both of these interplanetary sources caused considerable geomagnetic activity (Kp=8 to 9) despite their disparity as interplanetary triggers. We used our global ring current-atmosphere interaction model with initial and boundary conditions inferred from measurements from the hot plasma instruments on the Polar spacecraft and the geosynchronous Los Alamos satellites, and simulated the time evolution of H⁺, O⁺, and He⁺ ring current ion distributions. We found that the O⁺ content of the ring current increased after each shock and reached maximum values of ∼ 60% near minimum Dst of the great storm. We calculated the growth rate of electromagnetic ion cyclotron waves considering for the first time wave excitation at frequencies below O⁺ gyrofrequency. We found that the wave gain of O⁺ band waves is greater and is located at larger L shells than that of the He⁺ band waves during this storm interval. Isotropic pitch angle distributions indicating strong plasma wave scattering were observed by the imaging proton sensor (IPS) on Polar at the locations of maximum predicted wave gain, in good agreement with model simulations.     

Trajectories of Moving Objects on a Network: Detection of Similarities,Visualization of Relations,and Classification of Trajectories

Development in techniques of spatial data acquisition enables us to easily record the trajectories of moving objects. Movement of human beings, animals, and birds can be captured by GPS loggers. The obtained data are analyzed by visualization, clustering, and classification to detect patterns frequently or rarely found in trajectories. To extract a wider variety of patterns in analysis, this article proposes a new method for analyzing trajectories on a network space. The method first extracts primary routes as subparts of trajectories. The topological relations among primary routes and trajectories are visualized as both a map and a graph‐based diagram. They permit us to understand the spatial and topological relations among the primary routes and trajectories at both global and local scales. The graph‐based diagram also permits us to classify trajectories. The representativeness of primary routes is evaluated by two numerical measures. The method is applied to the analysis of daily travel behavior of one of the authors. Technical soundness of the method is discussed as well as empirical findings.     

Computer program for stability analysis of steep,cohesive riverbanks

The ability to predict the stability of eroding riverbanks is a prerequisite for modelling alluvial channel width adjustment and a requirement for predicting bank erosion rates and sediment yield associated with bank erosion. Mass‐wasting of bank materials under gravity occurs through a variety of specific mechanisms, with a separate analysis required for each type of failure. This paper presents a computer program for the analysis of the stability of steep, cohesive riverbanks with respect to planar‐type failures. Planar‐type failures are common along stream channels destabilized by severe bed degradation. Existing stability analyses for planar‐type failures have a number of limitations that affect their physical basis and predictive ability. The computer program presented here is based on an analysis developed by Darby and Thorne. The software takes account of the geotechnical characteristics of the bank materials, the shape of the bank profile, and the relative elevations of the groundwater and surface water to estimate stability with respect to mass failure along a planar‐type failure surface. Results can be displayed either in terms of a factor of safety (ratio of resisting to driving forces), or probability of failure. The computer analysis is able to determine the relative amounts of bed degradation and bank‐toe erosion required to destabilize an initially stable bank. Data for the analysis are supplied in the form of either HEC‐2 hydrographic survey data files or user‐supplied bank profile data, in conjunction with user‐supplied geotechnical parameter values. Some examples, using data from the Upper Missouri River in Montana, are used to demonstrate potential applications of the software. Copyright © 2000 John Wiley & Sons, Ltd.