Turbidity Patterns Research Articles

Hydrodynamics and sediment-transport in the nearshore of Poverty Bay, New Zealand: Observations of nearshore sediment segregation and oceanic storms

Nearshore regions act as an interface between the terrestrial environment and deeper waters. As such, they play important roles in the dispersal of fluvial sediment and the transport of sand to and from the shoreline. This study focused on the nearshore of Poverty Bay, New Zealand, and the processes controlling the dispersal of sediment from the main source, the Waipaoa River. Hydrodynamics and sediment-transport in water shallower than 15 m were observed from April through mid-September 2006. This deployment afforded observations during 3–4 periods of elevated river discharge and 5 dry storms. Similar wind, river discharge, wave, current, and turbidity patterns were characterized during three of the wet storms. At the beginning of each event, winds blew shoreward, increasing wave heights to 2–3 m within Poverty Bay. As the cyclonic storms moved through the system the winds reversed direction and became seaward, reducing the local wave height and orbital velocity while river discharge remained elevated. At these times, high river discharge and relatively small waves enabled fluvially derived suspended sediment to deposit in shallow water. Altimetry measurements indicated that at least 7 cm was deposited at a 15 m deep site during a single discharge event. Turbidity and seabed observations showed this deposition to be removed, however, as large swell waves from the Southern Ocean triggered resuspension of the material within three weeks of deposition. Consequently, two periods of dispersal were associated with each discharge pulse, one coinciding with fluvial delivery, and a second driven by wave resuspension a few weeks later. These observations of nearfield sediment deposition contradict current hypotheses of very limited sediment deposition in shallow water offshore of small mountainous rivers when floods and high-energy, large wave and fast current, oceanic conditions coincide. Consistently shoreward near-bed currents, observed along the 10 m isobath of Poverty Bay, were attributed to a combination of estuarine circulation, Stokes drift, and wind driven upwelling. Velocities measured at the 15 m isobath, however, were directed more alongshore and diverged from those at the 10 m isobath. The divergence in the currents observed at the 10 and 15 m locations seemed to facilitate segregation of coarse and fine sediment, with sand transported near-bed toward the beach, while suspended silts and clays were exported to deeper water.

The role of climate change in the occurrence of algal blooms: Lake Burragorang, Australia

The three‐dimensional hydrodynamic Estuary, Lake and Coastal Ocean Model (ELCOM) was coupled to the ecological Computational Aquatic Ecosystem Dynamics Model (CAEDYM) and to an underflow model to simulate the fate of the constituents from three flood underflow events in Lake Burragorang, Australia, in order to verify the changes in the hydrodynamical behavior that could lead to an algal bloom when the lake water level is low as a consequence of climate change. Simulated patterns of temperature, dissolved oxygen, and turbidity compared well with field data. The ELCOM–CAEDYM simulations demonstrated that the vertical excursion induced by an intrusion depended on the volume of the lake before the arrival of the inflow, on the volume of water inserted by the inflow, and on the proximity between the top insertion of the inflow and the surface layer of the lake. When the water level was low and the inflow volume was high, the underflow constituents mixed into the surface layer and triggered a major algal bloom.

Comparative data mining analysis for information retrieval of MODIS images: monitoring lake turbidity changes at Lake Okeechobee, Florida

In the remote sensing field, a frequently recurring question is: Which computational intelligence or data mining algorithms are most suitable for the retrieval of essential information given that most natural systems exhibit very high non-linearity. Among potential candidates might be empirical regression, neural network model, support vector machine, genetic algorithm/genetic programming, analytical equation, etc. This paper compares three types of data mining techniques, including multiple non-linear regression, artificial neural networks, and genetic programming, for estimating multi-temporal turbidity changes following hurricane events at Lake Okeechobee, Florida. This retrospective analysis aims to identify how the major hurricanes impacted the water quality management in 2003-2004. The Moderate Resolution Imaging Spectroradiometer (MODIS) Terra 8-day composite imageries were used to retrieve the spatial patterns of turbidity distributions for comparison against the visual patterns discernible in the in-situ observations. By evaluating four statistical parameters, the genetic programming model was finally selected as the most suitable data mining tool for classification in which the MODIS band 1 image and wind speed were recognized as the major determinants by the model. The multi-temporal turbidity maps generated before and after the major hurricane events in 2003-2004 showed that turbidity levels were substantially higher after hurricane episodes. The spatial patterns of turbidity confirm that sediment-laden water travels to the shore where it reduces the intensity of the light necessary to submerged plants for photosynthesis. This reduction results in substantial loss of biomass during the post-hurricane period.

Temporal and Spatial Turbidity Patterns Over 30 Years in a Managed Forest of Western Washington1

Abstract: Forest practices have progressively changed over the last 30 years in the Pacific Northwest to address water quality concerns. There have been some assessments of these new management practices made at a site scale but very few studies have attempted to evaluate their efficacy at reducing cumulative sediment production at a watershed scale. Such an evaluation is difficult due to the spatial and temporal variability in sediment delivery and transport processes. Due to this inherent variability, detecting a response to management changes requires a long‐term data record. We utilized a water quality dataset collected over 30 years at four locations in the Deschutes River watershed (western Washington) to assess trends in turbidity and whether sediment control procedures implemented over this time period had any detectable influence. The sample sites ranged from small headwater streams (2.4 and 3.0 km2) to the mainstem of the Deschutes River (150 km2). Declining trends in turbidity were detected at all the permanently monitored sites. The mainstem Deschutes River site, which integrates sediment processes from the entire study watershed, showed dramatic declines in turbidity even with continued active forest management. For the small basins, logging and road construction occurred in the 1970s and 1980s and turbidity declined thereafter, achieving prelogging levels by 2000. There are no temporal trends in flow that could be responsible for the observed trends in turbidity. Our results suggest that increased attention to reducing sediment production from roads and minimizing the amount of road runoff reaching stream channels has been the primary cause of the declining turbidity levels observed in this study.

Turbidity and temperature patterns in a reservoir and its primary tributary from robotic monitoring: Implications for managing the quality of withdrawals

A robotic water quality monitoring network, consisting of 2 in-reservoir profiling platforms and a unit positioned in the primary tributary, was used to document patterns of temperature (T) and turbidity (Tn) and the impact of runoff events on Tn levels over the spring to fall interval of 3 years. The patterns were evaluated in the context of water quality goals for T and Tn for reservoir withdrawal and potential benefits of specified management alternatives. Exceedences of a proposed withdrawal T goal of 21.1 °C (70 °F) and a conservative representation of the Tn goal of 15 NTU were demonstrated. The exceedences occurred in late summer during intervals of extensive drawdown for T and irregularly following runoff events for Tn. Conspicuous increases in Tn in the tributary and lacustrine portions of the reservoir were demonstrated in response to all monitored runoff events (n = 34). Lacustrine levels exceeded 75 NTU following several major events. The turbidity load from the tributary usually enters the reservoir as a turbid density current during runoff events, at a depth predicted well by stream temperature. The high frequency and vertical resolution attributes of the robotic monitoring (2 profiles per day for reservoir deployments) were invaluable in resolving impacts because these were usually attenuated within a week following events. The diminishment of reservoir Tn levels following events was demonstrated to be well represented by a first-order loss rate. The loss rate for the largest runoff event of the study (return interval ~25 y) was more than an order of magnitude lower than any other, indicating a difference in settling attributes of turbidity-causing particles for this extreme case. Benefits from a shift to delayed withdrawals for the existing intake, or installation of a multi-level intake facility, for improving status with respect to the water quality goals are suggested from the monitoring data. However, continuously meeting the Tn goals for particularly severe events may not be feasible through these approaches.

Energy Dissipation and Chemical Treatment to Improve Stilling Basin Performance

Surface water pumped from construction sites frequently contains high levels of turbidity and suspended sediment, which are not effectively removed using gravity-based systems. This study assessed the effects of modifying a permanent pool stilling basin with energy dissipaters and with the addition of polyacrylamide (PAM) on turbidity and suspended sediments. Turbidity was generated by injecting soil into flowing water at a fixed rate for 30 min in a source basin. Turbid water from this basin was pumped from the surface to the stilling basin with physical and chemical treatments. Three energy dissipater treatments were tested: bottom inlet level spreader (BILS; silt fence fabric installed with 40 mm opening from the basin bottom), coir baffles (900 g m-2 coir fabric with 0.45 open space fraction (OSF), and Pyramat baffles (synthetic fabric with 0.10 OSF). The tests were run either with or without PAM dosing by passing the flow over a solid PAM block at the stilling basin inlet. The physical treatments (i.e., energy dissipation) did not significantly affect the turbidity and total suspended solids (TSS) of the water exiting the basin, which were reduced by up to 29% and 36%, respectively. The chemical treatment was much more effective regardless of the physical treatment, either in combination or alone, reducing turbidity and TSS up to 88% and 84%, respectively. The baffle materials collected much more suspended sediment when PAM was added, with twice as much sticking to the coir than the Pyramat, although overall the latter may be more effective in settling the flocs. The patterns of turbidity and TSS within the basin suggest that only one porous baffle is adequate for PAM-treated water, and that the reduction observed near the outlet was likely floc interception by the sloped wall of the basin outlet. This study provides a relatively simple, inexpensive approach to improving the function of stilling basins for treating turbid water.

Effects of Prevailing Winds on Turbidity of a Shallow Estuary

Estuarine waters are generally more turbid than lakes or marine waters due to greater algal mass and continual re-suspension of sediments. The varying effects of diurnal and seasonal prevailing winds on the turbidity condition of a wind-dominated estuary were investigated by spatial and statistical analyses of wind direction, water level, turbidity, chlorophyll a, and PAR (Photosynthetically Active Radiation) collected in Lake Pontchartrain, Louisiana, USA. The prolonged prevailing winds were responsible for the long-term, large-scale turbidity pattern of the estuary, whereas the short-term changes in wind direction had differential effects on turbidity and water level in varying locations. There were temporal and spatial changes in the relationship between vertical light attenuation coefficient (Kd) and turbidity, which indicate difference in phytoplankton and color also affect Kd. This study demonstrates that the effect of wind on turbidity and water level on different shores can be identified through system-specific analyses of turbidity patterns.

Concurrent monitoring of vessels and water turbidity enhances the strength of evidence in remotely sensed dredging impact assessment

Remotely sensed assessment of dredging impacts on water turbidity is straightforward when turbidity plumes show up in clear water. However, it is more complicated in turbid waters as the spatial or temporal changes in turbidity might be of natural origin. The plausibility of attributing turbidity patterns to dredging activities would be greatly enhanced when demonstrating association between dredging infrastructure and water turbidity. This study investigated the possibility to strengthen the inference of dredging impact while simultaneously monitoring vessels and water turbidity in the northern Poyang Lake, China, where dredging was first introduced in 2001 and rapidly extended onwards. Time-series of Landsat TM and MODIS images of 2000–2005 were used to estimate the distribution and number of vessels as well as water turbidity. MODIS images revealed a significant increase in water turbidity from 2001 onwards. Landsat TM image analysis indicated a simultaneous increase in the number of vessels. Regression analysis further showed a highly significant positive relationship ( R 2=0.92) between water turbidity and vessel number. Visual interpretation of ship locations led to the conclusion that clear upstream waters developed turbidity plumes while passing the first cluster of vessels. We concluded that dredging caused the increase in water turbidity, and simultaneously monitoring the water turbidity and vessels enhanced the strength of evidence in remotely sensed dredging impact assessment.

Monitoring turbidity in Tampa Bay using MODIS/Aqua 250-m imagery

We developed an approach to map turbidity in estuaries using a time series (May 2003 to April 2006) of 250-m resolution images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite, using Tampa Bay as a case study. Cross-calibration of the MODIS 250-m data (originally designed for land use) with the well-calibrated MODIS 1-km ocean data showed that the pre-launch radiometric calibration of the 250-m bands was adequate. A simple single scattering atmospheric correction provided reliable retrievals of remote sensing reflectance at 645 nm (0.002 < R rs(645) < 0.015 sr − 1 , median bias = − 7%, slope = 0.95, intercept = 0.00, r 2 = 0.97, n = 15). A more rigorous approach, using a multiple scattering atmospheric correction of the cross-calibrated at-sensor radiances, retrieved similar R rs(645). R rs(645) estimates, after stringent data quality control, showed a close correlation with in situ turbidity (turbidity = 1203.9 × R rs(645) 1.087, 0.9 < turbidity < 8.0 NTU, r 2 = 0.73, n = 43). MODIS turbidity imagery derived using the developed approach showed that turbidity in Hillsborough Bay (HB) was consistently higher than that in other sub-regions except in August and September, when higher concentrations of colored dissolved organic matter seem to have caused underestimates of turbidity. In comparison, turbidity in Middle Tampa Bay (MTB) was generally lowest among the Bay throughout the year. Both Old Tampa Bay (OTB) and Low Tampa Bay (LTB) showed marked seasonal variations with higher turbidity in LTB during the dry season and in OTB during the wet season, respectively. This seasonality is linked to wind-driven bottom resuspension events in lower portion of the Bay and river inputs of sediments in the upper portion of the Bay. The Bay also experiences significant interannual variation in turbidity, which was attributed primarily to changes in wind forcing. Compared with the once-per-month, non-synoptic in situ surveys, synoptic and frequent sampling facilitated by satellite remote sensing provides improved assessments of turbidity patterns and thus a valuable tool for operational monitoring of water quality of estuarine and coastal waters such as in Tampa Bay.

Oceanography of Glacier Bay, Alaska: Implications for biological patterns in a glacial fjord estuary

Alaska, U.S.A, is one of the few remaining locations in the world that has fjords that contain temperate idewater glaciers. Studying such estuarine systems provides vital information on how deglaciation affects oceanographic onditions of fjords and surrounding coastal waters. The oceanographic system of Glacier Bay, Alaska, is of particular interest ue to the rapid deglaciation of the Bay and the resulting changes in the estuarine environment, the relatively high oncentrations of marine mammals, seabirds, fishes, and invertebrates, and the Bay’s status as a national park, where ommercial fisheries are being phased out. We describe the first comprehensive broad-scale analysis of physical and iological oceanographic conditions within Glacier Bay based on CTD measurements at 24 stations from 1993 to 2002. easonal patterns of near-surface salinity, temperature, stratification, turbidity, and euphotic depth suggest that freshwater nput was highest in summer, emphasizing the critical role of glacier and snowmelt to this system. Strong and persistent tratification of surface waters driven by freshwater input occurred from spring through fall. After accounting for seasonal nd spatial variation, several of the external physical factors (i.e., air temperature, precipitation, day length) explained a large mount of variation in the physical properties of the surface waters. Spatial patterns of phytoplankton biomass varied hroughout the year and were related to stratification levels, euphotic depth, and day length. We observed hydrographic atterns indicative of strong competing forces influencing water column stability within Glacier Bay: high levels of freshwater ischarge promoted stratification in the upper fjord, while strong tidal currents over the Bay’s shallow entrance sill enhanced ertical mixing. Where these two processes met in the central deep basins there were optimal conditions of intermediate tratification, higher light levels, and potential nutrient renewal. These conditions were associated with high and sustained hlorophylla levels observed from spring through fall in these zones of the Bay and provide a framework for understanding he abundance patterns of higher trophic levels within this estuarine system.

Use of Robotic Monitoring to Assess Turbidity Patterns in Onondaga Lake, NY

Selected temporal and vertical patterns of turbidity (Tn) are documented for an eutrophic urban lake, Onondaga Lake, NY, and their diagnostic value in identifying hydrodynamic and metabolic processes and in estimating clarity is established. The analysis is supported by five years (spring to fall) of daily robotic profiling of Tn, temperature (T), and dissolved oxygen, and an array of more temporally limited measurements that included Tn and T levels in the major tributary input of terrigenous solids; lake particle characterizations with a profiling particle counter and a scanning electron microscope coupled with automated image analysis and X-ray microanalysis; and Secchi disc transparency (SD). Major runoff events are demonstrated to cause conspicuous short-term increases in Tn that are manifested as metalimnetic peaks in summer and early fall, associated with the entry of the negatively buoyant primary tributary source as an interflow. The annual occurrence of Tn maxima within the oxycline of the metalimnion in October is documented. Evidence supports the position that this layer is a bacterial plate of oxidizing bacteria that develops seasonally in response to increasing vertical transport of reduced species from the hypolimnion with the approach to fall turnover. A strong relationship between SD and Tn in the upper waters is reported, that is demonstrated to have utility in resolving the dynamics of substantial changes in SD that occur in the lake during clear water phases.

Evaluating the impact of coastal land uses on water‐clarity conditions from Landsat TM/ETM+ imagery: Candarli Bay, Aegean Sea

Landsat TM and ETM+ imagery was evaluated as a potential data source for monitoring the coastal degradation of Candarli Bay and its basin on the eastern coast of the Aegean Sea. The bay is under pressure from conflicting uses, and there is an information need for future management plans for the area surrounding the bay. Spatial and temporal distributions of land use/land cover patterns were derived by unsupervised classification with the ISODATA algorithm. The post‐classification comparison technique was applied to evaluate decadal changes in land area. The turbidity patterns of the bay were determined from sea surface reflectances, and at‐satellite temperatures for the sea area were calculated. The processed images show that the water clarity conditions were affected by the adjacent coastal land uses and by river discharges. In accordance with the change‐detection analysis of land‐use patterns, the forested areas were decreased by 21%, whereas the increase in urban areas was determined as 105% within a decade.

Resolution of Turbidity Patterns from Runoff Events in a Water Supply Reservoir, and the Advantages of In Situ Beam Attenuation Measurements

The impact of runoff events on light scattering, or turbidity, levels in a water supply reservoir, and the comparative performance of three surrogate metrics of light scattering, are documented for the spring through fall interval of a high runoff year. The analysis is supported by: (1) frequent (42 d) field measurements of the beam attenuation coefficient at 660 nm (c660) and “optical” backscattering (OBS) collected with rapid profiling instrumentation at multiple sites; (2) laboratory measurements of c660 and turbidity (Tn); and (3) characterizations of inorganic particles with scanning electron microscopy interfaced with automated image and X-ray analyses. Conspicuous increases in light scattering levels are reported following runoff events, as reflected in increases in c660, OBS and Tn, associated with terrigenous inputs of clay minerals. The extent of this impact is demonstrated to be driven by the magnitude of the runoff event. Terrigenous inputs of turbidity are shown to enter as density currents, which travel the entire length of the reservoir for major runoff events, manifested as peak scattering levels in subsurface layers. Strong longitudinal and lateral differences are documented soon after runoff peaks. Scattering levels and spatial gradients are shown to diminish rapidly, with pre-event conditions approached within a week. Systematically lower c660 values are reported for laboratory measurements compared to in situ observations, particularly at high scattering levels, consistent with the operation of particle coagulation. In situ measurement of c660is identified as the preferred surrogate metric of light scattering.

Shear-induced structure formation in solutions of drag reducing polymers

The phenomenon of shear-induced structure formation has been investigated for several drag reducing polymers. Aqueous solutions of high molecular weight partially hydrolyzed polyacrylamide, polyacrylamide, and poly(ethylene oxide) have been examined in the concentration range of 100–4000 ppm by weight. Experimental protocols included rheological and rheo-optical characterization under simple shear flow, and molecular weight analysis by chromatography following various shear histories. All solutions exhibited time-dependent stresses and turbidity patterns under high shear, indicative of structure formation. Two regimes of behavior were found with the partially hydrolyzed polyacrylamide. At concentrations below 1500 ppm, aggregate formation occurred above a critical shear rate on time scales of minutes that relaxed back over similar time scales to an apparent homogenous state on cessation of flow. However, these sheared solutions developed irreversible, large-scale turbidity and eventual precipitation on quiescent storage over several days. At higher concentrations, phase-separated droplets formed under shear that also showed ripening of the turbidity and eventual precipitation upon quiescent storage for days. The kinetics of the semi-reversible aggregate formation and relaxation processes in the lower concentration regime showed a regular variation with shear rate and concentration. The strength of the structure formation and precipitation processes was lessened in the presence of salts. Similar behavior patterns were exhibited by the other systems, however, the strength of the structure formation was also somewhat lessened compared to the partially hydrolyzed polyacrylamide. Correlations with solutions being used in ongoing turbulent drag reduction studies suggest that such structure formation may play an important role in the drag reduction process.

The distribution of estuarine and oceanic water masses on the southern shore of O'ahu, Hawai'i: Ecological and coastal management implications, and novel methodology

The distribution of estuarine and oceanic water masses along the shelf of Mamala Bay, O'ahu, Hawaii, were determined by use of larval supply and recruitment patterns of benthic invertebrate species, stable C and N isotopic compositions of the suspension‐feeding bivalve, Spondylus tenebrosus, turbidity, drifter, and CTD data. The recruitment of different species among estuaries was used to associate larval species with particular estuarine waters. Recruitment patterns of these species along the shelf were then used to infer water‐mass distributions along the shelf. The spatial recruitment pattern of an oceanic lepadomorph barnacle, Conchoderma virgatum, was useful to infer shelf areas exposed to oceanic waters. Water‐mass distributions inferred from the recruitment distribution of these species concurred with spatial patterns of turbidity and stable C and N isotopic compositions of S. tenebrosus, as well as drifter observations. Water‐mass distributions observed in this study also concurred with biological distributional patterns observed in other studies, such as distributions of phytoplankton and zooplankton and the distribution of coral bio‐erosion in the Bay. The ecological implications of this work include further evidence of the physical control of recruitment and biological pattern and the possible control of patch dynamics on the scale of kilometers due to significant recruitment variability at this scale. The prevailing distribution of water masses determined in this study also has important implications for the management of watersheds associated with Mamala Bay.

Remote sensing of biotic effects: Zebra mussels (Dreissena polymorpha) influence on water clarity in Saginaw Bay, Lake Huron

In this study, Advanced Very High Resolution Radiometer (AVHRR) remote sensing reflectance (Rrs ), imagery from 1987–1993 is used to study changes in water clarity before and after zebra mussels (Dreissena polymorpha) were discovered in Saginaw Bay, Lake Huron. Spatial and temporal trends in the data indicate distinct and persistent increases in water clarity in the inner bay after the first large recruitment of zebra mussels in the fall of 1991. The pre‐Dreissena imagery show that turbidity in the inner bay was influenced by the Saginaw River discharge in spring, biological production (plankton) in summer, and wind‐driven resuspension in fall, with highest turbidity in spring and fall. Spatial patterns in the post‐Dreissena images were more similar regardless of season, with low reflectances in the shallow regions of the inner bay where zebra mussel densities were highest. A regression model based on point data from 24 sampling stations over the 7‐yr period indicates that reflectances varied significantly by site and zebra mussel densities, as well as seasonally. Trends in observed and predicted values of reflectances followed similar patterns at each station—highest values were found during 1991 and lowest during 1992 at all stations, with slightly higher Rrs in 1993 compared to 1992. Whereas AVHRR Rrs highlight the value of historical imagery for reconstructing seasonal and interannual turbidity patterns in near‐shore waters, a new generation of operational ocean color satellites, such as SeaWiFS (Sea‐viewing Wide Field‐of‐view Sensor) and the newly launched MODIS (moderate resolution imaging spectroradiometer), now provide for routine monitoring of important biological and physical processes from space.

The 1998 Coastal Turbidity Plume in Lake Michigan

In this paper, numerical models of coastal circulation, wind-waves, and sediment transport are applied to the March 1998 turbidity plume event in Lake Michigan to investigate the role of wind-induced circulation in the offshore transport of sedimentary material in Lake Michigan. Computer visualization is used to compare model results to the evidence of cross-isobath transport suggested in satellite imagery. Model results showed that circulation in Lake Michigan is highly episodic since it is almost entirely wind-driven in early spring. The characteristic wind-driven circulation pattern in the lake consists of two counter-rotating gyres, a counterclockwise-rotating gyre to the right of the wind, and a clockwise-rotating gyre to the left. The gyres are separated by a convergence zone along the downwind shore with resulting offshore flow and a divergence zone along the upwind shore with onshore flow. This two-gyre circulation pattern with offshore flow was very clearly seen during a northerly wind event in March 1998 in southern Lake Michigan. The strongest sediment resuspension occurred in the southern lake and the shallow waters along the coastline. This is because of the larger waves in southern Lake Michigan due to the dominant northerly wind in this early spring period. The two most significant sediment resuspension events were detected in the model results during the two storm events. Although results from the sediment transport model agree qualitatively with satellite imagery, they fail to simulate the initial eddy-like structure of the plume. Visualization is shown to be an effective tool for interpreting the complex turbidity patterns in the satellite imagery of the turbidity plume.

Differential in vitro association of vinca alkaloid-induced tubulin spiral filaments into aggregated spirals

Vinblastine, vincristine, vindesine, and vinorelbine, the four vinca alkaloids used in cancer therapy, differ in their antitumoral spectra and toxicities, but not in their inhibitory effects on microtubule assembly in vitro. At higher drug concentrations, vinca alkaloids induce the assembly of spiral filaments of tubulin, which, in turn, can interact laterally and form paracrystals. Using methods that distinguish spiral filaments and paracrystals (aggregated spirals), we found that spiral filament formation was largely independent of the incubation temperature, of the alkaloid used, and of the presence or absence of microtubule-associated proteins (MAPs). In contrast, the formation of aggregated spirals was markedly dependent on the alkaloid used, on the incubation temperature, and on the absence or presence of MAPs. Aggregated spirals failed to assemble in the presence of high concentrations of MAP-1A or MAP-1B, whereas they assembled readily with tau and MAP-2. Differences in patterns of turbidity development using pure tubulin allowed the classification of thirteen cytotoxic vinca alkaloids into five distinct groups, with centrifugal recovery of aggregated spirals in close agreement with the various turbidity patterns. With microtubule protein, i.e. tubulin preparations containing MAPs, only four groups were defined by turbidity patterns, and centrifugal protein recovery was more divergent. Vinblastine, vincristine, vindesine, and vinorelbine fell into distinct groups under both reaction conditions, and thus they appear to have qualitatively distinguishable in vitro interactions with tubulin. These differential effects on spiral filament and aggregated spiral assembly revealed that the four drugs induce different constraints on the tubulin molecule.

Mapping Reservoir Turbidity Patterns Using SPOT‐HRV Data

Abstract Although most orbital remote sensing systems are optimized for viewing terrestrial targets, data from these sensors has frequently been used for detecting and mapping the distribution of suspended sediments in water. In this paper, a linear regression‐based model for mapping turbidity is evaluated in a midwestern U.S. reservoir using October, 1994 SPOT‐HRV data. Results indicate that the red band (SPOT2) is the best predictor of turbidity (r=0.924, R2 = 84.5). Despite relatively low turbidity levels in the water, the radiometric resolution of the SPOT‐HRV sensor was found to be adequate for this application. The high spatial resolution of the sensor permitted observation of very detailed patterns of turbidity.

Study of the dynamics of estuarine and coastal waters using remote sensing: the Tinto-Odiel estuary, SW Spain

This paper deals with the application of satellite images to characterize some aspects of the circulation dynamics of the Tinto-Odiel estuary using turbidity patterns as ‘natural tracers’. 15 images (Landsat TM and Spot HRV) were processed to provide synoptic, instantaneous views of the circulation patterns under different environmental conditions. In addition, a comparison was made between results of oceanographic field work, using biplanes and fluorescent tracers, and satellite image turbidity patterns used as ‘ground truth’ data for specific hydroclimatic situations. This approach allowed (1) the identification and mapping of dynamic processes of interest during a theoretical tidal cycle, (2) the elaboration of additional information on the ‘flow schemes’ at the mouth of the estuary with improved spatial and temporal resolution, and (3) the supply of basic data to improve the knowledge of exchange processes between estuarine and coastal waters. The results of this study are considered to be useful for the management of the estuarine system.