Turbid Plume Research Articles

OPTIMIZATION OF THE CLOSURE OF A BREACHED BARRIER ISLAND IN THE GULF OF MEXICO

A chain of barrier islands in the Gulf of Mexico reduces storm and hurricane impacts along the Mississippi coast. Ship Island, one of the largest islands of this chain, was breached by hurricanes Camille and Katrina creating a 5.5 kilometer wide gap. US Army Corps of Engineers plans to restore the island nourishing 15 million cubic meters of sand. Extensive modeling studies were carried out to support the environmental impact assessment and to optimize design. The main objective of these studies was to determine the impact of the restored island on the environment. The possible increase of sedimentation rates in the adjacent navigation channel connecting a major port to the Gulf of Mexico was of particular interest. The Delft3D models, calibrated on measurements of waves, tidal levels and currents, were used to estimate the annual sediment transport rates. These models were subsequently applied to optimize the design of the closure of Camille Cut. The optimum construction sequence was established. Sediment losses from the fill, and the impact of turbidity plumes on the nearby sea grass fields were determined.

Analysis of the influence of river discharge and wind on the Ebro turbid plume using MODIS-Aqua and MODIS-Terra data

The turbid plume formed at many river mouths influences the adjacent coastal area because it transports sediments, nutrients, and pollutants.The effects of the main forcings affecting the Ebro turbid plume were analyzed using data obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the Aqua and Terra satellites over the period 2003–2011. Composite images were obtained for days under certain river discharge conditions (different flow regimes) and different types of wind (alongshore and cross-shore winds) in order to obtain a representative plume pattern for each situation.River discharge was the main driver of the Ebro River plume, followed by wind as the secondary force and regional oceanic circulation as the third one. Turbid plume extension increased monotonically with increased river discharge. Under high river discharge conditions (>355m3s−1), wind distributed the plume in the dominant wind direction. Seaward winds (mistral) produced the largest extension of the plume (1893km2), whereas southern alongshore winds produced the smallest one (1325km2). Northern alongshore winds induced the highest mean turbid value of the plume, and southern alongshore winds induced the lowest one. Regardless of the wind condition, more than 70% of the plume extension was located south of the river mouth influenced by the regional oceanic circulation.

Observation of a turbid plume using MODIS imagery: The case of Douro estuary (Portugal)

The Douro is one of the longest rivers in the Iberian Peninsula and represents the most important freshwater input into the Atlantic Ocean in the northwestern Portuguese coast. In order to fill the gaps on the comprehension of the spatial variability of the Douro estuarine plume, an innovative methodology was applied to observe and characterize this plume and its spatial and temporal variability. Using images of normalized water-leaving radiance at 555nm from MODIS (Moderate Resolution Imaging Spectroradiometer) in combination with long-term concurrent wind, tidal and river discharge data (2003–2011), this work evaluates the effect of the main drivers (river discharge, wind and tide) on the plume features. Expected strong relationships between river discharge and turbid levels were detected. A circular pattern is well distinct off Douro estuary when the flow exceeds 500m3s−1. Under upwelling favorable winds and high river discharge regime, an offshore expansion is observed. During southerly winds, there is a plume confinement to the coast. Easterly winds produce a bulge formation with an offshore detachment from the coast while westerly winds tend to confine freshwater close to the shoreline and decrease the cross-shore advection. Under high river discharges, a remarkable tidal influence in the near-field regions is observed close to the coast and near the river mouth.

Monitoring Turbid Plume Behavior from Landsat Imagery

A simple model based on available Landsat imagery data was used in order to characterize the dynamics of a rainstorm-induced turbid plume into a semi-arid, medium-sized reservoir. Additionally, a set of empirical expressions based on mouth river conditions was employed to estimate the spatial extent of the turbid plume, as well as the influence of the wind on the spreading and resuspension of sediment. This predicted plume behavior was then confirmed by the imagery data. Overall, the main contribution of the paper is a unified procedure of different approaches that can be applied to forecast turbidity effects during muddy inflow events in aquatic systems where minor field-measured information is available. The approach may be also considered as an assisting tool to provide managers with the capacity to develop real-time strategies to monitor flood events.

Prediction of the overflow of sediment from trailer dredgers

This paper describes a model of the sediment transport processes inside the hopper of a trailer suction hopper dredger. The model is part of the TASS system – a software program that enables the user to predict the spatial development and concentration of turbidity plumes arising from dredging activities by trailer suction hopper dredgers. TASS has been developed because of a recognised need by the dredging industry to improve the quality of predictions of the effects of dredging in environmental impact assessments. This paper describes the hopper process model and the validation of overflow predictions against validation measurements off the Dutch, German and Australian coasts. The model is shown to perform well in quantitative comparisons with data for dredging silt and sand in the Netherlands and Germany. A more qualitative comparison in Australia (owing to uncertainty in the nature of the soil being dredged) also indicates the hopper process model predicts the correct range of sediment discharge.

Seasonal Growth Responses of the Seagrass Zostera marina under Severely Diminished Light Conditions

Acute light attenuation events, such as those caused by red tide algal blooms or inflows of turbid plumes during monsoonal rains, are occurring with increased frequency in coastal waters. To explore seasonal growth responses of the seagrass Zostera marina to such severe light reduction events, we reduced radiation reaching Z. marina shoots by in situ shading with neutral density screens over 6-week periods in each of four seasons. Underwater photon flux densities (PFDs) in the shaded cages were reduced to 4.0–17.2 % of unshaded control values. Water temperatures ranged from 8.2 °C in the winter to 23.2 °C in the summer over the experimental period. Under reduced light, the aboveground biomass of Z. marina usually decreased more rapidly than belowground biomass. By the end of each experiment, total biomass had decreased to ~10 % of the control biomass in the summer, fall, and winter periods but to ~50 % of controls during spring. Detrimental effects of light reduction on seagrass growth were most severe in summer and least severe in spring. Thus, Z. marina is more susceptible to the negative effects of light reduction when water temperatures are high. Since red tide algal bloom events and turbid plumes usually occur during high water temperature periods in summer, these light attenuation events are likely major drivers of observed Z. marina declines in coastal areas.

Analysis of the most important river plumes on the Atlantic and Mediterranean Iberian coast by means of satellite imagery

Event Abstract Back to Event Analysis of the most important river plumes on the Atlantic and Mediterranean Iberian coast by means of satellite imagery Diego F. Novoa1*, Renato Mendes2, Maite D. Rodriguez1, João Miguel Dias2 and Ramón G. Gesteira1 1 Vigo University, Spain 2 Aveiro University, Portugal Rivers discharges cause the formation of buoyant plumes in the adjacent coastal area at their mouths, which are characterized by low-salinity water and controlled by outflow inertia, rotation (Coriolis) effects, buoyancy, wind, and tide forcing. The turbid plumes influence the adjacent coastal area, since they control the patterns of nutrients, sediments and/or pollutants of fluvial origin on the coastal ocean and can promote strong physical and chemical changes on seawater. These changes affect the biological characteristics of the area, such as primary production, species composition, abundance and distribution of existing microorganism, which demonstrates its high ecological importance. The characterization of the most important river plumes along the Atlantic Iberian coast and the influence of the main forcing drivers (river discharge, wind and tide) on them, was carried out through the analysis of plume mean-state images calculated using water leaving radiance data (nLw555) obtained from the MODIS (Moderate Resolution Imaging Spectroradiometer) sensor onboard the Aqua satellite during 2003-2013. Satellite data are downloaded from Ocean Color web site (http://oceancolor.gsfc.nasa.gov). Daily high-resolution L1 files from MODIS-Aqua were processed through SeaDAS software. Composite images, interpolated to a regular pixel grid with an approximate resolution of 500m, were built for different synoptic conditions of river discharge, wind regimes and tide, in order to obtain a representative average plume image of each situation and river for the posterior analysis. Results showed that the river discharge is the main forcing factor in the river plume extension. Wind effect is noticeable under high river discharge and tide is important for the estuarine outflow regimes although with some remarkable similarities and differences between the Atlantic rivers due to their intrinsic characteristics. Keywords: Atlantic Iberian plumes, MODIS, turbidity, river discharge, wind effect, tide forcing Conference: IMMR | International Meeting on Marine Research 2014, Peniche, Portugal, 10 Jul - 11 Jul, 2014. Presentation Type: Poster Presentation Topic: BIODIVERSITY, CONSERVATION AND COASTAL MANAGEMENT Citation: Novoa DF, Mendes R, Rodriguez MD, Dias J and Gesteira RG (2014). Analysis of the most important river plumes on the Atlantic and Mediterranean Iberian coast by means of satellite imagery. Front. Mar. Sci. Conference Abstract: IMMR | International Meeting on Marine Research 2014. doi: 10.3389/conf.fmars.2014.02.00080 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Apr 2014; Published Online: 18 Jul 2014. * Correspondence: Mr. Diego F Novoa, Vigo University, Ourense, Spain, diefernandez@uvigo.es Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Diego F Novoa Renato Mendes Maite D Rodriguez João Miguel Dias Ramón G Gesteira Google Diego F Novoa Renato Mendes Maite D Rodriguez João Miguel Dias Ramón G Gesteira Google Scholar Diego F Novoa Renato Mendes Maite D Rodriguez João Miguel Dias Ramón G Gesteira PubMed Diego F Novoa Renato Mendes Maite D Rodriguez João Miguel Dias Ramón G Gesteira Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Monitoring spatio-temporal variability of the Adour River turbid plume (Bay of Biscay, France) with MODIS 250-m imagery

Increased loads of land-based pollutants through river plumes are a major threat to the coastal water quality, ecosystems and sanitary heath. Identifying the coastal areas impacted by potentially polluted freshwaters is necessary to inform management policies and prevent degradation of the coastal environment. This study presents the first monitoring of the Adour River turbid plume (south-eastern Bay of Biscay, France) using multi-annual MODIS data. Satellite data are processed using a regional algorithm that allows quantifying and mapping suspended matter in coastal waters. The results are used to investigate the spatial and temporal variability of the Adour River turbid plume and to identify the risk of exposure of coastal ecosystems to the turbid plume waters. Changes in river plume orientation and spatial extent as well as suspended matter discharged through the river are correlated to the main hydro-climatic forcings acting in the south-eastern Bay of Biscay. The Adour River turbid plume is shown to be a highly reactive system mainly controlled by the river discharge rates and modulated by the wind changes. Despite the relatively small size of the Adour River, the Adour River turbid plume can have a non-negligible impact on the water quality of the southern Bay of Biscay and the MSM and associated contaminants/nutrients transported within the Adour turbid river plume have the potential to be disseminated far away along the northern shoreline or offshore. The main areas of influence of the river plume are defined over multi-annual (3 years) and seasonal periods. The results presented in this study show the potential of 250-m MODIS images to monitor small river plumes systems and support management and assessment of the water quality in the south-eastern Bay of Biscay.

Dynamics of Turbid Plumes Generated by Marine Aggregate Dredging: An Example of a Macrotidal Environment (the Bay of Seine, France)

Duclos, P.-A.; Lafite, R.; Le Bot, S.; Rivoalen, E., and Cuvilliez, A., 2013. Dynamics of turbid plumes generated by marine aggregate dredging: an example of a macrotidal environment (the Bay of Seine, France).On the French marine shelf, marine aggregates are currently dredged by trailing suction hopper dredgers (TSHD), without screening, with an overflow process, with or against currents. In the framework of the Groupement d'Interét Scientifique (GIS) Suivi des Impacts de l'Extraction de Granulats Marins (SIEGMA), the dynamics of the turbid plume formed by the overflow was studied at an experimental dredging site (0.6 km2), located in the Bay of Seine (eastern English Channel), a macrotidal environment where the seabed is composed of sandy gravel. An original field strategy based on Lagrangian monitoring, using the back-scattered signal of an Acoustic Doppler Current Profiler (ADCP), Laser In Situ Scattering and Transmissometry (LISST) measurements, water samples, and aerial photographs, has shown good results in describing suspended sediment concentration (SSC) dynamics from a turbid plume. The behaviour of suspended sediment has been studied, for the first time, to our knowledge, from their release at the dredger overflow to their deposition on the seabed. A fluid mixture, overflowed from the TSHD, with a mean concentration of 6 g L−1 of mineral and organic silty sands, induces the formation of a turbid plume at the rear of the TSHD, with an immediate dilution effect about 10–100 on SSC. Then, the SSC decreases through the process of lateral dispersion and sedimentation until the plume disappear in 2 hours. Evolution of the plume characteristics (SSC, particle size and nature, geometry) makes it possible to quantify the processes involved: dilution, advection, dispersion, and settling. The passive and dynamic behaviours of the plume are analysed. Extensions of deposits are calculated for spring tide conditions: 800 m for sand and 6.5 km for silt. This study has been conducted in macrotidal and specific dredging conditions (orientation of the dredging tracks against currents, dredger speed, loading capacity, overflow type), whose effects on plume dispersion have been quantified. Indicators relative to the effect of the plume on the water column (I/R) and to the plume duration (T1.25SSC) are proposed.

Use of optical and acoustic instruments to study the turbid plumes generated by three different types of dredges during dredging activities inside and outside of a port

The turbid plumes generated by different types of dredges have specific behaviours and diffusion patterns. The dredging of the Oil Port of Genoa Multedo (Italy) with three different dredges (grab, backhoe and trailing suction hopper) enabled us to study: the physical and hydrodynamic characteristics of the water column of the port and the area just outside it; the characteristics of the turbid plumes; and the different responses of our optical and acoustic instruments. In the dredging operations, a vessel equipped with a vertical acoustic Doppler current profiler and a conductivity–temperature–depth probe with a turbidimeter followed the different dredges during their daily operations. Using the acoustic backscatter and turbidity data acquired during the dredging phase, we investigated the turbidity variations caused by the dredging operations to study the evolution of the plume generated by the three different dredges. The grab plume was present only on the bottom up to a distance of 50 m from the grab, while at greater distances the turbidity fell to background values. The backhoe plume was present close to the bottom at a distance of 50 m from the dredging and, in the entire water column, at distances of 50–400 and 100 m inside and outside of the port, respectively. The trailing suction hopper dredge plume extended from the surface through the entire water column at distances from the dredging of 400 and 100 m inside and outside of the port, respectively. The highest values were found close to the bottom at distances from the dredging at 50 and 30 m inside and outside of the port, respectively. The choice of a combined monitoring system is a good practical solution for studying the differences between the turbid plumes created by the three dredging tools (grab, backhoe and trailing suction hopper dredge) under different hydrodynamic conditions. Furthermore, two different types of instrument should give complementary information on different aspects of sediment resuspension during a dredging operation.

Trawling-induced daily sediment resuspension in the flank of a Mediterranean submarine canyon

Commercial bottom trawling is one of the anthropogenic activities causing the biggest impact on the seafloor due to its recurrence and global distribution. In particular, trawling has been proposed as a major driver of sediment dynamics at depths below the reach of storm waves, but the issue is at present poorly documented with direct observations. This paper analyses changes in water turbidity in a tributary valley of the La Fonera (=Palamós) submarine canyon, whose flanks are routinely exploited by a local trawling fleet down to depths of 800m. A string of turbidimeters was deployed at 980m water depth inside the tributary for two consecutive years, 2010–2011. The second year, an ADCP profiled the currents 80m above the seafloor. The results illustrate that near-bottom water turbidity at the study site is heavily dominated, both in its magnitude and temporal patterns, by trawling-induced sediment resuspension at the fishing ground. Resuspended sediments are channelised along the tributary in the form of sediment gravity flows, being recorded only during working days and working hours of the trawling fleet. These sediment gravity flows generate turbid plumes that extend to at least 100m above the bottom, reaching suspended sediment concentrations up to 236mgl−1 close to the seafloor (5m above bottom). A few hours after the end of daily trawling activities, water turbidity progressively decreases but resuspended particles remain in suspension for several hours, developing bottom and intermediate nepheloid layers that reach background levels ∼2mgl−1 before trawling activities resume. The presence of these nepheloid layers was recorded in a CTD+turbidimeter transect conducted across the fishing ground a few hours after the end of a working day. These results highlight that deep bottom trawling can effectively replace natural processes as the main driving force of sediment resuspension on continental slope regions and generate increased near-bottom water turbidity that propagates from fishing grounds to wider and deeper areas via sediment gravity flows and nepheloid layer development.

Phytoplankton productivity in a turbid buoyant coastal plume

The complex dynamics associated with coastal buoyant plumes make it difficult to document the interactions between light availability, phytoplankton carbon fixation, and biomass accumulation. Using real-time data, provided by satellites and high frequency radar, we adaptively sampled a low salinity parcel of water that was exported from the Hudson river estuary in April 2005. The water was characterized by high nutrients and high chlorophyll concentrations. The majority of the low salinity water was re-circulated within a nearshore surface feature for 5 days during which nitrate concentrations dropped 7-fold, the maximum quantum yield for photosynthesis dropped 10-fold, and primary productivity rates decreased 5-fold. Associated with the decline in nitrate was an increase in phytoplankton biomass. The phytoplankton combined with the Colored Dissolved Organic Matter (CDOM) and non-algal particles attenuated the light so the 1% light level ranged between 3 and 10m depending on the age of the plume water. As the plume was 10–15m thick, the majority of the phytoplankton were light-limited. Vertical mixing within the plume was high as indicated by the dispersion of injected of rhodamine dye. The mixing within the buoyant plume was more rapid than phytoplankton photoacclimation processes. Mixing rates within the plume was the critical factor determining overall productivity rates within the turbid plume.

이차원 수치모형을 이용한 준설 탁도플륨의 혼합거동 연구

본 연구에서는 충남 서산에 위치한 부남호에서 준설시 발생하는 탁도플륨의 이송 및 확산과정을 2차원 수치모형인 RMA2 모형과 RMA4 모형을 이용하여 예측하였으며, 다항목수질모니터링시스템(YSI6600EDS)을 이용해 측정한 탁도분포와 비교하였다. 현장조사에서는 부남호에서 준설작업이 진행됨에 따라 인근지점에서의 연직방향 탁도 분포를 측정하였으며 표층에서 거리에 따른 수평방향 탁도 분포를 측정하였다. 부남호 전 구간에 대해서 2차원 흐름해석 모형인 RMA2 모형을 적용하였고, 실제 준설작업이 이루어지는 2호지에 대해서 RMA2 모형과 RMA4 모형을 적용하였다. 준설지점의 초기 농도값에 대한 저수지 내 각 지점에서의 거리에 따른 농도비를 현장측정 결과와 비교한 결과, 수치해석에 의한 탁도플륨의 이송확산 모의 결과는 준설작업에 대한 환경영향 범위를 예측하는 데에 적용될 수 있는 것으로 나타났다. The numerical simulations were performed to analyze the advection-diffusion processes of dredging-induced turbidity plume using RMA2 and RMA4 models in Bunam reservoir, Seosan, Chungnam. Field survey was also performed to measure the turbidity using the multi water quality monitoring system (YSI6600EDS). In the field survey, the vertical and horizontal distributions of the turbidity were measured during the dredging operation in Bunam reservoir. RMA2 model was used to simulate the velocity distributions in both the whole domain and the 2nd part of Bunam reservoir. RMA4 model was also used to simulate the concentration distribution in only the 2nd part of Bunam reservoir, where the dredging work were conducted. The comparison of the simulation results with the field data for the advection-diffusion of the turbidity plume using the concentration ratio concepts shows that the numerical model can be applied to analyze the environmental impact of dredging works.

The influence of the Mackenzie River plume on distribution and diversity of marine larval fish assemblages on the Canadian Beaufort Shelf

In the Beaufort Sea, freshwater input from the Mackenzie River creates a relatively warm and turbid plume across the coastal shelf region. To determine the influence of this plume on marine larval fish abundance, distribution, and assemblages, we sampled larval fish during July and August of 2007 using 500μm bongo nets on transects across the plume gradient at three sampling stations per transect, along with oceanographic measurements. Three larval fish assemblages were identified within three distinct oceanographic zones: intense plume, diffuse plume and oceanic. The intense plume assemblage was dominated by Saffron cod (Eleginus gracilis) and Pacific herring (Clupea pallasii); the diffuse plume assemblage was dominated by the Pricklebacks (sub-family Lumpeninae); and the oceanic assemblage was dominated by Arctic cod (Boreogadus saida). Even though there were differences in relative abundance of particular species among these areas, no significant differences in total abundances of larval fish were found.

Dynamics of Turbid Plumes Generated by Marine Aggregate Dredging: An Example of a Macrotidal Environment (the Bay of Seine, France)

Dynamics of Turbid Plumes Generated by Marine Aggregate Dredging: An Example of a Macrotidal Environment (the Bay of Seine, France)

Satellite assessment of the coupling between in water suspended particulate matter and mud banks dynamics over the French Guiana coastal domain

Particulate suspended matter concentration (SPM) were estimated over a 8 year time period (2002–2010) in the coastal waters of French Guiana from a regional algorithm applied to the MODIS monthly reflectance measurements. Comparison between SPOT images and MODIS-SPM maps revealed the strong spatio-temporal coupling between in water SPM and the dynamics of local (i.e. Kourou and Cayenne) mud banks. Highest MODIS SPM values (>13 g m−3 approximately) can be significantly associated with the subtidal part of the banks as well as to the related turbid plume. The migration of these mud banks induces strong interannual changes in SPM reaching up to 6% year−1 within increasing and decreasing patchy areas distributed alternatively along the coastline of French Guiana. Mud banks migration rates derived from MODIS SPM data reach in average about 2 km year−1 in agreement with previous studies. The MODIS time series have allowed for a detailed description of the seasonality and interannual variations in the in-water SPM loads. Seasonal changes in SPM are related to the onset of the trade wind season. Marked non-linear patterns including a sharp evolution in the SPM values around 2005 as well as additional high frequency modulations have been emphasized within the upward and downward SPM trend regions. Concurrent temporal variations in the frequency of northward swells (favoring mud banks migration and reworking) as well as interannual changes in the amount of sediment delivered by the Amazon River have been shown to play a major role in the SPM temporal patterns observed in the French Guiana coastal waters. Our results clearly demonstrate the advantage for ocean color data to describe mud banks dynamics through the assessment of in water SPM temporal variability.

A satellite view of riverine turbidity plumes on the NE-E Brazilian coastal zone

Turbidity plumes of São Francisco, Caravelas, Doce, and Paraiba do Sul river systems, located along the NE/E Brazilian coast, are analyzed for their dispersal patterns of Total Suspended Solids (TSS) concentration using Landsat images and a logarithmic algorithm proposed by Tassan (1987) to convert satellite reflectance values to TSS. The TSS results obtained were compared to in situ collected TSS data. The analysis of the satellite image data set revealed that each river system exhibits a distinct turbidity plume dispersal pattern. The behavior, dimension and degree of turbidity of the São Francisco River plume have been greatly altered by the construction of a cascade of hydroelectric dam reservoirs in its hydrological basin. The plume has lost its typical unimodal seasonal pattern of material dispersion and its turbidity has decreased due to the regulation of river flow by the dams and TSS retainance by the reservoirs. In contrast, the Doce and Paraíba do Sul river plumes are still subject to seasonal pulsations and show more turbid conditions than the SF plume, as dams are less numerous, set in the middle river sections and the natural river flow has been maintained. The Caravelas Coastal System river plume is restricted to near shore shallow waters dominated by resuspension processes. During austral spring and summer when NE-E winds prevail, all plumes generally disperse southward. Short-term northward reversals may occur in winter with the passage of atmospheric cold fronts. The São Francisco and Doce river plumes tend to disperse obliquely to the coast and transport materials further offshore, while the Caravelas and Paraíba do Sul plumes tend to disperse mainly parallel to the coast, enhancing TSS retention nearshore.

Seasonal variability of turbid river plumes off central Chile based on high-resolution MODIS imagery

We have studied the seasonal variability of four turbid river plumes along the central Chilean coast using daily, high-resolution images of surface turbidity from MODIS (Moderate Resolution Imaging Spectroradiometer) in combination with measurements of wind, river flow, and hydrographic data. Atmospherically corrected MODIS data reveal strong seasonal variability in the areal extent of plume water, as well as in turbidity levels, which are significantly correlated with seasonality in river discharge. A seasonal climatology of turbid plume patterns shows individual plumes merging into an extensive body of turbid waters attached to the coast during fall (April–June)–winter (July–September) (occurs about 10% of days in fall–winter). During spring (October–December) and summer (January–March), the individual plumes remain distinct and occupy a smaller area close to the coast, when observed (evident on less than 30% of days in spring–summer). In spring–summer most plumes are detected for the northern rivers (Mataquito and Maule). When the plumes merge into a coastal band in fall–winter, a turbid area of more than 1000km2 is observed in the study area between 34.85°S and 37.15°S. This occurs following peaks in river discharge combined with the effect of strong southward (downwelling-favorable) winds. An analysis of key non-dimensional numbers shows that buoyancy dominates plume dynamics during summer, whereas inertial forcing associated with river outflow is more important in winter near the coast. Farther offshore (>10km), the effects of rotation and wind tend to dominate the plume dynamics.

The annual particle cycle in Lake Van (Turkey)

The varved sediments of Lake Van provide a high-quality continental archive of seasonal to decadal-scale climate variability. In order to read the natural record, modern varve formation was studied on the basis of (1) remotely-sensed total suspended-matter (TSMrs) concentrations; (2) time-series of particle flux and water temperatures; and (3) turbidity, temperature, and oxygen profiles. TSMrs, validated by contemporaneous water-column sampling, shows great temporal and lateral variations (whitings and turbidity plumes). From 2006 to 2009, sequential sediment traps recorded high particle fluxes during spring and fall, medium fluxes during summer, and almost zero flux during winter. The mean total mass flux of 403mgm−2day−1 comprised 33% (seasonally up to 67%) calcium carbonate, 7% aquatic organic matter, 6% biogenic opal, and 54% detrital minerals. The CaCO3 fluxes are controlled by river discharge (precipitation and snowmelt) during spring, by high productivity during summer, and by river discharge (precipitation before snowfall starts) and mixing during fall. In November 2007, an anomalously high CaCO3 flux occurred as a result of a warm water surface supersaturated with calcite coinciding with an anomalous runoff event. The results demonstrate that the couplets of light and dark laminae in the short sediment cores are true varves representing spring–summer–fall and winter conditions, respectively. Consequently, varve formation can be linked to the seasonal climate pattern, providing a calibration that can be used to interpret the partially varved paleo-record of Lake Van and related environmental processes.

The use of a combined monitoring system for following a turbid plume generated by dredging activities in a port

The potential negative effects of dredging on a sensitive marine environment (e.g. phanerogamic meadows, beaches, benthic populations) can be justification for restrictions on the dredging project or the creation of a dredging monitoring plan. The dredging of the Port of Genoa (Italy) provided the opportunity to study the concentration of total suspended solids, the physical characteristics of the water column, and the winds and currents determining the hydrodynamic characteristics of the port, and to test a double monitoring system for turbidity control. In the dredging operation of the Port of Genoa, we positioned a couple of fixed monitoring systems operating 24/7, consisting each of a conductivity–temperature–depth probe and two acoustic Doppler current profilers (ADCP), near the two port entrances to monitor turbidity and currents. To make the monitoring strategy more efficient, to periodically control the data transmitted by the fixed stations and to ensure coverage of those areas not covered by the fixed monitoring system, a vessel equipped with a vertical ADCP and a conductivity–temperature–depth probe with a turbidimeter periodically followed the dredger during its daily operations. Using the data acquired during the pre-dredging and dredging phases, we considered turbidity and suspended solids variations caused by the dredging operation to study the evolution of the plume. The trailing suction hopper dredge (TSHD) plume extended from the surface throughout the entire water column at a distance of 50 m, with higher turbidity close to the bottom. At a distance of 200 m, the plume was much reduced. Instead, at a distance of 50 m, the turbidity produced by the backhoe was lower than that measured around the TSHD, while at a distance of 100 m the plume was reduced with only noticeable values near the bottom. Finally, we compared the turbidity data of the dredging with the background conditions near the Posidonia oceanica meadow present near the port. The data presented in this paper indicate that the choice of a combined monitoring system can be a good practical solution for reaching two different objectives: (a) to follow the evolution and movement of the turbid plume, and ensure that it does not flow out of the port, contaminating the surrounding area or damaging nearby coastal habitats or the Posidonia oceanica meadows; and (b) to study the differences between the turbid plumes created by two dredging tools (backhoe and TSHD) under different wind–wave conditions.