High Suspended Sediment Concentration Research Articles

In situ observation of contour currents in the northern South China Sea: Applications for deepwater sediment transport

Deepwater currents and related suspended sediment concentration were obtained by an Acoustic Doppler Current Profiler (ADCP) mooring system in the northern South China Sea from September 2011 to May 2013 to characterize the occurrence of contour currents and to evaluate their sediment transport capacity. Magnitude of the current velocity generally varied in the range of 0–2 cm/s, with a dominant flow direction of ∼250° (southwestward). The observed contour current, defined as the along-slope component of the deepwater currents, has a tunnel-like vertical structure with the largest velocity occurring in the middle of the “tunnel” and decreasing outwards. Both the magnitude and the depth range of the maximum velocity display evident inter-seasonal variations, with the strongest velocity in summer and the weakest in spring, while the thickness of the contour currents was the highest in winter and the lowest in spring. We also found that passing-through of the deep-reaching mesoscale eddies significantly affected the magnitude and direction of the contour currents. The suspended sediment concentration (SSC) estimated from echo intensities of the ADCP is the highest at the near-bottom (>400 μg/L) and decreases upwards to <10 μg/L at water depth shallower than 1750 m. High SSC is mostly observed during periods of low magnitude of the contour currents, suggesting resuspension of sediment from the seafloor is not the major controlling factor of these high-SSC events. Our observation also suggests that the major role that contour currents play is to transport sediment from the sources through keeping sediment suspended above the lower continental slope of the South China Sea.

Muddy waters: the influence of high suspended-sediment concentration on the diving behaviour of a bimodally respiring freshwater turtle from north-eastern Australia

Increased suspended-sediment concentrations (SS) in rivers can affect aquatic respiration in riverine fauna by impairing respiratory function. Bimodally respiring freshwater turtles are likely to be sensitive to changes in SS because increased concentrations may affect their ability to aquatically respire. However, the impact of SS on the diving behaviour of bimodally respiring freshwater turtles has not been formally investigated. To test this, we examined the influence of dissolved oxygen (DO) saturation (25%, 100%) and temperature (17°C, 25°C) on the diving behaviour of Elseya irwini under clear (0mgL–1) and turbid (79mgL–1) conditions. We hypothesised that low temperature and high DO % saturation would increase dive duration and that high SS would negate the effect of DO, decreasing dive duration under highly oxygenated conditions. Our data demonstrated that increased SS significantly reduced mean dive duration by 73% (97.4±10.1min in 0mgL–1 trials v. 26.4±3.2min in 79mgL–1 trials) under conditions of low temperature (17°C) and high DO % saturation (100%) only. Increased SS directly affects the utilisation of DO by this species, so as to extend submergence times (aquatic respiration) under optimal conditions, raising concerns about the effect of SS on the persistence of populations of physiologically specialised freshwater turtles.

Remote sensing of spatial-temporal distribution of suspended sediment and analysis of related environmental factors in Hangzhou Bay, China

In this study, a total of 37 images of Landsat Operational Land Imager/Thematic Mapper/Enhanced Thematic Mapper plus were adopted to delineate the qualitative changes of Suspended Sediment Concentration (SSC) in Hangzhou Bay, China. Combined with in-situ SSC, remote sensing reflectance of the water (Rrs), water depth and simulated currents, the influence of both seabed topography and tidal currents on the SSC distribution was analysed. The results showed: (1) four High SSC Areas (HSA) and two Low SSC areas (LSA) in Hangzhou Bay. (2) SSC has a negative correlation with bathymetry, which is especially obvious during mid to late period of flood tide. HSAs appear in the shallow water (3–7 m depth) area, while the LSAs distribute in the deep water area (10–15 m depth). (3) The surface SSC distribution during the mid to late period of flood tide can help us estimate the topography information. The results of this paper can be used to other coastal embayments similar to Hangzhou Bay.

Suspended sediment transport response to upstream wash-load supply in the sand-bed reach of the Upper Yellow River, China

Summary Wash load is a major component of suspended sediment transport in the sand-bed reach of the Upper Yellow River, China. This wash load sediment originates from the Loess region, with the high runoff mainly originating from the rock mountains of its upstream basin. These characteristics result in a mismatch between water and sediment sources and a low probability of high runoffs meeting high suspended sediment concentration (SSC) flows. As a result, higher runoff with lower SSC levels (HR-LS) and lower runoff with higher SSC values (HS) occur, whose SSCs do not follow the typical power form for flow discharges, C i = αQ β , where C i and Q are SSC and flow discharge, respectively. Here, we modify the traditional power form with an upstream wash-load supply function C 1− β to satisfy the relation between the water and wash load sediment concentrations in water–sediment mismatched cases, C i = αQ β C 1− β , where C is an input flow’s SSC. Using the daily flow discharges and SSCs of nine typical HR-LS flows and 18 HS flows in our study reach from 1960 to 2012, we find that β changes in response to input flow conditions and downstream transport distances. When the downstream transport distance is between 360 and 663.5 km, β varies between 0.3 and 0.6 in a HS input flow condition, while in the HR-LS input flow case, β tends to be greater than 0.6 (between 0.74 and 0.65). The entrainment rate of an HR-LS flow and the deposition rate of an HS flow appear to be asymmetrically balanced, establishing a primary mechanism for channel aggradation and upward fining of floodplains in our study reach.

Controls on Suspended Sediment Concentrations and Turbidity within a Reforested, Southern Appalachian Headwater Basin

Water quality data collected between 2007 and 2014 within the Allen Creek Watershed were used to: (1) determine the factors controlling the temporal variations in turbidity and suspended sediment concentration (SSC) within a representative, high-gradient headwater basin in the Southern Appalachians; and (2) assess the recovery of water quality following extensive logging operations during the early to mid-1900s. Regression analysis suggests that suspended sediment is primarily derived from upland areas and variations in concentration reflect rainfall intensity and total event precipitation. Overall, SSC and turbidity were low in stream waters in comparison to both reference values for stable streams and more developed basins in the region. Some floods were characterized by high SSC values, but limited turbidity and vice versa. Differences in measured SSC and turbidity between storms reflect different controls on the two parameters, and the apparent influence of natural organic matter on turbidity during rainfall events that are incapable of transporting sediment to the channel via overland flow. Low SSC and turbidity values are presumably related to the reforestation of hillslopes and riparian buffers following the cessation of logging operations. They also are due to a historical reduction in the sedimentological connectivity of hillslopes and tributaries with the axial channel that occurred during logging operations.

Effect of water–sediment regulation of the Xiaolangdi Reservoir on the concentrations, bioavailability, and fluxes of PAHs in the middle and lower reaches of the Yellow River

The water–sediment regulation of the Xiaolangdi Reservoir is conducted to control the relationship between riverine runoff and sediment transport of the Yellow River; however, there is no research about the effect of water–sediment regulation on the bioavailability and fluxes of hydrophobic organic compounds (HOCs). In this study, water and suspended sediment (SPS) samples were collected downstream of the Xiaolangdi Reservoir before, during, and after the water–sediment regulation in 2013. The 16 priority polycyclic aromatic hydrocarbon (PAH) concentrations of freely dissolved, total dissolved, and SPS-associated were determined. During water regulation, water discharged from the reservoir at a high flow rate led to the resuspension of downstream sediment. During sediment regulation, the sediment ejected from the reservoir resulted in higher SPS concentrations than that during water regulation. Both the freely and total dissolved PAH concentrations in river water during sediment regulation were the highest, followed by the concentrations during water regulation and before regulation. The freely dissolved PAH concentrations in river water during the water–sediment regulation were 2–11 times higher than those before water–sediment regulation. This was due to the fact that the resuspended sediment during water–sediment regulation could release PAHs into water phase, and more contaminants were released from the SPS during sediment regulation than during water regulation. The fluxes of sediment and the 16 priority PAHs (Σ16PAHs) during water–sediment regulation contributed to 32.4% and 35.7% of their annual fluxes, respectively, which were higher than the contribution (22.6%) of water discharge. This study suggested that the water–sediment regulation might reduce the long-term retention of sediment and PAHs in the reservoir. However, the environmental risk of PAHs as well as other contaminants downstream of the reservoir and in the estuary might increase during that period. Therefore, the effect of water–sediment regulation on the bioavailability and environmental risk of HOCs should be considered in the operation and management of the Xiaolangdi Reservoir in the future.

Detection of sea ice in sediment laden water using MODIS in the Bohai Sea: a CART decision tree method

An inversion algorithm based on the Classification and Regression Tree (CART) has been developed to retrieve sea ice from Moderate Resolution Imaging Spectroradiometer (MODIS) images in the Bohai Sea where the sea water is characterized by a high concentration of suspended sediment in coastal areas. The inversion algorithm has been successfully applied to the sea-ice extraction from 2009 to 2012. The estimated sea ice is compared with previous studies and the comparison shows reasonable agreement. The model is further examined using sea-ice data from higher-spatial-resolution satellites, and the result indicates that the CART method is able to successfully retrieve sea ice in high sediment environments in the Bohai Sea. To comprehensively understand the working principles of the CART, a series of sensitivity studies to model input parameters such as sampling locations, the number of bands, and the effect of the thermal infrared band (TIB), was conducted. The sensitivity studies show that the CART method is easy to set up and the results are realistic. The TIB may play an important role in sea-ice inversion in turbid waters. The algorithm is also compared with a ratio-threshold segmentation (RTS) method, a common way to retrieve sea ice from satellite images in open oceans, and the comparison indicates that the algorithm developed in the present article is superior to the RTS method in high sediment environments.

Sediment and nutrient dynamics during storm events in the Enxoé temporary river, southern Portugal

In temporary (or intermittent) rivers the first storm event after a dry period is responsible for transferring large amounts of sediment and nutrients into water reservoirs, thereby justifying close monitoring. The objective of this study was to analyse the contribution of storm events to sediment and nutrient transport in the Enxoé temporary river (southern Portugal) using detailed monitoring collected during three hydrological years (September, 2010 to August, 2013), and identify possible sediment and nutrient source areas based on the interpretation of hysteresis in the concentration–discharge relationship. The Enxoé River was monitored for suspended sediment concentration (SSC), total phosphorus (TP), particulate phosphorus (PP), soluble reactive phosphorus (SRP), and nitrate (NO3−). An empirical model was used to describe changes in solute concentrations, and the magnitude and rotational patterns of the hysteretic loops. Twenty-one storm events were registered. SSC, TP, PP, SRP, and NO3− concentrations varied between 1.6 and 3790.1, 0.05–11.4, 0–7.6, 0–0.67, and 0–27.84mgl−1, respectively. The highest SSC, TP, and PP concentrations were registered during the first storm event after an extended drought period. Annual sediment yields (13–480kgha−1y−1) and nitrate (4.4–45.5kgha−1y−1) were relatively low, while phosphorus losses (0.04–0.96kgha−1y−1) reached relatively high values during humid years. Sediment and phosphorus transport was influenced by the stream transport capacity and particle availability, whereas nitrate loads were influenced by rainfall, soil hydraulic characteristics, and land management. This work highlights the main processes involved in sediment and nutrients loads in a temporary river during storm events, with a quantification of the relevant elements.

The study of data fusion for high suspended sediment concentration measuring using the IGA-RBF method

To optimize the radial basis function (RBF), an improved genetic algorithm (IGA) was used for measuring high suspended sediment concentration (HSSC) in the Yellow River. The improved probabilities crossover and mutation were utilized to realize the twin goals of maintaining diversity in the population and sustaining the convergence capacity of the GA, and a new method was proposed to resolve the problem of deciding the optimal values of the probabilities of crossover and mutation. In this method, the effects of environmental factors, such as temperature, depth and flow rate on the capacitive differential pressure (CDP) sensors, were discussed. To compare the fusion effect of the IGA-RBF method, the sediment concentration data were fused and processed using unary linear regression (ULR), multiple linear regression (MLR), back propagation (BP) neural network, standard RBF (S-RBF) methods, adaptive GA-optimized RBF (AGA-RBF) and dynamic GA-optimized RBF (DAGA-RBF). The results show that the IGA-RBF method can effectively eliminate environmental influences and raise the measuring accuracy and stability of the system.

Remote Sensing of Suspended Sediment Over Gulf of Martaban

AbstractGulf of Martaban is located at the north of Andaman, and is one of the world most turbid areas. The presence of suspended sediment concentration (SSC) in the water body could reduce the underwater transmittance. This study has been conducted to investigate the variation of SSC over the Gulf of Martaban. Remote sensing reflectance (Rrs) of 667 nm is used as a proxy to represent the sediment SSC variation over the study area. The data for the period of July 2002 to March 2014 acquired from MODIS Aqua 4 km resolution are used in this study. As a result, there is no obvious yearly variation in the SSC cover area. The SSC variation over this study area is found to be seasonal. High homogenous SSC covers area observably during the northeast (NE) monsoon season that occurs from December to January. The sediment cover area could reach the latitude of 15°N that located at the south of the gulf. During southwest (SW) monsoon season that occurs from May to September, low and sparse SSC cover area is observed. As a consequence, the area covered by the SSC is higher during the NE monsoon season as compared to the SW monsoon season. Hence, the SSC cover area during the NE monsoon season is greater than the yearly averaged SSC cover area. Meanwhile the SSC cover area during the rainy SW monsoon season is less than the yearly and NE monsoon season.

ACOUSTIC INVESTIGATIONS OF TIDAL BORES IN QIANTANG RIVER

The continuous measurements of flow velocity/rate and suspended sediment concentration (SSC) in tidal rivers are crucial in estuarine studies. However, the accurate estimates of these terms are difficult and labor-intensive procedures are needed; thus, a robust and efficient method of the measurements is required. The changes of cross-sectional average suspended sediment concentration, tidal bore celerity and flow velocity were measured in the Qiantang River by using acoustic tomography systems. The results showed that the amount of SSC increased more than threefold during tidal bores. The acoustic systems could successfully measure the cross-sectional average velocity in the unsteady flows though the high SSC bred a short missing period after the bore arrival.

Possible submarine tsunami deposits on the outer shelf of Sendai Bay, Japan resulting from the 2011 earthquake and tsunami off the Pacific coast of Tohoku

Although it is accepted that large tsunami waves impact the sea floor, the response of surface sediments to tsunami is not yet fully understood. Tsunami by the 2011 off the Pacific coast of Tohoku earthquake caused considerable damage to Northeast Japan. Surface sediments on the outer shelf of Sendai Bay also show evidence of strong ground motion and agitation by the subsequent tsunami. Sediments in the hemipelagic mud below the erosional surface contain vein-like structures, providing evidence of strong ground motions induced by the earthquake. Two turbidite sequences are present above the erosional surface, in which 134Cs and 137Cs only occur in the upper turbidite. Unconsolidated mud on the inner–mid Sendai Shelf was agitated and resuspended by the high frictional velocities associated with the tsunami waves. The high concentration of suspended sediment in the water column above the shelf is likely to have generated turbidity currents and have made the lower turbidite. After the release of 134Cs by the accident at the Fukushima No. 1 Nuclear Power Plant, the second turbidity current generated and created the upper turbidite.

MODELING ON THE ESTUARINE TURBIDITY MAXIMUM OF YANGTZE ESTUARY BEFORE AND AFTER THE REGULATION WORKS USING Z-MODEL

Existence of the estuarine turbidity maximum (ETM) zone is ubiquitous in partially mixed estuaries. It is characterized by high suspended sediment concentration. The position of the TM usually corresponds to the head of the salt instruction. In the Yangtze Estuary, the ETM zone is extremely large in spatial scale, spreading over the entire mouth zone downstream the South Branch and inside the 10 m isobaths. The ETM is aslo accompanied by a board shallow area (basically around 6 m) in the mouth zone, namely the mouth bars. The presence of the mouth bars hampers the navigation significantly. Thus extensive engineering works are implemented to achieve deeper water depth with the help of dredging activities in the North Passage in the Yangtze Estuary. However after the completion of the engineering works, high siltation appears in the middle segment of the North Passage. The hypothesis is that the location of high siltation (expressed in the morphology) falls in the range of ETM zone modified by the completion of the engineering works. The formation and development of ETM and consequent morphodynamic development is focused on.A three-dimensional z-layer model Delft3D is employed. This study clearly shows that salinity gradients can be better simulated using the z-layer model, where the stratification at the upper limits of the salt wedge is better resolved. Afterwards, the consequent morphological changes are qualitatively demonstrated. The study shows the capability of this z-layer model to exploit the mechanism of generation and development of ETM, thus to explain the complex phenomenon of the high siltation in the North Passage of Yangtze estuary

A single algorithm to retrieve turbidity from remotely-sensed data in all coastal and estuarine waters

Ocean color remote sensing has been shown to be a useful tool to map turbidity (T) and suspended particulate matter (SPM) concentration in turbid coastal waters. Different algorithms to retrieve T and/or SPM from water reflectance already exist, however there are important questions as to whether these algorithms need to be calibrated specifically for different regions. In the present work the potential generality of a semi-empirical single band turbidity retrieval algorithm using the near infrared (NIR) band at 859nm in highly turbid waters is assessed. For completeness the use of 645nm in medium to low turbidity waters is also proposed. Radiative transfer simulations and in situ measurements from various European and South American coastal and shallow estuarine environments characterized by high concentrations of suspended sediments are analyzed. Reflectance and turbidity measurements were performed in the southern North Sea (SNS) and French Guyana (FG) coastal waters, and Scheldt (SC), Gironde (GIR) and Río de la Plata (RdP) estuaries. Simulations showed that uncertainty for turbidity estimation associated with different particle types and bidirectional effects is typically less than 6%. When applied to field data from the five different sites, the semi-analytical algorithm performed well: turbidity estimates were within 12% and 22% of in situ values. A good performance was also found when the entire database was analyzed (n=106) with a mean relative error of 13.7% and bias of 4.8%. The good performance of the algorithm for all these regions, despite differences in sediment characteristics, and the results of the radiative transfer simulations suggest the global applicability of the algorithm to map turbidity up to 1000FNU. Consequently regional algorithms to retrieve SPM concentration from reflectance can be designed by combining this global algorithm to retrieve T from water reflectance with a regional relationship to convert T to SPM. This has the very practical advantage that the measurements needed to calibrate the latter T/SPM conversion for any new region are much easier and cheaper than in situ reflectance measurements.

Variability of suspended sediment yields within the Loire river basin (France)

Summary Suspended sediment fluxes and their variability in time and space have received much attention over the past decades. Large databases compiling suspended sediment load ( SL ) data are often used to serve these purposes. Analyses of these databases have highlighted the following two major limitations: (i) the role of lowland areas in sediment production and transfer has been minimised, and studies on small-scale catchments (with a drainage area of ⩽ 10 2 km 2 ) are practically non-existent in the literature; and (ii) inhomogeneous data and calculation methods are used to estimate and compare the SL values. In this context, the present study aims to complete the existing studies by providing a reliable comparison of SL values for various catchments within lowland river basins. Therefore, we focused on the Loire and Brittany river basins ( France ). 111 small to large catchments covering 78% of this area and representative of the basins landscape diversity were chosen. We first present a large database of area-specific suspended sediment yields ( SY ) calculated from the suspended sediment concentration and flow discharge data over 7–40 yr of measurements at gauging stations. Two calculation methods are used, and the calculated loads are confined within a factor of 0.60–1.65 of the real values. Second, we analyse the temporal and spatial variability of the calculated SY values. Finally, using a nested catchment approach, we provide insight into sediment transport from upstream to downstream gauging stations and into the role of small- and medium- scale catchments in sediment production and transfers. The SL values at the outlet of the catchments range from 2.5 * 10 2 to 8.6 * 10 5 t yr −1 , and the SY values range from 2.9 to 32.4 t km −2 yr −1 . A comparison with the limited values available in the literature for this region corroborates our estimations. Sediment exports from the Loire and Brittany river basins are very low compared with mountainous regions and European exports. However, a strong spatial variability within this territory exists. The expected results on the SY spatial pattern distribution and the correlation between SY values and basin sizes are not observed. An analysis of the SY values at different time steps shows a strong effect of the seasonal availability of detached particles to be transported with a high concentration of suspended sediments during the winter and lower values during the summer and autumn. Annual variations are also observed, with export values varying by a factor 2 to 10 between years for one catchment and the amplitude of the annual variations varying between catchments. The influence of rainfall in the sediment exports is predominant, but investigations on physical characteristics of each catchment (e.g., lithology, slope, land use) are required to better understand the production and transfer processes within a drainage basin. These annual variations imply that long-term data are required to provide mean SY values representative of the catchment functioning. From our calculations, 18 complete years of data are required to obtain a mean SY value with less than 10% of variation on average around the mean. From our results on nested catchments over a long-time scale (40 yr), it appears that most of the suspended sediment load entering the water system is transported downstream. Covariations of the annual- SY values are generally observed for two gauging stations located on the same river. The nested catchment approach is an interesting tool for the identification of active sediment sources within a large catchment and for the construction of detailed sediment budgets.

An improved method for determining dredging source terms

The determination of sediment loss rates from dredging activities is important for quantifying the potential impact on the surrounding physical and biological environment. This paper describes an improved method for measuring and analysing data to determine measurable dredging ‘source terms’ using Sediview software and data from two vessel-mounted acoustic Doppler current profiler devices, one of which is mounted with a vertical beam. The methodology is described in detail and an example data set is presented based on measurements undertaken around a working back hoe dredger. The technique described in this paper offers an improvement over the traditional application of the software used to measure dredger source terms (i.e. the use of one vessel-mounted acoustic Doppler current profiler in a Janus configuration). The use of a vertically orientated acoustic beam allows for a greater range (depth) of acoustic backscatter measurements to be acquired, as the data are not contaminated by side-lobe reflections. Although partially dependent upon the dredging methodology, this improvement is important as high suspended sediment concentrations tend to occur near to the bed. Subject to robust calibration, an improved source term can be collected using two acoustic Doppler current profiler instruments and the software allows the determination of suspended sediment flux (kg/s) across an entire survey transect, by using discharge data from one instrument and calibrated concentration data from the other, rather than the use of a series of water column turbidity profiles and subsequent spatial interpolation (an alternative method to the use of the software).

Impact of tidal-stream arrays in relation to the natural variability of sedimentary processes

Tidal Energy Converter (TEC) arrays are expected to reduce tidal current speeds locally, thus impacting sediment processes, even when positioned above bedrock, as well as having potential impacts to nearby offshore sand banks. Furthermore, the tidal dissipation at potential TEC sites can produce high suspended sediment concentrations (turbidity maxima) which are important for biological productivity. Yet few impact assessments of potential TEC sites have looked closely at sediment dynamics beyond local scouring issues. It is therefore important to understand to what extent exploitation of the tidal energy resource will affect sedimentary processes, and the scale of this impact is here assessed in relation to natural variability. At one such site in the Irish Sea that is highly attractive for the deployment of TEC arrays, we collect measurements of sediment type and bathymetry, apply a high resolution unstructured morphodynamic model, and a spectral wave model in order to quantify natural variability due to tidal and wave conditions. We then simulate the impacts of tidal-stream energy extraction using the morphodynamic model. Our results suggest that the sedimentary impacts of ‘first generation’ TEC arrays (i.e. less than 50 MW), at this site, are within the bounds of natural variability and are, therefore, not considered detrimental to the local environment. Yet we highlight potential environmental issues and demonstrate how impact assessments at other sites could be investigated.

An Assessment of Sediment and Nitrogen Input into the Upper Merbok Estuary, Kedah, Malaysia

The increased loss of nutrients via agricultural runoff has serious potential ecological and public health implications. This paper discusses water quality and nutrient inputs into Merbok river in Northern Malaysia. Merbok river stretches 35 km long with depth ranging from 3 to 15 m. Merbok catchment areas of $$440~\mathrm{{km}}^{2}$$ are made up of alluvium deposits overlying an extensive span of ferruginous shale and mudstone with a few scattered outcrops of granite and ferruginous sandstone/quartzite. In 2006, the Merbok catchment consisted of 25.2 % urban areas, 48.6 % agricultural areas, 20.8 % forests, 0.6 % livestock farming areas, and 4.8 % was covered by other types of land uses. As early as 1990s, Merbok river has been classified as a very polluted river in terms of the ammonium nitrogen (NH4-N) and suspended sediment concentrations (SS). The results of our monthly survey of water quality and nutrient contents, which was carried out every month from October 2011 to September 2012 at 12 sampling stations, suggested and confirmed the previous findings. Such findings affirmed that nearly 3 decades ago, SS and NH4-N were high in the river catchment. The average SS was high (35 mg/l) (Class II of Landerarbeitsgemeinschaft Wasser (LAWA), (1998) water quality standard), at the lower end of Merbok river (M2), while the highest SS of 106 mg/l was recorded at Puntar river, which is upper tributary of Bongkok river. This is due to land clearing in the oil palm plantation and for rubber cultivation observed during sampling period. The maximum recorded NH4-N concentrations observed in the upper Merbok river ranged from 1.97 to 3.98 mg/l along Bongkok river. Moreover, relatively high concentrations were recorded from other tributaries such as the Lalang river (3.10 mg/l); Getah river (3.13 mg/l) and Tok Pawang river (3.53 mg/l), which were all above the limit of 2.4 mg/l or Class IV of the LAWA classification. The trend of data has referred to excessively contaminated rivers of heavy pollution burden. In addition, it was found that the maximum nitrate concentrations were increasing from 8.33 mg/l at the upper Bongkok river (B1) peaking at Bongkok B4 (9.24 mg/l) and decreasing to 6.01 mg/l near the tidal limit of Merbok river (M1) and 5.65 mg/l at M2 in the Merbok estuary, all of which were LAWA class III of heavily-polluted water. Land use and human activities in the upper catchment contributed to such significant pollution burden in the river.

MODIS observed increase in duration and spatial extent of sediment plumes in Greenland fjords

Abstract. The freshwater flux from the Greenland Ice Sheet (GrIS) to the North Atlantic Ocean carries extensive but poorly documented volumes of sediment. We develop a suspended sediment concentration (SSC) retrieval algorithm using a large Greenland specific in situ data set. This algorithm is applied to all cloud-free NASA Moderate Resolution Imaging Spectrometer (MODIS) Terra images from 2000 to 2012 to monitor SSC dynamics at six river plumes in three fjords in southwest Greenland. Melt-season mean plume SSC increased at all but one site, although these trends were primarily not statistically significant. Zones of sediment concentration &gt; 50 mg L−1 expanded in three river plumes, with potential consequences for biological productivity. The high SSC cores of sediment plumes ( &gt; 250 mg L−1 expanded in one-third of study locations. At a regional scale, higher volumes of runoff were associated with higher melt-season mean plume SSC values, but this relationship did not hold for individual rivers. High spatial variability between proximal plumes highlights the complex processes operating in Greenland's glacio–fluvial–fjord systems.

The analysis of phytoplankton blooms off the Yangtze River Estuary in the spring of 2007

The Yangtze River Estuary and the Zhejiang coastal waters have a high incidence of spring phytoplankton bloom and even red tide, but there are rarely phytoplankton blooms in the open waters off the Yangtze River Estuary in the spring considering its relative oligotrophy. From 25 April to 7 May 2007, two strong phytoplankton blooms were observed in the open sea area (the east by 125° E-box C), and the chlorophyll-a concentration, whether measuring through remote sensing or in situ, consistently indicated bloom characteristics. Chlorophyll-a concentration in this area increased significantly, even up to 11 mg·m−3 at individual stations during this period. Average chlorophyll-a measured by remote sensing in region C (125–127°E, 30–32°N) was 2.07 mg·m−3, while the climatic average was only 0.97 mg·m−3 during 2000 to 2008. Analyses demonstrated that suspended sediment concentrations had almost no change, but a slight decrease occurred during the two blooms periods as well as low nitrate and phosphate and higher silicate and salinity in box C. It was suggested that the increased chlorophyll-a concentration was not caused by the intrusion of dilute water from the estuary with high suspended sediment concentrations and nutrients, but probably due to local strong winds on the night of 26 April to the morning of 27 April. A further study with profile data of chlorophyll-a, temperature, salinity and other parameters indicated that strong mixing by the local wind was the main reason for the blooms.