High Suspended Matter Research Articles

Hydrocarbons in size-fractionated plankton of the Mediterranean Sea (MERITE-HIPPOCAMPE campaign)

Aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs, respectively) were analyzed in the dissolved fraction (<0.7 μm) of surface water and in various particulate/planktonic size fractions (0.7–60, 60–200, 200–500 and 500–1000 μm) collected at the deep chlorophyll maximum, along a North-South transect in the Mediterranean Sea in spring 2019 (MERITE-HIPPOCAMPE campaign). Suspended particulate matter, biomass, total chlorophyll a, particulate organic carbon, C and N isotopic ratios, and lipid biomarkers were also determined to help characterizing the size-fractionated plankton and highlight the potential link with the content in AHs and PAHs in these size fractions. Ʃ28AH concentrations ranged 18–489 ng L−1 for water, 3.9–72 μg g−1 dry weight (dw) for the size fraction 0.7–60 μm, and 3.4–55 μg g−1 dw for the fractions 60–200, 200–500 and 500–1000 μm. AH molecular profiles revealed that they were mainly of biogenic origin. Ʃ14PAH concentrations were 0.9–16 ng L−1 for water, and Ʃ27PAH concentrations were 53–220 ng g−1 dw for the fraction 0.7–60 μm and 35–255 ng g−1 dw for the three higher fractions, phenanthrene being the most abundant compound in planktonic compartment. Two processes were evidenced concerning the PAH patterns, the bioreduction, i.e., the decrease in concentrations from the small size fractions (0.7–60 and 60–200 μm) to the higher ones (200–500 μm and 500–1000 μm), and the biodilution, i.e., the decrease in concentrations in plankton at higher suspended matter or biomass, especially for the 0.7–60 and 60–200-μm size fractions. We estimated the biological pump fluxes of Ʃ27PAHs below 100-m depth in the Western Mediterranean Sea at 15 ± 10 ng m−2 day−1, which is comparable to those previously reported in the South Pacific and Indian Ocean.

Development of Total Suspended Matter (TSM) Algorithm and Validation over Gujarat Coastal Water, the Northeast Arabian Sea Using In Situ Datasets

TSM is an essential parameter as it affects the biogeochemistry of the ocean. The high TSM range affects light penetration that’s related to the photosynthesis of primary producers. The aim is to develop a TSM algorithm in Gujarat coastal water using remote sensing reflectance (Rrs), to monitor TSM concentration from the satellite. Seawater sampling and HyperOCR radiometer data collection were carried out in the northeast Arabian Sea. The high suspended matter was observed near the Gulf of Khambhat due to industries and riverine fluxes. For an accurate TSM algorithm, we compared the developed algorithm to previous studies. The TSM algorithm has been developed using the Rrs681/Rrs490 band ratio that has the highest linear correlation (R2 = 0.977, MSE = 19.06). Rrs band ratios demonstrated better compared to single Rrs bands. Satellite images were generated by applying the developed algorithm with the input of Rrs681 and Rrs490 from OLCI. The developed algorithm has been validated successfully with in situ TSM data points, collected across the Daman, Porbandar, and Okha coastal waters. The study indicates that the developed algorithm can be more robust and valuable for various satellite-based synoptic mapping of TSM, including the future Indian Oceansat-3 OCM mission.

Marine floating raft aquaculture extraction of hyperspectral remote sensing images based decision tree algorithm

• The HSI-FRA (Hyperspectral remote sensing index for floating-raft aquaculture) has been constructed. • The decision tree model is designed by combining MNDWI and prior knowledge. • The proposed method is suitable for extracting floating-raft aquaculture in coastal areas of high suspended matter. The accurate extraction and mapping of floating raft aquaculture (FRA) is significant to the scientific management and sustainable development of coastal zones. However, the current relevant methods rely on large sample size and complex classifiers, which have poor generalization ability and thus are not suitable for large-scale application. To address these issues, this study proposes a new hyperspectral index based on remote sensing images, namely hyperspectral index for floating raft aquaculture (HSI-FRA). Based on the analysis of the spectral information, the HSI-FRA utilizes four bands at 580 nm, 740 nm, 1040 nm, and 1290 nm, respectively, to enhance the spectral difference between the floating raft aquaculture and the seawater through band calculation, and constructs the extraction index of the floating raft aquaculture. Using the HSI-FRA, a decision tree classification process is carried out to realize the extraction of floating raft aquaculture information. The extraction accuracy in the three study areas of Dayu Bay of Zhejiang Province, Fengwei Town of Fujian Province and Chao'an Bay of Guangdong Province is 94.3%, 95.5% and 91.44%, respectively, which has Larger advantage than those of traditional methods. The experimental results show that the proposed method is simple, fast and accurate at separating the floating raft aquacultures in an offshore complex marine environment.

Zooplankton Assemblages in a Heavily Polluted River Ecosystem (Pinang River, Malaysia): Impacts of Anthropogenic Stressors on the Communities

River ecosystems are among the most affected habitats globally due to various anthropogenic stressors such as pollution, habitat degradation, hydromorphological alterations and impervious cover due to urbanization. It remains largely unknown how and to what extent zooplankton communities are affected by these stressors in a heavily polluted river ecosystem. This study investigated the abundance and distribution of zooplankton species and the factors affecting their abundance and distribution in Pinang River. A total of 29 taxa of zooplankton were recorded, which includes 27 taxa of Rotifera and two taxa of Copepoda. Among rotifers, the order Bdelloidea had the highest relative abundance (64.79%), followed by Testudinella sp. and Lecane sp. with 10% relative abundance respectively. Spearman’s correlation coefficient showed that the zooplankton abundance was negatively correlated with total dissolved solids and conductivity (P &lt; 0.01). Much higher total dissolved solids and water conductivity, much lower zooplankton abundance. This condition is probably to be unfavorable to the zooplankton population as it is attributed to the presence of extreme anthropogenic activities along the river that cause runoff with high suspended matter. Thus, variations in zooplankton biodiversity reflect the deterioration of water quality in the polluted river ecosystem.

Nitrogen fixation in the western coastal Bay of Bengal: Controlling factors and contribution to primary production

N2 fixation rates were measured at 18 stations in the western coastal Bay of Bengal (BoB) to evaluate its contribution to the external source of nitrogen and its controlling factors. During the study period (fall monsoon), East India Coastal Currents (EICC) flows equatorward resulting in spreads of low saline water along the coast. This leads to stratification and inhibition of nutrient supply to the mixed layer through vertical mixing, resulting in the existence of nitrogen-poor and warm waters in the upper layer. Such conditions may trigger N2 fixation in the upper ocean. To examine such possibility, the N2 fixation rates were measured and found to vary between 0.4 and 14.8μmol N m−2 d−1 in the photic layer during the fall monsoon. A linear relationship was observed between photic zone integrated N2 fixation rates and phosphate suggesting a possible severe limitation of phosphate in the BoB. Low N2 fixation rates were observed at off Godavari, Krishna and Mahanadi River estuaries in the inshore than offshore regions associated with low phosphate and high suspended matter. This suggests that phosphate may be removed through adsorption on the suspended matter resulting in severe limitation of N2 fixation in the western BoB. Based on the available seasonal data, 0.01 to 0.94 Tg/y of N2 fixation occurs and contributes to <1% of the primary production in the BoB.

Distribution of suspended particulate matter at the equatorial transect in the Atlantic Ocean

Abstract. A suspended particulate matter distribution against a hydrographical background was studied at the oceanographic transect across the equatorial Atlantic in the year 2000. An area of abnormally high suspended matter volume concentrations was found above the Sierra Leone Rise in the entire water column (eastern part of the transect). The suggested explanation for the anomaly is based on the ballast hypothesis whereby solid particles are incorporated as ballast into suspended biogenic aggregates, leading to increased velocities of sinking. This occurs within the Northwest African upwelling area, where the plankton exposed to the Saharan dust abundance form a significant number of aggregates, which are later transported equatorward via the Canary Current. An intermediate nepheloid layer associated with the Deep Western Boundary Current was recorded from the South American Slope at depths of 3200–3700 to 4300 m above the Para Abyssal Plain. Antarctic Bottom Water enriched in suspended matter was found mostly in the troughs at 40–41∘ W. It was detached from the bottom, coinciding with the core of the flow due to the bottom rise “dam” located up-stream. The grain size of particles along the entire transect has a polymodal distribution with 2–4 and 8–13 µm modes. The registered rise in percentage in some parts of the transect of the 7–21 µm sized particles suggests the presence of the well-known coarse mode (20–60 µm) formed by aggregation of transparent exopolymer particles (mucus).

CO1 Metabarcoding of Marine Water Samples from the 2nd Turkish Antarctic Expedition (TAE2) Highlights the Deficiencies in the Reference Barcoding Databases for the Continent

Based on climate projections, the Antarctic Peninsula is one of the regions on the earth expected to be most drastically affected by climate change in the 2nd half of the 21st century. In order to establish baseline levels of marine biodiversity using the environmental DNA approach, we undertook metabarcoding based on the CO1 gene. Samples were collected using 0.22 mM pore-sized Sterivex filters during TAE2 undertaken in 2018, from one site at Deception Island (2 filters), one site at Nansen Island (2 filters), and three sites (one offshore) at Robert Island. A total of 20 taxa were identified (unique hits with BLAST percent identity ≥ 97%) belonging to three kingdoms (Chromista, Plantae, Animalia), nine phyla, 11 classes, 17 orders, 19 families, and 20 genera. Of these, 18 were identified to the species level, one to the genus level, and the other one to the family level. Genetically identified taxa included seven planktonic algae, nine seaweeds, a stalked jellyfish, a nematode, a planktonic copepod, and a demersal fish. In addition, 129 unique OTUs were detected (unique hits with BLAST percent identity &amp;lt; 97%) as unidentified. These results indicate the high levels of undocumented genetic diversity (without CO1 barcode sequences in GenBank) in the Antarctic Peninsula region and adjacent waters, and the need for more work to complete the reference barcode databases for the continent. A dendrogram resulting from cluster analysis (Bray-Curtis similarity measure, group-average linkage) based on the presence/absence data of 20 identified species revealed three well-defined sample (i.e. filter containing DNA fragments of multiple taxa) groups, which almost coincided with their geographical locations. First group included samples (filters) collected from the coast of Deception Island and the second one from the coast of Robert Island, both in the South Shetland Islands, off the northern tip of the Antarctic Peninsula. The third group included samples from Nansen Island coast (off the west coast of Graham Land, Antarctic Peninsula) together with the only sample collected offshore, off Robert Island. The significance of this clustering, thus the difference among sampling sites with regard to species composition, was confirmed by Analysis of Similarity (ANOSIM) results (Global R = 0.982, p = 0.001). The highest number of identified taxa (per filter) and unidentified OTUs (per filter) were observed offshore off Robert Island. Considering that all of the other sampling sites were by the coasts of islands, this observation indicates i) the offshore waters might contain more DNA-bearing material than coastal sites, and/or ii) a methodological issue where the high phytoplankton and suspended matter concentrations by the coasts created a bottleneck in terms of capturing actual species diversity at the coasts, due to clogging of filters by phytoplankton and fine suspended particles.

Effects of Industrial Agriculture and Urbanization on Structure and Functional Organization of Macroinvertebrate of Coastal Streams in Cameroon

The impact of land use changes on watercourses is poorly documented in Cameroon. Therefore, this study examines the effects of agriculture and urbanization on water quality, the structure and functional organization of macroinvertebrates of streams in the coastal zone of Cameroon. Nine sampling stations including three per catchment area with different land occupations (agricultural, urban and forest) were selected. Benthic macroinvertebrates were sampled monthly from February to July 2018 and the physicochemical variables were measured simultaneously. The urban and agricultural streams showed highly polluted waters with high nutrient and suspended matter content, whereas the forest stream waters are moderately polluted. In addition, the hierarchical ascending classification indicated a proximity in water quality between the agricultural and forest streams for which the main physicochemical variables did not vary significantly. With regards to macroinvertebrates, the forest watercourse is characterized by the proliferation of pollution-sensitive taxa, high diversity indices and complex trophic structuring, indicating its good ecological status. In contrast the urban watercourse, heavily polluted is characterized by low diversity indices reflecting a simplification of the structure of stands dominated by the pollution-tolerant collector-gatherer stands. The majority of biological indices and functional feeding groups were not significantly different between the agricultural and forest streams, suggesting a less pronounced impact of agriculture on macroinvertebrates. Our results showed that, riparian vegetation even though constituted of perennial crops, reduces the effects of agricultural inputs on streams and promotes the establishment of diversified macroinvertebrate communities.

Assessment of Applicability of Satellite-Derived Ocean Color Data for Studying Variability of Total Suspended Matter in the Surface Layer of the Deep Part of the Black Sea

Purpose. Studies of spatial-temporal variability of total suspended matter are necessary for understanding the biochemical processes which form and support stable functioning of a marine ecosystem. The aim of the work is to assess applicability of satellite data for studying total suspended matter variability in the surface layer of the deep part of the Black Sea. Methods and Results. Application of the regression analysis yielded the linear regression equations that unite the in situ measurements of the total suspended matter concentrations in the surface layer in the northeastern (June, 2005–2015) and western (November, 2016, 2017 and December, 2017) deep sea areas, and the regional satellite products (the particulate backscattering coefficient, the absorption coefficient of colored detrital matter and the chlorophyll a concentration). Based on the measured and calculated data arrays, the maps of the total suspended matter concentrations in the surface layer of the northeastern Black Sea were constructed. The interannual changes in the in situ measured concentrations of the total suspended and lithogenic matters, as well as in the quasi-synchronous satellite regional products (the light absorption coefficient of colored detrital matter at 490 nm and the particulate backscattering coefficient at 555 nm) in June, 2005–2015 were considered. High total suspended matter concentrations were noted in 2012, just when extreme growth of the coccolithophorid population was observed in the Black Sea. The correlation coefficients were used to evaluate whether the relation between the total suspended matter concentration and the individual analyzed parameters was fast. Conclusions. Spatial distributions of the measured and calculated total suspended matter contents showed satisfactory agreement. In course of the whole observation period, difference between the values of the measured and calculated total suspended matter concentrations was on average 6–23 %. Possibility of application of the satellite-derived ocean color data for studying spatial-temporal variability of the total suspended matter content is shown.

Seasonal evolution of particulate and dissolved absorption coefficients in a subtropical estuary

The seasonal evolution of colored dissolved organic matter (CDOM), phytoplankton, and non-algal particulate absorption coefficients were measured for the first time along a salinity gradient within the Paranaguá Estuarine Complex (PEC), in southern Brazil. CDOM (mostly of autochthonous origin) inside the estuary exhibited a conservative behavior that dominates the absorption budget at lower wavelengths (~380 nm). On average, absorption by non-algal particles was more important than absorption by phytoplankton throughout the year and across all wavelengths, except for the maximum absorption band of chlorophyll-a (665–675 nm), where the algal component was predominant year-round. Phytoplankton optical properties were generally consistent with variability in phytoplankton cell counts, particularly during bloom periods. Simultaneous condition of high suspended matter concentrations and low turbidity conditions associated with sampling of mucilaginous materials released by centric diatoms exemplified the complex relationships between biogeochemical and optical properties in this region. The relationship between chlorophyll-a concentration and phytoplankton absorption exhibited seasonal oscillations related to the variation of algal assemblages, ultimately determining the magnitude of the packaging effect. Finally, separation of the signals of these three components in the visible domain is possible only in the near-ultraviolet range (380 nm), associated with CDOM dominance, and at 665 nm where the phytoplankton signature can be isolated.

Quantification of lake clarity in China using Landsat OLI imagery data

The eutrophication of lake and reservoir (hereafter referred to as lakes) has attracted concerns from the public and government in China. Water clarity is a reliable indicator for quantifying eutrophic status because of its strong association with chlorophyll-a, total suspended matter, and nutrients. Traditionally, water clarity is measured using Secchi disk depth (SD). By linking the spectral signal from water surface with in situ measured SD, remote sensing provides a useful tool for SD estimation at a large scale in a repetitive manner. Remote sensing derived water clarity has been reported in many regions with specific models established for different satellite overpasses concurrent with in situ measured SD, but national water clarity remained unknown in China. In this study, 2152 samples were collected from 34 field campaigns in 2013–2018, of which 1792 samples were gathered within ± 7 days of Landsat OLI overpasses. We used Landsat 8 OLI bands 1–4 to develop regression models (n = 1016), and 782 samples to validate model performances. We further collected three additional in situ SD datasets to validate the best performance model, and eventually used it to map SD at a national scale with OLI images mainly acquired in 2016. Our results indicated that the entire dataset of SD has a strong association with Landsat reflectance, yielding low root mean square error between measured and estimated SD (RMSE = 63 cm) for lakes in China. The national water clarity was averaged to 176 cm in 2016 with large spatial variability (S.D: 216 cm) due to the marked variation between turbid waters in the east plain area and clean water across the Tibet Plateau. Lakes in the northeastern (75 cm) and eastern (84 cm) China had low clarity due to shallow water depth combined with high suspended matter and algal abundance. Lakes in the Yungui Plateau (91 cm), Inner Mongolia and Xinjiang autonomous regions (114 cm) exhibited intermediate clarity; while lakes in the Tibet Plateau (294 cm) displayed the highest clarity. This investigation demonstrated that Landsat imagery with Rayleigh scattering correction reflectance combined with in situ observation can provide quantitative information about the lake clarity with surface area >8 ha. Moreover, this method has the potential to retrieve SD with archived Landsat imagery to determine the temporal variation of SD at national or continental scale which can be used to support inland water management and decision-maker for improving water quality.

Suspended-Matter Distribution Near the Western Coast of Crimea under the Impact of Strong Winds of Various Directions

In this paper, we study the mechanisms of the formation and distribution of suspended matter (SM) near the western coast of Crimea under the impact of strong winds of various directions using medium- and high-resolution satellite data. The SM concentration was noted to reach its maximal values ​​at southern winds, reaching values ​​of 200 mg/L. The zone of high SM concentration is located in the region of the western shelf of Crimea and is limited to an isobath of 50 m. The wave action during the south wind contributes to the resuspension of bottom sediments and the destruction of clay cliffs on the western coast of Crimea. After the storm, a northern coastal current arises that transfers the SM to the north. In northeastern winds, the highest SM concentrations are observed not on the coast, but in the sea part of the shelf between isobaths of 30 and 50 m. Such winds are likely to resuspend sediments in shallow water, which are then driven away from the coast by the action of wind driving. They are replaced by clean, cold waters from the deeper layers that are observed near the coast. The feature of northern and northwestern storms impact is the formation of a coastal jet current along the west coast. The current occurs in the frontal upwelling zone and carries the SM south to the deep sea. The SM concentration in this case is also significantly lower than during southern winds, although it can reach 3 mg/L.

EFFECT OF Pilsbryoconcha exilis AS ORGANIC MATTER REMOVAL IN THE RECIRCULATING AQUAPONIC SYSTEM

Aquaponics is a combination of aquaculture and hydroponics system. This system is expected to be able to overcome the problems of waste from aquaculture by utilizing Nitrogen (N) and Phosphorus (P) for vegetables. There are several obstacles found in aquaponics systems such as high suspended organic matter produced from the feed residue and fish metabolism. The addition of natural filters, namely freshwater mussels (Pilsbryoconcha exilis) is expected to solve these problems. This research was conducted for 40 days. The design used in this study was Factorial Completely Randomized Design with two main factors namely mussels density as factor-A and time of observation as factor-B. The treatments were P1 (0 mussels density), P2 (15 mussels density), and P3 (30 mussels density) for factor-A while time of observation were factor-B (D-0, D-10, D-20, D-30 and D-40). Each treatment was conducted in three repetition. The results showed that the time observation gave significantly different on water condition changes (P &lt;0.05), which will increase TSS, turbidity and chlorophyll value along with the increasing of time. P exilis in aquaponics was effective in reducing turbidity and chlorophyll concentration (P &lt;0.05). Therefore, aquaponics system with the highest mussels density (P3) with has lower turbidity and chlorophyll value than the one with 0 mussels density (P1).

Exploring effects of dredging and organic waste on the functioning and the quantitative biomass structure of the Ems estuary food web by applying Input Method balancing in Ecological Network Analysis

Detailed food webs of the three main Ems estuary reaches (Lower Reaches/LR, Middle Reaches/MR and Dollard/DO) representing the 1975–1980 period, were used for explorations. The effects of turbidity and organic waste were explored for ∼1955 (waste loads and low suspended matter) and ∼2005 (no waste loads and high suspended matter) by applying the Input Method-based balancing as part of the Ecological Network Analysis (ENA) package to analyse food web carbon flows. The total phytoplankton primary production (sum of true phytoplankton and resuspended microphytobenthos) of the LR in 2005 is reduced by 56% compared to 1955. For MR and DO the primary production reduction over the same period is ∼70%. Expressed in tons carbon the 2005 total primary production (including microphytobenthos) of the entire estuary is 59% of that in 1955. In 2005 the total (all living compartments) estuarine biomass is 63% of that in 1955. The data suggest a further fast future biomass decline. Compared to 1955 the relative biomass changes of the living compartments are in 2005 −71.1% for LR, −66.7% for MR and −70% for the Dollard. Results are in line with independent monitoring. The biomass changes per species range for LR from −1.3% (microzooplankton) and −1.5% (intertidal bivalves) to −71.7% (pelagic bacteria), for MR from −15.3% (mesozooplankton, Sprattus sprattus, Clupea harengus) to −90.5% (pelagic bacteria) and for DO from −6.6% (Chelon labrosus) to −97.4% (pelagic bacteria). The relative mean total biomass changes caused by the sanitation of the organic waste loads are −1.5% for LR, −5.0% for MR and −12.5% for DO. The IM-based balancing results in an increasing ratio between detritivory and herbivory and increase of the carbon cycling. The effects are strongest for the LR. The described changes are driven by i) the combination of changed system boundary conditions and the species specific diets and ii) the absence of international political collaboration because of a disputed border that results in the absence of an internationally agreed integral solution via one master plan Ems estuary. The varying changes at the species level and the strong connection of pelagic and benthic systems in intertidal flat estuaries demand an integral approach for assessments and management.

Experimental study on the evaporation and chlorine migration of desulfurization wastewater in flue gas.

Wastewater from a limestone-gypsum wet desulfurization system cannot be directly reused or discharged due to its high suspended matter content and complex water composition. Desulfurization wastewater evaporation in flue gas is an effective way to dispose wastewater. Multicomponent soluble chlorine salts exist in the desulfurization wastewater. During the evaporation, chlorine enters into the flue gas due to volatilization, which accelerates the enrichment rate of the Cl- concentration in the desulfurization slurry and leads to an increase in wastewater production. This study explored the chlorine migration of various chlorine salt solutions and typical desulfurization wastewater at high temperature during the evaporation process of concentrated wastewater by a laboratory-scale tube furnace and a pilot-scale system. Results showed that when NaCl-evaporated substance was heated, the chlorine ion hardly volatilized. For the evaporated substances of CaCl2 and MgCl2 solutions, some of the crystal water was lost, and hydrolysis occurred to generate gaseous HCl. NH4Cl was easily sublimed, and the decomposition temperature was lowest. A pilot study on spray evaporation of desulfurization wastewater in flue gas showed that the particle size of the evaporated product increased and the main particle size was within 2.5-10μm with increasing flue gas temperature. Increasing the mass ratio of gas to liquid significantly reduced the particle size of the atomized particles, thereby reducing the average particle size of the evaporated particles. The HCl concentration increased with increasing flue gas temperature. When the flue gas temperature was 350°C, the concentration of HCl was 40ppm, and the escape rate of chlorine in the desulfurization wastewater was approximately 30% using typical wastewater from a limestone-gypsum wet desulfurization system.

A comprehensive biogeochemical record and annual flux estimates for the Sabaki River (Kenya)

Abstract. Inland waters impart considerable influence on nutrient cycling and budget estimates across local, regional and global scales, whilst anthropogenic pressures, such as rising populations and the appropriation of land and water resources, are undoubtedly modulating the flux of carbon (C), nitrogen (N) and phosphorus (P) between terrestrial biomes to inland waters, and the subsequent flux of these nutrients to the marine and atmospheric domains. Here, we present a 2-year biogeochemical record (October 2011–December 2013) at biweekly sampling resolution for the lower Sabaki River, Kenya, and provide estimates for suspended sediment and nutrient export fluxes from the lower Sabaki River under pre-dam conditions, and in light of the approved construction of the Thwake Multipurpose Dam on its upper reaches (Athi River). Erratic seasonal variation was typical for most parameters, with generally poor correlation between discharge and material concentrations, and stable isotope values of C (δ13C) and N (δ15N). Although high total suspended matter (TSM) concentrations are reported here (up to ∼ 3.8 g L−1), peak concentrations of TSM rarely coincided with peak discharge. The contribution of particulate organic C (POC) to the TSM pool indicates a wide biannual variation in suspended sediment load from OC poor (0.3 %) to OC rich (14.9 %), with the highest %POC occurring when discharge is &lt; 100 m3 s−1 and at lower TSM concentrations. The consistent 15N enrichment of the particulate nitrogen (PN) pool compared to other river systems indicates anthropogenic N loading is a year-round driver of N export from the Sabaki Basin. The lower Sabaki River was consistently oversaturated in dissolved methane (CH4; from 499 to 135 111 %) and nitrous oxide (N2O; 100 to 463 %) relative to atmospheric concentrations. Wet season flows (October–December and March–May) carried &gt; 80 % of the total load for TSM (∼ 86 %), POC (∼ 89 %), dissolved organic carbon (DOC; ∼ 81 %), PN (∼ 89 %) and particulate phosphorus (TPP; ∼ 82 %), with &gt; 50 % of each fraction exported during the long wet season (March–May). Our estimated sediment yield (85 Mg km−2 yr−1) is relatively low on the global scale and is considerably less than the recently reported average sediment yield of ∼ 630 Mg km−2 yr−1 for African river basins. Regardless, sediment and OC yields were all at least equivalent or greater than reported yields for the neighbouring dammed Tana River. Rapid pulses of heavily 13C-enriched POC coincided with peak concentrations of PN, ammonium, CH4 and low dissolved oxygen saturation, suggesting that large mammalian herbivores (e.g. hippopotami) may mediate the delivery of C4 organic matter to the river during the dry season. Given recent projections for increasing dissolved nutrient export from African rivers, as well as the planned damming of the Athi River, these first estimates of material fluxes from the Sabaki River provide base-line data for future research initiatives assessing anthropogenic perturbation of the Sabaki Basin.

Impact of river discharge on distribution of zooplankton biomass, community structure and food web dynamics in the Western coastal Bay of Bengal

Observations were carried out along the western coastal Bay of Bengal, to examine the physical, chemical and biological parameters during the summer monsoon particularly when the rivers of India are in flood condition and discharge large quantities of fresh water into the Bay of Bengal. River discharge has a significant impact on plankton biomass in the coastal Bay of Bengal. High concentrations of nutrients were observed at the Southern coastal Bay of Bengal (SCB), which were associated with high suspended matter (SPM) that limits the phytoplankton biomass (Chl-a). In contrast, the Northern coastal Bay of Bengal (NCB) was characterized by low nutrients and SPM coupled with higher phytoplankton biomass and zooplankton abundance. Therefore primary production in the coastal Bay of Bengal appears to be controlled by light availability in the water column more so than by nutrients, particularly during the peak river discharge. Relatively higher zooplankton biomass and abundance have been found in NCB than in SCB. Zooplankton biomass showed a strong linear relationship with phytoplankton biomass in NCB. On the other hand, a strong linear relationship was observed with particulate organic carbon (POC) in the SCB.

River geochemistry, chemical weathering, and atmospheric CO2 consumption rates in the Virunga Volcanic Province (East Africa)

AbstractWe report a water chemistry data set from 13 rivers of the Virunga Volcanic Province (VVP) (Democratic Republic of Congo), sampled between December 2010 and February 2013. Most parameters showed no pronounced seasonal variation, whereas their spatial variation suggests a strong control by lithology, soil type, slope, and vegetation. High total suspended matter (289–1467 mg L−1) was recorded in rivers in the Lake Kivu catchment, indicating high soil erodibility, partly as a consequence of deforestation and farming activities. Dissolved and particulate organic carbon (DOC and POC) were lower in rivers from lava fields, and higher in nonvolcanic subcatchments. Stable carbon isotope signatures (δ13C) of POC and DOC mean δ13C of −22.5‰ and −23.5‰, respectively, are the first data to be reported for the highland of the Congo River basin and showed a much higher C4 contribution than in lowland areas. Rivers of the VVP were net sources of CH4 to the atmosphere (4–5052 nmol L−1). Most rivers show N2O concentrations close to equilibrium, but some rivers showed high N2O concentrations related to denitrification in groundwaters. δ13C signatures of dissolved inorganic carbon suggested magmatic CO2 inputs to aquifers/soil, which could have contributed to increase basalt weathering rates. This magmatic CO2‐mediated basalt weathering strongly contributed to the high major cation concentrations and total alkalinity. Thus, chemical weathering (39.0–2779.9 t km−2 yr−1) and atmospheric CO2 consumption (0.4–37.0 × 106 mol km−2 yr−1) rates were higher than previously reported in the literature for basaltic terrains.

The turbidity maximum zone in a shallow, well-flushed Sabaki estuary in Kenya

The spatial–temporal variability and the behaviour of the Estuarine Turbidity Maximum (ETM) zone in the shallow, ephemeral, well-flushed Sabaki estuary located in the northern region of the Kenya coast, were studied during a period of moderate river discharge. The estuary is one of the most turbid estuaries along the coast of East Africa, characterised by high sediment input and high suspended matter (SPM) concentrations. The estuary is completely flushed after every tidal cycle and it experiences high salinity and SPM concentration gradients at high water (HW). The ETM was present at HW during periods when the river runoff was near the long-term average of 73m3s−1 and also when the river runoff was relatively low (35m3s−1). The SPM concentrations in the ETM zone varied significantly depending on the river sediment input and phase of the semi-diurnal tide. The SPM concentrations in the ETM were on average 50% greater than those associated with river runoff. The ETM was located up-estuary during periods when river runoff was around the average and further down-estuary during periods of low river runoff, due to different sediment settling rates. There was a tendency for the accumulation of fine sediments and clay mud in a zone of low current velocities located in the lower middle region of the estuary below the freshwater–saltwater interface, causing formation of an ETM zone. The ETM was separated from the salt-limit due to the lag in time in the tidally-driven resuspension of bottom mud and subsequent tidally-driven advection of turbid water up-estuary during the flood period. The relatively low current velocities combined with high horizontal and vertical gradient in eddy diffusivity in the central region of the estuary, tended to favour rapid settling of flocculated sediments, leading to the formation of the ETM. The study concludes that rapid settling through non-turbulent pycnocline is the dominant mechanism responsible for the formation of the Sabaki estuary ETM. The study also shows that the formation of inter-tidal mudflats is related to the ETM dynamics.

Stormwater treatment for removal of synthetic surfactants and petroleum products by reverse osmosis including subsequent concentrate utilization

The results of research are presented on new runoff and waste water treatment technologies based on the use of reverse osmosis (RO) systems equipped with specially designed open-channel membrane devices for treating water with a high suspended matter content. A characteristic feature of the technology is the utilization of the RO concentrate, which is discharged from the system together with the wet sludge and all contaminants rejected from water. The dependences of the concentration of pollutants in the filtrate and the membrane performance on the salinity of feed water and its volume concentration factor in the RO unit have been shown. The parameters of units operating with these types of wastewater have been determined. The effect of feed water salinity on the petrochemicals and detergents rejection efficiencies has been studied. A settleability prediction procedure, based on determination of the rate of membrane fouling with suspended solids as a function of their particle size, has been proposed to calculate the settling efficiency of flush water after hydraulic washing of membrane devices.