High Water Turbidity Research Articles

Monitoring methods of feeding behaviour to answer key questions in penaeid shrimp feeding

AbstractThe penaeid shrimp farming industry is a fast‐growing sector which continues to suffer from significant feeding inefficiencies. Shrimp are slow to feed on pellets, with consumption dependent on a wide range of environmental and physiological parameters. Feed management on farms remains mainly based on feeding trays which can be difficult to observe and often result in overfeeding. While our understanding of shrimp feeding behaviour is beginning to improve under laboratory conditions, much less is known about shrimp behaviour in production ponds. Consequently, there is a growing interest within the industry to improve observations of shrimp feeding behaviour in situ, although this can be difficult due to high water turbidity and the benthic nature of shrimp. This review identifies key questions that remain unanswered in relation to shrimp feeding behaviour under commercial aquaculture conditions, and considers how they could be addressed using state‐of‐the‐art applications based on three technologies commonly used in other areas of aquaculture. The use of passive acoustics, computer vision and telemetry are highlighted, alongside their potential to help farmers achieve better feeding efficiencies and sustainability as well as to help understand shrimp feeding behaviour in relation to various biotic and abiotic parameters.

Applications of environmental DNA methods for charophyte biodiversity

The use of environmental DNA (eDNA) for qualitative species inventories offers great potential as a cost-effective tool for species identification. This requires that the target species release DNA, reference information is available and detection methods exist. Environmental DNA analyses are currently used routinely to inventory fish fauna (Wang et al. 2021), molluscs (Klymus et al. 2017) or insects (Uchida et al. 2020). For other groups, such as macrophytes, there is not much information available (Scriver et al. 2015). In plants, identifying suitable eDNA markers been much more challenging, as no single DNA region has been accepted for the purposes of barcoding. Within this project, we assessed if stoneworts (Charophytes, Characeae) can be detected by using eDNA analysis and if it can be used to support macrophyte monitoring. Charophytes are macroscopic green algae which, because of their role as habitat engineers, are of special importance for aquatic ecosystems. Many charophyte species are bound to clean, nutrient-poor fresh and brackish waters (e.g. Melzer 1999) and are regarded bioindicators for water quality by national and international directives (e.g. Habitats Directive, EU Water Framework Directive). Being sensitive to anthropogenic pressures, a drastic decline in populations with increasing eutrophication has been reported (Sand-Jensen et al. 2017) . However, the diversity of Characeae is often underestimated due to difficulties in morphological determination, and the genetic identification of charophytes has been established only in the recent few years (e.g. Nowak et al. 2016). We assessed the potential utility of eDNA to document the diversity of charophyte species. eDNA from a fresh water lake (Dreetzsee, Germany, 2018) and from a brackish water site (Darß-Zingst Lagoon System, Germany, 2018) was extracted from filtered or ethanol‐precipitated water samples, and we designed and tested eDNA markers based on four regions of the chloroplast genome - atpB, rbcL, psbC, and matK. Of the four regions, matK and rbcL were most likely to amplify DNA from charophyte species. Both sites exhibit a diverse charophyte flora, which we successfully could identify to species/group level by eDNA analysis. In a current study, the developed eDNA markers are used to scrutinize the charophyte population of the Schlei estuary (Germany, Schleswig-Holstein). Since conventional monitoring can only be carried out once a year at a few sites, Characeae have not been observed in recent years, or only very sporadically. As it is not possible to survey the entire Schlei, especially due to high water turbidity, the eDNA methodology is tested to assess the presence of Characeae species.

Performance of inclined plates settler integrated with constructed wetland for high turbidity water treatment

Abstract The purpose of this study was to investigate and demonstrate cost-effective treatment technologies for highly turbid waters, used for domestic purposes in rural areas of Tanzania where conventional community water treatment techniques are not available. Pilot-scale inclined plates settler integrated with constructed wetland (IPS-CW) system was investigated on earth dam water with turbidities ranging from 186 to 4,011 NTU. The IPS was used as a physical pretreatment system preceding the CW, meant for the removal of organic matter, nutrients, and pathogens. Major focus of the IPS-CW system was on turbidity and faecal coliform (FC) removal, and at 5 L/min flow rate mean maximum removal efficiencies of 95.9% and 94.3% were achieved, respectively. Total suspended solids, nitrate (NO3−), ammonium, biological oxygen demand (BOD5) and phosphate removal were studied and removal efficiencies of 97.4%, 91.7%, 71.3%, 91.7% and 49.8% were obtained at 5 L/min flow rate, respectively. Although the use of these combinations of technologies in improving drinking water quality is uncommon, results demonstrated that NO3− and BOD5 met WHO and TBS drinking water standards of ≤50 mg/l and ≤6 mg/L respectively. Due to low production cost and simplicity in operation, the system is relevant for application in rural communities.

Detection and alkaline inactivation of Cryptosporidium spp. oocysts and Giardia spp. cysts in drinking-water treatment sludge

Removing and inactivating Cryptosporidium spp. oocysts and Giardia spp. cysts are a challenge for drinking-water treatments, mainly because of their small sizes and resistance to chlorination. Moreover, protozoan detection methods are expensive and subject to high variability and low reproducibility, especially in high turbidity water. This research aimed at detecting and inactivating cysts and oocysts in drinking-water treatment sludge. In jar test treatability assays, 110 NTU study water was treated with polyaluminium chloride to obtain the sludge. The chosen method for detecting cysts and oocysts was direct centrifugation with ICN 7X solution followed by the immunomagnetic separation (IMS) with two acid dissociations. The inactivation of cysts and oocysts was identified by the inclusion of propidium iodide as a vital dye when the cell walls were damaged. This method's analytical quality control, which was performed with the EasySeed® suspension, obtained recovery of 3.3 ± 2.0 % and 24.8 ± 8.0 % for oocysts and cysts, respectively. Besides, the Giardia spp. recovery met the standards recommended for water by the USEPA Method 1623.1. Magnetic microspheres were found attached to the protozoan in the microscope slides after IMS, indicating some limitations of this purification method. The alkaline treatment tested a dose of 27 mg CaO/100 mL for 3 and 5 days, obtaining inactivation of 1.85 and 3.0 log for oocysts and 2.05 and 2.14 log for cysts, respectively. In this context, the alkaline treatment may be feasible to reduce the microbiological risk in water treatment sludge, considering an economic assessment.

The role of carbonate mineral dissolution in turbidity reduction in an oil sands end pit lake

Surface water turbidity from dispersed clay particles can hinder the development of aquatic ecosystems. One of the primary objectives for proposed oil sands end pit lakes is that they support ecological functions and lake-specific wildlife habitat. However, high surface water turbidity has been observed in the Base Mine Lake cap water, the first full-scale demonstration oil sands end pit lake. Our previous study showed that adjusting the solution pH through carbon dioxide (CO2) addition reduced surface water turbidity in oil sands tailings. Carbonate minerals such as calcite and dolomite were also previously identified in tailings, and thus the goal of this study was to determine the effect of calcite and dolomite dissolution through CO2-mediated pH reduction on turbidity and the stability of suspended clay particles. Calcite dissolution resulted in ∼99% reduction of turbidity. The suspended clay particle stability was analyzed using DLVO (Derjaguin-Landau-Verwey-Overbeek) theory with water chemistry data from this column study. An inverse correlation was observed between the amount of dolomite and the energy barrier values on day 42 of the experiment. These results suggest CO2-mediated calcite dissolution changes the water chemistry and is the most promising treatment condition for the settlement of suspended tailings particles.

Kinetic modelling of high turbid water flocculation using native and surface functionalized coagulants prepared from shed-leaves of Avicennia marina plants

Coagulation performance of shed-leaves of Avicennia marina plants collected from Alang coastline, Gujarat (India) was scrutinized for the treatment of mud and starch water suspensions. For which, native, hydrochloric acid, sodium hydroxide and sodium chloride treated A. marina shed-leaves were processed with minimum environmental impact. Experiments were accomplished for the concentration of water suspensions (10–50 g/L) at the range of pH 7.0–8.0. The performances of these coagulants were assessed in terms of reduction in turbidity, pH, alkalinity, hardness, electrical conductivity and solids from water suspensions. The removal of bulk impurities was noted due to the floc formation of coagulant through hydrolysing salts, thus, resulted in the highest settlement at pH 7.82, 7.90 for mud and starch water, accordingly. Native and functionalized A. marina coagulants (AMCs) were characterized and interpreted using scanning electron microscopy, elemental analyses, energy dispersive and Fourier transform infrared spectroscopy. HCl treated AMC was relatively effective with good coagulation performance (96.76%), when compared with native and other treated AMCs. The turbidity removal by all AMCs obeyed with World Health Organization (WHO) acceptable limit of finished water, where HCl treated AMC clarified 15.15 and 16.36 NTU of mud and starch water suspensions to produce a clear water of 0.92 and 1.61 NTU, respectively. The proficiency of prepared AMCs were compared with other natural coagulants and surface functionalized (HCl > NaOH > NaCl) AMCs prepared in this study exerted better performance than the native AMC. The critical coagulation rate from the second-order kinetics were evaluated and the results were highly satisfying. Other physico-chemical parameters of water suspensions were evident for the adequate removal of impurities by non-toxic plant-based coagulants.

Detection of Cyclospora cayetanensis in produce irrigation and wash water using large-volume sampling techniques

The recent increase of reported cyclosporiasis outbreaks associated with fresh produce has highlighted the need for understanding environmental transmission of Cyclospora cayetanensis in agricultural settings and facilities. Conducting such environmental investigations necessitates robust sample collection and analytical methods to detect C. cayetanensis in water samples. This study evaluated three sample collection methods for recovery of C. cayetanensis oocysts from water samples during seeded recovery experiments. Two filtration-based methods, dead-end ultrafiltration (DEUF) and USEPA Method 1623.1, were evaluated for oocyst recovery from irrigation water. A non-filter-based method, continuous flow centrifugation (CFC), was evaluated separately for recovery from creek water and spent produce wash water. Median C. cayetanensis recovery efficiencies were 17% for DEUF and 16–22% for Method 1623.1. The DEUF method proved to be more robust than Method 1623.1, as the recovery efficiencies were less variable and the DEUF ultrafilters were capable of filtering larger volumes of high-turbidity water without clogging. Median C. cayetanensis recovery efficiencies for CFC were 28% for wash water and 63% for creek water, making it a viable option for processing water with high turbidity or organic matter. The data from this study demonstrate the capability of DEUF and CFC as filter-based and non-filter-based options, respectively, for the recovery of C. cayetanensis oocysts from environmental and agricultural waters.

Dead-end ultrafiltration as a cost-effective strategy for improving arsenic removal from high turbidity waters in conventional drinking water facilities

Dead-end ultrafiltration (UF) was integrated to a conventional drinking water treatment process (pre-oxidation, coagulation-flocculation, decantation and sand filtration) as a strategy for arsenic control in drinking water. Different turbidities (control, 300 and 1000 NTU) and arsenic concentration (0.015 – 0.4 mg/L) were considered, in addition to the interference of iron and manganese on arsenic removal as these metals occur concomitantly. The efficiency of coagulation-flocculation processes was assessed, stablishing multilinear regression models for predictive purposes. These are processes highly dependent on surface water quality, in which the average removal of arsenic, iron and manganese decreased as their initial concentration increased, although the removal of colour and turbidity seems not to be a major concern. The results reinforced the limitation of conventional treatment process for attaining the threshold values especially for arsenic and manganese, an issue overcame by the implementation of an UF (RAs: 96.9% RMn: 88.9% and RFe: 99.7%). Not only the efficiency in attaining the threshold values, but the UF performance was reassured by its operation stability, that showed no expressive flux decay (J/J0 > 0.93). A sensitive analysis demonstrated that the implementation of an UF becomes more economically attractive in facilities of a greater treatment flowrate. As the treatment capacity increase (0.108 – 12,690 m3/h) the operating costs decreases (0.98 – 0.81 US$/m3). The overall results suggested that UF can be used to retrofit drinking water treatment plants in view of the increased concentration of arsenic, and other ions as iron and manages, in drinking water sources.

Research on flocculation effect of fly ash composite on high turbidity and high salinity mine water

Research on flocculation effect of fly ash composite on high turbidity and high salinity mine water

Calibrations of Suspended Sediment Concentrations in High-Turbidity Waters Using Different In Situ Optical Instruments

In environments of high suspended sediment concentration (SSC > 1 kg/m3), efficient measurements of SSC through accurate calibration relationships between turbidity and SSC are necessary for studies on marine sediment dynamics. Here, we investigated the performance of three types of optical instrument (OBS-3A, AQUAlogger 310TY, and RBRsolo3Tu with Seapoint sensor) in observations carried out at the middle of the Jiangsu coast, China. These instruments were calibrated in the lab using the water and suspended sediment samples collected from the observation site. It was found that both the calibration curves of OBS-3A and RBRsolo3Tu have an inflection point (at SSC of ca. 15 kg/m3 for OBS-3A and ca. 2 kg/m3 for RBRsolo3Tu), on either side of which turbidity increases (the left side) or decreases (the right side) with the increasing SSC. Only under SSCs smaller than the inflection point can OBS-3A and RBRsolo3Tu be applied to continuous SSC measurements at a fixed point. However, the turbidity output of AQUAlogger 310TY has always a positive correlation with SSC, which applies for SSC up to 40 kg/m3; thus, three fluid-mud events are quantified during this observation. AQUAlogger 310TY has important prospects for field applications in high-SSC environments.

Decentralized solar-powered drinking water ozonation in Western Kenya: an evaluation of disinfection efficacy

Background: Decentralized drinking water treatment methods generally apply membrane-based treatment approaches. Ozonation of drinking water, which previously has only been possible at large centralized facilities, can now be accomplished on a small-scale using microplasma technology. The efficacy of decentralized solar-powered drinking water treatment systems has not previously been described. Methods: We established a 1,000L decentralized solar-powered water treatment system located in Kisumu County, Kenya. Highly contaminated surface water is pumped to the treatment system, which includes flocculation and filtration steps prior to ozonation. Turbidity, total coliform bacteria, and E. coli were measured at various stages of water treatment, and bacterial log reduction values (LRVs) were calculated. Results: Forty-seven trials were conducted in which1000L of water were flocculated, filtered, and ozonated for 180 minutes. Baseline turbidity and E. coli concentrations were reduced from a median of 238 nephelometric turbidity units (NTU) and 2,419.7 most probable number/100mL, respectively, in surface water to 1.0 NTU and undetectable E. coli after ozonation for 180 minutes. The median E. coli LRV was 3.99. Conclusions: The solar-powered, decentralized water treatment system that utilizes ozonation for disinfection was founded to reduce E. coli by more than 3 log-orders of magnitude despite the high turbidity of the raw water. Further research is needed to characterize limitations, scalability, economic viability, and community perspectives that could help determine the role for similar systems in other settings.

Characterisation and performance of three Kenaf coagulation products under different operating conditions

The Sustainable Development Goal (SDG) 6.1, established by the United Nations General Assembly in 2015, targets universal and equitable access to safe and affordable drinking water for all by 2030. An essential factor in achieving this goal is the harnessing of “green” coagulants – naturally occurring, environmentally friendly materials which are effective coagulants for use in water treatment, with good availability in developing countries, inherent renewable properties and ease of biodegradation. In order to gain from these benefits, it is essential to fully understand how such coagulants may best be utilised, particularly concerning their practical application in developing countries. In this study, three different plant-based coagulation products (PCPs), namely Hexane (HxKP), saline (StKP) and crude (CrKP) extracts of Kenaf plant seed (Hibiscus cannabinus, a species of the Hibiscus plant), were applied to high (HTW), medium (MTW) and low (LTW) turbidity water in order to determine their performance and coagulation ability. The ability of the three Kenaf coagulant products (KCPs) to remove hydrophobic fractions of natural organic matter (NOM) was measured. The impact of KCPs on the treated water organic matter content (a known disinfection by-product (DBP) precursor) was examined using known surrogates of natural organic matter (NOM) i.e. the dissolved organic carbon (DOC), ultraviolet absorbance at 254 (UV254) and specific ultraviolet absorbance (SUVA254). Results obtained quantify the implications of using these coagulants during the water disinfection process. A parametric study, measuring the effect of different operating parameters, such as untreated water turbidity, pH, dosages, retention time, and KCP storage time, was completed. Turbidity removal performance for HxKP and StKP was very good with > 90% removal recorded for HTW and MTW, respectively, at pH seven within 2 hours retention time. Images obtained from scanning electron microscopy (SEM) analysis revealed a high likelihood of the coagulation mechanism of KCPs to be adsorption-interparticle bridging brought about by their flake-like structures and surfaces charges. Varying pH had no measurable influence on the coagulation performance of the KCPs. Comparing their efficiency with MoringaOleifera (MO, a previously researched PCP) and alum showed that HxKP had a negligibly different particle removal as MO. StKP turbidity removal performance was below HxKP by 1% for HTW and LTW and 2% for MTW but performed higher than the CrKP by 5% and 7% in HTW and MTW, respectively. The optimum dosage of HxKP and StKP reduced DBP surrogate values, indicating that its precursor is also minimized, although a slight shift from this optimum dosage showed a significant rise in their concentration thus signifying a potential increase in DBPs during disinfection.

Results of parallel independent visual evaluation of projective cover of the bottom during macrophyte assesment survey

A simple and cost-effective method for macrophyte stock assessment as visual survey, was tested. It demonstrated good efficiency for counting of Saccharina japonica. The method is based on visual evaluation of SAV projective cover. Such subjective data should be verified. For this purpose, the projective cover along the Tatar Strait coast was estimated independently by two observers. In total, 125 km of the coastline was surveyed with 322 parallel visual estimations at 81 stations. The estimations of both observers agreed well: the concordance coefficient was 0.73 for the total projective cover and 0.78 for the projective cover of S. japonica, at p < 0.0001. About 81 % of the total projective cover and 82 % of S. japonica projective cover were counted with high coherency, whereas poor coherency was noted for < 3 % of both parameters. Average difference between estimations of two observers was 0.083 ± 0.012 for the total projective cover and 0.090 ± 0.012 for S. japonica projective cover. However, comparison of the visual estimations from the sea surface with the SCUBA estimations made near the bottom showed that surface observations resulted in some underestimation of the total projective cover, though the difference was statistically insignificant (p = 0.68). The near-bottom SCUBA survey provides better assessment for small and cortical algae (Ralfsiales and partially Corallinales). Commercial stock of S. japonica was calculated using previously reported relationship between biomass and projective cover (r2 = 0.81). The stock estimations for certain areas on the data of two observers had no statistically significant differences (p = 0.46–0.80, depending on the criteria used), the total stock estimations were also very close (34 and 36 thousand tons for total stock and 26 and 24 thousand tons for its commercial part). The visual observations are useful for revealing general features of the vegetation spatial distribution. Linear regressions parameters of the algae abundance on latitude for the data of both observers were similar. They had the angular coefficients –0.13 ± 0.07 and –0.10 ± 0.07 for the total projective cover and –0.25 ± 0.07 and –0.23 ± 0.06 for S. japonica projective cover. In the southern part of survey, the average total projective cover was 0.59 ± 0.04, while it was slightly lower in the northern part: 0.53 ± 0.04; the same estimations for the projective cover of S. japonica differed more considerable: 0.49 ± 0.04 and 0.24 ± 0.03, respectively. There is concluded that the visual surveys of macrophytes are economically effective and allow to reduce labor efforts significantly, comparing with traditional SCUBA surveys (working time in 101 times, costs in 103 times). The video recording ensures the data verification by outside experts, as in the cases when observers cannot identify some species. However, capability of this method is limited by high water turbidity and other cases of worsened visibility. For successful implementation of visual surveys, its algorithm for various environmental conditions is developed and supplemented with necessary instructions.

Decentralized solar-powered drinking water ozonation in Western Kenya: an evaluation of disinfection efficacy

Background: Decentralized drinking water treatment methods generally apply membrane-based treatment approaches. Ozonation of drinking water, which previously has only been possible at large centralized facilities, can now be accomplished on a small-scale using microplasma technology. The efficacy of decentralized solar-powered drinking water treatment systems has not previously been described. Methods: We established a 1,000L decentralized solar-powered water treatment system located in Kisumu County, Kenya. Highly contaminated surface water is pumped to the treatment system, which includes flocculation and filtration steps prior to ozonation. Turbidity, total coliform bacteria, and E. coli were measured at various stages of water treatment, and bacterial log reduction values (LRVs) were calculated. Results: Forty-seven trials were conducted in which1000L of water were flocculated, filtered, and ozonated for 180 minutes. Baseline turbidity and E. coli concentrations were reduced from a median of 238 nephelometric turbidity units (NTU) and 2,419.7 most probable number/100mL, respectively, in surface water to 1.0 NTU and undetectable E. coli after ozonation for 180 minutes. The median E. coli LRV was 3.99. Conclusions: The solar-powered, decentralized water treatment system that utilizes ozonation for disinfection was founded to reduce E. coli by more than 3 log-orders of magnitude despite the high turbidity of the raw water. Further research is needed to characterize limitations, scalability, economic viability, and community perspectives that could help determine the role for similar systems in other settings.

Introducing the Self‐Cleaning FiLtrAtion for Water quaLity SenSors (SC‐FLAWLeSS) system

AbstractSensor‐based, semicontinuous observations of water quality parameters have become critical to understanding how changes in land use, management, and rainfall‐runoff processes impact water quality at diurnal to multidecadal scales. While some commercially available water quality sensors function adequately under a range of turbidity conditions, other instruments, including those used to measure nutrient concentrations, cease to function in high turbidity waters (> 100 nephelometric turbidity units [NTU]) commonly found in large rivers, arid‐land rivers, and coastal areas. This is particularly true during storm events, when increases in turbidity are often concurrent with increases in nutrient transport. Here, we present the development and validation of a system that can affordably provide Self‐Cleaning FiLtrAtion for Water quaLity SenSors (SC‐FLAWLeSS), and enables long‐term, semicontinuous data collection in highly turbid waters. The SC‐FLAWLeSS system features a three‐step filtration process where: (1) a coarse screen at the inlet removes particles with diameter > 397 μm, (2) a settling tank precipitates and then removes particles with diameters between 10 and 397 μm, and (3) a self‐cleaning, low‐cost, hollow fiber membrane technology removes particles ≥ 0.2 μm. We tested the SC‐FLAWLeSS system by measuring nitrate sensor data loss during controlled, serial sediment additions in the laboratory and validated it by monitoring soluble phosphate concentrations in the arid Rio Grande river (New Mexico, U.S.A.), at hourly sampling resolution. Our data demonstrate that the system can resolve turbidity‐related interference issues faced by in situ optical and wet chemistry sensors, even at turbidity levels > 10,000 NTU.

Improving a Multilevel Turbulence Closure Model for a Shallow Lake in Comparison With Other 1‐D Models

AbstractLakes differ from lands in water availability, heat capacity, albedo, and roughness, which affect local surface‐atmospheric interactions. This study modified a multilevel upper ocean model (UOM) for lake applications and evaluated its performance in Lake Taihu (China) with comprehensive measurements against three popular one‐dimensional (1‐D) lake models. These models were based on different concepts, including the self‐similarity (FLake), the wind‐driven eddy diffusion (LISSS), the k‐ε turbulence closure (SIMSTRAT), and a simplified turbulence closure (UOM). The surface flux scheme in these models was unified to exclude the discrepancies in representing air‐lake exchanges. All models in their default formulations presented obvious cold water temperature biases and largely underestimated the lake surface temperature (LST) diurnal range. For each model, these deficiencies were significantly reduced by incorporating new physics schemes or calibrated tunable parameters based on systematic sensitivity tests. The primary modifications for UOM included (1) a new scheme of decreased surface roughness lengths to better characterize the shallow lake, (2) a solar radiation penetration scheme with increased light extinction coefficient and surface absorption fraction to account for the high water turbidity, and (3) turbulent Prandtl number increased by a factor of 20 to reduce the turbulent vertical mixing. All other models were improved in these three aspects (roughness, extinction, and mixing) within their original formulations. Given these improvements, UOM showed superior performance to other models in capturing LST diurnal cycle and daily to seasonal variations, as well as summer‐autumn vertical stratification changes. The new UOM is well suited for application in shallow lakes.

Clarification of superficial waters of the magdalena river using seeds of Tamarindus indica as bio-coagulants

Biocoagulants have emerged as an environmentally friendly and efficient alternative to surface water clarification, allowing the use of agro-industrial waste as a bioavailable source for the treatment of high turbidity water. The objective of this research was to compare the efficiency in the surface water coagulation process of the Magdalena river using aluminum sulfate and tamarind seeds (Tamarindus indica) dissolved in aqueous solution and saline solution. The clarification process was carried out by testing jar, for this was performed an extraction of the hot and cold tamarind coagulant which were evaluated in conjunction with an inorganic coagulant in different mother dilutions (distilled water and saline) at concentrations of 35 and 40 mg/L and at a stirring speed of 100 and 200 rpm. The parameters of pH, electrical conductivity (S/cm), turbidity (NTU) and color (UPC) were measured during the clarification process. The results show a 97.2% reduction in inorganic treatment (SAL) compared to initial turbidity and a decrease in natural cold extracted (STF) and hot (STC) treatments of 58.2% and 39.1% respectively, when diluted in aqueous solution. While diluting in saline solution there was a greater removal of turbidity when applying aluminum sulfate, followed by STF and STC treatment, with removal values of 99%, 75% and 53% respectively. The highest coagulating activity occurred when applying a dose of 40mg/L and when diluting treatments in NaCl with maximum reported values for SAL, STF and STC treatment of 93%, 85% and 59%. Tamarind seeds proved to be an efficient coagulant for water clarification

Paleoenvironmental significance of microbial mat-related structures and ichnofaunas in an Ordovician mixed-energy estuary, Áspero Formation of Santa Victoria Group, northwestern Argentina

ABSTRACTThe study on a unique set of outstandingly preserved sedimentary surface textures (SSTs) found in the late Tremadocian Áspero Formation of northwestern Argentina, coupled with the sedimentological and ichnological analysis, indicate that they were formed in the intertidal to supratidal setting of a mixed-energy estuary recording storm and tide sedimentation. We recognize seven types of SSTs: probably biotic microbial mat-related SSTs (Kinneyia, elephant skin, exfoliating sandy laminae), abiotic SSTs (elliptical scours and convex parallel ridges type I “wrinkle marks” sensuAllen 1985), and problematic (convex parallel ridges type II and dot matrix texture). Elliptical scours and convex parallel ridges type I show features which indicate reworking of a cohesive sandy substrate in an intertidal or supratidal setting. Abundance of biotic SSTs with specific associated trace fossils reflect matground development and mat-grazing ichnofaunas, indicating the suppression of intense, penetrative bioturbation due to intense physicochemical stress. The “dot matrix” texture, described here for the first time, consists of a regular horizontal network of millimeter-scale pits; it appears associated with exfoliating sandy laminae, probably reflecting a mat-related origin. Three facies associations are defined through paleoenvironmental analysis. Facies association 1 is dominated by high-energy sandy and bioclastic storm deposits with tidal flat facies, and corresponds to the outer bay of a mixed-energy estuary; highly impoverished Cruziana assemblages and distal expressions of the Skolithos Ichnofacies reflect high energy and sedimentation rate. Facies association 2 shows tidal-channel and tidal-flat facies with subordinated storm deposits, representing the middle bay; impoverished Cruziana assemblages dominated by simple facies-crossing structures, with high-density monogeneric opportunistic suites, evidence physicochemical stress associated with subaerial exposure, frequent episodic deposition, high water turbidity, and/or brackish water conditions in these relatively sheltered tidal flats. Facies association 3 is formed by interdistributary-bay deposits with intercalation of channel-fill deposits in the upper part, and represents the river-dominated bay-head delta; low degrees of bioturbation in fine-grained facies indicate brackish- to fresh-water conditions. SSTs are found in tidal flat facies of facies association 2; they indicate an intertidal to supratidal environment subject to localized conditions of intense physicochemical stress. The paleoenvironmental interpretation of SSTs converges with the one performed through sedimentological and ichnological analysis, producing a robust and more detailed paleoenvironmental model for the Áspero Formation. Our study highlights the use of SSTs as a tool for supporting and refining paleoenvironmental analysis.

CDOM Optical Characteristics and Related Environmental Factors of High-turbidity Waters on the Loess Plateau

Chromophoric dissolved organic matter (CDOM) optical absorption characteristics, CDOM spectral slopes (S275-295), contribution of each component to water absorption, and the effects of environmental factors on them were analyzed to determine the sources and composition of CDOM in high-turbidity waters on the Loess Plateau. Samples in rivers and lakes (saline and freshwater) in the Loess Plateau area of Shaanxi and Inner Mongolia were collected in May 2018. The results demonstrated significant differences in CDOM absorption optical characteristics between rivers and lakes. The average aCDOM(440) (CDOM concentration, 8.45 m-1) in lakes was higher than that of rivers (2.70 m-1), and the saline lakes showed a higher CDOM concentration (13.52 m-1) than the freshwater lakes (3.38 m-1). Moreover, the light utilization efficiency of freshwater lakes is higher than that of saline lakes and turbid rivers. Great differences in pH and dissolved organic carbon (DOC) were observed between different types of water (P<0.01). The differences in electrical conductivity (EC), turbidity (Tur), and total suspended matter concentration (TSM) were significant with no statistical significances (P>0.1). The chlorophyll a concentration (Chla) in saline lakes was close to the Chla concentration in freshwater lakes if extreme values were excluded. In addition, the CDOM molecular weights of lake water were lower than those in the rivers, while CDOM molecular weights in saline lakes were lower than those in freshwater lakes based on the S275-295. Analyses of specific ultraviolet absorbance (SUVA254) were also conducted to determine the sources of CDOM in different water types, and the results showed that the more terrigenous humus were brought into the rivers and saline lakes compared with the freshwater lakes. Redundancy analysis (RDA) indicated that river and lake water quality parameters of the cumulative variance explained rates were 35.2% for river samples and 61.4% for lake samples, and 100% for samples in the saline and freshwater lakes individually. The results of RDA showed that dissolved oxygen (DO), water temperature, and EC exerted significant effects on CDOM optical properties of the river (P<0.01), while DOC, TSM, and Tur had a great influence on the CDOM optical properties of lakes (P<0.01). There was a strong correlation between pH and CDOM in the saline lakes, while DOC was significantly correlated with CDOM in the freshwater lakes (P<0.05).

Remote Sensing Monitoring on Spatial Differentiation of Suspended Sediment Concentration in a River-Lake System Based on Sentinel-2 MSI Imaging:A Case for Shengjin Lake and Connected Yangtze River Section in Anhui Province

Carrying out monitoring of suspended sediment concentration in river and lake systems is of great significance for understanding the laws of sediment transport in water and formulating policies on water environmental control. Taking Shengjin Lake and the connected Yangtze river section in Anhui province as the study area, band reflectance of a Sentinel-2 MSI sensor is simulated according to field spectral datasets, and the retrieval model is established by statistical regression from the synchronized suspended sediment concentration measurements. Then, the retrieved results from 28 scene MSI images during 2017-2019 are used to analyze the spatiotemporal variation of suspended sediment concentration in rivers and lakes, and the influence of water level variation on their spatial differentiation is also discussed. The results show that:① The retrieval model established by the ratio of the sixth band to the third band of the MSI sensor is suitable for high-turbidity water type, with high accuracy (R2=0.863, RMSE=22.211 mg·L-1). ② Spatially, the suspended sediment concentration near the lake entrances, northwestern parts of the upper and middle lake areas, and the lower lake is relatively higher, and that of Shengjin Lake is lower than that of the Yangtze River overall except for in summer. Temporally, the suspended sediment concentration in Shengjin Lake is relatively lower in summer and higher in other seasons, while the connected Yangtze River section exhibits the opposite intra-annual variation. ③ The water level, which is caused by the connectivity of rivers and lakes under the influence of the sluice, is the key factor affecting the spatial differentiation of suspended sediment concentration in the river and lake system. The suspended sediment concentration in Shengjin Lake contributes to the Yangtze River in dry and normal water periods, and that in the normal water period is more significant. In contrast, during the flood period, the correlation between suspended sediment concentration in the Yangtze River and that in Shengjin Lake is not obvious.