High Turbidity Levels Research Articles

Optimisation and validation of high-temperature oxidation of Cyclopia intermedia (honeybush) – From laboratory to factory

Inconsistent and poor quality honeybush herbal tea, produced from Cyclopia intermedia, required that comprehensive sensory profiling of this Cyclopia species be undertaken to identify not only its characteristic sensory attributes, but also to identify negative attributes, including taints responsible for poor quality. This was achieved by descriptive sensory analysis of infusions, prepared at “cup-of-tea” strength of a large sample set sourced from processors and retail outlets. The aroma attributes, “fynbos-floral”, “fynbos-sweet” and “woody”, and to a lesser extent, “fruity-sweet” and “apricot jam”, were the most prominent. The presence of taints such as “smokey” and “wet fur/farm animals” at relative high intensities in some samples indicated poor processing practices. The presence of “green grass” and “dusty” aroma notes is most likely attributable to under- and over-fermentation, respectively. Fermentation is the high-temperature oxidation step essential for the development of the characteristic sensory attributes of traditional honeybush tea. High turbidity levels of some infusions further confirmed sub-optimal processing of plant material. The effects of fermentation temperature (70, 80 and 90°C) and time (12, 16, 24, 36, 48, and 60h) on the sensory characteristics of C. intermedia infusions were thus investigated on laboratory-scale to establish optimum conditions. Different fermentation temperatures produced teas with slightly different sensory profiles, with infusions of plant material fermented at 70°C predominantly floral, at 80°C predominantly fruity and at 90°C overall most characteristic of C. intermedia. Fermentation at 90°C for 24h or 36h proved effective to increase the major positive aroma attributes to prominent levels, while decreasing the negative aroma attributes to negligible levels. These conditions were thereafter validated on factory-scale. Fermentation performed concurrently on the same batches of plant material on laboratory- and factory-scale delivered more or less the same product in terms of aroma profile and “cup-of-tea” strength, with the latter assessed according to the soluble solids content, colour and turbidity of the infusion. For optimum quality, inherent batch-to-batch variation in plant material may require careful monitoring of aroma development during fermentation between 24 and 36h. Application of the optimum fermentation temperature-time combination by industry will contribute towards improved and consistent product quality.

The parasite community of Phycis blennoides (Brünnich, 1768) from the Balearic Sea in relation to diet, biochemical markers, histopathology and environmental variables

The greater forkbeard Phycis blennoides is a benthopelagic fish distributed in the Mediterranean and NE Atlantic. The main goal of this study is to describe the complete parasite community of this species, which is at present unknown. A total of 188 specimens of P. blennoides were captured in the Balearic Sea (NW Mediterranean Sea) at 550–1250m depth during the four seasons of 2007, in summer of 2010 and in summer and autumn of 2011 at five distinct localities off the mainland slope off Catalonia coasts and off the insular slope off the Balearic Islands. Environmental and fish biological, parasitological, dietary, enzymatic and histological data were obtained and the relationships among them tested. A total of 20 different parasites were recovered, of which 11 constitute new host records. The most important parasites were the monogenean Diclidophora phycidis, the digeneans Bathycreadium brayi and Lepidapedon spp., the nematodes Capillaria gracilis, Collarinema collaris, Cucullanus sp. and Hysterothylacium aduncum, and the copepod Clavella alata. Overall, the parasite community of P. blennoides was characterized by high abundance, richness and diversity. Significant differences in the structure of the parasite community were detected between samples from <1000 to >1000m depth and between samples from off the mainland and insular slopes. Significant seasonal and/or geographical differences were found for some specific parasites. Abundance of the nematode C. collaris was associated to high levels of turbidity and O2 concentrations near the bottom. Abundances of H. aduncum, D. phycidis, B. brayi and Lepidapedon spp. were linked to high near-bottom temperature and salinity. Dietary analyses evidenced the role as potential intermediate hosts in parasite transmission by some prey (e.g. the teleost Gaidropsarus biscayensis for the cestode Grillotia cf. erinaceus and the nematodes Anisakis spp. or the euphausiid Meganyctiphanes norvegica for the acanthocephalan Echinorhynchus sp.). While the abundance of B. brayi, C. collaris, Cucullanus sp. and Echinorhynchus sp. was negatively linked to acetylcholinesterase activity (AChE), the abundance of Echinorhynchus sp. and H. aduncum correlated positively with lipid peroxidation levels. Cysts of unknown etiology in fish gills were detected at higher prevalence than in any other fish from the same area. Number and area of hepatic macrophage centres varied significantly among seasonal and geographical groups and seemed not significantly influenced by parasite infection levels.

Swine manure digestate treatment using electrocoagulation

Anaerobic biodigestion is an appropriate alternative for the treatment of swine wastewater due to its biogas generation properties and the possibility of its application as a source of energy for heating or electricity. However, digestate can still contain high levels of turbidity, organic carbon and nutrients and must be correctly managed as a biofertilizer, or treated to avoid any impact on the environment. Considering this, electrocoagulation (EC) shows promise as a technology because of its ease of handling and high efficiency in effluent remediation. This study aimed to evaluate the performance of EC in a batch system in the treatment of swine wastewater digestate. The wastewater used in the treatment was sampled from a 10 m3 biodigestor effluent (digestate) located at Concordia, Santa Catarina, Brazil. A batch-scale experiment was carried out to evaluate the following two variables: electrode distance (ED) and voltage applied (V). The removal efficiency levels (%) for the best operational condition (2 cm, 5 V) after 30 min were: 97 %, 98 %, 77 % and 10 % for color, turbidity, total organic carbon (TOC) and total nitrogen (TN), respectively. The EC batch system produced efficient results, underlining its promise as an alternative to be applied in the treatment of digestate.

Groundwater Quality Assessment Using Averaged Water Quality Index: A Case Study of Lahore City, Punjab, Pakistan

Water quality is considered as a major issue in mega cities of developing countries. The city of Lahore has over 10 million populations with the highest population density in the Punjab Province, Pakistan. Groundwater is the main source of drinking water in Lahore. The groundwater quality should be regularly monitored to cope up with drinking water quality issues. The water quality index (WQI), previously used in many studies was usually based on one-year data to analyze the water quality situation of the study area. However, the results obtained from the data, based on single observation from different points may have distortion. This might have occurred due to the inclusion of multiple types of errors induced in the data as a result of improper sampling design, lack of expertise in terms of both sampling method and sample testing, instrumental and human errors, etc. Therefore, the study evaluated the groundwater physicochemical parameters (turbidity, pH, total dissolved solids, hardness, chlorides, alkalinity and calcium) for three years. The averaged water quality index (AWQI) was computed using ArcGIS 10.3 model builder. The AWQI map indicated that the water quality in the study area was generally good except in few places like Anarkali, Baghbanpura, Allama Iqbal Town, Mughalpura and Mozang due to relatively higher turbidity levels. The results of this study can be used for decision making regarding provision of clean drinking water to the city of Lahore. Moreover, the methodology adopted in this study can be implemented in other mega cities as well to monitor groundwater quality.

Beer Clarification by Novel Ceramic Hollow-Fiber Membranes: Effect of Pore Size on Product Quality.

In this work, the crossflow microfiltration performance of rough beer samples was assessed using ceramic hollow-fiber (HF) membrane modules with a nominal pore size ranging from 0.2 to 1.4 μm. Under constant operating conditions (that is, transmembrane pressure difference, TMP = 2.35 bar; feed superficial velocity, vS = 2.5 m/s; temperature, T = 10°C), quite small steady-state permeation fluxes (J* ) of 32 or 37 L/m2 /h were achieved using the 0.2- or 0.5-μm symmetric membrane modules. Both permeates exhibited turbidity <1 EBC unit, but a significant reduction in density, viscosity, color, extract, and foam half-life with respect to their corresponding retentates. The 0.8-μm asymmetric membrane module might be selected, its corresponding permeate having quite a good turbidity and medium reduction in the aforementioned beer quality parameters. Moreover, it exhibited J* values of the same order of magnitude of those claimed for the polyethersulfone HF membrane modules currently commercialized. The 1.4-μm asymmetric membrane module yielded quite a high steady-state permeation flux (196 ± 38 L/m2 /h), and a minimum decline in permeate quality parameters, except for the high levels of turbidity at room temperature and chill haze. In the circumstances, such a membrane module might be regarded as a real valid alternative to conventional powder filters on condition that the resulting permeate were submitted to a final finishing step using 0.45- or 0.65-μm microbially rated membrane cartridges prior to aseptic bottling. A novel combined beer clarification process was thus outlined.

Extent and persistence of dissolved oxygen enhancement using nanobubbles

In this study, change in water-dissolved oxygen (DO) was analyzed under various synthetic water qualities and nanobubbles (NBs) application conditions, such as gas type, initial DO as well as water dissolved, suspended and organic matters contents. When oxygen, rather than air, was introduced into nitrogen-desorbed ultra-pure water, the stagnation time was significantly increased. It took ten days for DO concentration to drop back to saturation. The higher the initial DO concentration, the longer particles were observed above saturation due to particle stability improvement. The oxygen mass transfer rate of 0.0482 mg/L/min was found to reach a maximum at an electrolytic concentration of 0.75 g/L, beyond which the transfer rate decreased due to adsorption of negative ions of the electrolyte at the interface. High levels of turbidity caused by suspended solids have become a barrier to dissolution of NBs oxygen into the water solution, and thus affected the transfer performance. On the other hand, by applying NBs for just an hour, up to 7.2% degradation of glucose as representative organic matter was achieved. Thus, NBs technology would maintain a high DO extent for an extended duration, and thus can improve water quality provided that water chemistry is closely monitored during its application.

Assessment of groundwater quality in rural areas of Mbala District, Zambia

Access to good quality drinking water still remains a challenge in most rural areas of Zambia, Africa. The aim of this study was to assess the quality of groundwater for human consumption in rural areas of Mbala district in Zambia. A total of fifty nine (59) water samples were collected from fifty nine (59) boreholes in the aforementioned district. The water samples were analysed for physical, chemical and microbiological parameters using standard techniques specific for each parameter. Results were compared to the Zambian Bureau of Standards (ZABS) guideline values for drinking water and in some cases, with WHO guideline values if known. In general, most water parameters in Mbala district complied with ZABS drinking water guideline values. A few chemical parameters which include pH ranging from 5.1 to 6.98, sodium from 0.001mg/L to 49.9mg/L, sulphate from 2mg/L to 18.76mg/L, iron from 0 to 10.22mg/L and manganese from 0 to 0.23mg/L did not meet ZABS drinking water guideline values at a few boreholes. TSS and turbidity ranged from 0 to 133mg/L and 2 to 358NTU respectively. A few exceedances of the aforementioned parameters were recorded at a few boreholes. In contrast, significantly high turbidity levels (>20NTU) were recorded at a few boreholes in the district thus posing a significant threat to the health of the consumers. In terms of microbiological parameters, a few boreholes did not meet the ZABS drinking water guideline values for total coliforms rendering the water supplies from the affected boreholes unfit for human consumption unless boiled or treated with chlorine. Keywords : Groundwater, Zambia, rural areas, water quality, Mbala district

Development and evaluation of a small scale water disinfection system

Provision of microbiologically safe drinking water for people living in the rural areas of developing countries remains a major challenge to date. A simple gravity-driven membrane point of use system was developed based on woven fabric microfiltration (WFMF) membranes. The WFMF is a loose type of membrane (0.45 μm). However, complete disinfection is not achieved with the WFMF, hence it was incorporated with two disinfectants. This study aimed to combine the WFMF with two disinfectants (WaterGuard and bromochlor tablets) to bring the water to the accepted quality for drinking. Four different types of water were sourced, considering two factors: E. coli and turbidity content. The WFMF demonstrated excellent filtration performance by producing permeates with turbidity less than 1 NTU for feed turbidity ranging between 10 and 200 NTU. There was 95–99.8% E. coli removal for raw feeds with influent E. coli ranging between 500 and 44,500 CFU/100 mL. Total disinfection was achieved with both disinfectants; however, the effectiveness of the chemical disinfectants in E. coli removal was affected by the quality of water to be disinfected. The study showed that turbidity plays a major role in disinfection performances by increasing chlorine demand on water sources with high turbidity levels.

Underwater 3D Reconstruction for Underwater Construction Robot Based on 2D Multibeam Imaging Sonar

This paper presents an underwater structure 3D reconstruction method using a 2D multibeam imaging sonar. Compared with other underwater environmental recognition sensors, the 2D multibeam imaging sonar offers high resolution images in water with a high turbidity level by showing the reflection intensity data in real-time. With such advantages, almost all underwater applications, including ROVs, have applied this 2D multibeam imaging sonar. However, the elevation data are missing in sonar images, which causes difficulties with correctly understanding the underwater topography. To solve this problem, this paper concentrates on the physical relationship between the sonar image and the scene topography to find the elevation information. First, the modeling of the sonar reflection intensity data is studied using the distances and angles of the sonar beams and underwater objects. Second, the elevation data are determined based on parameters like the reflection intensity and shadow length. Then, the elevation information is applied to the 3D underwater reconstruction. This paper evaluates the presented real-time 3D reconstruction method using real underwater environments. Experimental results are shown to appraise the performance of the method. Additionally, with the utilization of ROVs, the contour and texture image mapping results from the obtained 3D reconstruction results are presented as applications.

Environmental change disrupts communication and sexual selection in a stickleback population.

Environmental change that disrupts communication during mate choice and alters sexual selection could influence population dynamics. Yet little is known about such long-term effects. We investigated experimentally the consequences that disrupted visual communication during mate choice has for the quantity and viability of offspring produced in a threespine stickleback population (Gasterosteus aculeatus). We further related the results to long-term monitoring of population dynamics in the field to determine if changes are apparent under natural conditions. The results show that impaired visual communication because of algal blooms reduces reliability of male visual signals as indicators of offspring survival during their first weeks of life. This relaxes sexual selection but has no effect on the number of offspring hatching, as most males have a high hatching success in turbid water. Despite eutrophication and high turbidity levels that interfere with communication during mate choice, the population has grown during recent decades. Large numbers of offspring hatching, combined with high variation in juvenile fitness, has probably shifted selection to later life history stages and maintained a viable population. Together with reduced cost of sexual selection and ongoing ecosystem changes caused by human activities, this could have promoted population growth. These results point to the complexity of ecosystems and the necessity to consider all influencing factors when attempting to understand impacts of human activities on populations.

Water Quality Assessment of Streams and Wetlands in a Fast Growing East African City

The combination of rapid urbanization, industrialization, population growth, and low environmental awareness poses a major threat to worldwide valuable freshwater resources, which provide important ecosystem services to humans. There is an urgent need to monitor and assess these resources, as this information is indispensable for sustainable decision-making and management. In this context, we analyzed the chemical and ecological water quality of the riverine environment of a fast growing city in Southwest Ethiopia for which we proposed possible remediation options that were evaluated with an empirical model. The chemical and ecological water quality was assessed at 53 sampling locations using the oxygen Prati index and the ETHbios, which is a biotic index based on macroinvertebrates. In addition, a microbiological analysis was performed to estimate the degree of fecal contamination. Finally, we analyzed the relationship between the oxygen content and the organic pollution to simulate the effect of organics removal from waste streams on the chemical water quality. Our results showed that the average values for dissolved oxygen (4.2 mg DO·L−1) and nutrients (0.9 mg oPO43−·L−1 and 12.8 mg TAN·L−1) exceeded international standards. Moreover, high turbidity levels revealed that land erosion is a severe problem in the region. Along the rivers, a significant increase in oxygen consumption and in nutrient concentrations was observed, indicating organic pollution originating from different diffuse and point sources of pollution. The lack of proper sanitation also led to exceedingly high abundances of fecal coliforms in the surface water (&gt;320 MPN·mL−1). However, fecal contamination was strongly reduced (&gt;92%) after the polluted river water passed Boye wetland, indicating the purification potential of natural wetlands and the importance of conserving and protecting those ecosystems. The simulation results of the model showed that water quality could be substantially improved if municipal, industrial, and institutional wastewater was efficiently collected and transported to a treatment facility. Waste stabilization ponds and constructed wetlands are highly promising techniques, as they provide a cheap, effective, reliable, and sustainable way to purify wastewater. It is advised that the environmental awareness of the people via sensitization, education, and law enforcement is increased, as this is essential for sustainable development.

Nutrient variability and its influence on nitrogen processes in a highly turbid tropical estuary (Bangpakong, Gulf of Thailand)

Estuarine ecosystems in SE Asia have been poorly studied when compared to other tropical environments. Important gaps exist particularly in the understanding of their biogeochemical function and contribution to global change. In this work we looked into N-turnover in the water column and sediments of the Bangpakong estuary (13°N). A seasonal sampling program was performed along the salinity gradient covering different stretches of the estuary (68km). Key physical and chemical characteristics were also monitored in order to unravel possible environmental controls. Results showed the occurrence of active denitrification in sediments (5.7–50.9nmol N-N2/(cm3·hr)), and water column (3.5–1044pmol N-N2/(cm3·hr)). No seasonal or spatial variability was detected for denitrification potential in sediment samples. However, in the water column, the denitrification activity peaked during the transition season in the downstream sites coinciding with high turbidity levels. Therefore, in that period of the year, the water column compartment may be an important contributor to nitrate reduction within the estuary. The rather low nitrification rates detected were not always measurable, probably due to the reduced oxygen content and high siltation. This study is one of the few dealing simultaneously with sediments and water column processes in a highly turbid tropical estuary. Therefore, it emerges as a valuable contribution for the understanding of the dynamics of the nitrogen cycle in tropical environments by exploring the role of estuarine N microbial activity in reducing the effects of increased nitrogen loads.

A Study on Stabilization of Water Treatment System Operation through Inter-blending Method: in Response to Heavy Precipitation by Climate Change

본 연구에서는 여름철 집중강우나 태풍 등으로 인한 유입수 탁질 증가 시의 정수처리공정의 안정성을 확보하기 위한 방안에 대해 연구를 수행하였다. 고탁도 유입수는 정수처리공정에서의 부하를증가시키기 때문에 공급수 수질의 안정성이 낮아져, 수질 안정성을 증대시키기 위하여 인터블랜딩(Inter-blending) 기법을 개발하였으며, 이를 통해 수질을 안정화시킬 수 있었다. 응집/침전 공정을거친 처리수를 유입단으로 반송하여 고탁도 유입수와 블랜딩 할 수 있도록 기존 정수처리 파일럿플랜트에 펌프와 블랜딩조를 구축하였고, 10∼30% 비율의 인터블랜딩을 실시하였으며, 이를 통해모래여과공정의 과부하를 감소시켜 처리효율이 안정화됨을 확인하였다. 점토 현탁액 spiking을 통하여 고탁도 유입을 모의하였으며, 탁도를 기준으로 평상시와 150∼200 NTU, 300 NTU 이상으로 구분하여 실험을 진행하였다. 평상시의 경우 처리효율 개선에는 큰 영향을 미치지 못하였으며, 탁도 150∼200 NTU의 경우에는 블랜딩 비율에 따라 탁도는 10∼29%, TOC는 10∼17% 감소하는 것으로 나타났으며, 탁도 300 NTU의 경우에는 탁도 11∼20%, TOC 8∼30%가 감소하는 것을 확인하였다.This paper aims to examine how to maintain stable water quality of raw water in response to urgent circumstancesof high contamination level by applying inter-blending to the treatment process of surface watercontamination due to heavy precipitation or typhoons during the summer. The turbidity category of 150-200NTU and more than 300 NTU were adjusted to high-turbidity concentration through cray suspension spiking,thereby stabilizing surface water quality. There was no significant effect on the improvement of processefficiency for the average category, turbidity of 10-29% depending on the blending ratio and TOC of 10-17%of processing efficiency for the category of 150-200 NTU, and turbidity of 11-20% and TOC 8-30% processingefficiency for the category of more than 300 NTU. The experiment confirmed that inter-blending could stabilizewater quality and minimize the overload effect during the process in case of high level of turbidity occurs.

An Index Approach to Metallic Pollution in Groundwater Sources of South Region of Pemba Island

The South Region of Pemba is one of the two Regions in Pemba Island. Residents within the region depend on groundwater as the main water source for the domestic and other social purposes. This study was conducted to assess the quality of drinking water in different areas of South region of Pemba. In order to evaluate the quality of groundwater in the study area, 17 groundwater samples were collected and analyzed for different physico-chemical parameters. In each water sample, four physicochemical parameters were analyzed, namely, electrical conductivity (EC), total dissolved solids (TDS), pH, and turbidity. For the case of metals, eleven metals, namely, Cd, Co, Cu, Cr (III), Li, Fe, Mg, Ni, Pb, Sr, and Zn were analyzed using standard procedures. The dataobtained were then compared with the available WHO and or USEPA drinking water standards. All the samples had EC and TDS within the recommended limits, while 53% and 29% of the samples had higher turbidity levels and lower pH, respectively than the WHO recommended guidelines. All the samples contained Co, Cu, Fe, Mg, Ni, Pb, and Zn within the maximum admissible limits. According to heavy metal pollution index (HPI), degree of contamination (Cd), and heavy metal evaluation index (HEI), only one area (Mgonanje-1) showed alarming risks. In most water samples, the ratio of concentrations of Li to Ni was greater than 1, while all Sr to Mg ratios were less than 1. Generally, the values of the analyzed physico-chemical parameters were within the recommended maximum admissible limits. However, the study recommends the stakeholders and other responsible authorities to take appropriate and corrective measures for the water sources located at the Mgonanje area.

Ethnomedicinal Knowledge on Water Purification in Selected Rural Areas of Ethiopia

Plants have been used for water purification dating back to perhaps 2000 BC as noted in Egyptian inscriptions. Plant coagulants have the potential to serve as alternative water treatment agents especially in rural areas. Hence this study aimed to examine four promising plants and their uses as local coagulants for purification of turbid water in order to tackle rural quality water problems. Semi-structured interviews, focus group discussions, market surveys, and observation were used to gather information from three rural areas. Jar test experiments were carried out for treatment of high (209 NTU), medium (63 NTU), and low level (26 NTU) turbidity with the flocculent dosages of 0.03 g/L of powdered plant material. The four plant species used for treatment of turbid water were Maerua subcordata (Gilg) DeWolf, Moringa stenopetala (Baker f.) Cufod., Sansevieria ehrenbergii Schweinf. ex Baker, and Sansevieria forskaliana (Schult. & Schult.f.) Hepper & J.R.I.Wood. The finding shows that societies in each study area still depend on plant species for purification of turbid surface water. Coagulation tests revealed that tubers of M. subcordata and seeds of M. stenopetala were able to remove turbidity up to 97% at high turbidity levels and performance was better than leaves of S. ehrenbergii and S. forskaliana. Complementing traditional water treatment knowledge with coagulation tests and purification of the specific protein coagulant could help to identify appropriate solutions for rural people with difficulty preparing purified water.

Effects of Turbidity on Prey Selection and Foraging Return of Adult Largemouth Bass in Reservoirs

AbstractPrevious laboratory studies have demonstrated that turbidity alters prey selection by Largemouth Bass Micropterus salmoides, but this has not been tested in the field. Laboratory studies have also suggested that daily rates of consumption by Largemouth Bass may decline as turbidity increases and that the rate of decline may differ among prey types, possibly providing a mechanism that drives the observed prey selection patterns. We conducted laboratory trials to measure daily consumption rates for Largemouth Bass when foraging on Bluegills Lepomis macrochirus and Gizzard Shad Dorosoma cepedianum; we also collected field data in three reservoir systems (Boomer, Sooner, and Guthrie lakes, Oklahoma) during 2 years to evaluate Largemouth Bass prey selection and consumption rates over a range of turbidity levels. In the laboratory trials, Largemouth Bass daily consumption rates declined with increased turbidity, but the decline was similar between the two prey types. We detected no correlations between turbidity and consumption rate (percentage of empty stomachs or mean weight of prey in stomach contents) in the field. Field‐measured prey selection was highly variable among reservoirs and between sampling years, yet all but one reservoir ×× year combination had significant correlations between prey selection and turbidity, which generally followed the predictions of previous laboratory results (greater use of fish prey [especially centrarchids] and reduced use of crayfish at high levels of turbidity). However, the use of crayfish prey under low‐turbidity conditions was higher than that expected based on previous laboratory trials. Further research is needed to determine which factors regulate the effects of increased turbidity on predator foraging return and to evaluate the food web implications of turbidity‐related changes in the diets of top predators.Received December 3, 2014; accepted June 25, 2015

First record of Peacock bass Cichla kelberi Kullander &amp; Ferreira, 2006 in the Brazilian Pantanal

Biological invasions impact many communities and ecosystems around the world. Thus, the detection of harmful species is particularly important. In this study, the occurrence of Peacock bass Cichla kelberi in the Brazilian Pantanal was registered. The main stream of the Paraguay River, the Padre Inacio stream and their connected lakes were sampled, in the Pantanal, Upper Paraguay River basin. Six specimens were sampled including three females at beginning of maturation. The high level of turbidity of the main channel of the Paraguay River is possibly restricting the dispersal of C. kelberi to other regions of the Pantanal. But, due to the voracious piscivory of this species and the impact had in other Neotropical regions, this record highlights that the occurrence of C. kelberi can be a new threat to one of the bestconserved wetlands in the world.

Eutrophication of turbid tropical reservoirs: Scenarios of evolution of the reservoir of Cointzio, Mexico

This study provides the first numerical simulation of physical and biogeochemical processes in a very turbid and highly eutrophic tropical reservoir of the Trans-Mexican Volcanic Belt in Mexico. The Cointzio reservoir (capacity 66Mm3) is characterized by a lack of water treatment plants upstream and a high content of very fine clay particles. It suffers serious episodes of eutrophication associated with high levels of turbidity and benthic anoxia. Different scenarios for future climate inputs, nutrient inputs and water levels were simulated. The results pointed out the potential negative long-term impact of climate change on this reservoir. In this region, an increase of average air temperature as high as 4.4°C is expected by the end of the century. When coupled with a low water level, this increase could lead to critical conditions with a severe depletion of dissolved oxygen and important algal blooms with chlorophyll a reaching values of up to 94μgL−1. The calculations indicated that a drastic reduction of nutrient inputs (up to 90%) would be required to significantly reduce chlorophyll a concentrations. If such mitigation measures are adopted, the maximum peak of chlorophyll a would be reduced by 55% after a ten-year period of efforts, with corresponding positive effect on dissolved oxygen concentrations. The main limitation of the chosen numerical approach comes from the assumption of a constant water level in the model. This may be particularly critical for shallow type reservoirs.While this region remains poorly studied, this study brings original information that will help stakeholders to adopt appropriate strategies for the management of their waterbodies that experience critical eutrophication.

Physico-chemical Parameters of Water in Bibi Lake, Ahmedabad, Gujarat, India

Water as a universal solvent has the capability to dissolve many substances including organic and inorganic compounds. The quality of water generally refers to the component of water present at the optimum level for suitable growth of plants and animals. Temperature, turbidity, nutrients, hardness, alkalinity, dissolved oxygen, etc. are some of the important factors that determines the growth of living organisms in the water body. The Bibi lake, a natural lake of Vatva taluka, Gujarat, India is completely surrounded by slum area whom discharge their domestic waste directly into the lake water creating environmental hazard. To understand the situation, water samples were collected monthly to analyze different physical and chemical parameters such as temperature, pH, electric conductivity, turbidity, alkalinity, dissolved oxygen, etc. The comparison of statistics with the standard values of W.H.O guidelines (1998) revealed the high level of turbidity, total dissolved solids, pH, hardness, alkalinity and phosphate in the water content. The accumulation of these pollutants poses a dangerous threat to both aquatic and human lives.

NUMERICAL MODELLING OF THE EFFECT OF THE GREEN VALVE ON AIR ENTRAINMENT AT HOPPER OVERFLOW

When a dredge mixture deserts a hopper through its overflow structure, often significant volumes of air are entrained into the mixture. The air entrainment is a result of “hydraulic jump” turbulence generated in the core of the (often circular) overflow structure. When the mixture discharges into the sea at the exit of the overflow structure, a density current is created in the near-field. The near-field sediment processes are important as they feed the more far-reaching dredge plumes. Once discharged, the trapped air tends to segregate from the overflow plume owing to its buoyancy and the rising of bubbles towards the surface of the sea is reported to have a pronounced effect on near-field dispersion and to obstruct settling of the mixture sediments. The near-field dispersion weakens the strength of the density current which is highly undesirable as it increases the foot-print of the dredge plume. Plumes with high levels of turbidity may have severe impacts on coastal environments, and dredge operations are therefore often forced to reduce production rates to reduce dredge plume foot-prints in order to comply with environmental regulations. One of the more recognized measures in reducing plume foot-prints is combating air entrainment with the so-called green valve device, also known as the environmental valve. The green valve is rigged within the shaft of the overflow structure and the fundamental idea is to increase the hydraulic resistivity inside shaft leading to increased submergence of the overflow, which results in less air entrainment.