Water Turbidity Levels Research Articles

Seasonal dynamics of Zostera noltii Hornem. in two Mediterranean lagoons

The density, biomass and shoot morphology of two populations of Zostera noltii were monitored from January 1998 to July 1999 at two shallow Mediterranean lagoons of Biguglia and Urbino, which differ in hydro-morphological conditions and nutrient loading. Monitoring included the principal biological and foliar parameters (shoot density, aboveground and belowground biomass, length, width and number of leaves, LAI and coefficient A: percentage of leaves having lost their apex), the organic matter contents of the sediment and the environmental conditions (salinity, turbidity, temperature, nutrient concentrations and dissolved oxygen levels). The two populations of Z. noltii displayed seasonal changes in density (1600–19600 m2), aboveground biomass (11–153 g. DW. m−2), leaf length (33–255 mm), and leaf width (0.9–1.8 mm). Temperature and turbidity were significant environmental factors influencing the temporal changes observed in the Z. noltii meadows studied. Conversely, the belowground biomass, the number of leaves per shoot and the LAI did not undergo any seasonal changes. In the Biguglia lagoon, the functioning dynamics of the Z. noltii seagrass beds are determined by the catchment area and the inputs of nutrients derived from it, whereas in the Urbino lagoon the dynamics of the Z. noltiibeds depend on low levels of water turbidity.

Statistical assessment of relationships between water flow in a river and water turbidity in water intakes

Probability distributions of water flow and its turbidity after passing through water intake structures are considered. Heavy tails with a power distribution are shown to exist. These distributions are used to find the dependence between water turbidity at the inlet to the water station and water flow in the river. Quantiles of these distributions are estimated to characterize the levels of water flow and turbidity with a given exceedance probability.

Cormorants keep their power: visual resolution in a pursuit-diving bird under amphibious and turbid conditions

Cormorants (Aves; Phalacrocoracidae) are active fliers, yet they forage by pursuit diving and capture of fish with the bill. In air, the cormorant’s cornea provides most of the total refractive power of the eye [1]. Underwater, however, corneal power is lost, as the cornea is now bathed in liquids of similar refractive index. The retention of a sharp image, while performing precise visual tasks underwater, requires that the cormorant’s optical system compensates for the loss of refractive power of the cornea. In addition, the underwater photic environment differs markedly from the aerial one, with the image quality undergoing a rapid deterioration through scatter and absorption [2,3]. Upon submergence, cormorants compensate for the loss of corneal power (>55 dioptres, D) and rapidly (>1000 D/sec) attain a state of emmetropia, i.e. they are well focussed [4], by marked changes in the shape of their very flexible lens [1,5]. However, the visual capacities of pursuit-diving birds under the optical demands imposed by moving from one medium to another and the respective differences in the photic environments have not been determined to date. We tested the aerial and underwater visual resolution of the great cormorant (Phalacrocorax carbo sinensis) for high contrast, square wave gratings. Stimuli were presented in a forced choice situation (ymaze) under high levels of natural illumination. Visual resolution was calculated from gratings of given bar widths at given distances from the y-junction to the stimuli. In clear water, the cormorants’ resolution was 8.9′ ± 0.5′ (minutes of arc, mean ± s.e, n = 5, range 10.4′ – 7.8′; Figure 1A), while in air it was 3.8′ ± 0.3′ (n = 3, range 4.3′ – 3.3′; Figure 1B). The birds’ choice underwater was performed while they swam at ~1.7 m/sec so that the testing of resolution replicated the naturally occurring dynamic discrimination of underwater events. The position at which an actual choice was made could be determined from the abrupt change in the orientation of the head toward the stimulus. In all tests, the choice was made between ~60 and 90 cm before the y-junction. Calculating underwater visual resolution for the positions of choice provided a value of 6.3′ ± 0.4′ (n = 5) underwater and 3.1′ ± 0.3′ (n = 3) in air. While vision is regarded as the major modality used in the detection and capture of prey by pursuit-diving birds, this is the first quantitative estimate of the amphibious visual capacity in any bird. Compared with other bird species, the cormorants’ resolution in air (Supplemental Table 1) was relatively low in both absolute terms (Figure 1C) and when body mass [6,7] or eye height above the ground [8] were considered. The cormorants’ resolution underwater was comparable with the higher values reported for fishes [9], Pinnipeds (e.g., seals, sea lions) [10] and Cetaceans (e.g., killer whales, dolphins) [11] (Figure 1C). Because visual resolution in single chambered eyes tends to increase with eye size [6,7], it was expected that cormorants, with corneo-scleral diameters of ~18–19 mm will have a lower resolution than aquatic mammals having eye diameters of ~20 mm (dolphins) and ~50 mm (baleen whales). The requirements to perform precise visuo-motor tasks in two optically different media, and the uniqueness of the lenticular system of these birds [1,5] make the vision of pursuitdiving birds a model of vertebrate capacities at the extreme. Performing visual tasks underwater is hindered by the rapid degradation of image brightness and contrast due to scatter and absorption of light by water molecules and by suspended particles (turbidity) [2]. We tested the visual resolution of cormorants (n = 5) under controlled, low levels of water turbidity (< 3 nephlometric turbidity units; NTU). The minimal resolvable stripe width was linearly correlated with turbidity (y = 3.71x + 7.6; R2 = 0.98; p < 0.001), hence, resolution declined with increasing turbidity within the tested range. The results obtained for clear water (~0.2 NTU) fitted the regression line well. Experimental results on the effects of turbidity on visually guided behavior of aquatic vertebrates are uncommon and, in fishes, are confined mostly to turbidity levels higher than 3 NTU and to the use of reactive distance as a behavioral measure [12]. Our results show that turbidity levels lower than 1 NTU have a clear effect on image formation underwater and consequently on the underwater visual environment in general. Low turbidity levels are commonly encountered in natural water bodies and thus are of crucial importance in our understanding of the evolution, sensory ecology, and microhabitat selection in aquatic organisms [13–15].

Effects of shellfish farming on the benthic environment

The benthic environment under and near three shellfish farms in Tasmania, Australia, which had had a relatively high level of production over many years was investigated. Benthic samples were collected along transects which ran across the farms, generally from 100 m upstream to 100 m downstream. Sediment deposition, redox values, sediment sulphide concentrations, organic carbon content and water turbidity levels near the bottom were significantly different between the farms but not between sites outside the farm, at the boundary and sites within the farm. Video recordings at one farm showed dense coverage of fine filamentous algae and patchy bacterial mats directly under some longlines and this algae is thought to have fallen off the mussel longlines. At another farm dense beds of seagrass were observed in the videos both under trays of oysters and outside the farm. The benthic infauna did not show clear signs of organic enrichment, and neither univariate nor multivariate measures of benthic infauna were significantly different between sites inside and outside the farm, although they were different between farms. It was concluded from these results that shellfish farming is having little impact, and much less than salmon farming, on the benthic environment in Tasmania. Thus extensive monitoring of shellfish farms would appear to be not necessary.

Effect of sanitation facilities, domestic solid waste disposal and hygiene practices on water quality in Malawi’s urban poor areas: a case study of South Lunzu Township in the city of Blantyre

Household water supply problems remain one of the major challenges facing developing countries. In Malawi, there is lack of documentation on the levels and causes of water pollution particularly in peri-urban areas so that meaningful interventions can be adopted. Therefore, a study was carried out in South Lunzu Township a peri-urban area in the city of Blantyre.The study revealed that the major form of sewerage disposal is the on-site sanitation system where about 58.8% of the respondents use traditional pit latrine while in terms of solid waste disposal, the Blantyre City Assembly which is responsible for solid waste collection, has only two collection vans to cater for more than half a million residents (Blantyre City Assembly, 1999. Urban Structure Plan, Draft Background Report, Blantyre.) hence indiscriminate disposal rampant in the area.Water samples collected from the major sources of domestic water supply showed that there are variations in the levels of water pollution between the ground water and surface water sources and between the wet and dry season. For instance, physically, the ground water turbidity levels were in the range of 2–12 mg/l during the dry season but increased to a maximum of 114 mg/l during the wet season while for surface water the turbidity increased from 4 to 408 mg/l over the seasons compared to the WHO standard set at 5 mg/l and the Water Department standard set at 25 mg/l. Chemical pollution for surface water sources show seasonal variations with an increase in the concentration during the wet season, for instance, iron levels ranged from 2.3 to 4.03 mg/l. This is above the WHO and Water Department drinking standards which are 1 and 3 mg/l, respectively. However, bacteriologically both the ground water and the surface water sources are grossly polluted. Ground water spring coliform count ranged from 190/100 ml to 9500/100 ml, and the well 3500/100 ml to 11,000/100 ml having the maximum during the wet season. Surface water results also indicated the coliform count ranging from 2900/100 ml to 4600/100 ml way higher than the WHO, MBS standard for drinking water which is 0 and the Water Department standard for untreated water of which range from 10–50 coliforms/100 ml.The results indicate that water resources have been polluted by lack of sanitation facilities, indiscriminate disposal of waste and the institutional set-up governing the provision of services in the area.

Membrane filtration of high turbidity sources

Membrane filtration processes have become widely used for low turbidity water sources that require particle removal and disinfection. In cases where the feed water contains high turbidity levels or high fouling tendencies, pre-treatment has been required to allow the membranes to operate efficiently. Submersion membranes have allowed direct treatment on many of these water supplies but operate under vacuum. This presents limitations on operating flux and design conditions for incorporating into existing facilities. The treatment unit designs are also very expensive to implement for small water treatment applications. A recently developed pressure driven ultrafiltration (UF) membrane is being tested on several different water sources and has demonstrated exceptional operation on high turbidity feed water sources. The module design includes a single potted end with the membrane fibers looped on the bottom to allow draining of solids from the module. The UF membrane filters outside to inside and has been operated on feed water turbidity levels up to 200 ntu. The availability of a pressure driven hollow fiber membrane that can efficiently filter high suspended solids water sources can provide a cost effective solution for many small to medium sized water supplies. Conditioning the feed water with a coagulant or direct filtration of high turbidity feed water can be used depending on the organic material present without settling or other clarification process. This eliminates the need for additional structural pretreatment and reduces overall system cost and size. Current limitations include the module size that makes this cost prohibitive for very large systems. Larger membrane systems where high-suspended solids are present in the feed water have been utilizing immersion membrane technologies more and more over the past few years. These systems typically operate under a vacuum and can be used for large water treatment plants as their design allows large filtration modules such as Memcor's CMFS filter block at 880 m3/hr. This allows significant capital cost reductions and allows membrane filtration to be competitive to conventional filtration technologies for virtually all filtration applications. This paper will review the economics and performance of both pressure driven and immersion membrane systems for small to large water supply systems on feed water containing high-suspended solid levels. Actual testing data for the new pressure driven hollow fiber UF membrane and immersion membrane systems will be provided on different water supplies including unconditioned surface water, filter backwash water and coagulated surface water.

Effects of SPENT FILTER BACKWASH recycle ON CRYPTOSPORIDIUM REMOVAL

Pilot studies were conducted to investigate the effect of recycling spent filter backwash water (SFBW) on Cryptosporidium and particle removal during conventional sedimentation and dual‐media filtration. When SFBW recycle configurations (3,000–19,000 oocysts/100 L) were used, Cryptosporidium concentrations in settled water were as low as or lower than when no recycle was used (6,000–22,000 oocysts/100 L). Filtered water oocyst concentrations were typically below the detection limit of 1 oocyst/120 gal (~0.25/100 L). Overall process removal was about 5 log without recycle and about 5.7 log for each recycle scenario based on calculations using raw Cryptosporidium concentrations and filtered water detection levels. As with Cryptosporidium removal, removal of turbidity and particles &gt; 2 μm for the entire process (sedimentation + filtration) was similar for operations with and without recycle. Typical median filtered water concentrations for particles &gt; 2 μm were &lt; 0.5 particles/mL for all recycle scenarios, including no recycle. Similarly, settled and filtered water turbidity levels for all studies were typically &lt; 2 and &lt; 0.03 ntu, respectively.

The treatment of groundwater containing hydrogen sulfide using microfiltration

Conventional treatment of groundwater that contains gaseous hydrogen sulfide (H 2S) has normally utilized air stripping as a means to remove this undesirable contaminant. The use of this treatment technique has several disadvantages which include noxious off-gas discharge, high finished water turbidity levels, increased copper corrosion, and deposition of elemental sulfur in the distribution system. Conventional filtration processes have not been historically applied to treatment of this type of water because of the difficulty in coagulating elemental sulfur. Microfiltration can be used as part of a treatment approach to satisfy the filtration and turbidity removal requirements for this type of groundwater. Microporus membranes range from 0.1 to 1.0 micron in pore size and have a level of retention significantly higher than conventional filtration systems (10 to 100 times) [1]. The mechanism of particle retention using microfiltration is physical instead of a physio-chemical separation as with media filters and therefore, coagulation of the particles is not required. In addition to H 2S removal, typical air stripping processes do not remove disinfection by-product (DBP) precursors that may be in the groundwater. The use of a coagulant prior to the filter can be used to reduce DBP precursor material and further improve the finished water quality. Microfiltration has been evaluated for reducing H 2S from groundwater for the City of Oviedo, Florida. Chlorine oxidation followed by microfiltration successfully removed the H 2S by first oxidizing it to elemental sulfur and then removing by filtration. The advantages of this process include lower finished water turbidity levels to improve disinfection efficiencies, elimination of noxious off-gasses, and reduction of sulfur from entering and settling in the distribution system. In addition, a coagulant was added to evaluate to removal of DBP processors to maximize the benefits from providing particle removal with the microfiltration process.

Effects of water turbidity and salt concentration levels on penetration of solar radiation under water

Two large, outdoor tanks were constructed in order to investigate the effects of water turbidity and salt concentration levels at various depths of water on penetration of solar radiation. These experiments were followed by a laboratory investigation that measured spectral transmittance and the extinction coefficient of water at different salt concentrations and turbidity levels. Both the outdoor and laboratory results indicate that the salt concentration level does not significantly affect solar radiation penetration. However, water clarity, quantified in terms of the turbidity level, plays a critical role on the magnitude of the solar radiation penetration, with the effect of turbidity on penetration increasing with the depth of water. A best-fit model is developed that gives the solar radiation penetration as a function of turbidity level and depth of water.

Flood damage analysis using multitemporal Landsat Thematic Mapper data

Abstract The paddy rice damage caused by a flood in the Kanto district in Japan has been analysed using multitemporal Landsat-5 Thematic Mapper images. The image acquired immediately after the flood showed the spread of turbid water over the paddy fields and the image acquired 1 month after the flood showed the paddy rice damage in the inundated areas. The flood damage assessment was undertaken using several multivariate analyses. (1) The correlation analysis revealed that the turbidity level of flood water was related to the rice damage. (2) The decrease of the rice yield was estimated from both images by multiple regression models. (3) The flood damage relationship was determined by a cluster analysis using the higher-order principal components of the multitemporal image. Based on the results of these analyses, distribution maps of the rice yield levels were estimated at each date and a classification of the flood damage pattern was obtained.

Thermal-hydraulic characteristics of pressurized water reactors during commercial operation: VII. Thermal-hydraulics of the PWR Paluel 1 steam generator during commercial operation

Downcomer fluid velocity, shell, fluid, and tube sheet temperature, and feedwater distributions across the cold and hot legs of Paluel 1 steam generator No. 81 are measured as a function of load. The results indicate that swirling motion in the downcomer is negligible compared with results reported earlier for the PWRs Bugey 4 and Tricastin 1. Overall circulation ratio and saturation pressure decrease almost linearly with increasing load. Carry- under and carryover are found negligible at all loads. A nonuniformly drilled feedwater ring distributes 80% of the feedwater onto the hot leg and 20% onto the cold leg. The combination of hydrocyclonic steam-water separator dryer design and nonuniformly drilled feedwater ring is successful in retaining a high percentage ( ∼ 70%) of the rather pure (compared with recirculation water) feedwater at tube sheet level across the hot leg, even at full load. Consequently, chemical quality, and turbidity level of secondary water above the tube sheet in the hot leg is found superior to that in the cold leg.