Showing papers on "Turbidity published in 1998"

Dominance of particle-attached bacteria in the Columbia River estuary, USA

Abstract: Particle-attached bacteria are a central component of the detrital food web of many turbid coastal and estuarine ecosystems. The Columbia River estuary, at the terminus of a 660000 km 2 water­ shed in northwestern North America, is a turbid, partially mixed system that has a flushing time of 1 to 3 d. Several large, well-defined estuarine turbidity maxima (ETM) extend the residence time ot both mineral and organic pcuticles transported through the estuary. Water samples collected in the North Channel of the estuary every 2 h for 148 h (6 tidal cycles) in May 1995 were analyzed to determine the concentration and production of particle-dttached and free-living bacteria, extracelluldr enzyme activ­ ity, turbidity, salinity, and particulate orgdnic carbon (POC) concentration. The concentration ot parti­ cle-attdched bdcteria, defined as those caught by a 3 pm filter, averaged 1.02 x lOG (SD = 1.00 x 10") cells ml-( and correlated with turbidity dnd POC, and thus to some extent with the tiddl cycle that main­ tains the ETM. The concentration of free-living bacteria was more constant, averaging 1.25 x 10" (SD = 0.4 x 10h) cells ml- 1 Particle-attdched bacterial cdrbon production, cdlculated from the rate of incorpo­ ration of1H-thymidine, dveraged 1.61 (SD = 1.10) ~lg 11 h- I , dccounted for 90 'Yo (SD = 9 %,) of total bdc­ lerial carbon production, and correlated with turbidity and POe. Extracellular enzyme dCtivity, mea­ sured as the rate of hydrolysis of fluorescently labeled compounds, increased with turbidity and was predominantly associated with particles. Particle-dttached bacteria probably dccount for most of the bacterial degradation of particulate orgdnic material in the estudry, and the transfer of that materidl into the detrital food web. The hydrodynamics of the estuary contribute to the dominance of Pdrticle­ attached bacteria by extending the residence time of pdrticles in the ETM, and by quickly flushing free­ living cells through the estudry, perhaps preventing the development of an estudrine population of free-living bacterid.

Evaluation of Water Quality Factors in Storm Runoff from Paved Areas

Abstract: Continuous water quality measurements of storm runoff into a single road inlet have been carried out at two experimental catchments in Belgrade, Yugoslavia, and Lund, Sweden. Both sites were equipped with similar instrumentation for measurements of overland flow, turbidity, pH, conductivity, and temperature. The data were recorded at 10-s time intervals during rainfall events. To measure suspended solids concentration, turbidity meters were calibrated in conditions very similar to the real world. A detailed description of the field-measuring facilities used in the Belgrade catchment and the results of the measurements from both sites are presented. After detailed examination of possible errors in measurement, only the reliable data were used for statistical analysis. Event mean, extreme, and aggregated values were analyzed. The results indicate that the antecedent dry weather period length has only a minor effect upon road sediments wash-off, but it has an influence upon conductivity. The "first-flush effect" of suspended solids appears only in a limited number of events. Cross-correlation coefficients of rainfall, overland flow, and water quality were calculated for each event, taking into account the time lag between observed characteristics. These coefficients showed that suspended solids loading rate is influenced by rainfall intensity and overland flow rate. The results presented in this paper have been used in development of the physically based wash-off model published by Deletic and colleagues.

Costs of water treatment due to diminished water quality: A case study in Texas

Abstract: The cost of municipal water treatment due to diminished water quality represents an important component of the societal costs of water pollution. Here the chemical costs of municipal water treatment are expressed as a function of raw surface water quality. Data are used for a 3-year period for 12 water treatment plants in Texas. Results show that when regional raw water contamination is present, the chemical cost of water treatment is increased by $95 per million gallons (per 3785 m3) from a base of $75. A 1% increase in turbidity is shown to increase chemical costs by 0.25%.

Fate and Distribution of Linear Alkylbenzene Sulfonates in the Littoral Environment

Abstract: A study was conducted of the fate and behavior of LAS in a shallow coastal zone adjoining the Bay of Cadiz (southwest of Spain). The area is subjected to strong tidal currents and receives directly the discharge of untreated wastewaters of a population of about 100 000 inhabitants. LAS showed a nonconservative behavior due to intense biodegradation and due to sorption and settling of material in suspension. The sorption to suspended matter affects the way in which its dispersion takes place in zones with high turbidity, since this fraction may represent up to 60% of the total quantity present in the medium. The surfactant character of LAS is also illustrated by a strong sorption at the water−atmosphere interface. In zones close to urban effluent discharge points, this translates into a steep vertical gradient in the LAS concentration, with values found in the top 3−5 mm of water depth some 2 orders of magnitude greater than those found at a depth of 0.5 m. Over a large part of the area studied, the LAS co...

Hyperspectral remote sensing of turbidity and chlorophyll a among Nebraska Sand Hills lakes

Abstract: This study was conducted to establish correlations between reflectance spectra, turbidity and chlorophyll a among 22 fresh to alkaline lakes in Nebraska, U.S.A., sampled in June and July of 1994. Peak reflectance ranged from 2-22 per cent between 500 and 600nm. Turbidity and chlorophyll a ranged from 1-82 NTU and 1-17 1 mu gl-1, respectively, with significant correlation (P<0.001) between the two. Reflectance first-derivatives corresponding to wavelengths 429 and 695nm, were significantly correlated with chlorophyll a (P<0.001), and derivatives at 429, 628 and 695nm were significantly correlated with turbidity (P<0.001) despite a wide range in water quality conditions.

Shallow gas in the muddy sediments of Eckernförde Bay, Germany

Abstract: The seafloor of central Eckernforde Bay is characterised by soft muddy sediments that contain free methane gas. Bubbles of free gas cause acoustic turbidity which is observed with acoustic remote sensing systems. Repeated surveys with subbottom profiler and side scan sonar revealed an annual period both of depth of the acoustic turbidity and backscatter strength. The effects are delayed by 3–4 months relative to the atmospheric temperature cycle. In addition, prominent pockmarks, partly related to gas seepage, were detected with the acoustic systems. In a direct approach gas concentrations were measured from cores using the gas chromatography technique. From different tests it is concluded that subsampling of a core should start at its base and should be completed as soon as possible, at least within 35 min after core recovery. Comparison of methane concentrations of summer and winter cores revealed no significant seasonal variation. Thus, it is concluded that the temperature and pressure influences upon solubility control the depth variability of acoustic turbidity which is observed with acoustic remote sensing systems. The delay relative to the atmospheric temperature cycle is caused by slow heat transfer through the water column. The atmospheric temperature cycle as ‘exiting function’ for variable gas solubility offers an opportunity for modelling and predicting the depth of the acoustic turbidity. In practice, however, small-scale variations of, e.g., salinity, or gas concentration profile in the sediment impose limits to predictions. In addition, oceanographic influences as mixing in the water column, variable water inflow, etc. are further complications that reduce the reliability of predictions.

Light scattering by small particles

Abstract: On-line turbidimeters are currently used for monitoring particle concentration in water and gas treatment processes. For small particle concentration, the intensity of scattered light is a linear function of the particle concentration, as long as a number of other parameters are kept constant: the refractive indexes of the particles and the surrounding medium, size, measuring angle and wavelength of the light. An international standard has been created in order to define the characteristics of the turbidimeters and the calibration suspension. The effects of the parameters are described and quantified. The special aspects of the measurement of very low turbidity values in water are treated: the zero value of water and the definition of the calibration conditions. A measuring method is presented which grants long-term stability without recalibration. The first industrial application for on-line turbidimeters was the monitoring of beer filtration in breweries, which started about 50 years ago. In the meantime, turbidimeters have been used in very diversified fields such as dust measurements in stacks, visibility in road tunnels and filtration control in the chemical industry. However, their main application today is the monitoring of drinking water treatment plants: control of the flocculation process by measuring the variations in the raw water (rivers, lakes, ground-water, sources) and the resulting properties, sand filtration survey and final quality control.

Multispectral remote sensing of turbidity among Nebraska Sand Hills lakes

Abstract: This study shows robust correlation of multispectral reflectance data (from Landsat Thematic Mapper) with turbidity among 21 lakes in Nebraska, USA, sampled in June, 1994. Mean lake reflectance percentages ranged from 5-12 (TM1), 4-18 (TM2), 2-12 (TM3) and 1-5 (TM4). Turbidity ranged from 2.7-82.3 nephelometric turbidity units. Correlations were highly significant (r 0.68; P 0.001) between each of the TM bands and turbidity. Linear models were useful for measurement among lakes in the region, despite potential bottom effects or variation in turbidity components due to a range of water quality.

Transport and retention of suspended particulate matter and bacteria in the Humber-Ouse Estuary, United Kingdom, and their relationship to hypoxia and anoxia

Abstract: Data are presented on dissolved oxygen (DO) concentrations and their relationship to salinity, suspended particulate matter (SPM), concentrations, and the turbidity maximum in the Humber-Ouse Estuary, United Kingdom, during summer 1995. Measurements in the upper Humber during March 1995 showed DO in the range 82% to 87% of saturation. Suspended particulate matter concentrations were 60,000 mg l−1) occurred within 1 m of the bed in the turbidity maximum region. A spring-neap record showed a dramatic and tidally controlled decrease in DO at very low salinities as the tides progressed from neaps to springs. An anchor station located down-channel of the turbidity maximum showed that about 95% of the variance in DO, which varied from 28% at low-water slack to 67% at high-water slack, could be explained in terms of salinity variation. At the up-channel margins of the turbidity maximum, DO increased from zero (anoxia) near high water to 60% near low water slack, in contrast to the behavior down-channel of the turbidity maximum. About 82% of the variance in DO could be explained in terms of salinity variations alone. Only 43% of the DO variance could be explained in terms of SPM alone. Up-channel of the turbidity maximum, SPM concentrations were relatively low (<3000 mg l−1) and DO levels varied from 48% of saturation near high water to 83% near low water slack. About 76% of the variance in DO could be explained in terms of salinity variations alone. Within the turbidity maximum region, DO varied from <2% saturation on the early flood and late ebb and maximized around 7% at high water slack. About 63% of the variance in DO could be explained in terms of salinity variation alone. This increased to 70% when suspended particulate matter was taken into account. Only 29% of the DO variance could be explained in terms of suspended particulate matter alone. Because bacteria were likely to have been the cause of the observed reduction in DO, the numbers of bacteria, both free-living and attached to particles, were measured in the turbidity maximum region. Numbers of free-living bacteria were low and most of the bacteria were attached to sediment particles. There was a linear correlation between total bacterial number and suspended particulate matter concentration, suggesting that the strong DO demand was exerted locally as a result of bacterial activity associated with increased suspended particulate matter concentrations. An order of magnitude analysis of DO consumption within the Ouse’s turbidity maximum, based on the premise that DO depletion was directly related to suspended particulate matter concentrations and that DO addition was due to reaeration, indicates that complete deoxygenation could have occurred with an oxygen depletion rate of ∼0.01 mg DO h−1/g suspended particulate matter during the residence time of waters within the turbidity maximum (∼7 d). This rate was sufficiently fast that anoxic to aerobic conditions were able to develop a spring-neap periodicity within the turbidity maximum, but too slow to generate substantial intratidal fluctuations in DO. This is in accordance with the observations, which show that relatively little of the intratidal variance in DO could be explained in terms of suspended particulate matter fluctuations, whereas most of the variance could be explained in terms of salinity, which behaved as a surrogate measure for the proximity of the turbidity maximum.

Assessing Water Quality in Catawba River Reservoirs Using Landsat Thematic Mapper Satellite Data

Abstract: This study investigates the potential of satellite-based remote sensing to assess water quality in the 11 reservoirs of the Catawba River basin. Near-simultaneous acquisition of both Landsat TM (Thematic Mapper) data and in situ water quality observations (turbidity, secchi disk depth, chlorophyll and surface temperature), in May of 1995, provided a statistical foundation for the development of algorithms that convert TM reflectance to each water quality parameter. The conversion models defined for turbidity, secchi disk depth, chlorophyll (power law function) and temperature (linear function) were used to produce digital cartographic products that depict the distribution of each parameter in the 11 reservoirs. A analysis of error demonstrates that accurate quantitative data products can be produced from Landsat TM imagery for the surface waters of the major reservoirs in this system with a spatial resolution of 30 m for turbidity and secchi disk depth, and a 120-m resolution for surface temperat...

Biogeochemical processes controlling methane in gassy coastal sediments—Part 2: groundwater flow control of acoustic turbidity in Eckernförde Bay Sediments

Abstract: To understand the origin of the methane distributions in sediments of Eckernforde Bay, three sites were sampled in May 1994 for determination of methane, sulfate and chloride concentrations in the sediment porewaters. In much of the Bay, bubbles of biogenic methane gas within the sediments lead to widespread ‘acoustic turbidity’ seen in acoustic surveys, masking the sedimentary structure below the gassy horizon. Acoustic windows, where the gas does not appear to be present, occur in several locations in the Bay, often surrounded by acoustically turbid sediments. Pockmarks, shallow depressions in the sediment, are also found in Bay sediments and may show acoustic turbidity at even shallower depths below the interface than surrounding sediments. One site of each type was sampled in this study. The site probably representative of much of the bay below 20 m water depth, revealed methane saturated conditions by about 75 cm depth below the interface, confirming inferences from acoustic scattering data that free gas was present in the sediment. Above this, the methane concentration profile was concave-upward, indicative of methane oxidation in the overlying, sulfate-reducing sediments. These porewaters showed a slightly decreasing chlorinity with depth. At an acoustic window site, methane concentrations rose to a maximum at about 125 cm depth, but did not reach saturation. Below this depth they decreased in a concave-down pattern. Chloride concentrations decreased markedly with depth, indicative of vertical freshwater flow from below. The third site was a pockmark exhibiting very shallow acoustic turbidity at about 25 cm depth. Here methane concentrations rose to exceed saturation within 25 cm depth below the interface and the porewaters became almost fresh by 1.5 m depth, indicative of a stronger flow of freshwater from below. These groundwater flows have competing effects on the methane inventory. They help exclude sulfate from the sediment, allowing the earlier/shallower onset of methanogenesis, but they also aid loss of methane through advection. A diagenetic model that couples the biogeochemistry of sulfate and methane is used to explain the presence or absence of methane gas in these sediments in relation to the flow rate of fresh groundwater from below. Model results indicate that acoustic windows within otherwise acoustically turbid sediments of the bay are likely due to relatively higher rates of vertical advection of fresh groundwater. The gassy pockmark, however, with an even higher vertical advection rate, seems to require the input of additional reactive organic carbon to explain its vertical methane distribution.

The sediment concentration–turbidity relation: its value in monitoring at Ranger Uranium Mine, Northern Territory, Australia

Abstract: Some earlier studies of erosion of the schist-dominated waste rock dump of Ranger Uranium Mine, Northern Territory, Australia, used turbidity as a surrogate for sediment concentration. Subsequent detailed studies of the turbidity–sediment concentration relation for a number of sites on the waste rock dump, reported in this paper, demonstrate that turbidity cannot be used to accurately predict sediment concentration. The results of this experiment suggest that environmental monitoring of erosion at mines in the Kakadu region of Northern Australia should use direct methods of measurement of the sediment concentration in runoff, and that turbidity measurements will not provide sufficient accuracy to satisfy audits of environmental compliance to regulatory guidelines.

Accumulation of muds and metals in the Hudson River estuary turbidity maximum

Abstract: In the Hudson River estuary, fine mud and toxic metals are enriched in the upstream turbidity maximum. The mechanisms causing the enrichment were assessed through the analysis of suspended-sediment concentration (SSC) (bottom and surface), particle size, and trace metal distributions. Bottom SSCs varied across the study area by a factor of ten, and the turbidity maximum activity was observed in between kilometers 45 and 80. The particle-size analysis defined two accumulation modes: 22.1 μm. The ratio of the fine-to-coarse mode increased from 1.75 to 2.75 in the turbidity maximum. The fine mud concentration (55–60%) in the turbidity maximum was found to have a high correlation (r=0.98;p<0.005) with the concentration of <2-μm particles. A conceptual model was derived in order to understand the possible mechanisms by which fine mud (and specifically <2-μm particles) is concentrated. The two dominant size modes were analyzed for toxic metals. The upstream tributaries are major sources of metals compared to point sources at downstream locations. In the turbidity maximum, Cd, Cu, Zn, and Pb are significantly enriched compared to average shale metal values and ERM toxicity guidelines by 580, 42, 10, 16 and 12, 7, 2.4, 1.4 times, respectively. Decreasing metal concentrations downstream of the turbidity maximum imply that Haverstraw Bay acts as temporary storage for fine particles and enriched metals. It is demonstrated in this study that toxic metals are enriched in Haverstraw Bay due to the mud accumulation. The high levels of toxic metals in the sediments of the Hudson River estuary are a major concern because human activities (dredging and river traffic) cause resuspension of sediments and can change the mobility patterns of bioavailable contaminants.

The Persistence of Anthropogenic Turbidity Plumes in a Shallow Water Estuary

Abstract: Increased turbidity and light attenuation (Kd) in the suspended sediment plumes created by hydraulic clam dredging were examined in Chesapeake Bay, MD, U.S.A. Turbidity andKdvalues were measured along transects in areas with and without dredge plumes. The turbidity andKdof individual plumes were tracked as they returned to background levels using both Lagrangian and Eulerian techniques. Existing aerial photographs and a geographical information system (ARC/INFO) were used to examine plume sizes and dredge boat locations in relation to bathymetry. Hydraulic clam dredging produced plumes with significantly higher turbidity and light attenuation compared to background values. Plume characteristics were determined primarily by bottom sediment type and water depth. The greatest increase in turbidity and light attenuation occurred when dredges operated in shallow water (<1·0 m) where bottom sediments had increased amounts of silt and clay. Plume turbidity andKddissipated exponentially over time. The initial change in concentration of suspended sediments was rapid as the coarse sediments settled to the bottom. The rate of plume decay slowed as diffusion and resuspension acted on the finer sediments remaining in suspension. Some Lagrangian rates of plume dissipation were faster than Eulerian rates due to resuspension in shallow waters. Examination of aerial photographs indicated that 72% of the dredge boats digitized in the Chester River were operating in less than 2 m water. The area of a plume measured per boat in the Chester River was highly variable, ranging from 0·01 to 0·64 m2.

Removing particles and THM precursors by enhanced coagulation

Abstract: The effectiveness of enhanced coagulation for removing particles and trihalomethane (THM) precursors at various alum dosages and coagulation pH values was assessed. Samples of both source water and filter effluent were examined by counting particles and measuring particle size distribution, turbidity, total organic carbon, ultraviolet light absorbance at 254 nm (UV 254 ), and THM formation potential. Removal of particles and turbidity increased substantially at alum dosages above 20 mg/L. Particle removal was not significantly different at adjusted pH (5.5) compared with ambient pH. Filter effluent particle counts were consistent with residual turbidity data; however, particle counting provided more information on the efficiency of the solid-liquid separation. Significantly more THM precursors were removed by enhanced coagulation at pH 5.5 than at ambient pH. Higher dosages were needed to achieve acceptable removal of THM precursors than were needed for removal of particles.

Dynamics of the turbidity maximum zone in a micro-tidal estuary: Hawkesbury River, Australia

Abstract: Bed sediment, velocity and turbidity data are presented from a large (145 km long), generally well-mixed, micro-tidal estuary in south-eastern Australia. The percentage of mud in the bed sediments reaches a maximum in a relatively narrow zone centred ≈30–40 km from the estuary mouth. Regular tidal resuspension of these bed sediments produces a turbidity maximum (TM) zone in the same location. The maximum recorded depth-averaged turbidity was 90 FTU and the maximum near-bed turbidity was 228 FTU. These values correspond to suspended particulate matter (SPM) concentrations of roughly 86 and 219 mg l−1, respectively. Neither of the two existing theories that describe the development and location of the TM zone in the extensively studied meso- and macro-tidal estuaries of northern Europe (namely, gravitational circulation and tidal asymmetry) provide a complete explanation for the location of the TM zone in the Hawkesbury River. Two important factors distinguish the Hawkesbury from these other estuaries: (1) the fresh water discharge rate and supply of sediment to the estuary head is very low for most of the time, and (2) suspension concentrations derived from tidal stirring of the bed sediments are comparatively low. The first factor means that sediment delivery to the estuary is largely restricted to short-lived, large-magnitude, fluvial flood events. During these events the estuary becomes partially mixed and it is hypothesized that the resulting gravitational circulation focuses mud deposition at the flood-determined salt intrusion limit (some 35 km seaward of the typical salt intrusion limit). The second factor means that easily entrained high concentration suspensions (or fluid muds), typical of meso- and macro-tidal estuaries, are absent. Maintenance of the TM zone during low-flow periods is due to an erosion-lag process, together with a local divergence in tidal velocity residuals, which prevent the TM zone from becoming diffused along the estuary axis.

The Use of Cationic Polymers as Primary Coagulants in Water Treatment

Abstract: The removal of natural organic matter (NOM) from drinking water supplies can be achieved with cationic polymers, used here in jar tests on simulated waters made from concentrates of humic substances. In applying organic polymers to the removal of UV absorbing compounds (used as a measure of trihalomethane precursors), a reservoir water was best treated with a high MW polydiallyldimethy-lammonium chloride (poly DADMAC). Similar results were obtained for a river water, where a cationic polyacrylamide (CPAM) of high charge was also effective. Chitosan performed reasonably for both waters, despite low charge and MW. Weakly basic polymers could be binding NOM via hydrogen bonding to free amino groups. Organic polymers generally did nearly as well as alum for both waters, taking out 86–100% of the colour that alum does, and performing even better when other particulates were present. Mixtures of alum and polymer are a way to have particles present if the original water is not of high turbidity. On fractionated waters, alum was best for removal of humic and fulvic acids as measured by UV absorbance, although polyDADMAC was as good for the river water; carbohydrates were a very minor component and there was little effect where data could be obtained; for proteins alum then DADMACs were the best performers for the river water.

Laboratory Study of Sedimentation for Improving Quality of Pond Effluents

Abstract: Laboratory studies with synthetic pond effluents demonstrated that concentrations of total suspended solids, total phosphorus, turbidity, biochemical oxygen demand, and total ammonia nitrogen could be reduced by sedimentation. Removal of 75% or more of total suspended solids and total phosphorus and 40% or greater removal of biochemical oxygen demand and turbidity occurred within 8 hours. Removal of total ammonia nitrogen was less than for the other variables. Pilot studies should be conducted on aquaculture farms to evaluate sedimentation or as an effluent treatment method.

Improvement of Flocculation Efficiency of Water Treatment by using Polymer Flocculants

Abstract: As water treatment plants have to supply water with satisfactory quality, timely responses to fluctuations in raw water quality are of importance. In most cases, metal salts type inorganic flocculants have been sufficient to maintain the water quality. However, due to various reasons there are situations where metal salts cannot solve the problem caused by the poor quality of inflow water. In this study, organic polymers such as polyamine and poly(diallyldimethylammonium chloride(DADM)) were synthesized and were applied to Nak-dong river raw water in Korea to check their efficiency in reducing turbidity and total organic carbon (TOC). Synthesized polyamine and poly(DADM) flocculants were effective as flocculants for water treatment and the addition of 1 mg l−1 of organic polymer caused a reduction of 50 % of the consumption of polyaluminium chloride (PAC). The effects of polymer, polymer amount, initial turbidity, and pH on the removal of turbidity and TOC were investigated. The adsorption and separation ...

Removal of bentonite causing turbidity by electro‐coagulation

Abstract: The efficiency of electro‐coagulation as a turbidity removal process has been investigated using bentonite as a turbidity source. The influence of certain operational parameters such as current input, contact time, electrolyte concentration, and initial turbidity on the coagulation efficiency were studied. The process was found to achieve excellent turbidity removals. The lowest residual turbidities were 0.5 and 0.75 NTU for the samples with initial turbidities of 112 and 52 NTU, respectively. This was obtained at a current of 0.5 A, a contact time of 5 minutes, and a calculated dissolved iron concentration of 10.8 mg/l. At a constant current of 0.5 A, a reduction in the contact time from 5 to 2 minutes in the case of turbidity level 1 (52 NTU) and from 5 to 1 minute in the case of turbidity level 2 (112 NTU) resulted in better turbidity removals. The optimal operational parameters for turbidity level 1 are a current of 0.5 A, a contact time of 2 minutes and an NaCl concentration of 2 g/l resulti...

Transformation of Phosphorus in the Elbe Estuary

Abstract: The distribution of dissolved and particle-bound phosphorus (P) was investigated in the Elbe estuary during March 1995. The forms of particulate P were studied with a sequential extraction technique. Organic P dominated particle-bound P in the outer reaches of the estuary (52%), decreased to a minimum of 21% in the turbidity zone, and increased to 33% further upstream. Fe-bound P was the second most important P species in the outer reaches (27%) and dominated in the turbidity zone (up to 57%) and upstream of the turbidity zone (up to 48%). The P:Fe ratio increased with decreasing salinity, from 0.11 in the outer reaches to about 0.22 at zero salinity. Dissolved inorganic P release from reverine suspended matter was about two to three times larger than release, from marine suspended matter and was dominated by release of Fe-bound P. Dissolved inorganic P release from marine and from riverine organic matter were of equal importance. Because marine suspended matter dominates in the estuary, this suggests riverine organic matter is remineralized much faster than marine organic matter. This is in line with the refractory nature of marine organic matter (no phytoplankton bloom) and the easily degradable character of the riverine suspended matter (phytoplankton bloom) in the Elbe estuary during March 1995.

Clear and Turbid Water in Shallow Norwegian Lakes Related to Submerged Vegetation

Abstract: Timms and Moss (1984) suggested that fertile shallow lakes may have alternative stable states, a clearwater state with dense vegetation and a turbid water state dominated by phytoplankton and with little submerged and floating-leaved vegetation. This phenomenon has also been observed and discussed by several other authors (e.g., Irvine et al., 1990; Jeppesen et al., 1990; van Donk et al., 1990; Blindow et al., 1993; Scheffer et al., 1993). According to the model of Scheifer (1989, 1990), the main controlling factor for the two alternative states is the turbidity of water regulating the vertical light penetration. When the nutrient level increases, phytoplankton growth is often stimulated, which in turn increases the turbidity. This leads to increased light attenuation and a reduction of the maximum growth depth of submerged vegetation. Increased nutrient concentrations will therefore reduce the bottom area covered by submerged vegetation until it is virtually absent. In shallow lakes with most bottom areas at similar depths, the change from high plant cover to plantless bottoms may be abrupt. Uncovered sediments in shallow lakes are much more vulnerable to resuspen-sion and more easily give rise to turbid water during periods of wind and wave action than in lakes with plant-covered sediments. Benthivorous fish may be favored under these circumstances and add to the turbidity by foraging on the sediment. A more-or-less stable turbid state may be the result.

Feasibility of Using a Turbidimeter to Quantify Suspended Solids Concentration in a Tidal Saltmarsh Creek

Abstract: A field infrared nephelometric turbidimeter was deployed to measure turbidity continuously in a tidal saltmarsh creek, and water samples were taken periodically and analysed for suspended solids concentrations. Five hundred and ninety-three (593) water samples were collected over 25 different time periods from May to October 1996. Suspended solids in the creek were found to be mostly medium silt. Measured suspended solids concentrations are statistically related to measured turbidity with a correlation coefficient of 0·827. The linear regression relationship between total suspended solids concentration and turbidity has a slope of 1·584 (mg l−1per FTU). Data and experience from this study indicate that turbidity measurements provide surrogate measurements of suspended solids concentration in mid-latitude tidal creeks. This feasibility study is an initial step toward monitoring exchanges of solids over a long time period in the coastal wetlands system.