Estimation of suspended sediment concentration from turbidity measurements using artificial neural networks

Suspended sediment concentration (SSC) is generally determined from the direct measurement of sediment concentration of river or from sediment transport equations. Direct measurement is very costly and cannot be conducted for all river gauge stations. Therefore, correct estimation of suspended sediment amount carried by a river is very important in terms of water pollution, channel navigability, reservoir filling, fish habitat, river aesthetics and scientific interests. This study investigates the feasibility of using turbidity as a surrogate for SSC as in situ turbidity meters are being increasingly used to generate continuous records of SSC in rivers. For this reason, regression analysis (RA) and artificial neural networks (ANNs) were employed to estimate SSC based on in situ turbidity measurements. The SSC was firstly experimentally determined for the surface water samples collected from the six monitoring stations along the main branch of the stream Harsit, Eastern Black Sea Basin, Turkey. There were 144 data for each variable obtained on a fortnightly basis during March 2009 and February 2010. In the ANN method, the used data for training, testing and validation sets are 108, 24 and 12 of total 144 data, respectively. As the results of analyses, the smallest mean absolute error (MAE) and root mean square error (RMSE) values for validation set were obtained from the ANN method with 11.40 and 17.87, respectively. However these were 19.12 and 25.09 for RA. It was concluded that turbidity could be a surrogate for SSC in the streams, and the ANNs method used for the estimation of SSC provided acceptable results.     

Evaluation of preservation methods for nutrient species collected by automatic samplers

Automatic samplers are a common method of data collection for numerous monitoring projects in the South Florida region and elsewhere. Although total phosphorus (TP) is the primary parameter of interest within this region, nitrogen species such as ammonia nitrogen (NH₄-N), nitrate+nitrite nitrogen (NO_x-N), and total kjeldahl nitrogen (TKN) are also collected and analyzed. Federal and state quality assurance guidelines require nutrient samples to be preserved by acidification with H₂SO₄ to a pH < 2 and stored immediately at 4 °C. However, the remoteness of manysampling locations in South Florida makes it difficult to supplyelectricity for the refrigeration of samples collected by autosamplers. In addition, the use of propane-powered refrigerated autosamplers is a costly and ineffective solution in the South Florida climate. Consequently, while samples collected at these remote locations are routinely pre-preservedwith acid, they are not cooled to 4 °C for a period fromone to seven days. This study evaluated if a statistically significant difference ( = 0.05) existed between concentrations of nitrogen species from a common source samplethat was either: processed immediately; refrigerated to 4 °C for seven days; or not refrigerated for seven days.In all cases, the collected sample was pre-preserved by adding 1 mL of 50% H₂SO₄ to each 1 L discrete sample container before each 7 day testing period. Differences in concentrations of the calculated parameter total nitrogen (TN)were also investigated.Analyses using the Wilcoxon Signed-Rank Test showed no significant differences among the three treatment groups for NO_x-N, TKN, TN and TP. Significant differences were observedwhen the NH₄-N samples that were processed immediately werepaired with NH₄-N samples that were left unrefrigerated or refrigerated for seven days. Information from this study can be used by researchers and managers in evaluating the usefulness of nutrient water quality data that is collected when sample refrigeration is not available.     

BTX measurements with diffusive samplers in the vicinity of a cokery: comparison between ORSA-type samplers and pumped sampling

In the framework of new European directives in the field of ambient air quality assessment specific requirements for measurement methods for benzene will be defined and have to be met in the future. In a residential area in the vicinity of a cokery a comprehensive monitoring programme for BTX compounds (benzene, toluene, xylenes) was carried out with diffusive samplers. Measurement results from 20 sites show a distinct spatial distribution of benzene concentrations which is caused by the emissions of the plant. Comparisons with two pumped measurement methods reveal excellent agreement in the case of benzene. An assessment of measurement uncertainty for the diffusive method is presented in terms of standard deviations from parallel measurements (precision) and by comparison with a reference method according to national and international standards. Data quality objectives required by an upcoming European directive for benzene can be met by diffusive sampling.     

Estimation of suspended sediment concentration in rivers using acoustic methods

Acoustic Doppler current meters (ADV, ADCP, and ADP) are widely used in water systems to measure flow velocities and velocity profiles. Although these meters are designed for flow velocity measurements, they can also provide information defining the quantity of particulate matter in the water, after appropriate calibration. When an acoustic instrument is calibrated for a water system, no additional sensor is needed to measure suspended sediment concentration (SSC). This provides the simultaneous measurements of velocity and concentration required for most sediment transport studies. The performance of acoustic Doppler current meters for measuring SSC was investigated in different studies where signal-to-noise ratio (SNR) and suspended sediment concentration were related using different formulations. However, these studies were each limited to a single study site where neither the effect of particle size nor the effect of temperature was investigated. In this study, different parameters that affect the performance of an ADV for the prediction of SSC are investigated. In order to investigate the reliability of an ADV for SSC measurements in different environments, flow and SSC measurements were made in different streams located in the Aegean region of Turkey having different soil types. Soil samples were collected from all measuring stations and particle size analysis was conducted by mechanical means. Multivariate analysis was utilized to investigate the effect of soil type and water temperature on the measurements. Statistical analysis indicates that SNR readings ob tained from the ADV are affected by water temperature and particle size distribution of the soil, as expected, and a prediction model is presented relating SNR readings to SSC mea surements where both water temperature and sediment characteristics type are incorporated into the model. The coefficients of the suggested model were obtained using the multivariate anal ysis. Effect of high turbidity conditions on ADV performance was also investigated during and after rain events.     

Exploratory study of suspended sediment concentrations downstream of harvested peat bogs

Peat bog harvesting is an important industry in many countries, including Canada. To harvest peat, bogs are drained and drainage water is evacuated towards neighboring rivers, estuaries or coastal waters. High suspended sediment concentrations (SSC) were found in the drainage water at one particular site during the 2001–2002 spring seasons in New Brunswick (Canada). The main objective of this study was to verify this observation at other sites, compare SSC levels leaving harvested peat bogs with those leaving an unharvested bog, and to determine if high SSC events happen only in Spring or all year round. Suspended sediment concentrations were monitored downstream of three harvested peat bogs and an unharvested reference bog located in New Brunswick during the ice free seasons of 2003–2004. On average, SSC at the harvested sites exceeded 25 mg/l, which is the recommended daily maximum concentration, 72% of the time, while the same concentration was exceeded 30% of the time at the unharvested sites. SSC were found to be significantly higher at harvested sites than at the reference sites for all seasons. The highest SSC medians were recorded in the Fall but SSC was elevated in all seasons. High SSC levels in receiving waters may be caused by field ditching activities and insufficient sediment controls. Findings suggest the NB Peat Harvesting 25 mg/l SSC guideline should be reviewed.     

Comparison of wood-dust aerosol size-distributions collected by air samplers

A method has been described previously for determining particle size distributions in the inhalable size range collected by personal samplers for wood dust. In this method, the particles collected by a sampler are removed, suspended, and re-deposited on a mixed cellulose-ester filter, and examined by optical microscopy to determine particle aerodynamic diameters. This method is particularly appropriate to wood-dust particles which are generally large and close to rectangular prisms in shape. The method was used to investigate the differences in total mass found previously in studies of side-by-side sample collection with different sampler types. Over 200 wood-dust samples were collected in three different wood-products industries, using the traditional 37 mm closed-face polystyrene/acrylonitrile cassette (CFC), the Institute of Occupational Medicine (IOM) inhalable sampler, and the Button sampler developed by the University of Cincinnati. Total mass concentration results from the samplers were found to be in approximately the same ratio as those from traditional long-term gravimetric samples, but about an order of magnitude higher. Investigation of the size distributions revealed several differences between the samplers. The wood dust particulate mass appears to be concentrated in the range 10-70 aerodynamic equivalent diameter (AED), but with a substantial mass contribution from particles larger than 100 microm AED in a significant number of samples. These ultra-large particles were found in 65% of the IOM samples, 42% of the CFC samples and 32% of the Button samples. Where present, particles of this size range dominated the total mass collected, contributing an average 53% (range 10-95%). However, significant differences were still found after removal of the ultra-large particles. In general, the IOM and CFC samplers appeared to operate in accordance with previous laboratory studies, such that they both collected similar quantities of particles at the smaller diameters, up to about 30-40 [micro sign]m AED, after which the CFC collection efficiency was reduced dramatically compared to the IOM. The Button sampler collected significantly less than the IOM at particle sizes between 10.1 and 50 microm AED. The collection efficiency of the Button sampler was significantly different from that of the CFC for particle sizes between 10.1 and 40 microm AED, and the total mass concentration given by the Button sampler was significantly less than that given by the CFC, even in the absence of ultra-large particles. The results are consistent with some relevant laboratory studies.     

An observational study of the carrying capacity of suspended sediment during a storm event

We measured the in situ suspended sediment concentration (SSC) and hydrodynamics (waves, currents, and sea level) concurrently during a storm event using self-recording instruments at offshore of the Shandong Peninsula in the Yellow Sea. We analyzed the temporal variation in suspended sediment carrying capacity and its correlation with wave, current, and water-level conditions. There was about 40% increase in SSC during the storm event. A 3-4-h lag was observed between the peak of wave height and SSC. The SSC increased in a fluctuating pattern up to the peak then decreased rapidly. This process was positively correlated with wave height and duration. The maximum SSC was 524.3 mg/l, which is about 10 times of that under normal weather conditions. This peak was observed after of a series of 1.8 m waves. The increased suspended sediments were the fine particles resuspended by the storm waves from seabed near the observation spot and transported by northward ebb currents from Shidao Bay.     

Use of fish functional traits to associate in-stream suspended sediment transport metrics with biological impairment

Loss of ecological integrity due to excessive suspended sediment in rivers and streams is a major cause of water quality impairment in the USA. Current assessment protocols for development of sediment total maximum daily loads (TMDLs) lack a means to link temporally variable sediment transport rates with specific losses of ecological functions as loads increase. In order to accomplish this linkage assessment, a functional traits-based approach was used to correlate site occurrences of 17 fish species traits in three main groups (preferred rearing habitat, trophic feeding guild, and spawning behavior) with suspended sediment transport metrics. The sediment transport metrics included concentrations, durations, and dosages for a range of exceedance frequencies; and mean annual suspended sediment yields (SSY). In addition, this study in the Northwestern Great Plains Ecoregion examined trait relationships with three environmental gradients: channel stability, drainage area, and elevation. Potential stressor responses due to elevated suspended sediment concentration (SSC) levels were correlated with occurrences of five traits: preferred pool habitat; feeding generalists, omnivores, piscivores, and nest-building spawners; and development of ecologically based TMDL targets were demonstrated for specific SSC exceedance frequencies. In addition, reduced site occurrences for preferred pool habitat and nest-building spawners traits were associated with unstable channels and higher SSY. At an ecoregion scale, a functional traits assessment approach provided a means to quantify relations between biological impairment and episodically elevated levels of suspended sediment, supporting efforts to develop ecologically based sediment TMDLs.     

Field assessment of flood event suspended sediment transport from ephemeral streams in the tropical semi-arid catchments

An assessment of suspended sediment transport was carried out in a number of semiarid catchments during flood events in order to quantify the degradation rates. In order to quantify these, a systematic sampling procedure of the episodic flood events was proposed for representative catchments. The procedure allows for an integration over the whole run-off episode using both the rising and falling limbs of the run-off hydrograph to compute the sediment quantities for each individual flood event. Higher sediment concentrations occurred in the rising limb than those at the recession for any stage of flow. The maximum suspended sediment concentration was observed at the peak of the flood hydrograph. An integration of the sediment concentration over its duration gave the total sediment yield from the flood event. For the ephemeral channels, only a small number of flood events were observed over a three-year experimental period each with a duration of the order of 3–6 h. It is notable that high sediment loads were associated with high flow volumes which were effectively the result of the catchment characteristics and incident rainfall causing the flood events in the respective catchments. A large percentage of the annual sediment yield from a catchment is transported by the ephemeral streams during a small number of flood events. The correct determination of the total sediment yield from any of the flood events depends entirely on the accuracy of the measurements. The understanding of run-off and sediment loss for the representative catchments aims at assisting planning, management and control of water and land resources for sustainable development in the semi-arid parts of the tropics. The sediment rates reveal the degradation of catchments which have repercussions on the crop and pasture production and this has a bearing on the soil and water conservation programmes in the delicate ecological balance of the semi-arid areas. Further, these rates will determine the lifespan of the reservoirs planned for the dry river valleys (ephemeral streams) and existing ones which serve livestock and domestic needs. These occasionally will require costly rehabilitation and scooping to increase effective storage unless conservation measures are taken, and these measures are bound to vary from place to place as per the representative catchments output.     

Laboratory and field comparison of measurements obtained using the available diffusive samplers for ozone and nitrogen dioxide in ambient air

This study presents an evaluation of the extent of differences between measurements performed by O(3) and NO(2) diffusive samplers and by the reference methods for diffusive samplers commercially available. The tests were performed in an exposure chamber under extreme conditions of controlling factors and under field conditions. For NO(2), the results of the laboratory experiments showed that most of the diffusive samplers were affected by extreme exposure conditions. The agreement between the samplers and the reference method was better for the field tests than for the laboratory ones. The estimate of the uptake rate for the exposure conditions using a model equation improved the agreement between the diffusive samplers and the reference methods. The agreement between O(3) measured by the diffusive samplers and by the reference method was satisfactory for 1-week exposure. For 8-hour exposures, the diffusive samplers with high uptake rates quantified better the O(3) concentration than the samplers with low uptake rates. As for NO(2), the results of the O(3) field tests were in better agreement with the reference method than the ones of the laboratory tests. The field tests showed that the majority of diffusive samplers fulfils the 25% uncertainty requirement of the NO(2) European Directive and the 30% uncertainty requirement of the O(3) European Directive for 1-week exposure.     

Geochemistry of the suspended sediment in the estuaries of the Mandovi and Zuari rivers, central west coast of India

The geochemistry of the suspended particulate matter (SPM) collected during the monsoon was determined to identify the sources of SPM and to understand the physicochemical processes in the Mandovi and Zuari river estuaries. The concentrations of SPM decrease seaward in both estuaries, but are relatively high at bay stations. Kaolinite is the most dominant clay mineral in the upstream of both rivers. Smectite increases seaward in both estuaries and is abundant in the bay. Upstream stations of Mandovi, where ore deposits are stored on the shore, exhibit high Fe, Mn, total rare earth elements (∑REE), and middle REE- and heavy REE-enriched patterns. Channel stations of both estuaries exhibit middle REE- and light REE-enriched patterns, which gradually changed seaward to middle REE- and heavy REE-enriched patterns. Canal stations exhibit the highest concentrations of major and trace metals. High metal/Al ratios occur at stations in the upstream of Zuari and at the confluence of canals in the Mandovi estuary. Enrichment factors of metals indicate that Mn is significantly polluted while other metals are moderately polluted. The δ ¹³C and δ ¹⁵N of organic matter indicate that the terrigenous organic matter at the upstream is diluted seaward by marine organic matter. Organic matter at bay stations is largely marine and altered-type. The compositions of SPM are controlled by the particulates from ore dust, the geology of the drainage basins, and the physicochemical processes in the estuaries. Particulates resuspended from the bay are dominated by ore dust, which are advected into the channels of both estuaries during the lull periods of the monsoon.     

Assessing uncertainty in annual nitrogen,phosphorus, and suspended sediment load estimates in three agricultural streams using a 21-year dataset

Accurate estimation of constituent loads is important for studies of ecosystem mass balance or total maximum daily loads. In response, there has been an effort to develop methods to increase both accuracy and precision of constituent load estimates. The relationship between constituent concentration and stream discharge is often complicated, potentially leading to high uncertainty in load estimates for certain constituents, especially at longer-term (annual) scales. We used the loadflex R package to compare uncertainty in annual load estimates from concentration vs. discharge relationships in constituents of interest in agricultural systems, including ammonium as nitrogen (NH₄-N), nitrate as nitrogen (NO₃-N), soluble reactive phosphorus (SRP), and suspended sediments (SS). We predicted that uncertainty would be greatest in NO₃-N and SS due to complex relationships between constituent concentration and discharge. We also predicted lower uncertainty with a composite method compared to regression or interpolation methods. Contrary to predictions, we observed the lowest uncertainty in annual NO₃-N load estimates (relative error 1.5–23%); however, uncertainty was greatest in SS load estimates, consistent with predictions (relative error 19–96%). For all constituents, we also generally observed reductions in uncertainty by up to 34% using the composite method compared to regression and interpolation approaches, as predicted. These results highlight differences in uncertainty among different constituents and will aid in model selection for future studies requiring accurate and precise estimates of constituent load.     

Hydrology, suspended sediment dynamics and nutrient loading in Lake Takkobu, a degrading lake ecosystem in Kushiro Mire, northern Japan

Suspended sediment and nutrient loadings from agricultural watersheds have lead to habitat degradation in Lake Takkobu. To examine their relationships with land-use activities, we monitored sediment, nutrient and water discharges into the lake for a 1-year sampling period. The Takkobu River contributed the largest portion of the annual water discharge into the lake, compared with the other tributaries. During dry conditions, lake water flowed into the Kushiro River, and conversely during flooding, Kushiro River water flowed into the lake. Inflows from the Kushiro River had a high proportion of inorganic matter, with high concentrations of total nitrogen and total phosphorus, attributed to agricultural land-use development and stream channelization practiced since the 1960s in the Kushiro Mire. Nutrient loadings from these two rivers were significantly higher during flooding than in dry conditions. However, there was no clear correlation between river discharge and nutrient concentrations. Since land-use activities in the Kushiro River and Takkobu River watersheds were concentrated near rivers, nutrients easily entered the drainage system under low flow conditions. In contrast, water discharged from small, forest-dominated watersheds contained a low proportion of inorganic matter, and low nutrient concentrations. The suspended sediment delivered to the lake during the sample period was estimated as approximately 607 tons, while the total nitrogen and total phosphorus inflows were about 10,466 and 1,433 kg, respectively. Suspended sediment input into the lake was 65%, and total nitrogen and total phosphorus were 40% and 48%, respectively, being delivered by the Kushiro River.     

Spatial and temporal variation in suspended sediment, organic matter, and turbidity in a Minnesota prairie river: implications for TMDLs

The Minnesota River Basin (MRB), situated in the prairie pothole region of the Upper Midwest, contributes excessive sediment and nutrient loads to the Upper Mississippi River. Over 330 stream channels in the MRB are listed as impaired by the Minnesota Pollution Control Agency, with turbidity levels exceeding water quality standards in much of the basin. Addressing turbidity impairment requires an understanding of pollutant sources that drive turbidity, which was the focus of this study. Suspended volatile solids (SVS), total suspended solids (TSS), and turbidity were measured over two sampling seasons at ten monitoring stations in Elm Creek, a turbidity impaired tributary in the MRB. Turbidity levels exceeded the Minnesota standard of 25 nephelometric units in 73% of Elm Creek samples. Turbidity and TSS were correlated (r ²?=?0.76), yet they varied with discharge and season. High levels of turbidity occurred during periods of high stream flow (May–June) because of excessive suspended inorganic sediment from watershed runoff, stream bank, and channel contributions. Both turbidity and TSS increased exponentially downstream with increasing stream power, bank height, and bluff erosion. However, organic matter discharged from wetlands and eutrophic lakes elevated SVS levels and stream turbidity in late summer when flows were low. SVS concentrations reached maxima at lake outlets (50 mg/l) in August. Relying on turbidity measurements alone fails to identify the cause of water quality impairment whether from suspended inorganic sediment or organic matter. Therefore, developing mitigation measures requires monitoring of both TSS and SVS from upstream to downstream reaches.     

扩散采样法测定室内空气中的BTEX

建立了扩散吸附管采样,热脱附仪和气相色谱联用测定室内空气中BTEX的监测分析方法,方法的最低检出限为0.0002mg/m3。该方法使用方便、便于携带、无需电源,且与传统的泵采样方法具有较好的可比性,适合于室内空气中BTEX的监测。     

Determining particle size distributions in the inhalable size range for wood dust collected by air samplers

In the absence of methods for determining particle size distributions in the inhalable size range with good discrimination, the samples collected by personal air sampling devices can only be characterized by their total mass. This parameter gives no information regarding the size distribution of the aerosol or the size-selection characteristics of different samplers in field use conditions. A method is described where the particles collected by a sampler are removed, suspended, and re-deposited on a mixed cellulose-ester filter, and examined by optical microscopy to determine particle aerodynamic diameters. This method is particularly appropriate to wood dust particles which are generally large and close to rectangular prisms in shape. Over 200 wood dust samples have been collected in three different wood-products industries, using the traditional closed-face polystyrene/acrylonitrile cassette, the Institute of Occupational Medicine inhalable sampler, and the Button sampler developed by the University of Cincinnati. A portion of these samples has been analyzed to determine the limitations of this method. Extensive quality control measures are being developed to improve the robustness of the procedure, and preliminary results suggest the method has an accuracy similar to that required of National Institute for Occupational Safety and Health (NIOSH) methods. The results should provide valuable insights into the collection characteristics of the samplers and the impact of these characteristics on comparison of sampler results to present and potential future limit values. The NIOSH Deep South Education and Research Center has a focus on research into hazards of the forestry and associated wood-products industry, and it is hoped to expand this activity in the future.     

Chlorophyll and suspended sediment mapping to the Caribbean Sea from rivers in the capital city of the Dominican Republic using ALOS AVNIR-2 data

This study aims to study the distribution of contaminants in rivers that flow into the Caribbean Sea using chlorophyll-a (Chl-a) and suspended sediment (SS) as markers and ALOS AVNIR-2 satellite sensor data. The Haina River (HN) and Ozama and Isabela Rivers (OZ-IS) that flow through the city of Santo Domingo, the capital of the Dominican Republic, were chosen. First, in situ spectral reflectance/Chl-a and SS datasets obtained from these rivers were acquired in March 2011 (case A: with no rain influence) and June 2011 (case B: with rain influence), and the estimation algorithm of Chl-a and SS using AVNIR-2 data was developed from the datasets. Moreover, the developed algorithm was applied to AVNIR-2 data in November 2010 for case A and August 2010 for case B. Results revealed that for Chl-a and SS estimations under cases A and B conditions, the reflectance ratio of AVNIR-2 band 4 and band 3 (AV4/AV3) and the reflectance of AVNIR-2 band 4 (AV4) were effective. The Chl-a and SS mapping results obtained using AVNIR-2 data corresponded with the field survey results. Finally, an outline of the distribution of contaminants at the mouth of the river that flows into the Caribbean Sea was obtained for both rivers in cases A and B.     

Distribution patterns of nitroaromatic compounds in the water, suspended particle and sediment of the river in a long-term industrial zone (China)

Nitroaromatic compounds are known to be hazardous to ecological and human health. To assess the status of nitroaromatic compounds contamination in the main rivers in the important industrial bases of the northeastern China, we collected water, suspended particulate matter (SPM) and sediment samples from 28 sites in the Daliao River watershed and analysed them for eight nitroaromatic compounds by gas chromatography. The total concentrations of eight nitrobenzenes in the water column including aqueous and SPM phases ranged from 740 to 15,828 ng L^???1, with a mean concentration of 3,460 ng L^???1. The total concentrations of eight nitrobenzenes in the sediment were 7.47 to 8,185.76 ng g^???1, with a mean concentration of 921.98 ng g^???1, and several times higher than those found from the Yellow River in China. 4-Nitrotoluene was the predominant contaminant in the water and sediment of the three rivers of the Daliao River watershed. 2,6-Dichloro-4-nitroaniline was generally dominant in the SPM. The levels of nitroaromatic compounds were different among different sites in the Daliao River watershed, mainly caused by the distribution of pollution sources. No obvious correlation was found between the total concentrations of eight nitrobenzenes concentrations and TOC or the slit-clay content of the sediments.