Mineral Suspended Solids Research Articles

Optical Constituent Concentrations and Uncertainties Obtained for Case 1 and 2 Waters From a Spectral Deconvolution Model Applied to In Situ IOPs and Radiometry

AbstractA spectral deconvolution model (SDM) for inversion of light absorption, a(λ) and backscattering, bb(λ), to estimate concentrations of chlorophyll (CHL), colored dissolved organic material (CDOM) and non‐biogenic mineral suspended solids (MSS) in offshore and shelf waters is presented. This approach exploits the spectral information embedded in the ratio bb(λ)/a(λ), without the need to know each parameter separately. The model has been applied to in situ inherent optical properties (IOPs), a(λ) and bb(λ), and to in situ remote sensing reflectance, rrs(λ). CHL, MSS, and CDOM estimates are provided by propagating uncertainties in input IOPs and material‐specific IOPs using a bootstrapping approach. Application of the SDM to a data set collected in the Ligurian Sea provides Mean Average Errors (MAE) of <0.7 mg m−3 for CHL, <0.02 m−1 for CDOM, and <0.2 g m−3 for MSS. The SDM is found to perform as well as, or in some cases better than, single parameter algorithms and other semi‐analytical algorithms (SAA) for each parameter for the Ligurian Sea data set. The SDM CHL product is tested using the NOMAD, Case 1 dominated, global data set and found to perform consistently with the quasi‐analytical algorithm (Lee et al., 2002, https://doi.org/10.1364/ao.41.005755) but with slightly poorer performance than standard OCx algorithms. However, the additional estimates of CDOM and MSS provided by the SDM suggest that the approach may be particularly useful for Case 2 waters. Successful retrieval of constituent concentrations with uncertainties suggests good potential to adapt this technique for satellite remote sensing.

Comparison of Landsat 8 and Landsat 7 for regional measurements of CDOM and water clarity in lakes

Abstract The potential strengths and limitations of the Landsat systems for water clarity and colored dissolved organic matter (CDOM) measurement were evaluated in Minnesota in the summers of 2013 and 2014. Optical water quality characteristics, including chlorophyll a , total suspended solids (TSS), dissolved organic carbon (DOC), and CDOM were collected along with imagery from Landsats 7 and 8. Sites represented a wide range of concentrations of CDOM, chlorophyll, and mineral suspended solids (MSS), the primary factors that affect reflectance. Clear images from September 24, 2013 (Landsat 7) and September 16, 2013 (Landsat 8) acquired for northern Minnesota eight days apart allowed comparison of the respective ETM + and OLI sensors for CDOM measurements. We examined a wide variety of potential band and band ratio models and found some two-variable models that included the NIR band worked well for Landsat 8 (R 2 = 0.82) and reasonably well for Landsat 7 (R 2 = 0.74). The commonly used green/red model had a poor fit for both sensors (R 2 = 0.24, 0.25), and five sites with high MSS were clear outliers. Exclusion of these sites and other sites not included with the Landsat 7 dataset yielded a less optically complex subset of 20 coincident lakes. For this subset strong models were found for many band and band ratio models, including the commonly used green/red model with R 2 = 0.79 for Landsat 7 and R 2 = 0.81 for Landsat 8. The less optically complex subset may explain why the green/red model has worked well in other areas. For optically complex waters CDOM models that used the new Landsat 8 ultra-blue and narrower NIR band worked best for the full dataset indicating that the new bands and other Landsat 8 characteristics, such as higher radiometric sensitivity and improved signal-to-noise ratios, improve CDOM measurements. For water clarity measured as Secchi depth (SD), we compared September 1, 2008 Landsat 7 and August 22, 2013 Landsat 8 images from path 28 using stepwise regression to identify the best model using all bands and band ratios including the new blue and narrower NIR band. The best water clarity model for Landsat 8 used the OLI 2/4 band ratio plus OLI band 1 and was nearly identical with a model using the OLI 2/4 band ratio plus OLI band 2. The latter model is similar to the model used for previous Landsat water clarity assessments, which used the ETM + 1/3 band ratio plus ETM + band 1. For SD measurements we found strong relationships with both sensors, with only slight improvements for the OLI sensor for the lakes in our datasets. In contrast to some previous reports that indicated Landsat 7's ETM + lacked sufficient sensitivity for reliable retrieval of CDOM, we found that overall both sensors worked well for water clarity and CDOM measurements. This will allow their continued use for current and historical measurements of important water characteristics on a regional scale.

Modelling an aerobic submerged membrane bioreactor with ASM models on a large range of sludge retention time

In this work, modelling of a submerged membrane bioreactor (SMBR) system for municipal wastewater treatment is evaluated using ASM1 and ASM3 models. Dynamic data (and pseudo steady state) collected in an aerobic SMBR working at high sludge retention time (SRT) are considered. Work is focused on suspended solids, excess sludge production, and nitrification kinetics. After a complete wastewater characterisation, satisfying prediction is obtained for volatile suspended solids (MLVSS) with default kinetic parameters. However, assumption of inert organics accumulation ( X I) makes inaccurate the simulation at high SRT (110 days). Results also show that mineral suspended solids are significantly solubilised in such a process, and this should be taken into account for modelling total suspended solids. Default parameters for nitrification (μ a , b a , K N ) were not exact, and thus a new set of parameters was identified. A unique set of values was proposed for μ a and ba, whereas half saturation coefficient ( K N ) was observed to vary with the MBR operating condition.

Potential impacts of nonalgal materials on water-leaving Sun induced chlorophyll fluorescence signals in coastal waters

It has been suggested that Sun induced chlorophyll fluorescence (SICF) signals could be used to estimate phytoplankton chlorophyll concentration and to investigate algal physiology from space. However, water-leaving SICF is also a product of the ambient light field. In coastal waters both algal and nonalgal materials affect the underwater light field. In this study we examine the independent impacts of varying loads of mineral suspended solids (MSS) and colored dissolved organic materials (CDOM) on water-leaving SICF signals using Hydrolight radiative transfer simulations. We show that SICF signals in coastal waters are strongly influenced by nonalgal materials. Increasing concentrations of CDOM and minerals can reduce the water-leaving SICF per unit chlorophyll by over 50% for the concentration ranges explored here (CDOM = 0 to 1 m(-1) at 440 nm, MSS=0 to 10 g m(-3)). The moderate-resolution imaging spectroradiometer (MODIS) fluorescence line height algorithm is shown to be relatively unaffected by increasing CDOM, but performance is significantly degraded by mineral concentrations greater than 5 g m(-3) owing to increased background radiance levels. The combination of these two effects means that caution is required for the interpretation of SICF signals from coastal waters.

Inverse Data Modelling for the Optical Properties of the Eutrophic Lake from Reflectance Spectra in Nanhu Lake of Changchun, China

In this study, we present an inverse data modelling for the optical properties of the eutrophic water from reflectance spectra in Nanhu Lake of Changchun, China. The lake water in Nanhu Lake is optically dominated by scattering from suspended matter, whereas the lake water is dominated by absorption from phytoplankton (CHLa), total suspended matter (TSM), and coloured dissolved organic matter (CDOM or referred to as yellow substance). The main reason is that the Nanhu Lake is highly affected by the input from rivers and drainage systems from the area of Changchun, which discharge a high concentration of CDOM, nutrients, and mineral suspended solids. The reflectance spectra at 400–900 nm were measured in Nanhu Lake using the ASD-field spectroradiometer. An inverse data modelling was applied to analyse the optical properties of the eutrophic lake water. The result shows that the optical properties of the eutrophical water can be effectively modelled from reflectance spectra for the eutrophic lake. However, further studies are still needed to refine the method for determining the optical properties of eutrophic waters under study.

Identification and characterisation of two optical water types in the Irish Sea from in situ inherent optical properties and seawater constituents

This paper examines relationships between the inherent optical properties (IOPs) of the Irish Sea and concentrations of optically significant constituents, measured as chlorophyll (Chl), mineral suspended solids (MSS) and coloured dissolved organic material (CDOM). In situ measurements of IOPs at 98 stations fell into two groups with distinct characteristics. Instances include the ratio of particulate backscattering to non-water absorption at 676 nm ( b bp676/ a n676), the ratio of the non-water absorption coefficients at 440 nm and 676 nm ( a n440/ a n676) and the ratio of particulate scattering to non-water absorption ( b p/ a n) at 676 nm. The two groups showed corresponding differences in the proportions of their constituent concentrations with Chl/MSS values typically above 0.4 mg g −1 for stations with b bp676/ a n676 < 0.33 and below 0.4 mg g −1 for stations with b bp676/ a n676 > 0.33. CDOM concentrations showed no significant differences between groups. The occurrence of correlated groups in the IOP and constituent concentration data indicates the existence of identifiable sub-types of coastal water within the conventional Case 2 classification whose optical characteristics were dominated either by phytoplankton or suspended minerals. By applying linear regression analysis to the two groups we derived effective material-specific IOPs for these natural particle assemblages. The coefficients obtained enabled the successful reconstruction of total absorption, scattering and backscattering coefficients for a given water body from measurements of Chl, MSS and CDOM. This procedure may be useful for assimilating measurements of seawater composition into bio-optical models in shelf seas.

Interpreting the colour of an estuary

This paper explores the possibility of using water colour to quantify the concentration of coloured dissolved organic matter (CDOM), and through it, dissolved organic carbon (DOC) and salinity in a turbid estuary in which suspended sediments also influence water colour. The motivation of the work is that the method could be applied to water colour measurements made remotely from an aircraft (or, in larger estuaries, a satellite) enabling near-synoptic mapping of surface salinity and DOC distributions. The paper describes observations at 29 stations distributed along the salinity gradient of the Conwy estuary in North Wales. At each station, surface water samples were collected and analysed for salinity, concentrations of DOC, chlorophyll and suspended particles and absorption spectra of CDOM, or yellow substance. Profiles were made of both upwelling and downwelling irradiance in four narrow band channels, and these were used to calculate irradiance reflection and attenuation coefficients. Results show that spectrally averaged light absorption in the estuary is caused principally and equally by mineral suspended solids and yellow substance, with water and chlorophyll in third and fourth place. The CDOM is strongly correlated ( R 2=0.99) in a negative sense with salinity, and more weakly correlated with DOC. There is a linear relationship between CDOM and the ratio of reflection coefficients in the red (670 nm) and blue-green (490 nm) parts of the spectrum, which could be applied to remote sensing; the slope and intercept of the relationship are however different to those found in less turbid water bodies. It is shown that the change in slope and intercept are consistent with the presence, in the Conwy estuary, of suspended particles which influence the water colour. A method is described and tested for inverting water colour measurements in a turbid estuary to give estimates of CDOM in the presence of suspended particles. The solution, which has not been adjusted to fit the data, produces profiles of CDOM, DOC and salinity, which behave reasonably but which currently have a limited accuracy. RMS differences between measured and optically derived parameters for the entire data set are 0.27 m −1 (CDOM), 4 PSU (salinity) and 67 μM (DOC) although better accuracy is obtained on individual surveys. The fact that there is little bias between predicted and observed parameters indicates that much of the scatter is caused by random measurement error and that the approach is fundamentally sound.

Turbidity in the southern Irish Sea

This paper presents new in situ optical and associated measurements from 85 stations in the central and southern Irish Sea. There is a strong linear relationship between the irradiance reflectance R A in the orange–red part of the spectrum (580–680 nm) and the diffuse attenuation coefficient, K, for white light: K=0.05+0.26 R A , where K is in m −1 and R A has been corrected to just above-surface reflectance and expressed as a percentage. The significance of this result is that this particular reflectance can be measured by the advanced very high resolution radiometer on board the NOAA series of satellites. In principle, therefore, cloud cover permitting, the transparency of the Irish Sea to sunlight, can be mapped from space. This result is shown to be consistent with a simple optical model in which light scattering is principally by mineral suspended solids, and light absorption is by water, mineral suspended solids and chlorophyll. Best fit between model and observations is achieved with a specific scattering coefficient of 0.5 m 2 g −1. The measurements were made during four cruises, at different times of year and across the range of turbidity found in the Irish Sea. The geographical distribution of suspended sediments confirms the presence, previously inferred from satellite imagery, of two separate turbidity maxima, one off Wicklow Head, the other off Anglesey. These correspond to the areas of strongest tidal currents. Yellow substance was found in highest concentration in a band along the Irish coast. Chlorophyll concentrations were generally low during these cruises. A residual problem is that a direct comparison of in situ reflectance and satellite measured reflectance possible on one of the cruises shows a serious discrepancy, although on average there appears to be a good agreement between satellite and in situ reflectance.

The distribution of fine suspended sediments in the surface waters of the Irish Sea and its relation to tidal stirring

A time series of 165 Advanced Very High Resolution Radiometer (AVHRR) visible band images covering the years 1982-1988 shows that the reflectance of the Irish Sea pulses on seasonal and spring-neap tidal time scales. The seasonal signal has been analysed by fitting a harmonic curve to a geographical grid of points. Maximum reflectance throughout the whole Irish Sea occurs in January or early February. The annual mean reflectance varies spatially by a factor of three from 0.8% to more than 2.4%. Seasonal amplitudes vary from 0.2% to 0.9%. A smaller, but still significant, cycle of reflectance occurs with the fortnightly springs-neaps cycle, with maximum reflectance occurring at spring tides. Both these cycles are in phase with the known variation of suspended sediments in the Irish Sea. Direct measurements, in situ and in the laboratory, of the inherent optical properties of sediments in the Irish Sea have been used to construct an algorithm relating AVHRR visible band reflectance RA to sediment concentration. The reflectance is most sensitive to changes in mineral suspended solids (mss) with phytoplankton pigments having a secondary effect and yellow substance hardly any at all. The algorithm is a saturating curve: initially RA increases in proportion to mss, but at high mss concentrations RA tends to an asymptotic value of 3.5%. The algorithm has been used to produce mean winter and summer maps of mss in the Irish Sea. Concentrations in winter are greater than those in summer (by a factor of 2.7 for the Irish Sea as a whole), but the spatial pattern is similar. Highest sediment concentrations occur in the shallow eastern Irish Sea and also in the regions of strongest tidal currents. The relationship between suspended sediment concentration and tidal stirring is explored using a simple energy model. Equating the potential energy of the sediment in suspension to the turbulent kinetic energy available from the tide suggests a linear relationship between the concentration of mss and the tidal power density. It is found that there is a significant relationship between these quantities in the water depth range 40 to 80m.

Absorption spectra of inorganic particles in the Irish Sea and their relevance to remote sensing of chlorophyll

Abstract Mineral suspended solids contribute significantly to the total suspended sediment load in shelf seas and estuaries. Even in moderate concentrations, mineral suspended solids affect algorithms for retrieving chlorophyll concentrations from remotely-sensed colour data. Brown and Simpson (1990) showed empirically that the slope of a log-log graph of chlorophyll against the blue-green reflectance ratio increased as the concentration of mineral suspended solids increased. In an attempt to explain this, we have measured the absorption spectrum of over 100 samples of mineral suspended solids collected from the Menai Strait in the Irish Sea. The absorption spectra of the mineral suspended solids particles on filters consistently show an exponential decrease with increasing wavelength across the visible spectrum. The absorption coefficient at a single wavelength is proportional to the concentration of mineral suspended solids. This spectrum has been incorporated into a simple model of the blue-green ratio in the presence of both chlorophyll and mineral suspended solids. The results are in qualitative agreement with Brown and Simpson's observations and can be made to be in quantitative agreement by correcting the absorption of mineral suspended solids on filters to in situ absorption using a pathlength correction factor β = 4. The main effect of mineral suspended solids is to decrease the sensitivity of the blue-green ratio to changes in chlorophyll in shelf seas and we conclude that the blue-green ratio may not be the best remote sensing tool for measuring chlorophyll in case 2 waters.

Modeling spectral diffuse attenuation, absorption, and scattering coefficients in a turbid estuary

Spectral diffuse attenuation coefficients were measured in the Rhode River and Chesapeake Bay, Maryland, on 28 occasions in 1988 and 1989. The model of Kirk was used to extract scattering and absorption coefficients from the measurements in waters considerably more turbid than those in which the model was previously applied. Estimated scattering coefficients were linearly related to mineral suspended solids. Estimates of total absorption coefficients were decomposed as the sum of contributions by water, dissolved organic matter, phytoplankton chlorophyll, and particulate detritus, each having a characteristic spectral shape. The 1988 data were used to develop a model of scattering and absorption coefficients based on the specific curves regressed against water‐quality parameters. Diffuse attenuation coefficients in the 1989 data ranging from 1 to 10 m−1 and photic depths ranging from &lt;1 to 4.5 m were predicted with a C.V. of about 25%.The problem of estimating concentrations of water‐quality constituents from optical measurements was indeterminate due to the similarity in shape of the specific curves of dissolved substances and depigmented particulates. Chlorophyll concentration could be estimated because it was strongly related to water‐corrected absorption in the 670‐nm waveband, but several outliers occurred due to biological variability in specific absorption of pigments.

Ultrafiltration for oily degreasing baths in electroplating surface treatment regeneration par ultrafiltration des bains de degraissage chimique dans une chaine de traitements de surface

Abstract The process of ultrafiltration plant used for remove dissolved and emulsifield oil of degreasing baths in Legrand electroplating surface treatments is discribed. In this way the bath life utilization is prolonged from 80 to 400 hours. Sequential batch operation is automaticaly programmed. Ultrafiltration membrane are of tubular configuration with polysulfone polymer which is resistant in the 2–13 pH range and thermally stable up to 60°C. The molecular cutoff is around 20,000: the concentrate stream is enriched up to 30% by weight by mineral oil and suspended solids are also removed. The permeate contained less than 80 mg.l‐1 amount of oil. Operating cost 500 000 F (1986) will be compensed on 2 years.