An algorithm to retrieve chlorophyll,dissolved organic carbon,and suspended minerals from Great Lakes satellite data

An algorithm that utilizes individual lake hydro-optical (HO) models has been developed for the Great Lakes that uses SeaWiFS, MODIS, or MERIS satellite data to estimate concentrations of chlorophyll, dissolved organic carbon, and suspended minerals. The Color Producing Agent Algorithm (CPA-A) uses a specific HO model for each lake. The HO models provide absorption functions for the Color Producing Agents (CPAs) (chlorophyll (chl), colored dissolved organic matter (as dissolved organic carbon, doc), and suspended minerals (sm)) as well as backscatter for the chlorophyll, and suspended mineral parameters. These models were generated using simultaneous optical data collected with in situ measurements of CPAs collected during research cruises in the Great Lakes using regression analysis as well as using specific absorption and backscatter coefficients at specific chl, doc, and sm concentrations. A single average HO model for the Great Lakes was found to generate insufficiently accurate concentrations for Lakes Michigan, Erie, Superior and Huron. These new individual lake retrievals were evaluated with respect to EPA in situ field observations, as well as compared to the widely used OC3 MODIS retrieval. The new algorithm retrievals provided slightly more accurate chl values for Lakes Michigan, Superior, Huron, and Ontario than those obtained using the OC3 approach as well as providing additional concentration information on doc and sm. The CPA-A chl retrieval for Lake Erie is quite robust, producing reliable chl values in the reported EPA concentration ranges. Atmospheric correction approaches were also evaluated in this study.     

Some Notes on Water Color in Keweenaw Bay (Lake Superior)

Spectral subsurface irradiance reflectance—intrinsic water color—was derived from above-water radiance measurements using a hand-held spectroradiometer along a transect on Keweenaw Bay, Lake Superior. The reflectance spectra were typical of oligotrophic lacustrine waters. The reflectance peak wavelength shifted from 484 nm at stations farthest offshore to 540 nm near the head of the bay. This change coincided with a decrease in Secchi-disk depth from 16 to 8 m, and an increase in concentrations of chlorophyll a and total suspended matter from about 0.45 to 0.60 mg m⁻³ and from 0.3 to 0.5 g m⁻³, respectively. The concentration of chromophoric dissolved organic matter (gilvin), expressed as the absorption of filtrate at 440 nm, varied between 0.11 and 0.2 m⁻¹. Like almost all inland waters, Keweenaw Bay should be classified as a Case 2 water due to the concentrations of gilvin and inanimate particles relative to plankton biomass. A model for chlorophyll-a estimation from spectral reflectance that adequately predicted concentrations in mesotrophic to highly eutrophic Case 2 waters elsewhere gave negative values when applied to the Keweenaw Bay transect. Evidently, there is a need of algorithm development for oligotrophic lacustrine waters. Estimates improved using a modified blue to green band ratio algorithm previously applied for remote sensing of oceanic waters. In optimization of semi-empirical algorithms for estimation of plankton biomass in Lake Superior, absorption by gilvin as well as by inanimate particles merits special consideration.     

Verification and Application of a Bio-optical Algorithm for Lake Michigan Using SeaWiFS: a 7-year Inter-annual Analysis

In this paper we utilize 7 years of SeaWiFS satellite data to obtain seasonal and interannual time histories of the major water color-producing agents (CPAs), phytoplankton chlorophyll (chl), dissolved organic carbon (doc), and suspended minerals (sm) for Lake Michigan. We first present validation of the Great Lakes specific algorithm followed by correlations of the CPAs with coincident environmental observations. Special attention is paid to the satellite observations of the extensive episodic event of sediment resuspension and calcium carbonate precipitation out of the water. We then compare the obtained time history of the CPA's spatial and temporal distributions throughout the lake to environmental observations such as air and water temperature, wind speed and direction, significant wave height, atmospheric precipitation, river runoff, and cloud and lake ice cover. Variability of the onset, duration, and spatial extent of both episodic events and seasonal phenomena are documented from the SeaWiFS time series data, and high correlations with relevant environmental driving factors are established. The relationships between the CPAs retrieved from satellite data and environmental observations are then used to speculate on the future of Lake Michigan under a set of climate change scenarios.     

Chromaticity analysis of the Chilika lagoon for total suspended sediment estimation using RESOURCESAT-1 AWiFS data — A case study

The chromaticity analysis of the Chilika lagoon has been attempted using RESOURCESAT-1 AWiFS data (10-bit radiometric resolution) of 26 November 2003. The total suspended sediment (TSS) concentration of surface waters of the lagoon was analyzed using a satellite-based chromaticity technique. The chromaticity coordinates of the entire lagoon were computed. As the lagoon is rich in biodiversity, five chromatically different regions have been identified based on different reflectance signatures. The technique is validated using the ground-truth data of high turbid water, low turbid water, aquatic vegetation, short grasses, and shallow turbid water. Different features clearly separate out on a chromaticity plot. The x-coordinate of the chromaticity shows better correlation with TSS in comparison to y-coordinate of chromaticity. The proposed approach is valuable for a quick estimate of TSS, an important geophysical parameter, which accounts for the water quality of the lagoon. The technique can be applied to compute the moderate TSS (e.g. up to 42 g m^− 3) in a lagoon or any inland water body given the chromaticity image.     

基于感官色度的含沙水体景观质量定量评价方法研究

水体景观质量评价是构成环境影响评价体系的重要部分。目前对水体景观质量中水体颜色的评价主要以定性评价为主,而传统的可定量评价水体颜色的指标色度并不适用于工程含沙水体。为此,本文提出了可用于含沙水体景观颜色定量评价的感官色度概念,定义水体感官色度为由水体中溶解物质和非溶解物质共同作用导致的肉眼直接观测到的水体颜色。通过分光光度法实验,确定了有色含沙水体感官色度测量的特征波长为350 nm,同时通过测量不同色度及浊度混合水体在特征波长下的吸光度发现,感官色度标准值与样品的吸光度呈良好的线性关系,并且与肉眼观测结果相符,表明本文定义的水体感官色度可以得到较准确的定量表征并且能够真实反映肉眼观测情况。据此建立了基于水质分析的感官色度评价方法。同时,通过对高含沙水体以及紫坪铺库区实际天然水体感官色度的测量,证明了感官色度评价方法应用于工程含沙水体景观质量定量评价的合理性和可行性。     

Temporal changes in the remote sensing reflectance at Lake Vänern

The Aerosol Robotic Network - Ocean Color (AERONET-OC) instrument located at the Pålgrunden site in Lake Vänern provides values of remote sensing spectral reflectance R_RS(λ) since 2008. These in situ R_RS(λ) indicated a temporal increase from 2015 at center-wavelengths in the green and red spectral regions. To investigate the environmental and climate processes responsible for this increase, water color trends in Lake Vänern were analyzed considering in situ limnological measurements, meteo-climatic quantities and additionally satellite-derived data products from the Moderate Resolution Imaging Spectroradiometer on board the Aqua platform (MODIS-A). Satellite ocean color R_RS(λ) data assessed against in situ R_RS(λ) from the Pålgrunden site showed satisfactory agreement at a number of spectral bands. Relying on these validation results, comprehensive statistical analysis were performed using MODIS-A R_RS(λ). These indicated periodical changes between 2002 and 2021 with clear minima occurring between 2010 and 2013. The complementary analyses of temporal changes characterizing limological and meteo-climatic quantities, and also relationships between these quantities and R_RS(λ), indicated the existence of complex and concurrent bio-geochemical processes influencing water color in Lake Vänern. In particular, significant correlations were observed between R_RS(λ) and turbidity, and also between R_RS(λ) and total biovolume. Additionally, an early warming of Lake Vänern surface waters was identified since spring 2014. This occurrence could potentially affect the vertical mixing and water exchange between turbid coastal and pelagic waters with implications for phytoplankton phenology.     

Surface Corrections for Remote Sensing Reflectance in Case 2 Waters of Lake Superior

We establish the average wavelength dependence for rough-surface reflectance S_rs(λ) in Lake Superior and determine its magnitude at any individual site by extrapolating the total reflectance or raw remote sensing reflectance R_rsT(λ) measured at the surface to the asymptotic limit of zero scattering where S_rs(λ) ≅ R_rsT(λ). The results show that S_rs(λ) differs from the flat-surface Fresnel reflectance of sky radiance used in standard determination of the remote sensing reflectance R_rs(λ) attributed to the scattering of light by particles and molecules in bulk water. In waters containing colored dissolved organic matter (CDOM), R_rs(λ) can be very low and radiometric measurements at ground level can often lead to negative estimates of R_rs(λ) if we assume simple mirror-like reflectance of the sky radiance as the basis for correcting radiometric data for surface reflectance. We examine the differences between Fresnel reflectance and S_rs(λ) and estimate the ratio of the concentrations of CDOM versus suspended particles that could produce negative values of R_rs(λ) if assume Fresnel reflectance in calculation of R_rs(λ).     

Sensitivity of remotely sensed pigment concentration via Mixture Density Networks (MDNs) to uncertainties from atmospheric correction

Lake Erie, the shallowest of the five North American Laurentian Great Lakes, exhibits degraded water quality associated with recurrent phytoplankton blooms. Optical remote sensing of these optically complex inland waters is challenging due to the uncertainties stemming from atmospheric correction (AC) procedures. In this study, the accuracy of remote sensing reflectance (R_rs) derived from three different AC algorithms applied to Ocean and Land Colour Instrument (OLCI) observations of western Lake Erie (WLE) is evaluated through comparison to a regional radiometric dataset. The effects of uncertainties in R_rs products on the retrieval of near-surface concentration of pigments, including chlorophyll-a (Chla) and phycocyanin (PC), from Mixture Density Networks (MDNs) are subsequently investigated. Results show that iCOR contained the fewest number of processed (unflagged) days per pixel, compared to ACOLITE and POLYMER, for parts of the lake. Limiting results to the matchup dataset in common between the three AC algorithms shows that iCOR and ACOLITE performed closely at 665 nm, while outperforming POLYMER, with the Median Symmetric Accuracy (MdSA) of ∼30 %, 28 %, and 53 %, respectively. MDN applied to iCOR- and ACOLITE-corrected data (MdSA < 37 %) outperformed MDN applied to POLYMER-corrected data in estimating Chla. Large uncertainties in satellite-derived R_rs propagated to uncertainties ∼100 % in PC estimates, although the model was able to recover concentrations along the 1:1 line. Despite the need for improvements in its cloud-masking scheme, we conclude that iCOR combined with MDNs produces adequate OLCI pigment products for studying and monitoring Chla across WLE.     

Membrane Process Design for the Reduction of Wastewater Color of the Mazandaran Pulp-Paper Industry, Iran

The aim of this study is evaluate the use of membrane bioreactor for wastewater treatment Mazandaran pulp and paper Industry. The qualification of wastewater is case study and Characteristics of this industry wastewater were determined by different experiments such as: COD, BOD, Color, densitometry, viscometry and TG/DTA analyzer. Also, the color creating agents in the investigated wastewater was characterized. Then In this study, flux, retention, and permeate quality of various Nanofiltration and low-pressure reverse osmosis membranes were investigated at two temperatures and by using a low shear (DSS Labstak M20®) and a high shear (CR250/2) filter. The overall aim was to study the suitability of Nanofiltration in purification of the discharge water from external activated sludge processes in the pulp and paper industry for reuse in the paper manufacturing process and to compare the results to Nanofiltration of paper machine process waters. The discharge waters were nanofiltered at a higher flux than paper machine process waters. The permeate was almost free of color and organic compounds but contained significantly more inorganic compounds than the permeate from the filtration of process waters. To successfully remove monovalent anions and inorganic carbon from the discharge water a low-pressure reverse osmosis membrane such as the TFC ULP membrane is needed. With that membrane the permeate flux is lower than for Nanofiltration membranes but the permeate quality is significantly better when considering inorganic ions such as sodium, chloride, nitrate and inorganic carbon (bicarbonate). The permeate flux was two times higher in the high shear filter than in the low shear filter but the retentions were significantly lower. The result of this study: decrease pollutants parameter in Tajan Rivers that is effluent because attention to surface water quality has limited in Iran.     

Water quality trends in Hamilton Harbour: Two decades of change in nutrients and chlorophyll a

Systematic water quality research and monitoring has been on-going in Hamilton Harbour since 1987 in response to the Remedial Action Plan (RAP) for this Area of Concern (AOC). Here we present a spatio-temporal analysis of water quality in the harbour and its biological response from 1987 to 2007. Overall nutrient concentrations have decreased by 16 (SRP), 26 (NH_3-Tot) and 36% (TP) in the harbour, chl a concentrations have decreased by 16% and NO_3/2 concentrations have increased by 27%. Hypoxia in the hypolimnion of Hamilton Harbour remains a common occurrence despite improvements in surface water quality conditions. Seasonal patterns in water quality in Hamilton Harbour are mainly driven by biological activity and show typical patterns observed in dimictic nutrient rich lakes. There is systematic spatial variability in water quality in the harbour which is related to the proximity of point and non-point sources; however, there is coherence among all stations sampled and similar temporal trends were observed for all stations. The biological response in the harbour suggests that phosphorus limited algal growth is becoming more prevalent in Hamilton Harbour and the rate of improvements in water quality should accelerate in the near future following further reductions in phosphorus loadings.     

A Comparison of Total Phosphorus,Chlorophyll a,and Zooplankton in Embayment,Nearshore, and Offshore Habitats of Lake Ontario

Lower trophic levels were compared in embayment, nearshore, and offshore habitats of Lake Ontario, 1995 to 1997, in the context of oligotrophication and invasion of dreissenid mussels. Total phosphorus (TP), chlorophyll a (chl a), Secchi disk depth, temperature, and zooplankton were measured to spatially and temporally contrast these habitats and to test for recently hypothesized “decoupling” of chl a from TP (lower than predicted chl a per unit TP, consistent with dreissenid mussel grazing). The embayment habitat had higher concentrations of TP and chl a, greater volumetric zooplankton density and biomass, and higher springtime water temperatures than both nearshore and offshore habitats, while overall areal zooplankton biomass was highest in the offshore. Furthermore, concentrations of TP and volumetric zooplankton density in nearshore habitats are now more similar to the offshore pelagia than they were three decades ago. Finally, a lower yield of chl a per unit TP was found in nearshore habitat compared to offshore and embayment habitats. The current lower yield of chl a per unit TP in nearshore habitat can be attributed more to Dreissena than to erosion and/or resuspension of sediments.     

Validation of 2015 Lake Erie MODIS image spectral decomposition using visible derivative spectroscopy and field campaign data

Timely identification of color-producing agents (CPAs) in Lake Erie is a challenging, but vital aspect of monitoring harmful algal blooms (HABs). In particular, HABs that include large amounts of cyanobacteria (CyanoHABs) can be toxic to humans, posing a threat to drinking water, in addition to recreational and economic use of Lake Erie. The optical signal of Lake Erie is complex (Becker et al., 2009; Moore et al., 2017), typically comprised of phytoplankton, cyanobacteria, colored dissolved organic matter (CDOM), detritus, and terrigenous inorganic particles, varying in composition both spatially and temporally. The Kent State University (KSU) spectral decomposition method effectively partitions CPAs using a varimax-rotated, principal component analysis (VPCA) of visible reflectance spectra measured using lab, field or satellite instruments (Ali et al., 2013; Ortiz et al., 2017, 2013). We analyze 2015 imagery acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor and field samples collected during the early 2015 cyanoHAB season. We identified four primary CPA spectral signatures, and the spatial distribution of each identified CPA, in the reflectance spectra datasets of both the MODIS and lab-measured water samples. The KSU spectral decomposition method results in mixtures of specific pigments, pigment degradation products, and minerals that describe the optically complex water. We found very good agreement between the KSU VPCA spectral decomposition results and in situ measurements, indicating that this method may be a powerful tool for rapid CyanoHAB monitoring and assessment in large lakes using instruments that provide moderate resolution imagery (0.3 to 1 km²).     

基于主波长水色参数的水库采砂遥感监测

利用遥感技术监测河道采砂行为,通常根据经验阈值划分水体悬浮物浓度高值区为采砂嫌疑区。针对分割阈值受大气纠正及悬浮物浓度反演模型精度限制难以自动客观确定的问题,提出了基于主波长水色参数自动识别异常浑浊水体的方法。采用Landsat8、Sentinel-2卫星图像数据,基于CIE-XYZ颜色系统,提取红、绿、蓝三波段遥感图像主波长水色参数,结合自然断点分类法将指示悬浮物浓度的主波长水色参数自动划分高、中、低3类,识别高值区为采砂嫌疑区。应用该方法研究浑浊水体时空分布,识别了2016—2017年广东鹤地水库九洲江、化州库湾水域的采砂现象,以及2019年11月—2020年4月广东枫树坝水库寻邬水水域的采砂现象。试验证明,方法具有抗大气干扰性强、自动性高、稳定可靠、适用于多源遥感图像的优势,可为传统人工巡查监管提供及时、有效的采砂嫌疑区时空分布信息,提升常态化采砂监管的能力。     

Optical scattering properties of organic-rich and inorganic-rich particles in inland waters

We present the results from a study of the particulate scattering properties of three bodies of water that represent a wide range of optical properties found in inland waters. We found a positive linear relationship (R² = 0.45, P < 0.005) between the mass-specific scattering coefficient at 532 nm (b_p*(532)) and the ratio of the inorganic suspended material (ISM) to the total suspended material (TSM) in our study areas. In contrast to earlier studies in which b_p*(532) was lower for inorganic particles than for organic particles, we found that the value of b_p*(532) for ISM (b_p*(532)_ISM = 0.71 m²/g) was approximately 1.6 times greater than the value found for organic suspended materials (OSM) (b_p*(532)_OSM = 0.45 m²/g). We found that the dependence of the particle scattering coefficient (b_p) on wavelength (λ) could be described accurately by a power law (with mean average percent error (MAPE) < 0.07) in waters dominated by inorganic particles. The model errors in waters dominated by organic particles, however, were much larger (MAPE > 0.1), especially in the spectral region associated with strong phytoplankton absorption. The errors could be reduced over this wavelength range by adding a term to the model to account for particle absorption, but the additional term tended to increase the error outside of this range. We conclude that information about the nature of the scattering particles in lake waters is necessary for the selection of an appropriate model for particle absorption and that a hybrid model that includes absorption over some wavelength ranges may be necessary.     

Identifying and classifying Great Lakes ship transits using a state machine approach

Invasive, aquatic organisms have entered the North America Great Lakes from ships' ballast water, often originating from Europe. Current approaches for preventing the introduction of such organisms in ballast water include ballast water treatment (BWT) or ballast water exchange (BWE). This paper examines BWE, which is conducted in (1) waters >200 nautical miles (nm) from shore, or (2) waters >50?nm from shore and >200?m deep. We used historical records of ships transiting from Europe to the Great Lakes during one year (2014) to determine the duration (in days) that ships were within waters that met the criteria for BWE. Ship paths were classified based upon transitions between location-assigned “states” (e.g., from European waters across the North Atlantic Ocean to North America), and from these state transitions, four types of routes were identified. On average, ships sailing these routes had between 3.5 and 4.7 d to perform BWE in areas >200?nm from shore and 4.7 to 6.2 d when >50?nm from shore and >200-m deep water. Conducting BWE in daylight hours, if deemed necessary for safety, shortened the time window for BWE, especially in winter months, by approximately 50–70%. The state “machine” approach could, in the future, be used to identify ships from specific regions (e.g., ports within waterways at high risk of harboring potentially invasive species). Reshaping the definition of regional boundaries based upon time-of-year, water temperature, or other variables would further refine the ability to identify high-risk transits.     

Coagulation and sedimentation in lakes,reservoirs and water treatment plants

Coagulation and sedimentation occur naturally in all lakes and reservoirs and, by design, in water treatment plants using surface supplies. Important factors that affect water quality in lakes and reservoirs include nutrient loading, areal hydraulic loading, and detention time together with the concentrations of land-derived Z(pedogenic) natural organic matter and hardness in waters entering the lake or reservoir. These, in turn, have important effects on the design and operation of potable water treatment systems. It is difficult and expensive to use the good physics to compensate for poor chemistry in water treatment plant design. There are many interesting and useful similarities among the physical and chemical characteristics of lakes, reservoirs, and water treatment plants.     

Light-absorbing components in the Great Lakes

Features of light absorption are critical in regulating the optical signal available for remote sensing. The magnitudes, spectral characteristics, spatial patterns, and, to a lesser extent, dynamics of light-absorbing components are documented for the Laurentian Great Lakes. This includes the open waters of each of the five lakes, and selected rivers, embayments and near-shore areas. The absorption coefficient, a(m^? 1), is partitioned according to the additive components (a_x) of colored dissolved organic matter (a_CDOM), non-algal particles (a_NAP), phytoplankton (a_φ), and water itself (a_w; known). Dependencies of a_x on various metrics of optically active constituents (OACs), cross-sections, are evaluated. A wide range of magnitudes of a_x and a, and contributions of a_x to a are documented. For example, the magnitude of a at a wavelength of 440 nm was nearly 10-fold greater in the western basin of Lake Erie than in the open waters of Lake Huron. Rivers, embayments, and near-shore areas generally had higher levels than the open waters. The largest a_x throughout the system was a_CDOM, originating mostly from terrestrial sources. Most of a_NAP was associated with clay mineral particles. The distribution of a_φ was highly correlated to chlorophyll concentration. The collected data set is appropriate to support initiatives to develop and preliminarily test mechanistic retrieval algorithms for OACs in the Great Lakes.     

Impact of Stratospheric Ozone Depletion on Photoproduction of Hydrogen Peroxide in Lake Ontario

Using a solar spectral irradiance model, the clear-sky ground-level ultraviolet irradiance spectra over Lake Ontario on the vernal/autumnal equinox and the summer solstice were calculated for two concentrations of stratospheric ozone. Using these UV spectra in conjunction with apparent spectral quantum yield values appropriate for UV-generated hydrogen peroxide from all aquatic photoreactions, the total photoproduction of H₂O₂ in Lake Ontario was estimated for clear sky conditions. It was determined that for a dramatic reduction of 37.5% in stratospheric ozone concentration, a) total photoproduction of H₂O₂ in Lake Ontario would only increase by 3.5%, b) spectral photoproduction of H₂O₂ dramatically increases by over a factor of 200 at 290 nm falling to about a factor of 6 at 300 nm, c) the enhanced ground-level UV-B radiation results in a 33% increase in its contribution to the total photoproduction of H₂O₂ in Lake Ontario, and d) although the increased UV-B irradiance is the primary energy source for increased formation of H₂O₂, the essentially non-impacted UV-A irradiance remains the dominant factor in the total formation of H₂O₂. Therefore, current reductions in stratospheric ozone concentrations will have minimal effect on the photoproduction of H₂O₂ in Lake Ontario.     

Priority organic pollutants in the urban water cycle (Toulouse, France)

Application of the European Water Framework Directive requires Member States to have better understanding of the quality of surface waters in order to improve knowledge of priority pollutants. Xenobiotics in urban receiving waters are an emerging concern. This study proposes a screening campaign of nine molecular species of xenobiotics in a separated sewer system. Five sites were investigated over one year in Toulouse (France) using quantitative monitoring. For each sample, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, nonylphenols, diethelhexylphthalate, linear alkylbenzene sulphonates, methyl tert-butylether, total hydrocarbons, estradiol and ethinylestradiol were analysed. Ground, rain and roof collected water concentrations are similar to treated wastewater levels. Run-off water was the most polluted of the five types investigated, discharged into the aquatic environment. The wastewater treatment plant reduced xenobiotic concentrations by 66% before discharge into the environment. Regarding environmental quality standards, observed concentrations in waters were in compliance with standards. The results show that xenobiotic concentrations are variable over time and space in all urban water compartments.