Non-algal Particles Research Articles

Abiotic control of underwater light in a drinking water reservoir: Photon budget analysis and implications for water quality monitoring

AbstractIn optically complex inland waters, the underwater attenuation of photosynthetically active radiation (PAR) is controlled by a variable combination of absorption and scattering components of the lake or river water. Here we applied a photon budget approach to identify the main optical components affecting PAR attenuation in Lake St. Charles, a drinking water reservoir for Québec City, Canada. This analysis showed the dominant role of colored dissolved organic matter (CDOM) absorption (average of 44% of total absorption during the sampling period), but with large changes over depth in the absolute and relative contribution of the individual absorption components (water, nonalgal particulates, phytoplankton and CDOM) to PAR attenuation. This pronounced vertical variation occurred because of the large spectral changes in the light field with depth, and it strongly affected the average in situ diffuse absorption coefficients in the water column. For example, the diffuse absorption coefficient for pure‐water in the ambient light field was 10‐fold higher than the value previously measured in the blue open ocean and erroneously applied to lakes and coastal waters. Photon absorption budget calculations for a range of limnological conditions confirmed that phytoplankton had little direct influence on underwater light, even at chlorophyll a values above those observed during harmful algal blooms in the lake. These results imply that traditional measures of water quality such as Secchi depth and radiometric transparency do not provide a meaningful estimate of the biological state of the water column in CDOM‐colored lakes and reservoirs.

Inferring inherent optical properties and water constituent profiles from apparent optical properties.

The BP09 experiment conducted by the Centre for Maritime Research and Experimentation in the Ligurian Sea in March 2009 provided paired vertical profiles of nadir-viewing radiances L(u)(z) and downward irradiances E(d)(z) and inherent optical properties (IOPs, absorption, scattering and backscattering coefficients). An inversion algorithm was implemented to retrieve IOPs from apparent optical properties (AOPs, radiance reflectance R(L), irradiance reflectance R(E) and diffuse attenuation coefficient K(d)) derived from the radiometric measurements. Then another inversion algorithm was developed to infer vertical profiles of water constituent concentrations, including chlorophyll-a concentration, non-algal particle concentration, and colored dissolved organic matter from the retrieved IOPs based on a bio-optical model. The algorithm was tested on a synthetic dataset and found to give reliable results with an accuracy better than 1%. When the algorithm was applied to the BP09 dataset it was found that good retrievals of IOPs could be obtained for sufficiently deep waters, i.e. for L(u)(z) and E(d)(z) measurements conducted to depths of 50 m or more. This requirement needs to be satisfied in order to obtain a good estimation of the backscattering coefficient. For such radiometric measurements a correlation of 0.88, 0.96 and 0.93 was found between retrieved and measured absorption, scattering and backscattering coefficients, respectively. A comparison between water constituent values derived from the measured IOPs and in-situ measured values, yielded a correlation of 0.80, 0.78, and 0.73 for chlorophyll-a concentration, non-algal particle concentration, and absorption coefficient of colored dissolved organic matter at 443 nm, respectively. This comparison indicates that adjustments to the bio-optical model are needed in order to obtain a better match between inferred and measured water constituent values in the Ligurian Sea using the methodology developed in this paper.

Impact of phytoplankton size and physiology on particulate optical properties determined with scanning flow cytometry

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 531:43-61 (2015) - DOI: https://doi.org/10.3354/meps11325 Impact of phytoplankton size and physiology on particulate optical properties determined with scanning flow cytometry Malcolm N. McFarland*, Jan Rines, James Sullivan, Percy Donaghay University of Rhode Island, Graduate School of Oceanography, 215 South Ferry Road, Narragansett, RI 02882, USA *Corresponding author: malcolm@my.uri.edu ABSTRACT: Layers and patches of phytoplankton at sub-meter scales in the vertical dimension and kilometer scales in horizontal dimensions are common features in the coastal ocean. These heterogeneous distributions of cells are fundamental to their population dynamics and the function of pelagic ecosystems. To better understand biological processes at these small scales, methods were developed to assess phytoplankton community composition and physiological characteristics based on high-resolution, in situ optical measurements. Scanning flow cytometry of discrete samples was used to determine the effects of phytoplankton and non-algal particle abundance, size, and pigment content on the spectral shape and relative magnitude of particulate attenuation, absorption, scatter, and backscatter coefficients. The slope of particulate attenuation varied with phytoplankton size and morphology, the slope of particulate absorption and the ratio of scatter to absorption varied primarily with cellular pigment content, and the backscatter ratio varied primarily with the relative abundance of non-algal particles. Determination of particle and phytoplankton characteristics from optical measurements over small spatial and temporal scales was tested with 2 independent high-resolution data sets collected from an in situ autonomous profiling system. Comparison of these high-resolution optical data with flow cytometric sample analyses generally agreed with the previously determined relationships but suggest that complex morphology of large colonial diatoms may result in higher than expected particulate attenuation slopes. High-resolution data revealed variations in community size structure and physiology that would be difficult to visualize with discrete samples or measures of total chlorophyll concentration. KEY WORDS: Phytoplankton composition · Optical properties · Flow cytometry · Small scale Full text in pdf format PreviousNextCite this article as: McFarland MN, Rines J, Sullivan J, Donaghay P (2015) Impact of phytoplankton size and physiology on particulate optical properties determined with scanning flow cytometry. Mar Ecol Prog Ser 531:43-61. https://doi.org/10.3354/meps11325 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 531. Online publication date: July 02, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Iron as a source of color in river waters

Organic chromophores of total organic carbon (TOC) and those of iron (Fe) contribute to the color of water, but the relative contributions of colored organic carbon (COC%) and Fe (Fe%) are poorly known. In this study, we unraveled Fe% and COC% in 6128 unfiltered water samples collected from 94 Finnish river sites of contrasting catchment properties. According to regression analysis focusing on TOC alone, on average 84% of the mean TOC consisted of COC, while 16% was non-colored or below the color-detection limit. COC and Fe were much more important sources of color than phytoplankton (chlorophyll a as a proxy) or non-algal particles (suspended solids as a proxy). When COC and Fe were considered as the only two sources of color, COC% ranged from 16.8% to 99.5% (mean 71%) and Fe% from 0.5% to 83.2% (mean 29%). Similar Fe% and COC% values were obtained when color was estimated from the absorption coefficients of COC and Fe at 490nm. Fe% increased as a function of the concentration of Fe and was well predicted by the TOC-to-Fe mass ratio. In 608 samples with TOC-to-Fe ratios of <4.5, Fe dominated the color. TOC-to-Fe ratios varied widely within most sites, but in relation to hydrology. In catchments with a peatland coverage of >30%, peak flow exported elevated amounts of TOC relative to Fe and resulted in a high COC%. Base flow, instead, mobilized elevated amounts Fe relative to TOC and resulted in a high Fe%. In a catchment covered with 31% of agricultural fields, peak flow transported eroded soil particles high in Fe and thus resulted in a high Fe%, while during base flow the water was high in COC%. This study demonstrated that Fe% and COC% vary widely in river water depending on the catchment properties and hydrology.

Brazilian inland water bio-optical dataset to support carbon budget studies in reservoirs as well as anthropogenic impacts in Amazon floodplain lakes: Preliminary results

Abstract. This work presents ongoing efforts and preliminary results for building a dataset that represents the first and most comprehensive bio-optical information available on Brazilian inland waters to support the development of remote sensing algorithms for monitoring aquatic systems. From 2012 to 2014 optical and limnological data was gathered along thirteen field campaigns in five Brazilian reservoirs, in an irrigation and domestic water supply reservoir located in semi-arid northeast of the country and in Amazonian floodplain lakes, thus covering the diversity of Brazilian inland waters. At each site 20 stations, on average, were sampled to acquire profiles of the following optical variables: absorption, attenuation, scattering, and backscattering coefficients and radiances/irradiances spectra above and in-water. Alongside these measurements, water samples were collected for determining concentrations of chlorophyll-a (Chl-a), Total Suspended Solid (TSS), Total Dissolved Carbon (TDC) and its organic/inorganic fractions, CDOM absorption, phytoplankton specific absorption [aph*] and Non-Algal Particles absorption [aNAP*]. Preliminary results show that Chl-a concentrations ranged from 0.6 to 243μg/L in reservoirs and 0.90 to 92μg/L in Amazonian lakes, while TSS concentrations ranged from 0.3 to 31mg/L in reservoirs and 0.5 to 162mg/L in Amazonian lakes. In situ beam attenuation coefficients ranged from 1.4 to 16m-1 in reservoirs and 12.5 to 38m-1 in Amazonian lakes, while diffuse attenuation coefficients of downwelling irradiance over the Photosynthetically Active Radiation (Kd(PAR)) extended from 0.35 to 4.5m-1 in reservoirs and 1.69 to 13.30m-1 in Amazonian lakes. Our research group is building this dataset anticipating future demands for algorithm validation regarding OLI/Landsat8 data and ESA Sentinel missions to be launched as of 2015.

Issues and Potential Improvement of Multiband Models for Remotely Estimating Chlorophyll-a in Complex Inland Waters

Remote estimation of chlorophyll-a (chl-a) in complex freshwaters remains a challenging problem due to the rapid spatial variability and wide range as influenced by terrestrial constituents. A controversial issue is whether or not 2-B models possess sufficient wavelength information for accurately estimating Chl-a concentrations from remote sensing data for freshwater environments. This study introduced a systemic approach and proved that adding additional wavelength information to 2-B model could not significantly improve the estimation of freshwater chl-a, but acted to increase model uncertainty. This convincing solution was based on a large synthetic data set (38 937 samples) combined with a set of in situ data (51 samples) collected in three cruises in Lake Huron. The synthetic data set has two distinct features: 1) large data items and 2) covers a broad range of chl-a ( ${\bf 0 - 1000}\;{\bf {mg}}/{{\bf m}^{\bf 3}}$ ), colored dissolved organic matter (CDOM) ( ${\bf 0 - 50}\;{\bf m}^{\bf - 1}$ ), and NAP (nonalgal particles) (0–500 mg/l). Additionally, this study reveals how hyperspectral wavelength selection, number of bands, bandwidth, and parameter calibration are associated with the uncertainty in remote sensing of chl-a. The systematic analysis approach was used to evaluate 34 chl-a algorithms by using optimal location and number of wavelengths as well as calibrated parameters. The study introduced a set of new 2-B, 3-B, and 4-B models derived also from using optimized parameters, suggested wavelengths, and bands available in MERIS and MODIS satellite images. Validation results demonstrated that these models are suitable to general freshwater environments because of broad ranges of biochemical and physical properties in both synthetic and in situ data.

Erratum to: Ecosystem health evaluation of agricultural reservoirs using multi-metric lentic ecosystem health assessment (LEHA) model

The objectives of this study were to determine the trophic state of agricultural reservoirs within the four major watersheds and evaluate ecosystem health using a multi-metric fish modeling approach of the lentic ecosystem health assessment (LEHA) in South Korea. Fish survey for the LEHA model was sampled twice from 12 reservoirs (oligotrophic to hypereutrophic reservoirs) during 2008–2010 along with data analysis of water quality monitored by the Ministry of Environment, Korea. The fish sampling gears used in the field were fyke net, trammel net, casting net, and kick net. A regression analysis of N:P ratios showed a negative linear function with total phosphorous (TP) values but not with total nitrogen. The greater relationship to TP was due to low variability and high ambient concentrations of N relative to P. The plots of “TSI (CHL)–TSI (TP)” and “TSI (CHL)–TSI (SD)” suggest that other factors other than phosphorus limited algal biomass (CHL–TP < 0), and that non-algal particles dominated light attenuation (CHL–SD < 0). Nutrients input into the reservoirs during the Asian monsoon exceeded actual nutrient availability for phytoplankton growth. A regression model of the fish trophic components against log-transformed TP showed that the proportions of omnivore and insectivore fish had a positive linear function and negative relationship with TP, respectively. According to the multi-metric LEHA model for agricultural reservoirs, the model value averaged 26 ± 6.5, indicating a “Fair” condition. Overall, ecosystem health was directly influenced by organic matter pollution and high algal production. This new tool appeared particularly relevant to detect the contamination effects on fish communities in reservoirs. The new national biological monitoring methodology in lentic ecosystem would be used as a key tool for ecological restorations and species conservations in Korean lentic ecosystems.

Absorption characteristics of particulates and CDOM in spring in the Lake Xingkai

Field surveys were carried out in the Lake Xingkai( including both the Great Lake Xingkai and the Small Lake Xingkai)in May 2013,and water samples were collected for examination of the absorption features. In the laboratory,tripton and chromophoric dissolved organic matter( CDOM) absorption of 20 water samples were measured through quantitative filter technique. Absorption coefficients were used to analyse the absorption characteristics,source,spatial distribution and relative contribution of optical active constituents over the range of PAR( 400-700 nm). The results showed that the absorption spectra of tripton are similar to nonalgal particles,indicating less phytoplankton presence in the water column. The total particulate absorption is dominated by the nonalgal particles,of which the contribution rate is up to 50% of the total absorption,and Sgis higher than that in water bodies being investigated elsewhere. Positive correlation of the particles was observed within ap( 440),ad( 440) and total suspended matter,inorganic suspended matter and organic suspended matter,respectively,while weak correlation was recorded in terms of chlorophyll-a( Chl. a) compared with results reported in literatures. In the current study,low correlations of the particles were observed within ag( 440),Chl. a and dissolve dissolved organic carbon( DOC). This is probably due to the fact that more colorless DOCs are present in the Lake Xingkai. Absorption coefficient and water quality parameters showed insignificant difference between the Great Lake Xingkai and the Small Lake Xingkai,though the latter is greatly impacted by farmland irrigation discharge,fisheries and tourism sewage.

Light absorption by phytoplankton and minerogenic particles in Cayuga Lake, New York

Features of light absorption are critical determinants of the underwater and emergent light fields of lakes. Patterns in time and space of the components (ax) of the light absorption coefficient (a), and their dependence on various optically active constituents (OACs), in the form of material-specific ax, were resolved for Cayuga Lake, New York, USA. Component a was partitioned according to the additive components of ax that include phytoplankton (aϕ), nonalgal particles (aNAP), and colored dissolved organic material (aCDOM). Specific absorption coefficients were developed that couple the concentration of chlorophyll a (Chl-a, an OAC) to aϕ, and the concentration of inorganic suspended particulate material (ISPM, an OAC), or the projected area of minerogenic particles per unit volume of water (PAVm, an alternate OAC), to aNAP. The critical role of such specific coefficients in contemporary strategies to retrieve OACs through remote sensing for inland waters is described, and characteristics consistent with the influences of pigment packaging and accessory pigments on the aϕ–Chl-a relationship are demonstrated. Nonalgal partical aNAP is reported to be primarily regulated by the level of minerogenic particles. The specific absorption coefficients developed for Cayuga Lake to support retrieval of the OACs of Chl-a, PAVm, and ISPM are considered in the context of the limited populations of estimates available for inland waters.

Bio-Optical Characteristics of the Northern Gulf of California during June 2008

Bio-optical variables in the Northern Gulf of California were analyzed using in situ and satellite data obtained during a cruise in June 2008. The study area was divided into three bio-optical regions: Upper Gulf (UG), Northern Gulf (NG), and Great Isles (GI). Each region was characterized according to phytoplankton pigment concentration, phytoplankton and nonpigmented material spectral absorption coefficients, and spectral reflectance. Observed patterns were an indication of the shift in bio-optical conditions from north to south going from turbid and eutrophic waters to mesotrophic ones. Although there was a good agreement between satellite and in situ Chla (RMSE ±33%), an overestimation of in situ Chla was observed. This was partly explained by the presence of nonalgal particles, as well as the influence of desert and continental aerosols, which is generally overcorrected in the standard processing. The UG and NG could be considered as Case 2 waters, but they did exhibit different bio-optical characteristics. This implies that both biological and optical properties should be invoked to better understand water reflectance variability in the study region and its implications for the remote sensing of Chla and biogeochemical processes.

HYDRODYNAMICS AND BIO-OPTICAL ASSESSMENT OF TWO PRISTINE SUBTROPICAL ESTUARIES IN SOUTHERN BRAZIL

Measuring small-scale physical processes and how they affect the spatial patterns of sea water's optical constituents plays a key role in understanding the functioning of complex coastal ecosystems such as estuaries. The spatial variations of physical and bio-optical water properties were investigated during one spring tidal cycle in austral summer, on two transects across the channel of the Medeiros and Itaqui sub-estuaries. These sub-estuaries are a biosphere reserve, and part of the Paranaguá Estuarine System, located on the Southern Brazilian coast. Both sub-estuaries were classified as Type 1a, wellmixed with low stratification. The salinity variations are in phase with the water level, and the tidal propagation is well represented by a standing wave. The vertical velocity profiles showed little vertical shear, and the intensity of the u-component of the velocity varied semi-diurnally. The upper estuary salt transport was dominated by tidal diffusion in an unstable water column. The optical environment presented a mixed dominance of optically active substances, as indicated by the absorption coefficients of dissolved and particulate matter. The colored dissolved organic matter (CDOM) showed overall conservative behavior and was dominant in light absorption below 550 nm in the Medeiros, while nonalgal particles play the most important role in light absorption in the Itaqui in the blue absorption band. The phytoplanktonic contribution is prominent in the red domain and increases as a function of saline intrusion. However, due to the influence of freshwater discharge and the re-suspension of bottom sediments induced by physical processes, the concentrations of the optical components in the water column do not generally have any simple relationships between them.

Spatial gradient and seasonal variation of trophic status in a large water supply reservoir for the South-to-North Water Diversion Project, China

Carlson trophic state indices (TSIs) have been frequently employed in the water quality literature. The current study reports the spatial distribution and seasonal variation of trophic status in Danjiangkou Reservoir (DJKR), which is a large water supply reservoir of the South-to-North Water Transfer Project in central China. The calculation of TSICHL indicated a mesotrophic state (40 ≤ TSICHL < 50) for most regions of the reservoir, whereas a eutrophic state was indicated if the assessment was based on either TSITP (calculated from total phosphorus) or TSISD (calculated from Secchi depth). As indicated by Carlson's two-dimensional deviations, factors other than phosphorus limited algal growth in January and May when non-algal particles affected light attenuation. However, phosphorus was the controlling factor of large algae blooms in July and November in 2007. TSISD had positive correlations with TSICHL and TSITP. It was found that total phosphorus, SiO2–Si and SD were the major factors regulating the trophic state (TSICHL) of DJKR. Light attenuation and SD were mainly affected by non-algal particles.

Inversion of bio-optical properties in the coastal upwelling waters of the northern South China Sea

Recent advances in hydrologic optics provide a potential tool for extracting maps of optical properties of optically significant constituents. During summer experiments in the northern South China Sea, a procedure for inverting optical properties in optically complex coastal upwelling waters was performed. We tested an optical inversion model (OIM) that provides estimates of the absorption attributable to optically significant constituents (including phytoplankton, non-algal particles (NAP), colored dissolved organic matter (CDOM)), as well as the chlorophyll a concentration and the phytoplankton size class, from the total spectral absorption. The OIM provided reasonable estimates of these bio-optical products, and attempts to invert the bio-optical properties in the coastal upwelling were successful. Several bio-optical parameters displayed robust relationships to the hydrologic characteristics. The biomass was strongly enhanced in the upwelling, where the phytoplankton population was dominated by the microphytoplankton. The inherent optical properties in the surface waters delivered distinct responses to the coastal upwelling. The distribution of backscattering ratios and particulate size distribution slopes indicated that the offshore surface waters were mainly dominated by small organic NAP, while the upwelling surface water was characterized by larger particles.

The Absorption of Light in Lakes: Negative Impact of Dissolved Organic Carbon on Primary Productivity

Colored dissolved organic matter (CDOM) absorbs a substantial fraction of photosynthetically active radiation (PAR) in boreal lakes. However, few studies have systematically estimated how this light absorption influences pelagic primary productivity. In this study, 75 boreal lakes spanning wide and orthogonal gradients in dissolved organic carbon (DOC) and total phosphorus (TP) were sampled during a synoptic survey. We measured absorption spectra of phytoplankton pigments, CDOM, and non-algal particles to quantify the vertical fate of photons in the PAR region. Area-specific rates of gross primary productivity (PPA) were estimated using a bio-optical approach based on phytoplankton in vivo light absorption and the light-dependent quantum yield of photochemistry in PSII measured by a PAM fluorometer. Subsequently, we calculated the effects of CDOM, DOC, and TP concentration on PPA. CDOM absorbed the largest fraction of PAR in the majority of lakes (mean 56.3%, range 36.9–76.2%), phytoplankton pigments captured a comparatively minor fraction (mean 6.6%, range 2.2–28.2%). PPA estimates spanned from 45 to 993 mg C m−2 day−1 (median 286 mg C m−2 day−1). We found contrasting effects of CDOM (negative) and TP (positive) on PPA. The use of DOC or CDOM as predictors gave very similar results and the negative effect of these variables on PPA can probably be attributed to shading. A future scenario of increased DOC, which is highly correlated with CDOM in these lakes, might impose negative effects on areal primary productivity in boreal lakes.

Bio-optical properties during the summer season in the Sea of Okhotsk

The Sea of Okhotsk is one of the most productive ocean regions in the world. However, the in situ bio-optical properties, which are crucial for satellite ocean-color of the productivity, remain uncertain in this region because little data have been available. We conducted an in situ observation and evaluated the bio-optical properties in terms of chlorophyll a (Chl a) concentration, spectral remote sensing reflectance (Rrs), and the light absorption coefficients of phytoplankton (aφ), non-algal particles (aNAP), and chromophoric dissolved organic matter (aCDOM) in the summer of 2006. The data covered a wide range of Chl a levels in surface waters from 0.3 to 8.5mgm−3. At 443nm, aCDOM dominated (64% on average) the total non-water absorption (at-w) in this study area. Based on the in situ Rrs data, surface Chl a concentrations that were estimated using the sea-viewing wide field-of-view sensor (SeaWiFS) OC4v6 and the moderate-resolution imaging spectroradiometer (MODIS) OC3M algorithms were significantly higher than the in situ data by more than 160% and 260%, respectively. In particular, the largest overestimation occurred in the region where aCDOM at 443nm accounted for more than 80% of at-w near the mouth of the Amur River. However, except the CDOM-rich stations, the performance of the OC4v6 and OC3M algorithms became better (i.e., their mean normalized biases were reduced to 50% and 66%, respectively). We conclude that the operational global algorithms were applicable to the summer season in the Sea of Okhotsk except the CDOM-rich region, in which new approaches for ocean-color algorithms (i.e., local algorithms) would be required.

Contrasting inherent optical properties and particle characteristics between an under-ice phytoplankton bloom and open water in the Chukchi Sea

Variability in the inherent optical properties (IOPs) of seawater and characteristics of the particle assemblage were examined along a transect in the Chukchi Sea during July 2011. This transect encompassed samples from open waters of the marginal ice zone exhibiting low concentrations of chlorophyll-a (Chla<1mgm−3), as well as an extensive phytoplankton bloom (Chla>30mgm−3) beneath consolidated pack ice. Measurements included the spectral coefficients for particulate beam attenuation, backscattering, and absorption, bulk indicators of particle concentration and composition, and the particle size distribution. Within the bloom microphytoplankton contributed >95% to the total Chla, and relatively small amounts of nonalgal particles were present. This assemblage exhibited low Chla-specific phytoplankton absorption coefficients (0.006m2mg−1 at 676nm) indicating a strong influence of pigment packaging, and a weak spectral dependence of the particulate backscattering coefficient. In contrast, the phytoplankton community in nutrient-depleted surface waters outside the sea ice had a strong contribution of picoplankton to Chla (54%) and an increased abundance of nonalgal particles. The Chla-specific phytoplankton absorption coefficient approached maximum values at 676nm (0.023m2mg−1) and particle backscattering had much stronger spectral dependence. Additional samples from near the sea floor exhibited characteristics of either mineral-dominated assemblages or a mixture of mineral and organic particles, and also displayed optical differentiation from the surface samples. The marked contrast in absorption, attenuation, and backscattering properties of these ecological regimes suggest that they can be discriminated from optical measurements available on a variety of in situ and remote-sensing platforms.

Remote Quantification of Total Suspended Matter through Empirical Approaches for Inland Waters

The present study is focused on remote quantification of total suspended matter (TSM) for turbid inland waters. In situ remote sensing reflectance (Rrs) and TSM at 863 stations over 10 inland water bodies from China, Australia, and USA were collected and examined. Four empirical regression models based on sensitive reflectance bands (SB), derivatives (SD), the band ratio proposed by Doxaran et al. (2002; Rrs850/Rrs550: DM), and optimal band ratios (OBR) were examined to estimate TSM. The performance varies due to TSM concentration and the Chl-a: TSM ratio. The four models perform well when the water bodies are dominated with non-algal particles at high TSM concentration and yielded higher accuracy (R^2 ranged from 0.83 to 0.91) with both DM and OBR models, while the OBR model outperformed other models when waters are dominated by phytoplankton. Our findings also indicate that phytoplankton in the water column affects the band ratio algorithm for TSM estimates. When data from all water bodies are considered collectively, the OBR model (R^2 = 0.92) marginally outperforms the other three models (0.89, 0.87, and 0.88 for DM, SB, and SD, respectively). Future studies should be undertaken to analyze the influence of phytoplankton abundance on water-leaving signals for TSM estimates. The results of the present study also need further analyses to gain a more in-depth understanding of inherent optical properties for optically active constituents (OACs), such as absorption and backscattering to interpret the observed variations.

Classification of Inland Waters Based on Bio-Optical Properties

Multiple bio-optical measurements of optically active substances were conducted in Taihu Lake, Chaohu Lake, Three Gorges Reservoir, and Dianchi Lake (China). A hierarchical cluster analysis was applied to remote sensing spectra (Rrs(λ)), by which those waters were clustered into three optically distinct types (Type I, Type II, and Type III). Absorption coefficients of phytoplankton were simulated using the linear function and the coefficients of the functions varied in different water types. The slope of colored dissolved organic matter (CDOM) absorption could be clustered into two classes, one class of high slope for Types I and II, whereas the other class of low slope for Type III. A uniform model was used for parameterization of the nonalgal particles absorption coefficients spectral between different water types. The power-law function was used to parameterize the scattering coefficient and the slope of scattering spectra could be classified into two groups of high slope for Types I and II, low slope for Type III. The composition of particles, particulate scattering, and nonalgal particulate absorption are the factors controlling the variability in Rrs(λ) for corresponding type waters. Those results support such a fact that it is indispensable to classify waters before developing a model to estimate water quality parameters for multi-type optical waters.

Variability in the light absorption coefficients of phytoplankton, non-algal particles, and colored dissolved organic matter in a subtropical bay (Brazil)

This study characterized the variability in magnitudes and spectral shapes of the absorption coefficients of phytoplankton, detritus, and colored dissolved organic matter (CDOM) in a dynamic bay (Santos Bay) in southeastern Brazil in response to the contributions of the main estuarine channel and large tide variations, therefore in different time scales. Two strategies were adopted: (1) monthly year-round sampling in the estuarine channel and Santos Bay and (2) sampling in Santos Bay during spring/neap tides and cold/warm months. Chlorophyll-a concentration and CDOM absorption were higher during warm (wet) months, while the relative contribution of organic and inorganic particles was driven by neap/spring tide cycles. Salinity partially accounted for changes in optical variables, especially for CDOM absorption and total suspended matter (TSM) during cold months and neap tides, respectively. The spectral shapes of detritus and CDOM absorption showed relatively little variability for the entire dataset and were not considered feasible for monitoring purposes. The spectral shape of phytoplankton absorption (index of cell size) varied broadly, with no remarkable dependence on the sampling conditions. Comparison of absorption coefficients measured by the Quantitative Filter Technique (QFT) and Transmittance Reflectance (TR) method showed higher phytoplankton coefficients toward longer visible wavelengths (flatter spectra) and shallower slopes of detritus absorption yielded by the TR method. Our results also suggest that measurements at the near red spectral region result from not only scattering signals but also non-algal particle absorption.

Coefficients of summer spectral absorption of particulate matter in Xin'anjiang Reservoir (Lake Qiandao)

通过对2013年夏季新安江水库(千岛湖)53个站点悬浮颗粒物的吸收光谱进行研究,系统分析了总颗粒物吸收系数a_p(λ)、非藻类颗粒物吸收系数a_d(λ)和浮游藻类光谱吸收系数a_ph(λ)的变化规律以及影响因素.结果表明:总颗粒物吸收除西北河流区上游段外,其他各站点均呈现出明显的浮游藻类吸收特性,反映新安江水库总颗粒物中浮游藻类贡献较高.全库a_p(440)在0.068~0.629m^-1之间变化,西北河流区总颗粒物吸收系数显著大于其他水域,而湖泊区与西南河流区则显著小于其他水域.非藻类颗粒物吸收光谱随着波长增加大致呈现出指数函数衰减的规律,其光谱斜率S_d均值为8.52±1.62μm^-1,存在显著的空间差异,但整体偏低,与新安江水库无机颗粒物含量低有关.a_d(440)与浮游藻类色素浓度存在显著的线性相关,表明夏季新安江水库非藻类颗粒物可能主要来源于浮游藻类降解.浮游藻类的光谱吸收在440和675nm附近有明显的吸收峰.a_ph(440)和a_ph(675)存在显著的空间差异,其与浮游藻类色素浓度存在极显著的正线性关系,而与总悬浮颗粒物浓度相关性较弱.;The spectral absorption coefficients of total particles a_p(λ), nonalgal particles a_d(λ) and phytoplankton a_ph(λ) in Xin'anjiang Reservoir(Lake Qiandao) were studied based on the data of 53 sampling sites in the summer of 2013. The results showed that the absorption spectra of total particles were similar to those of phytoplankton except the data at sites 9 and 10. It indicated that phytoplankton made larger contribution to the total particles. The values of the total particulate matter at 440nm a_p(440) ranged between 0.068 and 0.629 m^-1 in the water body. Moreover, the values of a_p(λ) in the northwestern area were significantly larger than those in other areas, while the values of a_p(λ) in the lake district and the southwestern riverine areas were the smallest. Absorption coefficients of nonalgal particles decreased exponentially from the short to the long wavelength. There were marked spatial variations of the exponential spectral slope coefficients of nonalgal particles S_d with the average value of 8.52±1.62μ m^-1. However, the values of S_d in Xin'anjiang Reservoir were generally low due to the low values of the inorganic suspended solids. Significant positive relationships were found between a_d(440) and phytoplankton pigment concentrations, suggesting that the degradation of phytoplankton was an important source of the nonalgal particles in summer. There were distinctive absorption peaks at the wavelength of 440 and 675nm in the absorption spectra of phytoplankton. In addition, there were significant spatial variations of the phytoplankton absorption coefficients at 440nm (a_ph(440)) and 675nm (a_ph(675)). Significant positive linear relationships were found between a_ph(440), a_ph(675) and phytoplankton pigment concentration, respectively, while weak relationships were showed between a_ph(440), a_ph(675) and the total suspended solids, respectively.