Non-living Particles Research Articles

Influence of microplastics and biogenic particles on the size spectra of tropical estuarine and marine pelagic ecosystems

Size spectra analysis has been widely used to study pelagic ecosystems worldwide. It has a solid theoretical and empirical basis and can be used to provide useful information on ecosystem structure and trophic efficiency. The objective of this study was to obtain complete Normalized Biovolume Size Spectra (NBSS), including zooplankton, microplastics, and other suspended particles, along an estuary-shelf gradient. Plankton net samples (300 μm mesh) were obtained in the Rio Formoso Estuary, in Tamandaré Bay and on the continental shelf off Tamandaré, Brazil, during two years (from April/2013 to May/2015). Particles were identified by image analysis (ZooScan) and infrared spectroscopy (FTIR). Generally, NBSS slopes were close to −1 (i.e., between −1.09 and −0.85), except for NBSSz (zooplankton only) in the Estuary (−1.59) and in the Bay (−1.44), where the steepest slopes were observed, due to the importance of small-sized zooplankton in these areas. The NBSSz slope was significantly steeper in the Estuary and in the Bay than on the Shelf. The inclusion of particles into the NBSS (NBSSp) turned the slope significantly less steep in the Estuary and in the Bay. Intercepts were significantly higher in the Estuary than in the other areas, after including particles in the analysis (NBSSp), due to the extremely high total volume of biogenic particles in the estuary. The most relevant impacts of microplastics were detected within the larger size classes (> 2.60 mm Feret length, > 0.58 log10 mm3). In the Estuary, large-sized microplastics were similarly important (in terms of volume) as zooplankton. Large-sized polyethylene and polypropylene were more relevant in the Bay, large-sized nylon fibers on the Shelf (in the rainy season). The present study, a pioneering effort towards a synthetic analysis of zooplankton, microplastics, and other particles, highlights the importance of including non-living particles in size-based studies and ecosystem models.

Metazoan zooplankton in the Bay of Biscay: a 16-year record of individual sizes and abundances obtained using the ZooScan and ZooCAM imaging systems

Abstract. This paper presents two metazoan zooplankton datasets obtained by imaging samples collected on the Bay of Biscay continental shelf in spring during the PELGAS (PELagique GAScogne) integrated surveys over the 2004–2019 period. The samples were collected at night with a 200 µm mesh-size WP2 net fitted with a Hydrobios (back-run stop) mechanical flowmeter and hauled vertically from the sea floor to the surface, with the maximum depth set at 100 m when the bathymetry was deeper than this. The first dataset originates from samples collected from 2004 to 2016 and imaged on land with the ZooScan and is composed of 1 153 507 imaged and measured objects. The second dataset originates from samples collected from 2016 to 2019 and imaged onboard the R/V Thalassa with the ZooCAM and is composed of 702 111 imaged and measured objects. The imaged objects are composed of zooplankton individuals, zooplankton pieces, non-living particles and imaging artefacts ranging from 300 µm to 3.39 mm in equivalent spherical diameter which were individually imaged, measured and identified. Each imaged object is geolocated and associated with a station, a survey, a year and other metadata. Each object is described by a set of morphological and grey-level-based features (8 bit encoding, 0 = black, 255 = white), including size, that were automatically extracted from each individual image. Each object was taxonomically identified using the web-based application Ecotaxa with built-in random-forest and CNN-based semi-automatic sorting tools, which was followed by expert validation or correction. The objects were sorted into 172 taxonomic and morphological groups. Each dataset features a table combining metadata and data at individual-object granularity from which one can easily derive quantitative population and community descriptors such as abundances, mean sizes, biovolumes, biomasses and size structure. Each object's individual image is provided along with the data. These two datasets can be used in combination for ecological studies, as the two instruments are interoperable, or they can be used as training sets for ZooScan and ZooCAM users. The data presented here are available at the SEANOE dataportal: https://doi.org/10.17882/94052 (ZooScan dataset, Grandremy et al., 2023c) and https://doi.org/10.17882/94040 (ZooCAM dataset, Grandremy et al., 2023d).

EVALUATION OF STANDARD OCEAN COLOUR CHLOROPHYLL-a ALGORITHMS IN THE NORTHERN PERSIN GULF: COMPARISON OF MAGNITUDE AND SEASONALITY

Abstract. The Persian Gulf is a peripheral sea that is quite turbid and visually complicated. Because of the complicated oceanic and atmospheric optical features of this maritime area, satellite remotely sensed chlorophyll-a (Chl-a, mg m−3) outputs have been used extensively. In this study, the seasonality and magnitude of Level-3 Chl-a time-series products, and daily Level-2 satellite-derived Chl-a concentrations were assessed using corresponding/concurrent in-situ observations gathered during 2008 to 2018. The results revealed that the field observations overestimated satellite-derived Chl-a by 115% in the deeper areas and up to 161% along the Iranian coastal waters. Comparison of inter-annual Chl-a time-series datasets with corresponding in-situ measurements showed that temporal patterns of the satellite-derived Chl-a values are not consistent with field observations. The monthly average of the satellite Chl-a series shows a different seasonal pattern in every region of the study area, and their magnitude over-estimated from 21% to 83% relative to in-situ observations. The absorption coefficients at 488–510 nm are primarily influenced by non-living particles instead of phytoplankton pigments, and no significant correlation are found between in-situ and Chl-a values from OC3/OC4 algorithms. Absorption coefficients spectra of water constituent’s shows that the contribution of phytoplankton pigments in particulate absorption coefficients at the blue-green bands are 48%–59%, and the particulate absorptions of water bodies are under the strong influence of non-living particles (40%–52%). Our results suggest that the red-green band-ratios algorithm centred at 675 nm and 555 nm presents more accurate results than OC3/OC4 over the study area.

E-Co-Affectivity: Exploring Pathos at Life’s Material Interfaces

E-Co-Affectivity: Exploring Pathos at Life’s Material Interfaces

Observations of Phytoplankton Community Composition in the Santa Barbara Channel During the Thomas Fire

AbstractThe Thomas Fire ignited on December 5, 2017 and burned nearly 300,000 acres of land in Ventura and Santa Barbara counties until January 12, 2018, making it the largest wildfire in California history at the time. During the fire, a persistent plume of ash, smoke, and soot extended up to 1,000 km offshore over the Santa Barbara Channel (SBC). The effect of this ash influx on the SBC phytoplankton community was investigated with an Imaging FlowCytobot (IFCB) onboard R/V Sally Ride during a research cruise in mid‐December 2017. Over 100,000 images of phytoplankton and nonliving particles were collected and each image was manually classified, resulting in time series of phytoplankton cells and detrital particles, including ash. Comparing the Thomas Fire conditions to historical monthly sampling in the SBC in December reveals significant differences in sea surface temperature, nutrient concentration, and phytoplankton community composition (PCC) in December 2017. During the Thomas Fire, dinoflagellates dominated the phytoplankton community (comprising up to 90% of the total phytoplankton cell biovolume per sample), while diatoms and picophytoplankton typically dominate surface ocean PCC in the SBC in December. While this study was not able to demonstrate a correlational relationship between PCC and wildfire ash concentration, the significant differences in surface ocean biogeochemistry in December 2017 compared to past winters is notable. Wildfire severity and frequency are annually increasing in California and globally with unknown impacts on the marine ecosystem; thus, this study provides an important baseline assessment for the SBC.

Discovery of High Abundances of Aster-Like Nanoparticles in Pelagic Environments: Characterization and Dynamics.

This study reports the discovery of Aster-Like Nanoparticles (ALNs) in pelagic environments. ALNs are pleomorphic, with three dominant morphotypes which do not fit into any previously defined environmental entities [i.e., ultramicro-prokaryotes, controversed nanobes, and non-living particles (biomimetic mineralo-organic particles, natural nanoparticles or viruses)] of similar size. Elemental composition and selected-area electron diffraction patterns suggested that the organic nature of ALNs may prevail over the possibility of crystal structures. Likewise, recorded changes in ALN numbers in the absence of cells are at odds with an affiliation to until now described viral particles. ALN abundances showed marked seasonal dynamics in the lakewater, with maximal values (up to 9.0 ± 0.5 × 107 particles·mL−1) reaching eight times those obtained for prokaryotes, and representing up to about 40% of the abundances of virus-like particles. We conclude that (i) aquatic ecosystems are reservoirs of novel, abundant, and dynamic aster-like nanoparticles, (ii) not all virus-like particles observed in aquatic systems are necessarily viruses, and (iii) there may be several types of other ultra-small particles in natural waters that are currently unknown but potentially ecologically important.

Spatio-temporal variability of red-green chlorophyll-a index from MODIS data – Case study: Chabahar Bay, SE of Iran

Chabahar Bay is a strategic and productive estuary in the south-east of Iran (north of Oman Sea). It is an optically complex bay, and its Chl-a content variations never studied. In this study, Red-Green Chlorophyll Index (RGCI) algorithm for estimating accurate Chl-a content was tested, validated and applied to Moderate Resolution Imaging Spectrometer (MODIS) data, using in situ bio-optical data collected seasonally from 2007 to 2015 in 35 stations. Chl-a concentrations varied from 7.7 to 31.3 mg m−3 with a mean value of 16.4 ± 5.9 mg m−3. The mean absorption at 443 nm and 555 nm data showed that the detrital particles and CDOM contents is relatively low and the mean absorption is dominated by phytoplankton and non-living particles. The RGCI algorithm was tuned for green band center position of 555 nm, and showed improvement over the traditional blue-green band ratio algorithms (e.g. OC3) with mean relative error of 37.4% and RMSE of 73.2% for Chl-a ranging between 2 and 80 mg m−3. The Wavelet Transform (WT) techniques were utilized to analyze the spatio-temporal stability and abnormality of MODIS Chl-a extracted using the tuned RGCI algorithm. Significant variability in time and space was observed, with higher Chl-a in the eastern segment and lower Chl-a in the middle of bay. The highest and lowest Chl-a concentrations were observed in summer and winter, respectively. WT components analysis and anomaly detection revealed the strong correlation of Chl-a concentrations and patterns with turbidity contents and adjacent river discharge. This study showed that the accuracy of RGCI algorithm depends on water body constituents and optimized green waveband position, and therefore the algorithm must be tuned regionally with in situ Chl-a data.

Modelling the Particulate Backscattering Coefficients of Turbid and Productive Coastal Waters

An optical model is developed to predict the spectral backscattering coefficients of phytoplankton (bbph(λ)) and non-living particles (bbss(λ)) in turbid and productive coastal waters. This model computes bbph(λ) and bbss(λ) values based on the measured absorption and attenuation coefficients and water constituents’ concentrations. The predicted values are validated with independent in-situ data from four different water types and compared with results from the independent model. The findings revealed that, in sediment-dominated coastal waters, the backscattering coefficient of phytoplankton is relatively smaller than that of non-living particles. In productive waters, the contribution by phytoplankton is significant due to high chlorophyll a concentration and the influence of complex morphology, intracellular structure and composition of phytoplankton. The results further showed that living algal matter in turbid productive waters may have a significant influence on the backscattering process and its spectral dependency which will have important implications for our understanding of the relationship between the backscattering to scattering ratio, particle size distribution and related properties.

Stick or Dye: Evaluating a Solid Standard Calibration Approach for Point-Source Integrating Cavity Absorption Meters (PSICAM)

Together with scattering, the process of absorption determines the propagation of light within the water column. It is influenced by the concentration and composition of optically active substances (phytoplankton, chromophoric-dissolved organic matter, and non-living particles). For this reason, the absorption coefficients of a water sample can provide corresponding information. However, the accurate determination of absorption coefficients in natural waters is often difficult due to the usually low concentration of absorbing material and the errors that scattering on particles introduce in the measurements. These problems can be overcome by instruments based on integrating cavities like the point-source integrating-cavity absorption meter (PSICAM). The accuracy of PSICAM measurements is to a large degree related to the accuracy of the measurement of the reflectivity inside its cavity, as this determines its mean optical path length. A reflectivity measurement (‘calibration’) is usually carried out by measuring a liquid dye (nigrosin) with known absorption coefficients, followed by bleaching and rinsing of the cavity. The procedure requires additional equipment like spectrophotometers and handling of a liquid standard. Therefore, it might be difficult or at least non-convenient under field conditions and is additionally a major obstacle for a potential automation of these systems. In the present study, an alternative calibration approach for a PSICAM is evaluated, taking advantage of a solid standard. The standard is characterized and its suitability for calibration is compared to that of a conventional, nigrosin-based reflectivity measurement. Furthermore, the application in an automated flow-through PSICAM system (HyAbS) used in the field is tested. The results show that the performance of the solid standard calibration is comparable to that of the nigrosine-based calibration. Furthermore, it improves the measurements of the automated system. Thus, due to its simplicity, the solid standard calibration might foster the use of PSICAM systems, which allow a more accurate determination of absorption coefficients in natural water samples compared to conventional spectrophotometric techniques. Furthermore, it will potentially facilitate further approaches to automate of these instruments.

Automated plankton image analysis using convolutional neural networks

AbstractThe rise of in situ plankton imaging systems, particularly high‐volume imagers such as the In Situ Ichthyoplankton Imaging System, has increased the need for fast processing and accurate classification tools that can identify a high diversity of organisms and nonliving particles of biological origin. Previous methods for automated classification have yielded moderate results that either can resolve few groups at high accuracy or many groups at relatively low accuracy. However, with the advent of new deep learning tools such as convolutional neural networks (CNNs), the automated identification of plankton images can be vastly improved. Here, we describe an image processing procedure that includes preprocessing, segmentation, classification, and postprocessing for the accurate identification of 108 classes of plankton using spatially sparse CNNs. Following a filtering process to remove images with low classification scores, a fully random evaluation of the classification showed that average precision was 84% and recall was 40% for all groups. Reliably classifying rare biological classes was difficult, so after excluding the 12 rarest taxa, classification accuracy for the remaining biological groups became > 90%. This method provides proof of concept for the effectiveness of an automated classification scheme using deep‐learning methods, which can be applied to a range of plankton or biological imaging systems, with the eventual application in a variety of ecological monitoring and fisheries management contexts.

Spatial variability and size structure of particles and plankton in the Fram Strait

Changes within marine pelagic fields in the Arctic affect global biogeochemical cycles. The size structure and distribution of particles and plankton (P&P) were studied in the main northward passage of Atlantic water to the Arctic region, which is affected in various ways by climate change. The wide size spectrum of P&P (3 µm–5 mm) was assessed by combining measurements from two complementary optical counters, a Laser In-Situ Scattering and Transmissometry (LISST) instrument and a Laser Optical Plankton Counter (LOPC). The measurements were performed in the upper 100 m layer at 55 stations in summer in 2013. The P&P were attributed to various functional groups – particles, phytoplankton, marine snow, and zooplankton – to test their spatial coupling with hydrodynamic forcing. Although our study confirms that the Fram Strait is a region of strong biophysical contrasts, the expected coastal-offshore gradient has not been distinguished clearly. Three mechanisms could explain P&P patches: particle flocculation due to contact with fresh waters from ice and fjords, enhanced production due to coastal upwelling as well as widening the range of warm surface water advection northwards. Particularly rich biological hot spots were recognised in the northern, shallow parts of the west Spitsbergen shelf, and near the marginal ice edges, confirming that these areas are highly vulnerable to marine predators. Moreover, combining optical measurements from two size-specific optical counters contributes greatly to reducing the substantial knowledge gap regarding wide size structure and distribution of thus far neglected seawater components, such as non-living particles and marine snow aggregates, occurring in this vulnerable Arctic region.

Springtime zooplankton size structure over the continental shelf of the Bay of Biscay

Abstract. Linking lower and higher trophic levels requires special focus on the essential role played by mid-trophic levels, i.e., the zooplankton. One of the most relevant pieces of information regarding zooplankton in terms of flux of energy lies in its size structure. In this study, an extensive data set of size measurements is presented, covering parts of the western European continental shelf and slope, from the Galician coast to the Ushant front, during the springs from 2005 to 2012. Zooplankton size spectra were estimated using measurements carried out in situ with the Laser Optical Plankton Counter (LOPC) and with an image analysis of WP2 net samples (200 μm mesh size) performed following the ZooScan methodology. The LOPC counts and sizes particles within 100–2000 μm of spherical equivalent diameter (ESD), whereas the WP2/ZooScan allows for counting, sizing and identification of zooplankton from ~ 400 μm ESD. The difference between the LOPC (all particles) and the WP2/ZooScan (zooplankton only) was assumed to provide the size distribution of non-living particles, whose descriptors were related to a set of explanatory variables (including physical, biological and geographic descriptors). A statistical correction based on these explanatory variables was further applied to the LOPC size distribution in order to remove the non-living particles part, and therefore estimate the size distribution of zooplankton. This extensive data set provides relevant information about the zooplankton size distribution variability, productivity and trophic transfer efficiency in the pelagic ecosystem of the Bay of Biscay at a regional and interannual scale.

Bacterium-Like Particles for Efficient Immune Stimulation of Existing Vaccines and New Subunit Vaccines in Mucosal Applications

The successful development of a mucosal vaccine depends critically on the use of a safe and effective immunostimulant and/or carrier system. This review describes the effectiveness and mode of action of an immunostimulating particle, derived from bacteria, used in mucosal subunit vaccines. The non-living particles, designated bacterium-like particles are based on the food-grade bacterium Lactococcus lactis. The focus of the overview is on the development of intranasal BLP-based vaccines to prevent diseases caused by influenza and respiratory syncytial virus, and includes a selection of Phase I clinical data for the intranasal FluGEM vaccine.

Biofouling: lessons from nature

Biofouling is generally undesirable for many applications. An overview of the medical, marine and industrial fields susceptible to fouling is presented. Two types of fouling include biofouling from organism colonization and inorganic fouling from non-living particles. Nature offers many solutions to control fouling through various physical and chemical control mechanisms. Examples include low drag, low adhesion, wettability (water repellency and attraction), microtexture, grooming, sloughing, various miscellaneous behaviours and chemical secretions. A survey of nature's flora and fauna was taken in order to discover new antifouling methods that could be mimicked for engineering applications. Antifouling methods currently employed, ranging from coatings to cleaning techniques, are described. New antifouling methods will presumably incorporate a combination of physical and chemical controls.

Improvement of plankton biovolume estimates derived from image-based automatic sampling devices: application to FlowCAM

The most commonly used biomass estimate for microalgae is obtained from cell biovolume, usually calculated from microscopically measured linear dimensions. Although reliable, this is a highly time-consuming and specialized technique. Automated sampling devices that acquire images of cells and use pattern recognition techniques to identify the images have been developed as an alternative to microscopy-based methods. There are some aspects of automatic sampling and classification methods, however, which can be improved for the analysis of field samples including living and non-living particles. In this work, we demonstrate how the accuracy of a state-of the-art technique for plankton classification (Support Vector Machine) can be improved up to 86% if a previous automated step designed to remove non-living images is included. There is a tendency with the currently applied automatic methods to misestimate cell biovolume due to the two-dimensionality of the images. Here, we present a data set of more than 500 samples to show that the greatest effect is caused by the incorrect estimation of biovolume of the chain-forming diatoms. This results in an overestimate of biomass of between 20 and 100% where chain-forming diatoms represent more than the 20% of the biomass of the sample. We show how the classification method can be adapted to provide not only taxonomic but also the morphological classification of cells in order to obtain a more reliable estimate of biovolume according to the predicted cell shape, in a way comparable with microscopy-based estimates.

The Distribution Characteristics of Fine Particles by Flow Cytometry in the Yangtze Estuary and the Adjacent East China Sea

The fine particles play a major role not only in complex processes of estuarine area but also in the distribution, transfer and transformation of pollutants in the estuarine environment. In this study, fine particles were detected and analyzed by flow cytometry in the Yangtze Estuary and the adjacent East China Sea. Two groups of organic autotrophic particles (R1 and R2) were detected by flow cytometry analysis. Another group of R3 was organic but nonliving, or inorganic particles. Particles of R1 and R2 only represent between 0.18% and 3.16% of total particles at the sampling stations. Particles of R3 dominated the estuarine stations. Their concentration had large fluctuations. We observed a seaward decrease in the number of organic nonliving particles and inorganic particles. Flow cytometry made it possible that study on the dynamics of fine particles. It is important in discovering the transfer mechanism and environmental behavior of fine particles in the estuarine area.

Are the soft, liquid-like structures detected around bacteria by ambient dynamic atomic force microscopy capsules?

High-resolution imaging of bacterial capsules by microscopy is of paramount importance in microbiology due to their role in pathogenesis. This is, however, quite a challenging task due to their delicate nature. In this context, recent reports have claimed successful exploitation of the capacity of atomic force microscopy (AFM) for imaging of extremely deformable (even liquid) surfaces under ambient conditions to detect bacterial capsules in the form of tiny amounts of liquid-like substances around bacteria. In order to further explore this supposed capacity of AFM, in this work, three staphylococcal strains have been scrutinized for the presence of capsules using such an AFM-based approach with a phosphate buffer and water as the suspending liquids. Similar results were obtained with the three strains. AFM showed the presence of liquid-like substances identical to those attributed to bacterial capsules in the previous literature. Extensive imaging and chemical analysis point out the central role of the suspending liquid (buffer) in the formation of these substances. The phenomenon has been reproduced even by using nonliving particles, a finding that refutes the biological origin of the liquid-like substances visualized around the cells. Deliquescence of major components of biological buffers, such as K(2)HPO(4), CaCl(2), or HEPES, is proposed as the fundamental mechanism of the formation of these ultrasmall liquid-like structures. Such an origin could explain the high similarity of our results obtained with three very different strains and also the high similarity of these results to others reported in the literature based on other bacteria and suspending liquids. Finally, possible biological/biomedical implications of the presence of these ultrasmall amounts of liquids wrapping microorganisms are discussed.

Variability and classification of remote sensing reflectance spectra in the eastern English Channel and southern North Sea

During spring and summer 2004, intensive field bio-optical campaigns were conducted in the eastern English Channel and southern North Sea to assess the mechanisms regulating the ocean color variability in a complex coastal environment. The bio-optical properties of the sampled waters span a wide range of variability, due to the various biogeochemical and physical processes occurring in this area. In-water hyperspectral remote sensing reflectances ( R rs) were acquired simultaneously with measurements of optically significant parameters at 93 stations. An empirical orthogonal function (EOF) analysis indicates that 74% of the total variance of R rs is partly explained by particulate backscattering ( b bp), while particulate and dissolved absorption only explain 15% of the ocean color variability. These results confirm, for the first time from in situ backscattering measurements, previous studies performed in other coastal environments. Whereas the amplitude factors of the first EOF mode are well correlated ( r = 0.75) with the particulate backscattering coefficient ( b bp), the highest correlation ( r = 0.83) is found with the particulate backscattering ratio ( b bp/ b p). This result highlights the fundamental role of the nature of the bulk particulate assemblage in the ocean color variability. An unsupervised hierarchical cluster analysis applied to our data set of normalized R rs spectra, leads to five spectrally distinct classes. We show that the class-specific mean R rs spectra significantly differ from one another by their bio-optical properties. Three classes particularly stand out: one class corresponds to a Phaeocystis globosa bloom situation, whereas the two others are associated with water masses dominated by mineral and non-living particles, respectively. Among the different bio-optical parameters, the particulate backscattering ratio, the chlorophyll concentration, and the particulate organic carbon to chlorophyll ratio, are the most class-specific ones. These different results are very encouraging for the inversion of bio-optical parameters from class-specific algorithms.

Cadmium uptake by marine micro-organisms in the English Channel and Celtic Sea

A series of shipboard experiments using the radiotracer 109Cd investigated the role of phytoplankton and bacteria in the uptake of dissolved Cd in the English Channel and Celtic Sea. The results demonstrate that Cd uptake is related to rates of primary production and bacterial numbers. Statistical analysis of plankton species abundance infer that Rhizosolenia, Chaetoceros and Pseudonitzschia diatom species are largely responsible for the higher Cd uptake observed in the >5 ?m size fraction during a diatom-dominated spring bloom. Total Cd uptake rates during winter non-bloom conditions were between 0.04 and 0.29 pmol l–1 h–1, and increased to between 0.43 and 1.23 pmol l–1 h–1 during diatom bloom conditions. These uptake rates are consistent with the seasonal surface depletion of Cd reported in the Celtic Sea and attributed to uptake by phytoplankton bloom material. A calculated Cd:C ratio of 3.1 ?mol mol–1 for natural plankton samples of the Celtic Sea agrees well with results of previous culture studies, which have reported ratios between 0.1 and 5.0 ?mol mol–1 for the coastal diatoms Thalassiosira weissflogii and T. pseudonana. Cd uptake was also linearly related to bacterial numbers, which was attributed to surface adsorption of Cd ions onto bacterial particles which have relatively high specific surface areas. These results demonstrate surface adsorption of Cd onto bacterial surfaces, and other biogenic non-living particles, i.e. ‘passive Cd uptake’, which is significantly augmented during a spring diatom bloom.

MODELING LIGHT ATTENUATION, SECCHI DISK, AND EFFECTS OF TRIPTON IN SENACA RIVER, NEW YORK, USA

: The development, testing, and application of a probabilistic model framework for the light attenuation coefficient for downwelling irradiance (Kd) and Secchi disc transparency (SD) that resolves the effects of several light attenuating constituents, including phytoplankton and nonliving particles (tripton), is documented. The model is consistent with optical theory, partitioning the magnitudes of the light attenuating processes of absorption and scattering according to the contributions of attenuating constituents as simple summations. The probabilistic framework accommodates variations in the character and concentrations of these constituents and ambient conditions during measurements, and recognizes a linear relationship between the magnitudes of absorption and scattering by tripton. The model is tested and applied for a 21 km reach of the Seneca River, New York, that features optical gradients caused by an intervening hypereutrophic lake and dam, and a severe infestation of the exotic zebra mussel. The model is applied to resolve the roles of phytoplankton and tripton in regulating measured longitudinal patterns of SD along the study reach of the river and increases in SD since the zebra mussel invasion, and to predict decreases in Kd since the invasion.