Total Light Attenuation Research Articles

Water Suspension and its Effect on Total Light Attenuation in Lake Waters

The paper presents the data obtained by the authors in 2012-2021 during field trips to freshwater reservoirs of Altai Krai. According to hydro-optical measurements, values of light attenuation index in the range of 400-800 nm calculated using the natural logarithm varied greatly within 2.3-19.7 m-1 and 2.9-35.0 m-1 in the surface layer of lakes Lapa and Krasilovskoye during the study period. The relative spectral contribution of water suspension and contributions of yellow matter, chlorophyll, and pure water constituents at wavelengths of 430, 550, and 670 nm were estimated to assess the optical effect of water suspension on the total light attenuation index. The calculation results demonstrated that water suspension had the maximum effect on light attenuation in waters of eutrophic lake Lapa during the autumn-winter period. The maximum effect at all three wavelengths was observed in autumn of 2015, and the contribution of water suspension to light attenuation reached 88.5%, whereas its minimum (1.8-2.4 %) was recorded in 2017. The maximum contribution of water suspension on light attenuation in waters of eutrophic-hypereutrophic lake Krasilovskoye slightly exceeded the value of 70% during the winter of 2014. The next maximums were revealed during the spring of 2014 and had values of 71.3 % at λ =430 nm and 71.1 % at λ =550 nm.
 Optical microscopy was used to estimate the size and concentration of water suspense particles. The average weighted value of radius for water suspense particles in the surface layer of lakes Lapa and Krasilovskoye was found to be 1.2 and 1.4 microns, respectively. The average particulate count for water suspense during the observation period varied in the range of 0.2·106 cm-3-14.7·106 cm-3 with values of 3.3·106 cm-3 for lake Lapa and 3.0·106 cm-3 for lake Krasilovskoye.

Influence of Wind Currents on Spectral Light Attenuation in Water

The paper deals with wind current dependences of spectral light attenuation measured in natural waters of lakes in the south of West Siberia. To reveal the significance of abiotic, i.e., physical factors affecting water transparency, we calculate relative spectral contributions of individual optically active water components in freshwater lakes established during hydrophysical research of 2019. In addition, the published data on the daily dynamics of spectral water transparency obtained by researchers of IWEP SB RAS for Lake Krasilovskoye in 2016 are partially analyzed. The greatest spectral contribution to the total light attenuation falls on suspension consisting mainly of phytoplankton algae particles and yellow matter. Wind current velocity is a determining factor affecting light attenuation dynamics because the upward redistribution of particle concentration in upper layers of the lake caused by wind-induced turbulent mixing occurs faster than the change in the yellow matter content as a result of physical-chemical processes responsible for its formation. In such cases, the intensity of turbulence (turbulent mass exchange) is usually characterized by flow (integral) Richardson number Ri, which is directly dependent on wind current velocity. In our experiment, Ri equals to 1.5.

The effects of two longpass filters on visual performance

PurposeThis study compared visual performance and optical properties of three filters. MethodTwo groups of twenty adults were recruited: wearers of progressive addition lenses (PAL, 46–73 years) and wearers of single vision lenses (SVL, 26–55 years). Three spectacle filters (Hoya, Japan) were compared: clear control, Standard Drive (STD), and Professional Drive (PRO) lenses. Optical transmittance was measured by a Jasco V-650 spectrophotometer. Best corrected visual acuity (BCVA) was measured in photopic (BCVAphotopic) and mesopic (BCVAmesopic) conditions and under glare (BCVAglare). Photopic contrast sensitivity (CS) was also measured. ResultsThe three longpass filters show cutoff at 426±2nm (STD/PRO) and 405±2nm (clear lens). BCVAglare improved with Drive filters compared to the clear one (p<0.05) from 0.03 to -0.02 (STD) and to -0.01 (PRO) for PAL and from -0.08 to -0.12 (STD and PRO) for SVL. For PAL, BCVAmesopic improved from 0.15 to 0.12 (STD, p<0.05) and 0.13 (PRO), while no substantial difference was observed for SVL. CS showed some improvements with Drive lenses at some angular frequencies between 6 and 18 cycles/deg, mainly for the PAL group. No BCVAphotopic differences were found. After testing all filters, each for two weeks, 79% (PAL) and 60% (SVL) of participants preferred Drive lenses. ConclusionsDrive lenses are found to maintain or improve some visual functions compared to the clear lens. The improvement of mesopic visual acuity, visual acuity under glare, and contrast sensitivity is mainly attributed to the reduction of intraocular light scattering as a consequence of the total light attenuation in the spectral range below the cutoff.

Spatial variability of hydrooptical characteristics of Lake Teletskoye

The paper presents the results of studies of the spatial distribution of primary hydrooptical characteristics, in particular, light attenuation ε by lake water at a wavelength of 550 nm, light absorption by yellow substance κys at a wavelength of 450 nm, and relative transparency Z measured with Secchi disk. The data were obtained in summer 2018 during field surveys of the Laboratory of Hydrology and Geoinformatics of IWEP SB RAS on Lake Teletskoye (Altai Mountains). The values of ε for the study period were within 0.4–2.3 m–1, κys – 0.5–3.0 m–1 (calculated at natural logarithm base), Z – 1.0–11.7 m. The yellow substance concentration calculated by the measured transmittance of yellow substance, varied within 2.6–14.1 g/m3, the chlorophyll concentration – 0.4–1.8 mg/m3. According to the data from the chemical analytical center of IWEP, the average concentration of total phosphorus in the surface layer of the lake during the study period was 10.8 mg/m3, total nitrogen – 731.3 mg/m3, total carbon – 3.35∙103 mg/m3. Besides, the relative spectral contribution of major optically active components of lake water (purewater, yellow substance,suspended matter and chlorophyll) to light attenuation across the lake water area was estimated. It was found that yellow substance makes the largest contribution to ε at all sampling points (22) of the lake. It is shown that the optical structure of the lake and the spatial variability of hydro-optical characteristics are closely related to the hydrological regime of the lake, meteorological conditions in the region and various optically active water components, whose concentration changes both in time and space under the influence of processes inside the lake in association with the catchment. The analysis of the spatial distribution of the indices of light attenuation and absorption by yellow substance in the lake water showed that Lake Teletskoye stands out not only for its hydro-optical characteristics, but also its hydrobiological and hydrochemical characteristics. Hence, the total light attenuation by lake water can serve as an objective marker of the hydrophysical structure of the lake and its ecological state.

Schulman acquires Citadel

The underwater light regime of a Mediterranean coastal lagoon (Albufera des Grau, Balearic Islands) was studied during four years in order to characterise the spatial and temporal variations in the light attenuation coefficient (K) and to assess the relative contribution of the different water components to total light attenuation.During the studied period K averaged 1.42 m−1 and ranged from 0.63 m−1 to 3.80 m−1. High temporal variability was observed in light attenuation coefficients, but the lagoon was spatially uniform.Percentage bottom irradiance in relation to specific requirements for the dominant macrophyte species (Ruppia cirrhosa) was used as an indicator of benthic light limitation. Macrophyte light limitation was expected to occur in the deepest areas of the lagoon during winter, the most turbid period of the annual cycle. During the macrophyte growing season, higher bottom irradiances were observed but a significant percentage of the lagoon benthos (17% in spring and 7% in summer) was expected to be light limited.In the deepest areas of the lagoon (>2 m) changes in bottom irradiance were related more to variations in the light attenuation coefficient than to variations in water level. However, water level appeared to play an important role in determining benthic light limitation at intermediate depths (1.5 m) for the range of K from 1.8 m−1 to 3.3 m−1.The partitioning of the light attenuation coefficient showed that phytoplankton was the main driver of the temporal dynamics of K, but only accounted for 44% of total light attenuation on average. The mean contributions of the other water components to K were: DOC (47%), tripton (6%), and water (3%). At low values of K, attenuation by DOC was responsible for up to 75% of total attenuation. An equation to predict K from the concentration of water components explained 93% of the variance.

Are large macroalgal blooms necessarily bad? Nutrient impacts on seagrass in upwelling-influenced estuaries.

Knowledge of nutrient pathways and their resulting ecological interactions can alleviate numerous environmental problems associated with nutrient increases in both natural and managed systems. Although not unique, coastal systems are particularly prone to complex ecological interactions resulting from nutrient inputs from both the land and sea. Nutrient inputs to coastal systems often spur ulvoid macroalgal blooms, with negative consequences for seagrasses, primarily through shading, as well as through changes in local biogeochemistry. We conducted complementary field and mesocosm experiments in an upwelling-influenced estuary, where marine-derived nutrients dominate, to understand the direct and indirect effects of nutrients on the macroalgal-eelgrass (Zostera marina L.) interaction. In the field experiment, we found weak evidence that nutrients and/or macroalgal treatments had a negative effect on eelgrass. However, in the mesocosm experiment, we found that a combination of nutrient and macroalgal treatments led to strongly negative eelgrass responses, primarily via indirect effects associated with macroalgal additions. Together, increased total light attenuation and decreased sediment oxygen levels were associated with larger effects on eelgrass than shading alone, which was evaluated using mimic algae treatments that did not alter sediment redox potential. Nutrient addition in the mesocosms directly affected seagrass density; biomass, and morphology, but not as strongly as macroalgae. We hypothesize that the contrary results from these parallel experiments are a consequence of differences in the hydrodynamics between field and mesocosm settings. We suggest that the high rates of water movement and tidal submersion of our intertidal field experiments alleviated the light reduction and negative biogeochemical changes in the sediment associated with macroalgal canopies, as well as the nutrient effects observed in the mesocosm experiments. Furthermore, adaptation of ulvoids and eelgrass to high, but variable, background nutrient concentrations in upwelling-influenced estuaries may partly explain the venue-specific results reported here. In order to manage critical seagrass habitats, nutrient criteria and macroalgal indicators must consider variability in marine-based nutrient delivery and local physical conditions among estuaries.

Possibilities and limitations of non-destructive monitoring of the unicellular green microalgae (Chlorophyta) in the course of balanced growth

Timely information about basic growth parameters, such as dry weight, cell number, and pigment (chlorophyll and carotenoid) content is of importance for the evaluation of physiological conditions and growth kinetics of microalgal suspension cultures. The possibility of non-destructive determination of these parameters using the optical density (total light attenuation due to light scattering and absorption by the microalgal cells and the pigments contained therein) spectra of the cell suspension was shown for unicellular green algae Ettlia carotinosa Komarek and Haematococcus pluvialis Flotow (Chlorophyceae). Estimation of the pigment content of morphologically heterogeneous cultures (such as H. pluvialis) with a reasonable accuracy required the light-scattering compensation of the measured extinction spectra. On the other hand, the scattering signal is useful for dry weight and cell density estimation (in the cultures with insignificant morphological heterogeneity). The spectral regions sensitive to the variation in the target culture parameters was found, and the spectral indices linearly correlated with the latter were constructed. The possibilities and limitations of the optical methods suitable for non-destructive monitoring of the microalgal cultures in the course of their balanced growth and the potential of the developed approach for microalga biotechnology are discussed.

Mixing Behavior of Colored Dissolved Organic Matter and Its Potential Ecological Implication in the Caloosahatchee River Estuary, Florida

Colored dissolved organic matter (CDOM) is one of the most important water quality constituents impacting light attenuation in estuaries; its concentration and distribution influence light quality and quantity available to phytoplankton and submerged aquatic vegetation. By combining field surveys (March 2009–January 2011) and laboratory studies, we examined the estuarine mixing behavior of CDOM and potential loss processes affecting mixing behavior in the Caloosahatchee River Estuary (CRE), Florida. The CDOM absorption coefficient at 355 nm (a CDOM(355), m−1) varied from 0.5 to 64 m−1, with higher values in the upper estuary and lower values downstream, and increased with increasing freshwater inflow. CDOM exhibited three apparent mixing patterns with respect to hypothetical conservative mixing, with (1) conservative behavior or (2) addition at lower inflow and (3) loss at higher inflow. Laboratory studies indicated that flocculation was not a major loss process and that CDOM was susceptible to photolysis. The concentration of CDOM declined as a function of cumulative solar irradiation with a rate of ∼0.003 m2 mol−1, suggesting a photobleaching half-life for CDOM of about 1 w. Apparent nonconservative mixing of CDOM increased or decreased light attenuation by 15–30 %, depending on freshwater inflow and location in the estuary. Light attenuation in the CRE was controlled primarily by CDOM in the upper estuary and by turbidity in the lower estuary, with the average contribution of CDOM to total light attenuation of 55 % (2–92 %) and turbidity of 23 % (3–79 %). The contribution of chlorophyll a (Chl a) to light attenuation was less than both CDOM and turbidity, accounting for about 12 % on average (2–24 %), regardless of location. These results suggest that any nutrient management scenario aimed at improving water clarity through reduction in Chl a concentration should consider the contributions of color and turbidity as well.

A comparative study on the varying exposure to atmospheric fine and coarse particles under urban and rural conditions

This paper is based on the results of three air quality studies conducted in Buenos Aires in Berlin, and in German spas between 2003 and 2007. A high comparability of results was ensured by using the same sampling techniques and analytical methods. Total particle sampling was achieved by active sampling of fine (PM2.5) and passive sampling of coarse particles ≥2.5 µm and giant particles ≥10 µm. The highly absorbing, black, predominantly carbonaceous particles (BC) of fine particle samples were determined by measuring the total light attenuation of filter samples and interpreting the extinction value as black carbon. The difference between the gravimetric total mass concentration of the PM2.5 samples and the BC is defined as the transparent, mostly mineral fine fraction. In coarse/giant particle samples the mean gray value was determined by means of automated light microscopy with subsequent single-particle analysis. “Opaque” particles were separated from the “transparent” particle fraction by applying a grey value threshold level. Microscopic measurement of individual particles was employed to establish the size distribution of the coarse and giant fraction. Due to different health effects, the separate detection of these components is suggested. Decline functions of particles are given, possibly providing useful information for a more detailed specification of the local particle distribution, and for a better estimate of the individual exposure. Atmospheric dispersal of particles was found effected mainly by source characteristics. An increased, spatially largely constant level of fine transparent particles in Berlin indicates a particle plume originating from photochemical processes. Buenos Aires, in contrast, is characterized by a lower background level of fine transparent particles but is considerably affected by fine black particles from diesel emissions and by a higher resuspension of coarse/giant transparent, mainly soil particles. Implications: Mini-volume and passive sampling combined proved to be suitable for measuring total particles by collecting fine, coarse, and giant particles. This approach allows the acquisition of highly space-resolved data on a weekly basis. A method was employed to calculate a size-fractionated particle concentration from passive samples. The results from three air quality studies using this method demonstrate that the black/opaque and transparent particles distinguished differ considerably in spatial distribution, not only due to varying atmospheric residence. Estimates of the exposure of humans, therefore, have to consider the different effects of rural and urban conditions, and differences between regional climates.

Light regime and components of turbidity in a Mediterranean coastal lagoon

The underwater light regime of a Mediterranean coastal lagoon (Albufera des Grau, Balearic Islands) was studied during four years in order to characterise the spatial and temporal variations in the light attenuation coefficient ( K) and to assess the relative contribution of the different water components to total light attenuation. During the studied period K averaged 1.42 m −1 and ranged from 0.63 m −1 to 3.80 m −1. High temporal variability was observed in light attenuation coefficients, but the lagoon was spatially uniform. Percentage bottom irradiance in relation to specific requirements for the dominant macrophyte species ( Ruppia cirrhosa) was used as an indicator of benthic light limitation. Macrophyte light limitation was expected to occur in the deepest areas of the lagoon during winter, the most turbid period of the annual cycle. During the macrophyte growing season, higher bottom irradiances were observed but a significant percentage of the lagoon benthos (17% in spring and 7% in summer) was expected to be light limited. In the deepest areas of the lagoon (>2 m) changes in bottom irradiance were related more to variations in the light attenuation coefficient than to variations in water level. However, water level appeared to play an important role in determining benthic light limitation at intermediate depths (1.5 m) for the range of K from 1.8 m −1 to 3.3 m −1. The partitioning of the light attenuation coefficient showed that phytoplankton was the main driver of the temporal dynamics of K, but only accounted for 44% of total light attenuation on average. The mean contributions of the other water components to K were: DOC (47%), tripton (6%), and water (3%). At low values of K, attenuation by DOC was responsible for up to 75% of total attenuation. An equation to predict K from the concentration of water components explained 93% of the variance.

A simple empirical optical model for simulating light attenuation variability in a partially mixed estuary

Representation of the subsurface light field is a crucial component of pelagic ecosystem and water quality models. Modeling the light field in estuaries is a particularly complicated problem due to the significant influence of high concentrations of dissolved and particulate matter that are derived from both terrestrial and estuarine sources. The goal of this study was to develop a relatively simple but effective way to model light attenuation variability in a turbuid estuary (Chesapeake Bay, United States) in a coupled physical-biological model. We adopted a simple, nonspectral empirical approach. Surface water quality data (salinity was used as a proxy of chromophoric dissolved organic matter [CDOM]) and light measurements from the Chesapeake Bay Program were used to determine the absorption coefficients in a linear attenuation model using regression methods. This model predicts Kc (specific attenuation due to phytoplankton/chlorophylla [chla]), Kt (specific attenuation due to total suspended solids), and Ks (a function of specific attenuation coefficients of CDOM in relation to salinity). The Bay-wide fitted relation between the light attenuation coefficient and water quality concentrations gives generally good estimates of total light attenuation, Kd. The direct inclusion of salinity in the relationship has one disadvantage: it can yield negative values for Kd at high salinities. We developed two separate models for two different salinity regimes. This approach, in addition to solving the negative Kd problem, also accounts for some changes in specific light absorption by chla, seston (nonphytoplankton particulate matter), and CDOM that apparently occur in different salinity regimes in Chesapeake Bay. The resulting model predicts the statistical characteristics (i.e., the mean and variance) of Kd quite accurately in most regions of Chesapeake Bay. We also discuss in this paper the feasibility and caveats of using Kd converted from Secchi depth in the empirical method.

Habitat requirements for submerged aquatic vegetation in Chesapeake Bay: Water quality, light regime, and physical-chemical factors

We developed an algorithm for calculating habitat suitability for seagrasses and related submerged aquatic vegetation (SAV) at coastal sites where monitoring data are available for five water quality variables that govern light availability at the leaf surface. We developed independent estimates of the minimum light required for SAV survival both as a percentage of surface light passing though the water column to the depth of SAV growth (PLW min) and as a percentage of light reaching reaching leaves through the epiphyte layer (PLL min). Value were computed by applying, as inputs to this algorithm, statistically dervived values for water quality variables that correspond to thresholds for SAV presence in Chesapeake Bay. These estimates ofPLW min andPLL min compared well with the values established from a literature review. Calcultations account for tidal range, and total light attenuation is partitioned into water column and epiphyte contributions. Water column attenuation is further partitioned into effects of chlorophylla (chla), total suspended solids (TSS) and other substances. We used this algorithm to predict potential SAV presence throughout the Bay where calculated light available at plant leaves exceededPLL min. Predictions closely matched results of aerial photographic monitoring surveys of SAV distribution. Correspondence between predictions and observations was particularly strong in the mesohaline and polythaline regions, which contain 75–80% of all potential SAV sites in this estuary. The method also allows for independent assessment of effects of physical and chemical factors other than light in limiting SAV growth and survival. Although this algorithm was developed with data from Chesapeake Bay, its general structure allows it to be calibrated and used as a quantitative tool for applying water quality data to define suitability of specific sites as habitats for SAV survival in diverse coastal environments worldwide.

Particulate light attenuation in a large subtropical lake

Deviations among Carlson's trophic state index values were used to quantify a 12-year history of seston composition and underwater light attenuation in Lake Okeechobee, Florida, U.S.A. Deviations between chlorophyll a, total phosphorus, and transparency-based trophic state indices indicated that (i) light attenuation is generally dominated by phosphorus-rich abiotic particles; (ii) abiotic light attenuation is maximal in a central lake region overlying soft mud sediments, and minimal in a near-littoral region overlying hard sand; and (iii) there has been a progressive increase in the relative contribution of algal pigments to total light attenuation between 1980 and 1992. Coincident with that 12-year trend, there have been declines in external nitrogen loads, lake water nitrogen:phosphorus ratios, and wind velocities. Surface water temperatures in the lake have significantly increased. Explanations for the trend in light attenuation include (i) more favorable meteorological conditions for algal growth, which increased the contribution of algae to overall light attenuation and (ii) reduced nitrogen:phosphorus ratios favoring proliferation of buoyant cyanobacteria, which are more effectively sampled by surface water monitoring. In either case, the trend did not coincide historically with enhanced nutrient loading, the common cause of algal proliferation in lakes.

Reflection losses in polystyrene fibres

The reflection losses, which occur during light guidance through polystyrene fibres of 30 μm diameter at their core-cladding interface, have been determined in order to evaluate their contribution to the total light attenuation of scintillating fibres. For the deviation (1 - q) of the reflection coefficient q from unity we obtained: 6 × 10 −5 (at 458 nm), 5.36 × 10 −5 (at 514 nm) and 5 × 10 −5 (at 633 nm). In addition, we found light losses in the polystyrene core, which we attribute to Rayleigh scattering on submicron density variations in polystyrene. The resulting scattering lengths are: 3.6 m (at 420 nm) and 9.5 m (at 530 nm).