Attenuation Of Blue Light Research Articles

Effects of combined ecological restoration measures on water quality and underwater light environment of Qingshan Lake, an urban eutrophic lake in China

Ecological restoration is vital in the management of eutrophic lakes. However, the effect of combined ecological restoration measures on the improvement of water quality and the light environment of urban eutrophic lakes requires further exploration. This study considered Qingshan Lake, a typical urban eutrophic lake in the middle reaches of the Yangtze River in China and explored the changes in the water quality and light environment before and after the implementation of combined ecological restoration measures from 2021 to 2022. The results showed that: (1) Ecological restoration significantly improved the transparency of Qingshan Lake (P < 0.05), with transparency increased from 33.1 cm to 96.0 cm. Total phosphorus, total nitrogen, chlorophyll a, permanganate index, suspended solids and turbidity decreased by 52.11 %, 65.47 %, 73.84 %, 92.11 %, 83.11 % and 77.52 %; respectively (P < 0.05). (2) Following ecological restoration, Qingshan Lake converted from severe eutrophication to mesotrophication, and the trophic level index decreased from 75.29 to 49.65 (P < 0.05). (3) Ecological restoration had a significant effect on improving underwater light environments. After ecological restoration, the light attenuation coefficient changed between 1.61–3.12 m−1, and the annual mean value decreased by 61.96 % (P < 0.05). The euphotic zone depth changed from 1.85 to 6.19 m, an increase of 167.68 %. (4) Ecological restoration reduced the attenuation of blue light, which reduced the red-blue ratio (R/B) of water. In general, turbidity had the greatest impact on light attenuation and R/B of Qingshan Lake, and ecological restoration combined with multiple measures had a positive effect on the management of eutrophic lakes.

Effects of canopy spectral composition on growth and photosynthetic fluorescence characteristics of Pinus koraiensis and Quercus mongolica seedlings

We investigated the responses of leaf and individual traits, growth, and fluorescence characteristics of seedlings of two dominant species of broad-leaved Korean pine forest in Changbai Mountain, i.e., Pinus koraiensis and Quercus mongolica, to five spectrum-attenuation treatments. Results showed that the architecture and growth of P. koraiensis and Q. mongolica seedlings were mainly regulated by ultraviolet B (UV-B) radiation and blue light. The attenuation of blue light significantly decreased leaf area ratio and relative growth rate of two species. The attenuation of UV-B radiation significantly increased leaf area ratio and relative growth rate of P. koraiensis seedlings by 41.8% and 47.7%, respectively, and significantly decreased plant height, total leaf area, and biomass accumulation of Q. mongolica seedlings. Furthermore, the attenuation of UV-B radiation significantly decreased the fluorescence regulation ability of two tree seedlings, with lower magnitude of P. koraiensis than Q. mongolica. The non-regulatory quantum yield (ΦNO) of P. koraiensis increased by 31.6%, and the ΦNPQ/ΦNO ratio, an indicator for photosynthetic fluorescence regulation ability, decreased by 37.5%. These results suggested that those two species might have evolved adaptation strategies to changes in canopy spectral compositions of their respective habitats. Q. mongolica seedlings tended to improve light capture ability through rapid morphological responses, while P. koraiensis seedlings preferred to increase carbon assimilation efficiency by adjusting fluorescence characteristics.

Effect of thickness of CAD/CAM materials on light transmission and resin cement polymerization using a blue light-emitting diode light-curing unit.

Evaluate the effect of thickness of high-translucency (HT) CAD/CAM materials on irradiance and beam profile from a blue light-emitting diode light-curing unit (LCU) and on the degree of conversion (DC) and maximum polymerization rate (Rpmax ) of a light-cured resin cement (LCC). The direct output from the LCU, the light transmission and irradiance ratio (IR) through one conventional composite and nine HT CAD/CAM materials (0.5, 1.0, 1.5, or 2.0-mm thick; n=5) were measured with a integrating sphere coupled to a spectrometer. The light beam was assessed with a beam profiler camera. The DC at 600 s and the Rpmax of one LCC was determined using a Fourier transform infrared spectrometer (n=5). Data were analyzed by ANOVA followed by Tukey's tests, and Dunnett's test was also used for irradiance data (α=0.05). A significant decrease in irradiance through all materials occurred as thickness increased. Thin CAD/CAM materials improved light homogeneity, which decreased with the increase in thickness. The DC of the LCC directly exposed to light was the same as when exposed to 45%, 25%, 15%, or 5% IRs. Rpmax decreased with the decrease in IR. Although the HT CAD/CAM materials reduced the irradiance from the LCU, minor effects were observed in the LCC's DC. Despite the light attenuation of blue light through different CAD/CAM materials that were up to 2-mm thick, the degree of conversion of one brand of light-cured resin cement was clinically acceptable when the LCU was used for 30 s.

Contrasting Sea‐Ice Algae Blooms in a Changing Arctic Documented by Autonomous Drifting Buoys

AbstractNovel observations of the seasonal evolution of an ice algal bloom on the Chukchi shelf were collected by two autonomous buoys deployed 180 km apart in first‐year drifting sea ice. High attenuation of blue light in the bottom of the ice indicated considerable accumulation of ice algae biomass with derived Chlorophyll‐a concentrations (Chl a) up to 184 mg m−2. Differences in the magnitude and persistence of ice algae biomass under each buoy appear to have been driven by differences in snow thickness, as ice thickness was similar between the sites. Minimal snow cover (0.02 m) around one buoy was associated with algae growth beginning in mid‐May and lasting 70 days. The second buoy had notably more snow (0.4 m), causing ice algae production to lag behind the first site by approximately 4 weeks. The delay in growth diminished the peak of ice algae Chl a and duration compared to the first site. Light attenuation through the ice was intense enough at both buoys to have a potentially inhibiting impact on water column phytoplankton Chl a. Modeling ice algae growth with observed light intensities determined that nutrients were the limiting resource at the low snow site. In contrast, the algae at the high snow site were light‐limited and never nutrient‐limited. These data point toward changes in ice algae phenology with an earlier and longer window for growth; and nutrients rather than light determining the longevity and magnitude of production.

Revealing the synergistic effects of cells, pigments, and light spectra on light transfer during microalgae growth: A comprehensive light attenuation model

As the sole energy for photosynthesis, light decrease rapidly with path due to absorption by pigments and scattering by cells in microalgal suspensions. By comprehensively considering cell concentrations, pigment components, and light spectra, a modified Cornet model for light transmission in microalgal suspensions is established. The developed model better fits experimental data with a higher adjusted R2, which is 5% higher than the model that is based only on cell concentration. The attenuation of blue light is the most severe, followed by red and green light. Among the three main pigments, total carotenoids contribute the most to the absorption of blue and green light (with contribution coefficients of 89.26 ± 4.53% and 46.04 ± 3.77%, respectively), and chlorophyll a contributes the most to the absorption of red light (with a contribution coefficient of 75.33 ± 5.08%). This study provides a better understanding and prediction of light transmission during microalgal cultivation.

Grapevine morphological shade acclimation is mediated by light quality whereas hydraulic shade acclimation is mediated by light intensity

Plants acclimate to shade by sensing light signals such as low photosynthetic active radiation (PAR), low blue light (BL) levels and low red-to-far red ratios (R:FR) trough plant photoreceptors cross talk. We previously demonstrated that grapevine is irresponsive to variations in R:FR and that BL-attenuation mediates morphological and architectural responses to shade increasing light interception and absorption efficiencies. However, we wondered if grapevine respond to low R:FR when BL is attenuated at the same time. Our objective was to evaluate if morphological, architectural and hydraulic acclimation to shade is mediated by low R:FR ratios and BL attenuation. To test this, we carried out experiments under natural radiation, manipulating light quality by selective sunlight exclusion and light supplementation. We grew grapevines under low PAR (LP) and four high PAR (HP) treatments: HP, HP plus FR supplementation (HP + FR), HP with BL attenuation (HP–B) and HP with BL attenuation plus FR supplementation (HP–B + FR). We found that plants grown under HP-B and HP-B + FR had similar morphological (stem and petiole length, leaf thickness and area), architectural (laminae’ angles) and anatomical (stomatal density) traits than plants grown under LP. However, only LP plants presented lower stomata differentiation, lower δ13C and hence lower water use efficiency. Therefore, even under a BL and R:FR attenuated environment, morphological and architectural responses were modulated by BL but not by variation in R:FR. Meanwhile water relations were affected by PAR intensity but not by changes in light quality. Knowing grapevine responses to light quantity and quality are indispensable to adopt tools or design new cultural management practices that manipulate irradiance in the field intending to improve crop performance.

Sand-Dust Image Restoration Based on Reversing the Blue Channel Prior

Images acquired under sand-dust weather conditions are severely degraded, with low contrast and severe color shift. The reason is that, due to the influence of sand-dust particles, light is scattered and absorbed, resulting in a blurred image and low contrast; the color shift is caused by the rapid attenuation of blue light. Therefore, to solve the problem of color shift and poor visibility in sand-dust images, this paper proposes a sand-dust image restoration method based on reversing the blue channel prior (RBCP). Under the influence of the blue channel, the dark channel prior (DCP) method will fail. Therefore, the method first reverses the blue channel of the sand-dust image and uses the dark channel prior method, which we call RBCP, and then, RBCP is used to estimate the atmospheric light and transmission map and recover the sand-dust image. The restored image shows significantly improved visibility. When estimating the transmission map, a guiding filter is used to improve the coarse transmission map, and a tolerance mechanism is introduced to modify the transmission map of bright areas in the sky to solve the problem of distortion in the sky. Finally, combined with the gray world, an adaptive color adjustment factor is introduced into the restoration model to remove the color shift. Experimental results via qualitative and quantitative evaluation demonstrate that the proposed method can effectively recover clear sand-dust images and produce results superior to those of other state-of-the-art methods.

Improvement or Worsening of Human Contrast Sensitivity Due to Blue Light Attenuation at 450 nm.

PurposeThe work was aimed at comparing contrast sensitivity performance in an indoor environment with two filters, which differ only in the presence of a band at 450±20 nm in the transmittance spectrum.Patients and MethodsThirty-nine subjects participated. The filters were the Standard (ST) and Professional (PRO) Drive lenses (Hoya, Japan), the latter showing the attenuation band at 450 nm. Photopic contrast sensitivity (CS) was measured at different spatial frequencies from 1.5 to 18 cpd through Functional Acuity Contrast Test with both lenses (LogCSST and LogCSPRO, respectively). The areas under the curves of LogCSST and LogCSPRO as a function of the spatial frequency were also considered.ResultsIn the range of the measured values of LogCSST for the thirty-nine participants, at each spatial frequency and also for the areas, the difference Δ = LogCSPRO – LogCSST was found to decrease and change sign from positive to negative as a function of LogCSST, thus allowing to deduce a threshold (LogCSthreshold) for LogCSST corresponding to Δ=0. Significant CS worsening was found with the PRO compared to the ST lens for the subjects showing LogCSST > LogCSthreshold. Vice versa, CS improvement was found when LogCSST < LogCSthreshold.ConclusionIn the choice of a blue-filtering lens, practitioners should take into consideration that the attenuation of light in the range 420–470 nm is expected to produce a CS worsening in subjects showing a relatively high initial CS (higher than a threshold CS). For these subjects, the general reduction of transmitted light intensity prevails on possible advantages. On the contrary, subjects showing a relatively low initial CS are expected to show a CS improvement because the attenuation of light in the range 420–470 nm is expected to reduce intraocular scattering and to mimic the effect as an optical filter of the human macular pigment, advantages which prevail on the reduction of the transmitted light intensity.

Blue light attenuation mediates morphological and architectural acclimation of Vitis vinifera cv. Malbec to shade and increases light capture

Grapevine is one of the most important fruit crops worldwide. Vineyard management practices affect light interception and spectral characteristics inside the canopy. Plant photoreceptors drive shade acclimation responses after the perception of light signals such as low photosynthetic active radiation (PAR), low blue light (BL) levels and low red-to-far red ratios (R:FR). Grapevine plants effectively acclimate to shade but are irresponsive to variations in R:FR perceived by phytochromes. To determine if BL attenuation mediate shade acclimation in this species, we manipulated sunlight reaching the plants by filtering. Vitis vinifera cv. Malbec plants were grown under low (LOW PAR) and high (HIGH PAR) neutral light environments, and under high light but attenuating the BL component of the spectrum (-BLUE). We evaluated morphological, biochemical and architectural responses to shade, and modelled light interception (LIE) and absorption (Ea) efficiencies. We found that plants grown under –BLUE mimicked morphological and architectural responses of plants cultivated under LOW PAR. In addition, LIE and Ea were higher in plants grown under –BLUE and LOW PAR than in HIGH PAR. Our findings suggest that morphological and architectural responses to shade are under the control of BL-photoreceptors in grapevine. However, BL attenuation failed to induce the accumulation of photosynthetic pigments in leaves observed under LOW PAR. Unchanged biomass accumulation across light treatments suggests that improved light capture counterbalanced irradiance reduction. These results might help in the design of practices that manipulate irradiance in the field, and that are increasingly being used as environment-friendly management tools to improve crop performance.

Femtosecond laser-colorized indium-tin-oxide films for blue light attenuation and image screening

Laser-colorized indium-tin-oxide (ITO) films are fabricated using femtosecond laser processing. By varying the laser fluences, nanostructures with cotton, brick and ripple forms are generated on the surface of ITO films, which produces cyan, yellow and orange colors. The fluence-dependent nanostructures on the surface of ITO films also significantly attenuates blue light so these materials are suited to eye protection and the screening of images behind ITO films for information security.

Epidermal UV-A absorbance and whole-leaf flavonoid composition in pea respond more to solar blue light than to solar UV radiation.

Plants synthesize phenolic compounds in response to certain environmental signals or stresses. One large group of phenolics, flavonoids, is considered particularly responsive to ultraviolet (UV) radiation. However, here we demonstrate that solar blue light stimulates flavonoid biosynthesis in the absence of UV-A and UV-B radiation. We grew pea plants (Pisum sativum cv. Meteor) outdoors, in Finland during the summer, under five types of filters differing in their spectral transmittance. These filters were used to (1) attenuate UV-B; (2) attenuate UV-B and UV-A < 370 nm; (3) attenuate UV-B and UV-A; (4) attenuate UV-B, UV-A and blue light; and (5) as a control not attenuating these wavebands. Attenuation of blue light significantly reduced the flavonoid content in leaf adaxial epidermis and reduced the whole-leaf concentrations of quercetin derivatives relative to kaempferol derivatives. In contrast, UV-B responses were not significant. These results show that pea plants regulate epidermal UV-A absorbance and accumulation of individual flavonoids by perceiving complex radiation signals that extend into the visible region of the solar spectrum. Furthermore, solar blue light instead of solar UV-B radiation can be the main regulator of phenolic compound accumulation in plants that germinate and develop outdoors.

Red Light Effects on Blue Light–Based Phototropism in Roots of Arabidopsis thaliana

Premise of research. Light has profound effects on plant development, and the interaction between red and blue light pathways can play a significant role in the phototropism of plant seedlings. The aim of this research was to clarify the involvement of red light effects on blue light phototropism in both roots and hypocotyls of Arabidopsis thaliana seedlings. Pivotal results. In contrast to the well-documented effects in hypocotyls, we found that red light inhibits blue light–based phototropism in roots of the Landsberg ecotype and that this inhibition is reduced in mutants lacking phytochromes A and B. Attenuation of blue light root phototropism by red illumination was also observed in Arabidopsis seedlings of the C24 ecotype, and this inhibition was not observed in a transgenic strain lacking all phytochromes (in which the deficiency is specific to the root only). However, in contrast to the Landsberg and C24 ecotypes, roots of Arabidopsis seedlings of the Columbia ecotype display a significant enhancement of blue light phototropism by red light pretreatment. Conclusions. Our results suggest that differences exist in the mechanisms of phototropism based on ecotype and that phytochromes are involved in the red light attenuation of blue light–based root phototropism when it occurs. This study is one of the first to consider red light effects specifically on root phototropism.

Blue light regulated shade avoidance

Most plants grow in dense vegetation with the risk of being out-competed by neighboring plants. These neighbors can be detected not only through the depletion in light quantity that they cause, but also through the change in light quality, which plants perceive using specific photoreceptors. Both the reduction of the red:far-red ratio and the depletion of blue light are signals that induce a set of phenotypic traits, such as shoot elongation and leaf hyponasty, which increase the likelihood of light capture in dense plant stands. This set of phenotypic responses are part of the so called shade avoidance syndrome (SAS). This addendum discusses recent findings on the regulation of the SAS of Arabidopsis thaliana upon blue light depletion. Keller et al. and Keuskamp et al. show that the low blue light attenuation induced shade avoidance response of seedling and rosette-stage A. thaliana plants differ in their hormonal regulation. These studies also show there is a regulatory overlap with the R:FR-regulated SAS.

Cryptochrome 1 and phytochrome B control shade‐avoidance responses in Arabidopsis via partially independent hormonal cascades

Plants respond to a reduction in the red/far-red ratio (R:FR) of light, caused by the proximity of other plants, by initiating morphological changes that improve light capture. In Arabidopsis, this response (shade avoidance syndrome, SAS) is controlled by phytochromes (particularly phyB), and is dependent on the TAA1 pathway of auxin biosynthesis. However, when grown in real canopies, we found that phyB mutants and mutants deficient in TAAI (sav3) still display robust SAS responses to increased planting density and leaf shading. The SAS morphology (leaf hyponasty and reduced lamina/petiole ratio) could be phenocopied by exposing plants to blue light attenuation. These responses to blue light attenuation required the UV-A/blue light photoreceptor cry1. Moreover, they were mediated through mechanisms that showed only limited overlap with the pathways recruited by phyB inactivation. In particular, pathways for polar auxin transport, auxin biosynthesis and gibberellin signaling that are involved in SAS responses to low R:FR were not required for the SAS responses to blue light depletion. By contrast, the brassinosteroid response appeared to be required for the full expression of the SAS phenotype under low blue light. The phyB and cry1 inactivation pathways appeared to converge in their requirement for the basic/helix-loop-helix (bHLH) transcription factors PHYTOCHROME INTERACTING FACTORs 4 and 5 (PIF4 and PIF5) to elicit the SAS phenotype. Our results suggest that blue light is an important control of SAS responses, and that PIF4 and PIF5 are critical hubs for a diverse array of signaling routes that control plant architecture in canopies.

In vivo evaluation of blue-light attenuation with tinted and untinted intraocular lenses

To evaluate blue-light attenuation in eyes with a tinted intraocular lens (IOL) or an untinted IOL. Department of Ophthalmology, University Hospital of Crete, Crete, Greece. Comparative case series. Patients had lens extraction and implantation of an Acrysof Natural tinted or Tecnis ZA9003 or Softec III untinted acrylic IOL. The luminance ratio of green (530 nm) and blue (465 nm) light (green:blue ratio) required for isoluminant perception was determined by heterochromatic flicker photometry. Patients were tested preoperatively and 20 days postoperatively. The parafoveal measure of the green:blue ratio, expressed in decibels, is proportional to the blue-light attenuation by the lens. Twenty-two patients received the tinted IOL and 21 the untinted IOL. Preoperatively, age was strongly linearly correlated with the green:blue ratio (r = 0.59, P < .001). The mean postoperative decrease in the green:blue ratio was greater in the untinted IOL group (P = .003). Postoperatively, the tinted IOL group had a significantly higher green:blue ratio than the untinted IOL group (P < .001). In the tinted IOL group, the green:blue ratio was linearly related to IOL dioptric power. Less blue light reached the retina with tinted IOLs than with untinted IOLs. The absorption properties of tinted IOLs seemed to resemble those of the aging human crystalline lens, while untinted IOLs resembled the lower levels of blue-light attenuation of younger lenses. Thus, tinted IOLs may protect against the presumed blue-light hazard. No author has a financial or proprietary interest in any material or method mentioned.

In vivo assessment of blue light attenuation of the crystalline lens and tinted and not tinted intraocular lenses

Abstract Purpose To compare lens absorption in vivo, as estimated by blue light luminance perception, of patients with tinted IOLs versus patients with clear IOLs, and with their status before cataract surgery. Methods We tested 43 patients with variant density of nuclear senile cataract (18 had 0 to 1+ and 25 more than 1+), before and after lens extraction and IOL implantation. 21 received clear IOL and 22 the AcrySof® Natural (Alcon). The absorption of blue light was assessed by measuring the parafoveal relative sensitivity of blue‐green radiation using Heterochromatic Flicker Photometry (MPS 9000 QuantifEYETM, ZeaVision©). Results Preoperative results indicate that blue light attenuation is increasing with age. The postoperative results show that tinted IOLs absorb significantly more compared to clear IOLs (p&lt;0.001). The difference in postoperative absorption with tinted IOLs from preoperative status was not statistically signifficant (p=0.3), and in the group of patients with 0 to 1+ cataract density the preoperative with the postoperative absorption was similar (p=0.941). On the contrary, the absorption of clear IOLs was significantly reduced postoperatively in the low cataract density group (p&lt;0.001) and also in the total group of patients (p&lt;0.001). Conclusion The tint may simulate the aged crystalline lens of patients with low cataract density in blue light attenuation.This may offer protection to the retina from the photochemical damage caused by high energy short wavelength radiation.

Colored dissolved organic matter in Tampa Bay, Florida

Absorption and fluorescence of colored dissolved organic matter (CDOM) and concentrations of dissolved organic carbon (DOC), chlorophyll and total suspended solids in Tampa Bay and its adjacent rivers were examined in June and October of 2004. Except in Old Tampa Bay (OTB), the spatial distribution of CDOM showed a conservative relationship with salinity in June, 2004 ( a CDOM(400) = − 0.19 × salinity + 6.78, R 2 = 0.98, n = 17, salinity range = 1.1–32.5) with little variations in absorption spectral slope and fluorescence efficiency. This indicates that CDOM distribution was dominated by mixing. In October, 2004, CDOM distribution was nonconservative with an average absorption coefficient ( a CDOM(400), ∼ 7.76 m − 1 ) about seven times higher than that in June (∼ 1.11 m − 1 ). The nonconservative behavior was caused largely by CDOM removal at intermediate salinities (e.g., a CDOM(400) removal > 15% at salinity ∼ 13.0), which likely resulted from photobleaching due to stronger stratification. The spatial and seasonal distributions of CDOM in Tampa Bay showed that the two largest rivers, the Alafia River (AR) and Hillsborough River (HR) were dominant CDOM sources to most of the bay. In OTB, however, CDOM showed distinctive differences: lower absorption coefficient, higher absorption spectral slopes, and lower ratios of CDOM absorption to DOC and higher fluorescence efficiency. These differences may have stemmed from (1) changes in CDOM composition by more intensive photobleaching due to the longer residence time of water mass in OTB; (2) other sources of CDOM than the HR/AR inputs, such as local creeks, streams, groundwater, and/or bottom re-suspension. Average CDOM absorption in Tampa Bay at 443 nm, a CDOM(443), was about five times higher in June and about ten times higher in October than phytoplankton pigment absorption, a ph(443), indicating that blue light attenuation in the water column was dominated by CDOM rather than by phytoplankton absorption throughout the year.

Phytoplankton Primary Production and Light in Waldo Lake, Oregon

ABSTRACT Waldo Lake is located in the Willamette National Forest along the west side of Oregon's Cascade Mountain Range. The lake is regarded as one of the most oligotrophic lakes in the world, chemically similar to distilled water, with very low rates of phytoplankton primary production and concentrations of chlorophyll a. Historically, vertical light transmission was considerable, with 1% of the lake's incident solar radiation penetrating to depths greater than 60 m. The lake remains exceedingly clear, as demonstrated by transmissometer profiles and Secchi-disk readings that range between 35 and 40 m. Deep chlorophyll maxima are usually found between 60 and 100 m where measurable light is less than 1% of surface illumination. Conversely, primary production rates and assimilation numbers are maximum in the lake's upper 20 m. Unusually large assimilation numbers in the upper 20 m suggests that the phytoplankton that occupy this stratum are photosynthetically efficient, capable of high rates of production with minimal chlorophyll. There are indications, however, that downward irradiance of blue, green and red light has shifted toward a condition in which the attenuation of blue light has increased more than green and red light. This may be attributed to an increase in phytoplankton density, expressed as a roughly 20-fold increase in phytoplankton primary production over the past 25–30 years. On this basis, Waldo Lake may have shifted from an ultraoligotrophic condition to a more eutrophic state.

Light absorption and photosynthesis of a benthic moss community: importance of spectral quality of light and implications of changing light attenuation in the water column

1. The underwater light climate and benthic moss communities of Grane Langsø were investigated in May 1997 to determine the potential effects on benthic production of changing water column attenuation and spectral quality of light.2. A reduction in water clarity in the lake since the 1960s was manifested as a marked increase in the attenuation of blue light, relative to red light, which can be attributed to increased dissolved organic carbon.3. The biomass of the benthic moss community ranged from a maximum of 195 gDW m−2 at a depth of 4 m to 39 g DW m−2 at a depth of 10 m and Drepanocladus exannulatus contributed 70% of the biomass at all depths.4. Absorption of PAR by D. exannulatus was maximal in the highly pigmented youngest parts of the plant and these correspondingly showed the highest rates of net photosynthesis. The absolute amount of chlorophyll‐a per g dry weight was greater at 10 m than 2 m, but the ratio of accessory pigments to chlorophyll‐a did not change. Deep growing plants did not show adaptation to changed light quality.5. Increased attenuation of blue light and the resultant overall decrease in water clarity is likely to impact negatively on net annual production of benthic macrophytes of Grane Langsø. Any further increase in dissolved organic carbon concentration has the potential to markedly decrease the depth to which mosses grow by reducing the length of time in a year during which net photosynthesis occurs.

The impact of phytoplankton on spectral water transparency in the Southern Ocean: implications for primary productivity

Spectral water transparency in the Northern Weddell Sea was studied during Austral spring. The depth of the 1-% surface irradiance level (“euphotic depth”) varied between 35 and 109 m and was strongly influenced by phytoplankton biomass. Secchi depths were non-linearly related to euphotic depth. In phytoplankton-poor water, the most penetrating spectral region was restricted to a relatively narrow waveband in the blue (∼488 nm), but the range was broader, between 488 and 525 nm when phytoplankton were abundant. Water transparency in the red spectral range was always low and only to a small extent affected by phytoplankton. Two independent procedures were used to quantify the impact of phytoplankton on spectral water transparency: (1) Regression analysis of spectral in situ vertical light attenuation coefficients in the sea, against coincident chlorophyll concentrations. This method gave chlorophyll-specific light attenuation coefficients; the y-intercept could be interpreted as a measure of light attenuation by pure water plus non-algal material. (2) Spectra of in vivo light absorption derived by spectroscopy, using phytoplankton enriched to varying degrees onto filters. Thus chlorophyll-specific absorption cross-sections were determined. Estimates obtained by both procedures were in close agreement. By integrating over the spectrum of underwater irradiance, in situ chlorophyll-specific absorption cross sections of phytoplankton suspensions, related to all photosynthetically active radiation, were calculated. Light absorption by phytoplankton for photosynthesis is accomplished mainly in the blue spectral range. Also dissolved and particulate organic matter contributed to the attenuation of blue light. Because in water poor in phytoplankton, underwater irradiance was progressively restricted to blue light, chlorophyll-specific absorption cross-sections of phytoplankton, averaged over the spectrum of photosynthetically active irradiance, increased with water depth. In water with elevated phytoplankton biomass, overall light attenuation was generally enhanced. However, because the spectral composition of underwater light changed relatively little with depth, except immediately below the water surface, light absorption cross-sections of phytoplankton changed little below 10 m depth. Vertical differences in the proportions of underwater light absorbed by the phytoplankton community here were mainly dependent on biomass variations. Because of the comparatively small attenuation of blue light by non-algal matter, the efficiency of light harvesting by phytoplankton at any given concentration of chlorophyll in Antractic waters is greater than in other marine regions. At the highest phytoplankton biomass observed by us, as much as 70% of underwater light was available for phytoplankton photosynthesis. When phytoplankton were scarce, <10% of underwater light was harvested by phytoplankton.