Contribution of epiphyte load to light attenuation on seagrass leaves is small but critical in turbid waters

2020 ◽  
Vol 71 (8) ◽  
pp. 929
Author(s):  
Yan Xiang Ow ◽  
Kai Jun Ng ◽  
Samantha Lai ◽  
Siti Maryam Yaakub ◽  
Peter Todd
Keyword(s):  
Water Column ◽  
Light Transmission ◽  
Light Attenuation ◽  
Attenuation Coefficients ◽  
Seagrass Meadows ◽  
Relative Contribution ◽  
Turbid Waters ◽  
Cymodocea Rotundata ◽  
The Relationship ◽  
Epiphyte Load

Quantifying contributors to light attenuation is useful for the management of seagrass meadows. Epiphytic growth on seagrasses can lead to diminished light for the host plant, impairing photosynthesis and growth. Here, we quantify the contributions of the water column and epiphytic load to light attenuation in a Cymodocea rotundata meadow at Chek Jawa, Singapore. Using a modified spectrometer and seagrass mimics (clear polyethene strips) colonised by epiphytes, we determined the relationship between light transmission (400–700nm) and epiphyte load. Subsequently, we derived the percentage of surface light that reaches the leaf surface (PLL) over a range of epiphyte biomass and water-column light-attenuation coefficients (Kd). Results indicated that the relative contribution to light attenuation by epiphytic biomass was greater in clearer waters (Kd<0.5) than in turbid waters. As Kd increases, the amount of epiphytic material required to reduce PLL to minimum light requirement (11%) decreases exponentially. At Chek Jawa, the average epiphytic load was 32mg DW cm−2, which was close to the estimated amount (33mg DW cm−2) required to reduce PLL to 11% at prevailing turbidity levels. Our findings suggest that high epiphyte load is benign in clear waters, but becomes critical in turbid waters.

A model for the light-limited growth of buoyant phytoplankton in a shallow, turbid waterbody

1994 ◽  
Vol 45 (5) ◽  
pp. 847 ◽  
Author(s):  
BE Sherman ◽  
IT Webster
Keyword(s):  
Wind Speed ◽  
Water Column ◽  
Chlorophyll Concentration ◽  
Light Attenuation ◽  
Euphotic Zone ◽  
Limited Growth ◽  
Potential Growth ◽  
Column Temperature ◽  
Turbid Waters ◽  
Neutrally Buoyant

A computer model was used to explore the relationship between buoyancy and the light-limited growth of phytoplankton in very turbid waters. The model simulates the potential growth of phytoplankton as a function of flotation speed, using field observations of photosynthetically active radiation, wind speed, surface-layer thickness (from water-column temperature data), and light attenuation made at Rushy Billabong on the River Murray from 28 November 1991 to 26 March 1992. A unique feature of the model is the simulation of the development and dispersal of surface scums as a function of wind speed. Under nutrient-replete conditions, the model predicted that phytoplankton with a flotation speed of 1-10 m day-1 (typical of Anabaena flos-aquae and Microcystis aeruginosa) would grow up to four times faster than would neutrally buoyant phytoplankton with the same maximum specific growth rate. In the shallow system modelled, high flotation speeds allowed a large proportion of the total population to rise into the euphotic zone shortly after the onset of stratification each day. Surface scums played an important role in maintaining the more buoyant phytoplankton populations close to the water surface. Under the very turbid conditions in the billabong (100 nephelometric turbidity units), self-shading became significant only when the mean chlorophyll concentration in the water column approached 100 mg chla m-3.

scholarly journals MODELLING, SIMULATION AND VISUALIZATION OF A MULTISPECIFIC PHILIPPINE SEAGRASS MEADOW

2019 ◽  
Vol XLII-4/W19 ◽  
pp. 77-82
Author(s):  
V. P. Bongolan ◽  
G. M. Torres ◽  
J. E. Branzuela
Keyword(s):  
Clonal Growth ◽  
Seagrass Meadow ◽  
Light Attenuation ◽  
Thalassia Hemprichii ◽  
Diffusion Limited Aggregation ◽  
Seagrass Meadows ◽  
Branching Angle ◽  
Coexisting Species ◽  
Cymodocea Rotundata ◽  
Model Features

Abstract. Seagrass meadows are constantly under threat from natural and man-made stresses due to its shallow existence in the coastal environment. Restoration and preservation of seagrasses by means of rehabilitation or transplanting strategies is possible, but the studies have been limited. An agent-based model of a mixed Philippine seagrass meadow is presented. Three species were used for testing: Enhalus acoroides, Thalassia hemprichii, and Cymodocea rotundata. The model features parameter-based clonal growth of seagrass species, recruitment of new seagrass apices through basic flowering/seeding, and a crowding logic for multiple coexisting species in a single meadow. Seagrass clonal growth is modeled using a modified Diffusion-Limited Aggregation (DLA) model. Each species has a preconfigured set of parameters for clonal growth including rhizome elongation, branching rate, vertical elongation rate, rhizome branching angle and shoot age. Seed recruitment is applied through occasional flowering/seeding events configurable per species. We developed a simple three-species competition model which controls the growth and direct competition effects based on a configurable population size and comparison radius. Upon further calibration and validation, the model would enable more accurate long-term predictions for different rehabilitation and transplanting strategies of mixed seagrass meadows. Further improvements can also be implemented, particularly taking into account the environmental variables within the meadows such as light attenuation and salinity, among other factors.

Phytoplankton Distribution and Light Attenuation in Port Hacking Estuary

1978 ◽  
Vol 29 (1) ◽  
pp. 31 ◽  
Author(s):  
BD Scott
Keyword(s):  
Water Column ◽  
Chlorophyll Concentration ◽  
Light Attenuation ◽  
Suspended Sediments ◽  
Tidal Exchange ◽  
Phytoplankton Distribution ◽  
Relationship Of ◽  
The Relationship ◽  
In Vivo Chlorophyll Fluorescence

The distribution of phytoplankton in a marine dominated estuary is described in terms of in vivo chlorophyll fluorescence, phytoplankton photosynthesis rates at constant irradiance, and the attenuation of solar irradiance by the water column. The phytoplankton distribution was consistent with the physiography and water circulation in the estuary. A method is described for estimating the proportions of suspended sediments, introduced with runoff from the land, which are removed from the estuary by tidal exchange or by sinking. Estimates of the proportions of phytoplankton and detritus in the water column are derived from the relationship of chlorophyll concentration to the extinction coefficient.

scholarly journals First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone

2020 ◽  
Author(s):  
Matthew G. Cooper ◽  
Laurence C. Smith ◽  
Asa K. Rennermalm ◽  
Marco Tedesco ◽  
Rohi Muthyala ◽  
...  
Keyword(s):  
Light Transmission ◽  
Light Attenuation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radiative Heating ◽  
Ablation Zone ◽  
Field Site ◽  
Attenuation Coefficients ◽  
Near Surface ◽  
Ice Surface

Abstract. Light transmission into bare glacial ice affects surface energy balance, bio-photochemical cycling, and light detection and ranging (LiDAR) laser elevation measurements but has not previously been reported for the Greenland Ice Sheet. We present in-ice solar irradiance measured over the spectral range 350–900 nm and 12–77 cm depth collected at a site in the western Greenland ablation zone. The acquired spectral irradiance measurements are used to calculate flux attenuation coefficients using an exponential decay Bouguer law model and are compared to values calculated from two-stream radiative transfer theory. Relative to asymptotic two-stream theory, our empirical attenuation coefficients are up to one order of magnitude larger in the range 350–530 nm, suggesting light absorbing particles embedded in ice enhance visible light absorption at our field site. The empirical coefficients accurately describe light attenuation in the ice interior but underestimate light attenuation near the ice surface. Consequently, Bouguer’s law overestimates transmitted flux by up to 50 % depending on wavelength. Refraction is unlikely to explain the discrepancy. Instead, vertical variation in the ice microstructure and the concentration of light absorbing particles appears to enhance near-surface attenuation at our field site. The magnitude of this near-surface attenuation implies that optical penetration depth is lower by up to 19 cm (28 %) at wavelengths relevant to visible-wavelength lidar altimetry of ice surface elevation (e.g. 532 nm for the Ice, Cloud, and Land Elevation Satellite-2) than is suggested by e-folding depths inferred from two stream theory for optically pure glacier ice. This enhanced near-surface attenuation implies shallower light transmission and therefore lower subsurface light availability for subsurface radiative heating and bio-photochemical cycling. We recommend radiative transfer models applied to bare ice in the Greenland Ice Sheet ablation zone account for vertical variation in light attenuation due to the vertical distribution of light absorbing particles and ice microstructure, and we provide new values of flux attenuation, absorption, and scattering coefficients to support model validation and parameterization.

A correction to the Poole and Atkins Secchi disc/light-attenuation formula

1980 ◽  
Vol 60 (3) ◽  
pp. 769-771 ◽  
Author(s):  
Terriss A. Walker
Keyword(s):  
Natural Waters ◽  
Marine Biology ◽  
Spectral Response ◽  
Light Attenuation ◽  
Field Work ◽  
Secchi Disc ◽  
Attenuation Coefficients ◽  
Method Of Calculation ◽  
Normal Human ◽  
The Relationship

Re-examination of the original and subsequent data from Secchi disc studies leads to a revised constant in the light attenuation formula applicable to general field-work.In theory, the depth at which a Secchi disc disappears from an observer's sight, Ds, is inversely proportional to the sum of attenuation coefficients for diffuse and collimated photopic light (Tyler, 1968). By definition, photopic light is measured by a sensor with the same spectral response curve as the normal human eye. In practice, the usefulness of the theoretical equation is restricted. More commonly, a simple empirically derived formula is used to estimate the attenuation coefficient for diffuse downwelling light, k, directly from Ds. Poole & Atkins (1929), in their pioneering work on light penetration in the sea, derived the relationship k × Ds – 17 for water in the English Channel. This formula is used extensively by workers who are unable to measure k directly and it is given regularly in oceanography and marine biology texts. More recently, a number of investigators have proposed alternative equations relating k to Ds in different regional seas (Table 1). However, Idso & Gilbert (1974) have fitted data of some of these authors, together with measurements of their own, to the original Poole and Atkins formula with good correlation. They suggest that k × Ds = 1.7 is a universal approximation for all natural waters. In view of the continuing importance of the Secchi disc as a measure of underwater light for primary production calculations and other studies, a universal formula is certainly desirable. However, re-examination of the Poole & Atkins measurements has revealed an error in the method of calculation of k.

scholarly journals Strategic resources and smallholder performance at the bottom of the pyramid

2019 ◽  
Vol 22 (3) ◽  
pp. 365-380 ◽  
Author(s):  
Matthias Olthaar ◽  
Wilfred Dolfsma ◽  
Clemens Lutz ◽  
Florian Noseleit
Keyword(s):  
Large Scale ◽  
Business Environment ◽  
Agricultural Economics ◽  
Local Market ◽  
Bottom Of The Pyramid ◽  
Fine Grained ◽  
Strategic Resources ◽  
Relative Contribution ◽  
The Relationship ◽  
Resource Based Theory

In a competitive business environment at the Bottom of the Pyramid smallholders supplying global value chains may be thought to be at the whims of downstream large-scale players and local market forces, leaving no room for strategic entrepreneurial behavior. In such a context we test the relationship between the use of strategic resources and firm performance. We adopt the Resource Based Theory and show that seemingly homogenous smallholders deploy resources differently and, consequently, some do outperform others. We argue that the ‘resource-based theory’ results in a more fine-grained understanding of smallholder performance than approaches generally applied in agricultural economics. We develop a mixed-method approach that allows one to pinpoint relevant, industry-specific resources, and allows for empirical identification of the relative contribution of each resource to competitive advantage. The results show that proper use of quality labor, storage facilities, time of selling, and availability of animals are key capabilities.

scholarly journals A Novel Thin-Film Technique to Improve Accuracy of Fluorescence-Based Estimates for Periphytic Biofilms

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1464
Author(s):  
Leon Katona ◽  
Yvonne Vadeboncoeur ◽  
Christopher T. Nietch ◽  
Katie Hossler
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Light Attenuation ◽  
Pulse Amplitude ◽  
Light Signal ◽  
Photosynthetic Parameters ◽  
Pam Fluorometry ◽  
Attenuation Coefficients ◽  
Thin Film Technique ◽  
Relative Errors

Recent studies suggest that photophysiological parameters for intact substrates with depth (e.g., periphytic biofilms, microphytobenthos) are overestimated by pulse-amplitude modulated (PAM) fluorometry. This overestimation results from depth-integration effects, following the activation of deeper photosynthesizing layers by an attenuated light signal. To mitigate this error, we propose a novel slide-based thin-film technique in which fluorescence is measured on a vertically representative subsample of the biofilm, spread evenly on a microscope slide. We compared bias and precision for photosynthetic parameters estimated through conventional PAM fluorometry on intact biofilms and through our novel slide-based technique, both theoretically and empirically. Numerical simulations confirmed the consistent overestimation of key parameters for intact biofilms, with relative errors up to 145%, compared to, at most, 52% on thin films. Paired empirical observations likewise demonstrated that estimates based on intact biofilms were consistently higher (up to 248%, p<0.001) than estimates from thin films. Numerical simulation suggested greater precision with the slide-based technique for homogeneous biofilms, but potentially less precision for heterogeneous biofilms with improper subsampling. Our empirical comparison, however, demonstrated some improvement in precision with the slide-based technique (e.g., the coefficient of variation for the maximum electron transport rate was reduced 30%, p=0.009). We recommend the use of the slide-based technique, particularly for biofilms that are thick or have small light attenuation coefficients. Care should be taken, however, to obtain vertically representative subsamples of the biofilm for measurement.

Particulate light attenuation in a large subtropical lake

1995 ◽  
Vol 52 (8) ◽  
pp. 1803-1811 ◽  
Author(s):  
Karl E. Havens
Keyword(s):  
Surface Water ◽  
Trophic State ◽  
Nutrient Loading ◽  
Light Attenuation ◽  
Algal Growth ◽  
Progressive Increase ◽  
Trophic State Index ◽  
Littoral Region ◽  
Relative Contribution ◽  
Total Light

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.

scholarly journals Soil Nutrient and Vegetation Diversity Patterns of Alpine Wetlands on the Qinghai-Tibetan Plateau

2021 ◽  
Vol 13 (11) ◽  
pp. 6221
Author(s):  
Muyuan Ma ◽  
Yaojun Zhu ◽  
Yuanyun Wei ◽  
Nana Zhao
Keyword(s):  
Species Diversity ◽  
Tibetan Plateau ◽  
Soil Properties ◽  
Soil Ph ◽  
Plant Biomass ◽  
Principal Component ◽  
Vegetation Diversity ◽  
Vegetation Biomass ◽  
Relative Contribution ◽  
The Relationship

To predict the consequences of environmental change on the biodiversity of alpine wetlands, it is necessary to understand the relationship between soil properties and vegetation biodiversity. In this study, we investigated spatial patterns of aboveground vegetation biomass, cover, species diversity, and their relationships with soil properties in the alpine wetlands of the Gannan Tibetan Autonomous Prefecture of on the Qinghai-Tibetan Plateau, China. Furthermore, the relative contribution of soil properties to vegetation biomass, cover, and species diversity were compared using principal component analysis and multiple regression analysis. Generally, the relationship between plant biomass, coverage, diversity, and soil nutrients was linear or unimodal. Soil pH, bulk density and organic carbon were also significantly correlated to plant diversity. The soil attributes differed in their relative contribution to changes in plant productivity and diversity. pH had the highest contribution to vegetation biomass and species richness, while total nitrogen was the highest contributor to vegetation cover and nitrogen–phosphorus ratio (N:P) was the highest contributor to diversity. Both vegetation productivity and diversity were closely related to soil properties, and soil pH and the N:P ratio play particularly important roles in wetland vegetation biomass, cover, and diversity.

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