Photosynthetic units

The increases in photosynthetic pigment content that occur in algae as the light intensity at which they are grown is lowered can be due to an increase (per cell, or per unit biomass) in the number of photosyn-thetic units, or in the average size (as absorption cross-section) of the photosynthetic unit, or both.381 In most green plants - the algae as well as the angiosperms - it appears that the increase in chlorophyll content during shade adaptation is largely due to an increase in the number...

Sin 0d0

Thus an alternative definition of the scattering coefficient is the integral of the volume scattering function over all directions. It is frequently useful to distinguish between scattering in a forward direction and that in a backward direction. We therefore partition the total scattering coefficient, b, into a forward scattering coefficient, bf, relating to light scattered from the beam in a forward direction, and a backward scattering coefficient (or simply, backscatter-ing coefficient) bb,...

Photosynthesis in the aquatic environment

Having considered the photosynthetic response of aquatic plants to light of different intensities and spectral qualities, we shall now examine how the availability of light influences where, when and how much photosynthesis takes place in aquatic ecosystems, and also the extent to which other parameters of the environment can limit photosynthesis. Aquatic production ecology is an enormous field a comprehensive account will not therefore be attempted. Rather, the broad principles governing the...

Spectral distribution of irradiance

Scalar Par Sensor

Any photon with wavelength from 400 to 700 nm is in principle available for photosynthesis however, the probability of a given photon being captured by the photosynthetic biomass within a water body will vary markedly with wavelength in accordance with the absorption spectrum of Fig. 5.5 Submersible scalar irradiance sensors. (a) Li-Cor Spherical Quantum Sensor LI-193SB, in lowering frame (Li-Cor Inc., Lincoln, Nebraska, USA). (b) Biospherical Quantum Scalar Irradiance Sensor QSP-200, in...

Direct measurement CO2 fixation and O2 liberation

Photosynthesis can be measured in terms of either CO2 fixed or O2 released. For terrestrial plants the method of choice is direct measurement of CO2 removal from the gas stream by monitoring the infrared absorption by CO2, but for obvious reasons this will not work in an aquatic medium. Because of the stoichiometry of the overall photosynthetic process ( 8.5), approximately one O2 molecule is liberated for every molecule of CO2 fixed. However, since the average composition of plant biomass...

Spectral distribution of irradiance at the Earths surface

The scattering and absorption processes that take place within the atmosphere not only reduce the intensity, but also change the spectral distribution of the direct solar beam. The lowest curve in Fig. 2.1 shows the spectral distribution of solar irradiance at sea level for a zenith Sun and a clear sky. The shaded areas represent absorption, and so the curve forming the upper boundary of these shaded areas corresponds to the spectral distribution as it would be if there were scattering but no...

Density fluctuation scattering

In understanding the basis of density fluctuation scattering in liquids, it is helpful to begin with a consideration of molecular, or Rayleigh, scattering by gases such as air. According to the Rayleigh theory, within any particle, such as an air molecule, in a light field, a dipole is induced by the electrical vector of the field. As the dipole oscillates at the frequency of the exciting radiation, it emits radiation of the same frequency in all directions. It is this radiation that is the...

Depth variation of pigment composition in unicellular algae

The majority of phytoplankton cells are subjected to continually varying irradiance as they circulate through the mixed layer and do not have the time to change their pigment composition in accordance with the prevailing light field. When, as in some of the clearer, less coloured waters, light penetrates so well that the euphotic zone is deeper than the mixed layer, however, then in the stable water below the thermocline the phytoplankton can remain at approximately the same depth for long...

Areal and volumetric efficiencies

We have seen that the efficiency of utilization of the light incident on the aquatic ecosystem for primary production is determined by two main factors the extent to which the aquatic plants succeed in competing with the other components of the system for the quanta in the underwater light field, and the efficiency with which the absorbed light energy is converted to chemical energy. We shall now consider the overall efficiency that results from the simultaneous operation of these two factors....

Solar radiation outside the atmosphere

The intensity and the spectral distribution of the radiation received by the Earth are a function of the emission characteristics and the distance of the Sun. Energy is generated within the Sun by nuclear fusion. At the temperature of about 20 x 106K existing within the Sun, hydrogen nuclei (protons) fuse to give helium nuclei, positrons and energy. A number of steps is involved but the overall process may be represented by The energy liberated corresponds to the slight reduction in mass that...

Indirect measurement chlorophyll fluorescence

An alternative to measurement of radiocarbon fixation or oxygen evolution for determining photosynthetic rate is to use measurement of what is referred to as the variable component of chlorophyll fluorescence. Since this has become in recent years a commonly used procedure, a simplified outline of what are believed to be the underlying biochemical processes is presented here. More detailed discussions of this complex topic may be found in Butler (1978), Kolber and Falkowski (1993), Schreiber et...

Mixed layer depth and phytoplankton production

It is instructive to consider under what conditions phytoplankton primary production may be prevented altogether as a result of the mixed depth exceeding the critical depth. Using Tailing's (1957b) model for calculating integral photosynthesis (see 11.5) we can derive an approximate expression for the critical depth where p is the ratio of respiration rate to light-saturated photosynthetic rate in the phytoplankton, Kd is the vertical attenuation coefficient for downwards irradiance of PAR, N...

Lrradiance meters

The most frequently and easily measured property of the underwater light field is irradiance. Knowledge of this parameter is valuable, not only because it provides information about how much light is available for photosynthesis, but also because irradiance plays a central role in the theory of radiation transfer in water. An irradiance meter, since it is meant to measure the radiant flux per unit area, must respond equally to all photons that impinge upon its collector, regardless of the angle...

Beam transmissometers

In the absence of absorption, the scattering coefficient could in principle be determined by measuring the loss of intensity of a narrow parallel beam passing through a known pathlength of medium. If absorption as well as scattering occurs, then the parameter measured by the instrument would in fact be the beam attenuation coefficient, c, rather than the scattering coefficient. If it is possible also to measure the absorption coefficient, a, of the water at the appropriate wavelength, then the...

Temperature

In considering the effect of temperature on aquatic photosynthesis, it is necessary to distinguish between the effects immediately following a change in temperature and the effects obtained if the plants are allowed to adjust to the new temperature for one to several days. Considering the immediate effects of temperature change first, if the photosynthetic rate of a phyto-plankton population or a marine or freshwater macrophyte is measured under saturating light, at a series of temperatures...

Chloroplasts

In eukaryotic plants, photosynthesis is carried out by the organelles known as chloroplasts, the best known members of the great class of related and interconvertible organelles known as plastids. Detailed accounts of these organelles may be found in Kirk and Tilney-Bassett (1978), Staehelin (1986) and Falkowski and Raven (2007) we shall here content ourselves with a rather brief treatment. The chloroplasts contain the pigments that capture the light, the electron carriers that use the absorbed...

Secchi depth

A crude visual method of estimating Kd, commonly used before the ready availability of photoelectric instruments but not used today, is based on the device known as the Secchi disc. A white disc, of diameter 20 to 30 cm, is lowered into the water and the depth at which it just disappears from view is noted. This is referred to as the Secchi disc transparency, or as the Secchi depth, ZSD. On the basis of their measurements in marine waters, Poole and Atkins (1929) made the empirical observation...

Scalar irradiance

Although some multicellular aquatic plants have their photosynthetic tissue so arranged as to achieve maximum interception of light incident from above, to the randomly oriented cells of the phytoplankton all light, from whatever direction it comes, is equally useful. Scalar irradiance E0, as we saw earlier ( 1.3), is defined as the integral of radiance distribution at a point over all directions about the point it is equivalent to the total radiant flux per m2 from all directions at a given...

Other limiting factors

Dark reaction enzyme system (Rubisco, triose phosphate dehydrogenase etc.) Dark reaction enzyme system (Rubisco, triose phosphate dehydrogenase etc.) Substrate concentration ( C02 ), arbitrary units Fig. 11.2 Idealized curve of rate of an enzymic reaction as a function of substrate concentration. Calculated from Michaelis-Menten equation. Substrate concentration ( C02 ), arbitrary units Fig. 11.2 Idealized curve of rate of an enzymic reaction as a function of substrate concentration. Calculated...

Preface to the third edition

Four things are required for plant growth energy in the form of solar radiation inorganic carbon in the form of carbon dioxide or bicarbonate ions mineral nutrients and water. Those plants which, in the course of evolution, have remained in, or have returned to, the aquatic environment have one major advantage over their terrestrial counterparts namely, that water - lack of which so often limits productivity in the terrestrial biosphere - is for them present in abundance but for this a price...

Photosynthesis as a function of the incident light

The rate of photosynthesis achieved by a phytoplankton cell or aquatic macrophyte depends on the rate of capture of quanta from the light field. This is determined by the light absorption properties of the photosynthetic biomass, which we have considered in some detail, and by the intensity and spectral quality of the field. The rate of photosynthesis is not, however, simply proportional to the rate of capture of photons. The efficiency with which the photosynthetic apparatus can make use of...

Rate of light absorption by aquatic plants

The rate of photosynthesis by an aquatic plant must ultimately be limited by (although it is not always simply proportional to) the rate at which the higher plant leaf, or multicellular algal thallus, or individual phytoplankton cell or colony, is absorbing quanta from the underwater light field. In the case of the leaf or the algal thallus, the rate of absorption of quanta of a given wavelength incident at a particular angle on a particular element of tissue surface is equal to E(1, 0,...

Satellite systems

Remote sensing of ocean colour from space is carried out by a variety of radiometers on spaceborne satellites launched by a number of nations around the globe. Coordination of these studies is carried out by the International Ocean-Colour Coordinating Group (IOCCG, www.ioccg. org), established in 1996. There are two types of orbits for Earth observation satellites, polar-orbiting and geostationary. Polar-orbiting satellites typically operate at an altitude of 700 to 800 km, with a revisit time...

The emergent flux

The particular light flux that is of the greatest interest in the present context is the upwelling light flux just below the surface. However, the flux that, after due correction, is remotely sensed, is the emergent flux -that part of the upwelling flux that succeeds in passing up through the surface. How are the two related Although about half the total upwelling light flux is reflected downwards again at the water-air interface, this does not represent a serious loss, since it is mainly the...

The dark reactions

The pathway by which, in the stroma of the chloroplast, the NADPH2 and ATP produced in the light reactions are used to convert CO2 to carbohydrate was elucidated largely by the work of Calvin and Benson, and is outlined in Fig. 8.18. The cycle is somewhat involved and needs Fig. 8.18 The photosynthetic CO2 fixation cycle. P phosphate group Pi inorganic phosphate. The enzymes involved in each step are (1) Rubisco (2) 3-phosphoglyceric acid kinase (3) glyceraldehyde-3-phosphate dehydrogenase (4)...

Tripton

The inanimate particulate matter, or tripton, of natural waters is the fraction whose light absorption properties have received the least attention because they are so difficult to measure. At typical concentrations the material does not absorb light strongly but scatters quite intensely and so its absorption properties cannot be characterized by normal spectropho-tometry with long-pathlength cells. One approach to overcoming these problems is to collect the particulate matter from a natural...

Highly productive aquatic ecosystems

To achieve a high rate of primary production, an aquatic plant community must achieve a high rate of collection of light energy and an efficient utilization of this absorbed energy by its photosynthetic system, followed by conversion of photosynthate to new cell material. In this section we are concerned with the ways in which some natural and man-made ecosystems manage to do this. We have discussed earlier (Chapters 3, 9 and 10), the major limitation on aquatic photosynthesis imposed by the...

Shade adaptation in aquatic angiosperms

All the adaptive changes we have considered so far are in the biochemical composition and consequent functioning of the photosynthetic apparatus. There are also other forms of ontogenetic adaptation, particularly in multicellular species, which can enable plants to cope with variation in the intensity of the light field. In higher plants, both aquatic and terrestrial, adapting to shade, at the same time as chlorophyll content ( of dry mass) increases, the leaves increase in area so as to...

Absorption spectra of photosynthetic systems

We might measure the absorption spectrum of, say, phytoplankton or a multicellular algal thallus, for a number of different reasons. We might seek information on what pigments are present. We might wish to compare the spectral position and shape of an in vivo absorption peak with those of the same peak in the isolated pigment with a view to assessing the extent to which the absorption properties are modified by binding to protein. We might want to know to what extent an alga is equipped to...

Radiance distribution

To understand fully the underwater light field we need a detailed knowledge of the angular distribution of radiant flux at all depths. Some information on the angular structure of the field can be derived from the measurements of irradiance discussed above. Irradiance reflectance (R Eu Ed) is a crude measure of angular structure. More information is contained in the three average cosines M for the total light field, pd for the downwelling stream and Mu for the upwelling stream, all of which can...

The bluelight effect

The underwater light field in oceanic waters becomes, as we have seen earlier, predominantly blue-green and eventually blue with increasing depth. There is evidence for the existence of specific effects of blue light on the development of the photosynthetic apparatus of certain phyto-plankton species. Wallen and Geen (1971a, b) found that cells of the marine diatom Cyclotella nana grown in blue light (0.8 Wm 2) contained 20 more chlorophyll a and had a 70 higher light-saturated photosyn-thetic...

Modelling the underwater light field

The nature of the underwater light field resulting from a given incident light field is determined by the inherent optical properties of the aquatic medium. In principle, therefore, it should be possible, if we know the inherent optical properties, to calculate the properties of the underwater light field. Such a calculation procedure could be used, for example, to explore in more detail than would be practicable by measurement, the exact way in which the nature of the light field depends on...

Effect of aquatic plants on the underwater light field

We have concerned ourselves so far in this chapter with the ability of phytoplankton and macrophytes to make use of the underwater light field. By harvesting light from the field, however, the plants in turn modify the light climate for any other plants below them in the water column. Within any substantial stand of aquatic macrophytes, such as a kelp forest, or a bed of seagrass or freshwater aquatic higher plants, the intensity of PAR is greatly reduced. Phytoplankton also increase the...

Apparent and quasiinherent optical properties

The vertical attenuation coefficients for radiance, irradiance and scalar irradiance are, strictly speaking, properties of the radiation field since, by definition, each of them is the logarithmic derivative with respect to depth of the radiometric quantity in question. Nevertheless experience has shown that their values are largely determined by the inherent optical properties of the aquatic medium and are not very much altered by changes in the incident radiation field such as a change in...

Diffuse scattering coefficients

As we saw in our discussion of radiation transfer theory ( 1.7), certain quasi-inherent optical properties of the medium - the diffuse scattering coefficients - play an essential role in our understanding of the underwater light field. These scattering coefficients have been defined previously ( 1.5) in terms of the light scattered backwards or forwards by a thin layer of medium from an incident light field that is not a parallel beam at right angles (as in the case of the normal scattering...

Membranes and particles

In electron micrographs of sections, chloroplasts are seen to be bounded by an envelope consisting of two (green algae, red algae, higher plants), three (Euglenophyta, dinoflagellates) or four (brown algae, diatoms, prymnesiophytes, haptophytes) membranes, and to be filled with a granular matrix. This matrix is referred to as the stroma and is composed of a concentrated solution or gel of proteins, consisting mainly of the enzymes used in carbon dioxide fixation. Embedded within the stroma...

Depth and shade adaptation

Given the demonstrated ability of so many phytoplankton species under laboratory conditions to increase their light-harvesting capability in dim light, especially in dim blue-green light, and given also the observed shade adaptation of natural phytoplankton populations taken from deep in the euphotic zone of stratified waters, we may reasonably conclude that ontogenetic adaptation of the phytoplankton photosynthetic apparatus to the low-intensity light field in these deep layers is a real...

Average transmission characteristics of the atmosphere

A valuable summary of the effects of the atmosphere as a whole on the transmission of solar radiation from space to the Earth's surface has been provided by Gates (1962) in terms of the average fate of the radiant flux incident on the northern hemisphere. Over a year, 34 of the incoming solar radiation is reflected to space by the atmosphere this is made up of 25 reflected by clouds and 9 scattered out to space by other constituents of the atmosphere. Another 19 of the incoming radiation is...

Depth variation of photosynthetic characteristics in unicellular algae

As we have noted earlier, depth adaptation of the photosynthetic system in phytoplankton is only to be expected in waters in which density stratification permits some of the cells to remain for long periods at depths where circulation is minimal but there is sufficient light for photosynthesis to take place. This situation exists throughout most of the ocean in the lower part of the euphotic zone. By what criteria can we recognize true depth adaptation of the phytoplankton photosynthetic system...

Effect of scattering

Since the air molecules are much smaller than the wavelengths of solar radiation, the efficiency with which they scatter light is proportional to 1 14, in accordance with Rayleigh's Law. Scattering of solar radiation is therefore much more intense at the short-wavelength end of the spectrum, and most of the radiation scattered by the atmosphere is in the visible and ultraviolet ranges. Some of the radiation scattered from the solar beam is lost to space, and some finds its way to the Earth's...

Optical characteristics of the water

We saw in the previous chapter that a major factor in limiting efficiency of utilization of incident light in aquatic ecosystems is the removal of a large proportion of the light energy by the aquatic medium. This occurs in waters in which the vertical attenuation of PAR by non-phytoplanktonic material is high (see Table 10.1). We would therefore expect, for example, brown-water lakes with a high concentration of CDOM to be on average less productive than lakes with low background colour. There...

Depth variation of pigment composition in macrophytes

Ramus et al. (1976) suspended samples of two green (Ulva lactuca and Codium fragile) and two red algal species (Chondrus crispus and Porphyra umbilicalis) for seven-day periods at depths of 1 and 10 m in harbour water at Woods Hole, Massachusetts, USA. Pigment compositions were determined. The samples were then reversed in position - the 1 m samples being lowered to 10 m, and vice versa - and after a further seven-day period, further pigment analyses were carried out. In all four species the...

Phytoplankton

The absorption of light by the photosynthetic pigments - chlorophylls, carotenoids and biliproteins - of the phytoplankton contributes to the attenuation of PAR with depth. Indeed in productive waters, the algae may be present in concentrations such that by self-shading they limit their own growth. Light absorption by algal cells grown in laboratory culture has received a great deal of attention because of the use of such cultures as experimental material in fundamental photosynthesis research....

Photosynthesis and wavelength of incident light

Chlorophyll Und Fucoxanthin

The spectral composition of underwater light in a given water body varies markedly with depth and at any specified depth it varies with the optical properties of the water (Chapter 6). Thus, in order to assess the suitability of a given underwater light field for photosynthesis by different kinds of aquatic plant, we need to know in what ways the photosynthetic rates of the various plant types depend upon the wavelengths of the light to which they are exposed. Some of the information we need...

Effect of cloud

In addition to the effects of the gaseous and particulate components of the atmosphere, the extent and type of cloud cover are of great importance in determining the amount of solar flux that penetrates to the Earth's surface. We follow here the account given by Monteith (1973). Fig. 2.3 Spectral distribution of solar quantum irradiance at the Earth's surface at three geographical locations (plotted from the data of Tyler and Smith, 1970). (a) Crater Lake, Oregon. USA (42 56' N, 122 07' W)....

Downward irradiance monochromatic

As a result of absorption and scattering of the solar flux, the downward irradiance, Ed, of the light field diminishes with depth. In Fig. 6.1, Ed for greenish-yellow light, expressed as a percentage of the value just below the surface, is plotted against depth in a freshwater impoundment. Irradiance diminishes in an approximately exponential manner in accordance with ln Ed (z) -Kdz + ln Ed (0) (6.2) where Ed (z) and Ed (0) are the values of downward irradiance at z m and just below the...

Reaction centres and energy transfer

The crucial step within photosystems I and II is the use of the absorbed light energy to transfer an electron from a donor molecule to an acceptor molecule. The particular donor and acceptor molecules are different in the two photosystems. The site in a photosystem at which this event occurs is known as the reaction centre. The central role of using the excitation energy to extract an electron from one molecule and transfer it to another is, in each photosystem, carried out by a special form of...

Evidence against chromatic adaptation

On the basis of the relation between water optical type and algal distribution outlined above, we would predict that in any clear, colourless coastal water, with maximum penetration in the blue waveband, green algae should be certainly a major, and probably a dominant, component of the algal biomass throughout much of the middle and lower sublittoral. The water bathing the coast of South Australia, in the region of the Great Australian Bight and the Gulf of St Vincent, is of a clear, colourless...

Index to water bodies

Lake, Lough (Ireland) or Loch (Scotland) R. River) Adriatic Sea, 73, 75, 396, 470, 473, 491, 502, 530, 531 Aegean Sea, Southern, 450 Aleutian Islands, 429 Algoa Bay, 346 Amazon R., 69, 79 Antarctic Circumpolar Current, 424, 425 Antarctic marginal ice zone, 355 Antarctic pack-ice, 508 Antarctic Peninsula, coastal, 258, 317 Arabian Sea, 44, 45, 75, 125, 357, 374, 426, 447 Aranguadi, L., 376 Arctic fjord, Spitsbergen, 472 Arctic Ocean, 64, 74, 121, 156, 201, Arctic Ocean, Canadian, 347...

The microphytobenthos

All benthic sediments - whether in tidal mudflats, surf beaches, coral reef lagoons, shallow coastal waters - which receive significant amounts of light, contain communities of microalgae. This benthic community, in any given aquatic ecosystem, is referred to as the microphytobenthos, or sometimes, epipelon. A full account of the epipelon is given in Round's (1981) book, The Ecology of Algae. The microphytobenthos usually consists predominantly of diatoms, but cyanobacteria, dinoflagellates and...

SeaWiFS Global Biosphere

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The absorption process

The energy of a molecule can be considered to be part rotational, part vibrational and part electronic. A molecule can only have one of a discrete series of energy values. Energy increments corresponding to changes in a molecule's electronic energy are large, those corresponding to changes in vibrational energy are intermediate in size and those corresponding to changes in rotational energy are small. This is indicated diagrammatically in Fig. 3.1. When molecules collide with each other in the...

Variableangle scattering meters

The scattering properties of natural waters are best determined by directly measuring the scattered light. The general principle is that a parallel beam of light is passed through the water, and the light scattered from a known volume at various angles is measured. In the ideal case, the volume scattering function, b( ), is measured from 0 to 180 this provides not only the angular distribution of scattering for that water but also, by integration, the total, forward and backward scattering...

Vertical movement by bluegreen algae

Blue-green algae have a completely different mechanism for moving up and down in the water column, involving the formation and collapse of gas-filled vacuoles within the cells. A comprehensive account of these Fig. 12.18 Freeze-fractured cell of Anabaena flos-aquae showing cylindrical gas vacuoles longitudinally and in cross-section (by courtesy of Professor D. Branton). The bar corresponds to 1.0 mm. Fig. 12.18 Freeze-fractured cell of Anabaena flos-aquae showing cylindrical gas vacuoles...

The nature of light

Picture Branches Optics

Electromagnetic energy occurs in indivisible units referred to as quanta or photons. Thus a beam of sunlight in air consists of a continual stream of photons travelling at 3 x 108ms_1. The actual numbers of quanta Fig. 1.1 The relationship between hydrologic optics and other branches of optics (after Preisendorfer, 1976). Fig. 1.1 The relationship between hydrologic optics and other branches of optics (after Preisendorfer, 1976). involved are very large. In full summer sunlight. for example,...

Integral photosynthetic rate

Understand the role of oceanic photosynthesis in the global carbon cycle and therefore the greenhouse effect, and also by the wealth of data on the distribution of phytoplankton biomass through the world's oceans, which has come from remote sensing. As pointed out by Behrenfeld and Falkowski (1997a) in their review of this topic, depth-integrated productivity models have been appearing in the literature on average once every two years for several decades. No attempt will be made here to...

Vertical attenuation coefficients for downward irradiance

As well as providing information about levels of phytoplankton, suspended solids and CDOM, remotely sensed radiances can be used to map vertical attenuation coefficients for downward irradiance. Austin and Petzold (1981) derived empirical relationships by means of which Kd(490) and Kd(520) could be obtained from the ratio of radiances in the CZCS 443 and 520 nm wavebands. Analysing SeaWiFS data mainly from Case 1 waters, Mueller (2000) arrived at the following algorithm for Kd(490) where nLw(1)...

Deep chlorophyll maximum

It seems likely that the increase in chlorophyll concentration in this deep layer, relative to that in the mixed layer, is due to an increase in chlorophyll concentration within the cells as well as to an increased population of phytoplankton.24,268,687,1022 Kiefer et al. (1976) found the chlorophyll per unit biomass in the deep phytoplankton layer to be about twice the value near the surface. At five stations in the eastern subtropical Atlantic, Veldhuis and...

Suspended solids

One of the water quality parameters that has been most extensively studied in this way is the concentration of total suspended solids (TSS). Increases in the amount of suspended particles will, at wavelengths where the particles do not absorb strongly, increase the backscattering coefficient of the water more than the absorption coefficient, and so, in accordance with eqns 6.3 and 6.5, increase the emergent flux. In the case of reservoirs in Mississippi, it was found that the irradiance...

The scattering properties of phytoplankton

Phytoplankton cells and colonies scatter, as well as absorb, light and can make a significant contribution to the total scattering behaviour of the aquatic medium, but to an extent that varies from one species to another this has been studied in detail, both experimentally and theoretically, by Morel, Bricaud and coworkers.160,162,943,948 A convenient parameter in terms of which to compare the scattering propensities of different species is the specific scattering coefficient, bc, which is the...

Measurement systems general considerations

Remote sensing photometers used in low-altitude aircraft normally have a fixed direction of view. They measure upward radiance at a series of points along a linear track determined by the flight path of the aircraft. For two-dimensional mapping, the aircraft must traverse the area of interest many times. The spectral distribution of the radiance at each point is determined using interference filters or a spectroradiometer. With increasing altitude the area that it is practicable to 'view'...

Evidence for phylogenetic chromatic adaptation

Changes in the pigment category of aquatic plants with depth are striking in sea water but hard to identify in fresh water, and so we shall here consider marine ecosystems. We shall begin by noting that in all marine waters there is ample light in all wavebands near the surface, and so the theory of chromatic adaptation, which is specifically concerned with light-limited situations, has nothing to tell us about the relative success of the different algal groups in this region resistance to wave...

The package effect

The absorbance spectrum of a cell or colony suspension (in the case of unicellular algae) or of a segment of thallus or leaf (in the case of multicellular aquatic plants) will always differ noticeably from that of dispersed thylakoid fragments. The in vivo spectra (e.g. Euglena, Fig. 9.1) will be found to have peaks that are less pronounced with respect to the valleys, and to have, at all wavelengths, a lower specific absorption per unit pigment. These changes in the spectra are due to what we...

Indirect factors

There are environmental factors other than light, CO2 and temperature that can have a major influence on the total amount of photosynthesis that takes place (i.e. on primary production in the ecosystem) by their effects on the amount of plant biomass present. Since our concern here is mainly with factors that influence photosynthesis directly we shall touch on these indirect factors only briefly. Inorganic nutrition - particularly the concentrations of the key elements phosphorus and nitrogen -...

Coloured dissolved organic matter CDOM gilvin yellow substance chemistry and origins

When plant tissue decomposes in the soil or in a water body, most of the organic matter is broken down by microbial actions within days or weeks to, ultimately, carbon dioxide and inorganic forms of nitrogen, sulfur and phosphorus. In the course of the decomposition process there is formed, however, a complex group of compounds loosely referred to as 'humic substances'. It is from these humic substances that the yellow-coloured dissolved organic matter in inland and marine waters is derived....

References and author index

The numbers in italic following each item are pages where the author's work is mentioned. 1. Aas, E. & H0jerslev, N. K. (1999). Analysis of underwater radiance observations apparent optical properties and analytic functions describing the angular radiance distribution. J. Geophys. Res., 104, 8015-24. 173, 183 2. Aas, E., H0kedal, J. & S0rensen, K. (2005). Spectral backscattering coefficient in coastal waters. Int. J. Remote Sens., 26, 331-43. 126 3. Aas, E. & Korsb0, B. (1997)....

The properties defining the radiation field

If we are to understand the ways in which the prevailing light field changes with depth in a water body, then we must first consider what are the essential attributes of a light field in which changes might be anticipated. The definitions of these attributes, in part, follow the report of the Working Groups set up by the International Association for the Physical Sciences of the Ocean (1979), but are also influenced by the more fundamental analyses given by Preisendorfer (1976). A more recent...

Aquatic plant distribution in relation to light quality

As we saw in Chapters 8 and 9, there are major differences between the main taxonomic groups of aquatic plants with respect to the kinds of photosynthetic pigment present and, as a consequence, major differences in the absorption spectra. Given the variation in intensity and spectral quality of the light field in the aquatic environment, we may reasonably suppose that for any given location within a water body there will be certain species that are well equipped to exploit the particular...

Gilvin CDOM and total absorption coefficients

The dissolved yellow humic substances in surface waters have (Chapter 3) an absorption spectrum rising exponentially into the blue. Where, as in many lakes, rivers and estuaries, CDOM is the dominant contributor to light absorption, there are generally found to be simple relationships between CDOM concentration and the ratio of reflectance in the blue to that at some longer wavelength. Bowers et al. (2000) studied the relationship between subsurface radiance reflectance (rrs 1 ) ratios and CDOM...

Efficiency of conversion of absorbed light

Once the light energy is absorbed by the chloroplast pigments of the phytoplankton or aquatic macrophytes it is used, by means of the photo-synthetic fixation of CO2, to generate useful chemical energy in the form of carbohydrate. We shall now consider the efficiency of this conversion of excitation energy to chemical energy. An upper limit to the efficiency is imposed by the nature of the physical and chemical processes that go on within photosynthesis. We saw in Chapter 8 that the transfer of...

Upward irradiance and radiance

As a result of scattering within the water, at any depth where there is a downward flux there is also an upward flux. This is always smaller, usually much smaller, than the downward flux but at high ratios of scattering to absorption can contribute significantly to the total light available for photosynthesis. Furthermore, in any water the upwelling light is of crucial importance for the remote sensing of the aquatic environment (Chapter 7), since it is that fraction of the upward flux which...

Phytoplankton increased reflectance

One empirical approach to the remote sensing of phytoplankton is to treat it as a special case of suspended solids and to use the increased reflectance in the near-infrared associated with the increased biomass. In the Landsat MSS red (600-700 nm) band, high concentrations of algae are associated with decreased radiance because of the chlorophyll absorption in this region. Strong (1974) observed in the case of Landsat pictures of an algal bloom on Utah Lake, USA, that there was a contrast...

Diurnal variation of solar irradiance

For a given set of atmospheric conditions, the irradiance at any point on the Earth's surface is determined by the solar elevation, b. This rises during the day from zero (or its minimum value in the Arctic or Antarctic during the summer) at dawn to its maximum value at noon, and then diminishes in a precisely symmetrical manner to zero (or the minimum value) at dusk. The exact manner of the variation of b with time of day depends on the latitude, and on the solar declination, d, at the time....

Angular distribution of the underwater light field

As sunlight enters a water body, immediately it penetrates the surface its angular distribution begins to change - to become less directional, more diffuse - as a result of scattering of the photons. The greater the depth, the greater the proportion of photons that have been scattered at least once. The angular distribution produced is not, however, a function of scattering alone the less vertically a photon is travelling, the greater its pathlength in traversing a given depth, and the greater...

Photosynthetic consequences of lightshade adaptation

Chlorophyceae Diagram

The physiological consequences of these biochemical changes are manifested as changes in the dependence of photosynthetic performance on light intensity. If photosynthetic rate per unit chlorophyll is measured as a function of irradiance then it is in some cases found that rates exhibited by low- and high-light-adapted cells or tissues are much the same at low irradiance, but the low-light-adapted plants level off and reach light saturation first. It is generally the case that...

Optical classification of natural waters

Natural waters vary greatly in the extent to which they transmit solar radiation and it is useful to have some broad indication of the optical character of a water without having to fully specify all the inherent optical properties. Jerlov (1951, 1976) has classified marine waters into a number of different categories on the basis of the curve of per cent transmittance of downward irradiance against wavelength. He recognized three basic types of oceanic water (I, II and III) and nine types of...

Phytoplankton fluorescence

The methods for remote sensing of phytoplankton described above make use of the fact that algal cells absorb light in a certain region of the spectrum. However, algal cells also emit light in the laboratory, typically about 1 of the light a photosynthesizing cell absorbs is re-emitted as fluorescence, with a peak at about - 685 nm. Fluorescence quantum yield (ff) in the sea is calculated on the basis of measurements of the spectral distribution of downwelling irradiance and upwelling radiance...

Vertical attenuation of irradiance

In the absence of scattering (b 0), Kd, the vertical attenuation coefficient for downward irradiance, is determined only by the absorption Fig. 6.17 Vertical attenuation coefficient for downward irradiance as a function of optical depth for b a 5, and a 1.0 m1. Data obtained by Monte Carlo calculation for vertically incident light.702 coefficient and the zenith angle, 0, of the light beam within the water, in accordance with Kd a cos 0. In a scattering medium, Kd is increased, partly because of...

Chlorophyllcarotenoidprotein complexes

Prasinoxanthin Absorption

Essentially all the chlorophyll and most of the carotenoid in chloroplasts occur complexed to protein. There is good reason to suppose that these Table 8.2 Major chloroplast carotenoids in various algal classes. Chloro- Xantho- Eustigmato- Bacillario- Chryso- Hapto- Eugleno- Phaeo- Pyrro- Crypto- Rhodo- Cyano- Prochloro-Carotenoid phyta phyceae phyceae phyceae phyceaeft phyta phyta phyta phyta phyta phyta phyta phyta These data for the Chlorophyta apply to higher plants also. Sublittoral...

The chlorophylls

The chlorophylls are cyclic tetrapyrrole compounds with a magnesium atom chelated at the centre of the ring system. Chlorophylls a and b are derivatives of dihydroporphyrin their structures are shown in Fig. 8.7a. In the coccoid marine prochlorophyte, Prochlorococcus marinus, chlorophylls a and b are replaced by the divinyl forms, a2 and b2,225,467 in which the ethyl group on ring II is replaced by a vinyl group. Chlorophyll d, which has so far been found only in cyanobacteria in the genus...

Significance of phylogenetic chromatic adaptation

The evidence taken together seems to me to lead to the conclusion that chromatic adaptation is a major factor influencing the depth distribution of the three types of benthic marine algae, but that it is not the only one, and in some instances other factors prevail. The fact that all algae that grow at depths where the light is predominantly green or blue-green have pigments, whether specialized carotenoids such as fucoxanthin or siphonaxanthin, or biliproteins such as R-phycoerythrin, which...

Contribution of the different components of the aquatic medium to absorption of PAR

Apart from the small amount of light scattered back out of the water, attenuation of PAR in water bodies is due to absorption, although the extent of this absorption within a given depth may be greatly amplified by scattering, which increases the average pathlength of the photons within that depth. The relative contribution of different components of the system to this absorption at a given wavelength is in proportion to their absorption coefficients at that wavelength. Absorption coefficients...

Chromatic adaptation in eukaryotic algae

Red algae do show changes in their pigment composition in response to changes in the spectral quality of the light field in which they are grown. The direction of the pigment change, however, quite apart from its quantitative extent, seems to depend on the intensity of the light. Brody and Emerson (1959) determined the ratio of phycoerythrin to chlorophyll in the unicellular red alga Porphyridium cruentum grown in green light (546 nm - absorbed mainly by phycoerythrin) or blue light (436 nm...

The scattering properties of natural waters

The scattering properties of pure water provide us with a suitable baseline from which to go on to the properties of natural waters. We shall make use here of a valuable review by Morel (1974) of the optical properties of pure water and pure sea water. For measurements of the scattering properties, water purified by distillation in vacuo or by repeated filtration through small-pore-size filters must be used ordinary distilled water contains too many particles. Scattering by pure water is of the...

Carbon dioxide

We shall first consider the extent to which CO2 availability limits the overall rate. Given that CO2 is a substrate that is used by an enzyme (system), then we may plausibly suppose that the photosynthetic rate at any given light intensity will vary with CO2 concentration approximately in accordance with the well-known Michaelis-Menten equation for enzyme kinetics where v is the rate of enzyme reaction at substrate concentration s, V is the maximum rate obtainable at saturating substrate...

Coloured dissolved organic matter light absorption

From the point of view of aquatic ecology, the significance of the soil humic material is that as water, originating as rainfall, drains through soil and into rivers and lakes, and ultimately into estuaries and the sea, it extracts from the soil some of the water-soluble humic substances and these impart a yellow colour to the water, with major consequences for the absorption of light, particularly at the blue end of the spectrum. James and Birge (1938) in the USA and Sauberer (1945) in Austria...

Particle scattering

The Rayleigh and Einstein-Smoluchowski theories of scattering apply only when the scattering centres are small relative to the wavelength of light this is true in the case of gas molecules and of the tiny density fluctuations in pure liquids. Even the most pristine natural waters, however, are not, optically speaking, pure and they invariably contain high concentrations of particles - mineral particles derived from the land or from bottom sediments, phytoplankton, bacteria, dead cells and...

Temporal variation in photosynthesis

Seasonal Variation Pyramids Biomass

The short answer to the question 'When does aquatic photosynthesis take place' is that it takes place when and to the extent that the various limiting constraints we have already discussed permit it to take place. Thus, to understand temporal variation in photosynthesis we need to know the manner in which these limiting factors vary with time. Considering diurnal variation first, there is of course no photosynthesis at night. Photosynthesis begins at dawn and ends at dusk. The total...

Depth variation of photosynthetic characteristics in macrophytes

Plants of the subtidal red alga Ptilota serrata collected from 24 m depth off northeastern America showed light saturation of photosynthesis at about 116mmolphotonsm 2s_1, whereas plants from 6m saturated at about 182 mmolphotonsm s-1.877 At very low light intensities (714 mmol photons m 2s_1) both kinds of plant achieved the same photo-synthetic rate per g dry mass but at higher intensity the deep-water plants levelled off first and achieved a maximum photosynthetic rate only half that of the...

Photoinhibition

The inhibition of photosynthesis at high light intensities must be taken into account in ecological studies, since the intensities typically experienced in the surface layer of natural waters in sunny weather are in the range that can produce photoinhibition. Indeed if the depth profile of phytoplankton photosynthetic activity is measured by the suspended bottle method in inland or marine waters, a noticeable diminution in the specific photosynthetic rate or the rate per unit volume is...

Depth distribution of benthic flora

The higher productivity of shallow water applies to the benthic flora also. Any surface within the euphotic zone of a water body is usually found to support a productive plant community. This applies not only to the more obvious macrophyte communities such as kelp forests, seagrass beds, brown and red algal associations on underwater rocks, but also to seemingly bare sand and mud surfaces, which usually harbour a dense microflora among the grains. This microflora, or microphytobenthos, is...

Seasonal adaptation multicellular benthic algae

Away from the tropics the average irradiance during daylight hours changes cyclically with the seasons during the year and we may reasonably suppose that it would be of advantage to the aquatic flora to adapt their photosynthetic systems to the seasonally varying light climate. This should especially be the case for the perennial benthic algae that survive throughout the year and therefore must photosynthesize as best they can at all seasons. However, the seasonal variation in temperature that...

And time of year

At any given point on the Earth's surface the daylength and the solar elevation reach their maximum values in the summer and their minimum values in the winter. Substituting into eqn 2.7 we can obtain expressions for the noon solar elevation on the longest summer day (d 23 27') sin b 0.39795 sin g + 0.91741 cos g (2.12) and the shortest winter day (d 23 27') sin b 0.39795sin g + 0.91741 cos g (2.13) as a function of latitude. At the latitude of Canberra (35 S) for example, the corresponding...

Biliproteins

The biliprotein chloroplast pigments are found only in certain algae the Rhodophyta, Cryptophyta and Cyanophyta. They are either red (phycoerythrins, phycoerythrocyanin) or blue (phycocyanins, allo-phycocyanins) in colour. They have been reviewed by Bogorad (1975), Gantt (1975, 1977), O'Carra and O'h Eocha (1976), Glazer (1981, 1985), MacColl and Guard-Friar (1987), Rowan (1989) and Mimuro and Kikuchi (2003). The biliproteins of the red and blue-green algae are closely related and we shall...

Correction for atmospheric scattering and solar elevation

We have already noted that about 90 of the upward radiance measured by a photometer in a satellite, or in a very high altitude ( 20 km) aircraft, above the ocean originates by scattering of the solar beam by air molecules and by aerosol particles (dust, water droplets, salt etc.) within the atmosphere - this is known as the path radiance. To arrive at a value of the water-leaving radiance, Lw(d,f), from the measured radiance, the path radiance must be removed, and furthermore the attenuation of...

Chromatic adaptation within the bluegreen algae

The most clear-cut examples are to be found among the blue-green algae (Cyanobacteria), and it was indeed in a blue-green algal species that ontogenetic chromatic adaptation was first described. Gaidukov (1902) observed that Oscillatoria rubescens was red in colour when grown in green light, and blue-green when grown in orange light he attributed these colour changes to the synthesis of different kinds of pigment. Boresch (1921) showed that the colour changes are due to shifts in the types of...

Downward irradiance PAR

As a broad indication of the availability of light for photosynthesis in an aquatic ecosystem, information on the penetration of the whole 4011 450 500 550 COO MO KB 750 Wi tnr* ''i 4011 450 500 550 COO MO KB 750 Wi tnr* ''i Pig. 6.4 Spectral distribution of downward irradiance in marine and inland waters, (a) The Gulf Stream (Atlantic Ocean) off the Bahama Islands (plotted from data of Tyler and Smith, 1970). (b) Batemans Bay, NSW, Australia (after Kirk, 1979). (c) Lake Burley Griffin, ACT,...

Chloroplast movements

The rate of light collection by chloroplasts depends not only on their pigment complement but also on their position and orientation within the cell. In some aquatic plants this can vary with light intensity. Amongst the higher plants1415 the general pattern of behaviour is that in low-intensity light the chloroplasts move to a position in the cell such that light absorption is maximized - they spread themselves out adjoining, and parallel to, those cell walls that face the incident light. In...