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April 10, 2015
PLANKTON: "We're an indolent lot... Shiftless microscopic drifters. Here in the oceans a million trillion trillion of us just float and aimlessly worship the sun. We have no brains at all. And we don't do anything at all except procreate with promiscuous abandon and generate most of Earth's oxygen. And we have no advice at all for you diligent bipeds who use your capacious intellects to so industriously befoul the seas. For about two billion years we got along quite well without you. And without us, you will suffocate".
.................. Lake Management- S.E. Jorgensen
Primary production represents the synthesis of organic matter of aquatic systems and the total process, photosynthesis, whose complex metabolic pathway can be oversimplified as follows:
light + 6CO2 + 6H2O ----> C6H12O6 + 6O2
Plants have photosynthetic pigments, one of which, cholorophylla is present in almost all photosynthetic organisms. Several other pigments, such as chlorophyll b, c, d and e, carotenoids, xanthophylls and biliproteins, can be found in plants.
The word "trophy" refers to the rate of organic matter supplied by or to the lake per unit of time. Lakes receiving a relatively large portion of their organic material from allochthonous (external) sources are termed dystrophic (brown water) lakes. Productivity of most dystrophic lakes is low. The difference between dystrophic and eutrophic lakes is the source of the organic matter- allochthonous and autotrophic respectively.
Among the algal communities, one can readily differentiate the following:
The general word psammon refers to all organisms growing or moving through sand. A group of algae found aggregated in the littoral zone is the metaphyton, which is neither strictly attached to substrata nor truly suspended. The metaphyton commonly originates from true floating algal populations that aggregate among macrophytes and debris of the littoral zone as a result of wind-induced water movements.
|Blue-green algae||Cyanophyta or Myxophyceae|
Whereas the planktonic Volvocales and Chlorococcales are ubiquitous in distribution among waters of differing salinity within the normal limnological range, the distribution of most species of desmids of the Conjugales is limited to low concentrations of the divalent cations, calcium and magnesium. Although not totally restricted to waters of low salinity, the desmids are most common and the species diversity is greatest in soft waters draining land forms developed in granitic or other igneous rocks, and especially in waters with a high content of dissolved organic matter. Their abundance and diversity are often greatest in bog waters that drain through deposits of the moss Sphagnum. Many desmids are distributed widely, but as a whole they are less cosmopolitan than most unicellular algae.
The group is commonly divided into the centric diatoms (Centrales), which have radial symmetry, and the pennate diatoms (Pennales), which exhibit essentially bilateral symmetry.
The four major groups of pennate diatoms are differentiated on the basis of cell thickenings and dilations:
Although many zooplankton change size and form seasonally, only a few phytoplankton undergo seasonal polymorphism or cyclomorphosis. One example as temperatures increase is the dinoflagellate Ceratium. Presumably, these changes are of adaptive significance in that they reduce the rate of sinking out of the photic zone.
The widely held assumption that winter productivity is insignificant is not universally valid, and rates of primary production under ice cover can constitute a very significant portion of the total annual primary productivity of the phytoplankton. Increasing light is the dominant factor contributing to the development of the spring "outburst", because water temperatures are still low. The spring maximum is frequently dominated by one species, a diatom, such as Asterionella, Cyclotella, or Stephanodiscus.
The decline of the spring maximum of phytoplankton and onset of summer populations in temperate lakes also is associated with a complex interaction of physical and biotic parameters. In many straightforward cases, reduction of nutrients in the photic zone of the epilimnion is responsible for slowing the growth of populations of the dominant as well as rarer algae. Since diatoms are often the dominant component of the spring maximum in temperate lakes, silica concentrations are often reduced to limiting levels (<0.5 mg/l) in less than two months when turbulence is low and sedimentation of diatom frustules occurs rapidly, subsequent to extensive growth of the diatoms.
As silica concentrations are reduced in productive lakes, diatom populations are often succeeded by a preponderance of first green algae and later blue-green algae. Growth in these eutrophic lakes can be so intense that combined nitrogen (NO3, NH4+) sources are reduced to below detectable concentrations in the trophogenic zone. When this happens, often by midsummer when the warmest epilimnetic temperatures occur, blue-green algae with efficient capabilities for fixing molecular nitrogen have a competitive advantage and can predominate. These lakes require, as a general rule, a reasonably sustained and heavy loading of phosphorus.
|Aquatic plant and animal production||low||high|
|Number of plant and animal species||many||many; can be substantially reduced in hypertrophic waters|
|General levels of biomass in waterbody||low||high|
|Occurrence of algal blooms||rare||frequent|
|Relative quantity of green and blue-green algae||low||high|
|Vertical extent of algal distribution||into hypolimnium (bottom waters) in thermally stratified waterbodies||usually only in surface waters|
|Aquatic plant growth in shallow shoreline area (littoral zone)||can be sparse or abundant; if present, usually consists of submerged and emergent vegetation||often abundant; usually an increase in the presence of filamentous algae and a decrease in macrophytes|
|Daily migration of algae||extensive||limited|
|Some characteristics of algal groups||Green algae: Desmids, Staurastrum|
Diatoms: Tabellaria, Cyclotella
Golden-brown algae: Dinobryon
|Blue-green algae: Anabaena, Aphanizomenon, Microcystis, Oscillatoria|
Diatoms: Melosira, Fragilaria, Stephanodiscus, Asterionella
|Dominant algae||Other commonly|
|Oligotrophic||Slightly acidic; very low salinity||Desmids Staurodesmus, Staurastrum||Sphaerocystis, Gloeocystis, Rhizosolenia, Tabellaria|
|Oligotrophic||Neutral to slightly alkaline; nutrient-poor lakes||Diatoms, especially Cyclotella and Tabellaria||Some Asterionella spp., some Melosira spp., Dinobryon|
|Oligotrophic||Neutral to slightly alkaline; nutrient-poor lakes or more productive lakes at seasons of nutrient reduction||Chrysophycean algae, especially Dinobryon, some Mallomonas||Other chrysophyceans, e.g., Synura, Uroglena; diatom Tabellaria|
|Oligotrophic||Neutral to slightly alkaline; nutrient-poor lakes||Chlorococcal Oocystis or chrysophycean Botryoccocus||Oligotrophic diatoms|
|Oligotrophic||Neutral to slightly alkaline; generally nutrient poor; common in shallow Arctic lakes||Dinoflagellates, especially some Peridinium and Ceratium spp.||Small chrysophytes, cryptophytes, and diatoms|
|Mesotrophic or Eutrophic||Neutral to slightly alkaline; annual dominants or in eutrophic lakes at certain seasons||Dinoflagellates, some Peridinium and Ceratium spp.||Glenodinium and many other algae|
|Eutrophic||Usually alkaline lakes with nutrient enrichment||Diatoms much of year, especially Asterionella spp., Fragilaria crotonensis, Synedra, Stephanodiscus, and Melosira granulata||Many other algae, especially greens and blue-greens during warmer periods of year; desmids if dissolved organic matter is fairly high|
|Eutrophic||Usually alkaline; nutrient enriched; common in warmer periods of temperate lakes or perennially in enriched tropical lakes||Blue-green algae, especially Anacystis (= Microcystis), Aphanizomenon, Anabaena||Other blue-green algae; euglenophytes if organically enriched or polluted|
Since there is a tendency for green and blue-green algae to be summer forms, although the diatoms may flourish at any time of year, the indices other than the diatom quotient refer only to summer collections, preferably made in June, July, and August. The diatom quotient is supposedly applicable at any time of year.
Nygaard regarded lakes containing associations giving a compound index of less than 1.0 as unproductive and those giving an index of more than 3.0 as definitely eutrophic; the intermediate values implied mesotrophy or weak eutrophy.
Lake characteristics Myxophycean Chlorophycean Diatom Euglophyte Compound Less productive, more transparent (pH<7.0,
Ca<10 mg/l) 0.0-0.4 0.0-0.7 0.0-0.3 0.0-0.2 0-1 More productive, less transparent (pH>7.0, Ca>10 mg/l) 0.1-3.0 0.2-9.0 0.0-1.75 0.0-1.0 1.2-25 Vaxjo and Lund District (4 lakes) Vastervik District (6 lakes) Aneboda District (4 lakes) Secchi Disk transparency (m) 0.82-0.38 3.05-1.41 6.04-4.48 Conductivity 155-296 66-178 39-60 pH 7.8-8.4 7.2-8.2 6.8-7.0 Number of Chlorococcales species 26-42 14-28 4-14 Number of Desmidiae species 3-15 6-17 20-35 Chlorophycean Index 2.6-14 1.0-3.0 0.2-0.5
It is also possible to make for any region a list of organisms of more frequent occurrence in unproductive waters and another list of species of more frequent occurrence in more productive waters. The ratio, in the plankton of any lake, of the number of species on one list to the number on the other can be used to assess the position of the lake in a scale of productivities.
The most important phyla are Pyrrhophyta (dinoflagellates), Chrysophyta and Cyanophyta (blue-green algae). Algae of concern in lakes and ponds are usually the blue-greens Anabaena flos-aquae, Microcystis aeruginosa and Aphanizomenon flos-aquae. Massive blooms of freshwater algae often cause die-off of fish and other organisms when the algal populations suddenly collapse. The death and rapid decomposition of the algae quickly lead to anoxia and asphyxiation of fish and other aquatic animals.
Some odours from lake water originate from the decomposition of algae and other aquatic plant materials. Several species of algae produce offensive odours while in the active growing state. Many natural surface waters not influenced by odour-producing algae have a TON (Threshold Odour Number) of 5, whereas others with excessive algal growth may have a TON exceeding 200.
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