Paleolimnology is the study of past conditions of inland fresh water bodies. A variety of measurements from lake and bog sediments are used to indicate past water temperature, physical properties, biology, and chemistry. The Experiential Science class have been taking core samples from Cowley Lake over the past six years ( at time to depths of 2.4 meters).
Samples were taken from ice and have been pressed into the sediment with pressures exceeding 2000 kg. In the core sampling process, the core is compressed so that the samples studied may be as little as 50% of the total sample depth.
Once the samples are extruded, cut in half, and samples along the length of the core, slides are prepared from the samples. Diatoms are identified and counted from these slides. The table below shows a typical analysis of diversity and counts.
Diatom cells are contained within a unique silica cell wall comprising two separate valves (or shells). The biogenic silica that the cell wall is composed of is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is then extruded to the cell exterior and added to the wall. Diatom cell walls are also called frustules or tests, and their two valves typically overlap one over the other like the two halves of a petri dish. In most species, when a diatom divides to produce two daughter cells, each cell keeps one of the two halves and grows a smaller half within it. As a result, after each division cycle the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide, they reverse this decline by forming an auxospore. This expands in size to give rise to a much larger cell, which then returns to size-diminishing divisions. Auxospore production is almost always linked to meiosis and sexual reproduction.
Decomposition and decay of diatoms leads to organic and inorganic (in the form of silicates) sediment, the inorganic component of which can lead to a method of analyzing past marine environments by corings of ocean floors or bay muds, since the inorganic matter is embedded in deposition of clays and silts and forms a permanent geological record of such marine strata.
The file below contains detailed information about the environmental conditions in which different diatoms live. Finding the silicate remains of long dead diatoms, give clues to the environmental conditions when they lived. The second chart provides a glossary and information about diatom biology.
diatom_chart.pdfDownload File
Samples were taken from ice and have been pressed into the sediment with pressures exceeding 2000 kg. In the core sampling process, the core is compressed so that the samples studied may be as little as 50% of the total sample depth.
Once the samples are extruded, cut in half, and samples along the length of the core, slides are prepared from the samples. Diatoms are identified and counted from these slides. The table below shows a typical analysis of diversity and counts.
Diatom cells are contained within a unique silica cell wall comprising two separate valves (or shells). The biogenic silica that the cell wall is composed of is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is then extruded to the cell exterior and added to the wall. Diatom cell walls are also called frustules or tests, and their two valves typically overlap one over the other like the two halves of a petri dish. In most species, when a diatom divides to produce two daughter cells, each cell keeps one of the two halves and grows a smaller half within it. As a result, after each division cycle the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide, they reverse this decline by forming an auxospore. This expands in size to give rise to a much larger cell, which then returns to size-diminishing divisions. Auxospore production is almost always linked to meiosis and sexual reproduction.
Decomposition and decay of diatoms leads to organic and inorganic (in the form of silicates) sediment, the inorganic component of which can lead to a method of analyzing past marine environments by corings of ocean floors or bay muds, since the inorganic matter is embedded in deposition of clays and silts and forms a permanent geological record of such marine strata.
The file below contains detailed information about the environmental conditions in which different diatoms live. Finding the silicate remains of long dead diatoms, give clues to the environmental conditions when they lived. The second chart provides a glossary and information about diatom biology.
diatom_chart.pdfDownload File
core depth
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100 104 108 112 116 120 |
diatom count diatom count diatom count diatom count diatom count diatom count diatom count Rhiocosphenia 11 Peronia 2 Navicula Pinnularia 17 Achnanthes Cocconeis 2 Cyclotella Stephanodiscu Cyclostephanos 1 Navicula Pinnularia 4 Achnanthes Cocconeis 1 Rhoicosphenia 4 Navicula Pinnularia 3 Eutonia 1 Navicula Pinnularia 2 Rhoicosphenia 4 Achnanthes Cocconeis 1 Navicula Pinnularia 3 navicula 3 cymbella amphora 4 navicula Navicula Pinnularia 3 cymbella amphora 4 Rhoicosphenia 4 Navicula Pinnularia 23 Gomphonema 5 Stephanodiscus Cyclostephanus 6 Pleurosigma 6 Cymbella Amphara 10 Achnanthes Cocconeis Navicula Pinnularia 24 Gomphonema 5 Stephanodiscus Cyclostephanus 6 Pleurosigma 1 Cymbella Amphara 10 Achnanthes Cocconeis Navicula Pinnularia 46 Achnaanthes Cocconeis 35 Cycloto Stephanodiscus 2 Cymbella Amphoro 17 Navicula Pinnularia 30 Achnaanthes Cocconeis 16 Cymbella Amphoro 11 Achnanthes Cocconeis 8 Navicula Pinnularia 49 Nitzschia Denticula 4 Cymbella Amphora 3 Surirella Complodiscus 2 Cyclotella Navicula 2 Rhocosphenia 1 Navicula 5 Bacillius 1 Fragilaria 14 Actinella 13 Cymbella 8 Isovalaur 6 Gyrosigma 3 Navicula 9 Amphora 4 Cymbella 39 Navicula 64 peronia 30 achnanthes 14 Rhoicosphenia 5 Eunotia 5 FRAGILARIA 2 Fragilaria 1 Rhoicosphenia 1 Peronia 1 Navicula 18 Cymbella Amphora 9 Peronia 2 Rhoicosphenia 8 Eunotia 2 Nitzschia Denticula 1 |
Bob Sharp along with Paul Hamilton from the Museum of Natural History developed the following key for identifying class or orders of diatoms. Bob also developed a detailed glossary and a key that identifies environmental conditions favoured by different orders.