Paleolimnology
Limnology is the study of fresh water and paleolimnology is the study of the fossils of fresh water aquatic life, largely those of the microscopic algae classified as "Diatoms." Diatoms are excellent bioindicators because they have a silica-based shell which persists for millenia and is species-specific for easy identification. There are many species of diatoms and each species lives in a very specific and narrow range of conditions.
Phosphorous loading in the water, acidity, turbidity, changes in nutrient status and temperature, can all be predicted with scientific certainty based on the kinds of diatoms that are found in lake sediments. Most lake sediments are layered, identifiable by color variations. For example, in a northern lake, the deeper parts of a lake had alternating thin layers of black and gray. Below these were thicker strata alternating pink and gray. The black and gray strata exist as flat sheets while the pink and gray ones were often contorted. Shallow-water sediments are arranged in strata too, but these are usually disrupted in the act of sampling them. Sediment type varies with water depth. Deeper-water sediments are fine-grained (silty clay or mud) while those in shallow water are coarse (fine sand and gravel, with shells, bits of wood and plant, and cinders). Since the shallow-water sediments are coarser and are made up of a wider variety of constituents, it is likely that they accumulate differently than the deeper water sediments.
Paleolimnology relates to both limnology and paleoecology. Paleolimnology studies the past environments of inland lakes, streams, freswater, brackish, and saline systems over thousands of years. It focuses on changes associated with such events as climate change, human impacts, and lifecycle processes. Paleolimnology is based on careful analyses of sediment cores, including the physical, chemical and mineralogical properties of sediments, and diverse biological records which include fossil diatoms, molluscs, pollen, pigments and chironomids. Many paleolimnology studies focus on the biological productivity of lakes, and the role of various processes that create change in lakes.
The study of diatoms found within the sediment layers of lakes provides insights into the environment at the time the layer was deposited.
Most lakes sedimentation occurs at a standard rate per year. The mid lake sedimentation is composed of much of the detritus that falls into the lake but very importantly the sedimentation also includes the remains of the diatoms that die and then settle to the lake bottom. In a sediment study, a one meter core sample represents the history of the lake back a given number of years so the core length needs to adequately cover the time period of interest. Once the core sample is taken, it is extruded from the core sampler, transported in a half tube, cut longitudinally in a way that avoids cross-layer contamination. Five slices are taken along the length of the core. These samples are prepared as slides and are then examined under 400 to 1000 times magnification to identify the types of diatoms and provide counts of each type. The diatomaceous algae species are recorded, the pollen of some weed species are noted. In areas of northern Canada, sediment records may date back to the last glaciation.
Diatoms (Bacillariophyta) are one of the most distinctive and successful groups of unicellular algae, occurring throughout the world in marine, brackish and fresh waters, as well as in damp subaerial habitats. They are usually estimated to contribute about 25-35 % of the world’s productivity (in terms of carbon fixation) and to be represented by 50 – 200 thousand species depending upon one’s definition of species. Diatoms are also used extensively to infer water quality in contemporary aquatic systems.
A diatom dichotomous key and a transmission microscope are essential for the study of diatoms. Both the diatom identification key and the diatom environmental conditions chart may be downloaded below.
Limnology is the study of fresh water and paleolimnology is the study of the fossils of fresh water aquatic life, largely those of the microscopic algae classified as "Diatoms." Diatoms are excellent bioindicators because they have a silica-based shell which persists for millenia and is species-specific for easy identification. There are many species of diatoms and each species lives in a very specific and narrow range of conditions.
Phosphorous loading in the water, acidity, turbidity, changes in nutrient status and temperature, can all be predicted with scientific certainty based on the kinds of diatoms that are found in lake sediments. Most lake sediments are layered, identifiable by color variations. For example, in a northern lake, the deeper parts of a lake had alternating thin layers of black and gray. Below these were thicker strata alternating pink and gray. The black and gray strata exist as flat sheets while the pink and gray ones were often contorted. Shallow-water sediments are arranged in strata too, but these are usually disrupted in the act of sampling them. Sediment type varies with water depth. Deeper-water sediments are fine-grained (silty clay or mud) while those in shallow water are coarse (fine sand and gravel, with shells, bits of wood and plant, and cinders). Since the shallow-water sediments are coarser and are made up of a wider variety of constituents, it is likely that they accumulate differently than the deeper water sediments.
Paleolimnology relates to both limnology and paleoecology. Paleolimnology studies the past environments of inland lakes, streams, freswater, brackish, and saline systems over thousands of years. It focuses on changes associated with such events as climate change, human impacts, and lifecycle processes. Paleolimnology is based on careful analyses of sediment cores, including the physical, chemical and mineralogical properties of sediments, and diverse biological records which include fossil diatoms, molluscs, pollen, pigments and chironomids. Many paleolimnology studies focus on the biological productivity of lakes, and the role of various processes that create change in lakes.
The study of diatoms found within the sediment layers of lakes provides insights into the environment at the time the layer was deposited.
Most lakes sedimentation occurs at a standard rate per year. The mid lake sedimentation is composed of much of the detritus that falls into the lake but very importantly the sedimentation also includes the remains of the diatoms that die and then settle to the lake bottom. In a sediment study, a one meter core sample represents the history of the lake back a given number of years so the core length needs to adequately cover the time period of interest. Once the core sample is taken, it is extruded from the core sampler, transported in a half tube, cut longitudinally in a way that avoids cross-layer contamination. Five slices are taken along the length of the core. These samples are prepared as slides and are then examined under 400 to 1000 times magnification to identify the types of diatoms and provide counts of each type. The diatomaceous algae species are recorded, the pollen of some weed species are noted. In areas of northern Canada, sediment records may date back to the last glaciation.
Diatoms (Bacillariophyta) are one of the most distinctive and successful groups of unicellular algae, occurring throughout the world in marine, brackish and fresh waters, as well as in damp subaerial habitats. They are usually estimated to contribute about 25-35 % of the world’s productivity (in terms of carbon fixation) and to be represented by 50 – 200 thousand species depending upon one’s definition of species. Diatoms are also used extensively to infer water quality in contemporary aquatic systems.
A diatom dichotomous key and a transmission microscope are essential for the study of diatoms. Both the diatom identification key and the diatom environmental conditions chart may be downloaded below.
diaton_ident_chart.pdf | |
File Size: | 835 kb |
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diatom_glossary.pdf | |
File Size: | 6189 kb |
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