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Forensic limnology is a sub-field of freshwater ecology, which focuses especially on the presence of diatoms in crime scene samples and victims. Different methods are used to collect this data but all identify the ratios of different diatom colonies present in samples and match those samples with locations at the crime scene. [1] [2] [3]
Diatoms are diverse microscopic algae with silica cell walls that have different characteristics such as color, shape, and size. There are 8,000 known species of diatoms. Diatoms do not have specialized nutrient and water conducting tissues, which affects their dispersion throughout ecosystems. [4] These microscopic organisms mainly inhabit freshwater environments because of their inability to survive the cleaning agents present in domestic water sources. [1]
Diatoms are identifiable based on each species' unique silica cell walls (known as "frustules") and vary depending on their environment. Because they have determinant properties[ clarification needed ] diatoms create flora profiles for scientists. When these microscopic algae die, their frustules become a part of the water sediment. The frustules of the deceased organisms can be compared with the living diatoms to determine characteristics of their environment. In early spring and the fall, the ratio of living diatoms to dead diatoms is high, whereas, in summer and winter the amount of dead diatoms outpopulates the living. [1] Based on this known information, diatoms can verify the time of year that samples were taken. Different types of diatoms can also be used to identify the properties of a sample's ecosystem. For example, a higher ratio of periphytic diatoms (i.e., those that are attached to a substrate), the higher the vegetation concentration, and the shallower the water. [4] The reason diatoms are a common tool to match water environments is because of the variability of their populations are predictable and constant, the organisms can be identified by using the light microscope, and their silica cell walls allow for preservation. [2]
Diatoms do not inhabit domestic water sources, which limits the situations that diatoms can be used to create flora profiles or time of death estimations. [1] Diatoms can only tell when or where evidence was found in some situations and not the time of death if there is no body fluid sample available to be collected. If a body is placed in freshwater post mortem then diatoms cannot be used to evaluate the time of death. Without the inhalation of water and some circulation present in the victim, the diatoms will not be able to enter the alveolar system and bloodstream making it difficult to extract a reliable sample. Another issue with the use of diatoms in order to provide evidential support is that diatoms can also be found on clothes, in food and drink, or air. [5] Because the body can preserve these microscopic algae, the presence of diatoms may not only be on a victim or suspect through their relation to a crime scene, which affects the reliability of the results collected from a scene. Diatoms can also be destroyed based on the biological make up of the body it encounters, this could affect the results in a criminal investigation. [3]
Materials taken from victims, suspects, or the crime scene can be tested to match locations of where the samples derived.
In order to use diatom testing there are some guidelines that scientists must follow. To get a more accurate result there must be at least 20 diatoms in a 100 microliter sample. When dealing with testing on a human body, having five complete diatoms from more than two different organs will also give a positive diagnosis. [2] Samples are taken from bone marrow, lung, spleen, liver, kidney, brain tissue, or from the area where the crime was discovered or occurred. [6] There are a number of different extraction methods, the most commonly used being the "acide digestion method", which is fast and inexpensive. [5]
When diatom testing on an organic sample scientists use phase contrast microscopy. While observing the diatoms are tallied and organized based on their different species. The ratio of specific specimen of diatoms in the water will have a similar ratio to the sample that is taken from the site where the diatoms were transferred. Scientists use this to match materials and people to specific locations at a crime scene. A diatom database (started in 2006) can be used as the "fingerprint system" for diatoms: a computer identifies diatoms to species based on shape and color characteristics. However, as of 2012, the database was not complete and was not used in courts. [6]
When using diatom testing, scientists observe the amount of diatoms present on the organism and may be able to estimate a generalized time of death. For example, if there are fewer than 20 different species of colonizing diatoms, then the organism's death could have been within the previous 7 to 12 days, but, if there are more than 50 different colonies of diatoms then it is determined that death possibly occurred several weeks ago. Certain diatoms narrow the time frame to more exact dates. For instance, late colonizers, such as Ankistrodesmus algae, may not start to colonize on an organism until 30 days after its death. [2]
As of 2012, a small percentage of forensic limnology is used as evidence in courts. The presence of diatoms in air, food, drink, and close contact is not variable enough to be supportive evidence in determining locations of events. Even so, an investigation requires the use of forensic limnology in order to estimate time of death, location of drowning, and the determining of suspect. If the results of forensic limnology are not used in prosecution, the results are used to understand the crime. [6]
Forensic science, also known as criminalistics, is the application of science principles and methods to support legal decision-making in matters of criminal and civil law.
A diatom is any member of a large group comprising several genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth's biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year, take in over 6.7 billion tonnes of silicon each year from the waters in which they live, and constitute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara, much of it from the Bodélé Depression, which was once made up of a system of fresh-water lakes.
An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term algae encompasses many types of aquatic photosynthetic organisms, both macroscopic multicellular organisms like seaweed and microscopic unicellular organisms like cyanobacteria. Algal bloom commonly refers to the rapid growth of microscopic unicellular algae, not macroscopic algae. An example of a macroscopic algal bloom is a kelp forest.
Zooplankton are the animal component of the planktonic community, having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequently, they drift or are carried along by currents in the ocean, or by currents in seas, lakes or rivers.
Forensic palynology is a subdiscipline of palynology, that aims to prove or disprove a relationship among objects, people, and places that may pertain to both criminal and civil cases. Pollen can reveal where a person or object has been, because regions of the world, countries, and even different parts of a single garden will have a distinctive pollen assemblage. Pollen evidence can also reveal the season in which a particular object picked up the pollen.
Diatomaceous earth, diatomite, celite or kieselgur/kieselguhr is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 mm to less than 1 μm, but typically 10 to 200 μm. Depending on the granularity, this powder can have an abrasive feel, similar to pumice powder, and has a low density as a result of its high porosity. The typical chemical composition of oven-dried diatomaceous earth is 80–90% silica, with 2–4% alumina, and 0.5–2% iron oxide.
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, such as a hand lens, is referred to as a macrofossil.
Biogenic silica (bSi), also referred to as opal, biogenic opal, or amorphous opaline silica, forms one of the most widespread biogenic minerals. For example, microscopic particles of silica called phytoliths can be found in grasses and other plants.
Forensic biology is the use of biological principles and techniques in the context of law enforcement investigations.
The following outline is provided as an overview of and topical guide to forensic science:
Forensic geology is the study of evidence relating to materials found in the Earth used to answer questions raised by the legal system.
Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles either have their origins in soil and rocks and have been transported from the land to the sea, mainly by rivers but also by dust carried by wind and by the flow of glaciers into the sea, or they are biogenic deposits from marine organisms or from chemical precipitation in seawater, as well as from underwater volcanoes and meteorite debris.
Aquatic science is the study of the various bodies of water that make up our planet including oceanic and freshwater environments. Aquatic scientists study the movement of water, the chemistry of water, aquatic organisms, aquatic ecosystems, the movement of materials in and out of aquatic ecosystems, and the use of water by humans, among other things. Aquatic scientists examine current processes as well as historic processes, and the water bodies that they study can range from tiny areas measured in millimeters to full oceans. Moreover, aquatic scientists work in Interdisciplinary groups. For example, a physical oceanographer might work with a biological oceanographer to understand how physical processes, such as tropical cyclones or rip currents, affect organisms in the Atlantic Ocean. Chemists and biologists, on the other hand, might work together to see how the chemical makeup of a certain body of water affects the plants and animals that reside there. Aquatic scientists can work to tackle global problems such as global oceanic change and local problems, such as trying to understand why a drinking water supply in a certain area is polluted.
Marine microorganisms are defined by their habitat as microorganisms living in a marine environment, that is, in the saltwater of a sea or ocean or the brackish water of a coastal estuary. A microorganism is any microscopic living organism or virus, that is too small to see with the unaided human eye without magnification. Microorganisms are very diverse. They can be single-celled or multicellular and include bacteria, archaea, viruses and most protozoa, as well as some fungi, algae, and animals, such as rotifers and copepods. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses as microorganisms, but others consider these as non-living.
Post-mortem chemistry, also called necrochemistry or death chemistry, is a subdiscipline of chemistry in which the chemical structures, reactions, processes and parameters of a dead organism is investigated. Post-mortem chemistry plays a significant role in forensic pathology. Biochemical analyses of vitreous humor, cerebrospinal fluid, blood and urine is important in determining the cause of death or in elucidating forensic cases.
Thalassiosira is a genus of centric diatoms, comprising over 100 marine and freshwater species. It is a diverse group of photosynthetic eukaryotes that make up a vital part of marine and freshwater ecosystems, in which they are key primary producers and essential for carbon cycling
DNA barcoding of algae is commonly used for species identification and phylogenetic studies. Algae form a phylogenetically heterogeneous group, meaning that the application of a single universal barcode/marker for species delimitation is unfeasible, thus different markers/barcodes are applied for this aim in different algal groups.
Cyclotella is a genus of diatoms often found in oligotrophic environments, both marine and fresh water. It is in the family Stephanodiscaceae and the order Thalassiosirales. The genus was first discovered in the mid-1800s and since then has become an umbrella genus for nearly 100 different species, the most well-studied and the best known being Cyclotella meneghiniana. Despite being among the most dominant genera in low-productivity environments, it is relatively understudied.
Marine protists are defined by their habitat as protists that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. Life originated as marine single-celled prokaryotes and later evolved into more complex eukaryotes. Eukaryotes are the more developed life forms known as plants, animals, fungi and protists. Protists are the eukaryotes that cannot be classified as plants, fungi or animals. They are mostly single-celled and microscopic. The term protist came into use historically as a term of convenience for eukaryotes that cannot be strictly classified as plants, animals or fungi. They are not a part of modern cladistics because they are paraphyletic.
Many protists have protective shells or tests, usually made from silica (glass) or calcium carbonate (chalk). Protists are a diverse group of eukaryote organisms that are not plants, animals, or fungi. They are typically microscopic unicellular organisms that live in water or moist environments.
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