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Limnology 101 Dan Obrecht MU Limnology obrechtd@missouri.edu
The Missouri Department of Natural Resources University of Missouri-Columbia Region VII, US Environmental Protection Agency, through the Missouri Department of Natural Resources, has provided partial funding for this project under Section 319 of the Clean Water Act
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Limnology is the science dealing with the physical, chemical, biological and meteorological study of inland waters.
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“Lake Types” Glaciated Lakes Reservoirs Oxbows
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Glaciated Lake Reservoir Oxbow
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How do the lake types differ?
Depth Residence Time Lifespan
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Depth Glaciated Lakes = Deep relative to area
Reservoirs = Vary, but often shallow for a given size relative to glaciated lake Oxbow = Shallow
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Why is depth important? Shallow lakes may mix sporadically throughout the summer, leading to more internal loading of nutrients. A deeper lake has a larger volume of water, which influences hydrology.
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Residence Time is the theoretical time it takes water to move through the waterbody. It is the reciprocal of Flushing Rate.
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Residence Time Glaciated Lakes = Moderate to high residence times
Reservoirs = Generally low to moderate residence times Oxbows = Varies with connectivity to river, generally low due to low volumes
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Why is Residence Time important?
Residence time can be used to gauge inputs relative to lake volume. A lake with a long residence time has low inputs, while a lake with a short residence time has greater inputs relative to lake volume.
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Residence time also indicates how much sedimentation can occur
Residence time also indicates how much sedimentation can occur. A long residence time translates to more material settling out to the bottom of the lake. A short residence time means this sedimentation does not occur.
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Lifespan Over time, lakes become shallower as organic and inorganic matter settles to the bottom. As the lake becomes shallower, it also becomes more productive; accelerating the rate of sedimentation. At some point the lake becomes a wetland.
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Lifespan Glaciated Lakes = High lifespan
Reservoirs = Short to moderate lifespan Oxbow = Short lifespan
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Phosphorus and Nitrogen (Causal Variables)
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Chlorophyll (photosynthetic pigment in algae) is a Response Variable
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Phosphorus vs Algal Biomass
Missouri Lakes – Phosphorus vs Algal Biomass
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Nitrogen vs Algal Biomass
Missouri Lakes – Nitrogen vs Algal Biomass
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Algae aren’t all bad! Base of the food web Source of dissolved oxygen
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Impairments associated with excess algae
Loss of aesthetic beauty Decreased recreation Taste and odor problems Increased cost to treat for drinking water Impacts on dissolved oxygen Toxins
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Transparency as measured by the Secchi Disk is another response variable.
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Suspended soil materials also influence water clarity in Missouri’s lakes.
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Where do the nutrients come from?
According to the EPA, the three top sources of pollution impairing lakes and reservoirs in the USA are:
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Agriculture
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Municipal Point Sources
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Urban Runoff
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Miscellaneous Terms
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Trophic State Classification
Oligotrophic = low nutrients, low algal biomass, high clarity, dissolved oxygen throughout water column Mesotrophic = moderate nutrients and algal biomass, some clarity
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Trophic State Classification
Eutrophic = rich in nutrients and algal biomass, turbid, loss of dissolved oxygen in lower layer during summer stratification Hypereutrophic = very nutrient rich, algal biomass levels that have a negative impact on lake use
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Eutrophication: The process of lake aging, in which productivity increases overtime as the lake becomes shallower.
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