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

Limnology is the science dealing with the physical, chemical, biological and meteorological study of inland waters.

“Lake Types” Glaciated Lakes Reservoirs Oxbows

Glaciated Lake Reservoir Oxbow

How do the lake types differ? Depth Residence Time Lifespan

Depth Glaciated Lakes = Deep relative to area Reservoirs = Vary, but often shallow for a given size relative to glaciated lake Oxbow = Shallow

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.

Residence Time is the theoretical time it takes water to move through the waterbody. It is the reciprocal of Flushing Rate.

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

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.

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.

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.

Lifespan Glaciated Lakes = High lifespan Reservoirs = Short to moderate lifespan Oxbow = Short lifespan

Phosphorus and Nitrogen (Causal Variables)

Chlorophyll (photosynthetic pigment in algae) is a Response Variable

Phosphorus vs Algal Biomass Missouri Lakes – Phosphorus vs Algal Biomass

Nitrogen vs Algal Biomass Missouri Lakes – Nitrogen vs Algal Biomass

Algae aren’t all bad! Base of the food web Source of dissolved oxygen

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

Transparency as measured by the Secchi Disk is another response variable.

Suspended soil materials also influence water clarity in Missouri’s lakes.

Where do the nutrients come from? According to the EPA, the three top sources of pollution impairing lakes and reservoirs in the USA are:

Agriculture

Municipal Point Sources

Urban Runoff

Miscellaneous Terms

Trophic State Classification Oligotrophic = low nutrients, low algal biomass, high clarity, dissolved oxygen throughout water column Mesotrophic = moderate nutrients and algal biomass, some clarity

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

Eutrophication: The process of lake aging, in which productivity increases overtime as the lake becomes shallower.