lakes so variable?
are a variety of reasons why lakes are so variable. Some of the most
important include the lakes size and shape, what activities
occur in the lands that drain into it (watershed), what ecoregion
the lake is located in, and when and how the lake basin was formed.
These factors, acting in various combinations, have created the multitude
of lake types found in Minnesota today.
are ecoregions and how do they influence lakes?
lies at a crossroads of ecological land types, with widespread differences
in soils, underlying geology, and plant and animal communities. These
differences are identified and classified into ecoregions, or broad
areas in Minnesota that share similar land uses, soils, land and surface
form (topography), and potential natural vegetation. Minnesota is
classified into seven ecoregions. Ninety-eight percent of Minnesotas
lakes occur in just four of them: Northern Lakes and Forests, North
Central Hardwood Forests, Western Corn Belt Plains, and Northern Glaciated
Plains. The other three ecoregions, Northern Minnesota Wetlands, the
Red River Valley, and the Driftless Area, contain few lakes, but are
rich in streams.
and rivers within ecoregions, because they occur in an area of similar
land type, often have similar physical characteristics, water chemistry,
and biological communities. It is often said that, A lake is
a reflection of its watershed, and therefore of its ecoregion.
In other words, what happens on the land and the basic characteristics
of the land (soil, geology, vegetation, drainage, etc.) affects the
quality and health of a lake or stream. The number, appearance, and
condition of lakes vary among ecoregions because of glacial history,
geology, soil type, land use, and climate. Typical values for chemical
and physical measurements have been compiled for the four lake-rich
ecoregions by evaluating information from minimally impacted lakes
and rivers. These values provide a yardstick for comparing
other lakes and rivers in the same ecoregion.
lakes in northern Minnesota different from those in southern Minnesota?
visited lakes across Minnesota, you probably recognize that the northern
lakes are often fairly small and relatively deep compared to the large,
shallow lakes common in southern Minnesota. These differences can
be understood by observing that these lakes occur in two different
ecoregions. Soils in the Northern Lakes and Forests ecoregion tend
to be lower in nutrients than soils in the Northern Corn Belt Plains
ecoregion, causing the northern lakes to be less productive.
the size and depth of a lake influence characteristics such as water
clarity and acidity. Lakes that are deep relative to their size, such
as those in northern Minnesota, tend to be clearer with less nutrient-rich
water. In contrast, lakes that are shallow relative to their size,
such as those in southern Minnesota, tend to be more eutrophic (enriched
with nutrients, resulting in more algae and greater plant growth).
Common land use practices also differ as one moves from southern to
differences also influence a lakes sensitivity to human impacts.
For example, watersheds in northern Minnesota are often rocky, with
thin soils that have a minimal capacity to buffer acidic input from
the atmosphere. Watersheds to the south have deeper soil, better able
to buffer acidic inputs, but with more potential to cause impacts
to lakes from sediments and turbidity.
my lake form?
it is known as the Land of 10,000 Lakes, Minnesota actually
boasts over 11,842 lakes at least 10 acres in size. Our lakes are
mostly the result of glaciers that passed over the state, leaving
behind rocky ridges of till, gouging out depressions, and depositing
thick plains of sandy outwash. When the glaciers melted about 10,000
years ago, blocks of ice buried in the till began to melt, leaving
small, deep lakes. The melting ice created rivers that carried large
volumes of water and sediment. These rivers and their sediment loads
filled depressions and dammed smaller streams to create lakes. Some
lakes have been created by human activity, such as the reservoirs
on the Mississippi or along the border with Canada. Other, more temporary,
lakes have been constructed by beavers.
the glaciers departed, Minnesotas lakes have been gradually
filling in with sediment and organic material as plants die and settle
to the bottom. Unfortunately, humans have dramatically accelerated
the aging process by adding nutrients and increasing sedimentation
due to land use practices, creating eutrophic (enriched) lakes that
experience algae blooms and excessive plant growth.
knowing about ecoregions help us manage lakes?
values for chemical and physical parameters have been compiled for
the seven ecoregions by monitoring unimpacted water bodies (lakes
or streams with minimal human disturbance). These values help us identify
what conditions might have existed before human settlement and help
us develop realistic expectations for how lakes or streams might be
restored to a more natural state. It is unrealistic to
expect a shallow, southern Minnesota lake to have the same water clarity
or productivity, for example, as a northern Minnesota lake. Ecoregions
help us understand these differences.
I contact if I have questions or a problem related to ecoregions?
Check your local telephone
listing, the Who to Contact
section of the Minnesota Shoreland Management Resource Guide Web site,
or the Web sites listed below for:
are some additional resources related to ecoregions?
Primer on Limnology. 1992. B.A. Monson.
Natural Heritage: An Ecological Perspective. 1995. J.R. Tester.
Lake and Watershed Data Collection Manual. 1994. Minnesota Pollution
Citizens Guide to Lake Protection. 1985. Minnesota Pollution
Control Agency and Freshwater Foundation.
Guidebook for Lake Associations. 1997. Minnesota Lakes Association
and The Center for Urban and Regional Affairs.