understanding water on the web
about us understanding data curricula resources
what's new at wow site map
lake ecology primer
physical
formation of lakes
lake variability
light
density stratification
watersheds
chemical
general lake chemistry
dissolved oxygen
nutrients
biological
lake zones
food webs
primary producers
chlorophyll
algal succession
consumers /
decomposers
tropic status
eutrophication
ecoregions
biological differences
 
 
  Ecoregions
 


Figure 23.

Observations of lake characteristics that are geographically-distinct have led to the ecoregion approach of lake classification developed by the U.S. Environmental Protection Agency (EPA) Research Laboratory at Corvallis, Oregon. Ecoregions are areas of relative homogeneity based on landuse, soils, land and surface form, and potential natural vegetation. Minnesota is divided into seven ecoregions (Figure 23), but most of its lakes are found in four of these. Minnesota Pollution Control Agency (MPCA) researchers found regional patterns in numbers of lakes, lake water quality, morphometry, and watershed characteristics (Table 5) among these ecoregions. For example, lakes of the Northern Lakes and Forests ecoregion have significantly lower total phosphorus and chlorophyll than lakes in the Western Corn Belt Plains ecoregion. Furthermore, the MPCA discovered through lake-user surveys that user perception of water quality varied by ecoregions. This has led to ecoregion-specific criteria for phosphorus and, in general, helped to clarify expectations and goals for protecting lakes in Minnesota.


Table 5
Ecoregion lake data summary
Values are typical for surface water (0-2 m) in summer (June-September).
PARAMETER Northern
Lakes and Forests
North Central Hardwood Forests Western Corn Belt Plains Northern
Glaciated Plains
Total Phosphorus (µg/L) 14 - 17 23 - 50 65 - 150 130 - 250
Chlorophyll-mean (µg/L) < 10 5 -22 30 - 80 30 - 55
Chlorophyll-max (µg/L) < 15 7 - 37 60 - 140 40 - 93
Secchi Disk (m) 2.4 - 4.6 1.5 - 3.2 0.5 - 1.0 0.3 - 1.0
Total Kjeldahl - N (mg/L) < 0.75 < 0.60 - 1.2 1.3 - 2.7 1.8 - 2.3
[Nitrite + Nitrate]-N (mg/L) < 0.01 < 0.01 0.01 - 0.02 0.01 - 0.1
Alkalinity (mg/L) 40 - 140 75 - 150 125 - 165 160 - 260
Color (Pt-Co units) 10 - 35 10 - 20 15 - 25 20 - 30
pH 7.2 - 8.3 8.6 - 8.8 8.2 - 9.0 8.3 - 8.6
Chloride (mg/L) < 2 4 - 10 13 - 22 11 - 18
TSS (mg/L) < 1 - 2 2 - 6 7 - 18 10 - 30
Turbidity (NTU) < 2 1 - 2 3 - 8 6 - 17
EC (uS/cm) 50 - 250 300 - 400 300 - 650 640 - 900
TN:TP ratio 25:1 - 35:1 25:1 - 35:1 17:1 - 27:1 7:1 - 18 - 1
* Summer averages by ecoregion, based on interquartile range (25th - 75th percentile) for ecoregion reference lakes. Derived in part from Heiskary, S.A. and C.B. Wilson (1990).

back to top
   
Water on the Web
about us  :  understanding  :  data  :  curricula  :  resources
what’s new  :  site search  :  site map  :  contact us

http://www.waterontheweb.org/under/lakeecology/18_ecoregions.html
date last updated: Wednesday March 03 2004