EDA: Guide to typical Minnesota water quality conditions

Minnesota has 7 ecoregionsLakes and streams around Minnesota have different physical and chemical properties based on where they are located. Water quality reflects the variety of geographic and environmental conditions in the state. This diversity makes it difficult to explain what constitutes “good” water quality for an individual body of water in Minnesota. 

To make it easier, MPCA offers this guide to typical water quality conditions in these seven  “ecoregions,” large expanses of land containing a geographically distinct collection of plants, animals, natural communities and environmental conditions:

Red River Valley

The Red River Valley is relatively flat and heavily cultivated. The ecoregion has few lakes, and surface water drains north through the Red River to Hudson Bay.

Stream turbidity has increased significantly in the last two decades. The removal of shelter belts and increased cultivation of marginal land has enhanced wind erosion, which may be responsible for the higher stream turbidity.

Below are typical measurements one might find for lakes and streams in this ecoregion.

Lakes*

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
Secchi
(in m)
Chl-a
(in ug/L)
TKN
(in mg/L)
8.6 - 8.8 2 - 6 <0.01 0.023 - 0.050 1 - 2 1.5 - 3.2 5 - 22 <0.60 - 1.2

* Because not enough lake data is available for this ecoregion, the numbers from the North Central Hardwood Forest ecoregion have been used instead. Conditions in and around lakes in these two ecoregions are similar.

Streams

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
FC
(in # of organisms
per 100 ml)
Temp
(degrees C)
BOD
(in mg/L)
8.0 - 8.4 11 - 59 0.01 - 0.21 0.11 - 0.3 6 - 23 20 - 220 0 - 21 1.8 - 4.1

Northern Minnesota Wetlands

This region is flat, heavily forested and contains many marshes and wetlands. It has few lakes, but two of them are among the largest in the state: Lake of the Woods and Red Lake Reservoir.

The water quality of streams in this ecoregion is generally very good, due to the relatively slight slope of stream beds and the abundance of ground cover along stream banks (also known as riparian vegetation).

A network of drainage ditches drain portions of the ecoregion, and agriculture accounts for less than 10 percent of land use.

Environmental concerns for this region include long-range atmospheric transport of pollutants (mercury, etc.) or are confined to specific areas associated with agricultural production, logging or potential peat-mining operations.

Below are typical measurements one might find for lakes and streams in this ecoregion.

Lakes*

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
Secchi
(in m)
Chl-a
(in ug/L)
TKN
(in mg/L)
7.2 - 8.3 <1 - 2 <0.01 0.014 - 0.027 <2 2.4 - 4.6 <10 <0.75

* Because not enough lake data is available for this ecoregion, the numbers from the Northern Lakes and Forests ecoregion have been used instead. Conditions in and around lakes in these two ecoregions are similar.

Streams

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
FC
(in # of organisms
per 100 ml)
Temp
(degrees C)
BOD
(in mg/L)
7.6 - 7.9 4.8 - 16 0.01 - 0.08 0.04 - 0.09 4.1 - 10 20 - 40 0 - 20 1.1 - 2.1

Northern Lakes and Forests

This heavily forested ecoregion is made up of steep, rolling hills interspersed with pockets of wetlands, bogs, lakes and ponds. Lakes are typically deep and clear, with good gamefish populations. These lakes are very sensitive to damage from atmospheric deposition of pollutants, storm water runoff from logging operations, urban and shoreland development, mining, inadequate wastewater treatment, and failing septic systems.

Agriculture is somewhat limited by the hilly terrain and lack of nutrients in the soil, though there are some beef and dairy cattle farms.

Below are typical measurements one might find for lakes and streams in this ecoregion.

Lakes

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
Secchi
(in m)
Chl-a
(in ug/L)
TKN
(in mg/L)
7.2 - 8.3 <1 - 2 <0.01 0.014 - 0.027 <2 2.4 - 4.6 <10 <0.75

Streams

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
FC
(in # of organisms
per 100 ml)
Temp
(degrees C)
BOD
(in mg/L)
7.6 - 7.9 1.8 - 6 0.01 - 0.09 0.02 - 0.05 1.7 - 4.3 11 - 20 0.5 - 17 0.8 - 1.7

North Central Hardwood Forest

This ecoregion is an area of transition between the forested areas to the north and east and the agricultural areas to the south and west. The terrain varies from rolling hills to smaller plains. Upland areas are forested by hardwoods and conifers. Plains include livestock pastures, hay fields and row crops such as potatoes, beans, peas and corn.

The ecoregion contains many lakes, and water clarity and nutrient levels are moderate. Land surrounding many of these lakes has been developed for housing and recreation, and the densely populated metropolitan area dominates the eastern portion of this region. Water quality problems that face many of the water bodies in the this area are associated with contaminated runoff from paved surfaces and lawns.

Below are typical measurements one might find for lakes and streams in this ecoregion.

Lakes

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
Secchi
(in m)
Chl-a
(in ug/L)
TKN
(in mg/L)
8.6 - 8.8 2 - 6 <0.01 0.023 - 0.050 1 - 2 1.5 - 3.2 5 - 22 <0.60 - 1.2

Streams

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
FC
(in # of organisms
per 100 ml)
Temp
(degrees C)
BOD
(in mg/L)
7.9 - 8.3 4.8 - 16 0.04 - 0.26 0.06 - 0.15 3 - 8.5 40 - 360 2 - 21 1.5 - 3.2

Northern Glaciated Plains

The rolling terrain of this ecoregion is heavily cultivated. The vast majority of natural vegetation in this area has been replaced by row crops including corn, wheat, soybeans and sunflowers.

Because of the extensive agricultural land use, many lakes and streams face increasing sedimentation and elevated nutrient levels.

Below are typical measurements one might find for lakes and streams in this ecoregion.

Lakes

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
Secchi
(in m)
Chl-a
(in ug/L)
TKN
(in mg/L)
8.3 - 8.6 10 - 30 .01 - .1 0.130 - 0.250 6 - 17 0.3 - 1.0 30 - 55 1.8 - 2.3

Streams

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
FC
(in # of organisms
per 100 ml)
Temp
(degrees C)
BOD
(in mg/L)
8.0 - 8.3 11 - 63 0.01 - 0.51 0.09 - 0.25 5.6 - 23.5 20 - 410 2.5 - 22 2.3 - 4.5

Western Cornbelt Plains

Much like the Northern Glaciated Plains, this ecoregion is heavily cultivated with row crops. Chief surface water quality problems are sedimentation and high levels of nutrients as sediment and fertilizers from agricultural land are washed into the area’s streams and shallow lakes.

The eastern side of the region is characterized by karst terrain, which may include sinkholes, disappearing streams and caves.

Below are typical measurements one might find for lakes and streams in this ecoregion.

Lakes

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
Secchi
(in m)
Chl-a
(in ug/L)
TKN
(in mg/L)
8.2 - 9.0 7 - 18 0.01 - 0.02 0.065 - 0.150 3 - 8 0.5 - 1.0 30 - 80 1.3 - 2.7

Streams

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
FC
(in # of organisms
per 100 ml)
Temp
(degrees C)
BOD
(in mg/L)
8.0 - 8.2 10- 61 1.4 - 7.4 0.16 - 0.33 5.2 - 22 70 - 790 3.5 - 20 2.0 - 5.5

Driftless Area

The smallest ecoregion in the state, the hilly Driftless Area is named for its lack of recent glacial activity. Soils are thin and karst formations underlay most of the area. Lakes are practically non-existent in this area.

Animal feedlots are prominent in this region and nitrate contamination of surface water is of special concern.

Because so few lakes exist in this ecoregion, typical conditions for lakes cannot be calculated.

Streams*

Field pH TSS
(in mg/L)
NOX
(in mg/L)
TP
(in mg/L)
Turb
(in NTU)
FC
(in # of organisms
per 100 ml)
Temp
(degrees C)
BOD
(in mg/L)
7.9 - 8.3 4.8 - 16 0.04 - 0.26 0.06 - 0.15 3 - 8.5 40 - 360 2 - 21 1.5 - 3.2

* Because not enough stream data is available for this ecoregion, the numbers from the North Central Hardwood Forest ecoregion have been used instead. Conditions in and around streams in these two ecoregions are similar.

Comparison tables

Below are tables combining the information presented in the previous section. These tables make it easier to compare how water quality varies across Minnesota’s ecoregions.

Typical summer lake water quality conditions in Minnesota’s ecoregions

Typical summer lake water quality conditions in Minnesota’s ecoregions
* Very few lakes exist in this ecoregion.

Typical annual stream water quality conditions in Minnesota’s ecoregions

Typical annual stream water quality conditions in Minnesota’s ecoregions