3.2.5 Wetlands

Approximately 29 percent of the land area within the Minnehaha Creek Watershed is shown on the National Wetland Inventory as wetland (see Figure 25 and Table 18).  Wetland scientists use two common classification schemes to identify wetland type – the US Fish and Wildlife Service’s “Circular 39” system, and a replacement classification system developed by Cowardin et al. for the Fish and Wildlife Service, commonly referred to as the Cowardin system.  The Circular 39 system was originally developed as a means for classifying wetlands for waterfowl habitat purposes.  Eight of the Circular 39 freshwater wetland types are found in Minnesota.  The Cowardin scheme is a hierarchical classification based on landscape position, substrate, flooding regime, and vegetation.  While the Cowardin scheme has been officially adopted by the Fish and Wildlife Service and other agencies, the Circular 39 system is still commonly used because of its simplicity and ease of use.

Table 18.  Circular 39 and Cowardin classification of wetland type of the National Wetlands Inventory wetlands in the MCWD.

Circular 39 Type

Area (acres)

Cowardin Class

Area (acres)

Type 1 - Seasonal

366.17

Aquatic Bed

2.84

Type 2 - Wet Meadow

77.03

Emergent

10,236.36

Type 3 - Shallow Marsh

9,771.61

Forested

933.93

Type 4 - Deep Marsh

347.95

Scrub Shrub

874.10

Type 5 - Open Water

20,804.46

Unconsolidated Bottom

21,186.87

Type 6 - Scrub Shrub

874.10

Unconsolidated Shore

5.52

Type 7 - Forested

906.78

 

 

Type 8 - Bog

0.53

 

 

Industrial Activity

26.56

 

 

Riverine

64.43

 

 

TOTAL

33,239.62

 

33,239.62

Source: Minnesota DNR.  See Figure 25.

In 2001-2003 the District undertook a Functional Assessment of Wetlands (FAW) on all wetlands greater than one-quarter acre in size.  This assessment used a variant of the Minnesota Routine Assessment Method.  In contrast to Table 18 above, which shows wetland acreage and type from the National Wetlands Inventory completed in the 1980s, Table 19 below shows the acreage and type as assessed in the field.   Using the results of that analysis, individual wetlands were assigned to one of four categories – Preserve, and Manage 1, 2, or 3 (see Figure 26).  Wetlands that were evaluated as Exceptional or High on certain ecological or hydrologic values were assigned to the Preserve category.  The balance of evaluated wetlands were assigned to a category based on this assessment of current functions and values, with Manage 1 wetlands exhibiting higher values and Manage 2 and 3 moderate or lower values.   Refer to the Functional Assessment of Wetlands (2003) for details of methodology, classification, and management recommendations.

Table 19.  Dominant wetland type in the MCWD as assessed in the Functional Assessment of Wetlands. 

Circular 39 Type

Area (acres)

Seasonal

1,301.8

Wet Meadow

2,364.9

Shallow Marsh

6,706.4

Deep Marsh

1,250.1

Open Water

2,201.6

Scrub Shrub

1,533.1

Forested

1,124.6

Bog

208.5

Lakes

5,688.8

Not typed

219.9

TOTAL

22,599.7

Note: Based on field assessment.  Excludes those areas determined in the field not to be wetlands, and stormwater ponds clearly excavated out of upland.   Does not include all lake acreage.  Includes some small areas that were not field assessed.

Source: MCWD 2003 Functional Assessment of Wetlands.  See Figure 26.

Table 20.  Wetland management classifications of wetlands in the MCWD as determined in the Functional Assessment of Wetlands.

Classification

Number

Area (acres)

% of total

Preserve

569

7,751.36

48.9%

Manage 1

972

3,058.34

19.3%

Manage 2

1,058

2,901.50

18.3%

Manage 3

683

2,144.12

13.5%

TOTAL

3,282

15,855.32

 

Note:  The FAW excluded large lakes and wetlands less than ¼ acre in size; those areas are included in the NWI, so total will not match Tables 18 or 19.

Source: MCWD 2003 Functional Assessment of Wetlands. See Figure 27.

The assessments included evaluation of functions and values such as vegetative diversity, wildlife and fish habitat, the wetland’s ability to protect downstream resources, opportunity to protect shoreline, and sensitivity to stormwater and urban development.    A number of wetlands, especially in the developing upper watershed, scored highly on vegetative diversity, fish and wildlife habitat, or aesthetics (see Figure 28).   Some of the wetlands were also evaluated for restoration potential.  Factors considered were the ease with which the wetland could be restored, the number of landowners within the historic basin, the size of the potential restoration area, the potential for establishing buffer areas or water quality ponding, and the extent and type of hydrologic alteration.  Restoration potential was characterized as high, moderate, or low, and is illustrated in Figure 29.