2.5.4 Wetlands

Approximately 48 percent of the land area within the Six Mile Marsh subwatershed is shown on the National Wetland Inventory as wetland (see Table 7). 

Table 7.  National Wetlands Inventory wetlands in the Six Mile Marsh subwatershed.

Circular 39 Type

Area (acres)

Cowardin Class

Area (acres)

Seasonal

136.8

Emergent

2,591.7

Wet Meadow

2,448.1

Forested

116.8

Shallow Marsh

51.8

Scrub Shrub

246.0

Deep Marsh

1,992.9

Unconsolidated Bottom

2,053.6

Open Water

246.0

 

 

Scrub Shrub

115.7

 

 

Forested

16.8

 

 

TOTAL

5,008.1

 

5,008.1

Source: Minnesota DNR. 

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 7 above, which shows wetland acreage and type from the National Wetlands Inventory completed in the 1980s, Table 8 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 12 and Table 9).  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 8.  Dominant wetland type in the Six Mile Marsh subwatershed as assessed in the Functional Assessment of Wetlands. 

Circular 39 Type

Area (acres)

Seasonal

401.2

Wet Meadow

592.8

Shallow Marsh

1,784.4

Deep Marsh

268.6

Open Water

748.0

Scrub Shrub

105.4

Forested

278.4

Bogs

202.1

Lakes

1,687.2

Not typed

30.7

TOTAL

6,098.8

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

Source: MCWD 2003 Functional Assessment of Wetlands.  See Figure 11.

Table 9.  Wetland management classifications of wetlands in the Six Mile Marsh subwatershed as determined in the Functional Assessment of Wetlands.

Classification

Number

Area (acres)

% of total

Preserve

92

332.0

7.4

Manage 1

411

1,175.0

26.3

Manage 2

224

494.2

11.1

Manage 3

148

2,466.6

55.2

TOTAL

875

4,467.8

 

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 7 or 8.

Source: MCWD 2003 Functional Assessment of Wetlands.  See Figure 12.

The Six Mile Marsh subwatershed has a large number of wetlands of various sizes distributed across the landscape, including several very large wetlands.  Many scored highly on vegetative diversity, fish and wildlife habitat, or aesthetics (see Figure 13).   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.  Several wetlands of moderate or high restoration potential are located throughout the subwatershed, including wetlands through which Six Mile Creek flows (see Figure 14).

A large amount of restorable wetland exists within the Six Mile Marsh Subwatershed.  MCWD will consider restoring wetlands as a primary approach to reducing nutrient loading, reducing runoff volumes, restoring ecology and achieving other District Goals within this subwatershed.