2.3.2 Biologic Integrity

Landscape

Development in this subwatershed has left few large areas of undisturbed or minimally disturbed forest and wetland in the subwatershed.   Three areas, including the Grays Bay outlet wetland complex; Diamond Lake; and part of the creek corridor in the Mississippi River gorge have been designated Regionally Significant Ecological Areas by the DNR (see Figure 6).   The Minnesota County Biological Survey (MCBS) did not identify any areas of biodiversity significance in the subwatershed.   The creek corridor and the Chain of Lakes in the lower subwatershed are part of a DNR-designated Metro Conservation Corridor. 

The Minnesota Natural Heritage Information System lists several rare species in this subwatershed, as shown in Table 1.

Table 1.  Rare species in the Minnehaha Creek subwatershed.

Species

Status

Acadian flycatcher

State concern

Biennial gaura

Being evaluated

Blanding’s turtle

State threatened

Lake sturgeon

State concern

Prairie vole

State concern

Pugnose shiner

State concern

Rock clubmoss

State threatened

Valerian

State threatened

Source:  Minnesota DNR.

Lakes

The MPRB has prepared vegetation surveys for some of the Chain of Lakes, and has conducted phytoplankton and zooplankton surveys of those lakes.  A vegetation survey compiled by the MPRB for Diamond Lake in 2004 indicated the presence of curly leaf pond weed on that lake.  Most of the city lakes have been colonized by Eurasian watermilfoil.

The MPRB periodically harvests milfoil on Harriet, Calhoun, Lake of the Isles, Cedar, and Nokomis to support swimming and boating.  Such harvesting was completed in 2004 on Harriet, Calhoun, Isles, and Cedar.   In addition, the MPRB is working together with the University of Minnesota to explore the use of a native weevil to naturally control nuisance milfoil growth. Lakes treated include Calhoun, Hiawatha, Harriet, and Isles.

Fishery.  Because of their status as regional resources, the Minnesota DNR conducts regular fish surveys of the Chain of Lakes.  Other lakes are surveyed less frequently.  Powderhorn Lake is managed by the DNR as part of its Fishing in the Neighborhood program and is stocked regularly with black crappie and bluegill and most recently with channel catfish.

Table 2.  DNR fish survey data.

Lake 

Survey Year

Fishery – fish stocked

Dominant Fish

Brownie

1993

Pan

Bluegill, black crappie

Cedar

2003

Sport

Bluegill, black crappie, northern pike, yellow perch, pumpkinseed sunfish, largemouth bass, muskellunge, walleye

Isles

2003

Sport – muskellunge

Bluegill, black crappie, largemouth bass, northern pike, yellow perch

Calhoun

2003

Sport – walleye and muskellunge

Bluegill, black crappie, northern pike, yellow perch, pumpkinseed sunfish

Harriet

2003

Sport – walleye and muskellunge

Bluegill, black crappie, yellow perch, pumpkinseed sunfish

Nokomis

2001

Sport – walleye and muskellunge

Yellow perch, black crappie, bluegill

Hiawatha

2001

Pan

Black bullhead, black crappie, bluegill, yellow perch

Diamond

1993

 

Black bullhead, carp, bluegill, green sunfish

Powderhorn

2003

Pan – black crappie and bluegill

Black crappie, bluegill, black bullhead

Source:  Minnesota DNR.

Streams

Minnehaha Creek has been listed on the State of Minnesota’s 303(d) list of Impaired Waters for its impaired biotic community.  A fish survey was conducted at nine locations on Minnehaha Creek in 2003.  Most of the fish species between I-494 and Minnehaha Falls were lake species with few adults, indicating a lack of suitable habitat for riverine species.  Lack of adults indicates that there is little refuge for overwintering and low flow periods.  Below the falls the creek is connected to the Mississippi River and there is better habitat for riverine species.

Macroinvertebrate sampling on Minnehaha Creek was conducted as a part of the 2004 MCWD Minnehaha Creek Stream Assessment.  Twenty-six sites were sampled; only about half yielded more than the 100 organisms typically needed to assure a statistically valid score.  An F-IBI score – an Index of Biotic Integrity identified to the organism’s family level – was calculated for thirteen reaches.  Macroinvertebrate family diversity was very low, primarily due to habitat limitations and the influence of the various impoundments and wetlands through which the creek flows.

Aquatic habitat in Minnehaha Creek is generally poor.  Stream substrates are homogenous and dominated by small gravels and sand, and gravel or cobble riffles are infrequent and widely spaced.  Large woody debris is virtually absent, limiting direct use by macroinvertebrates and fish and reducing the number of accumulation points for leaf and other debris.  Stream flows from Grays Bay dam discharge range from sustained high volumes and velocities to minimal or intermittent flows, creating undesirable conditions. 

The low diversity of macroinvertebrates reflects the lack of diversity in habitat.  Lack of riparian vegetation, erosion, sediment deposition, removal of large woody debris, sustained high flows, extreme flood peaks, lowered base flows, and to a lesser extent water quality combine to limit species diversity.  See Section 2.5.2 below for additional discussion.

Wetlands

A high density of wetlands are present in the subwatershed.  A number of wetlands were identified in the 2003 MCWD Functional Assessment of Wetlands (FAW) as having exceptional to high aesthetic values (see Figure 13).  Wetlands riparian to and in-line with Minnehaha Creek as well as several wetlands adjacent to lakes were noted as having high fish habitat potential.  Only a few of the larger wetlands were assessed as having high wildlife habitat potential, primarily because wetland size is an important factor.  Only a scattering of wetlands were identified as having exceptional to high vegetative diversity, unsurprising given the urbanized nature of the subwatershed and the likelihood of wetland disturbance and hydrologic impacts.