3.6 Impacts of Future Growth

Water Quantity and Quality

Land use change impacts downstream water quality by increasing the volume of runoff and the concentration and load of nutrients and sediment transported to receiving waters.  Table 10 illustrates how land use change such as the expected conversion of vacant land to other uses could be expected to ultimately impact water quality in the lakes in the subwatershed as well as Halsteds Bay.  The table also illustrates the impact of a regulatory program managing these impacts.

‘Ultimate development’ is defined as the conversion of all agricultural lands and one-half the upland forested area that remains undeveloped in the 2020 local government land use plans.  This conversion may take place by 2030 or require significantly more time; but it is assumed that at some point in the future these conversions will occur.  More detail regarding this modeling can be found in Technical Appendix A.

Table 10 contrasts three loading reduction scenarios.  Scenarios 1 and 2 contrast the required load reductions if there were no regulatory program to the requirements under the existing regulatory program.  The HHPLS assumed that there would be no load increase from future development; the third scenario in Table 10 indicates that even with a stringent regulatory program that strictly prohibits any new phosphorus loading, additional reductions would be necessary to achieve the desired phosphorus concentration goal of 50 Mu-g/L in Halsteds Bay.

Table 10.  Lake modeled 2020 and ultimate development water quality and the total phosphorus loading reduction necessary to achieve in-lake total phosphorus concentration goals.

 Pierson Lake Goal = 27 Mu-g/L

2000

2020

Ultimate Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

43

47

P load decrease needed to achieve 27 Mu-g/L (lbs/year)

 

305

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

39

 

43

P load decrease needed to achieve 27 Mu-g/L (lbs/year)

 

228

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS) 

Predicted in-lake TP (Mu-g/L)

 

38

P load decrease needed to achieve 27 Mu-g/L (lbs/year)

 

151

 

 Wasserman Lake  Goal = 50 Mu-g/L

2000

2020

Ultimate Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

83

86

P load decrease needed to achieve 50 Mu-g/L (lbs/year)

 

598

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

75

 

77

P load decrease needed to achieve 50 Mu-g/L (lbs/year)

 

464

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS) 

Predicted in-lake TP (Mu-g/L)

 

69

P load decrease needed to achieve 50 Mu-g/L (lbs/year)

 

345

 

 Steiger Lake  Goal = 30 Mu-g/L

2000

2020

Ultimate Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

41

44

P load decrease needed to achieve 30 Mu-g/L (lbs/year)

 

126

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

39

 

42

P load decrease needed to achieve 30 Mu-g/L (lbs/year)

 

109

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS) 

Predicted in-lake TP (Mu-g/L)

 

41

P load decrease needed to achieve 30 Mu-g/L (lbs/year)

 

92

 

Zumbra Lake  Goal = 25 Mu-g/L

2000

2020

Ultimate

Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

27

28

P load decrease needed to achieve 25 Mu-g/L (lbs/year)

 

20

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

27

 

27

P load decrease needed to achieve 25 Mu-g/L (lbs/year)

 

17

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS) 

Predicted in-lake TP (Mu-g/L)

 

27

P load decrease needed to achieve 25 Mu-g/L (lbs/year)

 

14

 

Stone Lake  Goal = 36-44 Mu-g/L

2000

2020

Ultimate

Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

50

51

P load decrease needed to achieve 36 Mu-g/L (lbs/year)

 

81

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

44

 

47

P load decrease needed to achieve 36 Mu-g/L (lbs/year)

 

59

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS) 

Predicted in-lake TP (Mu-g/L)

 

43

P load decrease needed to achieve 36 Mu-g/L (lbs/year)

 

37

 

Auburn East Lake  Goal = 50 Mu-g/L

2000

2020

Ultimate

Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

69

69

P load decrease needed to achieve 50 Mu-g/L (lbs/year)

 

386

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

63

 

60

P load decrease needed to achieve 50 Mu-g/L (lbs/year)

 

192

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS) 

Predicted in-lake TP (Mu-g/L)

 

57

P load decrease needed to achieve 50 Mu-g/L (lbs/year)

 

129

 

Auburn West Lake  Goal = 27 Mu-g/L

2000

2020

Ultimate

Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

43

44

P load decrease needed to achieve 27 Mu-g/L (lbs/year)

 

376

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

41

 

38

P load decrease needed to achieve 27 Mu-g/L (lbs/year)

 

244

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS) 

Predicted in-lake TP (Mu-g/L)

 

37

P load decrease needed to achieve 27 Mu-g/L (lbs/year)

 

232

 

Lunsten Lake  Goal = 70 Mu-g/L

2000

2020

Ultimate

Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

80

86

P load decrease needed to achieve 70 Mu-g/L (lbs/year)

 

220

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

80

 

73

P load decrease needed to achieve 70 Mu-g/L (lbs/year)

 

36

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS) 

Predicted in-lake TP (Mu-g/L)

 

70

P load decrease needed to achieve 70 Mu-g/L (lbs/year)

 

-

 

Parley Lake  Goal = 50-60 Mu-g/L

2000

2020

Ultimate

Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

84

90

P load decrease needed to achieve 60 Mu-g/L (lbs/year)

 

800

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

85

 

82

P load decrease needed to achieve 60 Mu-g/L (lbs/year)

 

575

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS) 

Predicted in-lake TP (Mu-g/L)

 

79

P load decrease needed to achieve 60 Mu-g/L (lbs/year)

 

485

 

 Halsteds Bay  Goal = 50 Mu-g/L

2000

2020

Ultimate

Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (Mu-g/L)

 

124

124

P load decrease needed to achieve 50 Mu-g/L (lbs/year)

 

5,795

Scenario 2: Current Regulatory Program

Predicted in-lake TP (Mu-g/L)

122

 

109

P load decrease needed to achieve 50 Mu-g/L (lbs/year)

 

4,370

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development

 (As assumed in HHPLS)

Predicted in-lake TP (Mu-g/L)

 

107

P load decrease needed to achieve 50 Mu-g/L (lbs/year)

 

4,224

Other Impacts

The Six Mile Marsh subwatershed ecosystem faces varying threats from degradation as a result of development pressure, urbanization, and subsequent channelization of stream conveyances that go beyond impacts to water quality and hydrology.   Development can directly or indirectly degrade and fragment habitat, and reduce or eliminate the opportunities for natural stormwater management provided by minimally disturbed grasslands, forests, woodlands, and wetlands.

The establishment of the connectivity between ecosystems will become increasingly difficult as development encroaches on the corridor.  Currently about 10 percent of the subwatershed is urbanized, and about one-third agricultural.  It is expected that about three-fourths the existing agricultural and one-half of the forested lands will be converted to low-density residential development by 2020.  These conversions to large-lot development would likely create a patchwork of remnant woodland, grassland, and wetland.  Many species require significant contiguous areas of habitat in which to hunt or brood.  The fragmentation that would result from development would limit the ecological integrity of the entire area.