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 Long Lake.  The table also illustrates the impact of a regulatory program managing these impacts.

‘Ultimate Development’ in Table 10 is defined as the conversion of all agricultural lands and one-half of 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 nutrient 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 interim phosphorus concentration goals for Long and Tanager Lakes.

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

Long Lake Interim TP Goal = 50 μg/L

2000

2020

Ultimate Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (μg/L)

 

71

71

P load decrease needed to achieve 50 μg/L (lbs/year)

 

633

Scenario 2: Current Regulatory Program

64

 

Predicted in-lake TP (μg/L)

 

65

P load decrease needed to achieve 50 μg/L (lbs/year)

 

445

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

 (As assumed in HHPLS) 

Predicted in-lake TP (μg/L)

 

64

Additional P load decrease needed to achieve 50 μg/L (lbs/year)

 

388

         

Tanager Lake  Interim TP Goal = 70 μg/L

2000

2020

Ultimate Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (μg/L)

 

117

117

P load decrease needed to achieve 70 μg/L (lbs/year)

 

868

Scenario 2: Current Regulatory Program

Predicted in-lake TP (μg/L)

115

 

110

P load decrease needed to achieve 70 μg/L (lbs/year)

 

725

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

 (As assumed in HHPLS) 

Predicted in-lake TP (μg/L)

 

109

Additional P load decrease needed to achieve 70 μg/L (lbs/year)

 

712

Other Impacts

The Long Lake Creek subwatershed corridor and key conservation areas (see Figure 19) face varying threats from degradation as a result of development pressure, rapid 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 if development encroaches on the corridor.  Currently about one-third of the subwatershed is urbanized.  It is expected that about half the existing agricultural and 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.