5.7 Phosphorus Load Reduction

One of the water quality goals for this subwatershed is the reduction of phosphorus loading into the lakes that exceed their total phosphorus goal or that are subject to a TMDL load reduction requirement.  Reduction of phosphorus loads from the subwatershed to achieve lake water quality goals will require the combined efforts of the regulatory program, operational programs, and capital projects.  The following tables set forth summary plans for how this could be accomplished. 

The tables break down modeled phosphorus loading to each lake by source:  atmospheric deposition, external sources, and internal sources.  Atmospheric deposition is a regional issue and is not dealt with here.  The primary means of addressing external loading are through the regulation of new loads generated by development and the reduction of existing loads from the subwatershed.

In some cases the phosphorus load contributed from the subwatershed is not sufficient to explain the current in-lake phosphorus concentration.  The most likely sources for this discrepancy are internal loading from lake sediments or aquatic vegetation.  Internal load management such as alum treatment to control sediment sources coupled with control of aquatic vegetation often helps to alleviate some internal loading.  Rough fish management may also be required.  A feasibility study would determine the most appropriate internal load reduction options.  

Pierson Lake

Pierson Lake's total phosphorus goal is 27 Mu-g /L.  It has a relatively small lakeshed, so opportunities for structural load reduction are limited.  The water quality varies considerably year to year.  It does not appear to respond as if it had an internal load problem, so there may be an unusual incoming load from some unknown sources or some other phenomenon may explain the variation.   A diagnostic study would be required to identify the source of variation before any strategies could be developed for its reduction (see Table 14).

Table 14.  Phosphorus load reduction plan for Pierson Lake.

(In-lake nutrient concentration goal = 27 Mu-g/L TP).

Source 

Reduction 

Ultimate Phosphorus Load [lb/yr]  

Planned Reductions [lb/yr]  

Final Loading [lb/yr]  

  

Atmospheric

Atmospheric deposition

NA

56

NA

56

 

External Loads

External load determined from modeling land use

 

271

 

 

  

 

LGU load reduction allocation (Table 13)

 

19

 

 

 

Existing regulation

 

77

 

 

 

Additional regulation

 

39

 

 

 

 

 

 

 

 

Total After Reductions

 

 

 

136

 

Internal / "Unknown" Loads

Internal/"unknown"

loads determined from  modeling land use

 

171

 

 

  

 

 Internal load management

 

120

 

Diagnostic study required to identify achievable reduction

 Total After Reductions

 

 

 

51

 

Total Load

 TOTAL 

 

498

 

245

  

 LOAD GOAL  

 

 

 

193

 

 DIFFERENCE 

 

 

 

50

 Adaptive

 management

Wasserman Lake

A TMDL study including a phosphorus reduction plan is currently being developed for Wasserman Lake.  Proposed reductions from the TMDL include: implementation of agricultural BMPs; utilization of a wetland between Marsh Lake and Wasserman Lake to treat flow from Pierson Lake; stream stabilization of an erosion area noted in the Upper Watershed Stream Assessment; reductions due to the new prohibition on the use of fertilizer with phosphorus; application of Low Impact Development techniques to future development in the city of Victoria; and an evaluation and implementation of internal load management.   Table 15 below sets forth a summary plan for how this could be accomplished in accordance with the TMDL.  The TMDL calculates reductions from the current conditions rather than future conditions. 

Table 15.  Phosphorus load reduction plan for Wasserman Lake.

(In-lake nutrient concentration goal = 40 Mu-g/L TP).

Source 

Reduction 

Current Phosphorus Load [lb/yr]  

Planned Reductions [lb/yr]  

Final Loading [lb/yr]  

  

Atmospheric

Atmospheric deposition

NA

42

NA

42

 

External Loads

External load determined from modeling land use

 

553

 

 

  

Reductions 

proposed in the

draft TMDL

Local agricultural BMPs

 

60

 

 

Marsh/Wasserman wetland restoration

 

37

 

 

Marsh/Wasserman stream stabilization

 

62

 

 

Phosphorus free fertilizer

 

26

 

 

Application of LID in Victoria development

 

198

 

 

 

Regulations

 

 

 

 

 

No increase in load 

 

 

 

 

 Total After Reductions

 

 

 

170

 

Internal / "Unknown" Loads

Internal/"unknown"

loads determined from modeling land use

 

549

 

 

  

 

 Internal load management

 

375

 

Est 70% reduction of internal loading

 Total After Reductions

 

 

 

174

 

Total Load

 TOTAL 

 

1,144

 

386

  

 LOAD GOAL  

 

 

 

395

 

 DIFFERENCE 

 

 

 

(-9)

 

Steiger Lake

Steiger Lake is located in the Carver Park Reserve.  It has a small lakeshed, so opportunities for structural external load reduction are limited.  Downtown Victoria redevelopment may provide opportunity-driven reductions to accomplish the LGU load reduction allocation.  A wet detention pond could be constructed to treat runoff from subwatersheds SMC 12 and 13 (see Figure 20).  After implementation of those reductions opportunities for additional reductions to meet the goal would be assessed as well as the long-term appropriateness of the goal (see Table 16).

Table 16.  Phosphorus load reduction plan for Steiger Lake.

(In-lake nutrient concentration goal = 30 Mu-g/L TP).

Source 

Reduction 

Ultimate Phosphorus Load [lb/yr]  

Planned Reductions [lb/yr]  

Final Loading
[lb/yr]
 

  

Atmospheric

Atmospheric deposition

NA

38

NA

38

 

External Loads

External load determined from modeling land use

 

230

 

 

  

 

LGU load reduction allocation (Table 13)

 

28

 

 

 

Pond at SMC-12/13

 

67

 

 

 

Existing regulation

 

17

 

 

 

Additional regulation

 

9

 

 

 Total After Reductions

 

 

 

109

 

Internal / "Unknown" Loads

Internal/"unknown"

loads determined from modeling land use

 

0

 

 

  

 

 Internal load management

 

0

 

 

 Total After Reductions

 

 

 

0

 

Total Load

 TOTAL 

 

268

 

147

  

 LOAD GOAL  

 

 

 

142

 

 DIFFERENCE 

 

 

 

5

 

Zumbra Lake

Lake Zumbra has a small lakeshed, so opportunities for structural external load reduction are limited.  Some small load reductions have been identified, such as application of residential BMPs.  Aquatic vegetation management may assist in reducing the small internal load (see Table 17). 

Table 17.  Phosphorus load reduction plan for Zumbra Lake.

(In-lake nutrient concentration goal = 25 Mu-g/L TP).

Source 

Reduction 

Ultimate Phosphorus Load [lb/yr]  

Planned Reductions [lb/yr]  

Final Loading
[lb/yr]
 

  

Atmospheric

 Atmospheric

 deposition

NA

39

NA

39

 

External Loads

 External load determined from modeling land use

 

72

 

 

  

 

 LGU load reduction allocation (Table 13)

 

8

 

 

 

 Existing regulation

 

3

 

 

 Total After

 Reductions

 

 

 

61

 

Internal / "Unknown" Loads

Internal/ "unknown"

loads determined from modeling land use

 

10

 

 

  

 

 Internal load management

 

0

 

 

 Total After

 Reductions

 

 

 

10

 

Total Load

 TOTAL 

 

121

 

110

  

 LOAD GOAL  

 

 

 

100

 

 DIFFERENCE 

 

 

 

10

 Adaptive

 management

Stone Lake

Stone Lake is located in the Carver Park Reserve.  Phosphorus load from watershed washoff cannot explain phosphorus concentrations in Stone Lake.  The large, unknown load to Stone Lake may be from an internal source, or the wetlands adjacent to the lake may be exporting phosphorus to the lake.  A diagnostic study would be required to identify the source of this unknown load and to develop strategies to reduce it.    An internal load reduction project followed by curly-leaf pondweed treatment (see Table 18) is proposed to help achieve water quality goals.

Table 18.  Phosphorus load reduction plan for Stone Lake.

(In-lake nutrient concentration goal = 36 Mu-g/L TP).

Source 

Reduction 

Ultimate Phosphorus Load [lb/yr]  

Planned Reductions [lb/yr]  

Final Loading
[lb/yr]
 

  

Atmospheric

Atmospheric deposition

NA

25

NA

25

 

External Loads

External load determined from modeling land use

 

70

 

 

  

 

 LGU load reduction allocation (Table 13)

 

2

 

 

 

 Existing regulation

 

22

 

 

 Total After Reductions

 

 

 

46

 

Internal / "Unknown" Loads

Internal/ "unknown"

loads determined from  modeling land use

 

92

 

 

  

 

 Internal load management

 

65

 

Est 70% reduction of internal loading

 Total After Reductions

 

 

 

27

 

Total Load

 TOTAL 

 

187

 

98

  

 LOAD GOAL  

 

 

 

105

 

 DIFFERENCE 

 

 

 

(-7)

 

Auburn East

Auburn Lake East received City of Victoria wastewater treatment plan effluent until 1973.  There is a large, unaccounted for phosphorus load source that may be a remnant of those old discharges or due to some other source or sources.  A diagnostic study would be required to determine the source and evaluate options for improvement.  Auburn East's in-lake phosphorus goal is 50 Mu-g/L.  However, because it discharges directly to Auburn West and that discharged volume conveys a significant phosphorus load to Auburn West, Auburn West cannot attain its water quality goal unless Auburn East attains better water quality than its goal.  Water quality modeling shows that the in-lake phosphorus concentration in Auburn East would have to be reduced to about 44 Mu-g /L for Auburn west to attain its goal.  The load reduction plan in Table 19 assumes that 44 Mu-g /L goal and also assumes that upstream lakes that contribute to Auburn East – Wasserman, Steiger, Stone, and Zumbra – meet their water quality goals.   An internal load reduction project followed by curly-leaf pondweed treatment is proposed.

Table 19.  Phosphorus load reduction plan for Lake Auburn East.

(In-lake nutrient concentration goal = 44 Mu-g/L TP).

Source 

Reduction 

Ultimate Phosphorus Load [lb/yr]  

Planned Reductions [lb/yr]  

Final Loading
[lb/yr]
 

  

Atmospheric

Atmospheric deposition

NA

29

NA

29

 

External Loads

External load determined from modeling land use

 

646

 

 

  

 

LGU load reduction allocation (Table 13)

 

34

 

 

 

Reduction due to upstream lakes at goal

 

131

 

 

 

Existing regulations

 

63

 

 

 

 

 

 

 

 

 Total After Reductions

 

 

 

418

 

Internal / "Unknown" Loads

Internal/ "unknown"

loads determined from  modeling land use

 

406

 

 

  

 

 Internal load management

 

284

 

Est 70% reduction of internal loading

 Total After Reductions

 

 

 

122

 

Total Load

 TOTAL 

 

1,081

 

569

  

 LOAD GOAL  

 

 

 

580

 

 DIFFERENCE 

 

 

 

(-11)

 

Auburn West

Lake Auburn West is located downstream of Lake Auburn East and other lakes upstream of that lake.  Their water quality influences its water quality.  The lakes upstream of Auburn West have higher total phosphorus goals than Auburn West's stringent 27 ug/L.  To achieve that goal, the upstream lakes must also attain their goals.  Alternatively, the goal for Auburn West could be revised to reflect its location in the series of lakes.  An internal load reduction project followed by curly-leaf pondweed treatment is proposed, and should be completed at the same time improvements are made to Auburn East (see Table 20).

Table 20.  Phosphorus load reduction plan for Lake Auburn West.

(In-lake nutrient concentration goal = 27 Mu-g/L TP).

Source 

Reduction 

Ultimate Phosphorus Load [lb/yr]  

Planned Reductions [lb/yr]  

Final Loading
[lb/yr]
 

  

Atmospheric

Atmospheric deposition

NA

34

NA

34

 

External Loads

External load determined from modeling land use

 

477

 

 

  

 

LGU load reduction allocation (Table 13)

 

3

 

 

 

Reduction due to upstream lakes at goal

 

157

 

 

 

Existing regulations

 

12

 

 

Total After Reductions

 

 

 

305

 

Internal / "Unknown" Loads

Internal/ "unknown"

loads determined from modeling land use

 

267

 

 

  

 

Internal load management

 

187

 

Est 70% reduction of internal loading

 Total After Reductions

 

 

 

80

 

Total Load

 TOTAL 

 

778

 

419

  

 LOAD GOAL  

 

 

 

401

 

 DIFFERENCE 

 

 

 

18

 

Lunsten Lake

Lunsten Lake is a very shallow lake that responds more as a wetland.  It has a very high modeled internal load, which is not unexpected for a lake of this type.  The load reduction plan below assumes that lakes upstream of Lunsten will meet their phosphorus goals, and that application of regulation to development in the subwatershed will provide the necessary load reduction to meet Lunsten's goal of 70 ug/L (see Table 21).

Table 21.  Phosphorus load reduction plan for Lunsten Lake.

(In-lake nutrient concentration goal = 70 Mu-g/L TP).

Source 

Reduction 

Ultimate Phosphorus Load [lb/yr]  

Planned Reductions [lb/yr]  

Final Loading
[lb/yr]
 

  

Atmospheric

Atmospheric Deposition

NA

26

NA

26

 

External Loads

External Load Determined from Modeling Land Use

 

581

 

 

  

 

LGU load reduction allocation (Table 13)

 

23

 

 

 

Reduction due to upstream lakes at goal

 

110

 

 

 

Existing regulations

 

110

 

 

Total After Reductions

 

 

 

338

 

Internal / "Unknown" Loads

Internal/ "unknown"

loads determined from modeling land use

 

408

 

 

  

 

Internal load management

 

0

 

 

 Total After Reductions

 

 

 

408

 

Total Load

 TOTAL 

 

1,015

 

772

  

 LOAD GOAL  

 

 

 

794

 

 DIFFERENCE 

 

 

 

(-22)

 

Parley Lake

A TMDL study including a phosphorus reduction plan is currently being developed for Parley Lake.  Proposed reductions from the TMDL include: implementation of agricultural BMPs; corridor and wetland restoration between Turbid Lake and Lunsten Lake; stream corridor and wetland restoration on tributaries to Parley Lake; stormwater management improvements at the Crown College campus; achievement of upstream water quality goals; application of more stringent regulations prohibiting new net phosphorus loading from development; a prohibition on outletting currently landlocked areas; and a diagnostic of sources of internal loading and implementation of internal load management.   Table 22 below sets forth a summary plan for how this could be accomplished in accordance with the TMDL.  The TMDL calculates reductions from the current conditions rather than future conditions. 

Table 22.  Phosphorus load reduction plan for Parley Lake.

(In-lake nutrient concentration goal = 60 Mu-g/L TP).

Source 

Reduction 

Ultimate Phosphorus Load [lb/yr]  

Planned Reductions [lb/yr]  

Final Loading
[lb/yr]
 

  

Atmospheric

Atmospheric eposition

NA

64

NA

64

 

External Loads

External load determined from modeling land use

 

1,168

 

 

  

Reductions 

proposed in the

draft TMDL

Local agricultural BMPs

 

77

 

 

Turbid-Lunsten corridor restoration

 

146

 

 

Parley tributary wetland restoration

 

95

 

 

Local Crown College runoff improvements

 

22

 

 

Reduction due to upstream lakes at goal

 

53

 

 

 

 Regulations

 

 

 

 

 

   No net increase in P 

 

 

 

 

 Total After Reductions

 

 

 

775

 

Internal / "Unknown" Loads

Internal/ "unknown"

loads determined from modeling land use

 

1,971

 

 

  

 

 Internal load management

 

1,129

 

 

 Total After Reductions

 

 

 

842

 

Total Load

 TOTAL 

 

3,203

 

1,681

  

 LOAD GOAL  

 

 

 

1,684

 

 DIFFERENCE 

 

 

 

(-3)