Keeping it Blue, Reducing Phosphorus, May 2019.

By: Ted Peters, Director Geneva Lake Environmental Agency

Photo: Bill Lang

Phosphorus

• Extensive in nature but not in high concentrations

• Little bit can cause big problems

• Phosphate PO4-3

• Essential element for life, backbone of DNA, ATP - cell energy

• Macro-nutrient for plants - roots and flowers

-Found in the mineral Apatite -inorganic

-Erodes into small particles that are washed into surface waters or made into fertilizer

inorganic

-Assimilated by plants

organic

-Consumed by animals

organic

-

Animal waste

Organic

Decomposition of waste

inorganic

-Plants and animal die

Organic

-Decomposition of organic matter

inorganic

Forms of Phosphorus

• Found and reported in many different forms –phosphorus cycle.

• Organic- incorporated into plant tissue

• Inorganic – ionic, PO4

• Total phosphorus

• Organic and inorganic

• Dissolved, suspended

Different forms found at different times and locations within lakes.

Total Phosphorus: Season vs. DepthGeneva Lake

0

0.02

0.04

0.06

0.08

0.1

0.12

mg

/l

month

Total Phosphorus Values at different depths in Geneva Lake, WI at Selected dates, 2017.

bottom

surface

% inorganic

0

0

79.8

19.3

76.3

35.2

0.0477

0.0122

Depth

0.5

0.5

43

0.5

43

0.5

Total

Nov.

Inorganic

0

0

0.0379

0.0022

0.0364

0.0043

Inorganic Pphosphorus vs. Total Phosphorus at Selected Times and Depths

Geneva Lake Walworth CO. WI Source: USGS and GLEA

Date 2018

April

August

Sept.

0.125

0.00835

0.0475

0.0114

Phosphorus in Lakes• Relationship of phosphorus to fertility is well documented.

• Major concern – eutrophication – aging

• Organic – incorporated in biomass, algae, vascular plants, other organisms.

• Inorganic, ionic PO4, the form most used by plants.

• Doesn’t take much to cause a problem

• ug/l ,

• Limiting nutrient

• Managing phosphorus in lakes is vital to healthy lakes

• Keeping it out of the lake is the best management approach.

Zebra Mussels and Phosphorus• Mussels filter out a lot of organic

phosphorus (algae).

• They don’t assimilate it all, discharge it in their nutrient rich pseudo-feces.

• This becomes available to the bottom dwelling algae.

• Shift in total biomass from open water plankton algae to lake bottom filamentous algae.

• Trophic State Index relationship doesn’t fit as tight. Relationship between phosphorus levels, water clarity and chlorophyll “a”. -

Internal Phosphorus Loading• Phosphorus attached to bottom sediments is released into the

water

• Driven by low or no oxygen conditions - late summer stratification.

• Causes increase in deep water total phosphorus values.

• Does not effect TP values in the upper waters during stratification.

• Fall mixing makes phosphorus available throughout the water column,

• On Geneva Lake we don’t see a significant increase in TP at turnover.

Total Phosphorus Values at 43 m, Summer of 2017, Geneva Lake WI.

Source: USGS, GLEA

0

0.02

0.04

0.06

0.08

0.1

0.12

mg

/l

month

Evaluating Phosphorus Levels

• Standards established in Wisconsin Administrative Code NR 102.06

• Based upon lake types - NR 102.06 (2)(i)

• Geneva Lake is considered a stratified two-story fishery lake within the Fish and Aquatic Life use category.

NR 102.06(4)(b)1

• Geneva Lake: 15 ug/l

• Geneva Lake presently meets that standard.

Geneva Lake Phosphorus ValuesRelative to Its Phosphorus Standard

Figure 3. Total phosphorus, and recommended total phosphorus standard for Geneva Lake, WI. Source: Dale Robertson, U.S. Geological Survey, Personal Communication Jan. 23, 2018.

The average spring phosphorus value over the last 23 years has been 12 ug/l with a max of 40 ug/l in 2013 and a minimum of 6 ug/l in 1999 and 2012.

Trophic State Index - TSI• Based Upon the relationship

between:

• Nutrients - Total phosphorus concentration

• Productivity – chlorophyll “a”

• Water clarity – secchi reading

Major Sources of Phosphorusto Geneva Lake

• No significant point sources.

• Several models have been used to ID phosphorus loading to Geneva Lake.

• Generally based upon watershed land use.

• All have indicated that major source of phosphorus is primarily from the watershed.

Sources of Phosphorus to Geneva Lake WI.

84%

7%

2%7%

Total Phosphorus Loading to Geneva Lake WI, for the Combined

1998 and 1999 years.Source: USGS

tributaries

atmosphere

groundwater

waterfowl

Sources of Phosphorus to Geneva Lake WI.

Watershed Sources of Phosphorusto Geneva Lake.

Sub-Watershed Loading to Geneva Lake

Sub-watershed

discharge

CFS(1) TP ug/l area (ac) lb/d(2)

dischage

CFS(1) TP ug/l area (ac) lb/d(2)

discharge

CFS(1) TP ug/l area (ac) lb/d(2)

Buttons Bay 0.32 68 1255.8 0.12 0.78 1440 1255.8 5.99 12.01 75 1255.8 0.49

Birches 0.46 42 1325.0 0.11 0.56 43 1325.0 0.13 3.88 122 1325.0 2.60

Southwick 9.53 26 557.7 0.14 13.42 46 557.7 0.34 19.07 110 557.7 1.14

Trinke 0.32 52 449.2 0.09 5.65 150 449.2 0.46 13.06 106 449.2 0.75(1) Cubic feet per second (2) pounds per day.

11/8/97 Base flow 7/19/00 Base flow 5/13/98 High flow

Table. Phosphorus loading to Geneva Lake from selected tributaries.(Robertson et al. 2002.)

Management of Phosphorus

• Best Management Practice for phosphorus and lakes is to keep it out of lakes.

• Our modeling and studies tell its coming from the watershed.

• Agricultural and high density urban land use are significant sources.

• Generally speaking it about the soil,

and keeping it in place on the land.

Recommended Management PracticesSEWRPC

• Land use is going to change – increase residential, decrease in agricultural, loss of open and wooded areas.

• Reduction of rural and urban nonpoint sources.

• Reduce soil loss and pollution through sound conservation and nutrient management plans.

• Good urban house keeping of yards, streets, and impervious areas.

• Encourage infiltration of runoff.

• Strong construction site erosion control and storm water management.

Can’t get loss in enjoying the pleasure of the lake, need to keep aware of what is

happening to the lake.