Phosphorus in the Great Lakes: The Rules Have Changed Harvey Bootsma

Great Lakes Water Quality Agreement Total Phosphorus Target Concentrations: Lake Superior = 5 mg / L Lake Michigan = 7 mg / L Lake Huron = 5 mg / L Lake Erie = 10 / 15 mg / L Lake Ontario = 10 mg / L Targets set as part of GLWQA. Why phosphorus? It’s the “limiting nutrient”.

P loading trends in the Great Lakes To meet concentration targets, loading targets were set. Before setting these, scientists and managers had to understand how P behaved in the lakes, so they could predict how changes in P load would affect P concentration. As you can see, loading targets for most lakes have been met. But occasional exceptions in Erie and Ontario. Dolan and Chapra, 2012

Lake Erie Algal Bloom NOAA / NASA We had algal problems in the 60’s and 70’s, and then thought we had solved the problem. But in the past 10 years, the monster of eutrophication has raised its ugly head again. The question is: why? NOAA / NASA

Phosphorus Concentrations in Lake Erie TP concentrations in Erie have generally increased over the past two decades. It’s now above the 10 ug/L target. EPA, Great Lakes National Program Office

More P is in dissolved reactive form All phosphorus is not the same. In addition to increased P loading, the forms of P have changed. Now more of the P is the type that algae can use. P. Richards, Heidelberg College

Hypoxia in Lake Erie Lakes need P and they need algae to support the food web. But you can have too much of a good thing. Excess algae sinks to bottom, decomposes, and uses of oxygen. The result is loss of important food web components. Stuart Ludsin, The Ohio State University Tom Johengen, U. of Michigan CILER

Factors favoring toxin-forming cyanobacteria (blue-green algae) 1. High dissolved phosphorus concentrations. 2. Warm temperatures. 3. Calm conditions. 4. Selective grazing by zebra mussels and quagga mussels. The other major impact: toxic algae. Increased P loading and invasive mussels have combined to create a perfect storm for nuisance and harmful algae. 5. Alteration of nitrogen : phosphorus ratio by mussels.

Soil P Storage Change (kg ha-1) P in Wisconsin Cropland Average [P] (ppm) 2000- 04 Soil P Storage Change (kg ha-1) One of the causes: increased P in agricultural soils. Higher than needed by most crops. Bundy and Sturgul (2001)

P in New York Cropland Ketterings et al. (2005) Likewise in New York state. Ketterings et al. (2005)

Figure provided by Potash and Phosphate Institute In Ontario farmland, P inputs were previously much higher than removals. More recently, a balance between inputs and removal is being approached. Figure provided by Potash and Phosphate Institute

Long-term Influence of Soil P on Lake P Soil P inputs reduced after year 250 Soil [P] Sediment [P] P Inputs to Soil (g m-2 y-1) Phosphorus Density (g m-2) We are here Water [P] at current input Carpenter’s soil – lake P model. Soils have a huge store of P, with a very slow turnover time. Even if P inputs to soil are decreased, soil and lakes will respond very slowly. Water [P] Net P Input to soil Year Source: S.R. Carpenter, 2005, Proc Nat. Acad. Sci. 102:10002-10005.

Milwaukee River Transect, April 2005 So how do we manage the “phosphorus shunt”? Our only option remains to control P loading to the lake. Need to know where the P is coming from. We know agriculture is important, but urban sources, such as runoff and storm sewers are probably also important. SRP (mg L-1)

Mean Depth (m) Vollenweider (1968 Horne & Goldman (1983) Phosphorus Loading (g P m-2 year-1) The problem is more challenging for shallow lakes than for deep lakes. Mean Depth (m) Vollenweider (1968 Horne & Goldman (1983)

Annual P Load Total P in Lake (metric tons) (metric tons) Huron 3,000 8,843 Michigan 3,000 14,760 The lakes contain more P than what is loaded annually. So algae can really be influenced by how P is processed within a lake.

Tom Nalepa, NOAA GLERL

Nearshore Phosphorus loads, May – July 2006 10 km Milwaukee region Nearshore Phosphorus loads, May – July 2006 Cladophora zone River load: 120 mg P m-2 Milwaukee R. Menomonee R. Mussel Excretion: 506 mg P m-2 Kinnickinnic R. Mussels have removed P from the water, and made it more concentrated on the lake bottom. If you are an alga that grows on the lake bottom, this makes you happy. 10 km

And here is the algae that grows on the lake bottom And here is the algae that grows on the lake bottom. Impacts tourism, power plants, human health, and food web.

Big change in summer chlorophyll If you’re an alga living in the water column, this is bad.

Pelagic prey fish: lakewide fall survey (9-110 m) And if you’re a fish that feeds on this plankton, it’s also bad. USGS-GLSC bottom trawl survey

Management Challenge: The Phosphorus Conundrum Will a reduction in P loading fix the Cladophora problem? Will a reduction in P loading exacerbate the problem of low plankton production offshore? The rules of the game have changed. We need to determine the P loading “sweet spot” for each lake. Linking agricultural and water quality management. Some important questions.

Green Streets Stormwater Retention Plan

Syracuse, NY

Porous pavement

MMSD 2020 Water Quality Initiative MMSD Greenseams Program

Lake Whitefish Condition Madenjian et al. 2002

Baumann and Walling (2013)

Baumann and Walling (2013)

UK water company Thames Water is now extracting phosphate from sewage waste

Graph showing world phosphate rock production, 1900–2012, reported by US Geological Survey

18 %

Laundry Detergent

Changing agricultural practices

Improved sewage treatment