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Algal temperature rates - blooms in winter

Fri, 10/16/2009 - 7:14am — Karoline
I am trying to simulate blue green algae blooms in a shallow lake. Measurements have shown highest concentrations in september and june, when water temperatures are around 25°C. My simulation showed algae peaks in winter (december to february). Consequently I played with algal temperature rates at put them to: AT1: 20 AT2: 24.5 AT3: 27.5 AT4: 28 AK1: 0.001 AK2: 0.99 AK3: 0.99 AK4: 0.1 So, algal growth should be impossible below 20°C, right? But nonetheless I am getting algae peaks from december to february, when water temperatures are below 15°C, which I do not understand. Can anyone give me an explanation?
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Water Quality
Fri, 10/16/2009 - 5:02pm — chris

Hi Karoline, Algae growth should be very low in winter with the temperature rates you have. What's the maximum algae growth rate? Also, do you have any algae flowing into the lake during winter from tributaries or branch inflows? If so, what are the concentrations? chris
Mon, 10/19/2009 - 12:56am — Karoline

Hi Chris, thanks for helping! The maximum algae growth rate (AG) is 0.08. I do not have any algae in the tributaries/branches. That means algae is switched -ON- in "active constituents in tributary inflow files" but concentrations are 0. Karoline
Mon, 10/19/2009 - 12:36pm — chris

Hi Karoline, A maximum growth rate of 0.08 days is very low. I suggest running the preprocessor and looking at the pre.opt file to make sure that the model is reading the correct column for algae concentration in the tributaries and branch inflows. The pre.opt provides a summary (average, max, min) of concentrations in the constituent files. chris