Rain, Rain –
How Long Till the Effects Go Away?
Total phosphorus in Lake Woodrail ranged between 15 and 20 ug/L during the middle of May. Phosphorus concentrations increased dramatically during May 25 th and 26 th, with values going from 18 to 41 ug/L (Figure 1). This substantial increase in phosphorus was a result of 3.2 inches of rain during May 23-25 (Figure 1). Runoff from the suburban watershed supplied phosphorus to the lake. Nitrogen and non-volatile suspended solids (soil materials) also increased. While suspended solids values dropped back down to a normal level quickly (Figure 1), phosphorus and nitrogen levels remained elevated. It took over a week for nitrogen to return to pre-rain levels, while phosphorus was elevated for 2 full weeks. These data show how watershed runoff can have an impact on in-lake nutrient and suspended solids concentrations, and how that impact varies for different parameters.


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