Primary production rate
In each section of the Pond 217 and 218, we routinely measured photosynthetic and community respiration rate by measuring changes in O2 concentration rate in light and dark bottles (Wetzel and Likens 2010). Then, net-photosynthetic rate – irradiance curve (P-I curve) was estimated for each section of the both ponds. Using the P-I curve, extinction coefficient and daily changes in photosynthetically available radiation (PAR) in the water column, we estimated specific production rate (\(\mu\): μg O2chl-a -1 d-1). To minimize specificity in light conditions at measured date, we calculated μ using temporal profile of PAR for three days before each sampling date. Then average value for these three days was used in analysis. Details of the method estimating primary production rate were described in supplemental methods.