Samplings
Sampling was performed biweekly during the experiment by collecting 11-L
water from the bottom to surface with repeated deployment of a 2.2-L
tube sampler. Duplicate water samples were taken in each treatment
(section) of the two ponds, and used for measuring water chemistry and
abundance of phytoplankton and small zooplankton (copepod nauplii and
rotifers). Besides these samples, crustacean plankton were collected by
filtering a total of ca. 30-L of vertically integrated water from three
different sites in each section with a 100 μm mesh net, and fixed with
99% ethanol for enumeration. During sampling, we measured vertical
profiles of water temperature, dissolved oxygen (DO) concentration,
conductivity and pH using a multiparameter probe (600XLM, YSI) at each
section of both ponds. We also measured photosynthetic active radiation
(PAR) using a spherical quantum sensor (LI-193; LiCor, Inc.) at 10-cm
intervals from the surface to bottom and calculated extinction
coefficients of PAR in the water.