Environmental parameters
Environmental parameters
We randomly selected 50 sites in the shallow, nearshore
zone of the lake (1–3 m from the shore, where depth
Volume 35 March 2016 | 189averaged ∼1 m and was ≤2 m; Fig. 1). Sites were 50 to
60 m apart. We measured 6 environmental variables at
each of the 50 sites during the wet and dry seasons in
2010 for a detailed assessment of the current trophic status and physicochemical characteristics of the lake. We
measured water temperature once with a digital thermometer. We made ≥3 measurements of chlorophyll a (chl a)
concentration/site with a fluorometer (Aquafluor Handheld Fluorometer, Turner Designs, Sunnyvale, California).
Concentration of dissolved O2 (DO), pH, and conductivity
were measured using handheld DO (DO2 Meter 9200®;
Jenway, Stone, UK), pH (ecoTestr pH2; Oakton Instruments, Vernon Hills, Illinois), and conductivity (ECTestr
11+ Eutech Instruments; Oakton Instruments) meters.
From each site, we collected 3 random sediment cores to
a depth of 10 to 15 cm for subsequent determination of
organic content in the laboratory by organic mass-loss on
ignition (Downing and Rath 1988). We homogenized
samples with a spatula, dried them for 24 h at 70°C to
constant mass, and weighed them. We ignited the dry samples in a muffle furnace for 4 h at 500°C, allowed them to
cool to room temperature in a desiccator, and weighed
them. At sites 1 to 20, we recorded Secchi depth, total P
(HACH Lange test kit; HACH Corporation, Loveland, Colorado), total N (HACH Lange test kit), and Ca (HACH
Lange test kit) (Fig. 1
