This freshwater mesocosm study was conducted in 19 out of 110 mesocosms at the Large Experimental Array of Ponds (LEAP) at the Gault Nature Reserve in Mont-St-Hilaire, QC, Canada (45°32' N, 73°08' W, 122 m a.s.l.) between May and October 2018 for a total of 147 days. On 24 May 2018, the mesocosms (1100L stock tanks, Rubbermaid, Huntersville, NC, USA) were filled with approximately 1000 liters of unfiltered lake water via a pipeline from oligotrophic Lac Hertel, located 1 km upstream of the experimental facility. 

These data consist of two datasets that were used for our paper. 

1. Dissolved oxygen as measured with data loggers (MiniDOTs, PME, Vista, California, USA) in 12 mesocosms
2. Phytoplankton biomass as measured with a FluoroProbe (bbe Moldaenke, Schwentinental, Germany) in 19 mesocosms

Dissolved oxygen

We tracked DO dynamics in twelve mesocosms using data loggers (MiniDOTs, PME, Vista, California, USA) attached to the side of the mesocosms at a depth of approximately 20 cm from May to October 2018. Water temperature (°C) and DO (in mg/l) were measured every 20 minutes for 145 days in 2018. Four loggers were in mesocosms at pH 5.5, four at pH 6.5 and four at pH 8.5. All analyses focused on temperature-corrected values of DO (in % saturation). Outlier values > 4 standard deviations away from the mean DO across all data points (98 % DO saturation) were attributed to temporary probe disturbance or malfunction and were thus excluded from analyses of DO across time and mean DO per phase (but not in the wavelet analysis). These values (DO saturation < 40 % or > 150%) represented 0.4 % of all data points.

Phytoplankton biomass

We measured total phytoplankton community biomass in the twelve mesocosms with the DO loggers throughout the experiment, albeit at a much lower temporal resolution than DO (twice per week) from June to October 2018. In addition, we measured chlorophyll a in additional seven control mesocosms, which were positioned at the side of the experimental array. These control mesocosms maintained their base line pH throughout the entire experiment, even during phase 2 and, therefore, represent a temporal control. 2L of mesocosm water was sampled from across the water column and chlorophyll a concentration in a subsample was determined fluorometrically with a FluoroProbe (bbe Moldaenke, Schwentinental, Germany). 2L of mesocosm water was sampled from across the water column and chlorophyll a concentration in a subsample was determined fluorometrically with a FluoroProbe (bbe Moldaenke, Schwentinental, Germany). Through the excitation of chlorophyll a and accessory pigments with various LEDs, the Fluoroprobe detects the biomass (ug/L) of four 'spectral groups' that roughly correspond to main phytoplankton taxa: (i) ‘green’ algae (Chlorophyta and Euglenophyta), (ii) ‘brown’ algae (Bacillariophyta, Chrysophyta and Dinophyta), (iii) ‘blue’ algae (Cyanophyta) and (iv) ‘red’ algae (Cryptophyta). Sampling started on day 1 (14 June, 2018) and ended on day 147 (17 October, 2018) for a total of 23 sampling points. Chlorophyll a concentrations > 80 µg / liter (n=21) were attributed to a faulty reading of the fluoroprobe and were thus excluded from analyses.

For the paper, we only used a subset of the phytoplanktion data (i.e., fluoroprobe.csv). We used this line of code to subset the dataset.

selected <- c("A4", "A5", "A6", "D4", "D5", "D6", "J4", "J5", "J6", "K4", "K5", "K6", "CL1", "CL2", "CL11", "CL3", "CL4", "CL5", "CL6")
d<- df[df$pond %in% selected,]