Sampling Methods
As part of an ongoing monitoring program, we sample total and soluble Fe and Mn weekly throughout the stratified period. For this study, water samples were collected at the reservoir outtake depths of 0.1, 1.6, 3.8 m (epilimnion), 5.0 m (metalimnion), 6.2, 8.0, and 9.0 m (hypolimnion) using a 4-L Van Dorn sampler, thereby matching the MUX sampling depths. Samples for soluble Fe and Mn were syringe-filtered using 0.45 µm nylon filters. Both total and soluble metals samples were preserved with trace metal grade nitric acid to pH < 2. Samples were analyzed using Inductively Coupled Plasma Mass Spectrometry (ICPMS). Minimum reporting levels were 0.005 mg/L (Fe) and 0.0001 mg/L (Mn). The dataset, including methods for sample collection and analysis, can be found in Schreiber et al. (2022).
To assess short-term variability in metals concentrations and to calibrate and validate PLSR models, additional samples were collected every 2-4 hours during two 24-hour campaigns. The first campaign occurred on 16-17 October 2020 (n=7; Figure S8); the second campaign occurred on 10-11 June 2021 (n=8; Figure S9). All sampling data (weekly and high-frequency) were used to calibrate PLSR models.