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.