SAMPLING TIMES Sampling occurred between the hours of 9:00 and 15:00 EST and are denoted in the DateTime column as 12:00. Since 2021, we usually only sample from 1.6 m in BVR and FCR regularly, with occasional one off sampling in CCR and SNP.
SAMPLE COLLECTION AND EQUIPMENT Unfiltered water samples were collected at the following depths for each reservoir or lake: 0.1, 1.5, 3, 3.5, 4, 5, 6, 6.5, 6.8, 7, 7.5, 9, and 12 meters within Beaverdam Reservoir, which has a Zmax of 13 meters at full pond; 0.1, 5, 6, 12, 14, 18, 19, 20, and 21 meters within Carvins Cove Reservoir, which has a maximum depth (Zmax) of 21.3 meters at full pond; 0.1, 5, 6, 7, 30, and 34 meters within Claytor Lake; 0.1, 1, 1.6, 2, 2.8, 3.8, 4, 4.1, 4.5, 5, 6, 6.2, 7, and 9 meters within Falling Creek Reservoir, which has a Zmax of 9.3 meters at full pond; 0.1, 4, 5, 6, 8, 9, 10, 12, 13, 13.5 and 14 meters within Gatewood Reservoir, which has a Zmax of 14 meters; 0.1, 6, 7, 8, 25, 28 and 30 meters within Smith Mountain Lake; 0.1, 5, 7, 8, 14, 25, 28 and 31 meters within Spring Hollow Reservoir, which has a Zmax of >60 m; and 0.1, 1, and 9 meters within Lake Sunapee, which has a Zmax of 33 meters. A 4-L Van Dorn water sampler was used to collect samples (Wildco, Yulee, Florida, USA) which were stored in opaque 2-L high-density polyethylene bottles. Samples were refrigerated and filtered within 48 hours of collection with GF/C filters and filters were immediately frozen after filtration. Samples were generally analyzed within 4 months of collection date.
CHEMICAL ANALYSES AND EQUIPMENT Samples were extracted using a 96% ethanol solution at room temperature for 3-24 hours (Wasmund et al. 2006) and then analyzed by spectrophotometric analysis. To quantify the concentration of phaeophytin within the sample, the analysis adopts the acidification recommendation of Parker et al. (2016), in which 240 microliters of 0.1 N HCl was added to the sample. The sample was homogenized and left to sit for 90 seconds for samples analyzed through 2018, or 120 seconds for samples analyzed after 2019. Samples were quantified using the monochromatic spectrophotometric method for chlorophyll a after correction for the presence of pheopigments, to provide a metric of "live" phytoplankton at the time of collection (Lorenzen 1967). The phaeophytin concentration (a metric of "dead" but still fluorescing phytoplankton) is also reported. In 2014, total chlorophyll a was corrected for phaeophytin but values for phaeophytin were lost during digitization. Samples were deemed below detection based on the difference between values quantified before and after acidification. Both extraction and analysis were performed in the absence of direct light to prevent the degradation of chlorophyll a. Samples collected were not always analyzed, leading to occasional incomplete water column profiles for certain dates within the dataset.
DUPLICATE VALUES Prior to 2022 duplicated field and method replicate values were not flagged. In 2022-current, duplicate values were averaged and flagged with 5. If the values were averaged and the pigment in the extract of the averaged sample was below detection then these columns were flagged as 45, for a flag of 4 for pigment below detection and a flag of 5 for averaged duplicate value.
Multiple whole-ecosystem experiments have been conducted at Falling Creek Reservoir, including intermittent operation of hypolimnetic oxygenation (HOx) and pulsed epilimnetic mixing (EM) engineering systems. We encourage you to contact the lead author of the data package for more information.
REFERENCES
Lorenzen, C.J. 1967. Determinations of chlorophyll and pheo-pigments: spectrophotometric equations. Limnol. Oceanogr. 12:343-346.
Parker, S. P., W. B. Bowden, and M. B. Flinn. 2016. The effect of acid strength and postacidification reaction time on the determination of chlorophyll a in ethanol extracts of aquatic periphyton. Limnology and Oceanography: Methods 14:839-852.
Wasmund, N., I. Topp, and D. Schories. 2006. Optimising the storage and extraction of chlorophyll samples. Oceanologica 48(1):125-144.