An evaluation of a spectral fluorometer for monitoring chlorophyll a in New York State lakes

Abstract Prestigiacomo AR, June SG, Gorney RM, Smith AJ, Clinkhammer AC. 2022. An evaluation of a spectral fluorometer for monitoring chlorophyll a in New York State lakes. Lake Reserv Manage. 38:318–333. The quantification of chlorophyll a in surface waters through sampling and laboratory extraction methods has limitations, including the lack of phytoplankton composition analysis and delayed analysis time. Recently, automated instruments have been developed to quickly provide estimation of total chlorophyll a and characterize phytoplankton composition into functional groups. Here, we analyzed a dataset of paired, laboratory-extracted chlorophyll a samples (Chl-a) and chlorophyll a estimated from a spectrofluorometer (FluoroProbe, bbe Moldaenke; FPChl-a) for comparability at several time scales. We found that FPChl-a was highly correlated to Chl-a (r > 0.8) but overestimated Chl-a by 1.5–2 times on average. Summer average FPChl-a was higher than summer average Chl-a, resulting in incorrect lake evaluations against selected thresholds. Linear least squares regression of Chl-a/FPChl-a was highly significant (P < 0.01) and demonstrated a good fit (r2 > 0.75) but had high variability, consistent with FPChl-a performance values reported in the scientific literature. Factors such as FPChl-a magnitude and algal dominance were statistically important factors affecting the Chl-a/FPChl-a relationship. We developed a multiple linear regression method for postcalibrating FPChl-a to equivalent Chl-a values (adjusted FPChl-a) and applied it to the FPChl-a dataset. Adjusted FPChl-a values were unbiased and compared well with Chl-a (mean residual equal to 0 µg/L). Adjusted FPChl-a summer averages resulted in correct waterbody evaluation in more than 90% of lakes. We propose that the FluoroProbe, properly postcalibrated to adjusted FPChl-a, can be used as a surrogate of Chl-a in open water monitoring applications, reducing the need for traditional laboratory Chl-a samples for lake monitoring and management.