Advancing two‐component partitioning of light scattering in C ayuga L ake, N ew Y ork

Abstract

The particulate scattering and backscattering coefficients (bp and bbp) were partitioned into the additive contributions of minerogenic (bm and bb,m) and organic (bo and bb,o) components for nearshore and pelagic areas of Cayuga Lake, New York, over a 7 month period in 2013. The analysis was based on paired measurements of (1) bulk bp and bbp, (2) light‐scattering properties of mineral particles, with an individual particle analysis (IPA) technique, and (3) concentrations of chlorophyll a ([Chl]) and particulate organic carbon (POC), as two indices to quantify organic particle scattering. bm and bb,m were estimated through Mie theory calculations with IPA results as inputs. bo and bb,o were estimated with both system‐specific and oceanic bio‐optical models parameterized on [Chl] or POC. POC performed better than [Chl] as the index for both bo and bb,o. The averages of the ratios (bm + bo) : bp and (bb,m + bb,o) : bbp at 660 nm, were 1.02 and 1.03, respectively; the average relative errors were 18.2% and 15.6%. Multiple empirical bio‐optical models developed for Case 1 oceanic waters (for bo and bb,o estimates) approached the closure performance of the system‐specific relationships. In addition to systematically accounting for more bbp than bp, terrigenous minerogenic particles made greater contributions to both bp and bbp in the nearshore area proximate to tributary inputs than in pelagic waters. A strong positive dependency of the backscattering ratio (bbp : bp) on the bm : bp ratio was observed for both nearshore and pelagic areas.

Characterizations of calcite particles and evaluations of their light scattering effects in lacustrine systems

“…Indeed, this paper is an interpretive application of SAX–Mie findings to expand particle analyses and optical characterizations of calcite in lacustrine systems, focused primarily on the rich previously tested data set (9 yr) from Cayuga Lake. Detailed and successful closure testing has been published for this lake, directed at b p (Effler and Peng ) and both b p and b bp (Peng and Effler ; Table ), to support this interpretive application. The secondary consideration of this paper, the broadening of calcite characterizations in 11 other lakes, relies on the credibility established over the growing number of lakes for which the SAX–Mie protocols have been tested (Table ).…”

“…Single summer samples were collected in the upper waters of most of these lakes. The most extensive sampling ( N = 215) was conducted in Cayuga Lake (Effler and Peng ; Peng and Effler ), to support resolution of temporal (April–October) structure (once every 2 weeks over 1999–2006; weekly or biweekly in 2013). The Cayuga Lake samples were composites of equal volumes of sub‐samples collected from depths of 0 m, 2 m, and 4 m for the earlier study period, whereas in 2013 these were collected at the surface.…”

“…The Cayuga Lake samples were composites of equal volumes of sub‐samples collected from depths of 0 m, 2 m, and 4 m for the earlier study period, whereas in 2013 these were collected at the surface. The following descriptions of methods are abbreviated treatments of the earlier works (largely directed at testing closure; Table ), including for Cayuga Lake (Effler and Peng ; Peng and Effler ), which were extended here for the other lakes of this study.…”

“…The C‐Star (path‐length 10 cm, acceptance angle 1.2°) was calibrated according to the manufacturer's protocol (WETLabs 2011, p. 8). Additional bulk measurements of spectral c and a ( b p by difference) and b bp at nine wavelengths (WETLabs ac‐s and BB9 meters, respectively) were made in 2013 in Cayuga Lake (Peng and Effler ).…”

“…) have been reported for multiple lacustrine systems over the last 10 yr (Table ), supporting the credibility of both the minerogenic and organic component estimates. Successful independent testing (i.e., applicability) of the Case 1 Chl a ‐based, and particulate‐organic‐carbon‐based, bio‐optical models for b o and b b , o for a lake has also recently been demonstrated (Peng and Effler ).…”