Nondestructive assessment of phytopigments in riverbed sediments by use of instrumental color measurements

Abstract

Purpose The quantification of phytopigments in riverbed sediments deserves further attention because it provides information about eutrophic levels, and therefore about sediment and water quality. Due to the current interest in the study of eutrophication processes, there is a need for the development of a rapid, simple, cost-effective, and nondestructive method of quantifying phytopigment content. We describe one method based on color measurements and without the need for extraction and chemical assay.

Materials and methods Sediment cores were collected along the watercourse of the Anllóns River (northwest Spain). The reflectance color measurements were analyzed with the CIELAB color parameters, using Cartesian (L*a*b*) and cylindrical (L*C*abhab) coordinates. Phytopigments (chlorophyll a, chlorophyll b, phaeopigments and total carotenoids) were extracted with dimethylsulphoxide and were determined spectrophotometrically.

Results and discussion The CIELAB color parameters were significantly correlated with phytopigment content (involving logarithmic, inverse, and simple data). The linear regression equations were used to predict chlorophyll a, chlorophyll b, and carotenoid contents, as well as the total pigment contents from parameter a* (redness–greenness of the color) and parameter C*ab (chroma of the color), and values of adjusted R 2 were close to 0.9. The closest relation between phytopigments and color parameters corresponded to chlorophyll a, which may be estimated by means of Chla = 46.4–70.6 log10 (a*) and Chla = −15.7 + 238.1 (1/C*ab) as predictive equations. The phaeophytinization quotient is somewhat questionable due to the low adjusted R 2 values obtained.

Conclusions This work demonstrates that it is possible to determine phytopigment contents in riverbed sediments by means of a nondestructive colorimetric method employing the CIELAB color parameters. In addition, the abundance of phytopigments in the sediment core showed no clear trend either along the longitudinal axis of the river or in relation to sediment depth