Chlorophyll-a determination via continuous measurement of plankton fluorescence: methodology development

A methodology is presented for the continuous measurement of chlorophyll-a concentration due to plankton, in surface water environments. A Turner 10-AU fluorometer equipped with the F4T5.B2/BP lamp (blue lamp), a Cs 5-60 equivalent excitation path filter, and a 680 nm emission filter, has been used. This configuration allows the in vivo, in situ determination of chlorophyll-a by measuring the fluorescence due to the pigments. In field work the fluorometer, data logging and positioning equipment were placed aboard a manageable boat which navigated following a scheme of regularly spaced crossings. Some water samples were collected during the measurement for laboratory chlorophyll-a measurements by the spectrophotometric method, thus providing for calibration and comparison. Spatial chlorophyll-a concentration distributions can be easily defined in large volumes, such as reservoirs, etc. Two distinct environments have been monitored: in the Vargem das Flores reservoir chlorophyll-a concentrations varied between 0.7 and 2.6 mg/m3, whereas in the Lagoa Santa lake these values lied in the 12 to 18 mg/m3 range. The simplicity, versatility and economy of the method, added to the large amount of data that can be gathered in a single run, clearly justify its use in field environmental studies.