METHOD FOR EVALUATING ALGAL PRODUCTION AND DEGRADATION BASED ON NITROGEN LEVELS IN PARTICULATE ORGANIC-MATTER

A population of Ulva rotundata (Bliding, C., A critical survey of European taxa in Ulvales. Part I. Opt. Bot. Lund, A8 (3), 1-160) was studied for 7 months in a shallow brackish eutrophic lagoon (Prevost Lagoon, Languedoc, France). Biomass was measured in square-meter quadrates, and algal growth in on-site cages. Carbon and nitrogen levels were spatiotemporally monitored in Ulva thalli and in particulate organic matter. Thalli rapidly degraded into particulate matter from the surface to the bottom, increasing nitrogen concentrations and decreasing carbon concentrations. We propose a method for estimating algal production and possible carbon loss in this type of lagoon, based on nitrogen levels in particulate organic matter. Algal production over the whole period can be evaluated by adding instantaneous biomass levels corresponding to the main particulate nitrogen peaks.