ESTIMATION OF THE ANNUAL PRIMARY PRODUCTION OF STREAM EPILITHIC BIOFILMS BASED ON PHOTOSYNTHESIS-IRRADIANCE RELATIONS

The main objective of this study was to estimate annual primary produc tion in two undisturbed streams: La Solana (LS) and Riera Major (RM). Using hourly values of irradiance, community-specific photosynthesis i rradiance relations (P-I) measured in the laboratory were used to esti mate anal net and gross primary production over an annual cycle. The m odel (referred to as P-I model), showed good agreement (r(2) = 0.53 an d r(2) = 0.62, p<0.001 for LS and RM, respectively) between estimated values and those measured in the field. The P-I model was also applied to estimate annual primary production after nutrient enrichment. Annu al primary production was 50 gC m(-2) y(-1) for RM and 157 gC m(-2) y( -1) for LS before nutrient addition, but increased to 440 gC m(-2) y(- 1) after nutrient addition. Light conversion efficiency (Ef) was highe r for RM (0.25 %) than for LS (0.16 %) and it was significantly enhanc ed after nutrient additions (0.55 %). A comparison between the annual primary production values obtained in this study with those from other lotic systems in different climatic zones indicated that stream order , nutrient concentration and light availability are probably mon impor tant than climate type in determining annual values of primary product ion in fluvial systems.