Macrophytic, epipelic and epilithic primary production in a semiarid Mediterranean stream

Abstract

Summary 1. Primary production by Chara vulgaris and by epipelic and epilithic algal assemblages was measured in a semiarid, Mediterranean stream (Chicamo stream, Murcia, Spain) during one annual cycle.2. The rates of gross primary production (GPP) and community respiration (CR) were determined for each algal assemblage using oxygen change in chambers. The net daily metabolism (NDM) and the GPPd−1 : CR24 ratio were estimated by patch‐weighting the assemblage‐level metabolism values.3. Gross primary production and CR showed significant differences between assemblages and dates. The highest rates were measured in summer and spring, while December was the only month when there were no significant differences in either parameters between assemblages. GPP was strongly correlated with respiration, but not with algal biomass.4. Chara vulgaris showed the highest mean annual metabolic rates (GPP = 2.80 ± 0.83 gC m−2 h−1, CR = 0.76 ± 0.29 gC m−2 h−1), followed by the epilithic assemblage (GPP = 1.97 ± 0.73 gC m−2 h−1, CR = 0.41 ± 0.12 gC m−2 h−1) and epipelic algae (GPP = 1.36 ± 0.22 gC m−2 h−1, CR = 0.39 ± 0.06 gC m−2 h−1).5. The epipelic assemblage dominated in terms of biomass (82%) and areal cover (88%), compared with the other primary producers. Epipelic algae contributed 84% of gross primary production and 86% of community respiration in the stream.6. Mean monthly air temperature was the best single predictor of macrophyte respiration and of epipelic GPP and CR. However, ammonium concentration was the best single predictor of C. vulgaris GPP, and suspended solid concentration of epilithon GPP and CR.7. Around 70% of the variation in both mean GPP and mean CR was explained by the mean monthly air temperature alone. A multiple regression model that included conductivity, PAR and nitrates in addition to mean monthly air temperature, explained 99.99% of the variation in mean CR.8. Throughout the year, NDM was positive (mean value 7.03 gC m−2 day−1), while the GPP : CR24 ratio was higher than 1, confirming the net autotrophy of the system.