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.

Effects of dilution stress on the functioning of a saline Mediterranean stream

“…Similar results were found in Chíca-mo stream, a hyposaline Mediterranean stream near the study stream, where around 70% of the GPP and ER variation was explained by air temperature, while suspended solid concentration was the only predictor of epilithon production and respiration (Velasco et al, 2003).…”

“…During the study, stream production predominated over stream consumption reflecting that Rambla Salada is an autotrophic ecosystem with a positive mean MDN and a mean P/R higher than 1. Other studies found the autochthonous production increased in importance when aridity avoided riparian vegetation development and environmental conditions allowed algal growth, relating autotrophy with aridity in Mediterranean streams (Gasith & Resh, 1999;Velasco et al, 2003).…”

“…Both factors are subjected to strong seasonal variations in Mediterranean streams and are the most important factors governing metabolic processes, although the pattern of variation depends on riparian vegetation cover, which determines light availability. In open canopy streams, maximum values of GPP and ER occur in summer and spring when temperature and radiation are high (Velasco et al, 2003). However, in closed canopy streams, GPP is maximum in early spring when light incidence on the stream surface increases, while the maximum ER occurs in autumn when organic matter accumulations are highest (Acuña et al, 2004).…”

“…Several studies have determined the factors controlling metabolic rates in Mediterranean streams (Mollá et al, 1994;Mollá et al, 1996;Velasco et al, 2003;Acuña et al, 2004Acuña et al, , 2005, but the effects of salinity on stream functioning have not been studied.…”

“…In such cases, temperature is a good predictor of GPP and ER, although flood disturbance has a considerable influence on the biomass and production of primary producers (Velasco et al, 2003). These systems have autotrophic metabolism throughout the year, with high primary production rates that, in turn, support high secondary production rates (Perán et al, 1999;Barahona et al, 2005).…”