Photosynthetic activity of epilithic algal communities in sections of the Torna stream (Hungary) with natural and modified riparian shading

Abstract

The photosynthetic activity of epilithon grown in the Torna-stream (Hungary) was studied. Samples were collected from natural sections with closed canopy and natural stream bed and from modified sections with trapezoid river bed and shores lacking riparian vegetation. We assumed that human modifications would have a significant impact on epilithic photosynthesis, and therefore expected to observe corresponding changes in photosynthesisirradiance (P-I) parametric. The laboratory P-I measurements were carried out monthly between April 2008 and September 2009 with epilithon after 3 weeks of in situ colonization. The maximum rate of the photosynthesis (P max ) correlated positively with the chlorophyll a content of the samples. Natural sites had lower biomass and P max values than modified sites, and the biomass differed substantially in spring and summer, the P max differed significantly only in spring. Natural sections had higher biomass-specific photosynthesis values than modified sections in all seasons, but the difference was significant only in summerautumn: in summer the samples from the natural sections had significantly higher photosynthetic efficiency. In spring and summer, the photoadaptation parameters (I k ) of communities grown in modified sections were substantially higher than in natural sections. Light availability appeared to be the major factor regulating the seasonal photosynthetic activity of epilithic communities.

Establishment of equilibrium states and effect of disturbances on benthic diatom assemblages of the Torna-stream, Hungary

“…The regional Water Authority provided daily discharge data. The chlorophyll-a content of the epilithon was extracted directly from the substratum surface with 90% acetone (Ü veges & Padisák, 2011), and was measured according to Wetzel and Likens (2000 using a Metertech UV/VIS Spektrophotometer, SP8001). To avoid the impact of pheopigments, the acid method was applied (Lorenzen, 1967;Tett et al, 1975).…”

Biofilm Responses to Flow Regulation by Dams in Mediterranean Rivers

“…These conditions favour the accrual of primary producer biomass despite the usually lower light and near‐limiting phosphorus concentrations below dams (Stevenson, ; Biggs et al ., ; Taulbee et al ., ). The primary producers in the biofilm had higher photosynthetic efficiencies below the dams, announcing that they had higher primary production (Rohácek and Barták, ) despite the lower irradiance occurring in these reaches (Üveges and Padisák, ), except in the Cinca River. Lower irradiances could be non‐limiting in the shallow waters characterizing the reaches downstream of dams.…”