Algae-environment relationships in an impoundment stretch of the River Grosse Erlauf (Austria)
Braun, Bernhard; Schagerl, Michael
This study was conducted to reveal important abiotic variables for structuring the phytoplankton community along an impoundment of the River Grosse Erlauf. A Principal Component Analysis based on abiotic parameters resulted in three components (nutrients, water transit time and seasonality) that explained 59% of the total variance in the data set. A Multiple Regression Analysis was carried out to analyse the relationship between principal components and chlorophyll a as a surrogate for algal biomass. Around 50% of the chlorophyll a variation could be explained by two components given by the PCA (seasonality and transit time). A Cluster Analysis based on the environmental variables resulted in four groups which showed no spatial patterns but temporal ones. For three out of the four groups, indicator species could be identified. Green algae and cyanoprokaryotes were indicative for spring and summer when precipitation was high, diatoms dominated in autumn. In total 73 taxa could be detected with diatoms mainly contributing to that number. The relationship between taxa and environmental factors were studied by a Canonical Correspondence Analysis. Diatoms mainly occurred at average conditions; their occurrences could not be explained by the considered environmental gradients. Spirogyra and Phormidium were negatively related to transit time indicating a washing off at high discharge, whereas Cryptomonas, Pediastrum and Oscillatoria showed preferences to elevated water temperatures.