engleski

Response of periphyton to nutrient addition in tufa-depositing environment

The effects of nutrient addition on primary producers, protozoans and meiofauna as well as on tufa deposition were examined in a short-term in situ experiment using nutrient diffusing substrata. The study was carried out in the tufa depositing barrage lake system NP Plitvice Lakes (Croatia). To address the question of whether the extent of tufa deposition and the flow velocity modify the periphyton response to nutrient addition, we selected two sites (fast flow – FF and slow flow - SF) on each of the two barriers having low (LTD) and high tufa deposition rate (HTD). The nutrients examined were nitrogen (N) and phosphorus (P), and their combination (P+N). Both N and P were limiting nutrients for autotrophs in periphyton and the response to nutrient enrichment was lower at HTD sites. Combination of HTD and FF were the most limiting factors for periphyton. Nutrient enrichment did not impede calcite deposition and P enrichment even enhanced calcite deposition, probably due to a denser autotrophic periphyton matrix. HTD supported lower taxa richness of heterotrophs in periphyton and flow velocity had taxa-specific effects. Nutrient addition led to a decrease in number of heterotrophic taxa in FF, while there was no effect in SF. Ciliate response to flow was taxa specific. The effect of nutrients on abundance of heterotrophs was rather weak, except for omnivorous and bacteriovorous ciliates. Our results showed a direct effect of N and P on autotrophic periphyton in this tufa-depositing system, and only a weak effect on protozoans and micro-metazoans.

flow velocity; chlorophyll a; protozoa; nutrient limitation

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