Environmental and periphyton response to stream revitalization – A pilot study from a tufa barrier

Abstract

The formation of tufa barriers is driven by specific physicochemical and biological factors which make them very sensitive to environmental changes. The barriers provide great microhabitat complexity and are therefore inhabited by various periphytic organisms, whose metabolic activity alters the microenvironment, directly or indirectly affecting the physicochemical conditions of calcite precipitation. After the invasive plant species Ailanthus altissima (Mill.) Swinge was identified as one of the main factors causing current dryness of streams at the Skradinski buk barrier (Krka National Park, Croatia), the invasive species was removed, resulting in changes in the hydromorphology of the barrier and reactivating previously dry streams. The objective of this study was to determine potential differences between control and revitalized sites (reactivated streams) with regards to periphyton and the associated environmental changes over an annual cycle. Clear patterns were observed between sites reflecting the substantial changes in the landscape following invasive species removal. Revitalized sites had lower flow velocity, conductivity, pH, alkalinity and total water hardness values while exhibiting higher values of dissolved organic matter, nitrites and orthophosphates due to the presence of soil-derived organic material and intensive soil drainage. Organic matter content was generally higher at revitalized sites but did not inhibit tufa deposition. The influence of the surrounding forest soil was reflected not only in the mineralogical analysis of tufa sediment, but also in the abundance and diversity of periphyton. Revitalized site communities exhibited higher abundance and diversity and were dominated by bacterivorous and omnivorous ciliates and cercozoans due to the abundant food resources of the soil. The results presented show that ecosystem responses to hydromorphological changes generated by invasive species removal can be efficiently detected and monitored at microscale (i.e., periphyton scale) through a comprehensive interdisciplinary approach. As the first study to examine the relationship between aquatic ecosystems and sediments in the context of tufa stream revitalization, this pilot study provides data and guidelines for future management plans applicable to various tufa depositing systems facing invasive species propagation, allowing better understanding and protection of this unique and vulnerable karstic feature.