High diversity of macrophytes in the »green river« Krka (Slovenia)

Abstract

AbstractThe presence, abundance, and distribution of aquatic macrophytes and their growth forms in the river Krka in Slovenia were studied. The studied slow‐flowing lowland River Krka is also called a »green river« since it is overgrown with macrophytes from its source to its outflow to the river Sava. The environmental parameters of the river ecosystem were also assessed using the modified version of the RCE (Riparian, Channel, and Environmental Inventory) method. Within 24 sections reaching from 100 to 250 m, 23 taxa of macrophytes were found. Sections were distributed noncontinuously from the source to the outflow more or less equally along the river course. The invasive alien species Elodea canadensis reached the highest relative abundance, followed by Ranunculus trichophyllus, Potamogeton crispus, Myriophyllum spicatum, Ceratophyllum demersum, and Potamogeton nodosus. Potamogeton crispus was present in most of the studied sections followed by Nasturtium officinale and M. spicatum. The river offers suitable conditions for the high diversity of macrophytes regarding the type of substrate, low flow velocity, heterogeneity of habitats, and relatively high concentrations of nutrients. In comparison to the survey performed in 2003, when the river Krka was surveyed continuously from the source to the outflow, we found that seven of the submerged and natant macrophytes were not detected in 2020. Macrophytes, growing in the river Krka, indicated meso‐ to eutrophic conditions. Five species recorded in the river Krka are listed on the Red list of endangered species in Slovenia, indicating the need to conserve the river ecosystem.