Tracing Nitrogen Distribution and Biotic Responses in Spring-Fed Karst Rivers: A Pilot Study

The evaluation of nitrogen pathways in river systems and the identification of suitable aquatic ecosystem response indicators are essential for maintaining river health. Ni-trogen, in its various forms, is a key physico-chemical quality element that underpins the biological communities determining the ecological status of surface waters. Ele-vated nitrogen loads in freshwater ecosystems can trigger adverse processes such as eutrophication and acidification, both of which are linked to biodiversity loss. We hy-pothesize that specific biotic indicators can reflect nitrogen-related stress in aquatic ecosystems, acting simultaneously as biodiversity components and as bioaccumulating indicators. To test this hypothesis, we examined four study sites within the Koiliaris River watershed (Crete, Greece). Our approach aims to enhance understanding of ni-trogen dynamics at the river-basin scale by providing complementary insights into how nitrogen is processed, stored, and transferred within the aquatic ecosystem. To this end, total nitrogen content was quantified in four matrices: water, sediments, aquatic mosses, and macroinvertebrates. This study represents a pilot, exploratory assessment indicating that water may act as the primary pathway of nitrogen availability for aquatic biota in the studied streams.