The influence of nitrate pollution on elemental and isotopic composition of aquatic and semi-aquatic bryophytes

Abstract

Bryophytes can play an important role in key ecosystem processes and represent potential candidates as bioindicators for environmental monitoring programmes. Nitrate (NO3−) pollution poses a growing threat to both aquatic and terrestrial ecosystems, potentially leading to imbalances in nutrient levels and altering the chemical composition of organisms, thereby impacting ecosystem function. However, the specific effects of NO3− pollution on the elemental and isotopic composition of aquatic and semi-aquatic bryophytes remain uncertain. In this study, we examined the influence of NO3− pollution from spring water on the elemental composition of aquatic and semi-aquatic (hygrophytic) bryophyte species and their respective water sources. Our investigation encompassed diverse land use, lithology, and climate conditions to identify suitable bryophyte species as bioindicators of NO3− pollution. We observed higher NO3− concentrations in spring water from intensively farmed and urban areas compared to natural and extensively farmed areas (e.g., pastures). These higher concentrations were positively correlated with the nitrogen (N) content and δ15N isotope ratio in bryophytes. However, spring water NO3− pollution did not significantly affect the overall chemical composition of the water sources, except for Cl−, Cr, and Zn. Our findings highlight Apopellia endiviifolia and Oxyrrhynchium speciosum as promising candidate species for bioindication of aquatic NO3− pollution, due to their δ15N sensitivity to increasing NO3−, i.e., they respond to variations in the ratio of δ15N isotopes in their environment. The identification of these species will assist land managers in effectively monitoring NO3− pollution in freshwater systems, thereby addressing public health concerns and supporting wildlife conservation priorities.