Long-established and new active biomonitors jointly reveal potentially toxic element gradients across spatial scales in freshwater ecosystems

At the core of the adaptive ecosystem management paradigm, environmental monitoring, especially using biomonitors, mandates the search for tools and approaches to overcome its current limitations, both in terms of novel species and analytical techniques to extract information from the data. In this context, a large field bio-monitoring study was performed in order to validate a candidate active biomonitor, the macrophytic alga Chara gymnophylla, using a long-established biomonitor (the aquatic moss Fontinalis antipyretica) as reference, innovative spatial analysis approaches and the area of two of the main freshwater ecosystems of the Cilento Vallo di Diano e Alburni National Park as experimental setting. Specifically, the concentrations of 19 potentially toxic elements (Al, As, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, V, Zn) in 3 alga and 3 moss bags placed in each of 41 sites along the Bussento and Calore Salernitano rivers were analyzed. The coherence of element gradients between biomonitors, the spatial heterogeneity in element distribution and their spatial scales were evaluated using robust multivariate approaches, random models and spectral decomposition of the spatial gradients. Results demonstrate the substantial uniformity in responses between the biomonitors, both showing similar element spatial distributions, within and between-site variability, the same spatial connectivity and spatial variations at similar scales. On the one hand, the approach adopted and the findings obtained allow definitely validating Ch. gymnophylla as a novel active biomonitor of potentially toxic elements in freshwater ecosystems and, on the other hand, deriving clear contamination scenarios, with indication of the alleged sources.