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.

Environmental monitoring in sensitive areas is crucial to develop and adapt governance policies. In this context, biomonitoring provides information not only on environmental contamination gradients, but also on the actual pollutant bioavailabilities and, using bioaccumulators, on their possible transfer through the food webs. The spatial distribution of suitable bioaccumulators, however, may limit the effectiveness of biomonitoring. To relieve this constraint, we investigated the usefulness of Mentha aquatica as a novel cosmopolitan biomonitor of potentially toxic elements (PTEs) in freshwater ecosystems, using Helosciadium nodiflorum, a widely recognized biomonitor, as a reference for environmental concentration gradients. The biomonitors were then employed in deriving spatial gradients of macronutrient (Ca, K, Mg, P, S), micronutrient (Co, Cr, Cu, Fe, Mn, Na, Ni, Si, V, Zn) and non-essential element (Al, As, Cd, Pb) concentrations in the area of one of the largest Italian national parks. Over two years and a large number of sites, M. aquatica roots provided PTE concentration gradients comparable to those obtained using H. nodiflorum roots, demonstrating their usefulness in PTE biomonitoring and widening the range of suitable biomonitors for freshwater ecosystems. At the same time, the joint use of M. aquatica and H. nodiflorum enhanced the accuracy of concentration gradients measured in two of the main freshwater ecosystems within the “Cilento, Vallo di Diano e Alburni” National Park (southern Italy). The study, performed for two consecutive years over 43 sites along the Bussento and Calore Salernitano rivers, pointed out several criticalities, attributable either to natural or anthropogenic sources. High natural concentrations of Al, As, Na, Si and V were mainly related to local characteristics (proximity to sea, sediment texture) or generalized lithological background (pyroclastic deposits on carbonates), whereas local high concentrations of Co, Fe and Mn were mainly related to direct or indirect anthropogenic sources (proximity to urban centers, wastewater treatment plants). Moreover, unusual high concentrations of Cd, Cr, Ni and Zn were observed at three spring mouths, suggesting changes in their bioavailability due to spring water physico-chemistry.

In statistics, the identification of environmental criticalities, one of the primary goals of environmental monitoring and management, translates into the detection of spatial outliers. Detected in relation to purposely defined sets of indicators, both global and local outliers are pivotal in the identification not only of the severity and spread of criticalities, but also of their nature and causes. The present research exemplifies a procedural framework to identify environmental criticalities, using two different approaches for the detection of spatial outliers in river ecosystems related to several sets of parameters (organic C, inorganic C, Ca, Co, Cr, Fe, K, Mg, Mn, N, Na, P, S, Si, V, Zn, Cl−, F−, NO3−, SO42−, chlorophyll a, chlorophyll b, pheophytin a, pheophytin b, total carotenoids, pH, and electrical conductivity), including emerging contaminants. To this end, indicator sets diagnostic for specific criticalities, derived from an empirical dataset of water quality parameters, were employed, using detection techniques based on geographically weighted principal component analysis and a modified pairwise Mahalanobis distance–based algorithm. Clear and accurate criticality scenarios were derived, highlighting both the strengths and the limitations of the proposed approach, especially in relation to the classic threshold-based methods.