Human activities disrupt the temporal dynamics of salinity in Spanish rivers

Abstract

Human activities are not only increasing salinization of rivers, they might also be altering the temporal dynamics of salinity. Here, we assess the effect of human activities on the temporal dynamics of electrical conductivity (EC) in 91 Spanish rivers using daily measures of EC from 2007 to 2011. We expected rivers weakly affected by human activities to have low and constant ECs, whereas rivers strongly affected by human activities should have high and variable ECs throughout the year. We collected information on land use, climate, and geology that could explain the spatiotemporal variation in EC. We identified four groups of rivers with differences in EC trends that covered a gradient of anthropogenic pressure. According to Random Forest analysis, temporal EC patterns were mainly driven by agriculture, but de-icing roads, mining, and wastewater discharges were also important to some extent. Linear regressions showed a moderate relationship between EC variability and precipitation, and a weak relationship to geology. Overall, our results show strong evidence that human activities disrupt the temporal dynamics of EC. This could have strong effects on aquatic biodiversity (e.g., aquatic organisms might not adapt to frequent and unpredictable salinity peaks) and should be incorporated into monitoring and management plans.

Warding off freshwater salinization: Do current criteria measure up?

“…This will create opportunities for defining new metrics for salinity thresholds, which better take account of the relationship between exposure time and concentration in some regions. Another largely unresolved question concerns how best to capture temporal dynamics of salinity and better understand their potential effect (e.g., for aquatic insects, a salinity peak which occurs when adults are emerging may be less toxic than one which occurs when larvae are developing (Moyano Salcedo et al, 2022).…”