Geochemical reference functions as a tool for detecting environmental change: Application to trace-elements in the Sacca di Goro (Italy)

Assessing trace-element distributions in lagoon sediments requires accounting for sedimentological and lithogenic controls that influence their content. Conventional sediment assessment indices provide standardized measures of enrichment and contamination, but rely on fixed reference values that may not fully capture the geochemical characteristics of a specific system. A pristine or pre-industrial reference would provide a direct basis for defining natural background conditions, but such material can be difficult to identify in highly dynamic environments such as lagoon, and no specific reference is available for the Sacca di Goro (Po Delta, Italy). A sediment dataset collected during previous monitoring of the lagoon in 2003–2005 was used to characterize the geochemical structure of the system and establish Historical Geochemical Reference Functions (HGRFs). These functions were applied to sediments collected in 2023 to identify departures from the reference relationships. HGRFs identified no significant departures for Pb, Cu and V, whereas Ni and Cr showed positive departures. Zn also showed a positive pattern, although this was not statistically significant after accounting for spatial dependence and multiple comparisons. These results indicated that the recent behaviour of Ni and Cr differs from the relationships represented by the 2003–2005 dataset. The HGRFs results were also considered alongside conventional sediment assessment indices, providing an additional perspective on the geochemical differences between the two datasets. HGRFs provide a complementary, system-specific reference based on empirical geochemical relationships rather than fixed regional values. Their application allows recent observations to be evaluated against the geochemical structure documented by previous monitoring and helps identify element-specific departures that may warrant further investigation.