Zinc and Copper Have the Greatest Relative Importance for River Macroinvertebrate Richness at a National Scale.

It is important to discover what change led to the improvement in European macroinvertebrate biodiversity in the period from 1990-2000s and what prevents further desirable gains from taking place today. A 30-year data set from 1,457 macroinvertebrate monitoring sites spread across England, with 65,032 discrete observations was combined with 41 chemical, physical, habitat, and geographic variables. This data set was analyzed using generalized linear mixed-effect models and generalized additive mixed models. To include all combinations of the variables required to address each question, required over 20,000 model runs. It was found that no variables were more consistently and strongly associated with the overall family richness than Zn and Cu. Zn and Cu led both for the era of large gains in richness up to 2005 and also in the later period of 2006-2018 when few further gains were made.