Land Use Impacts on Local and Regional Freshwater Biodiversity Can Compromise Current Management Goals

Land use and other anthropogenic activities are degrading freshwater ecosystems and their biodiversity worldwide. Although results from long-term monitoring networks suggest that freshwater biodiversity may not be undergoing significant change, information about how freshwater biodiversity has changed and the effectiveness of current environmental goals remains limited. We used nationwide survey data of stream diatoms, macroinvertebrates, and lake diatoms, macroinvertebrates, and macrophytes to examine how land use has changed freshwater biodiversity in Finland and how effective good ecological status class, that is, the main environmental goal for freshwater ecosystems in the European Union, is for protecting biodiversity. We employed RIVPACS-type multitaxon distribution models with independent validation sites to assess observed to expected ratios of local taxa (O/E) as well as differences in observed and expected regional frequencies of taxa. Land use negatively impacted local diversity of both examined stream communities (mean difference in O/E to near natural reference streams > 0.076), while lake communities were affected by only agriculture and multiple pressures (mean difference in O/E to near natural reference lakes > 0.093). Regional taxon prevalences were significantly reduced in all land use groups for diatoms (21%-61% of taxa), lake macrophytes (21%-39%), and macroinvertebrates (11%-65%), but also increased particularly for diatom (24%-26%) and macrophyte (29%) species in agricultural areas. Species with decreased frequency were generally sensitive species, while species that increased in their frequency were tolerant species typical for mesotrophic or eutrophic conditions. In the good ecological status class, frequencies were also changed, and for some groups such as stream macroinvertebrates, there were substantial changes (66% of taxa declined), indicating that the current management goal may be partially insufficient to protect freshwater biodiversity. Our study highlights that there is a need to incorporate freshwater biodiversity in the environmental objectives to ensure effective conservation and restoration efforts.