Long-term ecological observatories needed to understand ecohydrological systems in the Anthropocene: a catchment-scale case study in Brittany, France

Over the last half century, humans have become the dominant force driving many of Earth’s cycles. Intensive agriculture has simultaneously increased nutrient loading of pastoral landscapes and decreased the capacity of these ecosystems to retain or remove excess nutrients. Widespread degradation of terrestrial and aquatic ecosystems has triggered the establishment of ecological observatories, including the Zone Atelier Armorique (ZAAr) in western France, a part of the International Long-Term Socio-Ecological Research (LTSER) network. The ZAAr includes a patchwork of land covers and uses, including old-growth forests, intensively cultivated row crops, and ancient bocage fields surrounded by hedgerows. In addition to traditional ecological research at ZAAr, the last 8 years have seen the development of multiproxy and multiscale approaches to address surface and groundwater quality. Here, we present a comprehensive analysis of this 8-year dataset, including vegetation, soil water storage, and stream and groundwater chemistry. We observed contrasting responses of different catchment components to climate forcing and direct disturbance. Our results highlight a clear relationship between land use and surface water quality, while groundwater quality appeared largely unrelated to land use, suggesting strong differences in aquifer nitrogen removal rates. There were large differences in nutrient fluxes among dry and wet years, with multiyear memory effects apparent for some parameters. Given such complex interactions, including emergent dynamics and decadal to centennial time lags, we conclude that multidimensional observations such as those supported by the ZAAr and other LTSER sites, are critical to understanding ecohydrological systems in the Anthropocene.