Understanding the hydrological and landscape connectivity of lakes

•Context: Connectivity is a key property of water, enabling the flow of energy, material and individuals within and between sites. Climate and land use changes can profoundly modify connectivity, yet few studies have quantified the patterns in connectivity among lakes at national scales. •Objectives: Our objectives were: i) to examine relationships between a broad range of lake connectivity metrics, ii) to evaluate how lake connectivity varies nationally, regionally and in relation to land cover. •Methods: We calculated hundreds of metrics of freshwater connectivity for all lakes in Great Britain > 1 ha (n = 10,095), quantifying connectedness in their catchments and surrounding landscape. Patterns of metrics, as well as their correlations and inter-connectedness, were examined at multiple scales. •Results: Strong correlations existed within groups of metrics for lake, pond and river connectivity. However, both pond and river metrics varied independently of lake metrics. The most and least urban river basin districts showed noticeable differences in metric correlation. Lake area, pond count and river length in catchments were selected as a core set of connectivity metrics, which explain most of the variation across national and regional scales. •Conclusions: Connectivity metrics can be synthesised to core groups that are easily calculated and effectively account for lake, pond and river connectivity. From a landscape management perspective, hydrological connectivity was highest per unit area in the zone nearest the lake. When interpreting ecological responses, the connectivity metric within each core group can be selected based on suitability and data availability. The minimum set of three metrics is recommended to support comparative, global studies.