Connecting Modelling, Monitoring, Mesocosm Experiments, and Remote Sensing to understand complex Phytoplankton Dynamics in River-Connected Lakes

Abstract

Worldwide, freshwater ecosystems are under increasing anthropogenic pressure by global warming-induced changes in hydrological regimes and land-use. This has far-reaching consequences for connected river-lake systems as nutrients and organic matter received from the terrestrial surrounding upstream may unfold short and long-term effects throughout the entire aquatic network. However, studies of connected river-lake systems are scarce and often limited by low temporal and spatial resolution. By linking theoretical models with field studies and mesocosm experiments we investigated how local nutrient loading impacts phytoplankton growth and propagation along connected lake systems differing in flow regime, lake depth and residence time. We studied the effects of residence time on phytoplankton and nutrient dynamics in large-scale enclosures at the IGB-LakeLab. Our field study encompassed 19 lakes in NE-Germany, contrasting in connectivity and morphology. High temporal and spatial resolution was achieved by combining water constituent measurements and automated in-situ probes with ground-based, space- and airborne measurements. Our results suggest that - depending on flow regime, lake characteristics and water residence time - similar point sources lead to different maximum intensity, spatial range and regional-scale magnitude of eutrophication events in river-connected lakes. We highlight the potential of combining in-situ measurements with remote sensing to improve lake meta-ecosystem monitoring.