Global warming effects on macrophytes’ role in lowland rivers

Rivers are impacted by various pressures, including changing temperatures driven by climate change and other factors. Many rivers crossing lowland landscapes show changes in their thermal regime and are intensively overgrown with aquatic plants, macrophytes. Thus, the macrophytes’ impact on the microclimate of rivers, metabolism and biodiversity, changes in channel hydraulics and the effect on biogeochemistry need to be better understood. An increase in macrophyte biomass, for example, can lead to a decrease in surface water temperature and a decrease in solar radiation reaching the water, buffering temperature fluctuations. There is a need to analyse the role of aquatic macrophytes on water temperature dynamics and their critical importance for local biodiversity of primary producers and the controlling environmental factors of rivers. The project addresses this knowledge gap via an in-depth study of the influence of aquatic macrophytes on water temperature and aquatic metabolism in small lowland rivers by integrating monitoring approaches, targeted experiments and integrated modelling. The project team uses statistical models incorporating key independent variables from meteorological, hydro-morphological, and aquatic vegetation factors to provide accurate predictions of water temperature and its variability. River hydraulics and aquatic macrophyte characteristics are expected to jointly influence seasonal water temperatures by reducing the amplitude of temperature fluctuations in macrophyte-dominated stretches. Macrophyte patches in lowland rivers can buffer temperature increases and daily fluctuations, thereby mitigating shifts in algal diversity toward more temperature-tolerant species and cascading food web effects. Spatial thermal heterogeneity increases in river sections with macrophyte patches, enhancing diversity and ecosystem functions like photosynthesis among primary producers. To address these scientific questions, we investigate the temporal and spatial heterogeneity of water temperature through automated monitoring approaches and employ different statistical approaches to identify key variables. Controlled flume experiments complement the field studies in rivers to analyse causal relationships, and the gained data will be used to set up enhanced models to predict future changes due to climate change. Based on advanced modelling approaches, new insights will be gained into temperature-vegetation feedback processes and multitrophic interactions, to derive improved management strategies for an enhanced river ecosystem resilience, considering ecological interactions. Thus, this study advances our understanding of primary production, ecosystem respiration, and community dynamics in rivers in a warming world. The project team consists of scientists from Poland and Austria, teaming up expertise in hydrology, modelling and ecosystem research to address climate change effects in rivers in Poland and Austria.