Microhabitat patterns of soft-bodied benthic algae in a lowland river largely fed by groundwater

In lowland rivers largely fed by groundwater, the aquifer resurgence plays a major role in supporting local plant diversity. However, large knowledge gaps exist with regard the role of groundwater on algal diversity and spatial arrangement. In this context, our main aim was to evaluate the distributive gradients of soft-bodied benthic algae across a mid-size lowland river with a bottom dominated by hard substrate (Oglio River, north Italy). Along the investigated river sector, a clear segregation both for taxa and for environmental data was observed, especially in terms of pH, hydrological variables and nutrient availability. Overall, we recorded an important contribution of groundwater supply in shaping the structure and complexity of algal communities at the microhabitat level (in the meter range) during the river base flow. All these considerations shed new light on the response of algal taxa to a relevant groundwater ingression in a lowland river.