Release of Nutrients and Organic Matter from River Floodplain Habitats: Simulating Seasonal Inundation Dynamics

Abstract

River floodplains form a complex mosaic of aquatic, semi-aquatic, and terrestrial habitats. While spatially distinct, these habitats are connected through water, carbon and nutrients, and thus ecosystem processes in one habitat type may have ramifications for others. In the laboratory, we studied the effects of inundation duration (12, 36 and 96 h)and water temperature (4, 12 and 25 °C) on the release of nutrients and organic carbon from sediments of seven habitat types, and from leaves (Populus nigra L.), from the nearnatural,braided, Tagliamento River in NE Italy. The relative content of POC, TN, and TP was similar in the sediment size fraction <2.0 mm across all habitat types, 9.3 % to 11.9 % C,0.007 % to 0.046 % N, and 0.013 % to 0.019 % P. Leaves contained a mean of 73 % C, 0.86 % N, and 0.06 % P. Leaching released, on average, 0.017 % C, 1.79 % N, and 0.018 % P of the respective element in the sediments. Leaching peaked during the first 12 h of inundation at 12 °C and 25 °C, but was delayed at 4 °C. Leaf litter was a key source for C and P, while sediments, especially those from terrestrial habitats, were an important source for N; thereby emphasizing the unique role that each habitat plays in the floodplain mosaic.