Vertical hydrological exchange, and ecosystem properties and processes at two spatial scales along a floodplain river (Tagliamento, Italy)

Abstract

AbstractWe examined the effect of vertical hydrological exchange on physicochemical variables, periphyton biomass (ecosystem properties), and sediment respiration (ecosystem process) at 2 spatial scales along a large gravel-bed river (Tagliamento River, northeastern Italy). At the regional scale, we investigated a 29-km-long, expanding and contracting, losing (average flow decrease 2.5 m3 s−1 km−1) and a 12.5-km-long, stable, gaining (average increase 0.3 m3 s−1 km−1) reach. At the local scale, we sampled riffle head and riffle tail units nested within the losing and gaining reaches. At the regional scale, we characterized vertical exchange by strong downwelling (negative vertical hydraulic gradient; VHG) in the losing and moderate upwelling (positive VHG) in the gaining reach. Nutrients, such as NO3-N and dissolved N (DN), and periphyton biomass (AFDM) showed a significantly (p < 0.05) lower concentration in the losing than in the gaining reach. A contrasting pattern emerged for sediment respiration. Exp...