CONICET | Buscador de Institutos y Recursos Humanos

River-ﬂoodplain systems host very high biodiversity and provide a great variety of ecosystem services duelargely to their high environmental heterogeneity, which is strongly dependent on spatial and temporal scales ofobservation. We aimed to describe the main patterns of environmental variation of the subtropical system of theMiddle Paraná River at diﬀerent scales of analysis using univariate and multivariate statistics. Physical, chemicaland biological variables were analyzed during diﬀerent hydro-sedimentological phases along four consecutiveyears in 31 aquatic environments. We considered four aquatic habitat types with diﬀerent degrees of hydrological connectivity and water ﬂow characteristics (major rivers, secondary channels, ﬂoodplain lakes permanently connected to the major rivers, and ﬂoodplain lakes temporarily connected to the major rivers) from twogeomorphologic units with diﬀerent drainage patterns: anastomosing and meandering. The environmentalheterogeneity was mainly associated with the habitat types and relative contributions of lateral tributaries withdiﬀerent water qualities to each unit, in combination with the inﬂuence of the hydro-sedimentological regime.The heterogeneity of the system was signifcantly higher during low water than during high water phases.However, although the extreme ﬂood reduced dissimilarities between habitat types within each geomorphologicunit, it increased diﬀerences between major rivers and between units. In conclusion, at diﬀerent spatial scales,ﬂoods may simultaneously have a homogenization eﬀect due to increased hydrological connectivity and a differentiation eﬀect due to enhanced inputs of water from regions with variable geological characteristics and landuses. Finally, geomorphologic units can play a key role in maintaining the environmental heterogeneity duringﬂoods of high magnitude, even when land barriers among aquatic environments disappear.

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