Complex effects of channelization and levee construction on western Tennessee floodplain forest function

Abstract

Data on vegetation composition and structure, soil and leaf nutrient pools, soil redox potential, and surface water hydrologic connectivity were collected from floodplains along six river reaches in western Tennessee to examine the effects of channel modifications on associated riparian systems. Comparisons among channelization treatments (non-channelized reaches, channelized and leveed reaches, channelized but non-leveed reaches) and floodplain geomorphology (depression and nondepressional sites) showed that hydrologic connectivity was affected by channelization treatments, particularly leveeing. The disconnected floodplains were drier, maintained higher nutrient pools, and had greater herbaceous biomass than floodplains still connected to channel hydrology. Runoff onto floodplains from the agriculturally dominated landscape of channelized and leveed tributaries, and flooding stress in the form of scour on floodplains along streams without levees may explain the observed pattern. Channel and floodplain hydrologic processes were most strongly connected for unchannelized streams. Unchannelized streams were varied in soil redox potential, water table, and nutrient pools. Vegetation composition reflects both historical hydrologic regimes and disturbances, and thus complex relationships to channel modifications. Results suggest both the subsidy (i.e., nutrient inputs) and the stress of flood events have been altered by anthropogenic activities, but these alterations were greatest in channelized systems compared to unchannelized systems.