The effects of drying and re-flooding on the sediment and soil nutrient dynamics of lowland river-floodplain systems: A synthesis

Lowland river-floodplain systems are characterized by a high degree of vari ability in both the frequency and period of inundation of various parts of the floodplain. Such variation should profoundly affect the processes under lying nutrient transformations in these systems. This paper explores the ef fect of various hydrologic regimes on nutrient cycles. Partial drying of we t (previously inundated) sediments will result in an increased sediment aff inity for phosphorus and will produce a zone for nitrification coupled with denitrification. Hence, partial drying may reduce the availability of nitr ogen (N) and phosphorus (P). Conversely, complete desiccation of sediments may lead to the death of bacteria land subsequent mineralization of N and P ), a decrease in the affinity of P for iron minerals, a decrease in microbi al activity and a cessation of all anaerobic bacterial processes (e.g. deni trification). Colonization of exposed sediments by terrestrial plants may l ead to N and P moving from the sediments to plant biomass. Re-wetting of de siccated soils and sediments will result in an initial flush of available N and P (which can be incorporated into bacterial or macrophyte biomass), co upled with an increase in bacterial activity, particularly nitrification. I nundation of floodplain soils will result in the liberation of C, N and P f rom leaf litter and floodplain soils. This will result in an increase in pr oductivity, which ultimately may lead to the onset of anoxia in floodplain soils and, consequently, an increase in anoxic bacterial processes such as P release and denitrification. Copyright (C) 2000 John Wiley & Sons, Ltd.