REGULATED RIVERS: RESEARCH & MANAGEMENT Regul. Riers: Res. Mgmt. 14: 203–216 (1998) NUTRIENT DYNAMICS OF LARGE RIVER FLOODPLAINS ANDREW SPINK a,b, *, RICHARD E. SPARKS b , MARK VAN OORSCHOT a AND JOS T.A. VERHOEVEN a a Department of Plant Ecology and Eolutionary Biology, Utrecht Uniersity, PO Box 800.84, 3508 TB Utrecht, The Netherlands b Illinois Natural History Surey, LTRMP Lab, 704 N Schrader Ae, Haana, IL 62644, USA ABSTRACT A range of river floodplain sites in North America and Europe were investigated, to determine what factors were determining nutrient richness and productivity. A principal component analysis revealed that phosphorus richness of the soil and plant growth were strongly associated with the size of the river and the position of the site, both in relation to the distance to the source of the river and to the river channel. N mineralisation and available P were significantly correlated with river water quality. A phytometer experiment revealed that a large amount of the stress experienced by plants growing on the floodplain was due to other than soil factors, and fertiliser experiments showed that at several of the sites, production was not limited by nutrients. Climatic factors (temperature, latitude) also determine plant production. The hydrological regime that a floodplain is subjected to is a vital factor for determining both nutrient dynamics and plant production, but it is not straightforward to characterise due to the complex and variable nature of the flood pulse. © 1998 John Wiley & Sons, Ltd. KEY WORDS: nutrient dynamics; river floodplains INTRODUCTION Two major theoretical paradigms are used to understand river ecosystems. The river continuum concept (Vannote, 1981) analyses a river in terms of a longitudinal gradient, from its headwaters to the estuary. The position in this gradient is a good predictor of both size of inputs and process rates. By contrast, the flood pulse theory emphasises the position on the lateral gradient of the floodplain. For large river floodplains the distance from the river channel may be a better predictor of process rates than the distance from the source of the river. In the majority of natural ecosystems, nutrients (especially N and P), play a major role in limiting primary productivity. Even in systems such as dune slacks, where another stress (drought) might be expected to be limiting, nutrient additions still cause a change in the vegetation composition and increase in productivity (Willis, 1963). Riverine wetlands stand apart from this generalisation in two respects. First, river floodplains include some of the most productive habitats in the world (Brinson et al., 1981). This is associated with the flood pulse, in that they are frequently inundated with water bearing sediments rich in organic matter and nutrients. Secondly, disturbance (biomass destruction: Grime, 1974) rather than stress (lack of biomass accumulation: Grime, 1974) is a major factor in structuring their communities. The disturbance is disturbance is associated with the flood pulse (Junk et al., 1989). The necessity for adaption to varying flooding regimes is a major evolutionary constraint for floodplain biota. However, it is necessary to distinguish seasonal floodpulses from large infrequent floods. Vegetation is adjusted to seasonal floods (e.g. there is a clear wooded vegetation line at the elevation where the usual flood duration is tolerable to trees), but if an extreme flood occurs then trees are killed and successional processes within the former floodplain forest are reset to an earlier stage (Yin, 1998). * Correspondence to: Maria van Osstraat 13, 6717 TH Ede, The Netherlands. E-mail: aspink@baan.nl Contract grant sponsor: STEP program of the European Union; Short Grant for Exploratory Research (SGER) from US National Science Foundation; Long Term Resource Monitoring Program CCC 0886–9375/98/020203 – 14$17.50 © 1998 John Wiley & Sons, Ltd. Receied 29 August 1996 Accepted 24 Noember 1997