Biomass production in pioneer Spartina anglica patches: Evidence for the importance of seston particle deposition

Salt marsh formation can be initiated by the colonization of bare tidal fla ts by pioneer halophytes such as Spartina anglica. In the present study, gr owth of S. anglica in the edge and centre zones of pioneer patches colonizi ng a tidal flat in a marine bay in the south-west Netherlands was investiga ted. Average biomass and shoot length was significantly lower in centre zon es than in edge zones of the patches. Multiple linear regression showed tha t 84% of the variance in aboveground biomass in the centre zones could be e xplained by sediment phosphorus and nitrogen concentrations. No such relati onship existed in the edge zone. This suggests that biomass production in t he centre zones of the patches is nutrient limited, but that factors other than sediment nitrogen and phosphorus content determine growth of Spartina in the edge zones. The sediment nitrogen and phosphorus concentrations in the centre zones of the patches were significantly related with sediment carbon concentrations, indicating that the pool of particle-bound nutrients in the sediment to an important extent is associated with organic particles. Determination of st able carbon isotope signatures of the sedimentary organic matter showed tha t an increasing carbon content of the sediment in the centre zone of the pa tches land a rise in plant biomass) coincides with a higher contribution of non-Spartina derived carbon to the sedimentary organic matter pool. Sustai ned biomass production in the centre zones of the patches, thus, probably d epends on deposition of allochthonous organic particles and the nutrient in puts inherent in this process. Due to the construction of large-scale hydro -engineering works, however, conditions for deposition of waterborne partic les are currently unfavourable. The consequences of reduced carbon and nutr ient inputs into the patches will be particularly in the (older) centre zon es, where the nutrient pools in non-refractory organic matter have been dra ined in the years of previous growth. Accordingly, it is hypothesized that the canopy-enhanced sedimentation for which Spartina is well-known, via pos itive feed-back effects on plant growth can be crucial for plant vitality, and, hence, for successful colonization of unvegetated areas. (C) 1998 Acad emic Press.