Production and dynamics of salt marsh vegetation and the effects of experimental treatment with sewage sludge. Biomass, production and species composition.
Fertilization with a 10-6-4 sewage sludge fertilizer increased the total peak standing crops of salt marsh vegetation, in spite of the presence of considerable amounts of heavy metals and chlorinated hydrocarbons in the sludge. Increases in standing crop were detected in the second year of treatment and remained for three years of treatment. The increases in biomass are believed to be due to the nitrogen additions. Spartina alterniflora, which was the dominant species in low marsh areas, progressively excluded Salicornia spp. from the fertilized plots after an initial increase of Salicornia. In high marsh areas, fertilization initially increased the standing crop of Distichlis spicata but this was later replaced by Spartina patens. S. alterniflora did not respond to fertilization in the high marsh. The amount of dead matter in both high and low marsh was highest in the fall, after death of the sward, and decreased slowly to a low point in midsummer. The amount of dead matter was never equal to peak live biomass, implying decomposition or tidal export. The production achieved by the most heavily fertilized plots are among the highest recorded for marsh plants, except that of tall form S. alterniflora in exceptionally favourable sites. The treatments have converted low marsh vegetation, consisting mainly of dwarf form S. alterniflora, into a sward approaching the biomass and morphology of tall form. The so-called 'forms' are thought to be a response to nitrogen supply.