Nitrogen cycling in salt-marsh and mangrove sediments at Western Port, Victoria

Abstract

The metabolism of organic nitrogen compounds in sediments from salt-marsh (Sarcocornia quinqueflora) and mangrove (Avicennia marina) areas at Western Port, Victoria, was investigated. Organic nitrogen compounds were metabolized at potential rates of up to 3.9 µmol cmF3 day^-1 for amino acids, 23 µmol cm^-3 day-( for dipeptides, and 5 µmol cm^-1 day^-1 for an amide. These were higher than the rate of ammonium regeneration in the absence of added substrate (<0.08 µmol cm^-3 day^-1); this indicates that organic nitrogenous compounds play a major role in nutrient cycling in coastal sediments. Rates of some transformations were highly correlated with sediment organic-matter content, total nitrogen content or concentration of soluble reactive phosphorus in the sediments, but overall there were few significant correlations between metabolic rates and edaphic conditions. Degradation of organic nitrogenous compounds in these sediments is likely to be influenced strongly by the availability of phosphorus, the quantity and quality of detrital inputs, and the size and activity of microbial populations.