Sediment quality assessments frequently report porewater ammonia concentrations that exceed water quality guideline values.Considerable data are available for ammonia in estuarine and marine sediments that represent background porewater concentrations. A review of porewater ammonia concentrations in 322 estuarine/marine sediments in the United States showed a log-normal distribution of data with a mean concentration of
ammonia concentrations (mean ± standard deviation) of 9.0 ± 15 mg total NH3–N/L (10.9 mg total NH3/L) for marine sediments excluding dredged material, and 40.7 ± 38.9 mg total NH3–N/L (49.4 mg total NH3/L) for dredged materials only (Sims and Moore, 1995; Moore et al., 1997).