AMMONIA VARIATION IN SEDIMENTS - SPATIAL, TEMPORAL AND METHOD-RELATEDEFFECTS

In aquatic systems, ammonia is a common nutrient and pollutant that or iginates from both natural and anthropogenic sources. The effects of s ediment and pore-water collection methods, and sediment spatial and te mporal variability on ammonia concentrations, were evaluated. Sediment and pore-water collection methods included grab sampling with an Ekma n dredge and hand corer followed by centrifugation, in situ suction, a nd in situ peeper methods. Samples were collected from three sites ove r a period of several months, with site replicates spaced from 30 to 6 0 cm and from 6 to 9 m apart. Pore-water ammonia concentrations differ ed significantly between the collection methods on most occasions. Amm onia concentrations were highest in the Ekman and corer pore-water sam ples as compared to the in situ pore waters collected from the peepers and by suction. Spatial heterogeneity in sediment ammonia concentrati ons was significant and generally increased with distance. Seasonal fl uctuations in ammonia concentrations were evident, with high values in warmer months. Storage effects were observed with pore water ammonia over a 1- to 4-week period. Results show that collection methods and n atural variability contribute significantly to measured ammonia concen trations and are important considerations in aquatic ecosystem assessm ents.