Reprint Series No. 26

NITROGEN EXCHANGE BETWEEN THE SEDIMENTS AND WATER COLUMN IN VEGETATED AND NON-VEGETATED SITES IN PADILLA BAY, WASHINGTON

Nicolle R. Rutherford

March 1997

Bibliographic Citation
Rutherford, Nicolle R. 1997. Nitrogen exchange between the sediments and water column in vegegated and non-vegetated sites in Padilla Bay, Washington. Master of Science Thesis, Western Washington University, Bellingham, Washington . 40 pp. Washington State Department of Ecology (Publication No. 97-110), Padilla Bay National Estuarine Research Reserve Reprint Series No. 26.

Abstract
Nitrogen dynamics between the sediments and water column were compared in cores from vegetated and non-vegetated sites in Padilla Bay, Washington. Sediment cores were incubated, and sacrificed at 0, 6, 12, 24 and 48 hour time intervals to determine changes in ammonium, nitrite+nitrate, and particulate nitrogen concentrations. Ammonium and nitrite+nitrate concentrations were significantly higher in the porewaters than in the water column at both sites. Particulate nitrogen concentrations in the sediments of cores from the vegetated site were significantly higher than those in cores from the non-vegetated site. Over the 48-hour incubation, water column concentrations of ammonium and nitrite+nitrate did not vary significantly in cores from either site. However, in the porewaters, there was a significant increase in ammonium concentrations in cores from the vegetated site, and a significant increase in nitrite+nitrate in cores from the non-vegetated site. These results indicate that the nitrogen transformations within the sediments of the vegetated and non-vegetated sites are different. At the vegetated site, the accumulation of ammonium suggests extensive ammonification, while the accumulation of nitrite+nitrate at the non-vegetated site may be due to nitrification. At both sites, the sediments are acting as a source of nitrogen. However, the role of the sediments and the transformations taking place within them may change depending on the oxidation state of the sediments, the organic loading and distribution, the season, the growth stage of the macrophytes, and the abundance of benthic algae.