Nitrogen budgets in relation to microbial transformations in lakes

• Published in: Ambio Vol. 23; no. 6; pp. 367 - 377
• Main Authors: Ahlgren, I. (Uppsala Univ. (Sweden). Limnologiska Inst.), Soerenson, F, Waara, T, Vrede, K
• Format: Journal Article
• Language: English
• Published: Royal Swedish Academy of Sciences 01-09-1994
• Subjects: Amino acids; AZOTE; Bacteria; Bacterioplankton; CARGA CONTAMINANTE; CHARGE POLLUANTE; DENITRIFICACION; DENITRIFICATION; EUTROFIZACION; EUTROPHICATION; EUTROPHISATION; LAC; LAGOS; LAKES; Nitrates; NITRIFICACION; NITRIFICATION; NITROGEN; NITROGENO; Phytoplankton; POLLUTANT LOAD; Quaternary ammonium compounds; Sediments; SUECIA; SUEDE; SWEDEN
• ISSN: 0044-7447; 1654-7209

Microbial nitrogen fluxes were measured in two eutrophic lakes and compared with nitrogen budgets based on measurements of inflows to and outflows from the lakes. Phytoplankton primary production was largely dependent on regenerated nitrogen and ammonium was the preferred form. Pelagic bacteria could satisfy their need for nitrogen by uptake of dissolved free amino acids during most of the year and also contributed considerably to the regeneration of inorganic nitrogen. Microbial denitrification of nitrate to molecular nitrogen and permanent retention in the sediments are the most important pathways of nitrogen loss from aquatic ecosystems. Estimates of denitrification in lake sediments were made using14N-nitrate as a tracer and measurement of the partition of14N and15N in the formed dinitrogen gas, and were compared with estimates based on budget calculations. The two methods gave rates of the same order of magnitude. The source of the denitrified nitrate was mainly simultaneous nitrification of ammonium. Annual denitrification losses were 5-25% of the external nitrogen loading, which is in the lower range ot rates previously reported from lakes. Permanent retention of nitrogen in the sediments of the lakes was 14-33% of the external loading.