Ammonium regeneration in eutrophicated coastal waters of Sweden

Abstract

Rates of ammonium regeneration were measured in the Kattegat and Laholm Bay, a shallow, eutrophicated embayment in the southeastern Kattegat. Over the year, average rates in the central outer part of Laholm Bay were 51 nmol 1-' h-' and near the outlet of the River Nissan 49 nmol 1-' h-'. Elevated rates were observed during the peak of the spring bloom, and rates increased with depth throughout spring (contrary to autumn, when rates decreased with depth). Die1 variations were more pronounced in March (wlth rates during night and early morning 7 times higher than those in the evening) than in September when variations were within the error of the method. Rates measured during autumn in the central outer part were 2.5 times h g h e r than in spnng. Correcting these for the observed die1 variations resulted in 1.5 times higher rate of ammonium regeneration during autumn. In a transect extending outwards from the River Nissan, a positive correlation between the recycling factor (r) and the ammonium regeneration rate was found, even if the ammonium regeneration contributed only to part of the ammonlum uptake (due to allochthonous ammonlum input from the river) Ammonium regeneration rates (R) were generally found to exceed those of ammonium uptake (U), resulting in ratios of U: R being < 1, and should be considered as potential rates.