Effect of Coastal Upwelling on Nitrogen Regeneration from Sediments and Ammonium Supply to the Water Column in Concepcion Bay, Chile

Abstract

Ammonium regeneration was studied in sediments collected from two stations located in Concepcion Bay, Chile, a semi-enclosed and shallow system. This system is under the effects of the coastal upwelling processes for about 57% of every year. To understand the importance of the benthic system in ammonium dynamics, quantification is required of, at least, detrital inputs (with sediment traps), ammonium recycling rates (using experimental incubations of intact sediment cores), and ammonium loss through burial in the sediment column. The mean annual ammonium flux of 3·41 mmol m −2day −1is comparable to the estimated benthic flux in very high productivity areas. The sediment thus constitutes an important ammonium source for the water column with respect to other sources, such as inputs from salt marshes, rivers and shelf waters. Seasonal variation in ammonium fluxes reflects the seasonality in macrofaunal activity, detrital inputs to the sediment–water interface, and the oxygen content of bottom water. These variables are enhanced in summer and may be an effect of the upwelling process. Ammonium benthic flux measurements and calculated burial rates are utilized to estimate the nitrogen budget of the sediments in the two stations studied. Approximately 76–83% of total nitrogen is regenerated as a product of the remineralization of organic matter produced during upwelling events which settles onto anoxic sediment.