Aspects of nitrogen and carbon cycling in the northern Bering Shelf sediment. I. The significance of urea turnover in the mineralization of NH4+

Abstract

The impact of macrofauna on nitrogen and carbon mineralization was investigated in sediment of the shallow water Bering Sea Shelf. The main effort was focused on the probable role of macrofauna in the production of urea and the significance of urea turnover in the production of NH,+ Macrofaunal biomass was regulated by the quality and quantity of organic nitrogen available for degradation. This was illustrated by a low macrofaunal biomass in the sediment underlying the low productive Alaska Coastal water and a high macrofaunal blornass below the highly productive Bering Shelf/Anadyr water. A high macrofaunal biomass was correlated with high rates of urea gross production, high concentrations of urea and NH,+, and high sediment-water exchange rates of urea and NHdf. Based on a conceptual model of nitrogen mineralization in the Bering Shelf/Anadyr sediment, it was suggested that urea hydrolysis could b e responsible for u p to 80 % of the gross production of NH4+ The model intimated that a substantial part of the NH4+ produced (44 %) could have been cycled within the sediment.

Benthic algae control sediment—water column fluxes of organic and inorganic nitrogen compounds in a temperate lagoon

“…Lomstein et al 1998). The same variability has been found in deeper estuaries, where in some cases DON was an important component of the TDN efflux (Lomstein et al 1989;Blackburn et al 1996) and in others it was small or insig- Comparison between light and dark (A) sediment fluxes and (B) macroalgal uptake/release of dissolved nitrogen. Error bars ϭ SE; n ϭ 72 each for light and dark for all measurements except amino acids, where n ϭ 60.…”

“…Measurements of bulk DON, however, mask the dynamics of individual compounds, which vary widely in molecular weight and bioavailability (Burdige and Zheng 1998). For example, bioavailable compounds such as amino acids and urea may make up a significant portion of the DON pool and contribute to the benthic flux of DON (Boucher and Boucher-Rodoni 1988;Lomstein et al 1989;Burdige and Zheng 1998). In addition, these small, labile organic compounds may represent an important source of N for both heterotrophic and autotrophic microorganisms, as well as for benthic plants (Jorgensen 1982;Admiraal et al 1984;Lomstein et al 1989;Keil and Kirchman 1993;Nilsson and Sundback 1996;Rondell et al 2000).…”

“…For example, bioavailable compounds such as amino acids and urea may make up a significant portion of the DON pool and contribute to the benthic flux of DON (Boucher and Boucher-Rodoni 1988;Lomstein et al 1989;Burdige and Zheng 1998). In addition, these small, labile organic compounds may represent an important source of N for both heterotrophic and autotrophic microorganisms, as well as for benthic plants (Jorgensen 1982;Admiraal et al 1984;Lomstein et al 1989;Keil and Kirchman 1993;Nilsson and Sundback 1996;Rondell et al 2000). In the work presented here, we investigated the role of the two dominant groups of benthic primary producers, macroalgae and microalgae, in regulating sedimentwater column exchanges of DIN, bulk DON, and specific labile DON compounds (dissolved free and combined amino acids [DFAA, DCAA], urea) in Hog Island Bay, a shallow lagoon on the Virginia coast.…”

Biogeochemical processes and nutrient cycling within an artificial reef off Southern Portugal

“…Artificial reef structures enhance settlement of organic matter in the seabed with the biological and chemical degradation of dead plants and animals leading to benthic remineralization (Ambrose & Anderson, 1990;Lomstein et al, 1989;Rizzo, 1990 reported in a study on a benthic-pelagic coupling system, indicating that fresh organic input result in benthic activity enhancement (Gutiérrez et al, 2000). As animal metabolic activities and decomposition processes may be transforming larges quantities of particulate nitrogen into dissolved-reduced forms (Dame et al, 1986), the extremely low levels of organic nitrogen found in the seabed beneath the reef may be due to rapid turned over of nitrogen..…”

In situ soft sediment nutrient enrichment: A unified approach to eutrophication field experiments

“…We used Nutricote® N (70 d, 40-0-0 N:P:K), a controlled release coated urea fertiliser containing no phosphorus, potassium or trace elements. A nitrogen-only fertiliser was used since it is typically the limiting nutrient in these systems, and urea quickly hydrolyses to ammonium (NH 4 + ) (Lomstein et al, 1989), the most common form of nitrogen in New Zealand estuaries (Tay et al, 2013). Fertiliser was applied to each plot in a series of 20 evenly spaced 3 cm diameter 15 cm deep holes made in the sediment using a hand held corer.…”