Rates of nitrification and carbon uptake in the Rh�ne River plume (northwestern Mediterranean Sea)

Abstract

Nitrification rates were measured along a salinity gradient in the Rhône River estuary, using specific inhibitors (allylthiourea and chlorate) coupled with the measurement of change in nitrite concentration and inorganic carbon uptake by nitrifiers. Rates of ammonium and nitrite oxidation were similar up to 15 practical salinity units (from 1 to 2 μmol N oxidized liter(-1) day(-1)). For higher salinities, nitrite and ammonium oxidation rates were 0.14 and 0.23 μmol N oxidized liter(-1) day(-1), respectively. Ammonium oxidizers assimilated 19-150 × 10-3 μmol C liter(-1) day(-1), while nitrite oxidizers fixed 4.8-72.6 × 10-3 μmol C liter(-1) day(-1). The amounts of nitrogen oxidized and C incorporated demonstrated a linear correlation (r (2) > 0.99). The ratio of N oxidized to C incorporated ranged between 14.3 to 12.3 for ammonium oxidizers, and between 31.6 and 29 for nitrite oxidizers, the lower values being measured in seawater.

Community metabolism and nutrient cycling in the Mississippi River plume: evidence for intense nitrification at intermediate salinities

“…The distribution of DIN concentrations and nitrification rates across the Rh6ne River plume salinity gradient (Feliatra & Bianchi 1993), however, differ m many respects from those observed in the Mississippi River plume during the present investigation. Concentrations of NH4+ (9.83 pM), NO2-(3.85 pM), and NO3-(1 12.8 pM) were highest in the Rh6ne River and decreased with increasing salinity (Feliatra & Bianchi 1993). Highest rates of nitrification were also observed in the Rh6ne River and declined with increasing salinities.…”

Nitrification in the euphotic zone as a source for nitrite, nitrate, and nitrous oxide at Station ALOHA

“…However, note that the highest rates observed at Station ALOHA on each cruise were found below 150 m, whereas the deepest sample assayed by Olson (198 la) was from 148 m; above 150 m the two data sets exhibit a fair degree of similarity. Nitrification rates of >200 pmol m-3 d-l have been measured or estimated in other, less oligotrophic marine environments (Ward 1982;Pris-CU and Downes 1985;Feliatra and Bianchi 1993), whereas the farthest offshore stations examined in nitrification studies of the Southern California Bight (Olson 198 1 a) and off the coast of Washington (Ward et al 1984) exhibited ammonium oxidation rates in the PNM of up to 20 pmol m-3 d-l. We think that we are converging on lower euphotic zone nitrification rates representative of the central gyre habitat.…”

“…This large range probably reflects both a lack of obligate coupling between the oxidation of ammonium and carbon fixation in nitrifying bacteria and a varied response of nitrifiers to different environmental parameters. We have adopted the lower value of 8.3 (Billen 1976) because of the observation by Feliatra and Bianchi (1993) that nitrifiers in seawater generally have the lowest N : C when compared to nitrificrs in other natural aquatic environments.…”

Comparison of nitrifier activity versus growth in the Scheldt estuary—a turbid, tidal estuary in northern Europe

“…It is questionable whether these ratios are applicable in nature where environmental conditions as well as bacterial populations and composition are variable. Factors such as temperature (Bianchi et al 1997), salinity (Feliatra & Bianchi 1993), oxygen concentrations (Carlucci & McNally 1969, Goreau et al 1980, and substrate availability (Belser 1984) can affect the N:C ratio. The assumption that slow-growing nitrifiers (Helder & de Vries 1983) have a conversion factor similar to nitrifiers under optimal growth conditions, in such a heterogeneous and highly variable system as an estuary, is quite possibly erroneous.…”