Temporal variability in nitrification rates and related biogeochemical factors in Monterey Bay, California, USA

Abstract

The scales of temporal variability in the rate of ammonium oxidation and a suite of related biogeochemical parameters were investigated in the surface layer of the water column of Monterey Bay, California, on the west coast of the USA. Samples were collected on bimonthly (approx. every 2 mo) cruises during the course of 2 yr. The signal of El Niño was evident in the water column temperature and nitrate distributions during the initial cruise in February 1998. Throughout the 2 yr period, variation in temperature and salinity was small and consistent with seasonal upwelling. The biological parameters, however, varied much more than might have been predicted by the minimal variability in hydrographic signals. Ammonium assimilation rates, chlorophyll a concentrations and bacterial abundance varied by 41-, 65-and 147-fold, respectively. Ammonium oxidation rates often exhibited a subsurface maximum near the bottom of the euphotic zone, and varied by a factor of 4.5 over the 2 yr study. The presence of the rate maximum was not obviously related to the dominant seasonal signals of hydrography or to other biological variables. Nitrification rates were much less variable in the bay than in Elkhorn Slough, a small estuary that opens onto the bay. The small variability in ammonium oxidation rates may be related to more dynamic responses in the community composition of the ammonia-oxidizing bacteria. Different groups of ammonia-oxidizing bacteria were detected as dominants in clone libraries from the Monterey Bay and Elkhorn Slough. The time scale of bimonthly sampling was evidently inadequate to resolve the response of nitrification rates to direct physical forcing in the bay.

Differential contributions of archaeal ammonia oxidizer ecotypes to nitrification in coastal surface waters

“…The inability to measure rates of 15 NH 4 oxidation in some highly productive surface waters is most likely related to the intense competition for ammonia and nitrate by phytoplankton during periods following upwelling (Kudela et al, 1997;Kudela and Dugdale, 2000). Measured nitrification rates in MB surface waters ranged from 0.03 to 69 nmol l À 1 day À 1 (Figure 2), consistent with those reported previously (Ward, 2005). No statistical differences were evident in average rates for each sampling period (F 1,40 ¼ 1.76, P ¼ 0.19; Table 1).…”

“…In our data sets of amoA genes and nitrification, there is good representation over the range of typical values observed in coastal surface waters (Ward, 2005;Mincer et al, 2007;Beman et al, 2008;Santoro et al, 2010). Consistent with our finding that their abundance alone can explain observed rates of nitrification in surface waters of MB, a direct relationship between WCA amoA genes and nitrification rates was observed (Figure 4).…”

“…All of these point toward nitrification rates being maximal deeper in the euphotic zone, where phytoplankton growth and light intensities are lower (Ward, 2005). No relationship between nitrification rates and ammonium concentrations was observed (Supplementary Table S1).…”

Molecular and biogeochemical evidence for ammonia oxidation by marine Crenarchaeota in the Gulf of California

“…However, 15 NH 4 þ oxidation rates measured in the Guaymas and Carmen Basins are in line with previously reported rates from the ETNP and elsewhere in the Pacific: Sutka et al (2004) found maximum rates of 24.7 nmol N l À1 day À1 at 65 m depth in the ETNP, whereas Ward and Zafiriou (1988) measured rates of approximately 20 nmol N l À1 day À1 in the ETNP near the mouth of the GOC. 15 NH 4 þ oxidation rates ranged from 20 to 80 nmol N l À1 day À1 in the Monterey Bay and were not related to AOB diversity (Ward, 2005), whereas rates ranged from 1.0 to 137.4 nmol N l À1 day À1 at station ALOHA (Dore and Karl, 1996). In the GOC, maximum 15 NH 4 þ oxidation rates were greater in the Guaymas Basin (93.1 versus 39.4 nmol N l À1 day À1 ), and the depth profiles from these basins were distinct: 15 NH 4 þ oxidation rates increased gradually and plateaued in the Carmen Basin, whereas rates peaked sharply and declined in the Guaymas Basin (Figures 5c and h).…”

Planktonic and whole system metabolism in a nutrient-rich estuary (the Scheldt estuary)

“…Several authors have stated that CR is likely to be enhanced in the presence of light (Grande et al 1989b;Martinez 1992;Langdon et al 2003) although such observations were not always corroborated (Grande et al 1989a,b). NIT has been found to be inhibited by a factor of 40% to 50% in light (Horrigan and Springer 1990;Ward 2005). In the Scheldt estuary, the euphotic zone (1% surface irradiance) is very shallow due to high SPM concentrations and does not represent a major portion of the water column.…”