Nitrite maximum

In the water column, ammonification and nitrification can sometimes lead to the formation of subsurface ammonium and nitrite concentration maxima that are usually located toward the base of the euphotic zone in stratified water columns. This is called the primary nitrite maximum. Some of this nitrite is also contributed by releases... 

Depth profiles from the eastern tropical North Pacific (Figure 24.8) show the effects of nitrogen metabolism under 02-deficient conditions. The thermocline is characterized by a sharp decline in O2 concentrations that coincides with increasing nitrate and phosphate concentrations. The oxycline is produced by the respiration of sinking POM under vertically stagnant conditions. Below the oxycline, in depths where O2 concentrations are suboxic, phosphate concentrations continue to increase, but at a slower rate. In contrast, nitrate concentrations decline and reach a mid-water minimum that coincides with a nitrite maximum. The latter is referred to as the secondary nitrite maximum. (At this site the primary nitrite maximum is located at 50 m.)... 

At this site in the eastern tropical North Pacific, denitrification is responsible fiar the midwater loss of nitrate and production of nitrite. The size of the secondary nitrite maximum is dependent on the relative rates of its production from NO3 and its loss via dissimilatory reduction to N2. The amount of nitrate lost to denitrification is shown as the difference between the measured nitrate and the calculated nitrate. The latter was estimated by multiplying the observed phosphate concentrations by the average nitrate-to-phosphate ratio in the three deepest samples (11.9 1.6pmolN/L). Note that the zone of denitrification is restricted to mid-depths, i.e., the depths of the OMZ at this site. 

In suboxic waters, a secondary ammonium maximum can also be present. It typically lies just above the secondary nitrite maximum. This secondary maximum is supported by high rates of ammonification. Because the waters are suboxic, nitrification rates are slow permitting the buildup of ammonium. 

Primary nitrite maximum Subsurface concentration maximum in nitrite found toward the base of the euphotic zone in stratified water columns. Mainly caused by ammonification and nitrification. 

A sharp maximum of nitrite with concentrations of 0.02-0.30 p,M is usually observed at the same level. This maximum is characterized by very large temporal and spatial variability, probably because nitrite is very labile and 2-3-m sampling intervals are comparable to the thickness of the nitrite maximum which, according to our observations, is usually less than 5 m. The increase in ammonium starts at approximately the same depth 00= 15.90-16.00kgm 3) with a vertical gradient of about 0.15-20 pAlnr1. 

Lomas, M. W., and Lipschultz, F. (2006). Forming the primary nitrite maximum Nitrifiers or phytoplankton Limnology And Oceanography 51, 2453—2467. 

Olson, R. J. (1981a). N tracer studies of the primary nitrite maximum. Jouma/ of Marine Research i9, 203-226. 

Ward, B. B., Olson, R. J., and Perry, M. J. (1982). Microbial nitrification rates in the primary nitrite maximum off southern-Califomia. Deep-Sea Research Part A-Oceanographic Research Papers 29,247—255. 

CoUos, Y., and Slawyk, G. (1983). Ammonium and nitrate in the tropical and equatorial Atlantic Relations with the primary nitrite maximum. Mar. Biol. Lett. 4, 295—308. 

Figure 14.3 Vertical sections of (B) temperature, (C) salinity, (D) O2, (E) N02 and (F) NOs", extending from Oman to India, constructed using data collected by the Research Vessels Sagar Kanya andThomas G. Thompson during June-September, 1995. Locations of stations comprising the section are shown in (A) with reference to the secondary nitrite maximum zone (after Naqvi, 1991) and the zone of minimum (Winkler) O2 at 300 m as demarcated by the 0.25 ml L contour (dotted curve) (Wyrtki,1971).

Garfield, P. C., Packard, T. T., Friederich, G. E., and Codispoti, L. A. (1983). A subsurface particle maximum layer and enhanced microbial activity in the secondary nitrite maximum of the northeastern tropical Pacific Ocean. J. Mar. Res. 41, lAl-ld. 

Structure and dynamics of the primary and secondary nitrite maximum layers... 

Figure l6.11 Vertical distributions of Chlorophyll a, [N02 + NOs ], and [N02 ] for the water column at Station ALOHA in October 1992. The conspicuous N02 maximum beginning at approximately 100 m is positioned below the deep Chlorophyll a maximum layer (DCML) and is coincident with the top of the nitracline.This primary nitrite maximum (PN M) is further divided into upper and lower regions (UPNM and LPNM, respectively) with a tailing of the LPNM. These m or features are the result of competing microbiological N02 production and utilization processes as shown in Fig. 16.2. From Dore and Karl (1996b).

Figure 16.12 Temporal and spatial (depth) variations in the primary nitrite maximum layer at Station ALOHA. (A) Shown are five representative profiles of NO2 between 80 and 200 m from February 1990 to September 1992 displayii the two-peaked structure (U = UPNM and L = LPNM) of the general feature. Note concentration variations and changes in reference depths of the key features. A = February 1990, B = July 1990, C = December 1990, D = October 1991, E = September 1992. From Dore and Karl (1996b). (B) Temporal variations in the positions of the UPNM and LPNM relative to the nitracline. Shown also are the mean depths for these features over the observation period. From Dore and Karl (1996b).

Nitrites Maximum Contaminant Level (MCL) and Maximum Contaminant Level Goal (MCLG) limits have been determined as 1 mg/L each by the Environmental Protection Agency (EPA). Infants below the age of six who drink water containing nitrite in excess of the MCL could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue baby syndrome. 

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