Nitrate depth profiles

Sampling sites are also referred to as station locations. For water column work, depth profiles are constructed from seawater samples collected at representative depths. Temperature and salinity are measured in situ with sensors. Remote-closing sampling bottles deployed from a hydrowire are used to collect water for later chemical analysis, either on the ship or in a land-based laboratory. The standard chemical measurements made on the water samples include nutrients (nitrate, phosphate, and silicate), dissolved O2, and total dissolved inorganic carbon (TDIC) concentrations. 

Representative euphotic zone depth profiles of DIN ( j,MN) in waters where ammonium was present. Shown are concentrations of nitrate, nitrite, and ammonium. The SUPREA cruise was conducted in August-September 1978 in the equatorial Atlantic Ocean off the Ivory Coast. 

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.)... 

A notable example of a ooastal system in which intense denitrification occurs seasonaiiy is the west Indian shelf and inshore waters, in this setting, denitrification has been observed to oompletely remove ali nitrate and nitrite, enabiing suifate reduction to proceed. Water column depth profiles documenting the spatiai and temporai deveiopment of these conditions are provided in the supplemental information for Chapter 24.4.5 that is available at http //elsevierdirect.eom/companions/97801230885305. 

Figure 28-1 Depth profile of nitrate in sediment from freshwater Lake Spbygard in Denmark. A similar profile was observed in saltwater sediment. Measurements were made with a biosensor containing live bacteria that convert N03 into N20, which was then measured amperometrically by reduction at a silver cathode. [From l h. Larsen, i Kjosr. and N. P. Revsbech. A Microscale NO Biosensor for Environmental Applications," Anal- Chem. 1997, <59.3527.]... 

Pickens et al. (1978) worked on nitrate contamination in wells drilled in a shallow sandy aquifer. An N03 plume was detected in carefully sampled depth profiles (section 7.3), as shown in Fig. 16.1. The contamination was attributed to extensive use of nitrate fertilizers. 

From the above, make a list of compounds that are introduced into the ground along with each type of applied fertilizer (e.g., K, S04). These compounds should be analyzed, along with nitrate, in accessible wells in depth profiles of the type shown in Fig. 16.1. 

Figure 1 Depth profiles of (a) XCO2, (b) dissolved CO2, (c) silicic acid, (d) nitrate, and (e) phosphate from the Indian Ocean (27° 4 S, 56° 58 E GEOSECS Station 427) (source Weiss et al, 1983).

Depth profiles of cell densities in the photic zone generally show E. huxleyi to live within the mixed layer. Cortes et al. (2001) studied the seasonal depth distribution of coccohthophorid species off Hawaii. Sampling showed that the main production occurred in the middle photic zone (50-100 m), which lay within the mixed layer for most of the year. While the depth of maximum E. huxleyi density varied during the annual cycle, it generally lay between the shallowest sampling level (10 m) and 100 m. Depth profiles off Bermuda (Haidar and Thierstein, 2001) found that maximum densities of E. huxleyi were nearly always shallower than 100 m, and more commonly within the upper 50 m. The highest cell densities for E. huxleyi recorded were at 1 m depth in March, after the seasonal advection of nitrate into the mixed layer. Seven years of water-column particulate data off Bermuda confirm that alkenone concentrations in the surface mixed layer are 2-4 times higher than in the deep fluorescence maximum at 75-110 m (Conte et al., 2001). 

Figure 8 Depth profile of O2, bio-available phosphorus (SRP), nitrate (NO3), and anunonium (NH4, 1990 only) concentrations in February 1961 and March 1990 during Lake Victoria stratification (reproduced by permission of E. Schweizerbart Science Publishers from Verh. Int. Ver. LimnoL, 1993, 25, 39-48).

Figure 6. Time-series depth profiles of ammonium, nitrate, and temperature in the inshore region (Stations 47, 55, 58, 62, 69, and 70) and the offshore region (Stations 48, 56, 59, 67, and 71) between Long Point and Whites Point off Los...

Figure 3 Depth profiles for nitrate and filterable concentrations of trace element nutrients (iron, zinc, and cobalt) in the subarctic North Pacific Ocean (ocean station Papa, 50.0°N, 145.0°W, Aug. 1987). Data from Martin JH, Gordon RM, Fitzwater S, and Broenkow WW (1989) VERTEX Phytoplankton/iron studies in the Gulf of Alaska. Deep-Sea Research 36 649-680.

As exemplified by the silicate profile, all biolimiting elements do not behave identically. In the case of dissolved silicon and TDIC, their concentration maxima lie below the nitrate and phosphate maxima. This reflects the different mechanisms by which the elements are resolubilized. Nitrate and phosphate are regenerated from soft parts. This process seems to occur more readily than the dissolution of hard parts, which releases silicate causing the nitrate and phosphate concentration maxima to lie at shallower depths. Since TDIC is released in nearly equal amounts from soft parts as CO2 and the dissolution of calcareous hard parts as CO3, the resulting concentration maximmn lies below that of nitrate and phosphate. 

Pore-water nitrate profiles in marine sediments typically show one of three profile shapes. In sediment with rapid rates of organic matter oxidation relative to rates of solute supply from the overlying water, both oxygen and nitrate concentrations decrease more or less exponentially from overlying water concentrations at the sediment—water interface to zero, with oxygen depletion preceding or simultaneous with nitrate depletion at shallow sediment depth (see 105 m and 440 m profiles in Fig. 6.12). These types of profiles are common in continental shelf and upper slope sediments, and are due to relatively large carbon rain to the sediments (relatively... 

---