Nitrate concentration during seasons

In the equatorial Atlantic, surface nitrate concentrations vary seasonally with the rate of upweUing. Measurable nitrate is present in the east during the boreal summer but apparendy absent year-round in the west (Oudot and Morin, 1987). 

Strong seasonal patterns were evident for NO2 + NO3 and PO4 concentrations (Fig. 18.3). Nitrite -f nitrate concentrations were highest during winter if winter and... 

Fig. 1.8 Pore water concentrations of ammonium (upper panel, NH4+) and phosphate (lower panel, P043") in the Bangrong mangrove forest, Phuket, Thailand during the dry season. Nitrate concentrations were <1 uM. Modified from Holmer etal. (2001).

Nutrient concentration has a marked seasonal variation in the middle Ebro. Nutrient loads transported by the river are relevant during the high flow season (December-April), while nitrate inputs from agriculture can also be relevant. In this period, crop fertilization is carried out, precipitation is higher, and plant nitrogen uptake is lower [37], Although nutrient loads are high, dilution causes NO3 and... 

In contrast, during the low flow season (June-October) important nutrient loads from both point and non-point sources are relevant. Summer irrigation drives nitrate inputs to stream waters [38], The lower dilution capacity of the river causes higher concentrations of nitrate and DOC, as well as an increase in phosphate content with... 

Figure 16. Outflow chemistry from two snowmelt seasons (1986 and 1987) at Emerald Lake, a high-elevation lake in the Sierra Nevada Mountains of California. Maximum N03 concentrations are coincident with ANC minima during the early stages of snowmelt in 1986 and with a rain-on-snow event in 1987. Nitrate episodes are smaller in magnitude than at sites in the eastern United States, hut western lakes may he more susceptible to episodic acidification because they have a lower baseline acid-neutralizing capacity than most eastern lakes. (Reproduced with permission from reference 180. Copyright 1991 American Geophysical Union.)...

We re-visited the issue of water column N distributions to see if we could find distinctive seasonal patterns related to estuarine type, location within an estuary and climate variability (i.e., wet, dry, average inflow conditions). We obtained ammonium (referred to hereafter as NH4), nitrite (NO2), nitrate (NO3), and phosphate (PO4) concentration data from 44 USA estuarine systems. Several locations (e.g., tidal freshwater, oHgohahne, mesohahne, polyhahne) were selected in some systems and in a dozen cases we also obtained concentration data during dry, average and wet years (Frank et al., 2007). 

There have been several subsequent dual isotope fertilizer studies. The high concentrations of NO in shallow groundwater in the Abbotsford aquifer, British Columbia (Canada), were attributed to nitrification of poultry manure, with lesser amounts of ammonium fertilizers (Wassenaar, 1995). A study of denitrification in a riparian zone showed a higher slope ( 0.7) for the relative fractionation of 5 0 to (Mengis et al., 1999). Nitrate from 10 major karst springs in Illinois during four different seasons was found to be mainly derived from nitrogen fertilizer (Panno et al., 2001). 

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). 

In Scandinavia the concentrations of sulphate in precipitation are generally highest during the spring, while the emissions of sulphur dioxide in Europe have a maximum in January (about 2 times the emissions in summer). This delay can be attributed to a precipitation minimum in western Europe during the early spring, and more rapid conversion of sulphur dioxide to sulphate with increased solar radiation. The seasonal variation of the concentration of nitrate in precipitation is similar, but with a longer maximum period ( ). 

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