Alafia River Minimum Flows and Levels - Southwest Florida Water ...

2.4.1.2 Nitrogen
Nitrogen concentrations are most often reported by the USGS as the readily bioavailable
forms; nitrate or nitrate+nitrite. For purposes of this discussion, it was
assumed that total nitrate, dissolved nitrate, and nitrate+nitrite are essentially
equivalent, unless both were reported. In this case, the highest concentration
was used for data analysis. Total Kjeldahl nitrogen, total organic nitrogen,
ammonia nitrogen (also a readily bio-available form) and total nitrogen are not
considered here, because considerably fewer observations were generally made
for these parameters. All nitrogen concentrations are reported as mg/l N.
Although there was not a significant correlation between nitrogen and
phosphorus concentrations, the temporal pattern exhibited by nitrogen suggests
that elevated concentrations seen in the 1970s thru the mid-1980s may be
mining related, since apparently amines or ammonia may be used in the
processing/extraction of the ore. The data show a rather dramatic decline in
concentrations around 1983 (see Figure 2-36), although the 1990 to 1999 mean
concentration of nitrate+nitrite nitrogen of 0.68 mg/l N is still ten times higher than
the 1956 to 1959 mean concentration of 0.06 mg/l N. Analogous to phosphorus,
there has been a substantial decline in inorganic nitrogen concentrations;
however, current concentrations and loadings may still be an order of magnitude
higher than would be expected naturally. It appears that historically nitrogen
concentrations in the Alafia River were as low as those encountered in the
Withlacoochee River (Figure 2-37), where mean nitrate concentration is 0.12
mg/l N.
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