|
<br />Table 6, Concentrations of biologically available nitrogen and phosphorus and N:P values for Pueblo Reservoir, 1987
<br />and 1989
<br />[N, dissolved-inorganic nitrogen: P. dissolved orthophosphorus: N:P. mass ratio of dissolved-inorganic nitrogen and dissolved orthophosphorus; II
<br />mgIL, milligrams per liter; <. less than: >. greater lhan; --, missing dalal
<br /> Sampling slle 1
<br /> Sample 3B 5C 7B
<br /> period N P N P N P
<br /> (mgIL) (mgIL) N:P (mgIL) (mgIL) N:P (mgIL) (mgIL) N:P
<br /> 1987
<br />Aprit 0.35 0,019 18 0.25 0,009 28 0.006
<br />May ,21 .024 8.6 .034 dXlI >34 0,058 <,001 >58
<br />June .079 .009 8.8 .032 <,OOt > 32 .076 <.001 >76
<br />July ,11 ,017 6.6 ,050 <,001 > 50 ,034 ,017 2.0
<br />August ,059 <.001 >59 .034 <,001 > 34 ,033 <,001 > 33
<br />September ,021 <,001 > 21 ,041 <.001 >41 ,045 <,001 >45
<br />October ,070 <.001 >70 ,38 ,013 29 .10 ,001 102
<br /> 1989
<br />May .096 .025 3.8 .17 .016 It .22 ,018 12
<br />June .15 ,013 12 ,15 ,001 146 .15 ,012 13
<br />August .20 ,020 10 ,064 ,005 13 ,t7 ,005 33
<br />September ,070 ,02t 3,3 ,t5 ,Ot6 9.4 ,32 .014 23
<br /> I Sampling site location shown in plate I.
<br />34 Physical, Chemica', and Biological Chersctenatlc. 01 Pueblo Raservolr, Colorado, 198H9
<br />
<br />....,... '''''I
<br />."J' ,.... .
<br />...1,).) .!
<br />able approximate boundary for defining the potential
<br />limiting nutrient" (Ryding and Rast, 1989).
<br />
<br />None of the water samples collected in 1987 and
<br />1989 at sampling sites 3B, 5C, and 7B had cumulative
<br />concentrations of dissolved ammonia and dissolved
<br />nitrite plus nitrate less than the growth-limiting level
<br />for phytoplankton, 0,020 mgIL (table 6). Thirty-six
<br />percent of the samples for site 3B, 73 percenl of the
<br />samples at site 5C, and 64 percent of the samples at
<br />site 7B had dissolved-orthophosphate concentrations
<br />less than or equal to the growth-limiting levels for phy-
<br />toplankton, 0.010 mgIL (table 6). Values for N:P
<br />ranged from 2 to 146 for the 32 samples collected
<br />(table 6). Several N:P values are reported greater than
<br />the reported value because the orthophosphate concen-
<br />trations were reported as less than the level of detec-
<br />tion. At site 3B, 8 of the II samples collected had N:P
<br />values greater than 8, the level at which phosphorus
<br />may be a limiting nutrient to phytoplankton growth.
<br />All II samples collected for site 5C had N:P values
<br />larger than 8. At site 7B, 9 of the 10 samples collected
<br />had N:P values larger than 8, The large percentage of
<br />phosphorus concentrations less than the growth-
<br />limiting level and the large percentage of N:P values
<br />greater than 8 indicate that phosphorus concentrations
<br />
<br />in Pueblo Reservoir commonly are present at levels
<br />that may potentially limit phytoplankton growth. In the
<br />samples collected, nitrogen concentrations do not seem
<br />to be potentially limiting for phytoplankton growth.
<br />
<br />Trace Elements
<br />
<br />Trace elements occur in relatively small concen-
<br />trations (commonly less than I mgIL). Trace-element
<br />concentrations were analyzed from water samples col-
<br />lected near the reservoir surface and near the reservoir
<br />bottom. Concentrations of trace elements in Pueblo
<br />Reservoir can be affected by concentrations entering
<br />the reservoir from the Arkansas River, by settling of
<br />suspended sediment from the water column, by mobili-
<br />zation of trace elements from the bottom sediments,
<br />and by biologically mediated reactions. Additionally,
<br />Goldman and Home (1983) reported that the absolute
<br />and biologically available quantities of many trace ele-
<br />ments are subject to spatial and temporal variations as
<br />a result of variations in the physiochemical environ-
<br />ment of the water column.
<br />
<br />A statistical summary of total-recoverable and
<br />dissolved trace-element concentrations in Pueblo Res-
<br />
|