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Examples Of Organic N Measurements

Soluble organic-N is sometimes a significant fraction of total soluble N (Figure 1).


             Figure 1. Soluble organic and planktonic N in Lake Mendota, Wisconsin


The relative amounts of particulate and dissolved organic N vary considerably for different water bodies and for the same water body with location, depth, and time (Table 1).


Table 1. Ranges of particulate and dissolved organic N
in several lakes
(Data from Wetzel 1975)

          Lake
Particulate Organic
N (g N/L)

Dissolved Organic
N (g N/L)

Furesø, Denmark
Ysel, Netherlands
Bodensee, Germany
Lucerne, Switzerland
Rotsee, Switzerland
Wintergreen, Michigan
Lawrence, Michigan
       30-190
       250-1400
       10-160
       70-390
       180-1200
       50-2350
       20-110
     440-640
     590-1840
     50-150
     80-180
     270-660
     500-1320
     80-240

Dissolved organic N concentrations are usually a small fraction of dissolved organic C concentrations (DOC) (Table 2).


Table 2. Median concentrations of dissolved total
amino acids.
(Thurman 1985)


Concentration (g N/L)*
% DOC**
Seawater
Ground Water
Streams
Lakes (oligotrophic)
Lakes (eutrophic)
Marshes
Sediment Interstitial
    Waters
   50 (20-250)
   50 (20-305)
   300 (50-1000)
   100 (30-300)
   600 (300-6000)
   600
   2000 (500-10,000)
     2-3
     2-3
     2-3
     2-3
     3-13
     4
     2-4
Notes: * Ranges in parentheses.
** Calculated assuming 100 g/L = 1 mol/L.



Organic N made up 10-20% of the total N (soluble + particulate) in the Sangamon River, near Monticello, IL (Figure 2) (Demissie and Keefer 1996).


      Figure 2. N Species in the Sangamon River



The relative amounts of particulate and dissolved organic N vary considerably for different water bodies and for the same water body with location, depth, and time. Table 1 presents particulate and dissolved organic N in several lakes.

The relative amounts of organic N and inorganic N species in ground water depend on many factors, including land use, aquifer hydraulic properties, and redox conditions. Table 4 presents concentrations of NO3-, NH4+, and TKN in water samples from wells in the Big Ditch watershed in Champaign County, IL. The shallow wells are screened near the water table. The deep wells sample deeper sand layers. Organic N (the difference between TKN and NH4+) is a significant fraction of total dissolved N in some samples.


Table 4. N species in ground water in the Big Ditch watershed

Concentration (mg N/L)
Well Depth NO3-* NH4+* TKN* Org N
1 Shallow 0.17 1.05 0.88
1 Deep 0.33 0.46 0.13
2 Shallow 0.21 0.21
3 Shallow 6.44
3 Deep 0.36 0.47 0.11
4 Shallow 0.49 0.86 0.37
4 Deep 0.27 0.33 0.06
5 Shallow 3.25 0.24 0.14
5 Deep 0.14 0.16 0.02
6 Shallow 8.33
6 Deep 0.57 0.73 0.16
7 Shallow 0.16 0.16
7 Deep 0.20 0.24 0.04
8 Shallow 0.40
8 Deep 0.58 0.50
9 Shallow 0.45 0.72 0.28
9 Deep 1.24 1.52 0.28
10 Shallow
10 Deep 0.11 0.41 0.30
11 Shallow 0.14 0.14
Notes: * A blank in the NO3-, NH4+, or TKN column indicates the analyte was undetectable. Method detection limits were 0.06, 0.07, and 0.12 mg/L for NO3-, NH4+, and TKN.
A blank in the organic N column indicates either TKN was less than NH4+ or both NH4+ and TKN were undetectable.

T. R. Holm, Unpublished data, Illinois State Water Survey.


 
 

References Cited:

Demissie, M. and L. Keefer. 1996. Watershed Monitoring and Land Use Evaluation for the Lake Decatur Watershed. Miscellaneous Publication 169. Illinois State Water Survey.

Thurman, E. M. 1985. Organic Geochemistry of Natural Waters. Dordrecht:Nijhoff-Junk.

Wetzel, R. T. 1975. Limnology. Philadelphia:Saunders.


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