158 R.T. Prentkietal. 



drainage water per unit of pond volume is much higher for trough ponds 

 than for low centered polygon ponds. 



If the ponds sampled in the transect in 1973 (Figure 4-31) are classed 

 by dominant vegetation in or around the pond, then the moss ponds are 

 significantly more colored than the Carex and Arctophila ponds 

 (t = 4.05, 1.011(23) = 2. 807) (Table 4-24). The conclusion could be drawn that 

 the moss vegetation forms more materials that absorb UV light. However, 

 an interpretation based on dominant vegetation is confounded by the 

 origin of the two pond types, as all moss ponds are trough ponds and all 

 Carex and Arctophila ponds are low-centered polygon ponds. 



Furthermore, these pond types and vegetative types are 

 geographically separated on the shelf of an old lake basin. The ponds with 

 the lowest UV absorbance (color correlates with absorbance at 250 nm) in 

 1972 and 1973 lie in the most recent lake basin formed on the shelf of the 

 much older lake (Ponds A, B, C, E, J, 24 and 25) (Figure 4-31, Figure 3-1). 

 The ponds on either side of the old lake shelf (Ponds X, 4 and D on the 

 eastern side of the shelf and Ponds 2, 23, 1, 10, 26, 9, 8, 22 and 3 on the 

 western or in-shore side) had a higher UV absorbance. Interestingly 

 enough, these intermediately colored ponds (absorbance at 250 nm was 0.4 

 to 0.8) around the most recently drained lake basin are most often 

 Arctophila ponds. The ponds with the most color were primarily trough 

 ponds above the western shore of the old basin located between high 

 mounded polygons which are much older (14,000 yr). 



The small year-to-year variations in the humics appear to be a 

 function of differences in the water budget, especially in the amount of 

 overland runoff later in the summer. Thus, 1973 was a wet year with 

 overland runoff beginning by 19 August, while 1972 was a dry year with 

 little mid- or end-of-summer rainfall. On the average, the color in 1973 

 (Figure 4-31) was not significantly different from the color in the drier 

 year, 1972 (Figure 4-32). From 1972 to 1973, the intensity of color in the 

 lowest colored ponds decreased, while it increased for the highest colored 

 ponds (Figure 4-32). Thus, when rainfall runoff was the greatest, the 

 central ponds whose immediate vegetation-covered drainage basin was 

 smallest (because of the abundance of ponds) were diluted the most and 

 became reduced in color. 



We calculate that 50 to 70% of the total DOC is made up of these UV- 

 absorbing humic materials. The data come from the ratio of total DOC to 

 the absorbance at 250 nm before and after the addition of small amounts 

 of anion resin which differentially removed the colored materials. This 

 resin (Biorad AG50-8x) irreversibly binds the polycarboxylic humic acids 

 and perhaps also some of the negatively charged non-U V-absorbing DOC. 

 The measurement, however, was made only twice in replicate and 

 considering the variability of humics that must occur from pond to pond, 

 these percentages of humic compounds in the DOC pool must be taken as 

 an indication of a general range rather than as an absolute value. 



