362 J.E. Hobbieetal. 



first year was composed of 33% green and 67% yellow material. The total 

 weight loss of each fraction was calculated from the loss from litterbags. 

 This total loss was partitioned into loss by leaching and loss by hydrolysis 

 based on experiments described above with plastic bags and HgCli. The 

 leaching loss was further partitioned by experiments in which litter was 

 incubated in plastic bags with pond water but without a killing agent. 

 After two weeks, some of the organic matter lost from the leaves was still 

 present as DOC; this was called refractory DOC. The organic matter lost 

 from the leaves and oxidized by the microbes was called usable DOC. 

 After the second year, the loss from the brown material can not be 

 partitioned and almost all loss is attributed to trituration. By the fourth 

 year, the remaining material was less than 20 Mm in diameter and was 

 easily moved around the pond. It is treated in the budget as if it were all 

 completely decomposed by the end of this period but we cannot be certain 

 of this. 



Over the 4 years, most of the plant litter was lost by trituration (18.7 g 

 C) while only 8.05 g C was lost by leaching and 5.19 g C by hydrolysis 

 (Table 8-9). These totals can also be used for the total amount of 

 decomposition occurring in a single year in this pond. Obviously the data 

 are not accurate enough to determine whether some plant material 

 remains undecomposed and is eventually added to the sediments. If only 5 

 to 10% (or 1.6 to 3.2 g C m ^') of the total produced was added each year, 

 it could account for the organic accumulation in the sediments. 



Another source of organic matter to the pond is the roots of aquatic 

 plants. These add up to 100 g C m ^^ yr " ^ to the sediments in the plant bed 

 or 33 g C m "^ to the whole pond (see Chapter 5). An unknown amount of 

 this production remains undecomposed. 



Changes in Inorganic Composition during Decomposition 



The inorganic composition of the Carex samples removed after 1, 2, 

 4, and 8 weeks of decomposition was analyzed in 1972. The elements 

 measured were P, K, N, Ca, Mg, Fe, Mn, and Zn. In addition, laboratory 

 measurements of loss from fresh lemming feces were made. 



The fresh green leaves of Carex lost almost all of their P and K within 

 one week. The yellow and brown litter had very low concentrations of P 

 and K at the start of the experiment while the P and K of lemming feces 

 was mostly lost during the first 4 days. The elements tied to the structural 

 material of the plants, Mg, Ca, and Fe, increased relatively over 8 weeks 

 as the proportion of structural material in the total remaining material 

 increased. All other elements remained at essentially the same relative 

 concentrations in the detritus and in the lemming feces throughout the 

 experimental period. 



