630 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



multiplied by the number of 40-hr intervals in a year (219) to estimate the annual 

 production. The production of Tetraspora was estimated by direct observations of 

 appearance in sampling grids made periodically during the growing season. The mean dry 

 weight of a volumetric quantity was established and then proportioned to the volume of 

 Tetraspora observed to occur in U-Pond. 



Inventories of filamentous algae and submerged macrophytes are based on periodic 

 measurements of primary productivity and standing crop [see Emery, Klopfer, and 

 Weimer (1974) for a detailed description] . A method described by Verduin (1964) was 

 used to measure pond-wide primary production, which accounts for the photosynthesis of 

 all plant life in the pond inclusive of phytoplankton, macroalgae, and submerged 

 macrophytes. Results of these measurements express the net accumulation of plant mass 

 per unit time. Hence a summation of the montlily rates of net productivity for the entire 

 year provides one estimate for the annual quantity of submerged plant biomass that may 

 accumulate plutonium. For verification of this estimate, submerged plant standing crop 

 was measured at the beginning and end of the growing season by the areal sampling 

 methods described by Emery, Klopfer, and Weimer (1974). Areal sampling of submerged 

 plant biomass was also done periodically to provide a direct accounting of changes in 

 standing crop. So that standing crop could be measured, in this way plant material was 

 harvested from known surface areas, dried, weighed, and projected on a weight basis to 

 the area of the pond observed to be covered by these algae and macrophytes. Results of 

 both methods of estimating the pond's production of submerged plant biomass were in 

 reasonable agreement with each other (less than an order of magnitude difference). 



Emergent macrophytes represent 10 to 15% of the pond's biomass at the peak of the 

 growing season. The annual production of emergent plants was estimated by the same 

 method used for submerged plants. 



Pond invertebrates live mainly in association with rooted macrophytes and to a lesser 

 extent in the organic floe covering much of the pond's bottom. A O.lS-ft'^ Ekman dredge 

 was used to estimate the area concentrations of invertebrates living in the organic floe. 

 The more densely populated surfaces of macrophytes were quantitatively sampled by 

 direct collection and enumeration of invertebrates from the plants (mainly Potamogeton), 

 for which dry weights were also determined. Dry weights of the various types of 

 invertebrates were assessed per unit weight of plant material and then projected to the 

 pond-wide weiglit of tlie specific plant types to estimate an invertebrate standing crop. 

 All invertebrate life was assumed to appear in the pond on an annual basis; hence the 

 maximum standing crop served to represent the weight of invertebrates produced 

 annually by U-Pond. 



The goldfish population in U-Pond is largest during the summer months. During the 

 colder months this population appears to decrease by several orders of magnitude, and 

 few goldfish are observed during the winter. Since this goldfish population appears to 

 reproduce annually and undergo substantial depletion in the colder months, the only 

 valid expression of annual production can be based on the summer standing crop. For this 

 reason the standing crop observed in August 1974, the only time when goldfish were 

 counted, will serve as the expression of annual production. 



The standing crop of goldfish was estimated by first estabhshing a weight for an 

 individual and then counting the numbers of individuals appearing in 125, 9-m^ grids 

 placed randomly about tlie pond. The mean number of individuals was converted to mean 

 weiglit per unit area and proportioned to the entire pond area. 



