Secondary Productivity Sample Clauses

Secondary Productivity. Zooplankton samples were collected each month from July through November, taken from the northern, middle, and southern portions of the lake. A vertical tow plankton net with 80µ mesh and a silk bucket was used to collect zooplankton. Vertical tows were made from the bottom to the surface and from 5m to the surface to allow density comparisons between the entire water column and the epilimnion. A zooplankton sample was also taken in Outlet Creek from the same location as the water quality and chlorophyll samples.

Secondary Productivity. For the most part, zooplankton from Xxxxxxxx Lake and Outlet Creek were identified by species, with the exception of cyclopoids and calanoids (both subclass Copepoda, order Eucopepoda). For the purposes of reporting here, results were tallied by four categories into totals for Daphnia spp., Bosmina spp. (both subclass Branchiopoda, order Cladocera), copepods, and rotifers (class Monogononta, order Ploima). The majority of zooplankton identified were either Daphnia spp. or cyclopoids (28% Daphnia spp., 2% Bosmina spp., 44% cyclopoid, 10% calanoid, 16% rotifer). Tables 6-10 summarize the zooplankton results (Table 10 is the sum of Tables 6-9).

Secondary Productivity. Zooplankton were limited with respect to both density and species diversity. Only two species of cladocerans were found, including one species each of Daphnia spp. and Bosmina spp. Zooplankton in Xxxxxxxx Lake are likely limited by low phytoplankton production. They may also be limited due to an abundant kokanee population, which crops off the larger sized zooplankton. The collection of zooplankton samples from the epilimnion and from the bottom to the surface indicated that zooplankton are utilizing areas below the epilimnion, although they tend to be more concentrated nearer the surface. Zooplankton likely spend the day-light hours in the upper part of the hypolimnion or lower part of the metalimnion, and by dusk move up into the metalimnion and epilimnion. This is a typical diurnal vertical migration behavior displayed by many zooplankton, especially larger-sized cladocerans, to avoid size-selective predation by visual predators (Xxxxx and Xxxxxxx 1976). Samples for this study were collected near the middle of the day, generally between 10:00 a.m. and 3:00 p.m., and may therefore reflect zooplankton migration toward the hypolimnion. The spatial pattern of zooplankton densities in this study is consistent with that found by Xxxx and Xxxxxx (2005). Species population data are inherently highly variable, which is also true in this instance, as illustrated by the data displayed in Figures 11-13. Therefore, trends in zooplankton density with time or location are difficult to discern. Nonetheless, Daphnia spp. appear to have declined in the lake over the study period, while copepods remained relatively steady or slightly increased (Figure 9). The temporal pattern of zooplankton densities is consistent with that found by Nine and Xxxxxx (2005): Daphnia spp. peaked in July, copepods peaked in October, and Bosmina spp. remained relatively low but increased slightly in the fall. Zooplankton densities in Outlet Creek were similar to average densities found in the lake through the entire water column (compare Figures 9 and 10). However, copepods increased substantially in Outlet Creek in the fall (after initiation of lake drawdown in October) (Figure 10).