Gandy, Cadence, Ecology, Susquehanna University, 514 University Avenue, Selinsgrove, Pennsylvania, 17870, gandy@susqu.edu; Rose, Michael, Ecology, Susquehanna University, 514 University Avenue, Selinsgrove, Pennsylvania, 17870, rosem@susqu.edu; Holt, Jack, Biology/Ecology Susquehanna University 514 University Avenue Selinsgrove Pennsylvania, 17870, holt@susqu.edu.
The upper Middle Creek watershed is punctuated by two reservoirs, Walker Lake and Faylor Lake, which differ in their major morphometric measures. Though the discharge of the respective streams is comparable, Walker Lake contains more than 10 times the volume of Faylor Lake (46km3 and 4km3, respectively). Similarly, maximum depth of Walker is 9m while Faylor is 4.5. Thus, Walker Lake becomes thermally stratified in early June and remains stratified into October. Faylor Lake does not become thermally stratified.
This study focuses on the plankton communities, both phytoplankton and zooplankton, of the two reservoirs through the months of June and July during 2022 and 2023. When weighted for biovolume, the phytoplankton of Walker Lake is dominated by filamentous cyanobacteria, but Faylor Lake is dominated by chlorophytes and then by cyanobacteria in July. Taxa richness in both lakes was 24 for both reservoirs in 2023 and for Faylor Lake in 2022. Walker Lake had a taxa richness of 16 in 2022.
Faylor Lake also has a water column occupied mostly by the free-floating vascular plant, Ceratophyllum demersum. During the summer months the surface of Walker Lake displays a surface bloom of cyanobacterial filaments and colonies (e.g. Planktothrix, Anabaena, and Aphanizomenon).
The zooplankton communities of both lakes are dominated by widely distributed taxa. The Faylor Lake community is dominated by cladocerans (e.g. Ceriodaphnia dubia and Bosmina longirostris) but the Walker Lake community generally is dominated by copepods (e.g. Microcyclops rubellus) in Walker Lake. Other dominant taxa in Walker Lake include the rotifer Keratella cochlearis and the cladoceran Daphnia magna. The dominant zooplankters of Faylor Lake are coarse filter feeders, but M. rubellus is an omnivore. Both K. cochlearis and D. magna filter bacteria and detritus. Average zooplankton taxa richness for both lakes ranged between 10 and 13.
Though both reservoirs are impaired, Walker Lake is decidedly eutrophic. The differences between the two reservoirs cannot be attributed to land use in their watersheds because they both are primarily agricultural. We suspect that differences in the summer ecology of the two reservoirs is due to the differences in their morphometry coupled with the small turnover rate of Walker relative to Faylor.
plankton, reservoir, stratification, morphometry