Phytoplankton communities in New England lakes - 2005-2006
2020-06-01T17:54:12Z (GMT) by
We sampled six lakes located in Connecticut, two connected to the ocean and inhabited by anadromous alewife populations (Bride and Dodge; AA) and four physically disconnected from the ocean, two with landlocked alewife populations (Pattagansett and Rogers; LL), and two with no alewife population (Linsley and Hayward; NA). Bride Lake (41º19’N, 72º14’W) is 18.2 ha in area with a maximum depth of 10.7 m and contains one of the largest runs of anadromous alewife in Connecticut (Post and Walters 2009). Dodge Pond (41º19’N, 72º12’W) is 13.9 ha in area with a maximum depth of 15.5 m. Pattagansett Lake (41º22’N, 72º13’W) is 49.2 ha in area with a maximum depth of 10.1 m and Rogers Lake (41º21’N, 72º18’W) is 106.0 ha in area with a maximum depth of 20.0 m. Pattagansett and Rogers lakes are separated from the ocean by dams built by early colonial Americans (Twining and Post 2013) and the landlocked alewife populations in them at the time of this study were independently derived from anadromous ancestors (Palkovacs et al. 2008). Linsley Pond (41º19’N, 72º47’W) is 9.4 ha in area with a maximum depth of 13.4 m and Lake Hayward (41º30’N, 73º19’W) is 79.6 ha in area with a maximum depth of 10.7 m. Lakes with landlocked populations are separated from the ocean by man-made dams built by early colonial Americans (Twining and Post 2013). All of our study lakes are dimictic and are stratified from late spring (typically April) until late autumn (typically late November). Except for differences in the incident and life history form of alewife, all of our study lakes contain a similar fish community, including yellow perch, bluegill, and pumpkinseed (Howeth et al. 2013).
All lakes were sampled for phytoplankton once per month during the growing season (April through September) in 2005, except Hayward which was sampled once per month in 2006. For each lake and date, phytoplankton were collected from three depths in the epilimnion (top, middle, and bottom) using a Van Dorn sampler. Equal parts of each sample were combined, and 250 ml of the combined sample was preserved with 0.5% glutaraldehyde and stored in opaque bottles at 5ºC. Data on total phosphorus (TP), copepod and cladoceran biomass, and alewife density were also collected monthly (see Post et al. 2008 for collection details).
Algal samples were permanently mounted with HPMA (2-hydroxypropyl methacrylate) resin to count and measure phytoplankton (Crumpton 1987). The volume of each sample used to make the permanent mounts varied between 10-20 ml to ensure mounts would have 20-30 cells per field at 200x. The volumes of sample filtered for each permanent mount were based on chlorophyll a (chl a) concentration of samples taken concurrently in the field (Post et al. 2008), where samples with chl a < 5 µgL-1 had 20 ml filtered, samples with 5 µgL-1 > chl a > 15 µgL-1 had 15 ml filtered, and samples with chl a > 15 µgL-1 had 10 ml filtered. Three permanent mounts were made per lake and date sampled.
Algae were identified to genus in 60 whipple fields (20 per mount) at 63x. Fields were arrayed in an S-shaped pattern on each slide to prevent double counting. Individuals overlapping the edge of the field on the top or left edges were counted, while those which were overlapping the field on the bottom or right edges were not. The greatest linear axial dimension (GLAD) was measured for each individual. When individuals were colonial, the GLAD of the entire colony was measured. Algae that extended outside of the field (generally colonial or filamentous algae) were measured at lower magnification. All linear dimensions of ten randomly selected individuals of each genus were measured for each lake. These dimensions were averaged and the ratios of these dimensions to GLAD were determined for each genus. Using these ratios, biovolume equations based on GLAD were developed for each genus (modified from Hillebrand et al., 1999; Table A1). Genera that only occurred in one lake and had a biovolume less than 1e-7 mm3L-1 on each date they were observed were dropped from the analyses (22 genera). Biovolumes were corrected for the average reduction in size (29%) of phytoplankton when fixed with glutaraldehyde (Hillebrand et al. 1999). Biovolumes of diatoms were not corrected, as their sizes are not thought to be affected by glutaraldehyde fixation (Boyd and Johnson 1995).
(1) lake - lake from which the algal community data was collected;
(2) no. - unique identified for each algal individual sampled within each lake;
(3) date - date on which the algal sample was collected from the lake;
(4) slide - replicate slide number from each lake sample;
(5) volume of sample (ml) - volume of lake water sample that was filtered and fixed on slide;
(6) whipple field - identifier for whipple fields sampled on each slide;
(7) Genus - genus of the algae identified;
(8) Phylum - phylum of the algae identified;
(9) Form - growth form of the algae identified (single celled, colony, filamentous);
(10) length - GLAD of the algae identified;
(11) mag - magnification at which the algae was measured;
(12) biovolume - biovolume estimate for the algae individual based on GLAD and above-described formulas for algae biovolume.