Summer records did not show a clear change in cyanobacterial volume per cell in two Wisconsin lakes, 1995–2007 to 2008–2020

We tested whether summer cyanobacterial cell density and biovolume changed in the same proportion in Lakes Mendota and Monona, Wisconsin. We used NTL-LTER version knb-lter-ntl.88.32 and complete June–August records. The panel had 302 sample dates and 48 lake-years. We gave months and eligible years equal weight. The primary measure was the later-to-earlier ratio of biovolume per cell. From 1995–2007 to 2008–2020, this ratio was 1.27 in Mendota and 0.72 in Monona. Nominal 97.5% intervals from 9,999 shared three-year block resamples were 0.69–2.41 and 0.42–1.29. Neither lake gave clear evidence of a change in volume per cell. The intervals also did not establish a stable conversion from counts to volume. Wider seasonal windows changed the point estimates, while all planned checks kept the primary result uncertain. An exact split by source labels assigned more of each observed change to cell-share changes than to within-label changes. This split is count accounting, not a causal result. A separate CSV program matched all main estimates. Limits include two sample sites, missing summers, short blooms between visits, taxonomic changes, and unmodelled measurement error. The package has unchanged source data, provenance, code, all results and resamples, figures, and offline repeat instructions.

cyanobacteria · phytoplankton · biovolume · cell density · Lake Mendota · Lake Monona · null result · environmental monitoring