The median oxygen trend gap between middle and lower fixed sampled depths was uncertain in 149 northern lake records, 1980–2017

Lake oxygen loss can differ with depth. We tested the gap between trends at middle and lower fixed sampled depths in EDI edi.698.4. The sample has 4,161 late-summer profiles from 149 lakes at 30–70 degrees north in 1980–2017. We selected one date per lake-year and used a fixed sampled reference depth for each lake. We fitted oxygen trends at 50% and 90% of that depth with a sample-date term. The median lower-minus-middle slope was +0.012 mg/L per decade. Its 95% region bootstrap interval was −0.040 to +0.048. With shared five-year calendar blocks and region resampling, the interval was −0.126 to +0.101. All planned sample and date checks also left the median gap uncertain. The mean gap was uncertain too. Thus, the test did not establish a common depth ordering of oxygen loss. It did not establish equal rates. An initial oxygen-floor check gave opposite mean gaps in two groups, but both median intervals included zero. The sample is concentrated in North America. Sampled depth is not lake volume or a thermal layer. We preserve the complete compressed source tables, all selections, results, figures, code, hashes and offline repeat instructions. Independent source-value and regression checks passed. A clean run matched 36 output files.

lake oxygen · vertical profiles · ecological change · paired trends · reproducible null result · environmental monitoring