Screening legacy long-closure static-chamber records for greenhouse-gas interpretation in wastewater stabilization ponds: a reproducible case study from the arid Peruvian Andes

Legacy static-chamber records from wastewater stabilization ponds may retain information on gas buildup but can be unsuitable for flux estimation when closures exceed conventional protocols. We applied a reproducible screening workflow to chamber-headspace records of CH₄, N₂O and CO₂ from the Omo wastewater treatment plant, southern Peru (1,410 m). The workflow applies seven sequential gates covering raw signal, quality control, chamber state, temporal design, thresholds, replication and covariate timing; the first five are flux-critical. Three campaigns (August–October 2022) yielded 36 observations per gas from one sampled cell per pond stage at post-closure days 1, 3, 7 and 9, which are temporal repeats, not spatial replicates. The audit found that 1 Hz traces, calibration and leak-test records and purge windows were not retained, that closures of 1–9 d were approximately 48–432 times longer than a 30-min protocol, and that 52.8% of ΔCO₂ fell below the operational threshold. Post-closure time was the strongest predictor of ΔCH₄, ΔN₂O and ΔCO₂ (standardized β = 0.830, 0.741 and 0.541; all p < 0.001), no Tukey-adjusted cell contrast was significant, and pond cell and organic load were aliased. The records are therefore classified as chamber-headspace accumulation, not validated fluxes. The transferable contribution is the workflow itself.