Nantucket Harbor water-quality data used to evaluate spatial and temporal heterogeneity, 2010–2025

Analysis-ready data underlying a study of spatial and temporal variation in Nantucket Harbor water quality. The files include Nantucket Natural Resources Department observations of total nitrogen, Secchi depth, and chlorophyll a at stations NAN1, NAN2, NAN3, and NAN5 (2010–2025), together with 2025 Maria Mitchell Association buoy measurements and derived datasets used to analyze temperature, dissolved oxygen, oxygen saturation, and degree-hours above 23 °C. Version 3 adds the consolidated master analysis script, complete screening and verification records, corrected Secchi event-level data representing 320 independent site-date sampling events, and the final publication-quality figures. The original source workbooks are preserved unchanged.