Nitrogen cycling in a high-nutrient tidal river revealed through high-resolution sampling and nitrate isotope mixing models.

This dataset contains nitrate isotope (δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻) measurements and associated nutrient concentrations (NOₓ, NH₄⁺, and PO₄³⁻), along with physicochemical parameters, from surface water, groundwater, and spatial surveys conducted during two field campaigns (wet and dry periods) in the Hawkesbury River tidal freshwater zone, New South Wales, Australia. Revised January 2026. Dataset expanded to include full raw discharge, velocity, and direction time series for all stations.