High‐resolution pore‐water sampling with a gel sampler

Sediment pore‐water profiles were sampled at high resolution (millimeter scale) with a polyacrylamide gel probe. This simple procedure involves inserting a 1‐mm‐thick gel held in a plastic probe into sediment. The gel reaches diffusive equilibrium in <1–2 h. For anions, the gel was sectioned, back‐equilibrated into distilled‐deionized water, and anions determined by high‐performance liquid chromatography. Laboratory trials showed recovery of 104±4% Cl, 102±2% NO 3 , 101±1% SO 4 , and 102±2% NH 4 . For Fe and Mn, the gel was fixed in 0.01 M NaOH for ∼3 h, subsectioned, extracted with 1 M HNO 3 , and analyzed by atomic absorption spectrometry. Field trials were undertaken in Esthwaite Water, a seasonally anoxic lake in the English Lake District. Gel probe data compared well with conventional pore‐water extractions.