Organic matter in stream sediments is considered the key factor to control sediment oxygen demand in agricultural watershed. This study was conducted to compare the binding characteristics of proton and metal ion to humic substances. Sediment samples from Bayou Plaquemine Brule watersheds, main channel and tributaries were extracted by a modified IHSS procedure to isolate the humic substances as related to the different agricultural watersheds. The humic acids (HAs) were purified by membrane-filtration, re-precipitated, and freeze-dried. The simplified discrete binding group type of model (Model A) will be applied to this binding study. Model A considered only a single carboxyl group type and a single phenolic hydroxyl group type with a variable electrostatic interaction factor that is expressed as a polynomial equation. Metal binding experiments will be performed using a batch-type dialysis equilibration method, and mass and charge balance expressions will be used to calculate individual components of the systems. Binding behaviors of proton and cations to HAs extracted from different sites will be compared.