Importance of suspended particulates in riverine delivery of bioavailable nitrogen to coastal zones

Total nitrogen (TN) loadings in riverine sediments and their coastal depoce nters were compared for Il river systems worldwide to assess the potential impact of riverine particulates on coastal nitrogen budgets. Strong relatio nships between sediment specific surface area and TN allow these impacts to be estimated without the intense sampling normally required to achieve suc h budgets. About half of the systems showed higher nitrogen loadings in the riverine sediments than those from the coastal depocenter. In spite of unc ertainties, these comparisons indicate that large, turbid rivers, such as t he Amazon, Huanghe, and the Mississippi, deliver sediments that in turn rel ease significant or major fractions of the total riverine nitrogen delivery . Riverine particulates must therefore be considered an essential factor in watershed nutrient loading to coastal ecosystems and may affect delivered nutrient ratios as well as total nutrient loading. The relative importance of particulate versus dissolved delivery has decreased over recent decades in the Mississippi as a result of damming and fertilizer use in the watersh ed.