Physical versus biogeochemical interpretations of nitrogen and phosphorus attenuation in streams and its dependence on stream characteristics

We investigate the influence of biogeochemical nutrient attenuation rates versus physical solute travel times on nutrient transport and attenuation in streams with different characteristics. Comparative results indicate smaller biogeochemical in‐stream attenuation rate and greater decrease of this rate with stream depth for phosphorus than for nitrogen. Because physical solute travel times also decrease with stream depth, equally for both nutrients, the resulting relative nutrient mass attenuation becomes essentially independent of stream depth for phosphorus but decreases with stream depth for nitrogen. Coarse interpretation models, without relevant representation of subgrid physical transport variability may lead to systematic misinterpretation of relative nitrogen mass attenuation behavior as a predominantly biogeochemical attenuation rate effect instead of a physical transport time effect. Incorrect understanding and distinction between physical and biogeochemical processes and effects may generally induce misleading cause‐effect conclusions on environmental loads and prevent us from reaching environmental goals of worldwide importance.