Mechanisms by which forest ecosystems influence nutrient fluxes in freshwaters are initially disrupted by deforestation, which alters these fluxes in variable ways, depending upon the nutrient and the effects of deforestation on the factors controlling freshwater nutrient loading. These factors are geological weathering; precipitation and climate; terrestrial biological processes; physical–chemical reactions in the soil; and physical, chemical, and biological processes within aquatic ecosystems – for dissolved nutrients – and topography, soil erodibility, precipitation, watershed susceptibility to mass wasting, stream channel characteristics, proximity of vegetation to surface water, and extent of roading – for nutrients in particulate form. Other important factors include the extent of the watershed deforested, the presence of buffer strips, the nature of the treatment given to a watershed following deforestation, soil fertility, soil buffering capacity, and the abundance of large water bodies in a watershed. Despite this complexity, it can be concluded that (1) the usual increase in nitrification following deforestation is one of the most important determinants of freshwater nutrient loading; (2) northern hemisphere temperate deciduous hardwood forests are likely to exhibit greater nutrient flux changes after deforestation than temperate coniferous forests; (3) deforestation with herbicides is likely to cause relatively greater nutrient flux changes than deforestation without herbicides; and (4) deforestation-caused changes in freshwater nutrient loading are usually short-lived, particularly for nitrogen – generally up to 7 years, but usually considerably less. However, base cation changes may occur for more than 10 years.