Do nutrients vary seasonally in streams?
Geographic patterns in the occurrence and distribution of nutrient concentrations in streams are complicated by naturally occurring seasonal fluctuations in climate (such as those related to streamflow) and uptake by aquatic and riparian vegetation and human factors (such as those related to the application of fertilizer and manure and irrigation). At many sites in the eastern half of the United States, total nitrogen concentrations were highest in the spring when streamflow is highest and fertilizer application occurs, while total phosphorus concentrations were highest in the summer and autumn when streamflow is lowest and less water is available to dilute effluent from point sources. At other sites, particularly in the upper Midwest, both nitrogen and phosphorus concentrations were highest during high streamflow in the spring. In the western half of the United States, seasonal patterns were less distinct due to the highly variable topography and climate and the ubiquitous use of dams
