『Abstract
　By constructing nitrogen (N) budgets from 1880 to 2002 for watersheds that have undergone urbanization, intensive agricultural specialization or experienced minimal change, we document an uneven timeline of increase in anthropogenic N inputs. N loading to the watersheds of the Lake Michigan Basin grew six-fold from 1880 to 2002, peaking in 1987. Human activities influenced N inputs as early as 1880, and the magnitude and timing of increase differed markedly across regions in accord with population growth, land use, and type of agriculture. The greatest increase occurred from 1950 to 1980, corresponding with rapidly accelerating use of artificial fertilizers, but increases in atmospheric deposition and shifting patterns in crop and livestock production also affected trends. Net anthropogenic N inputs have changed little since about 1980, showing a modest decline due to a leveling out of fertilizer use and greater export of animal feed and products. Using a model that predicts riverine N export from watershed N loadings and river discharge, we found that river TN fluxes from all tributaries increased approximately threefold from 1900 to 2000 but have stabilized or declined over the past two decades, consistent with national surveys that show near-constant or declining riverine TN concentrations. For the LMB, the past two decades has been a period of relative stasis in N inputs to its terrestrial systems and N export from watersheds. This retrospective analysis also points to the challenge of forecasting future trends in N budget terms, which can both increase and decline in response to policy and societal transitions.

Keywords: Nitrogen; NANI; N export; River; Catchment; Nutrient budget; Nutrient loading; Lake Michigan』

Abbreviations
Introduction
Methods
　Study area
　N budget construction
　Fertilizer N
　Atmospheric N deposition and volatilization
　Biological N-fixation
　Trade of N in food and feed
　Historical estimates of riverine N export
　Uncertainty analysis
Results
　Human activities in the LMB
　N inputs to the Lake Michigan Basin
　　Fertilizer N
　Biological N-fixation
　Atmospheric N deposition
　Net trade of N in food and feed
　Total anthropogenic N inputs
　Historical changes in riverine N fluxes
Discussion
　Historical reconstruction of riverine TN export
　Total N inputs to Lake Michigan
Conclusions
Acknowledgments
References