『Abstract
　Catchment nitrogen (N) budgets are a valuable tool to assess relative magnitude of N inputs and predict losses via riverine export. However, a range of computational approaches may be chosen, potentially affecting the modeled relationship between inputs and exports. To determine the influence of various assumptions and computational details on the effectiveness of N input estimates in predicting riverine N export, we compared eight separate net anthropogenic N input budgets and one soils compartment budget for each of 18 Lake Michigan catchments. N input estimation methods that took into account seasonal fluctuations in livestock numbers and estimated crop N-fixation by legume yield rather than area harvested best predicted river N export. The average annual river export of N from the 18 catchments ranged from less than 300 kg N km^-2 year^-1 in forested areas to more than 800 kg-N km^-2 year^-1 in agricultural catchments and 1,580 kg-N km^-2 year^-1 in small urban catchments. Using the most effective model (R²=0.95, median prediction error = 1.8％) riverine N exports were found to account for 21％ of N inputs. Other methods predicted riverine N exports less well (R²=0.61-0.73), bias was greater, and the fractional export of N inputs by rivers decreased to 〜13％. The soil N budget also was a less effective predictor of river export. This comparison demonstrates that N budgeting that incorporates more detailed description of agricultural N sources can substantially improve prediction of riverine N exports from catchments with a wide range of landscape characteristics.

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

Introduction
Methods
　Study area
　Nitrogen budgets
　　N fertilizer inputs
　　Total atmospheric N deposition
　　Net trade of N in food and feed
　　Animal N mature and NH3 volatilization
　　Crop N fixation
　　Data aggregation and final budgets
　Riverine TN concentrations and fluxes
Statistical analysis
Results
　Crop N fixation
　Fertilizer
　Net atmospheric N deposition
　Net import of N in food and feed
　Comparison of N input estimates
　Relationship between N inputs and riverine TN export
Discussion
　Comparison of methods of N input estimation
　Prediction of river export from alternative N budgets
　Factors influencing the relationship between catchment N input and river export
Acknowledgments
References