Global N removal by freshwater aquatic systems using a spatially distributed, within-basin approach
Figure S1L Characteristics of the global system of rivers, combining small rivers located within each grid cell (orders 1–5) and large rivers of the STN-30 river network (orders S1–S6 equivalent to orders 6–11), including (a) mean drainage area and lengths of each order and (b) total length and number globally, and mean width (+/− 1 standard deviation) of each order. (12.32Kb)
Figure S2: Proportion of total aquatic removal that is due to (a) lakes versus percent of basin covered by lakes and (b) reservoirs versus percent of basin covered by reservoirs. (18.48Kb)
Figure S3: Proportion of total basin removal that is due to aquatic systems versus mean basin runoff in the 402 largest basins. (5.530Kb)
Table S1: Selected characteristics of basins included in Figure 6 and the modeled fate of total N inputs using the base scenario. (691bytes)
Wollheim, Wilfred M.
Vorosmarty, Charles J.
Bouwman, A. F.
Harrison, John A.
Peterson, Bruce J.
Seitzinger, Sybil P.
Syvitski, James P. M.
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We explored the role of aquatic systems in the global N cycle using a spatially distributed, within-basin, aquatic nitrogen (N) removal model, implemented within the Framework for Aquatic Modeling in the Earth System (FrAMES-N). The model predicts mean annual total N (TN) removal by small rivers (with drainage areas from 2.6–1000 km2), large rivers, lakes, and reservoirs, using a 30′ latitude × longitude river network to route and process material from continental source areas to the coastal zone. Mean annual aquatic TN removal (for the mid-1990s time period) is determined by the distributions of aquatic TN inputs, mean annual hydrological characteristics, and biological activity. Model-predicted TN concentrations at basin mouths corresponded well with observations (median relative error = −12%, interquartile range of relative error = 85%), an improvement over assumptions of uniform aquatic removal across basins. Removal by aquatic systems globally accounted for 14% of total N inputs to continental surfaces, but represented 53% of inputs to aquatic systems. Integrated aquatic removal was similar in small rivers (16.5% of inputs), large rivers (13.6%), and lakes (15.2%), while large reservoirs were less important (5.2%). Bias related to runoff suggests improvements are needed in nonpoint N input estimates and/or aquatic biological activity. The within-basin approach represented by FrAMES-N will improve understanding of the freshwater nutrient flux response to anthropogenic change at global scales.
Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 22 (2008): GB2026, doi:10.1029/2007GB002963.
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