The regional and global significance of nitrogen removal in lakes and reservoirs
Date
2008-06-25Author
Harrison, John A.
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Maranger, Roxane J.
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Alexander, Richard B.
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Giblin, Anne E.
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Jacinthe, Pierre-Andre
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Mayorga, Emilio
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Seitzinger, Sybil P.
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Sobota, Daniel J.
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Wollheim, Wilfred M.
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https://hdl.handle.net/1912/3097As published
https://doi.org/10.1007/s10533-008-9272-xAbstract
Human activities have greatly increased the transport of biologically available N through
watersheds to potentially sensitive coastal ecosystems. Lentic water bodies (lakes and
reservoirs) have the potential to act as important sinks for this reactive N as it is
transported across the landscape because they offer ideal conditions for N burial in
sediments or permanent loss via denitrification. However, the patterns and controls on
lentic N removal have not been explored in great detail at large regional to global scales.
In this paper we describe, evaluate, and apply a new, spatially explicit, annual-scale,
global model of lentic N removal called NiRReLa (Nitrogen Retention in Reservoirs and
Lakes). The NiRReLa model incorporates small lakes and reservoirs than have been
included in previous global analyses, and also allows for separate treatment and analysis
of reservoirs and natural lakes. Model runs for the mid-1990s indicate that lentic systems
are indeed important sinks for N and are conservatively estimated to remove 19.7 Tg N
yr-1 from watersheds globally. Small lakes (< 50 km2) were critical in the analysis,
retaining almost half (9.3 Tg N yr-1) of the global total. In model runs, capacity of lakes
and reservoirs to remove watershed N varied substantially (0-100%) both as a function of
climate and the density of lentic systems. Although reservoirs occupy just 6% of the
global lentic surface area, we estimate they retain approximately 33% of the total N
removed by lentic systems, due to a combination of higher drainage ratios (catchment
surface area : lake or reservoir surface area), higher apparent settling velocities for N, and
greater N loading rates in reservoirs than in lakes. Finally, a sensitivity analysis of
NiRReLa suggests that, on-average, N removal within lentic systems will respond more
strongly to changes in land use and N loading than to changes in climate at the global
scale.
Description
Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 93 (2009): 143-157, doi:10.1007/s10533-008-9272-x.