Article

Biogeochemistry

, Volume 93, Issue 1, pp 143-157

The regional and global significance of nitrogen removal in lakes and reservoirs

  • John A. HarrisonAffiliated withSchool of Earth and Environmental Sciences, Washington State University Email author 
  • , Roxane J. MarangerAffiliated withDépartement des Sciences Biologiques, Université de Montréal
  • , Richard B. AlexanderAffiliated withUS Geological Survey
  • , Anne E. GiblinAffiliated withMarine Biological Laboratory, The Ecosystems Center
  • , Pierre-Andre JacintheAffiliated withIndiana University-Purdue University
  • , Emilio MayorgaAffiliated withInstitute of Marine and Coastal Sciences, Rutgers/NOAA CMER Program, Rutgers University
  • , Sybil P. SeitzingerAffiliated withInstitute of Marine and Coastal Sciences, Rutgers/NOAA CMER Program, Rutgers University
  • , Daniel J. SobotaAffiliated withSchool of Earth and Environmental Sciences, Washington State University
  • , Wilfred M. WollheimAffiliated withWater Systems Analysis Group, Complex Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire

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Abstract

Human activities have greatly increased the transport of biologically available nitrogen (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 year−1 from watersheds globally. Small lakes (<50 km2) were critical in the analysis, retaining almost half (9.3 Tg N year−1) of the global total. In model runs, capacity of lakes and reservoirs to remove watershed N varied substantially at the half-degree scale (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 ~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 average 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.

Keywords

Nitrogen Lakes Reservoirs Denitrification Global limnology Nitrogen removal