Global distribution of N2O emissions from aquatic systems: natural emissions and anthropogenic effects

doi:10.1016/S1465-9972(00)00015-5

Chemosphere - Global Change Science

Volume 2, Issues 3–4, 1 July 2000, Pages 267-279

https://doi.org/10.1016/S1465-9972(00)00015-5 Get rights and content

Abstract

Context Abstract: Atmospheric concentrations of nitrous oxide, a greenhouse gas, are increasing due to human activities. Our analysis suggests that a third of global anthropogenic N₂O emission is from aquatic sources (rivers, estuaries, continental shelves) and the terrestrial sources comprise the remainder. Over 80% of aquatic anthropogenic N₂O emissions are from the Northern Hemisphere mid-latitudes consistent with the geographic distribution of N fertilizer use, human population and atmospheric N deposition. These N inputs to land have increased aquatic as well as terrestrial anthropogenic N₂O emissions because a substantial portion enters aquatic systems and results in increased N₂O production. Thus, wise management of N in the terrestrial environment could help reduce/control both aquatic and terrestrial N₂O emissions.

Main Abstract: The global distribution of N₂O emissions from rivers, estuaries, continental shelves, and oceans are compared to each other, and to terrestrial emissions, using existing gridded inventories. Rivers, estuaries and continental shelves (1.9 Tg N y⁻¹) account for about 35% of total aquatic N₂O emissions; oceanic emissions comprise the remainder. Oceanic N₂O emissions are approximately equally distributed between the Northern and Southern Hemispheres; however, over 90% of emissions from estuaries and rivers are in the Northern Hemisphere. N₂O emissions from rivers, estuaries, and continental shelves combined equal oceanic emissions in both the 20°–45°N and 45°–66°N latitudinal zones. Over 90% of river and estuary emissions are considered anthropogenic (1.2 Tg N y⁻¹); only 25% of continental shelf emissions are considered anthropogenic (0.1 Tg N y⁻¹); oceanic emissions are considered natural. Overall, approximately one third of both aquatic and of terrestrial emissions are anthropogenic.

Natural terrestrial emissions are highest in tropical latitudes while natural aquatic emissions are relatively evenly distributed among latitudinal zones. Over half of both the anthropogenic terrestrial and aquatic emissions occur between 20° and 66°N. Anthropogenic N inputs to the terrestrial environment drive anthropogenic N₂O emissions from both land and aquatic ecosystems, because a substantial portion of the anthropogenic N applied to watersheds enters rivers, estuaries and continental shelves.

Introduction

Total global N₂O emissions include a wide range of sources from terrestrial and aquatic systems, with both natural and anthropogenic components (e.g., Khalil and Rasmussen, 1992, Matthews, 1994, Bouwman et al., 1995, Bange et al., 1996). A clear understanding of the magnitude of the various natural and anthropogenic sources and their geographic distribution is necessary to quantify factors contributing to the current increases in atmospheric N₂O concentrations, to predict future potential increases, and to develop realistic and cost-effective strategies to reduce future emissions. There have been a number of analyses of the magnitude and global distribution of terrestrial and deep ocean sources (e.g., Nevison, 1994, Bouwman et al., 1995); however only recently have such analyses been done for freshwater and coastal marine systems (Seitzinger and Kroeze, 1998).

N₂O emissions from freshwater and coastal marine ecosystems are estimated to amount to 1.9 Tg N y⁻¹ (Seitzinger and Kroeze, 1998), which is similar in magnitude to estimated N₂O emissions from a number of other sources, including arable land, grasslands, and animal excreta (Bouwman et al., 1995). Much of the N₂O emission from these aquatic systems is anthropogenic and thus contributes to the current increase in atmospheric N₂O. In addition, large increases in future N₂O emissions from these aquatic systems are predicted as a result of increases in human activities (Kroeze and Seitzinger, 1998). Bouwman et al. (1995) presented an analysis of the total and latitudinal distribution of most of the known terrestrial sources and Nevison et al. (1995) has done so with oceanic sources. We now extend that analysis by adding freshwater and coastal marine N₂O emissions.

In the current paper we compare: (1) N₂O emissions from rivers, estuaries and continental shelves with N₂O emissions from oceanic regions, (2) anthropogenic and natural emissions from aquatic systems, and (3) aquatic and terrestrial N₂O emissions, both natural and anthropogenic. These comparisons are done at a global scale as well as on a latitudinal basis to provide insight into the geographic distribution of the different sources. Gridded (1° × 1°) estimates of N₂O emissions from published studies are used in these analyses.

Section snippets

Methods

We calculated N₂O emissions for the following latitudinal zones for the northern and southern hemisphere: 0°–20°, 20°–45°, 45°–66° and 66°–90°.

Emissions from oceans: We obtained the gridded (1° × 1°) global N₂O emission inventory for ocean emissions from Nevison (1994) through the Emission Database for Global Atmospheric Research (EDGAR) (Olivier et al., 1996). The EDGAR database had been converted from the original 2.8° × 2.8° grid of Nevison (1994) to a 1° × 1° grid, which resulted in a loss of 0.2

Aquatic N₂O emissions

N₂O emissions from rivers, estuaries and continental shelves: Global watersheds receive inputs of nitrogen (N) from a variety of anthropogenic sources (Fig. 1). The three anthropogenic sources of new fixed N are synthetic fertilizer, combustion of fossil fuels and biological N₂-fixation associated with cultivated crops. Together, these sources contribute an amount of N (about 90–130 Tg N y⁻¹) similar to the natural biological fixation of N₂ in non-agricultural soils (∼140 Tg N y⁻¹) (Galloway et

Concluding remarks

It should be kept in mind that the above analyses are based on N₂O emissions inventories currently available in gridded format. As noted above, there are a number of missing sources (Mosier et al., 1998), as well as more recent estimates of abiotic sources (Prather et al., 1995). Emissions from all sources have considerable uncertainty associated with them. As we improve our understanding of factors controlling N₂O emissions in ecosystems worldwide, most certainly our estimates will need to be

Acknowledgements

We would like to thank L. Bouwman and J. Olivier for assistance with obtaining the terrestrial and ocean data bases from EDGAR. This work was supported in part with funding from NOAA NJ Sea Grant (SPS) (NJSG-99-423), NOAA Coastal Ocean Program (SPS) and Wageningen University (CK).

Sybil Seitzinger’s current research includes studies of: denitrification in rivers, estuaries and continental shelves; dissolved organic nitrogen inputs and bioavailability in aquatic ecosystems; and global modeling of N transport by world rivers and associated nitrous oxide production. Anthropogenic impacts are key components of her studies. She also enjoys windsurfing, ice climbing, snow boarding, white water kayaking, and traveling.

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Global distribution of N2O emissions from aquatic systems: natural emissions and anthropogenic effects

Abstract

Introduction

Section snippets

Methods

Aquatic N2O emissions

Concluding remarks

Acknowledgements

Nitrous oxide in coastal waters

Global Biogeochem. Cycles

Global analysis of the potential for N2O production in natural soils

Global Biogeochem. Cycles

Uncertainties in the global sources distribution of nitrous oxide

J. Geophys. Res.

Denitrification in continental shelf sediments has major impact on the oceanic nitrogen budget

Global Biogeochem. Cycles

A three-dimensional model of the global ammonia cycle

J. Atmos. Chem.

Stability dependent theory for air–sea gas exchange

J. Geophys. Res.

Nitrogen fixation: anthropogenic enhancement – environmental response

Global Biogeochem. Cycles

Regional nitrogen budgets and riverine N & P fluxes for the drainages to the North Atlantic Ocean: natural and human influences

Biogeochemistry

Diurnal variation of nitrogen cycling in coastal, marine sediments. II. Nitrous oxide emission

Marine Biology

The global sources of nitrous oxide

J. Geophys. Res.

Nitrogen inputs to rivers, estuaries and continental shelves and related nitrous oxide emissions in 1990 and 2050: a global model

Nutrient Cycling Agroecosyst.

Closing the global N2O budget: a retrospective analysis 1500–1994

Global Biogeochem. Cycles

Methane emission from animals: a global high resolution database

Global Biogeochem. Cycles

Global distribution of N₂O emissions from aquatic systems: natural emissions and anthropogenic effects

Aquatic N₂O emissions

Global analysis of the potential for N₂O production in natural soils

Closing the global N₂O budget: a retrospective analysis 1500–1994