Sustaining the World's Large Marine Ecosystems

The Global Environment Facility (GEF) is frequently asked by countries to help
support the agreed-upon incremental cost of actions to reduce such nitrogen flux.
Actions range from assisting in: (1) development of joint institutions for
ecosystem-based approaches for adaptive management; (2) on-the-ground
implementation of nitrogen abatement measures in the agricultural, industrial,
and municipal sectors; and (3) breaching of floodplain dikes so that wetlands
recently converted to agriculture may be reconverted to promote nitrogen
assimilation. The excessive levels of nitrogen contributing to coastal
eutrophication constitute an emerging global environment problem that is crosssectoral
in nature. Excessive nitrogen loadings and oxygen depletion events
causing significant mortalities among marine resource species have been
identified as a major coastal problem in several LMEs that are receiving GEF
assistance, including in the Baltic Sea, Black Sea, Mediterranean Sea, Yellow
Sea, South China Sea, Bay of Bengal, Gulf of Mexico, and Patagonian Shelf
LMEs.
Preliminary global estimates of nitrogen export from freshwater basins to coastal
waters have been determined by Seitzinger and Kroeze (1998). A GEF/LME
global project, “Promoting Ecosystem-based Approaches to Fisheries
Conservation and Large Marine Ecosystems”, has filled gaps relating to LME
nitrogen loadings and provided forecasts for 64 LMEs (Seitzinger et al. 2008).
The project has used GIS-based models relating land use and human activities in
watersheds to nutrient transport by rivers to coastal systems (Figure 19). The
project specifically used an innovative Nutrient Export from Watersheds Model
(NEWS) to predict inorganic nitrogen (N) export by rivers to the coast as a
function of watershed N inputs (point and diffuse sources), hydrology, and other
factors. The model was used to examine dissolved inorganic nitrogen (DIN)
export into all 64 LMEs. The aim is to optimize use of land for food and energy
production while at the same time conserving coastal habitats, and to understand
the links between land-based activities and nutrient inputs to coastal systems.
Nutrient sources, sinks, and controlling factors in watersheds are explicit
components of the model, and the effect of a range of scenarios on DIN river
export can be explored.
A Watershed Perspective: Rivers are a central link in the chain of nutrient
transfer from watersheds to coastal systems. Nutrient inputs to watersheds
include natural (biological N2-fixation, weathering of rock releasing phosphate) as
well as many anthropogenic sources. At the global scale, anthropogenic nitrogen
inputs to watersheds are now greater than natural inputs (Galloway et al. 2004).
Anthropogenic nutrient inputs are primarily related to food and energy production
to support the over 6 billion people on Earth with major sources including
fertilizer, livestock production, sewage, and atmospheric nitrate deposition
resulting from NOx emissions from fossil fuel combustion. The single largest
change in the nitrogen cycle comes from increased reliance on synthetic
inorganic fertilizer, invented and widely used in the last century. Over the next 50
years, human population, agricultural production, and industrialization are
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