ScienceDaily (Jan. 30, 2008) — Like bank accounts, the nutrient cycles that influence the natural world are regulated by inputs and outputs. If a routine withdrawal is overlooked, balance sheets become inaccurate. Over time, overlooked deductions can undermine our ability to understand and manage ecological systems.

Recent research by the Université de Montréal (Canada) and the Cary Institute of Ecosystem Studies (Millbrook, New York) has revealed an important, but seldom accounted for, withdrawal in the global nitrogen cycle: commercial fisheries. Results highlight the role that fisheries play in removing nitrogen from coastal oceans.

Nitrogen is essential to plant and animal life; however, it is possible to have too much of a good thing. During the past century, a range of human activities have increased nitrogen inputs to coastal waters. Fertilizer run-off is the best documented and most significant source of terrestrial nitrogen pollution. Nitrogen-rich fertilizer applied to farmland eventually makes its way into coastal waters via a network of streams and rivers.

Research spearheaded by Roxane Maranger (Université de Montréal) and Nina Caraco (Cary Institute) demonstrates that commercial fisheries play an important but declining role in removing terrestrial nitrogen from coastal waters. Accounting for this withdrawal is crucial; terrestrial-derived nitrogen can stimulate coastal phytoplankton growth, leading to eutrophication. Eutrophic waters are characterized by reduced dissolved oxygen, decreased biodiversity, and species composition shifts.

Because fish accumulate nitrogen as biomass, and humans move fish from the ocean to the table, commercial fisheries return part of this terrestrial-generated nitrogen back to the land. In the 1960s, nitrogen removal in fish harvest was equivalent to 60% of the nitrogen fertilizer delivered to coastal ecosystems throughout the world. Today, this figure has dropped to 20%; fish harvest has not (and cannot) keep pace with escalating nitrogen runoff.

A continued decline in the proportion of nitrogen withdrawn by fishery harvests will contribute to an increase in the balance of nitrogen in coastal waters. From a historical perspective, this is bad news. Throughout the world, these ecosystems are becoming richer in nitrogen, resulting in increased phytoplankton blooms, anoxic bottom waters, and coastal dead zones.

This research is published as the cover story in the February issue of Nature Geoscience.

Nitrogen is an essential component of protein; fish store nitrogen in their biomass when they feed in coastal waters. (Credit: Image courtesy of Institute of Ecosystem Studies)

Related Stories

Bad News For Coastal Ocean: Less Fish Out, Means More Nitrogen In (Feb. 2, 2008) — Commercial fisheries play an unexpected role in the decline of water quality in coastal waters. The study, the first to examine the world's 58 coatal regions, shows how failing to maintain ecosystems ...  > read more

Nitrogen Loss In Seagrass Fields Is Retained By Animals And Microorganisms In Ecosystem (May 25, 2008) — The nitrogen cycle plays a major role in seagrass fields. A Dutch researcher studied the nitrogen dynamics of seagrasses in Indonesia. He discovered that the interaction between seagrasses, animals ...  > read more

Increased Atmospheric Nitrogen In North Atlantic Ocean Basin May Be Stimulating Algal Blooms (July 7, 1999) — The amount of atmospheric nitrogen polluting North Carolina waters and other parts of the North Atlantic Ocean Basin has increased significantly over the past three decades, and parallels increasing ...  > read more

Phosphorus Found To Be Another Culprit In Gulf Of Mexico's 'Dead Zone' (Nov. 15, 2006) — Nitrogen is flowing down the Mississippi River and into the Gulf of Mexico faster than it can be consumed by floating microscopic plants called phytoplankton, increasing the size of the "dead zone" ...  > read more

Satellite Imagery Pinpoints El Niño's Disruption Of Marine Ecosystem (Sep. 8, 2000) — New studies have detailed El Niño's extensive consequences in the ocean environment, showing that warm, nutrient-depleted waters ushered in during the El Niño resulted in a ...  > read more

Search ScienceDaily

What's In Our Air?