I was just thinking of starting a thread about nutrient cyles and fishing earlier in the week.

Bad News For Coastal Ocean: Less Fish Out, Means More Nitrogen In

http://www.sciencedaily.com/releases/2008/01/080128171537.htm

ScienceDaily (Feb. 2, 2008) — A Canada-U.S. research team has found that commercial fisheries play an unexpected role in the decline of water quality in coastal waters. In a recent issue of Nature Geoscience, Roxane Maranger and Nina Caraco explain that the collapse of the fisheries from decades of over fishing has played a significant role in disturbing the balance between nitrogen entering and leaving costal water systems.

The study, the first to examine the world's 58 coatal regions, shows how failing to maintain ecosystems in a sustainable manner has wide-ranging consequences. Using data provided by the United Nations, Maranger and Caraco found that commercial fishing has played an important, yet declining, role in removing man-made nitrogen from coastal waters.

"Fish accumulate nitrogen as biomass, and when humans move fish from the ocean to the table through commercial fisheries, they are returning part of this terrestrial nitrogen generated by humans back to the land," said Maranger, a biology professor at the Université de Montréal (Canada).

Caraco, an aquatic biogeochemist at the Cary Institue of Ecosystem Studies (Millbrook, New York, U.S.) notes: "While nitrogen is essential to plant and animal life in oceans, human export of nitrogen from land to ocean has resulted in exploding nitrogen levels in coastal waters over the past century. Nitrogen-rich fertilizer that's applied to farmland eventually makes its way into coastal waters via a network of streams and rivers. Fertilizer run-off is a significant source of nitrogen pollution to many coastal regions around the world."

Four decades ago, commercial fishing removed the equivalent of 60 percent of the nitrogen from coastal oceans that entered as fertilizers. Today, this figure has dropped to 20 percent. "From a historical perspective, this is bad news," says Maranger. "Increased nitrogen levels in coastal ocean ecosystems throughout the world have resulted in excessive plant growth, lack of oxygen, severe reductions in water quality and in fish and other animal populations."

In order to manage coastal ecosystems in a sustainable manner, while fully understanding the impact that humans are having on the nitrogen cycle, the scientists recommend the role of commercial fisheries be reexamined.

The principal investigator of this study received support from the Fond québécois de la recherche sur la nature et les technologies.

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When Accounting For The Global Nitrogen Budget, Don't Forget Fish

http://www.sciencedaily.com/releases/2008/01/080124132431.htm

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.