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Understanding Nitrogen’s impact on coastal zones

On the cover of this month’s issue of BioScience, the tranquil scene of an evening in the tidal marsh belies the complex biological interplay of nutrients and organisms found within. The impacts and mechanisms of nutrient enrichment in this coastal zone, particularly of nitrogen introduced by human activity, are well documented in literature — but a new study in December’s BioScience suggests that understanding the forms of nitrogen in the system is a missing piece of the coastal management puzzle.

The study, led by Dr. Jennifer Bowen, associate professor and associate chair of the Northeastern’s Department of Marine and Environmental Sciences, synthesizes a decade of research from her team and collaborators, focused on understanding human impacts on the structure and function of salt marsh systems. Dr. Bowen has long used the living labs of the Boston area coasts to examine how urban ecosystems and microbial communities influence biogeochemical cycling.

Her latest work examines nitrogen forms and flows in the TIDE project, a long-term nutrient enrichment experiment led by co-author Linda Deegan of the Woodwell Climate Research Center that is based at the NSF supported Plum Island Long-Term Ecological Research site in northern Massachusetts. Co-author Anne Giblin of the Marine Biological Laboratory, Woods Hole, is lead principal investigator of the Plum Island research site. The research team also includes Anna Murphy, a postdoc in Bowen’s lab at the Marine Science Center, as well as Hillary Sullivan of the Woodwell Climate Research Center, Ashley Bulseco, a former PhD student of Bowen’s and currently a professor at Eckerd College, Thomas Mozdzer of Bryn Mawr College, and James Nelson of the University of Louisiana at Lafayette. It was co-author David Johnson of the Virginia Institute of Marine Science who captured the journal’s cover photo, noting the clouds rolling in over the confluence of two branches of West Creek at Plum Island during early evening data collection one summer.  

Urbanization, industry, and large scale food production have resulted in steady and increasing influxes of excess reactive nitrogen [from man-made systems]to the coasts, causing eutrophication and damage to coastal habitats. By taking up some of this nitrogen, wetlands serve a critical role in reducing these impacts. But Bowen et al. present analyses demonstrating that the impacts of nitrogen input cannot be assessed unilaterally; rather, there are varied impacts of each specific form of nitrogen.

Some forms of nitrogen relieved nutrient limitation and increased primary production in the marsh, whereas others supported higher rates of organic decomposition and muted the rates of primary production. The study argues that both the form and quantity of nitrogen influx to the coasts, and how these different forms of nitrogen mediate the balance between marsh carbon storage and loss, will be crucial for managing coastal wetlands as sea levels continue to rise. 

“Understanding how salt marsh ecosystems will respond to global change drivers such as nutrient enrichment and sea level rise requires expertise across a range of disciplines,” Bowen said. “Our team includes biogeochemists, microbial ecologists, and people specializing in plants, invertebrates, and fisheries species that all shed light on different aspects of the whole ecosystem response to these disturbances.

This study underscores the importance of the long-term research investment by the National Science Foundation, who funded this work, and in the convergence of researchers from across fields to address questions with important implications for the management of critical coastal resources.”

Read the paper here.

Coastal photo by Dr. David Johnson, @DavidSamJohnson

Author: Sierra Muñoz