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February 2017
LTER in the News
News from the National Science Foundation  Other Media 
Recent LTER Publications
Collaborative Solutions to Nitrogen Runoff | Journal of Soil and Water Conservation 

How do you begin to approach wicked problems, those that span socioeconomic and ecological spheres, when solutions involve multiple and varied stakeholders? Researchers at the Kellogg Biological Station LTER began to tackle one of U.S. agriculture’s greatest challenges, excess nitrogen pollution, by hosting “The N Roundtable,” to improve the flow of information through a farming landscape that has changed dramatically in the past few decades.
As precision agriculture, big data, and private farm advisors have supplemented agricultural extension specialists, nitrogen management has become ever more complex. Trust, competing values, usability, and diffusion of innovations can  play as large a role as soil chemistry, said roundtable participants.

Nutrient runoff—often caused by incomplete uptake of nitrogen fertilizer—drives increased eutrophication of lakes and streams, groundwater contamination, and increased emissions of the greenhouse gas nitrous oxide. Members of the roundtable shared a common interest in addressing these concerns and recommended several strategies—including better tailoring of decision support tools, stronger linkages between public and private advisors, and improved data sharing, but also strengthening integration of social and biophysical research.
—Madison Harris
Ocean Hotspots for Carbon Storage | Proceedings of the National Academy of Sciences

Sediment trap recovery
The global carbon cycle doesn’t have many off-ramps, but the deep ocean is one of them. Researchers with the California Current Ecosystem (CCE) LTER have found that twice as much carbon finds its way to the deep ocean at mesoscale ocean fronts as elsewhere in the ocean.

Normally, phytoplankton take up carbon from seawater, get eaten by zooplankton, and excreted. If the fecal pellets sink slowly, much of the carbon and nutrients they contain gets recycled before they sink from the active layer. Researchers studying the deep oceans off the coast of Santa Barbara found that diatoms at this ocean front formed denser silicate shells than normal and therefore they (and fecal pellets containing them) sank faster, shuttling carbon to the ocean bottom.
If a similar dynamic holds true at other mesoscale fronts, the process may be responsible for over a quarter of total organic carbon sequestration in the California Current and other coastal upwelling ecosystems. Understanding the role of ocean circulation in carbon storage affects predictions of how much carbon the oceans will be able to store in the future.
—Erin O' Reilly
The Spruce and the Hare: Backing Up Leopold’s Intuition | Forest Ecology and Management

Snowshoe hares prefer many other plants to white spruce seedlings, but when the population of hares skyrockets—as it does about once a decade—they can decimate even a bumper crop of spruce seedlings. Researchers with the Bonanza Creek LTER reconstructed over 40 years of browsing history by analyzing the age and browse scars of thousands of seedlings and saplings at 18 locations on the floodplain of Alaska’s Tanana River.

White spruce is the dominant boreal tree species and a key source of timber, but climate change is rapidly re-making the Arctic. Understanding the multiple factors that affect white spruce recruitment and establishment may help to predict, and even influence, where these valuable trees can get—and keep—a foothold.

The study, published in Forest Ecology and Management, fingered hot dry summers and as a major source of seedling mortality and early snowfall as protective, but the overwhelming factor influencing seedling establishment was whether seeds got started in the lull between hare population booms.

The authors included a short homage to the beloved naturalist Aldo Leopold, who observed a similar dynamic between oaks and rabbits on his Wisconsin farm in 1949.
—Marty Downs
Urban Streams Cycle Nitrogen as Fast as Unbuilt Systems | FEMS Microbiology Ecology

Urban watersheds—with their fertilized lawns, street runoff, treated and untreated wastewater—have proportionally more nitrogen flowing through them than undeveloped landscapes do. But are urban streams somehow less able to process that nitrogen? New research out of the Baltimore Ecosystem Study LTER says: no. The study, based on 385 urban watersheds and published in the journal FEMS Microbial Ecology, found that urban watersheds have similar, if not higher, nitrogen processing rates than natural areas.

Nitrogen is a vital nutrient that cycles through nearly all ecosystems. But too much nitrogen can exacerbate algal blooms and contribute to aquatic dead zones. Previous studies of urban watersheds have focused on how much nitrogen flows through them, but done little to understand nitrogen processing rates and how they might differ based on climatic, geographic, or social factors. The BES study revealed that those factors had less influence on  urban streams than on their undeveloped counterparts, a finding that is in line with the urban homogenization hypothesis.

Despite this display of resilience on the part of the urban ecosystem, human-induced nitrogen input still outpaces processing. Certain development techniques, including green roofs and bioretention cells, may allow more complete nitrogen uptake by regulating the flow of water through the systems, giving the diverse microbial communities found in urban streams and landscapes time to work.
—Alina Werth
LTER Synthesis
What (and When) is the Point of No Return? | Ecological Monographs
How—and when—do ecosystems change character? Are those shifts reversible? And what signs might precede them? Such questions are hard enough to answer in a single place. One might think that incorporating different kinds of ecosystems would only complicate the problem. But a group of scientists in the Long-Term Ecological Research Network is finding a remarkably consistent pattern by combining models and data across several long-term ecological experiments.

Their study, published in Ecological Monographs, asks how the intensity and duration of changes interact to determine whether an ecosystem shift is temporary or more likely to be permanent.
Intense grazing driving a dry grassland toward a persistent shrubland is one of the classic examples of regime-shift. The researchers ran many simulations using a model that has been well-validated against over 100 years of grazing studies in the Chihuahuan Desert. Their model suggested that grasslands could re-establish after even moderately-intense grazing—as long as the grazing didn’t continue for too long. But the higher the intensity of disturbance, the narrower was the window of time in which change would be temporary.

They also examined the role of spatial patchiness and temporal variability, finding that as a system moved toward a threshold, spatial patchiness intensified—potentially serving as a marker for impending regime-shift.

To determine how generally applicable the results might be, they ran models of other ecosystems and found the similar outcomes. And they delved into long-running on-the-ground experiments in which a disturbance—such as excess nutrients, invasive species, or fire suppression—was removed after driving the system to the brink of irreversible change.

At the ecosystem scale, such experiments are rare, as they require decades of manipulation and observation, but the results for the three examples they considered were consistent with model results. In the near term, they argue, the most robust test of these principles would be to undertake deliberate experiments in systems that respond rapidly—such as lakes, annual plant communities, and microbial ecosystems.
—Marty Downs
The Patos Lagoon Estuary (PLE) in southern Brazil is one of the coastal sites in the Brazilian Long Term Ecological Research Program (BLTE). Jose H. Muelbert announced on the ILTER list that PLE researchers have just published a thematic volume with integrated results of their long term studies in the journal Marine Biology Research.

Photo Credits (top to bottom): Kellogg Biological Station, A. Giraldo Lopez/CCE LTER, Dave Doe (CC-BY 2.0), Baltimore Ecosystem Study LTER, Scott Bauer/USDA (CC-BY-2.0)
Copyright © 2017 LTER Network Office, All rights reserved.

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