What a Drag: The Global Impact of Bottom Trawling plus 2 more |
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- What a Drag: The Global Impact of Bottom Trawling
- Up to 70 Percent of Northeast U.S. Coast May Adapt to Rising Seas
- Fire and Ice: Gauging the Effects of Wildfire on Alaskan Permafrost
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What a Drag: The Global Impact of Bottom Trawling Posted: 14 Mar 2016 10:00 AM PDT
Summary: Recent scientific work outlines the severe consequences the practice of bottom trawling has on loose sediment on the ocean floor. Bottom trawling is a widespread industrial fishing practice that involves dragging heavy nets, large metal doors and chains over the seafloor to catch fish. Although previous studies documented the direct impacts of bottom trawling on corals, sponges, fishes and other animals, an understanding of the global impact of this practice on the seabed remained unclear until now. The first calculation of how much of the seabed is resuspended (or stirred up) by bottom-trawling shows that the sediment mass is approximately the same amount of all sediment being deposited on the world’s continental shelves by rivers each year (almost 22 gigatons).
Contact Information: Leslie Gordon, USGS ( Phone: 650-329-4006 ); Media Office, WHOI ( Phone: 508-289-3340 ); Recent scientific work outlines the severe consequences the practice of bottom trawling has on loose sediment on the ocean floor. Bottom trawling is a widespread industrial fishing practice that involves dragging heavy nets, large metal doors and chains over the seafloor to catch fish. Although previous studies documented the direct impacts of bottom trawling on corals, sponges, fishes and other animals, an understanding of the global impact of this practice on the seabed remained unclear until now. The first calculation of how much of the seabed is resuspended (or stirred up) by bottom-trawling shows that the sediment mass is approximately the same amount of all sediment being deposited on the world’s continental shelves by rivers each year (almost 22 gigatons). Understanding regional and global magnitudes of resuspended sediment is an essential baseline for the analysis of the environmental consequences for continental shelf habitats and their associated seafloor and open-ocean ecosystems. The scientists found new ways to look at and into the seabed to document the evidence of the effects of bottom trawling. Bottom trawling can result in vastly different effects on different types of seabed sediment (such as sand, silt or mud), each with different ecological consequences. Trawling destroys the natural seafloor habitat by essentially rototilling the seabed. All of the bottom-dwelling plants and animals are affected, if not outright destroyed by tearing up root systems or animal burrows. By resuspending bottom sediment, nutrient levels in the ambient water, and the entire chemistry of the water is changed. Resuspended sediment can lower light levels in the water, and reduce photosynthesis in ocean-dwelling plants, the bottom of the food web. The resuspended sediment is carried elsewhere by currents, and often lost from the local ecosystem. It maybe deposited elsewhere along the continental shelf, or in many cases, permanently lost from the shelf to deeper waters. Changing parts of the seafloor from soft mud to bare rock can eliminate those creatures that live in the sediment. Species diversity and habitat complexity are directly affected by changing the physical environment of sand, mud or rock that results from trawling.
“This study raises serious concerns about the future stability of continental shelves – the very source of the vast majority of the fish we consume,” said geological oceanographer and lead author Ferdinand Oberle, now a visiting scientist at the U.S. Geological Survey, and previously with the Woods Hole Oceanographic Institution, and MARUM, the Center for Marine Environmental Sciences, University of Bremen (Germany) when the study was done. “A farmer would never plow his land again and again during a rainstorm, watching all his topsoil be washed away, but that is exactly what we are doing on continental shelves on a global scale.” As part of the study, scientists developed a new, universal approach to calculate bottom-trawling-induced sediment resuspension that gives marine management a new and important tool to assess the impact from bottom trawling. Previous studies characterized the seabed as either “trawled” or “untrawled” but with these novel methodologies it was possible to show systematically a range of bottom-trawling-induced changes to the seabed and classify them in accordance with how often the seabed was disturbed by bottom trawlers. “The global calculations were a big surprise and we calculated them at least 10 times to make sure we were not making a mistake. I am still in awe of these results and their environmental implications,” said USGS oceanographer Curt Storlazzi, a coauthor of the paper who helped develop the computational models for the study. These new understandings about the effects of bottom trawling, come out of scientific cruises on the Research Vessel METEOR from Germany to the offshore area northwest of the Iberian peninsula with a team of international scientists. During the cruises, scientists conducted sidescan-sonar surveys and collected bottom current data. Laser sediment particle samplers and a remotely-operated submersible vessel were utilized as well. After the cruises, laboratory work involving lead-isotope dating and sediment grain-size analysis, and the development of a sediment mobilization model contributed to the conclusions of the study. Two new research papers to come out of this study were published in Elsevier's “Journal of Marine Systems,” and are available online: “What a drag: Quantifying the global impact of chronic bottom trawling on continental shelf sediment” “Deciphering the lithological consequences of bottom trawling to sedimentary habitats on the shelf”
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Up to 70 Percent of Northeast U.S. Coast May Adapt to Rising Seas Posted: 14 Mar 2016 09:00 AM PDT
Summary: Much of the coast from Maine to Virginia is more likely to change than to simply drown in response to rising seas during the next 70 years or so, according to a new study led by the U.S. Geological Survey. The study is based on a new computer model that captures the potential of the Northeast coast to change, driven by geological and biological forces, in ways that will reshape coastal landscapes.
New model corrects assumption that drowning is only scenario for low-lying coastsContact Information: Erika Lentz ( Phone: 508-457-2238 ); Heather Dewar ( Phone: 443-498-5584 ); Much of the coast from Maine to Virginia is more likely to change than to simply drown in response to rising seas during the next 70 years or so, according to a new study led by the U.S. Geological Survey. The study is based on a new computer model that captures the potential of the Northeast coast to change, driven by geological and biological forces, in ways that will reshape coastal landscapes. In a paper published Monday in Nature Climate Change, the researchers reported that 70 percent of the Northeast Atlantic Coast is made up of ecosystems that have the capacity to change over the next several decades in response to rising seas. For example, barrier islands may migrate inland, build dunes, change shape, or be split by new inlets as tides, winds, waves and currents sculpt their sands. Marshes trap sediment and break down decaying plants into new soil, which may elevate them sufficiently in some areas to keep pace with sea-level increases. While most sea-level rise models that cover large areas show low-lying coastal land converting to open water in coming decades, many of these inundation models over-predict the land likely to submerge. The USGS model, developed in collaboration with Columbia University’s Earth Institute, produces a more nuanced picture of sea level rise as a mosaic of dry land, wetlands, and open seas, rather than as a uniform response across the landscape. The USGS model is the first to factor in natural forces and make detailed predictions from the 2020s through the 2080s over a large coastal area, some 38,000 square kilometers (about 9.4 million acres). It is an advance over most regional models, which project drowning as the only outcome as the oceans rise. These are often referred to as “bathtub models” and assume the coast is progressively submerged as sea levels rise. Projections from inundation models are straightforward: some coastal land will remain above the levels of the rising seas and some will drown. The new model includes the potential for dynamic coastal change and shows where in response to future sea levels, coastal lands fall on a continuum between dry land and open water. “Geologists have always known that the coast has some potential for give and take,” said lead author Erika Lentz, a research geologist at the USGS Coastal and Marine Science Center in Woods Hole, Massachusetts. “But the standard bathtub models of sea level rise don’t reflect that. This approach couples what we do know about these systems with what we still need to learn—how different ecosystems may respond to different sea-level rise scenarios— to estimate the odds that an area will persist or change instead of simply drown.” By casting results in terms of odds, the new model provides a more accurate picture of sea-level rise vulnerability for informing adaptation strategies and reducing hazards, the USGS researchers say. They make it clear, however, that just because an area is less likely to drown might not mean it is less vulnerable. “Our model results suggest that even natural changes may pose problems,” Lentz said. “For example, the likelihood that barrier islands will change could impact the infrastructure and economies of coastal communities, and the barrier islands or marshes may not protect coastal communities in the same way they do today.” In fact, the outcome is uncertain for the Northeast’s low-lying developed coastlines, where seawalls, buildings and other immovable structures thwart some natural processes. The model found the region’s developed coastal lands lying 1 meter (about 3 1/2 feet) or less above sea level will likely face a tipping point by the 2030s, when humans’ decisions about whether and how to protect each area will determine if it survives or drowns. A 2012 USGS study identified the densely populated region from Cape Hatteras to Boston as a hot spot where seas are rising faster than the global average, so land managers urgently need to understand how their coastal landscape may change, said John Haines, coordinator of the USGS Coastal and Marine Geology Program. “The model allows us to identify vulnerable areas, and that information can be very valuable to land managers as they consider whether to protect, relocate or let go of certain assets,” Haines said. “Even when the results are uncertain, it’s useful to know there’s a 50 percent chance that an important habitat or infrastructure project may be lost in a few decades.” To come up with their model for the Northeastern United States, the researchers mapped all coastal land between 10 meters (about 33 feet) above sea level and 10 meters below it, from the Virginia-North Carolina line to the Maine-Canada border. They factored in a variety of forces that affect coastal change, from planetary phenomena like the movement of Earth’s tectonic plates to local ones like falling groundwater levels that cause land surfaces to sink. Looking at parcels of 30 meters by 30 meters—about the size of two NBA basketball courts side by side—they weighed the balance of forces on each parcel. Using scenarios that assume humans will continue adding moderate to high levels of greenhouse gases to the atmosphere through the 21st century, the team projected global sea level rise for the 2020s through the 2080s, and applied that to the coast. The model then estimated the likelihood, from 0 to 100 percent, that each parcel will persist above sea level at the end of each decade. Predictions for many parcels fell close to 50 percent in the first few decades, a tossup between drowning and surviving. The uncertainty was greatest when the researchers had to wrestle with more than one question that can’t yet be definitively answered. Among them are, how fast will seas rise, can coastal marshes make new soil quickly enough to stay above the waves, and what engineering strategies will people use to protect some shorelines? “By building in our understanding of the sea level rise response of the coastal landscape, we’re providing a more realistic picture of coastal change in the Northeastern U.S. over the next several decades,” Lentz said. The researchers’ next step will be to group the basketball-court-sized parcels into larger areas, such as major coastal cities, national wildlife refuges, and national seashores, and assess the vulnerability of these areas to future change and drowning. This information may assist decisionmakers as they develop management priorities to address longer-term coastal challenges. This research was supported by the USGS Coastal and Marine Geology Program and the Department of the Interior Northeast Climate Science Center (NE CSC), which is managed by the USGS National Climate Change and Wildlife Science Center. The NE CSC is one of eight that provides scientific information to help natural resource managers respond effectively to climate change. |
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Fire and Ice: Gauging the Effects of Wildfire on Alaskan Permafrost Posted: 14 Mar 2016 05:51 AM PDT
Summary: USGS scientists, in collaboration with researchers at the University of Minnesota and University of Alaska Fairbanks, have mapped belowground permafrost in areas of Alaska that have been affected by wildfire, years-to-decades after the fires occurred.
Contact Information: Jon Campbell ( Phone: 703-648-4180 ); Burke Minsley ( Phone: 303-236-5718 ); USGS scientists, in collaboration with researchers at the University of Minnesota and University of Alaska Fairbanks, have mapped belowground permafrost in areas of Alaska that have been affected by wildfire, years-to-decades after the fires occurred.
“There has been global concern for many years about the effects of the warming climate on high-latitude permafrost and its vast stores of organic carbon," said Virginia Burkett, USGS Associate Director for Climate and Land Use Change. “When permafrost thaws, carbon currently locked up in the frozen ground is released to the atmosphere as carbon dioxide or methane. Wildfires amplify carbon emissions from declining permafrost in ways we are just now beginning to understand." Exceptionally warm and dry weather caused hundreds of wildfires in Alaska and Canada in 2015. Millions of acres of land were burned, causing immediate risk and disturbance to local residents and ecosystems, with plumes of smoke that carried all the way to the lower 48 states. During two years of extensive field surveys in interior Alaska, the research team combined field observations with geophysical measurements that crossed the boundaries of historical and recent fires to analyze the impacts of wildfire on the underlying permafrost. The impact of fire on permafrost can be highly variable across different landscapes. “Data from the geophysical surveys give us a detailed picture of how permafrost is distributed in the subsurface. This new information helps improve our understanding of how permafrost has changed in response to fire,” said Burke Minsley, a USGS geophysicist and lead author of the study. “The geophysical techniques we used can be compared to medical imaging that probes the human body without surgery,” Minsley continued. “We can ‘see’ permafrost conditions underground without expensive and disruptive drilling. Data about wildfires and permafrost conditions can be combined with satellite remote sensing observations to help extend interpretations over much larger areas across the state.” Scientists have long known that severe fires can remove the layer of organic material at the ground surface that serves to insulate permafrost and maintain frozen conditions. This study documented locations where permafrost appears to be resilient to disturbance from fire, areas where warm permafrost conditions exist that may be vulnerable to future change, areas where permafrost has thawed, and one location where permafrost appears to be recovering after fire. More information is needed to quantify fire impacts on permafrost in order to assess future vulnerabilities. The research article was recently published online in the Journal of Geophysical Research: Earth Surface , a journal of the American Geophysical Union. Learn more Recent USGS press releases on permafrost: |
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