Key Findings

Credit: US LTER

Between 2010 and 2017, the PAL LTER study area experienced cooler winter air temperatures, cooler summer surface ocean temperatures, and longer ice seasons relative to the first decade of the 21st century (but not relative to the 1950s-1970s). This has slowed sea ice declines, which is associated with increased primary productivity and ocean CO2 drawdown. Springtime phytoplankton productivity and krill recruitment increased in years with high winter sea ice, which fed directly into penguin diets. These processes are allowing researchers to assess the potential for food web recovery.

Credit: PAL LTER

Rapid warming in the WAP coincides with increases in gentoo penguin and decreases in Adélie penguin populations. While foraging ranges of Adélies and Gentoos overlap with each other and with krill density maxima near Palmer Station, the vertical grazing ranges of the two penguin species differ . This suggests that declines in Adélie penguin populations along the WAP are more likely due to direct (snowfall) and indirect (food web alterations) climate impacts on their life histories, rather than direct competition for food.

Credit: PAL LTER

Humpback whale populations are growing at their biological maximum as they recover from intense  commercial whaling. New cetacean research at PAL LTER shows that humpbacks forage in close proximity to the penguins near Palmer Station, and in similar portions of the water column used by Adélie penguins during critical chick rearing periods. Palmer LTER researchers plan to quantitatively assess whether this observation is an indication of competition between baleen whales and penguins.

Credit: PAL and US LTER

Over the past five decades, the West Antarctic Peninsula (WAP) has experienced changes related to rapidly warming winter atmospheric temperatures, dramatic sea ice declines, and accelerated glacial melting. Interactions between ocean and atmospheric climate cycles (El Niño, Southern Annual Mode) influence shoreward heat delivery associated with deep warm ocean waters and alter the upper mixed ocean layer, productivity at the base of the food web, and carbon cycling on the continental shelves.

Credit: Erika Zambello

A 20-year landscape-scale experiment at VCR LTER was the first to show the role of restoration in reestablishing carbon burial in seagrass meadows, which matches natural systems after a decade. Virginia Coast Reserve scientists authored the international protocol through Verified Carbon Standards for issuing seagrass restoration carbon offset credits on the voluntary market. Carbon stored in sediments and sequestered in seagrass biomass is vulnerable to marine heatwaves that are projected to increase.

Credit: Gordan Campbell at Altitude Gallery

Over the last 30 years, nearly half of the upland area on the barrier islands has changed from grassland to shrub thickets, similar to transitions observed in other drylands. For coastal systems, this transition is driven by regional climate (higher winter temperatures, lower precipitation) and shrub feedbacks on microclimate (warmer winter and cooler summer temperatures). Shrub thickets may reduce the ability of islands to build upward and migrate landward in response to sea-level rise and storms.

Credit: Erika Zambello

Long term VCR LTER and comparative studies define a threshold sea-level rise rate beyond which marshes cannot keep pace and drown. An early warning indicator of this state change is an increase in recovery time following flooding disturbances. Storms cause marsh loss by erosion in proportion to wave energy at the marsh edge. Smaller, more frequent storms, not hurricanes, are responsible for most marsh erosion, and this can be reduced by adjacent oyster reefs and seagrass meadows that attenuate waves.

Credit: Gordan Campbell at Altitude Gallery

Historically, this undeveloped landscape has been a shifting mosaic; a new 30-year retrospective now shows directional change and accelerating ecosystem loss. Barrier island upland area has declined by a third, and island marsh loss due to storm overwash has increased, especially in the last decade. Feedbacks between vegetation and sediment transport determine barrier island dune shape, and this affects island migration and the long term resilience of islands to storms.

A research technician samples greenhouse gases on the KBS LTER Main Cropping Systems Experiment
Credit: Kurt Stepnitz

Agriculture emits quantities of greenhouse gases equivalent to those from the transportation sector, and long term LTER research has revealed how farmers can better manage intensive row crop systems to mitigate climate change. Plant-microbe-soil interactions can enhance soil carbon sequestration, reduce nitrous oxide emissions, and promote methane oxidation. Implemented widely, improved management could make cropping systems a major mitigator of climate change.

A KBS LTER graduate student collects soil cores in a prairie strip on the Main Cropping Systems Experiment.
Credit: Kurt Stepnitz

Twenty-plus years of nitrogen fertilization have caused rhizobia in soybeans to evolve toward reduced nitrogen fixation. These evolutionary changes have ecological consequences, as the evolution of reduced cooperation alters soil nitrogen availability. Directed changes to the microbial community, through plant-soil management or added bioinoculants, represents an important frontier for improving cropping system resilience.

A prairie strip growing in wheat at the KBS LTER Main Cropping Systems Experiment.
Credit: Kurt Stepnitz

Simplification of agricultural landscapes reduces abundance of predatory insects, at substantial cost to farmers and society. Diverse landscapes harbor generalist predators such as ladybird beetles, which control crop pests such as soybean aphids, limiting the need for insecticide use. Given global declines in insect abundance, increasing the diversity of habitats and their spatial arrangement across landscapes could enhance biodiversity and provide biocontrol services worth hundreds of millions of dollars per year, while reducing the need for insecticides.

Old-growth forest-stream ecosystems store enormous amounts of carbon. Andrews LTER researchers found that forest biomass accumulated at relatively linear rates over a century – counter to theoretical predictions that biomass accumulation would slow during forest succession. They also found that climate change related mortality at Andrews is low compared to other forests in the western U.S. and that forest harvest reduced stream dissolved organic carbon flux for over 50 years. According to predictions, valleys may be buffered from increasing temperature, but a warming climate could also push old-growth forests to become net carbon emitters.

Credit: AND LTER

Due to increased shading from forest regrowth, streams in recovering forest experience declining temperatures, despite a warming climate. Site history is essential to correctly interpreting climate change response to such trends.

Credit: Lina DiGregorio

Cross-site comparisons reveal varying long term trends in nitrogen exports, and varying responses to warming trends. Although theory predicts that streamflow should recover quickly after disturbance, paired watershed comparisons found decreases in summer flow (relative to undisturbed watersheds) in regenerating post-harvest forests 25 to 45 years old.

Credit: Eriks Zambello

The northern spotted owl, an iconic species in federal lands policy, continues to decline. Over 4,000 invertebrate species have been recorded at AND LTER since 1991. Native climate-sensitive bird species appear to be persisting, despite multi-decade warming, likely because old forests buffer micro-climate.

Credit: BES LTER

Researchers at BES LTER developed new theory and methods for characterizing the multidimensional, multidisciplinary nature of urban ecosystems. This work sparked the development of a new “urban systems science” which has become a key component of sustainability science across the globe.

Baltimore LTER research showed that nutrient cycling and retention in urban watersheds are driven by complex dynamics, with surprisingly high nitrogen retention, climate sensitivity, and surface water-groundwater interactions. These studies have been a foundation for novel analyses of how ecosystems are affected by contaminants of emerging concern.

Credit: BES LTER

The BES LTER Household Telephone Survey provided information on environmental knowledge, perceptions, values, and behaviors of residents, their influence on ecosystem structure and function, and the ways that ecosystem structure and function may affect residents’ physical activity, social cohesion, perception of neighborhood desirability, and willingness to relocate.

Baltimore LTER research has helped challenge the assumption that urban biodiversity is low by showing that biological communities in urban environments are diverse and dynamic. This diversity ultimately affects human well-being, and fluxes of water, energy, carbon, and nutrients.

Credit: Mike Rawlins

Over half of the fresh water and water-borne nutrients flowing from land to the Alaska Beaufort Sea each year are delivered during a two-week period in the spring — earlier than most seasonal Arctic research begins. These inputs are dominated by three large rivers that flow into the central Alaska Beaufort Sea. The composition of nutrients in river water also varies markedly across Alaska’s North Slope; proportions of inorganic versus organic nutrients in rivers feeding the Beaufort Sea increase with watershed steepness from west to east across the region.

Credit: BLE LTER

Most consumers in Beaufort Sea lagoons exhibit omnivorous (generalist) feeding strategies. Food web structure shifts with the seasons as food sources change from ice cover to open water. Multiple food sources provide sustenance to consumers including allochthonous (marine and terrestrial/ riverine organic matter) and autochthonous (microphytobenthic and phytoplankton) organic matter.

Two Inupiat BLE LTER students stand at the base of an eroding shoreline on Barter Island
Credit: BLE LTER

Consistent with reports from other regions of the Arctic and the Beaufort Sea Coast, coastal erosion rates appear to have increased along the shores of Elson Lagoon near Utqiaġvik (formerly Barrow) over the last half century. Areas with historically low erosion rates are changing faster, but rates do not exceed those of areas with historically high erosion.

Researcher James McClelland sampling water during ice break-up in Kaktovik Lagoon, Alaska.
Credit: Ken Dunton

Beaufort Sea lagoons experience large seasonal variations in temperature and salinity related to the Arctic freeze-thaw cycle. In the most extreme cases, lagoons swing from completely freshwater conditions during the spring to hypersaline conditions during the winter. Variations in salinity regimes among lagoons are modulated by ocean exchange characteristics and proximity to river mouths. Water transparency is highest during ice break-up, but following ice retreat, wind driven sediment resuspension increases light attenuation.

The thermokarst failure at Lake NE-14.
Credit: ARC LTER

Warming will increase nutrient cycling in soils, increasing its fertility and nutrient supplies to streams and lakes. Data from long term fertilization studies at ARC LTER are used to model tundra responses to climate change and disturbance. Long term phosphate fertilization has altered the Kuparuk River’s structure and function, but lake response to fertilization is complicated by lake morphometry – benthic and planktonic communities exhibit different responses in deep versus shallow lakes.

Species must deal with the rapidly melting snow.
Credit: ARC LTER

Microbial communities decreased from soil, to streams, to lakes. About half of the common lake bacteria detected were rare species in soils and headwater streams. Initial inoculation from soils was followed by species sorting downslope. With warming, microbial trophic structure has become more homogenous across soil horizons, and plant biomass and woody plant dominance has increased. Arctic LTER researchers have found that, in lakes, warming caused fish populations to cycle between large and small individuals. Models predicted faster growth, which would require more food, increased reproduction, and decreased generation time.