• Energy Research

Tidal habitats host a diversity of species and provide hydrological services such as shoreline protection and nutrient attenuation. Accretion of sediment and biomass enables tidal marshes and swamps to grow vertically, providing a degree of resilience to rising sea levels. Even if accelerating sea level rise overcomes this vertical resilience, tidal habitats have the potential to migrate inland as they continue to occupy land that falls within the new tide range elevations. The existence of developed land inland of tidal habitats, however, may prevent this migration as efforts are often made to dyke and protect developments. To test the importance of inland migration to maintaining tidal habitat abundance under a range of potential rates of sea level rise, we developed a spatially explicit elevation tracking and habitat switching model, dubbed the Marsh Accretion and Inundation Model (MAIM), which incorporates elevation-dependent net land surface elevation gain functions. We applied the model to the metropolitan Washington, DC region, finding that the abundance of small National Park Service units and other public open space along the tidal Potomac River system provides a refuge to which tidal habitats may retreat to maintain total habitat area even under moderate sea level rise scenarios (0.7 m and 1.1 m rise by 2100). Under a severe sea level rise scenario associated with ice sheet collapse (1.7 m by 2100) habitat area is maintained only if no development is protected from rising water. If all existing development is protected, then 5%, 10%, and 40% of the total tidal habitat area is lost by 2100 for the three sea level rise scenarios tested.

AbstractQuantifying global patterns of terrestrial nitrogen (N) cycling is central to predicting future patterns of primary productivity, carbon sequestration, nutrient fluxes to aquatic systems and climate forcing. With limited direct measures of soil N cycling at the global scale, syntheses of the 15N:14N ratio of soil organic matter across climate gradients provide key insights into understanding global patterns of N cycling. In synthesizing data from over 6000 soil samples, we show strong global relationships among soil N isotopes, mean annual temperature (MAT), mean annual precipitation (MAP) and the concentrations of organic carbon and clay in soil. In both hot ecosystems and dry ecosystems, soil organic matter was more enriched in 15N than in corresponding cold ecosystems or wet ecosystems. Below a MAT of 9.8°C, soil δ15N was invariant with MAT. At the global scale, soil organic C concentrations also declined with increasing MAT and decreasing MAP. After standardizing for variation among mineral soils in soil C and clay concentrations, soil δ15N showed no consistent trends across global climate and latitudinal gradients. Our analyses could place new constraints on interpretations of patterns of ecosystem N cycling and global budgets of gaseous N loss.

There is wide agreement that anthropogenic climate warming has influenced the phenology of forests during the late twentieth and early twenty-first centuries(1,2). Longer growing seasons can lead to increased photosynthesis and productivity(3), which would represent a negative feedback to rising CO2 and consequently warming(4,5). Alternatively, increased demand for soil resources because of a longer photosynthetically active period in conjunction with other global change factors might exacerbate resource limitation(6,7), restricting forest productivity response to a longer growing season(8,9). In this case, increased springtime productivity has the potential to increase plant nitrogen limitation by increasing plant demand for nitrogen more than nitrogen supplies, or increasing early-season ecosystem nitrogen losses(10,11). Here we show that for 222 trees representing three species in eastern North America earlier spring phenology during the past 30 years has caused declines in nitrogen availability to trees by increasing demand for nitrogen relative to supply. The observed decline in nitrogen availability is not associated with reduced wood production, suggesting that other environmental changes such as increased atmospheric CO2 and water availability are likely to have overwhelmed reduced nitrogen availability. Given current trajectories of environmental changes, nitrogen limitation is likely to continue to increase for these forests, possibly further limiting carbon sequestration potential.

Abstract In China, agricultural residues (particularly from rice) are widely used for energy and other applications, albeit on a localized scale and often at poor rates of efficiency. If some portion of this biomass were to be reallocated and transported to central biomass energy facilities, an initial component of the design process would be to gain an understanding of the spatial distribution of biomass production. In this paper, we present a method that utilizes China-wide data sets of net primary production (NPP) from the moderate-resolution imaging spectrometer (MODIS) and detailed land cover maps produced from Landsat-enhanced thematic mapper plus (ETM+) data to calculate the spatial distribution of rice straw for the period 2000–2004. Through a comparison with census statistics, we show that remote measures of rice straw can reasonably predict census results at the provincial scale. Remote sensing results have the added benefits of being a quick and inexpensive solution for providing spatially detailed information. Therefore, these data can be used for applications such as the spatial optimization of energy production infrastructure. In an error analysis including climate and land use variables, we found that data on sown rice area is the largest source of error. Therefore, the most important improvement to this method would be more accurate and more frequently updated maps of agricultural land use.

Future climates are forecast to include greater precipitation variability and more frequent heat waves, but the degree to which the timing of climate variability impacts ecosystems is uncertain. In a temperate, humid grassland, we examined the seasonal impacts of climate variability on 27 y of grass productivity. Drought and high-intensity precipitation reduced grass productivity only during a 110-d period, whereas high temperatures reduced productivity only during 25 d in July. The effects of drought and heat waves declined over the season and had no detectable impact on grass productivity in August. If these patterns are general across ecosystems, predictions of ecosystem response to climate change will have to account not only for the magnitude of climate variability but also for its timing.

With over 1 billion cattle in the world as well as over 2 billion sheep, goats and buffalo, these animals contribute approximately 15% of the global human protein supply while producing a significant proportion of anthropogenic emissions of greenhouse gases and global nutrient fluxes. Despite increasing reliance on grazers for protein production globally, the future of grazers in a changing world is uncertain. Factors such as increased prevalence of drought, rising atmospheric CO _2 concentrations, and sustained nutrient export all have the potential to reduce cattle performance by reducing the nutritional quality of forage. However, there are no analyses to quantify changes in diet quality, subsequent impact on cattle performance and cost of supplementation necessary to mitigate any predicted protein deficiency. To quantify the trajectory of nutritional stress in cattle, we examined more than 36 000 measurements of dietary quality taken over 22 yr for US cattle. Here, we show that standardizing for spatial and temporal variation in drought and its effects on forage quality, cattle have been becoming increasingly stressed for protein over the past two decades, likely reducing cattle weight gain. In economic terms, the replacement costs of reduced protein provision to US cattle are estimated to be the equivalent of $1.9 billion annually. Given these trends, nitrogen enrichment of grasslands might be necessary if further reduction in protein content of forages is to be prevented.

There are many reasons that the isotopic signature of deposited N is unlikely to be causing the declines in plant δ15N. Although our analysis of foliar δ15N was limited to after 1980, declines in foliar, tree-ring and sediment δ15N pre-date the onset of widespread inorganic N fertilizer use, as well as any timing ofshifts to more reduced forms of N in deposition. Also, despite variation in the isotopic signatures of N deposition and its sources, there is no evidence currently that the signature of atmospheric N deposition has been declining overtime. A global, comprehensive dataset on the signature of N deposition does not exist and would be helpful to generate. Yet, even if the isotopic signature of N deposition has been declining, changes in N availability can have a stronger influence on plant δ15N than the signature of added N. Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Tecnológica Nacional. Facultad Regional Santa Cruz. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia de Santa Cruz; Argentina Fil: Guerrieri, Rossella. Centre for Ecological Research and Forestry Applications; España Fil: Gundale, Michael J.. Swedish University of Agricultural Sciences; Suecia Fil: Hietz, Peter. University of Natural Resources and Life Sciences; Austria Fil: Werner, Christiane. Albert Ludwigs University of Freiburg; Alemania Fil: Fang, Yunting. Chinese Academy of Sciences; República de China Fil: Elmore, Andrew J.. University of Maryland; Estados Unidos Fil: Nelson, David M.. University of Maryland; Estados Unidos Fil: Templer, Pamela H.. Boston University; Estados Unidos