Local dynamical equivalence of certain food webs

An important challenge in theoretical ecology is to find good coarse-grained representations of complex food webs. Here, we use the approach of generalized modeling to show that it may be possible to formulate a coarse-graining algorithm that conserves the local dynamics of the model exactly. We show examples of food webs with a different number of species that have exactly identical local bifurcation diagrams. Based on these observations, we formulate a conjecture governing which populations of complex food webs can be grouped together into a single variable without changing the local dynamics. As an illustration, we use this conjecture to show that chaotic regions generically exist in the parameter space of a class of food webs with more than three trophic levels. While our conjecture is at present only applicable to relatively special cases, we believe that its applicability could be greatly extended if a more sophisticated mapping of parameters were used in the model reduction.     

New developments in water efficiency

1Water LossInitiativesUnaccounted-for water(or unbilled water)has beenreceiving newscrutiny at both the state and nationallevels.For years,water conservationeffortsin Europehave emphasized reduction in water loss to a muchgreater extent thaninthe United S…     

A numerical study of the air flow within and around a single tree

A three-dimensional non-hydrostatic numerical model has been used to investigate the air flow and turbulence around a single tree.The results for velocity and turbulence distributions have been compared with available data from windtunnel experiments; the agreement is satisfactory.Simulations have been carried out for different meteorological conditions (wind speed, thermal stratification) as well as for different canopy characteristics (stem height, crown diameter, crown height, porosity).Dedicated to Prof. F. Wippermann on the occasion of his 65th birthday.     

Relationship between aboveground and belowground biomass ofSpartina alterniflora (Smooth Cordgrass)

Aboveground and belowground biomass ofSpartina alterniflora were harvested during the period of peak aerial biomass from six sites along a latitudinal gradient ranging from Georgia to Nova Scotia. An equation relating live aboveground to live belowground biomass for short-form plants was formulated, using data collected in Delaware marshes. When data from the other sites were substituted into the equation, the mean live belowground biomass it predicted was within 15% of the value determined by harvesting at four of the five sites. At all sites, short-form plant live belowground biomass was concentrated in the upper 10 cm. Dead belowground biomass was located mostly in the top 15 cm in southern marshes, but was more evenly distributed with depth in northern marshes. Results were more ambiguous for tall-form plants, probably because of greater spatial variability in biomass distribution, and greater seasonal biomass dynamics.     

On the wind field in the Loisach valley — Numerical simulation and comparison with the LOWEX III data

Summary A three-dimensional nonhydrostatic model, forced by a surface energy budget, has been used to study thermally induced circulation in mountainous terrain. The numerical results were compared with observed wind data of the LOWEX-Experiment realized in the Loisach valley near Garmisch. Although the qualitative agreement in space and time is reasonable, the model underpredicts especially the valley wind by a factor of two. The complex structure of the simulated airflow in this region illustrates the difficulties of field experiments to find out the main characteristics of such circulations. In two sensitivity studies, the effect of the size of the integration region and the effect of a slight variation in direction of the larger scale wind is discussed.With 18 Figures     

Atmospheric dust contribution to deep-sea particle fluxes in the subtropical Northeast Atlantic

The lithogenic flux of sediment trap material was analyzed from a three year time series (February 2002–March 2005) at 2000 m depth in the Northeast Atlantic (Kiel 276, 33°N, 22°W) with regards to the seasonal and interannual variability of flux intensity and mineralogy—by applying an automated particle SEM-EDX analysis (scanning electron microscope-energy dispersive X-ray analysis). The lithogenic flux shows strong interannual variations with highest lithogenic flux rates occurring during January–February and April–March coupled to the total particle flux. Mean lithogenic flux rates for the sample years are 7.1 (2002–2003), 5.1 (2003–2004) and 16.1 mg m^?2 d^?1 (2004–2005). Mineral assemblages from the three sample years reveal distinct major minerals related to specific source regions. Clay minerals dominate the lithogenic fraction within the years 2002 and 2004 with illite (2002–2003) and palygorskite (2003–2004) being the major clay minerals. During the year 2004–2005, quartz is the major lithogenic mineral accompanied by smectite. The mineral assemblages hint to a mixture of North African source areas with dominant sources in Mauritania and north western parts of NW Africa for the years 2002–2004 and central Sahara (Algeria–Mali) within the year 2004–2005.     

Three-dimensional bounding surface architecture and lateral facies heterogeneity of a wet aeolian system: Entrada Sandstone,Utah

Aeolian deposits form noteworthy reservoirs (for example, Norphlet Formation and Rotliegend Group) in hydrocarbon extraction and carbon capture and storage contexts, but stratigraphic architecture imparts significant heterogeneity. Bounding surfaces result from autogenic and allogenic controls and can represent important changes in dune-field dynamics. To further evaluate the impacts of facies heterogeneity and flow-inhibiting bounding surfaces on reservoir performance and reconstruct ancient erg evolution, the stratigraphic architecture of aeolian systems must continue to be studied at multiple scales. This study pairs traditional methods (for example, measured stratigraphic sections) with advanced technologies (for example, drone-derived outcrop models) to precisely resolve the metre to kilometre-scale three-dimensional stratigraphic architecture of wet aeolian Middle Jurassic Entrada Sandstone outcrops located at Rone Bailey Mesa near Moab, Utah, USA. Five facies are identified, primarily based on sedimentary fabrics, and are grouped into three associations named dune, sabkha and sand sheet. Statistical analyses of gamma-ray spectrometer and automated mineralogy data indicate a distinct mineralogical difference between dune (quartz-rich) and sabkha (more feldspathic) packages, suggesting that gamma-ray logs may be used to better predict facies distribution in the subsurface. Seven modelled super bounding surfaces are planar to undulatory, with no perceived spatial trends. Five modelled interdune migration surfaces are undulatory but exhibit an average 0.09° angle of climb roughly parallel to the palaeocurrent direction. Two modelled superposition surfaces are linear to sinuous in plan-view. Laterally discontinuous sabkha packages observed are interpreted to be remnants of closed, damp, interdune flats located between ca 8.5 to 17.0 m tall, sinuous, transverse bedforms or patches of such bedforms. Based on stratigraphic architecture interpretations, the Entrada Sandstone preserves signals of allogenic forcing and localized autogenic bedform cannibalization of the substrate. The findings of this study, some of which are not commonly recognized in wet aeolian facies models, enhance the understanding of erg evolution and can parameterize static models of aeolian reservoirs.     

Estimating geoid height change in North America: past, present and future

The forthcoming GRAV-D gravimetric geoid model over the United States is to be updated regularly to account for changes in geoid height. Its baseline precision is to be at the 10–20 mm level over non-mountainous regions. The aim of this study is to provide an estimate of the magnitude, time scale, and spatial footprint of geoid height change over North America, from mass redistribution processes of hydrologic, cryospheric and solid Earth nature. Geoid height changes from continental water storage changes over the past 50 years and predicted over the next century are evaluated and are highly dependent on the used model. Groundwater depletion from anthropogenic pumping in regional scale aquifers may lead to geoid changes of 10 mm magnitude every 50–100 years. The GRACE time varying gravity fields are used to (i) assess the errors in a glacial isostatic adjustment model, which, if used to correct the GRAV-D model, may induce errors at the 10 mm geoid height level after ~20 years, (ii), evaluate geoid height change over ice mass loss regions of North America, which, if they remain unchanged in the future, may lead to geoid height changes at the 10 mm level in under a decade and (iii), compute sea level rise and its effect on the geoid, which is found to be negligible. Coseismic gravitational changes from past North American earthquakes are evaluated, and lead to geoid change at the 10-mm level for only the largest thrust earthquakes. Finally, geoid change from volcanic processes are assessed and found to be significant with respect to the GRAV-D geoid model baseline precision for cataclysmic events, such as that of the 1980 Mt. St. Helens eruption. Recommendations on how to best monitor geoid change in the future are given.