Academic literature on the topic 'Ecology|Environmental science'

Evaluation of Experimental Design Options in Environmental Nano-Science Research As an experimental research design plays a pivotal role in executing a research problem, it is imperative of a researcher to develop a suitable and sound research design. Utilizing robust statistical methods can further enhance the study power and thus allow drawing a logical conclusion. The same holds true for basic environmental science research, including research related to the effects of engineered nanomaterials in the environment.

I apply the GMTS approach to graphical modelling of time series to data sets from economics, ecology and environmental science. This approach improves on traditional approaches to modelling insofar as it selects the most parsimonius model. I improve on this approach by removing some redundancies in the GMTS approach. However, a bias in terms of which links are selected means that it is unlikely that this model will select the best causal model.

Environmental issues are often complex with many different constituents operating according to a broad range of communication techniques. In order to foster negotiations, different perspectives need to be articulated in lucid ways sensitive to various viewpoints and circumstances. In my thesis I investigate how certain approaches to environmental discourse effect dialogue and negotiation. My first two chapters focus on environmental problems surrounding rangeland ecology along the U.S./Mexico border; whereas the last two chapters explore more theoretical conflicts concerning the philosophy of nature. Throughout the thesis I show the significance of nonhumans (prairie dogs, cattle, biological assessment sheets, environmental laws, etc.) in the human community. Only by considering the roles of nonhumans do we broaden and enrich the conversation between ourselves concerning environmental issues.

<p> One of the least researched phenomena within the alpine regions of mountain biomes is the combination of primitive plants, algae, fungi, and lichens that are generally referred to as biological soil crusts. Sites containing well-developed biological soil crusts were examined in a variety of alpine, non-forested, vegetated landscapes in the North Cascade Mountains of Washington, USA. For each site, data were recorded for percent ground cover of biological soil crusts, slope aspect, and slope gradient of the terrain where the crust communities were located. For all of the sites, biological soil crusts were common, with a percent ground cover median of 29% and a range of 11% to 73%. The arrangement of the biological soil crusts on all sites was quite similar: all were clumped, as opposed to single, and random, as opposed to uniform. All of the soil crusts were found on soil exposed to direct sunlight. Few, if any, crusts were found in the shade of heavy forbs, or forest, or under accumulations of organic litter. When biological soil crusts were found associated with higher-order vegetation, it was with sparse graminoids, ericaceous woody shrubs, and stunted or krummholz Pinaceae trees. The biological soil crusts from this study exist on all locally undisturbed soil slope-gradients from 0% to almost 100%, and occurred on all aspects except for those in the Southwest quadrant. This study contains an extended literature review for desert and high latitude circumpolar crusts, as well as alpine biological soil crusts. Studies of biological soil crusts in subalpine and alpine environments are not common; it is hoped that this study will stimulate more research interest in these often overlooked pioneer biotic communities.</p>

<p> An observed 20-30% increase in forest net ecosystem exchange (<i> NEE</i>) on partly cloudy days is often attributed to there being more uniform canopy illumination by diffuse radiation when clouds are present. However, the sky on such days is typically populated by fair-weather cumulus clouds, bringing dynamically changing shadow-to-light conditions on the order of minutes to the forest, with radiation alternating from 1000 W m^-2 in the clear sky to less than 400 W m^-2 in under-cloud shadows. These dynamically changing conditions cannot be investigated by the conventional time-averaged eddy-covariance flux method, which requires nearly steady-state turbulent conditions over much longer 20-30-min periods in order for the fluxes to converge to stationary values. We examine the &ldquo;true&rdquo; dynamics of the whole-canopy response to the light change by using a practical ensemble-flux method applied to eddy-covariance flux measurements from two distinct forest ecosystems: Harvard Forest (HF, 42.53&deg;N, 72.17&deg;W), temperate mid-latitude forest near Petersham, Massachusetts, USA, and Tapaj&oacute;s National Forest (LBA, 2.86&deg;S, 54.96&deg;W), an Amazonian evergreen tropical forest near Santarem, Par&aacute;, Brazil. Using the rapid change in radiative flux that occurs during the transition from cloud-induced shadow to light as a reference starting point, we combine sets of conditional illumination-change shadow-to-light and light-to-shadow transition events characteristic of cumulus-cloud conditions and parametrize distributions of light and shadow durations and rates of light change of the radiative-flux time series for different cloud conditions reported by standard weather stations. We investigate the sensitivity of the dynamics of forest response to the illumination transitions initiated by these conditional events, and identify an unexpected transient <i> NEE</i> maxima when <i>NEE</i> increases above the clear-sky steady-state equilibrium values (<i>NEE</i>_eq) within the first 10 min of the light period after the shadow-to-light transition, that we hypothesize to be a physiological forest response to the abrupt light change due to presence of the intercellular CO₂ pool in the leaf tissues. Overall <i>NEE</i> builds up during the sunlit periods, but in shadow heat and water stresses are reduced, thus increasing the water use efficiency (<i>WUE</i>). To conduct this analysis, we obtain similarity criteria for realizations defined by conditional events to combine them into the ensembles. With 300 similar realizations grab-sampled at 1-s intervals, we can reliably estimate (&le; 5% standard error) dynamic ensemble fluxes resolved on a 5-s time scale. By the successful application of the first-order system of the delay differential equations with the exponential approach-to-equilibrium solutions, we are able to justify the utility of the &ldquo;Big-Leaf&rdquo;-model approach to describe whole-canopy fluxes and provide the dynamic parametrizations of the &ldquo;Big-Leaf&rdquo; Active Thermal Layer as well as of the Transient Internal Layer above both forests when the light switches on after the cloud pass. By combining results of sensitivity analysis with modelled solutions applied to the real day-long fluctuating-light time series, we show that the variable light during fair-weather clouds (Shadow period duration &lt; 100 s, Light period duration &ge; 300 s) is responsible for an increase in <i>NEE</i> above the <i>NEE</i>_eq of 15-25% for HF and 10-15% for LBA. This indicates that there is a fluctuating-light <i>NEE</i>-enhancement mechanism that can be considered to be a viable alternative to the existing hypothesis of a diffuse-radiation <i> NEE</i>-enhancement mechanism on partly-cloudy days. We show that on such days <i>Diffuse Fraction</i> can be linearly-related to <i> Cloudiness</i> estimated using the shadow-to-light change in a conditional-event radiative-flux ratio, connecting these two <i>NEE</i>-enhancement mechanisms. Combination of increased NEE with the relatively high plateau in <i>WUE</i> allows forests to operate efficiently in partly-cloudy conditions with maxima located in the <i>Cloudiness</i> range [0.1-0.3] and <i>Diffuse-Fraction</i> range [0.35-0.6], suggesting forest adaptations to the preferred lighting conditions and fair-weather cloudiness. </p><p>