Compositional loess modeling

Cleveland (1979) is usually credited with the introduction of the locally weighted regression, Loess. The concept was further developed by Cleveland and Devlin (1988). The general idea is that for an arbitrary number of explanatory data points xi the value of a dependent variable is estimated ^yi. The ^yi is the tted value from a dth degree polynomial in xi. (In practice often d = 1.) The ^yi is tted using weighted least squares, WLS, where the points xk (k = 1; : : : ; n) closest to xi are given the largest weights. We de ne a weighted least squares estimation for compositional data, C-WLS. In WLS the sum of the weighted squared Euclidean distances between the observed and the estimated values is minimized. In C-WLS we minimize the weighted sum of the squared simplicial distances (Aitchison, 1986, p. 193) between the observed compositions and their estimates. We then de ne a compositional locally weighted regression, C-Loess. Here a composition is assumed to be explained by a real valued (multivariate) variable. For an arbitrary number of data points xi we for each xi t a dth degree polynomial in xi yielding an estimate ^yi of the composition yi. We use C-WLS to t the polynomial giving the largest weights to the points xk (k = 1; : : : ; n) closest to xi. Finally the C-Loess is applied to Swedish opinion poll data to create a poll-of-polls time series. The results are compared to previous results not acknowledging the compositional structure of the data

Fairy, tadpole, and clam shrimps (Branchiopoda) in seasonally inundated clay pans in the western Mojave Desert and effect on primary producers

Abstract Background Fairy shrimps (Anostraca), tadpole shrimps (Notostraca), clam shrimps (Spinicaudata), algae (primarily filamentous blue-green algae [cyanobacteria]), and suspended organic particulates are dominant food web components of the seasonally inundated pans and playas of the western Mojave Desert in California. We examined the extent to which these branchiopods controlled algal abundance and species composition in clay pans between Rosamond and Rogers Dry Lakes. We surveyed branchiopods during the wet season to estimate abundances and then conducted a laboratory microcosm experiment, in which dried sediment containing cysts and the overlying algal crust were inundated and cultured. Microcosm trials were run with and without shrimps; each type of trial was run for two lengths of time: 30 and 60 days. We estimated the effect of shrimps on algae by measuring chlorophyll content and the relative abundance of algal species. Results We found two species of fairy shrimps (Branchinecta mackini and B. gigas), one tadpole shrimp (Lepidurus lemmoni), and a clam shrimp (Cyzicus setosa) in our wet-season field survey. We collected Branchinecta lindahli in a pilot study, but not subsequently. The dominant taxa were C. setosa and B. mackini, but abundances and species composition varied greatly among playas. The same species found in field surveys also occurred in the microcosm experiment. There were no significant differences as a function of experimental treatments for either chlorophyll content or algal species composition (Microcoleus vaginatus dominated all treatments). Conclusions The results suggest that there was no direct effect of shrimps on algae. Although the pans harbored an apparently high abundance of branchiopods, these animals had little role in regulating primary producers in this environment

What difference can drop-in substitution actually make? A life cycle assessment of alternative water repellent chemicals

Per- and polyfluoroalkyl substances (PFASs) are used in durable water repellents (DWRs) on outdoor garments and manufacturers are currently phasing out hazardous PFASs. A critical question is: which alternatives should be chosen? The answer should depend on a holistic assessment, but the published inventory data and methodological guidance for assessing PFAS in products is slim and typically limited to hazard assessment. We aim to provide a holistic assessment of the potential environmental consequences of this phase out of DWRs, going beyond the more traditional hazard-focused substitution assessment to also include a broad life-cycle-based assessment of PFASs and their drop-in alternatives. In this study, potential environmental consequences of the phase out were evaluated by applying a life cycle assessment (LCA) to shell jackets with side-chain fluorinated polymer based (i.e., PFASs) or non-fluorinated alternative DWRs with the aim to support a substitution assessment. We demonstrated an innovative approach to impact assessment by inclusion of PFAS related fate and toxicity and invested effort towards contributing new primary inventory data by using a combination of industry dialogue and performance measurements from our larger project context. From a methodological point of view, this paper demonstrates the state-of-the-art in product LCA of persistent textile chemicals and identifies the current limits of this assessment approach. It also delivers new LCI data of use to other analysts. The LCA results in this paper suggest that jackets without PFASs are environmentally preferable. Potential problem shifting due to increased washing and reimpregnation of the jackets did not outweigh PFAS-related potential toxicity impacts as indicated by LCA results. Based on the results presented here, specific DWRs within the non-fluorinated DWR group could not be identified as preferable to others. This LCA does however provide a relevant starting point for more detailed studies on specific DWR systems and it supports moves to phase-out PFASs from non-essential DWR uses

Sublethal Effects of Mercury on Growth and Reproductive Performance of Layers

Mercury in our environment has been implicated in egg shell thinning and poor hatchability among various species of wild birds. We have used domestic chickens to determine the effect of a range of sublethal levels of two dietary mercury compounds, i.e., inorganic mercuric chloride and organic methylmercuric chloride

Effects of Mercury on Production and Reproduction of Laying Hens--Second Egg Laying Cycle

Hens fed diets containing various levels of two mercury sources from the time of hatching were studied during a second laying cycle. Early growth data and data pertaining to the first laying cycle were reported in the 1973 Poultry Day reports (A.S. Series 73-18). It was concluded from these earlier phases of the study that inorganic mercury at levels up to 20 ppm in the diet does not influence growth or egg production, quality and hatchability. Methylmercury at levels of 2.5 ppm or less also appeared to be well tolerated with no visible harmful effects. However, detrimental effects of higher levels became increasingly apparent with progression of that phase of the experiment

Mercury Toxicity in Chick Embryos

Mercury accumulating to high levels in animal tissue is generally in the form of methylmercury which is readily absorbed but only slowly eliminated. While methylmercury can be formed by microorganisms in lake bottom sediments and concentrated up the biological food chain, inorganic mercury or its metabolic equivalent is sometimes available to animals