Geoadditive regression modeling of stream biological condition

Indices of biotic integrity have become an established tool to quantify the condition of small non-tidal streams and their watersheds. To investigate the effects of watershed characteristics on stream biological condition, we present a new technique for regressing IBIs on watershed-specific explanatory variables. Since IBIs are typically evaluated on an ordinal scale, our method is based on the proportional odds model for ordinal outcomes. To avoid overfitting, we do not use classical maximum likelihood estimation but a component-wise functional gradient boosting approach. Because component-wise gradient boosting has an intrinsic mechanism for variable selection and model choice, determinants of biotic integrity can be identified. In addition, the method offers a relatively simple way to account for spatial correlation in ecological data. An analysis of the Maryland Biological Streams Survey shows that nonlinear effects of predictor variables on stream condition can be quantified while, in addition, accurate predictions of biological condition at unsurveyed locations are obtained.     

Geographical gradients in diet affect population dynamics of Canada lynx

Geographical gradients in the stability of cyclic populations of herbivores and their predators may relate to the degree of specialization of predators. However, such changes are usually associated with transition from specialist to generalist predator species, rather than from geographical variation in dietary breadth of specialist predators. Canada lynx (Lynx canadensis) and snowshoe hare (Lepus americanus) populations undergo cyclic fluctuations in northern parts of their range, but cycles are either greatly attenuated or lost altogether in the southern boreal forest where prey diversity is higher. We tested the influence of prey specialization on population cycles by measuring the stable carbon and nitrogen isotope ratios in lynx and their prey, estimating the contribution of hares to lynx diet across their range, and correlating this degree of specialization to the strength of their population cycles. Hares dominated the lynx diet across their range, but specialization on hares decreased in southern and western populations. The degree of specialization correlated with cyclic signal strength indicated by spectral analysis of lynx harvest data, but overall variability of lynx harvest (the standard deviation of natural-log-transformed harvest numbers) did not change significantly with dietary specialization. Thus, as alternative prey became more important in the lynx diet, the fluctuations became decoupled from a regular cycle but did not become less variable. Our results support the hypothesis that alternative prey decrease population cycle regularity but emphasize that such changes may be driven by dietary shifts among dominant specialist predators rather than exclusively through changes in the predator community.     

Effects of thermobarical pretreatment of cattle waste as feedstock for anaerobic digestion

Lab-scale experiments were conducted to assess the impact of thermobarical treatment of cattle waste on anaerobic digestion. Treatment was at temperatures of 140–220 °C in 20 K steps for a 5-min duration. Methane yields could be increased by up to 58% at a treatment temperature of 180 °C. At 220 °C the abundance of inhibitors and other non-digestible substances led to lower methane yields than those obtained from untreated material. In an extended analysis it could be demonstrated that there is a functional correlation between the methane yields after 30 days and the formation rate and methane yield in the acceleration phase. It could be proved in a regression of these correlation values that the optimum treatment temperature is 164 °C and that the minimum treatment temperature should be above 115 °C.     

Quantifying the uncertainty of variance partitioning estimates of ecological datasets

Environmental and Ecological Statistics - An important objective of experimental biology is the quantification of the relationship between sets of predictor and response variables, a statistical...     

A new method to estimate air-quality levels using a synoptic-regression approach. Part I: Present-day O3 and PM10 analysis

In order to make projections for future air-quality levels, a robust methodology is needed that succeeds in reconstructing present-day air-quality levels. At present, climate projections for meteorological variables are available from Atmospheric-Ocean Coupled Global Climate Models (AOGCMs) but the temporal and spatial resolution is insufficient for air-quality assessment. Therefore, a variety of methods are tested in this paper in their ability to hindcast maximum 8 hourly levels of O₃ and daily mean PM₁₀ from observed meteorological data. The methods are based on a multiple linear regression technique combined with the automated Lamb weather classification. Moreover, we studied whether the above-mentioned multiple regression analysis still holds when driven by operational ECMWF (European Center for Medium-Range Weather Forecast) meteorological data. The main results show that a weather type classification prior to the regression analysis is superior to a simple linear regression approach. In contrast to PM₁₀ downscaling, seasonal characteristics should be taken into account during the downscaling of O₃ time series. Apart from a lower explained variance due to intrinsic limitations of the regression approach itself, a lower variability of the meteorological predictors (resolution effect) and model deficiencies, this synoptic-regression-based tool is generally able to reproduce the relevant statistical properties of the observed O₃ distributions important in terms of European air quality Directives and air quality mitigation strategies. For PM₁₀, the situation is different as the approach using only meteorology data was found to be insufficient to explain the observed PM₁₀ variability using the meteorological variables considered in this study.     

Vertical emission profiles for Europe based on plume rise calculations

The vertical allocation of emissions has a major impact on results of Chemistry Transport Models. However, in Europe it is still common to use fixed vertical profiles based on rough estimates to determine the emission height of point sources. This publication introduces a set of new vertical profiles for the use in chemistry transport modeling that were created from hourly gridded emissions calculated by the SMOKE for Europe emission model. SMOKE uses plume rise calculations to determine effective emission heights. Out of more than 40 000 different vertical emission profiles 73 have been chosen by means of hierarchical cluster analysis. These profiles show large differences to those currently used in many emission models. Emissions from combustion processes are released in much lower altitudes while those from production processes are allocated to higher altitudes. The profiles have a high temporal and spatial variability which is not represented by currently used profiles.     

Bioremediation of benzene-, MTBE- and ammonia-contaminated groundwater with pilot-scale constructed wetlands

In this pilot-scale constructed wetland (CW) study for treating groundwater contaminated with benzene, MTBE, and ammonia-N, the performance of two types of CWs (a wetland with gravel matrix and a plant root mat) was investigated. Hypothesized stimulative effects of filter material additives (charcoal, iron(III)) on pollutant removal were also tested. Increased contaminant loss was found during summer; the best treatment performance was achieved by the plant root mat. Concentration decrease in the planted gravel filter/plant root mat, respectively, amounted to 81/99% for benzene, 17/82% for MTBE, and 54/41% for ammonia-N at calculated inflow loads of 525/603 mg/m²/d, 97/112 mg/m²/d, and 1167/1342 mg/m²/d for benzene, MTBE, and ammonia-N. Filter additives did not improve contaminant depletion, although sorption processes were observed and elevated iron(II) formation indicated iron reduction. Bacterial and stable isotope analysis provided evidence for microbial benzene degradation in the CW, emphasizing the promising potential of this treatment technique.     

Specialization and interaction strength in a tropical plant-frugivore network differ among forest strata

The degree of interdependence and potential for shared coevolutionary history of frugivorous animals and fleshy-fruited plants are contentious topics. Recently, network analyses revealed that mutualistic relationships between fleshy-fruited plants and frugivores are mostly built upon generalized associations. However, little is known about the determinants of network structure, especially from tropical forests where plants' dependence on animal seed dispersal is particularly high. Here, we present an in-depth analysis of specialization and interaction strength in a plant-frugivore network from a Kenyan rain forest. We recorded fruit removal from 33 plant species in different forest strata (canopy, midstory, understory) and habitats (primary and secondary forest) with a standardized sampling design (3447 interactions in 924 observation hours). We classified the 88 frugivore species into guilds according to dietary specialization (14 obligate, 28 partial, 46 opportunistic frugivores) and forest dependence (50 forest species, 38 visitors). Overall, complementary specialization was similar to that in other plant-frugivore networks. However, the plant-frugivore interactions in the canopy stratum were less specialized than in the mid- and understory, whereas primary and secondary forest did not differ. Plant specialization on frugivores decreased with plant height, and obligate and partial frugivores were less specialized than opportunistic frugivores. The overall impact of a frugivore increased with the number of visits and the specialization on specific plants. Moreover, interaction strength of frugivores differed among forest strata. Obligate frugivores foraged in the canopy where fruit resources were abundant, whereas partial and opportunistic frugivores were more common on mid- and understory plants, respectively. We conclude that the vertical stratification of the frugivore community into obligate and opportunistic feeding guilds structures this plant-frugivore network. The canopy stratum comprises stronger links and generalized associations, whereas the lower strata are composed of weaker links and more specialized interactions. Our results suggest that seed-dispersal relationships of plants in lower forest strata are more prone to disruption than those of canopy trees.     

UV-radiation versus grazing pressure: long-term floating of kelp rafts (<Emphasis Type="Italic">Macrocystis pyrifera</Emphasis>) is facilitated by efficient photoacclimation but undermined by grazing losses

Large quantities of floating macroalgae are traveling in coastal waters of the SE Pacific and in other temperate climate zones. While afloat, these algae are potentially exposed to full solar radiation, including UVA and UVB, which can have profound effects on their physiological and growth performance. Latitudinal variations in UV-radiation (UVR) are hypothesized to affect floating algae differently with higher impacts at low latitudes than at high latitudes. In addition, UVR together with grazing might accelerate the demise of floating kelps. This hypothesis was tested with outdoor laboratory experiments in which sporophytes of the giant kelp Macrocystis pyrifera (L.) C. Agardh were exposed to a combination of different UVR regimes (PAR only, PAR + UV) and grazing at three sites along the Chilean coast (20°S, 30°S, and 40°S). A latitudinal trend in irradiance was detected with increasing values from 40°S to 20°S. Surprisingly, floating M. pyrifera responded with a high acclimation potential within this latitudinal UVR gradient. At 20°S, floating kelps were slightly sensitive to UVR, which was reflected in reduced blade growth. At 30°S, physiological responses were hardly affected by the prevailing irradiance but sporophyte growth and thus persistence mainly depended on the presence or absence of amphipod grazers. At high latitudes, grazing had only minor impacts on algal biomass and blade growth, and kelps thrived well under all tested environmental conditions. Overall, our results reveal that floating M. pyrifera was only slightly affected by UVR and that sporophytes can efficiently acclimate over a latitudinal UVR gradient that spans from 20°S to 40°S. Given this high acclimation potential, we suggest that these (and possibly other) positively buoyant algae are important dispersal agents over a wide range of temperate latitude conditions.