Laboratory evaluation of thermophilic-anaerobic digestion to produce Class A biosolids. 2. Inactivation of pathogens and indicator organisms in a continuous-flow reactor followed by batch treatment.

Thermophilic-anaerobic digestion in a single-stage, mixed, continuous-flow reactor is not approved in the United States as a process capable of producing Class A biosolids for land application. This study was designed to evaluate the inactivation of pathogens and indicator organisms in such a reactor followed by batch treatment in a smaller reactor. The combined process was evaluated at 53 degrees C with sludges from three different sources and at 51 and 55 degrees C with sludge from one of the sources. Feed sludge to the continuous-flow reactor was spiked with the pathogen surrogates Ascaris suum and vaccine-strain poliovirus. Feed and effluent were analyzed for these organisms and for indigenous Salmonella spp., fecal coliforms, Clostridium perfringens spores, and somatic and male-specific coliphages. No viable Ascaris eggs were observed in the effluent from the continuous reactor at 53 or 55 degrees C, with greater than 2-log removals across the digester in all cases. Approximately 2-log removal was observed at 51 degrees C, but all samples of effluent biosolids contained at least one viable Ascaris egg at 51 degrees C. No viable poliovirus was found in the digester effluent at any of the operating conditions, and viable Salmonella spp. were measured in the digester effluent in only one sample throughout the study. The ability of the continuous reactor to remove fecal coliforms to below the Class A monitoring limit depended on the concentration in the feed sludge. There was no significant removal of Clostridium perfringens across the continuous reactor under any condition, and there also was limited removal of somatic coliphages. The removal of male-specific coliphages across the continuous reactor appeared to be related to temperature. Overall, at least one of the Class A pathogen criteria or the fecal coliform limit was exceeded in at least one sample in the continuous-reactor effluent at each temperature. Over the range of temperatures evaluated, the maximum time required to meet the Class A criteria by batch treatment of the continuous-reactor effluent was 1 hour for Ascaris suum and Salmonella spp. and 2 hours for fecal coliforms.     

Laboratory evaluation of thermophilic-anaerobic digestion to produce Class A biosolids. 1. Stabilization performance of a continuous-flow reactor at low residence time.

There is increasing interest in the United States in producing biosolids from municipal wastewater treatment that meet the criteria for Class A designation established by the U.S. Environmental Protection Agency. Class A biosolids are intended to be free of pathogens and also must meet requirements for reduction of the vector-attraction potential associated with untreated sludge. High-temperature processes are considered to produce Class A biosolids if the combination of operating temperature and treatment time exceeds minimum criteria, but this option is not applicable to mixed, continuous-flow reactors. Such reactors, or any combination of reactors that does not meet the holding time requirement at a specific temperature, must be demonstrated to inactivate pathogens to levels consistent with the Class A criteria. This study was designed to evaluate pathogen inactivation by thermophilic anaerobic digestion in a mixed, continuous-flow reactor followed by batch or plug-flow treatment. In this first of a two-part series, we describe the performance of a continuous-flow laboratory reactor with respect to physical and chemical operating parameters; microbial inactivation in the combined continuous-flow and batch treatment system is described in the second part. Sludges from three different sources were treated at 53 degrees C, while sludge from one of the sources was also treated at 55 and 51 degrees C. Relatively short hydraulic retention times (four to six days) were used to represent a conservative operating condition with respect to pathogen inactivation. Treatment of a fermented primary sludge led to an average volatile-solids (VS) destruction efficiency of 45%, while VS destruction for the other two sources was near or below 38%, the Class A criterion for vector attraction reduction. Consistent with other studies on thermophilic anaerobic digestion of sludges at short residence times, effluent concentrations of volatile fatty acids (VFAs) were relatively high. Also consistent with other studies, the most abundant VFA in the effluent was propionate. Gas production ranged from 0.3 to 0.5 m3/kg VS fed and from 0.8 to 1.3 m3/kg VS destroyed.     

A Multi-scale Spatial Analysis of Native and Exotic Plant Species Richness Within a Mixed-Disturbance Oak Savanna Landscape

Impacts of human land use pose an increasing threat to global biodiversity. Resource managers must respond rapidly to this threat by assessing existing natural areas and prioritizing conservation actions across multiple spatial scales. Plant species richness is a useful measure of biodiversity but typically can only be evaluated on small portions of a given landscape. Modeling relationships between spatial heterogeneity and species richness may allow conservation planners to make predictions of species richness patterns within unsampled areas. We utilized a combination of field data, remotely sensed data, and landscape pattern metrics to develop models of native and exotic plant species richness at two spatial extents (60- and 120-m windows) and at four ecological levels for northwestern Ohio’s Oak Openings region. Multiple regression models explained 37–77 % of the variation in plant species richness. These models consistently explained more variation in exotic richness than in native richness. Exotic richness was better explained at the 120-m extent while native richness was better explained at the 60-m extent. Land cover composition of the surrounding landscape was an important component of all models. We found that percentage of human-modified land cover (negatively correlated with native richness and positively correlated with exotic richness) was a particularly useful predictor of plant species richness and that human-caused disturbances exert a strong influence on species richness patterns within a mixed-disturbance oak savanna landscape. Our results emphasize the importance of using a multi-scale approach to examine the complex relationships between spatial heterogeneity and plant species richness.     

Cavity excavation and enlargement as mechanisms for indirect interactions in an avian community

Direct and indirect species interactions within ecological communities may play a strong role in influencing or maintaining community structure. Complex community interactions pose a major challenge to predicting ecosystem responses to environmental change because predictive frameworks require identification of mechanisms by which community interactions arise. Cavity-nesting communities are well suited for mechanistic studies of species interactions because cavity nesters interact through the creation of and competition for cavity-nest sites. In this study, we use a cavity-nest web as a predictive framework for identifying potential indirect species interactions within a cavity-nesting community. From 2002 to 2005, we monitored abundance and nests of cavity-nesting birds in the longleaf pine (Pinus palustris) ecosystem. Using a nest-web approach, we identified a potential indirect interaction between the Red-cockaded Woodpecker (Picoides borealis) and large secondary cavity nesters, mediated by the Northern Flicker (Colaptes auratus). We used structural equation modeling to test a path model of this interaction, using cavity excavation and enlargement as mechanisms which drive the relationship between these species. Through experimental manipulation of cavity availability, we blocked links described in our model, confirming cavity creation and enlargement as processes that influence community structure. We found that a single-species management technique could potentially disrupt this indirect relationship by affecting Northern Flicker cavity-excavation behavior. This study is the first demonstration of how experimental cavity manipulation can be used to test inferred processes derived from a nest web and highlights the need to understand how mechanisms underlying species interactions can complicate ecosystem responses to environmental change.     

Database-driven models of the world's Large Marine Ecosystems

We present a new methodology for database-driven ecosystem model generation and apply the methodology to the world's 66 currently defined Large Marine Ecosystems. The method relies on a large number of spatial and temporal databases, including FishBase, SeaLifeBase, as well as several other databases developed notably as part of the Sea Around Us project. The models are formulated using the freely available Ecopath with Ecosim (EwE) modeling approach and software. We tune the models by fitting to available time series data, but recognize that the models represent only a first-generation of database-driven ecosystem models. We use the models to obtain a first estimate of fish biomass in the world's LMEs. The biggest hurdles at present to further model development and validation are insufficient time series trend information, and data on spatial fishing effort.     

The effectiveness of surrogate taxa to conserve freshwater biodiversity

Establishing protected areas has long been an effective conservation strategy and is often based on readily surveyed species. The potential of any freshwater taxa to be a surrogate for other aquatic groups has not been explored fully. We compiled occurrence data on 72 species of freshwater fishes, amphibians, mussels, and aquatic reptiles for the Great Plains, Wyoming (U.S.A.). We used hierarchical Bayesian multispecies mixture models and MaxEnt models to describe species’ distributions and the program Zonation to identify areas of conservation priority for each aquatic group. The landscape‐scale factors that best characterized aquatic species’ distributions differed among groups. There was low agreement and congruence among taxa‐specific conservation priorities (<20%), meaning no surrogate priority areas would include or protect the best habitats of other aquatic taxa. Common, wideranging aquatic species were included in taxa‐specific priority areas, but rare freshwater species were not included. Thus, the development of conservation priorities based on a single freshwater aquatic group would not protect all species in the other aquatic groups.     

Multiple determinants of community structure in shallow marsh habitats,Cape Fear River estuary,North Carolina,USA

The nekton of tidal creeks was studied at 17 sampling localities from September 1977 through August 1978, in the Cape Fear River estuary, North Carolina, USA. Prior to these dates, collections were made at 9 stations beginning in January 1977; these data were used to supplement conclusions drawn from the larger effort. Species recruited from the ocean utilized marsh habitats only temporarily and dominated the catches with over 70% of the total abundance. Their distribution was influenced by salinity gradients and to a lesser extent by substrate characteristics. In addition, temporal habitat partitioning with associated size differences of related species played an important role in structuring marsh nekton communities. A clearly defined ecotone was associated with the mesohaline-polyhaline transition zone, in slainities between 14 and 21 S. Numerous marine stenohaline forms were restricted to salinities above 16 S, thus increasing species richness in high salinity marshes. Despite differences in freshwater flows in 1977 and 1978, major features of the various marsh communities (species associations and relative abundances) exhibited little change throughout the Cape Fear estuary, indicating that these communities were relatively persistent in time. Standing crops for ocean-spawned species at the end of the growing season indicated that considerable annual export in the form of living biomass of fish and shellfish takes place from the marshes. Since most individuals of these species return to the ocean in the fall, an important energy link between the marshes and nearshore marine environment is demonstrated.     

Genetic evidence for monogamy in the cooperatively breeding red-cockaded woodpecker

We examined the genetic relationship among putative parents, offspring, and helpers in 224 red-cockaded woodpeckers (Picoides borealis) from the Sandhills of North Carolina. Comparison of DNA similarity with a pedigree constructed from 3,823 individually-marked birds observed from 1979 to 1992 provided verification of observed relatedness in the sampled population (R ² = 0.87,df = 14,P<0.001). In this population, breeding pairs may or may not have helpers, most of which are males that remain on their natal territory. Our sample included helpers assisting their parents, helpers assisting a related male and an unrelated female, and helpers assisting an unrelated pair. Band by band comparison and examination of similarity among DNA profiles indicated that all offspring from non-helped nests were sired by their putative parents (n = 28 families). Similarly, all but one offspring in helped nests were also sired by their putative parents (n = 16 families). In the exceptional case, the offspring evidently was sired by a male external to the group. Analysis of similarity values supported the conclusion that matings by helpers or extra-group males are rare or non-existent. Our results indicate that in this species advantages gained by individuals remaining on their natal territories as helpers do not generally include siring offspring. Correspondence to: S. Haig     

农业生态系统中氮的利用效率与氮的管理

在生产玉米、水稻和小麦的作物系统中既要满足增长的食物需求又要保护环境质量,面对这样一个全球性的挑战,我们不知会成功还是会失败.要使发达国家大规模的作物系统和发展中国家小规模的作物系统中产量、利润和环境保护这三者之间的关系尽可能优化,关键就是要实现氮的供应与作物需求之间的同步性,既不多也不少.为了迎接挑战而制订的研究议程和有效政策,要求我们定量地理解当前这些系统中氮利用的效率及损失的水平、生物物理法控制这些要素的水平和采用改善后的管理措施所获得的经济回报水平.对于这些问题,尽管在基础生物学、生态学和生物地球化学方面的研究进展能提供一些答案,但我们不应该低估科学研究所遇到的重大挑战,因为在全世界很有限的生产耕地上作物系统必须保持产量增加,而对其中氮的控制日益困难.