Anaerobic digestion of food waste in a hybrid anaerobic solid–liquid system with leachate recirculation in an acidogenic reactor

Recirculation of the leachate in the acidogenic reactor was proposed to enhance anaerobic digestion of food waste in the hybrid anaerobic solid–liquid (HASL) system. Recirculation of the leachate in the acidogenic reactor provided better conditions for extraction of organic matter from the treated food waste and buffering capacity to prevent excessive acidification in the acidogenic reactor. It ensured faster supply of nutrients in the methanogenic reactor in experiment. The highest dissolved COD and VFA concentrations in the leachate from the acidogenic reactor were reached for shorter time and were 16,670 mg/l and 9450 mg/l in control and 18,614 mg/l and 11,094 mg/l in experiment, respectively. Recycling of the leachate in the acidogenic reactor intensified anaerobic digestion of food waste and diminished time needed to produce the same quantity of methane by 40% in comparison with anaerobic digestion of food waste without recirculation.     

Forest edge creates small-scale variation in reproductive rate of sika deer

Habitat edges are considered to have an important role in determining the abundance of deer in forest landscapes, but to our knowledge there are few lines of evidence indicating that forest edge enhances the vital rate of deer. We examined pregnancy of female sika deer in Boso peninsula, central Japan, and explored how forest edges, food availability in forests, and local population density influence the pregnancy rate of sika deer. Local deer density was estimated by the number of fecal pellets, and food availability in forests was estimated by combining GIS data of vegetation distribution and the relationship between vegetation biomass and local deer density. Forest edge length was also determined by GIS data. Model selection was performed with multiple logistic regression analyses using the AIC to find the best model for accounting for the observed variation in pregnancy rates of the deer. Multiple logistic regression analysis showed that the length of forest edge had a positive effect on the pregnancy rate of females, whereas food availability in forests and local deer density had little effect. This forest edge effect was detected in a 100–200-m radius from deer captured locations, indicating that deer pregnancy is primarily determined by habitat quality within a 10-ha area. This result was confirmed by tracking females with GPS telemetry, which found that the core areas of the home range were less than 12 ha. The positive effect of edges and the lack of density dependence could be a result of high plant productivity in open environments that produces forages not depleted by high deer densities. Our results support the view that land management is the cause of the current problem of deer overabundance. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

贵州水银洞金矿紫茎泽兰重金属元素测定与分析

利用原子吸收法对贵州水银洞金矿紫茎泽兰及其基质中Cr、Pb、Zn、Cd、Hg和As含量进行了测定和分析。结果表明,贵州水银洞金矿废水处理区土壤Hg(12.575 mg·kg^-1)和As(501.374 mg·kg^-1)已严重超标,Hg和As的平均含量分别是国家土壤环境质量三级标准(GB15618-1995)的8.383倍和12.534倍,污染极为严重;紫茎泽兰对该矿区不同的重金属富集能力不同,尤其对该矿区Cr有较强的富集作用,具有一定的Cr污染修复潜力。紫茎泽兰对所测定的6种重金属元素的吸收转移能力有较大的差异,整个植株对Pb、Zn 和Cr具有很强的吸收转移能力。其茎、叶对不同的重金属元素的吸收转移能力也呈现出很大的差异,紫茎泽兰茎对Cr、Pb和Cd具有很强的吸收转移能力,而叶对Zn、Pb和Hg具有很强的吸收转移能力。除As外,紫茎泽兰对Cr、Pb、Zn、Cd和Hg都具有不同程度的耐受能力,对该矿区的生态恢复具有重要的作用。     

Differential effects of food availability on population growth and fitness of three species of estuarine, bacterial-feeding nematodes

The significance of bottom-up controls on biological communities has been a long-standing topic of interest in ecology. However, before environmental effects on communities can be properly assessed, a thorough knowledge of the individual species' responses is required. We studied effects of food availability on population development and on different life-history traits in three species of bacterial-feeding nematodes, Diplolaimelloides oschei, Diplolaimelloides meyli (both Monhysteridae) and Pellioditis marina (Rhabditidae), which co-occur on macrophyte detritus in the Westerschelde Estuary (SW Netherlands). The bacteria Escherichia coli was offered in five food-availability treatments corresponding to initial cell densities from 3 × 10¹⁰ cells ml^− 1 to 3 × 10⁷ cells ml^− 1. The three bacterial-feeding nematode species studied here showed differential responses to food availability, which agreed with the general idea that Rhabditidae have extreme colonization abilities under very high food availability, while Monhysteridae tend to have a somewhat slower population development and comparatively lower food requirements. Several life-history traits, including juvenile mortality and development time, did not exhibit a clear food-availability dependence, but bioenergetics-related parameters did. Results on the F1 generation may, however, be affected by strong maternal effects on life-history traits of their progeny. Patterns of food-availability dependence of population increase and size at maturity were similar in P. marina. Both Diplolaimelloides species, however, exhibited a large body size at maturity but a very low population increase at the highest food availability, suggesting a trade-off between biomass and reproduction. Comparison with published data on other nematode species reveals that nematode responses to food availability as well as to other environmental factors are highly species-specific.     

Early life-history processes in benthic octopus: Relationships between temperature, feeding, food conversion, and growth in juvenile Octopus pallidus

Initial growth in cephalopods is exponential, making early life-history critical in determining growth trajectories. Few captive studies have however examined the early life-history of cephalopods in fluctuating temperatures as would be encountered in the wild. This study investigates the relationship between early growth and the significant factors affecting growth, namely food intake, food conversion and fluctuating environmental temperatures. Pale octopus (Octopus pallidus) hatchlings were reared in captivity under either a warming or cooling temperature regime. Individual variations and periodicity in feeding rates (F_r), food conversion rates (C_r), growth rates (G_r), and the relationship between these variables and temperature were examined weekly. Food conversion rates were variable between individuals but also within individual octopus, which exhibited large fluctuations in C_r over time, exceeding 100% d^− 1 in one instance. Although individual F_r, C_r and G_r displayed fluctuations over time, there was no evidence of periodicity for any of the variables. Changes in temperature were not significantly correlated to changes in F_r, C_r or G_r. Feeding rate did not appear to influence growth rate or food conversion rate. Food conversion rate was negatively correlated to feeding rate in the same week, and positively correlated to growth rate. Short periods of low or no food consumption were common and the high values obtained for food conversion rate for some individuals suggest that octopus can grow substantially with little or no food intake. Individual variability observed in octopus growth may be dependent on the growth mechanism involved, specifically a fine balance between the continuous hyperplasic and hypertrophic growth found in cephalopods.     

Effects of food nitrogen content and concentration on the forms of nitrogen excreted by the calanoid copepod, Acartia tonsa

Nitrogen excreted as ammonium, urea, and dissolved primary amines (DPA), and nitrogen ingested by the planktonic calanoid copepod, Acartia tonsa, were measured while fed 4 foods with different N/C ratios in high (500 μg C l^− 1) and low (50 μg C l^− 1) concentrations. Adult copepods were fed the ciliate, Uronema marinum (N/C = 0.26), the diatom, Thalassiosira weissflogii, in log-phase growth (N/C = 0.20), and in senescent-phase growth (N/C = 0.12), and detritus derived from the saltmarsh grass, Spartina alterniflora, (N/C = 0.04). Total nitrogen excreted ranged from 0.06 to 0.18 μg N copepod^− 1 d^− 1 whereas nitrogen ingested exhibited considerably more variation (0.01 to 0.39 μg N copepod ^− 1d ^− 1). Ammonium was the dominant form of nitrogen excreted and was influenced by both food concentration and N/C ratio. Copepods fed foods with N/C ratios resembling their own body composition (log-phase diatoms and ciliates) excreted more ammonium when fed higher concentrations of food. In contrast, copepods fed foods with lower N/C ratios than their own body composition excreted more ammonium when fed lower concentrations of food, suggesting that they were catabolizing body protein for survival. Excretion of urea varied with food N/C ratio, with more urea excreted when the copepods were fed higher N/C foods. The excretion of DPA did not vary with either food concentration or food N/C ratio. Homeostasis serves to conserve the N/C ratio of copepods. Thus nitrogen excretion by healthy copepods should be expected to increase with ingestion only when copepods have high quantities of nitrogen-rich foods relative to the body composition of the copepods.     

Using polyclonal antibodies to detect predation by dogwhelks Nucella lapillus (L.)

Interactions between predators and their multiple prey species can vary greatly among locations where they coexist. As a method to assess spatial variation in predation by intertidal dogwhelks on their dominant prey, immunoassays of dogwhelk gut contents from experimental populations and field collected individuals were evaluated using polyclonal antibodies raised separately to soluble proteins from Mytilus edulis L. mussels and Semibalanus balanoides (L.) barnacles. Both antisera produced strong reactions against their homologous antigens but no cross reactions between prey species. Experimental trials tested the critical hypothesis that prey species had equal detection intervals in dogwhelk guts. Two groups of 225 dogwhelks were starved for 14 days, provided with either mussels or barnacles for five days, and then sampled over 22 days. Independent immunoassays of dogwhelk gut contents against each antibody revealed a consistent, weak cross reaction between the anti-mussel antibody and dogwhelk gut tissues. After accounting for this cross reaction, the strength of immunoassays against both prey species declined exponentially and at similar rates. The proportions of dogwhelks that tested positive for their provided prey species declined linearly through time and were not significantly influenced by prey type. Prey were detectable throughout the sampled post-feeding period and were projected to have detection limits of 24.4 days (barnacles) and 26.5 days (mussels), demonstrating that immunoassay results are not biased by dissimilar prey detection intervals. Reactions against the antibody from the non-provided prey were time invariant and occurred at relatively low frequencies. Immunoassays of dogwhelks collected from five intertidal sites on Swans Island, Maine, USA revealed patterns similar to field observations, though immunoassays classified far fewer individuals as non-feeders and more as barnacle feeders than indicated by direct field observations. Unlike single observations, immunoassays also revealed the presence of both prey in dogwhelks from four sites, though most individuals tested positive for only a single prey type. Immunoassays facilitate concurrent collections of predation data from many individuals and will enable further local- to regional-scale assessments of dogwhelk predation at additional sites around the Gulf of Maine.     

The influence of age on the use of potential enrichment objects and synchronisation of behaviour of pigs

This experiment aimed to identify how a pig's age affected the extent and synchrony of use of different environmental enrichment materials, and how this use changed over time. Ten diverse novel objects were each presented to three replicate litters of 3 weeks of age (sucklers) and three replicate groups of three animals of 5 (weaners) weeks and 13 (growers) weeks of age. Video recordings were made of the pigs’ behaviour over a period of 5 days and subsequently analysed for activity, inactivity and object directed behaviour of three animals per group on days 1 and 5. The observed performance of any given behaviour, when at least one other member of the group was also performing that behaviour, was compared with the probability that such concurrence occurred by chance and these results were used to calculate the degree of synchronisation. Gender had no effect on the duration of object use or approach latency. Growers displayed a shorter latency to approach the objects initially compared to sucklers and weaners (mean seconds; 2153 versus 2660 versus 980 for sucklers, weaners and growers, respectively, S.E.D. 542, p = 0.007). Sucklers used the objects to a much lesser extent than either the weaners or growers (mean duration object interaction (s); 129 versus 1253 versus 1412 for sucklers, weaners and growers, respectively, S.E.D. 93, p < 0.001). Overall object use decreased between days 1 and 5 (mean duration object interaction (s); 1326 versus 536 for days 1 and 5, respectively, S.E.D. 76, p < 0.001). All of the age groups synchronised their behaviour to a much greater extent than expected by chance. The sucklers showed a higher degree of synchrony of activity (K; 0.890 versus 0.776 versus 0.682 for sucklers, weaners and growers respectively, S.E.D. 0.013, p < 0.001) and inactivity (K; 0.963 versus 0.905 versus 0.909 respectively, S.E.D. 0.007, p < 0.001), but lower degree of synchrony for object directed behaviour (K; 0.149 versus 0.375 versus 0.370 respectively, S.E.D. 0.025, p < 0.001), than the weaners and growers. The degree of synchronisation of object directed behaviour decreased over the 5-day period, irrespective of age (K; 0.382 versus 0.214 for days 1 and 5 respectively, S.E.D. 0.020, p < 0.001). Significant correlations (r = 0.678–0.879) were found between the degree of synchrony and extent of object interaction only for the sucklers. Since pigs showed behavioural synchronisation, object availability should be considered when providing desirable enrichment in order to avoid excessive competition in larger commercial groups.     

Catabolic diversity of periphyton and detritus microbial communities in a subtropical wetland

The catabolic diversity of wetland microbial communities may be a sensitive indicator of nutrient loading or changes in environmental conditions. The objectives of this study were to assess the response of periphyton and microbial communities in water conservation area-2a (WCA-2a) of the Everglades to additions of C-substrates and inorganic nutrients. Carbon dioxide and CH₄ production rates were measured using 14 days incubation for periphyton, which typifies oligotrophic areas, and detritus, which is prevalent at P-impacted areas of WCA-2a. The wetland was characterized by decreasing P levels from peripheral to interior, oligotrophic areas. Microbial biomass and N mineralization rates were higher for oligotrophic periphyton than detritus. Methane production rates were also higher for unamended periphyton (80 mg CH₄-C kg⁻¹ d⁻¹) than detritus (22 mg CH₄-C kg⁻¹ d⁻¹), even though the organic matter content was higher for detritus (80%) than periphyton (69%). Carbon dioxide production for unamended periphyton (222 mg CO₂-C kg⁻¹ d⁻¹) was significantly greater than unamended detritus (84 mg CO₂-C kg⁻¹ d⁻¹). The response of the heterotrophic microbial community to added C-substrates was related to the nutrient status of the wetland, as substrate-induced respiration (SIR) was higher for detritus than periphyton. Amides and polysaccharides stimulated SIR more than other C-substrates, and methanogenesis was greater contributor to SIR for periphyton than detritus. Inorganic P addition stimulated CO₂ and CH₄ production for periphyton but not detritus, indicating a P limitation in the interior areas of WCA-2a. Continued nutrient loading into oligotrophic areas of WCA-2a or enhanced internal nutrient cycling may stimulate organic matter decomposition and further contribute to undesirable changes to the Everglades ecosystem caused by nutrient enrichment.     

Physiological advantages may contribute to successful invasion of the exotic Cyprinus carpio into the Xingyun Lake, China

Feeding and growth traits of Cyprinus carpio and Cyprinus pellegrini (both at age-0) were compared in three experiment, in an attempt to analyze potential causes for the displacement of the native C. pellegrini in the Xingyun Lake, Yuxi, Yunan, China. Experiment I was conducted in water which fluctuated between 15 and 20°C. Experiment II and III were conducted in a laboratory and water temperature was maintained between 20°C and 25°C, respectively. Three common trends were noted for all three experiments: (1) feeding rate of C. carpio was lower than that of C. pellegrini, and this difference was found to be significant in experiment I; (2) growth rate of C. carpio was higher than C. pellegrini, and the difference was found to be significant in experiment II; (3) food conversion efficiency and energy retention efficiency for C. carpio were higher than those of C. pellegrini, and significant differences were noted in experiment I and II. Since the growth period for fish in the Xingyun Lake generally occurs when water temperatures are between 15 and 25°C, it can be suggested that C. carpio has advantages over C. pellegrini in growth and food utilization efficiency, and lower food consumption than C. pellegrini. These physiological traits of C. carpio might allow this species to be more resistant to food shortage and predation, and may be partially responsible for the displacement of C. pellegrini by C. carpio.