Reciprocal subsidies between freshwater and terrestrial ecosystems structure consumer resource dynamics

Cross-ecosystem movements of material and energy, particularly reciprocal resource fluxes across the freshwater-land interface, have received major attention. Freshwater ecosystems may receive higher amounts of subsidies (i.e., resources produced outside the focal ecosystem) than terrestrial ecosystems, potentially leading to increased secondary production in freshwaters. Here we used a meta-analytic approach to quantify the magnitude and direction of subsidy inputs across the freshwater-land interface and to determine subsequent responses in recipient animals. Terrestrial and freshwater ecosystems differed in the magnitude of subsidies they received, with aquatic ecosystems generally receiving higher subsidies than terrestrial ecosystems. Surprisingly, and despite the large discrepancy in magnitude, the contribution of these subsidies to animal carbon inferred from stable isotope composition did not differ between freshwater and terrestrial ecosystems, likely due to the differences in subsidy quality. The contribution of allochthonous subsidies was highest to primary consumers and predators, suggesting that bottom-up and top-down effects may be affected considerably by the input of allochthonous resources. Future work on subsidies will profit from a food web dynamic approach including indirect trophic interactions and propagating effects.     

北极4个亚区的影响分析

在评价北极陆地生态系统影响时,人们常常强调物种和生态系统对环境变化响应的地理变化,这种变化往往与气候、生物多样性、植被带、生态系统结构和功能的南-北梯度相关联,可是,环境、生态系统的功能和结构上,以及环境史和当前气候变化的明显东-西变化显然也很重要.尽管一些地方变得温暖,但另一些地方却降温了,海洋、群岛和山脉等地理屏障的东西差异过去也对物种和植被带响应气候变化而改变分布区的能力产生了很大影响,同时,这些地理屏障为种群遗传分化和生物多样性热点区的形成提供了必要的隔离条件,这些屏障在未来气候变暖时,也将影响物种重新分布的能力.为了说明这种东西向的变化,同时也避免过分笼统或过于专业化,基于大尺度的天气和气候形成因素,北极气候影响评价项目确定了4个主要亚区.通过模拟与4个北极气候影响评价亚区有关的主要信息,导致物种分布区发生改变的地理屏障,特别是大陆的分布和海洋产生的隔离,明显会影响植被带的向北移动.对植被区向北移动的地理限制或者促进将影响将来碳的贮存和释放,以及生物圈与大气之间水和能量的交换.此外,气候变化使受威胁物种数量在各个亚区之间差别很大(白令海地区别尤其是热点),各个植被亚区重新分布的能力差异将影响每个区的生物多样性.总而言之,亚区分析表明,在整个北极地区水平上概括生态系统结构和功能的反应、物种的丧失,以及生物圈对气候系统的反馈的趋势是困难的,说明需要对北极陆地生态系统对于气候变化响应的空间变化性有深刻的认识.     

Altered menstrual cycles in women with a high dietary intake of persistent organochlorine compounds

Dietary exposure to persistent organochlorine compounds (POCs) has been found to affect the menstrual cycle in both animals and humans. In Sweden, the major exposure route for POCs is the consumption of fatty fish from the Baltic Sea. Thus, women who eat relatively large amounts of this fish constitute a suitable study group when investigating a possible association between dietary exposure to POC and menstrual cycle disruption. Questionnaires were sent to the exposed women, as well as to a socioeconomically similar cohort of controls, and information was collected on their menstrual cycles. Since the exposed women tended to smoke more than the controls, all results were adjusted for smoking habits. A cohort comparison found that the exposed women on average had 0.46 (95% confidence interval: 0.03, 0.89) days shorter menstrual cycles than controls. However, within the exposed cohort no effects were found of the proxy variables early life exposure and high consumption of Baltic Sea fatty fish. The results give some support to previous results from studies on women with similar exposure, but are not conclusive with respect to whether there is a causal association between POC exposure and menstrual cycle disruption.     

Potassium, phosphorus, or nitrogen limit root allocation, tree growth, or litter production in a lowland tropical forest

We maintained a factorial nitrogen (N), phosphorus (P), and potassium (K) addition experiment for 11 years in a humid lowland forest growing on a relatively fertile soil in Panama to evaluate potential nutrient limitation of tree growth rates, fine-litter production, and fine-root biomass. We replicated the eight factorial treatments four times using 32 plots of 40 x 40 m each. The addition of K was associated with significant decreases in stand-level fine-root biomass and, in a companion study of seedlings, decreases in allocation to roots and increases in height growth rates. The addition of K and N together was associated with significant increases in growth rates of saplings and poles (1-10 cm in diameter at breast height) and a further marginally significant decrease in stand-level fine-root biomass. The addition of P was associated with a marginally significant (P = 0.058) increase in fine-litter production that was consistent across all litter fractions. Our experiment provides evidence that N, P, and K all limit forest plants growing on a relatively fertile soil in the lowland tropics, with the strongest evidence for limitation by K among seedlings, saplings, and poles.     

Mobility of chloroaromatic compounds in soil: case studies of Swedish chlorophenol-contaminated sawmill sites

This paper summarizes recent studies on the environmental fate of chloroaromatic compounds in chlorophenol (CP)-contaminated soil and groundwater at Swedish sawmill sites. Relative proportions of CPs, polychlorinated phenoxy phenols (PCPPs), polychlorinated diphenyl ethers (PCDEs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) were determined in preservatives, particulate organic matter (POM), dissolved organic matter (DOM), groundwater, and particles filtered from groundwater. All compound classes were found in the different compartments. The fraction of PCPPs, PCDEs, PCDDs, and PCDFs had increased in the soil samples relative to the proportions in the preservatives. This increase showed correlation with the hydrophobicity, that is, PCDDs had the largest increase. Similar correlation was found between hydrophobicity and the importance of partitioning to POM over DOM. The more water soluble compound group, CP, was found equally distributed between POM and DOM. For PCPPs, PCDEs, PCDDs, and PCDFs, the relative partitioning to POM increased with increased hydrophobicity. Despite the relative partitioning towards POM, compared with DOM, cotransport with DOM and suspended colloidal fractions was found to substantially increase the transport of these compounds in the groundwater samples.     

Very high correlations between fresh weight and lipid-adjusted PCB-153 serum concentrations: irrespective of fasting status, age, body mass index, gender, or exposure distributions

Background and aim

Persistent organochlorine pollutants (POPs) have in epidemiological studies been associated with health hazards. The exposure window might be crucial and it is, accordingly, important to analyze exposure concentrations in samples collected at the window of interest. This makes the use of stored blood samples extremely interesting. However, small blood volumes from stored samples in biobanks means that the researchers in epidemiological studies most often have to select a limited number of biomarkers representing the POP exposure and abstain from analyses of lipid concentrations. This raises the question of the necessity of lipid adjustment. The aim of the present study was to evaluate the correlation between fresh weight and lipid adjusted concentrations.

Methods

We included data from studies were we have used the PCB congener 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB-153) as a biomarker for POP exposure and where fresh weight as well as lipid adjusted PCB-153 concentrations are known (n = 1628). The variety of the cohort members in the different studies gave us the possibility to better understand how well these measures correlate.

Results

When all individuals were included in the analyses a correlation coefficient of 0.95 between fresh weight and lipid adjusted serum concentrations was obtained. Restricting the analyses to specific subgroups (based on gender, fasting status, age and BMI) gave correlation coefficients between 0.85 and 0.97.

Conclusions

This study does strongly support the use of samples from biobanks in epidemiological studies for analyzing PCBs, at least regarding PCB-153, even though it is not possible to lipid adjust the results.     

Methods for measuring denitrification: diverse approaches to a difficult problem.

Denitrification, the reduction of the nitrogen (N) oxides, nitrate (NO3-) and nitrite (NO2-), to the gases nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2), is important to primary production, water quality, and the chemistry and physics of the atmosphere at ecosystem, landscape, regional, and global scales. Unfortunately, this process is very difficult to measure, and existing methods are problematic for different reasons in different places at different times. In this paper, we review the major approaches that have been taken to measure denitrification in terrestrial and aquatic environments and discuss the strengths, weaknesses, and future prospects for the different methods. Methodological approaches covered include (1) acetylene-based methods, (2) 15N tracers, (3) direct N2 quantification, (4) N2:Ar ratio quantification, (5) mass balance approaches, (6) stoichiometric approaches, (7) methods based on stable isotopes, (8) in situ gradients with atmospheric environmental tracers, and (9) molecular approaches. Our review makes it clear that the prospects for improved quantification of denitrification vary greatly in different environments and at different scales. While current methodology allows for the production of accurate estimates of denitrification at scales relevant to water and air quality and ecosystem fertility questions in some systems (e.g., aquatic sediments, well-defined aquifers), methodology for other systems, especially upland terrestrial areas, still needs development. Comparison of mass balance and stoichiometric approaches that constrain estimates of denitrification at large scales with point measurements (made using multiple methods), in multiple systems, is likely to propel more improvement in denitrification methods over the next few years.