A meta‐analysis of the effects of nutrient enrichment on litter decomposition in streams

The trophic state of many streams is likely to deteriorate in the future due to the continuing increase in human‐induced nutrient availability. Therefore, it is of fundamental importance to understand how nutrient enrichment affects plant litter decomposition, a key ecosystem‐level process in forest streams. Here, we present a meta‐analysis of 99 studies published between 1970 and 2012 that reported the effects of nutrient enrichment on litter decomposition in running waters. When considering the entire database, which consisted of 840 case studies, nutrient enrichment stimulated litter decomposition rate by approximately 50%. The stimulation was higher when the background nutrient concentrations were low and the magnitude of the nutrient enrichment was high, suggesting that oligotrophic streams are most vulnerable to nutrient enrichment. The magnitude of the nutrient‐enrichment effect on litter decomposition was higher in the laboratory than in the field experiments, suggesting that laboratory experiments overestimate the effect and their results should be interpreted with caution. Among field experiments, effects of nutrient enrichment were smaller in the correlative than in the manipulative experiments since in the former the effects of nutrient enrichment on litter decomposition were likely confounded by other environmental factors, e.g. pollutants other than nutrients commonly found in streams impacted by human activity. However, primary studies addressing the effect of multiple stressors on litter decomposition are still few and thus it was not possible to consider the interaction between factors in this review. In field manipulative experiments, the effect of nutrient enrichment on litter decomposition depended on the scale at which the nutrients were added: stream reach > streamside channel > litter bag. This may have resulted from a more uniform and continuous exposure of microbes and detritivores to nutrient enrichment at the stream‐reach scale. By contrast, nutrient enrichment at the litter‐bag scale, often by using diffusing substrates, does not provide uniform controllable nutrient release at either temporal or spatial scales, suggesting that this approach should be abandoned. In field manipulative experiments, the addition of both nitrogen (N) and phosphorus (P) resulted in stronger stimulation of litter decomposition than the addition of N or P alone, suggesting that there might be nutrient co‐limitation of decomposition in streams. The magnitude of the nutrient‐enrichment effect on litter decomposition was higher for wood than for leaves, and for low‐quality than for high‐quality leaves. The effect of nutrient enrichment on litter decomposition may also depend on climate. The tendency for larger effect size in colder regions suggests that patterns of biogeography of invertebrate decomposers may be modulating the effect of nutrient enrichment on litter decomposition. Although studies in temperate environments were overrepresented in our database, our meta‐analysis suggests that the effect of nutrient enrichment might be strongest in cold oligotrophic streams that depend on low‐quality plant litter inputs.     

Stability of strong species interactions resist the synergistic effects of local and global pollution in kelp forests

Foundation species, such as kelp, exert disproportionately strong community effects and persist, in part, by dominating taxa that inhibit their regeneration. Human activities which benefit their competitors, however, may reduce stability of communities, increasing the probability of phase-shifts. We tested whether a foundation species (kelp) would continue to inhibit a key competitor (turf-forming algae) under moderately increased local (nutrient) and near-future forecasted global pollution (CO(2)). Our results reveal that in the absence of kelp, local and global pollutants combined to cause the greatest cover and mass of turfs, a synergistic response whereby turfs increased more than would be predicted by adding the independent effects of treatments (kelp absence, elevated nutrients, forecasted CO(2)). The positive effects of nutrient and CO(2) enrichment on turfs were, however, inhibited by the presence of kelp, indicating the competitive effect of kelp was stronger than synergistic effects of moderate enrichment of local and global pollutants. Quantification of physicochemical parameters within experimental mesocosms suggests turf inhibition was likely due to an effect of kelp on physical (i.e. shading) rather than chemical conditions. Such results indicate that while forecasted climates may increase the probability of phase-shifts, maintenance of intact populations of foundation species could enable the continued strength of interactions and persistence of communities.     

基于非点源污染控制的景观格局优化方法与原则

对目前国内外较为常用的基于非点源污染控制的景观格局优化方法及其设计原则进行了系统的评述 ,以促进其推广应用并提高其污染控制效果。还通过分析这些方法在我国的应用前景 ,强调了探索适合我国国情的景观格局优化方法对于控制非点源污染的重要意义。     

溶解性有机质对土壤中有机污染物环境行为的影响

土壤中溶解性有机质(DOM)是生物活性和物理化学反应活性都很活跃的有机组分,主要通过疏水吸附、分配、氢键、电荷转移、共价键、范德华力等多种作用与有机污染物结合,提高溶液中有机污染物的溶解度,改变土壤中有机污染物的吸附-解吸、迁移-转化等环境行为．DOM对有机污染物的吸附-解吸、迁移-转化过程的影响有双重性：一方面,DOM与有机污染物在土壤表面的共吸附可增加土壤对有机污染物的吸附容量,促进有机污染物在土壤中的吸持;另一方面,DOM对有机污染物的增溶作用,有利于土壤中有机污染物的解吸,提高移动性．作为光敏剂,DOM能提高土壤中有机物的光解反应速率．在一定条件下,DOM也可影响土壤中有机污染物的水解过程．DOM对土壤中有机污染物环境行为的影响与DOM和有机污染物的性质及其相互作用的介质条件密切相关．     

Applications of biofilms in bioremediation and biotransformation of persistent organic pollutants, pharmaceuticals/personal care products, and heavy metals

In this review, the strategies being employed to exploit the inherent durability of biofilms and the diverse nutrient cycling of the microbiome for bioremediation are explored. Focus will be given to halogenated compounds, hydrocarbons, pharmaceuticals, and personal care products as well as some heavy metals and toxic minerals, as these groups represent the majority of priority pollutants. For decades, industrial processes have been creating waste all around the world, resulting in contaminated sediments and subsequent, far-reaching dispersal into aquatic environments. As persistent pollutants have accumulated and are still being created and disposed, the incentive to find suitable and more efficient solutions to effectively detoxify the environment is even greater. Indigenous bacterial communities are capable of metabolizing persistent organic pollutants and oxidizing heavy metal contaminants. However, their low abundance and activity in the environment, difficulties accessing the contaminant or nutrient limitations in the environment all prevent the processes from occurring as quickly as desired and thus reaching the proposed clean-up goals. Biofilm communities provide among other things a beneficial structure, possibility for nutrient, and genetic exchange to participating microorganisms as well as protection from the surrounding environment concerning for instance predation and chemical and shear stresses. Biofilms can also be utilized in other ways as biomarkers for monitoring of stream water quality from for instance mine drainage. The durability and structure of biofilms together with the diverse array of structural and metabolic characteristics make these communities attractive actors in biofilm-mediated remediation solutions and ecosystem monitoring.     

Soil initial bacterial diversity and nutrient availability determine the rate of xenobiotic biodegradation

Understanding the relative importance of soil microbial diversity, plants and nutrient management is crucial to implement an effective bioremediation approach to xenobiotics-contaminated soils. To date, knowledge on the interactive effects of soil microbiome, plant and nutrient supply on influencing biodegradation potential of soils remains limited. In this study, we evaluated the individual and interactive effects of soil initial bacterial diversity, nutrient amendments (organic and inorganic) and plant presence on the biodegradation rate of pyrene, a polycyclic aromatic hydrocarbon. Initial bacterial diversity had a strong positive impact on soil biodegradation potential, with soil harbouring higher bacterial diversity showing ~ 2 times higher degradation rates than soils with lower bacterial diversity. Both organic and inorganic nutrient amendments consistently improved the degradation rate in lower diversity soils and had negative (inorganic) to neutral (organic) effect in higher diversity soils. Interestingly, plant presence/type did not show any significant effect on the degradation rate in most of the treatments. Structural equation modelling demonstrated that initial bacterial diversity had a prominent role in driving pyrene biodegradation rates. We provide novel evidence that suggests that soil initial microbial diversity, and nutrient amendments should be explicitly considered in the design and employment of bioremediation management strategies for restoring natural habitats disturbed by organic pollutants.     

Periphyton response to simulated nonpoint source pollution: local over regional control

We investigated functional and structural responses of periphyton communities to simulated nonpoint source (NPS) pollution over a 2-year period. Periphyton communities were examined in three unique but hydrologically connected habitats in the lower Muskegon River: river, wetland, and lake. Our study addressed several major questions: (1) what are the effects of nonpoint source pollutants on periphyton structure and function, (2) to what degree do environmental conditions, including the pollutant delivery system and hydrologic conditions, affect periphyton response, and (3) do periphyton communities show synchronous responses to nonpoint source pollution? Nutrients were added over a 21-day period in each of the four seasons over 2 years. The effect of road salt on metabolism was evaluated in the winter and spring seasons in the river habitat only. In general, the periphyton community showed complex responses to the NPS amendments, but there was little evidence of nutrient limitation in this system based on community structure, biomass accrual, metabolism, or alkaline phosphatase activity. This result was unexpected given the relatively low ambient concentrations of phosphorus. We discuss the possibilities that nutrient delivery was ineffective or that herbivory and/or irradiance might have constrained periphyton growth, but ultimately conclude that our results suggest that periphyton communities in the lower Muskegon River watershed were (1) nutrient-replete, (2) tolerant of short-term salt additions, and (3) influenced more by local conditions (habitat) than by regional (watershed) factors. In systems where nonpoint source pollutant delivery is diffuse and hydrologic residence time is short, the influence of nonpoint source pollutants on periphyton may be either modest or too difficult to detect using traditional endpoints.     

Soil amendment application frequency contributes to phytoextraction of lead by sunflower at different nutrient levels

Phytoextraction has been proposed as an alternative remediation technology for soils polluted with heavy metals, but is generally perceived to be too slow. Enhancing accumulation of trace pollutants in harvestable plant tissues is a prerequisite for such technology to be practical. The main aims of this paper were to investigate whether a combination of nutrients and ethylenediaminetetraacetic acid (EDTA) enhanced Pb uptake of sunflower (Helianthus annuus) plants, and if timing of EDTA application altered Pb uptake and environmental persistence. Plants were grown in greenhouse pot experiments. Pb distributions and uptake of the whole plant were studied using chemical and flame atomic absorption spectrometry analyses. Pb mobilization by EDTA appeared to be dose dependent, with more mobilization for the high than the low dose. There were distinct differences in mobilization patterns of various nutrient amendments. EDTA mobilized Pb more in the medium than the highest and lowest nutrient levels. Heterogeneous soil humus components exerted mobilizing and stabilizing effects, so the medium nutrition was most effective for phytoextraction. At low nutrient levels, Pb concentration in the shoot with one low EDTA application was less than two applications to the same total EDTA dosage. So in the poor soil, two applications of EDTA was more effective than once. The half-life of two low EDTA treatment applications was longer than for one application, to the same total dosage. In general, sunflower was suited to phytoremediation of moderately Pb-contaminated soil by phytoextraction.     

环境条件对植物稳定碳同位素组成的影响

植物稳定碳同位素技术是近年兴起的一项快速、可靠的技术。利用稳定碳同位素技术可以揭示碳同化的过程的许多方面的信息。1 3C和1 2 C同位素效应 ,使它们在进行碳循环时发生稳定碳同位素的分馏。植物光合作用过程中CO2 经气孔扩散分差和RUBPCase及PEPCase羧化分馏是造成植物稳定碳同位素比率 (R =1 3C/ 1 2 C)不同于源CO2 中碳同位素比率的主要原因。遗传因素和环境因子同时决定植物碳同位素组成。植物稳定碳同位素技术同时还是古气候重建和预测未来环境变化的理论基础。本文综述了光照、温度、水分、二氧化碳、矿质营养、盐分和大气污染物等环境因素对植物稳定碳同位素组成影响方面的研究进展。     

Effect of nutrient enrichment on the distribution and sedimentation of polychlorinated biphenyls (PCBs) in seawater

The effect of nutrient enrichment on the distribution of polychlorinated biphenyl's (PCBs) in the microbial food web and the residence time of PCBs in seawater was studied in an experimental mesocosm system. Two 5 m high temperature and light controlled mesocosm tubes (⊘ = 0,5 m) were filled with seawater from the northern Baltic Sea. Inorganic phosphorus and nitrogen were added daily to one mesocosm, while the other served as a control. Experiments were conducted at 5, 10 and 20°>C. Three ¹⁴C-labelled PCBs of different degree of chlorination were added to subsamples of the mesocosms: 4 chlorobiphenyl (MCB), IUPAC # 3; 2,2′,5,5′-tetrachlorobiphenyl (TCB), IUPAC # 52 and 2,2′, 4,4′,5,5′-hexachlorobiphenyl (HCB) IUPAC # 153. The biomasses and growth rates of the microorganisms as well as the sedimentation rate of particulate organic material increased with nutrient enrichment. The size distribution of the microorganisms changed with nutrient status, from dominance of picoplankton (< 2 μm) in the control towards increased importance of micro (> 10 μm) and nanoplankton (2– 10 μm) in nutrient enrichment. The specific growth rate of the bacterial community was found to be more temperature dependent than that of the phytoplankton community. The relative proportion of PCBs in the >2 μm fraction was observed to be in the order MCB < TCB < HCB, while the opposite distribution prevailed in the < 2 μm fraction. We hypothesize that this is due to the combined effect of the different Kow values of the PCBs and a different composition of the particulate organic carbon in the > 2 μm and < 2 μm fractions (e.g. different lipid composition). The residence time of the PCBs in the mesocosm generally decreased with nutrient enrichment, but was dependent on the degree of chlorination of the PCB. Our results indicate that the transport of organic pollutants up through the food web is more important in nutrient poor than in nutrient rich waters and that the importance of sedimentation is higher in eutrophic ecosystems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modification of benthic insect communities in polluted streams: combined effects of sedimentation and nutrient enrichment

Responses of the benthic insect community of a southern Appalachian trout stream to inorganic sedimentation and nutrient enrichment were monitored over a period of eight months. Entry of pollutants from point sources established differentially polluted zones, allowing an assessment of impacts due to sedimentation alone and in association with elevated nutrient levels. Input of sediment resulted in a significant increase in bed load and decrease of pH at the substrate-water interface (P < 0.05). The zone receiving nutrient runoff from livestock pasture exhibited elevated levels of nitrate and phosphate, but available data indicated such concentrations to be quite low. Species richness, diversity, and total biomass of filter feeding Trichoptera and Diptera, predaceous Plecoptera, and certain Ephemeroptera were significantly reduced in the polluted zones. Inorganic sedimentation, operating indirectly through disruption of feeding and filling of interstitial spaces, was considered to be the primary factor affecting filter feeding taxa. Decomposition of compounds associated with materials in the bed load may depress pH and eliminate acid sensitive species of Plecoptera and Ephemeroptera. Such processes of acidification may be particularly important to Appalachian streams since the pH of regional surface waters is characteristically acidic prior to sedimentation. Accumulation of particles on body surfaces and respiratory structures, perhaps as a function of wax and mucous secretion or surface electrical properties, appears to be the major direct effect of inorganic sedimentation on stream insects. Growths of the filamentous bacterium Sphaerotilus natans were also frequently associated with silted individuals in the zone receiving nutrient addition. Distribution of the bacterium suggested that silted substrates, perhaps as related to the presence of iron compounds, are required for colonization in dilute nutrient solutions. The primary effect of Sphaerotilus colonies appears to be augmentation of particle accumulation through net formation by bacterial filaments. Data indicate that inorganic sedimentation and nutrient addition operate synergistically, eliminating a significantly greater number of taxa than exposure to one pollutant alone.     

Reduction of mineral nutrient availability accelerates flowering of Arabidopsis thaliana

The time of flowering is regulated by various environmental cues, and in some plant species, it is known to be affected by abiotic stresses. We investigated the effect of nutrient stress caused by an abrupt reduction of mineral nutrition on flowering of Arabidopsis thaliana. We used a hydroponic culture system that enabled us to precisely control nutrient levels. When plants were grown in full-strength nutrient solution for several weeks and then transferred to a diluted medium, the time from sowing to bud appearance was significantly shortened. This acceleration of flowering was more pronounced in short days than in long days, and stronger in the ecotype Landsberg erecta than in Columbia and San Feliu-2. The response was also affected by the age of plants at the beginning of nutrient stress and by the concentration of the diluted medium: earlier treatment and more diluted solutions strengthened the effect. Flowering was affected by nutrient stress, not by a change in the osmotic potential of the medium: addition of mannitol to a 1000-fold diluted solution had no effect on the promotion of flowering. When 3-week-old Landsberg erecta plants were exposed to 1000-fold diluted nutrient solution in an 8-h day length, flower bud appearance was strongly and reproducibly advanced by 10.8–12.8 d compared with control plants (which developed buds 41.1–46.2 d after sowing). This treatment can serve as an optimized protocol for future studies concerning physiological, molecular and ecological aspects of flower induction by nutrient stress in A. thaliana.     

环境条件对植物稳定碳同位素组成的影响

植物稳定碳同位素技术是近年兴起的一项快速、可靠的技术。利用稳定碳同位素技术可以揭示碳同化的过程的许多方面的信息。13C和12C同位素效应,使它们在进行碳循环时发生稳定碳同位素的分馏。植物光合作用过程中CO2经气孔扩散分差和RUBPCase及PEPCase羧化分馏是造成植物稳定碳同位素比率(R=13C/12C)不同于源CO2中碳同位素比率的主要原因。遗传因素和环境因子同时决定植物碳同位素组成。植物稳定碳同位素技术同时还是古气候重建和预测未来环境变化的理论基础。本文综述了光照、温度、水分、二氧化碳、矿质营养、盐分和大气污染物等环境因素对植物稳定碳同位素组成影响方面的研究进展。     

碳源与氮源限制下细菌代谢调节研究进展

营养限制是微生物最常面临的环境胁迫之一。除了在营养物质匮乏的海洋、冰川、沙漠、深层地表等自然环境中,越来越多的人工环境也出现了营养限制的特征,例如各类微污染水体、提标改造的废水生物处理系统等。基质浓度极大地影响着包括细菌在内的许多微生物的生长、代谢及群落结构,最终导致其功能的改变。为了在营养限制条件下维持生存,微生物首先需感知营养供给的减少,其后通过基因、蛋白质、信号分子、代谢产物等对各代谢过程进行全局调控,最后改变基质亲和力、生长速率、运动能力、形态等以适应营养不足。胞内各种信号物质及其触发的响应是微生物应对营养胁迫的关键。本文分别梳理了以细菌为代表的微生物应对碳源、氮源限制时的关键信号物质、受体蛋白/调控过程及响应结果,并分析了碳氮限制响应过程中的相互作用,以期为极端环境微生物的认识、营养限制条件下微生物的应用,尤其是低浓度污染物生物处理、生物监测等领域提供理论基础。     

A theoretical explanation of the Piper-Steenbjerg effect

The relation between plant yield and plant nutrient concentration is sometimes found to be negative, a phenomenon called the Piper-Steenbjerg (PS) effect. A model was used to examine the underlying causes of the PS effect, and the conditions under which it is most likely to occur. The model uses the nutrient productivity concept for plant growth and a nutrient uptake equation in which root growth rate and external nutrient concentration determine the uptake rate. The study suggests that the PS effect occurs when the fast growth of plants grown in an initially higher nutrient medium eventually leads to a more rapid depletion of external nutrients than the slow growth of plants grown in an initially lower nutrient medium. The fast growth of plants combined with a rapid decrease of nutrient uptake leads to a fall in plant nutrient concentration. When these large plants with very low nutrient concentrations are compared with the smaller, slow-growing plants, a PS effect may be found depending on the time at which the plants are harvested, and on the range of initial values of the external nutrient content. When it occurs, the effect is greatest when the depletion volume per unit new root (V_d) is lowest, and when the mobility of nutrients in the medium is highest (α=1). The results are sufficiently general to apply to a variety of nutrients, plant species and growth media.     

受干扰的生态系统Ⅰ.柞蚕林的养分循环

本文通过田间实验与测试揭示了柞蚕林养分循环状态和干扰因素对养分平衡的影响。结果表明,地下部储存的养分占总积累的比重较大。同时叶部养分向树体转移能力较强。柞蚕林二级生产力是以收获蚕茧为主要形式,其养分输出水平对系统的养分平衡产生的影响主要表现对树体养分内循环方面。林木养分储量的下降是造成生产力衰退的重要原因。对养分循环格局的认识有助于对该系统干扰强度进行调控,以增强柞蚕林生态系统的稳定性。     

The distribution of Epichloe typhina in natural plant populations of the host plant Calamagrostis purpurea

The distribution of the systemic fungus Epichloe typhina was studied in natural populations of the host grass Calamagrostis purpurea. By searching for stroma in field and dissecting and staining plant parts in the lab I found that E. typhina was only present in nutrient rich and more wet habitats and totally absent from nutrient poor areas. A greenhouse experiment showed that under high nutrient conditions infected plants produced significantly more shoots than did healthy plants, while no difference was found when plants were grown in low nutrient conditions. Thus, the results suggest that the occurrence as well as the effect of E. typhina is strongly affected by environmental factors similar to the case of other systemic diseases, such as rusts and smuts.     

Nutrient enrichment weakens the stabilizing effect of species richness

With global freshwater biodiversity declining at an even faster rate than in the most disturbed terrestrial ecosystems, understanding the effects of changing environmental conditions on relationships between biodiversity and the variability of community and population processes in aquatic ecosystems is of significant interest. Evidence is accumulating that biodiversity loss results in more variable communities; however, the mechanisms underlying this effect have been the subject of considerable debate. We manipulated species richness and nutrients in outdoor aquatic microcosms composed of naturally occurring assemblages of zooplankton and benthic invertebrates to determine how the relationship between species richness and variability might change under different nutrient conditions. Temporal variability of populations and communities decreased with increasing species richness in low nutrient microcosms. In contrast, we found no relationship between species richness and either population or community variability in nutrient enriched microcosms. Of the different mechanisms we investigated (e.g. overyielding, statistical averaging, insurance effects, and the stabilizing effect of species richness on populations) the only one that was consistent with our results was that increases in species richness led to more stable community abundances through the stabilizing effect of species richness on the component populations. While we cannot conclusively determine the mechanism(s) by which species richness stabilized populations, our results suggest that more complete resource-use in the more species-rich low nutrient communities may have dampened population fluctuations.     

引江济湖的主要目的不是稀释污染物,而是修复自然水文节律及自净能力

引水(江河等)济湖是常提的湖泊富营养化治理措施,但实际效果十分有限。围绕"如何科学实施江湖连通"这个问题,文章首先通过案例分析和模型模拟,指出引水冲释的效果取决于是否有足够的低磷源水,而这个条件往往难以满足。然后,比较阻隔湖泊与通江湖泊的水质,分析总结长江通江湖泊水质良好的机制,即自然水位波动利于水生植被发育、湖滨带季节性变浅和干涸利于分解吸附污染物、湖水泥沙多且流动导致浮游藻类对营养的利用效率下降、生态复杂性较高,指出江河与湖泊的连通工程应以修复自由水文连通和自然水位波动为主要目的,从而增强湖泊自净能力,并给出实施建议。文章对国内外引水济湖工程进行了系统综述,提出了科学的新连通模式,对有效实施江河与湖泊的连通工程具有重要指导价值。     

Assessing temporal and spatial trends in estuarine nutrient dynamics using a multi-species stable isotope approach

Coastal urbanisation can alter estuarine nutrient dynamics through the input of point-source and diffuse pollutants, and nutrient concentrations can be highly influenced by seasonal and episodic rainfall and river flow. Understanding of both the spatial and temporal variability of nutrient dynamics is therefore critical to managing these estuaries. This can be achieved by periodically analysing the stable isotopes a range of aquatic taxa with variable nutrient turnover rates, mobility and distribution within the estuary. In two subtropical urban estuaries with different land use patterns, we analysed the carbon and nitrogen stable isotopes of phytoplankton, shrimp, prawns and fish at various proximities to pollution sources in dry and wet seasons. The fast nutrient turnover rates and ubiquity of phytoplankton in the estuary resulted in stable isotopes varying over fine-scale spatial scales, particularly in relation to proximity to point-source pollution. The slower nutrient turnover rates and localised habitat use of prawns, resulted in stable isotopes varying over larger spatial (between pollution sources) and temporal (seasonal) scales. The much slower nutrient turnover rates and high mobility throughout the estuary of fish resulted in stable isotopes varying over very large-scale spatial scales (between estuaries). These results illustrate a wide range of spatial and temporal changes to estuarine nutrient dynamics in subtropical urban estuaries in relation to rainfall conditions and nutrient inputs. This research also highlights the application of stable isotopes in assessing estuarine trophodynamics, and provides direction on the types of organisms that should be used to assess different spatial and temporal trends.