Direct and indirect control of grassland community structure by litter, resources, and biomass

Multiple factors linked through complex networks of interaction including fertilization, aboveground biomass, and litter control the diversity of plant communities. The challenge of explaining plant diversity is to determine not only how each individual mechanism directly influences diversity, but how those mechanisms indirectly influence diversity through interactions with other mechanisms. This approach is well established in the study of plant species richness, but surprisingly little effort has been dedicated toward understanding the controls of community evenness, despite the recognition that this aspect of diversity can influence a variety of critical ecosystem functions. Similarly, studies of diversity have predominantly focused on the influence of shoot, rather than root, biomass, despite the fact that the majority of plant biomass is belowground in many natural communities. In this study, I examine the roles of belowground biomass, live aboveground biomass, litter, and light availability in controlling the species richness and evenness of a rough fescue grassland community using structural equation modeling. Litter was the primary mechanism structuring grassland diversity, with both richness and evenness declining with increasing litter cover. There were few relationships between shoot biomass, shading, and diversity, and more importantly, no relationship between root biomass and diversity. The lack of relationship between root biomass and species richness and evenness suggests that, even though root competition in grasslands is intense, belowground interactions may not play an important role in structuring community diversity or composition.     

A multi-agent simulation to assess the risk of malaria re-emergence in southern France

A multi-agent simulation (MAS) was developed to assess the risk of malaria re-emergence in the Camargue in southern France, a non-endemic area where mosquitoes of the genus Anopheles (Culicidae) live. The contact rate between people and potential malaria vectors, or the human biting rate, is one of the key factor to predict the risk of re-emergence of malaria, would the parasite be introduced in the region. Our model (called MALCAM) represents the different agents that could influence malaria transmission in the Camargue – people, mosquitoes, animal hosts and the landscape – in a spatially explicit environment. The model simulates spatial and temporal variations in human biting rate at the landscape scale. These variations depend on the distribution of people and potential vectors, their behaviour and their interactions. A land use/cover map was used as a cellular-spatial support for the movements of and interactions between mobile agents. The model was tested for its sensitivity to variations in parameter values, and for the agreement between field observations and model predictions. The MALCAM model provides a tool to better understand the interactions between the multiple agents of the disease transmission system, and the land use and land cover factors that control the spatial heterogeneity in these interactions. It allows testing hypotheses and scenarios related to disease dynamics by varying the value of exogenous biological, geographical, or human factors. This application of agent-based modelling to a human vector-borne disease can be adapted to different diseases and regions.     

香港汀角红树植物、沉积物及双壳类动物重金属含量

汀角有香港面积最大的硬底质红树林,作者调查了该红树林区沉积物、红树植物以及双壳类动物体内重金属(Cu、Pb、Zn和Ni)的含量.总体看,沉积物中重金属含量与其他地点相比较低,红树植物根际沉积物中重金属含量高于光滩.红树植物组织内重金属含量较低,体内Pb、Zn的含量均低于根际沉积物,但对Cu、Ni有一定的富集,Cu可在根部和叶内富集,而Ni只在根部富集,并束缚于此.双壳类动物对4种重金属的吸收存在较大差异,Zn、Cu的富集明显高于Pb和Ni的富集程度.5种动物中又以岩蠔最高,体内的Zn、Cu分别达到3913, 378mg/g.从重金属含量看,作为食用动物有一定的风险.     

Whole-stream response to nitrate loading in three streams draining agricultural landscapes

Physical, chemical, hydrologic, and biologic factors affecting nitrate (NO3(-)) removal were evaluated in three agricultural streams draining orchard/dairy and row crop settings. Using 3-d "snapshots" during biotically active periods, we estimated reach-level NO3(-) sources, NO3(-) mass balance, in-stream processing (nitrification, denitrification, and NO3(-) uptake), and NO3(-) retention potential associated with surface water transport and ground water discharge. Ground water contributed 5 to 11% to stream discharge along the study reaches and 8 to 42% of gross NO3(-) input. Streambed processes potentially reduced 45 to 75% of ground water NO3(-) before discharge to surface water. In all streams, transient storage was of little importance for surface water NO3(-) retention. Estimated nitrification (1.6-4.4 mg N m(-2) h(-1)) and unamended denitrification rates (2.0-16.3 mg N m(-2) h(-1)) in sediment slurries were high relative to pristine streams. Denitrification of NO3(-) was largely independent of nitrification because both stream and ground water were sources of NO3(-). Unamended denitrification rates extrapolated to the reach-scale accounted for <5% of NO3(-) exported from the reaches minimally reducing downstream loads. Nitrate retention as a percentage of gross NO3(-) inputs was >30% in an organic-poor, autotrophic stream with the lowest denitrification potentials and highest benthic chlorophyll a, photosynthesis/respiration ratio, pH, dissolved oxygen, and diurnal NO3(-) variation. Biotic processing potentially removed 75% of ground water NO3(-) at this site, suggesting an important role for photosynthetic assimilation of ground water NO3(-) relative to subsurface denitrification as water passed directly through benthic diatom beds.     

Effects of Flow Augmentations in the Snake River Basin on Farms Profitability1

Abstract: For over 10 years, several species of salmon have been identified as either threatened or endangered in the Snake River Basin of Idaho. The United States Bureau of Reclamation, in cooperation with the National Marine Fisheries Service, has proposed a variety of plans to increase stream flows in the Snake River Basin to facilitate movement by juvenile salmon smolts to the ocean. This research examines two of the flow augmentation plans proposed by the Bureau of Reclamation as well as two alternative plans, one founded purely on existing priority‐based water rights and another geared toward minimizing the effects of flow augmentations on farms profitability. Results from a basin‐wide model of agricultural production in the Snake River Basin, the Snake River Agricultural Model, present evidence that (1) older water rights are used towards production of less valuable crops, (2) flow augmentation scenarios have unequal effects on farms profitability across agricultural regions within the basin, and (3) irrigation water is valued from US$4 to US$59 an acre‐foot.     

Heavy metal mobility in runoff water and absorption by eggplant fruits from sludge treated soil

Sewage sludge addition to agricultural lands requires judicious management to avoid environmental risks arising from heavy metal and nitrate contamination of surface water and accumulation in edible plants. A field study was conducted on a silty-loam soil of 10% slope at Kentucky State University Research Farm. Eighteen plots of 22 x 3.7 m each were separated using metal borders and the soil in six plots was mixed with sewage sludge and yard waste compost mix (SS-YW) at 15 t acre(-1), six plots were mixed with sewage sludge (SS) at 15 t acre(-1), and six unamended plots that never received sludge were used for comparison purposes. Plots were planted with eggplant, Solanum melongena L. as the test plant. The objectives of this investigation were to: 1) assess the effect of soil amendments on the transport of NO3, NH4, and heavy metals (Cd, Cr, Ni, Pb, Zn, Cu, and Mo) into surface water; 2) investigate the effect of soil amendments on heavy metal bioavailability in eggplant fruits at harvest; and 3) assess chemical and physical properties of soil following addition of soil amendments and their impact on the yield and quality of eggplant fruit. SS-YW treatments reduced runoff water by 63% while plots incorporated with sewage sludge alone reduced runoff water by 37% compared to control treatment. The SS-YW treatments transported more mineral nitrogen (NO3-N and NH4-N) in runoff water than SS treatments. Total marketable yield (lbs acre(-1)) and number of eggplant fruits were greatest in SS-YW treatments. This response may be due to improved soil porosity, water, and nutrient retention of the soil amended with SS-YW mixture. Concentrations of heavy metals in soil amended with sludge were below the U.S. Environmental Protection Agency (USEPA) limits. Chromium, Ni, Zn, and Cu were taken up by eggplant fruits but their concentrations were below the Codex Commission allowable levels.     

Refinery evaluation of optical imaging to locate fugitive emissions

Fugitive emissions account for approximately 50% of total hydrocarbon emissions from process plants. Federal and state regulations aiming at controlling these emissions require refineries and petrochemical plants in the United States to implement a Leak Detection and Repair Program (LDAR). The current regulatory work practice, U.S. Environment Protection Agency Method 21, requires designated components to be monitored individually at regular intervals. The annual costs of these LDAR programs in a typical refinery can exceed US$1,000,000. Previous studies have shown that a majority of controllable fugitive emissions come from a very small fraction of components. The Smart LDAR program aims to find cost-effective methods to monitor and reduce emissions from these large leakers. Optical gas imaging has been identified as one such technology that can help achieve this objective. This paper discusses a refinery evaluation of an instrument based on backscatter absorption gas imaging technology. This portable camera allows an operator to scan components more quickly and image gas leaks in real time. During the evaluation, the instrument was able to identify leaking components that were the source of 97% of the total mass emissions from leaks detected. More than 27,000 components were monitored. This was achieved in far less time than it would have taken using Method 21. In addition, the instrument was able to find leaks from components that are not required to be monitored by the current LDAR regulations. The technology principles and the parameters that affect instrument performance are also discussed in the paper.     

Environmental degradation by mud in tropical estuaries

In wet tropical countries, the intense rainfall and the lack of effective restrictions on human activities in the river catchment leads to increased rates of soil erosion. This has increased the sediment loads many times over from the natural level. As a result, estuarine and coastal waters are becoming increasingly muddy with associated losses for society in terms of increased flooding and a degradation of the environment, the fisheries and the economic use of these waters. It is suggested that science-based models be used to predict the fate of mud in estuaries and coastal waters when planning development in river catchments, particularly in wet tropical countries. This would help integrate land and water management. Modelling technology is demonstrated by a combination of field and model studies in four turbid tropical estuaries, namely the Fly River in Papua New Guinea, the Mekong River in Vietnam, the Cimanuk River in Indonesia, and Hinchinbrook Channel in Australia. The final model is adapted to local conditions and extensively uses data assimilation especially for open boundary conditions. There can be a feedback between the hydrodynamics and the mud dynamics when the system silts; in wet tropical countries this can occur rapidly, sometimes in only 30 years. Electronic Publication     

Modulation of steroidogenesis by coastal waters and sewage effluents of Hong Kong, China, using the H295R assay

BACKGROUND, AIM, AND SCOPE: The presence of a variety of pollutants in the aquatic environment that can potentially interfere with the production of sex steroid hormones in wildlife and humans has been of increasing concern. The aim of the present study was to investigate the effects of extracts from Hong Kong marine waters, and influents and effluents from wastewater treatment plants on steroidogenesis using the H295R cell bioassay. After exposing H295R cells to extracts of water, the expression of four steroidogenic genes and the production of three steroid hormones were measured. MATERIALS AND METHODS: Water samples were collected during the summer of 2005 from 24 coastal marine areas and from the influents and effluents of two major waste water treatment plants (WWTPs) in Hong Kong, China. Samples were extracted by solid phase extraction (SPE). H295R cells were exposed for 48 h to dilutions of these extracts. Modulations of the expression of the steroidogenic genes CYP19, CYP17, 3betaHSD2, and CYP11beta2 were determined by measuring mRNA concentrations by real-time polymerase chain reaction (Q-RT-PCR). Production of the hormones progesterone (P), estradiol (E2), and testosterone (T) was quantified using enzyme linked immunosorbent assays (ELISA). RESULTS: Extracts from samples collected in two fish culture areas inhibited growth and proliferation of H295R cells at concentrations greater or equal to 10(5) L equivalents. The cells were exposed to the equivalent concentration of active substances in 10,000 L of water. Thus, to observe the same level of effect as observed in vitro on aquatic organisms would require a bioaccumulation factor of this same magnitude. None of the other 22 marine samples affected growth of the cells at any dilution tested. Twelve of the marine water samples completely inhibited the expression of CYP19 without affecting E2 production; inhibition of CYP17 expression was observed only in one of the samples while expression of CYP11beta2 was induced as much as five- and ninefold after exposure of cells to extracts from two locations. The expression of the progesterone gene 3betaHSD2 was not affected by any of the samples; only one sample induced approximately fourfold the production of E2. Although more than twofold inductions were observed for P and T production, none of these values were statistically significant to conclude effects on the production of these two hormones. While influents from WWTPs did not affect gene expression, an approximately 30% inhibition in the production of E2 and a 40% increase in P occurred for the exposure with influents from the Sha Tin and Stonecutters WWTPs, respectively. Effluents from WWTPs did not affect the production of any of the studied hormones, but a decrement in the expression of the aldosterone gene CYP11beta2 was observed for the Sha Tin WWTP exposure. No direct correlation could be established between gene expression and hormone production. DISCUSSION: Observed cytotoxicity in the two samples from fish culture areas suggest the presence of toxic compounds; chemical analysis is required for their full identification. Although effluents from WWTPs did not affect hormone production, other types of endocrine activity such as receptor-mediated effects cannot be ruled out. Interactions due to the complexity of the samples and alternative steroidogenic pathways might explain the lack of correlation between gene expression and hormone production results. CONCLUSIONS: Changes observed in gene expression and hormone production suggest the presence in Hong Kong coastal waters of pollutants with endocrine disruption potential and others of significant toxic effects. The aromatase and aldosterone genes seem to be the most affected by the exposures, while E2 and P are the hormones with more significant changes observed. Results also suggest effectiveness in the removing of compounds with endocrine activity by the WWTPs studied, as effluent samples did not significantly affect hormone production. The H295R cell showed to be a valuable toll in the battery required for the analysis of endocrine disrupting activities of complex environmental samples. RECOMMENDATIONS AND PERSPECTIVES: Due to the intrinsic complexity of environmental samples, a combination of analytical tools is required to realistically assess environmental conditions, especially in aquatic systems. In the evaluation of endocrine disrupting activities, the H295R cell bioassay should be used in combination with other genomic, biological, chemical, and hydrological tests to establish viable modes for endocrine disruption and identify compounds responsible for the observed effects.