The Role of Macrophytes in the Retention of Phosphorus in the River Thame,England

The effects of the growth of the dominant species of macrophytes on phosphorus transport in the River Thame, a nutrient enriched lowland clay catchment in southern England, were assessed using a mass-balance approach. Macrophyte abundance was estimated between late March and early June at three sites along the river. the plant biomass of phosphorus and the total phosphorus content of sediments in the main part of the river channel and sediments associated with the plant roots were measured on each occasion. Total phosphorus concentrations in the river water were measured at weekly intervals at a gauging station at the lower end of the study reach.

The results showed that the phosphorus content of plants at the site most impacted by sewage derived phosphorus was < 1% of the flux of total phosphorus estimated for the water column in April and May. Phosphorus contained in the total standing crop of macrophytes at the least impacted site was estimated as approximately 3% of the mean daily flux of total phosphorus in the water. Although no trends were found in the total phosphorus contents of the roots, shoots or sediments through the season, differences in the phosphorus content of the sediments were found between sites with different phosphorus loading. Higher porewater and Equilibrium Phosphate Concentrations (EPC_oS) were recorded at the site most impacted by sewage effluent when compared to an upstream sampling site.     

Phosphorus loading in the Frome catchment, UK: seasonal refinement of the coefficient modeling approach

This paper describes the results of an export coefficient modeling approach to predict total phosphorus (TP) loading in the Frome catchment, Dorset, UK from point and diffuse sources on a seasonal (monthly) basis in 1998 and on an annual basis for 1990-1998. The model predicted an annual TP load of 25 605 kg yr(-1), compared with an observed (measured) value of 23400 kg yr(-1). Monthly loads calculated using the export coefficient model agreed well with monthly observed values except in months of variable discharge, when observed values were low, probably due to infrequent, and therefore unrepresentative, sampling. Comparison between filterable reactive phosphorus (FRP) and TP concentrations observed in the period 1990-1997 showed that trends in FRP could be estimated from trends in TP. A sensitivity analysis (varying individual export coefficients by +/-10%) showed that sewage treatment works (STWs) (3.5%), tilled land (2.7%), meadow-verge-seminatural (1.0%), and mown and grazed turf (0.6%) had the most significant effect (percent difference from base contribution) on model prediction. The model was also used to estimate the effect of phosphorus stripping at STWs in order to comply with a pending change in the European Union wastewater directive. Theoretical reduction of TP from the largest STW in the catchment gave a predicted reduction in TP loading of 2174 kg yr(-1). This illustrates the value of this seasonal export coefficient model as a practical management tool.     

Arthropods in no-tillage soybean agroecosystems: Community composition and ecosystem interactions

Sampling data are provided and concepts discussed regarding soil and foliage arthropod communities in conventional and no-tillage soybean agroecosystems Soil arthropod communities from the two cropping systems were also compared with that from an adjacent old field. Biweekly arthropod samples were collected from conventional, no-tillage, and old-field systems Soil arthropods were sampled by quadrat and pitfall trap methods, foliage arthropods were collected by sweep net Quadrat sampling revealed that ground beetle number, species diversity, and biomass were significantly higher (P<0.05) in no-tillage than in conventional tillage systems. Pitfall trap data indicated higher densities and species diversity for most major soil macro-arthropod guilds Foliage arthropod guilds from no-tillage treatments showed higher species diversity throughout the growing season than those of conventional tillage, possibly because of greater structural diversity provided by weeds and litter in notillage systems No-tillage systems supported a larger and more diverse arthropod community than conventionally grown soybeans, suggesting a need for pest management strategies that simultaneously consider many variables. Both foliar grazing and leaf nitrogen content were higher in conventional than in no-tillage systems, indicating a possible causal connection between soil tillage and insect herbivory rates     

陕西民俗文化旅游资源的保护与开发

陕西民俗文化旅游资源丰富,具有较高的社会价值和旅游价值,但由于政府部门的疏于重视和广大民众认识的浅薄,导致陕西民俗文化旅游资源受到严重的破坏,同时也造成不良风气的大量出现,使这些价值未能得以发挥.针对这一现状,以全国民俗文化的保护和开发为参照,结合陕西民俗文化旅游资源的自身特点,从保护和发展两个方面涉及的具体问题为出发点,就具体的问题提出了具体的建议,希望以此引起各方重视.参5.     

Characterizing source-sink dynamics with genetic parentage assignments

Source-sink dynamics have been suggested to characterize the population structure of many species, but the prevalence of source-sink systems in nature is uncertain because of inherent challenges in estimating migration rates among populations. Migration rates are often difficult to estimate directly with demographic methods, and indirect genetic methods are subject to a variety of assumptions that are difficult to meet or to apply to evolutionary timescales. Furthermore, such methods cannot be rigorously applied to high-gene-flow species. Here, we employ genetic parentage assignments in conjunction with demographic simulations to infer the level of immigration into a putative sink population. We use individual-based demographic models to estimate expected distributions of parent-offspring dyads under competing sink and closed-population models. By comparing the actual number of parent-offspring dyads (identified from multilocus genetic profiles) in a random sample of individuals taken from a population to expectations under these two contrasting demographic models, it is possible to estimate the rate of immigration and test hypotheses related to the role of immigration on population processes on an ecological timescale. The difference in the expected number of parent-offspring dyads between the two population models was greatest when immigration into the sink population was high, indicating that unlike traditional population genetic inference models, the highest degree of statistical power is achieved for the approach presented here when migration rates are high. We used the proposed genetic parentage approach to demonstrate that a threatened population of Marbled Murrelets (Braclhyrarmphus marmotus) appears to be supplemented by a low level of immigration (approximately 2-6% annually) from other populations.     

Offensive and defensive sperm competition roles in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidae)

Sperm competition is predicted to generate opposing selection pressures on males. On one hand, selection should favour ‘defensive’ adaptations that protect a male’s ejaculate from displacement, while, on the other hand, selection should favour ‘offensive’ adaptations that overcome paternity assurance mechanisms of rivals. Here, we use the sterile male technique to assess sperm precedence when a male dung beetle Onthophagus taurus mates in both a defensive (first male) and an offensive (second male) role. Significant variation in a male’s sperm precedence (both P ₁ and P ₂) was detected, and an individual’s defensive (P ₁) and offensive (P ₂) abilities were positively correlated. Thus, it appears that sexual selection simultaneously selects for ‘defensive’ and ‘offensive’ adaptations in O. taurus. We discuss a variety of male traits in O. taurus that potentially contribute to a male’s ability to be successful when mating in an ‘offensive’ and a ‘defensive’ role.