Different proxies for the reactivity of aquatic sediments towards oxygen: A model assessment

Information on benthic carbon mineralization rates is often derived from the analysis of oxygen microprofiles in sediments. To enable a direct comparison of different sediment environments, it is often desirable to characterize sediments by a single proxy that expresses their “reactivity” towards oxygen. For this, there are three commonly used proxies: the oxygen penetration depth (OPD), the oxygen flux at the sediment-water interface (DOU), and the maximum volumetric oxygen consumption rate (R_max). The OPD can be directly determined from the oxygen depth profile, while the DOU is usually obtained by a linear fit to the oxygen gradient either in diffusive boundary layer. The oxygen consumption rate R_max requires the fitting of a reactive-transport model to the data profile. This article shows that the OPD alone is a suboptimal proxy, because it shows a strong dependence on the half-saturation constant K_s, and secondly, because it is sensitive to the particular re-oxidation conditions right above the oxic-anoxic interface. Similarly, the volumetric oxygen consumption rate R_max is rather strongly dependent on the kinetic model formulation employed. To show this we fitted three different (Bouldin, Blackman and Monod) kinetics to the same oxygen data profiles. When fitting these models, the R_max values obtained differed by 20% for exactly the same oxygen profile. Accordingly, if one reports R_max values, it is crucial to specify the kinetic model alongside. Overall, DOU emerges as sediment reactivity proxy which is the least model dependent.     

Application of a temperature-dependent von Bertalanffy growth model to bullhead (Cottus gobio)

The most studied and commonly applied model of fish growth is the von Bertalanffy model. However, this model does not take water temperature into account, which is one of the most important environmental factors affecting the life cycle of fish, as many physiological processes that determine growth, e.g. metabolic rate and oxygen supply, are directly influenced by temperature. In the present study we propose a version of the von Bertalanffy growth model that includes mean annual water temperatures by correlating the growth coefficient, k, explicitly and the asymptotic length, L_∞, implicitly to water temperature. All relationships include parameters with an obvious biological relevance that makes them easier to identify. The model is used to fit growth data of bullhead (Cottus gobio) at different locations in the Bez River network (Drme, France). We show that temperature explains much of the growth variability at the different sampling sites of the network.     

冬季条件下曝气生物滤池处理模拟灰水的应用研究

文章采用陶粒滤料为载体,研究了在冬季低温条件下化学混凝-曝气生物滤池工艺对模拟灰水的中试研究。实验结果表明,在冬季水温为3℃-15℃的条件下,初沉处理大大减轻了后续曝气生物滤池的运行负荷的同时也提高了整个工艺的搞冲击能力。当曝气生物滤池水力负荷为3．8m／h时,COD、LAS的去除效率分别在70％、80％以上。NH4-N去除效率受LAS、COD、温度影响较大,整个工况去除效率在15％～75％。NH4-N的去除效率随着COD负荷的增加,其去除效率受到严重的影响。COD的去除负荷率为2．85kg／（m^3滤料·d）升高到5．04kg／（m^3滤料·d）时,NH4-N的去除率则由61％-77％,下降到26％～41％,说明了异养微生物的生长严重抑制了硝化亚硝化细菌的生长。     

Experimental analysis of thermal performance of evacuated tube and flat-plate solar air collectors at different air flow rates

The thermal performances of an evacuated tube collector (ETC) and flat-plate solar air collector (FPC) are experimentally investigated at different air flow rates. To investigate the performance of the ETC and FPC, experimental set-ups were fabricated. Air was used as a working fluid and tested at the same climatic conditions. The ETC had 15 evacuated tubes with a surface area of 1.66 m². The experimental set-up consisted of a header with a hollow pipe (square pipe) in the centre through which the air flowed. The flat-plate collector had a surface area of 1.35 m². The FPC had a black painted absorber sheet which divides the collector into two sections. The air flowed through the upper and the lower sections parallel to the collector to minimize the overall heat loss. The temperature of the outlet air depends on several factors along with the airflow rate and the intensity of the solar radiation. It was found that during the day at high flow rates, the efficiency of the ETC varies from 0.12 to 0.5, and for the flat plate it was from 0.29 to 0.68. The maximum temperature of the air was 56.7°C for the ETC and 25.7°C for the FPC.     

Integrating soil carbon cycling with that of nitrogen and phosphorus in the watershed model SWAT: Theory and model testing

In this paper we describe and test a sub-model that integrates the cycling of carbon (C), nitrogen (N) and phosphorus (P) in the Soil Water Assessment Tool (SWAT) watershed model. The core of the sub-model is a multi-layer, one-pool soil organic carbon (S_C) algorithm, in which the decomposition rate of S_C and input rate to S_C (through decomposition and humification of residues) depend on the current size of S_C. The organic N and P fluxes are coupled to that of C and depend on the available mineral N and P, and the C:N and N:P ratios of the decomposing pools. Tillage explicitly affects the soil organic matter turnover rate through tool-specific coefficients. Unlike most models, the turnover of soil organic matter does not follow first order kinetics. Each soil layer has a specific maximum capacity to accumulate C or C saturation (S_x) that depends on texture and controls the turnover rate. It is shown in an analytical solution that S_x is a parameter with major influence in the model C dynamics. Testing with a 65-yr data set from the dryland wheat growing region in Oregon shows that the model adequately simulates the S_C dynamics in the topsoil (top 0.3 m) for three different treatments. Three key model parameters, the optimal decomposition and humification rates and a factor controlling the effect of soil moisture and temperature on the decomposition rate, showed low uncertainty as determined by generalized likelihood uncertainty estimation. Nonetheless, the parameter set that provided accurate simulations in the topsoil tended to overestimate S_C in the subsoil, suggesting that a mechanism that expresses at depth might not be represented in the current sub-model structure. The explicit integration of C, N, and P fluxes allows for a more cohesive simulation of nutrient cycling in the SWAT model. The sub-model has to be tested in forestland and rangeland in addition to agricultural land, and in diverse soils with extreme properties such high or low pH, an organic horizon, or volcanic soils.     

The resource curse revisited and revised: A tale of paradoxes and red herrings

We critically evaluate the empirical basis for the so-called resource curse and find that, despite the topic's popularity in economics and political science research, this apparent paradox may be a red herring. The most commonly used measure of “resource abundance” can be more usefully interpreted as a proxy for “resource dependence”—endogenous to underlying structural factors. In multiple estimations that combine resource abundance and dependence, institutional, and constitutional variables, we find that (i) resource abundance, constitutions, and institutions determine resource dependence, (ii) resource dependence does not affect growth, and (iii) resource abundance positively affects growth and institutional quality.     

常绿-半常绿杨树对磷素的利用特性

缺磷是限制农林业产量的一个重要因子,传统的农林业生产主要通过施肥和土壤改良来满足植物对磷的需求,近年来人们开始发掘磷高效利用植物来替代传统方法提高磷的利用效率.A-65/27、A-65/31及A-61/186是目前世界上仅有的3个常绿杨树无性系,共同特点是容易扦插繁殖,造林成活率高,生长快,材质好.3个无性系的推广将极大地丰富南方用材林树种资源.为揭示磷素胁迫条件下常绿杨无性系对土壤中磷素的利用特性,通过沙培试验,设计5个磷素处理水平(磷的质量浓度依次是0.00、0.0310、0.0619、0.1239、0.1858 g·L~(-1)),进行不同磷素处理水平下常绿杨生长及生理生态特性的研究.结果表明:当磷的质量浓度为0.0619 g·L~(-1)时已经能满足常绿杨生长对磷的基本需求;磷素不足会明显的影响到常绿杨的生长.低磷胁迫下常绿杨高度、地径及生物量明显降低;低磷胁迫下光合速率也明显下降,通过对气孔导度及胞间二氧化碳浓度的变化趋势分析,导致光合速率下降的主要原因是非气孔限制因素,同步叶绿素荧光的测定表明光系统Ⅱ受到了一定的影响,这是非气孔限制因素之一.     

Is The Ca + K + Mg/Al Ratio in the Soil Solution a Predictive Tool for Estimating Forest Damage?

The ratio between (Ca +K +Mg) and Al in nutrientsolution has been suggested as a predictive tool forestimating tree growth disturbance. However, the ratiois unspecific in the sense that it is based on severalelements which are all essential for plant growth;each of these may be growth-limiting. Furthermore,aluminium retards growth at higher concentrations. Itis therefore difficult to give causal and objectivebiological explanations for possible growthdisturbances. The importance of the proportion ofbase-cations to N, at a fixed base-cation/Al ratio, isevaluated with regard to growth of Picea abies.The uptake of elements was found to be selective;nutrients were taken up while most Al remained insolution. Biomass partitioning to the roots increasedafter aluminium addition with low proportions of basecations to nitrogen. We conclude that the low growthrates depend on nutrient limitation in thesetreatments. Low growth rates in the high proportionexperiments may be explained by high internal Alconcentrations. The results strongly suggest thatgrowth rate is not correlated with the ratio in therooting medium and question the validity of usingratios as predictive tools for estimating forestdamage. We suggest that growth limitation of Picea abies in the field may depend on lowproportions of base cations to nitrate. It istherefore important to know the nutritional status ofthe plant material in relation to the growth potentialand environmental limitation to be able to predict andestimate forest damage.     

Melanin-based colorations signal strategies to cope with poor and rich environments

One hypothesis for the maintenance of genetic variation states that alternative genotypes are adapted to different environmental conditions (i.e., genotype-by-environment interaction G×E) that vary in space and time. Although G×E has been demonstrated for morphological traits, little evidence has been given whether these G×E are associated with traits used as signal in mate choice. In three wild bird species, we investigated whether the degree of melanin-based coloration, a heritable trait, covaries with nestling growth rate in rich and poor environments. Variation in the degree of reddish-brown phaeomelanism is pronounced in the barn owl (Tyto alba) and tawny owl (Strix aluco), and variation in black eumelanism in the barn owl and Alpine swift (Apus melba). Melanin-based coloration has been shown to be a criterion in mate choice in the barn owl. We cross-fostered hatchlings to test whether nestlings sired by parents displaying melanin-based colorations to different extent exhibit alternative growth trajectories when raised by foster parents in poor (experimentally enlarged broods) and rich (experimentally reduced broods) environments. With respect to phaeomelanism, barn owl and tawny owl offspring sired by redder parents grew more rapidly in body mass only in experimentally reduced broods. With respect to eumelanism, Alpine swift offspring of darker fathers grew their wings more rapidly only in experimentally enlarged broods, a difference that was not detected in reduced broods. These interactions between parental melanism and offspring growth rate indicate that individuals display substantial plasticity in response to the rearing environment which is associated with the degree of melanism: at least with respect to nestling growth, phaeomelanic and eumelanic individuals are best adapted to rich and poor environments, respectively. It now remains to be investigated why eumelanism and phaeomelanism have a different signaling function and what the lifelong consequences of these melanism-dependent allocation strategies are. This is important to fully appraise the role played by environmental heterogeneity in maintaining variation in the degree of melanin-based coloration.     

Accounting for rate instability and spatial patterns in the boundary analysis of cancer mortality maps

Boundary analysis of cancer maps may highlight areas where causative exposures change through geographic space, the presence of local populations with distinct cancer incidences, or the impact of different cancer control methods. Too often, such analysis ignores the spatial pattern of incidence or mortality rates and overlooks the fact that rates computed from sparsely populated geographic entities can be very unreliable. This paper proposes a new methodology that accounts for the uncertainty and spatial correlation of rate data in the detection of significant edges between adjacent entities or polygons. Poisson kriging is first used to estimate the risk value and the associated standard error within each polygon, accounting for the population size and the risk semivariogram computed from raw rates. The boundary statistic is then defined as half the absolute difference between kriged risks. Its reference distribution, under the null hypothesis of no boundary, is derived through the generation of multiple realizations of the spatial distribution of cancer risk values. This paper presents three types of neutral models generated using methods of increasing complexity: the common random shuffle of estimated risk values, a spatial re-ordering of these risks, or p-field simulation that accounts for the population size within each polygon. The approach is illustrated using age-adjusted pancreatic cancer mortality rates for white females in 295 US counties of the Northeast (1970–1994). Simulation studies demonstrate that Poisson kriging yields more accurate estimates of the cancer risk and how its value changes between polygons (i.e., boundary statistic), relatively to the use of raw rates or local empirical Bayes smoother. When used in conjunction with spatial neutral models generated by p-field simulation, the boundary analysis based on Poisson kriging estimates minimizes the proportion of type I errors (i.e., edges wrongly declared significant) while the frequency of these errors is predicted well by the p-value of the statistical test.