Dynamics of grass–clover mixtures—An analysis of the response to management with the PROductive GRASsland Simulator (PROGRASS)

A dynamic plot-scale model PROGRASS was developed to simulate the seasonal and inter-annual dynamics of productive, cut grass/clover mixtures in response to management, and specifically to examine the role of root development on grass/clover interactions. The model was parameterized by virtue of data for dry matter yield, leaf area index, root mass, soil mineral N uptake and biological N fixation from a long-term field trial in north-eastern Switzerland. It was tested using 5 years of independent data for yield and clover fraction from a field experiment with two management regimes carried out on the Swiss Central Plateau. The results of transient simulations indicated that under intensive fertilization grass dominance was initiated by preferential allocation of assimilates to the roots. The rapid growth of the grass root system lowered the substrate C:N ratio, favouring carbon allocation to the shoot, which eventually provided competitive advantages with respect to light interception. Under extensive management, limited N acquisition capacity of the grass root system maintained preferential allocation to the roots, limiting shoot development in the grass and leading to clover dominance. Co-existence regimes with dominance by one of the components were also found in equilibrium experiments, with a transition regime from clover to grass dominance for annual N applications in the range 100–200 kg N ha⁻¹ y⁻¹ that reflected adjustments of the root system to fertilization. It is concluded that the dynamics of grass/clover mixtures is driven by negative and positive feedbacks in the soil–plant system that are strongly controlled by root development and therefore by the allocation patterns of the grass component.     

黄河水中悬浮粒子对镉离子的交换吸附等温线

研究了黄河水中悬浮粒子对 Cd²⁺ 的交换吸附等温线以及赖氨酸和门冬氨酸对吸附作用的影响．研究结果得到一类具有一个“拐点”、两个“平台”的新型河流等温线,用分级离子交换等温式求出平衡常数 K₁ 和 K₂ ．当低浓度的氨基酸存在时,对镉与悬浮粒子的交换吸附起促进作用．促进作用的程度与氨基酸的等电点有关,赖氨酸的促进作用较门冬氨酸大．     

RECHARGE TO ALLUVIAL VALLEY AQUIFERS FROM OVERBANK FLOW AND EXCESS INFILTRATION1

ABSTRACT: Recharge is an important parameter for models that simulate water and contaminant transport in unconfined aquifers. Unfortunately, measurements of actual recharge are not usually available causing recharge to be estimated or possibly added to the calibration procedure. In this study, differences between observed water-table elevations and water-table elevations simulated with a model based on the one-dimensional Boussinesq equation were used to identify both the timing and quantity of recharge to an alluvial valley aquifer. Observed water table elevations and river stage data were recorded during a five-year period from 1991 to 1995 at the Ohio Management Systems Evaluation Area located in south-central Ohio. Direct recharge attributed to overbank flow during and shortly after flood conditions accounted for 65 percent of the total recharge computed during the five-year study period. Recharge of excess infiltration to the aquifer was intermittent and occurred soon after large rainfall events and high river stage. Specification of constant recharge with time values in ground-water simulation models seems inappropriate for stream-aquifer systems given the strong influence of the river on water table elevations in these systems.     

Need and nestmates affect begging in tree swallows

We conducted an experiment on nestling tree swallows (Tachycineta bicolor) to examine predictions from signalling models for the evolution of conspicuous begging behaviour. Specifically, we examined the relationship between (1) nestling begging intensity and hunger, (2) begging intensity and parental provisioning and (3) begging intensity and nestmate condition. Forty broods of 9-day-old nestlings were removed from their nests for 1 h and assigned to one of the following three treatments: (1) all nestlings in the brood deprived of food (n = 13), (2) all nestlings in the brood fed (n = 11) or (3) half the nestlings in the brood deprived and half fed (n = 16). Videotapes before and after the treatments showed that begging intensity increased in broods in which all of the nestlings had been deprived and decreased in broods in which all of the nestlings had been fed. Deprived nestlings in the half-and-half treatment did not change their begging intensity in response to treatment, while fed nestlings in this treatment group showed a decrease in begging intensity. Parent tree swallows increased their feeding rate to deprived broods and decreased their rate to fed broods. Within broods, parents decreased their feeding rate to fed nestlings, but showed no significant change in feeding to deprived nestlings. Our results suggest that begging intensity is influenced by hunger and that parents appear to respond to variation in begging intensity. The begging of nestmates also appears to influence begging independently of need. These results are consistent with predictions derived from signalling models of begging. Received: 20 June 1997 / Accepted after revision: 19 January 1998     

Comparative toxicity of a brominated flame retardant (tetrabromobisphenol A) on microalgae with single and multi-species bioassays

The potential threat of emerging chemicals to the aquatic flora is a major issue. The purpose of the study was to develop a multispecies microalgae test in order to determine the impact of species interactions on the cytoxicity of an emergent toxic contaminant: the tetrabromobisphenol A (TBBPA). Single and multi-species tests were thus performed to study the effects of this flame retardant on two microalgae (Pseudokirchneriella subcapitata and Nitzschia palea) commonly observed in freshwater. A synthetic medium was designed to allow the growth of both species. The algae were exposed to 1.8, 4.8, 9.2, 12.9 and 16.5 μM of TBBPA for 72 h. After staining with fluorescein diacetate (FDA), viable cells of each alga species were analyzed by flow cytometry based on chlorophyll autofluorescence and intracellular esterase activity. Density and abundance of viable cells were assessed to follow the population growth and the cell viability. In TBBPA treated samples, the growth of the two microalgae was significantly inhibited at the three highest concentrations (9.2, 12.9 and 16.5 μM) in the two tests. At the end of the experiment (t = 72 h), the cell viability was also significantly smaller at these concentrations. The decreases of growth rate and viable cell abundance in TBBPA treated populations of N. palea were significantly higher in multi-species test in comparison with the single-species test. No significant differences were noticed between the two tests for P. subcapitata populations exposed to TBBPA.     

Surface Water Seepage Effects on Shallow Ground‐Water Quality Along the Rio Grande in Northern New Mexico1

Abstract: Interactions between surface irrigation water, shallow ground water, and river water may have effects on water quality that are important for both drinking water supplies and the ecological function of rivers and floodplains. We investigated water quality in surface water and ground water, and how water quality is influenced by surface water inputs from an unlined irrigation system in the Alcalde Valley of the Rio Grande in northern New Mexico. From August 2005 to July 2006, we sampled ground water and surface water monthly and analyzed for concentrations of major cations and anions, specific conductance, pH, dissolved oxygen, and water levels. Results indicate that irrigation ditch seepage caused an increase in ground water levels and that the Rio Grande is a gaining stream in this region. Temporal and spatial differences were found in ion concentrations in shallow ground water as it flowed from under the ditch toward the river. Ground‐water ion concentrations were higher when the ditch was not flowing compared with periods during peak irrigation season when the ditch was flowing. Ditch inputs diluted ion concentrations in shallow ground water at well positions near the ditch. Specifically, lower ion concentrations were detected in ground water at well positions located near the ditch and river compared with well positions located in the middle of an agricultural field. Results from this project showed that ditch inputs influenced ion concentrations and were associated with ground‐water recharge. In arid region river valleys, careful consideration should be given to management scenarios that change seepage from irrigation systems, because in some situations reduced seepage could negatively affect ground‐water recharge and water quality.     

Urban Land Use,Channel Incision,and Water Table Decline Along Coastal Plain Streams,North Carolina1

Abstract: This study evaluates the effects of urban land use on stream channels and riparian ground‐water levels along low‐order Inner Coastal Plain streams in North Carolina. Six sites with stream catchments of similar size (1.19‐3.46 km²) within the Tar River Basin were selected across an urban land use gradient, as quantified by a range of catchment total impervious area (TIA; 3.8‐36.7%). Stream stage and ground‐water levels within three floodplain monitoring wells were measured manually and using pressure transducers from May 2006‐June 2007. Channel incision ratio (CIR), the ratio of bank height to bankfull height, was also measured at each monitoring site and along stream reaches within the study area (12 urban and 12 rural sites). Riparian ground‐water levels were inversely related to catchment TIA (%). As TIA (%) and stormwater runoff increased, the degree of stream channel incision increased and riparian ground‐water tables declined. In urban floodplains (>15% TIA), the median ground‐water level was 0.84 m deeper than for the rural settings (<15% TIA). This has resulted in a shift to drier conditions in the urban riparian zones, particularly during the summer months. CIR was found to be a reliable surface indicator of “riparian hydrologic drought” in these settings.     

饮用水质安全保障的研究与技术发展趋势:Ⅱ.基于微界面过程的水质净化技术

非均相介质体系下的复杂界面是污染物赋存与水质净化过程的载体,微界面反应过程是强化水质净化过程的手段与途径。设计构建针对不同污染物与净化目标的高效界面,阐明基于微界面过程的水质转化与净化机制,建立微界面水质净化过程调控方法,是饮用水质安全保障研究的重要内容。本文从非均相体系下微界面水质过程调控、微界面尺度物质相互作用强化、特殊功能的高效界面构建、非稳态条件下界面反应抑制等角度,综合论述了微界面水质过程调控、强化与控制的重要科学问题与饮用水质净化技术方向。     

Pollinators,pests, and predators: Recognizing ecological trade-offs in agroecosystems

Ecological interactions between crops and wild animals frequently result in increases or declines in crop yield. Yet, positive and negative interactions have mostly been treated independently, owing partly to disciplinary silos in ecological and agricultural sciences. We advocate a new integrated research paradigm that explicitly recognizes cost-benefit trade-offs among animal activities and acknowledges that these activities occur within social-ecological contexts. Support for this paradigm is presented in an evidence-based conceptual model structured around five evidence statements highlighting emerging trends applicable to sustainable agriculture. The full range of benefits and costs associated with animal activities in agroecosystems cannot be quantified by focusing on single species groups, crops, or systems. Management of productive agroecosystems should sustain cycles of ecological interactions between crops and wild animals, not isolate these cycles from the system. Advancing this paradigm will therefore require integrated studies that determine net returns of animal activity in agroecosystems.

Electronic supplementary material

The online version of this article (doi:10.1007/s13280-015-0696-y) contains supplementary material, which is available to authorized users.