利用不同物候期水生植物配置提高浮床人工湿地的除氮效果

为验证利用不同物候期水生植物配置提高碳氮比失衡湿地脱氮能力的可行性,设计了向水芹菜(Oenanthe javanica)浮床人工湿地系统中添加轮叶黑藻(Hydrilla verticillata)的实验,研究了在秋、冬季低温条件下,暖季型植物分解释碳对系统氮去除效果的影响.结果表明,添加轮叶黑藻显著提高了系统水体碳氮比,促进反硝化作用,提高总氮和硝态氮的去除率.在4个周期中,与对照组相比,物候期组合型浮床人工湿地系统的总氮去除率分别提升23.03%、10.90%、18.55%和22.93%,硝态氮去除率分别提升38.28%、20.74%、17.87%和17.06%.由此可见,利用暖季型和冷季型植物配置提高碳氮比失衡湿地氮去除率是可行的.     

济南市不同区域水生生物与水环境因子的响应关系

水生生物与水环境因子是水生态系统中重要的组成部分,研究水生生物与水环境因子的响应关系对制定水生态系统修复方案具有重要意义.于2014年5、8和10月,对济南市水生态系统进行野外采样调查.共设36个采样点,采集鱼类、底栖动物、浮游动物和浮游植物四种生物,并测定了26个水环境因子.采用Spearman相关分析法、小提琴图法和冗余分析法,筛选主要的水环境因子,分析济南市水生生物丰富度和主要水环境因子的分布特征,以及两者间的相互关系.结果表明,共筛选出6个主要的水环境因子,分别为流量（Flow）、溶解氧（DO）、栖息地质量指数（QHEI）、电导率（Cond）、化学需氧量（COD）和总氮（TN）.黄河区Flow、DO、QHEI和水生生物丰富度均较高,小清河区COD、TN、Cond和水生生物丰富度最低.黄河区Cond与鱼类丰富度呈显著相关,城区TN与底栖动物丰富度呈显著相关,小清河区COD、DO和QHEI对水生生物丰富度有显著影响,徒骇马颊河区TN对水生生物丰富度有显著影响.该研究为济南市水生态修复方案的制定提供参考,也为其他城市水生态文明建设提供一种思路.     

Mercury transport in response to storm events from a northern forest landscape

Concentrations and fluxes of mercury (Hg) species in surface waters of forested watersheds are affected by hydrological events. The mechanisms of Hg transport during these events are poorly understood and yet may influence Hg bioavailability and exposure to aquatic biota. Three storm events with varying magnitude and intensity were investigated (June, September and November 2005) at a forested watershed in the Adirondack region of New York State, USA. Concentrations of Hg species increased during these events, both above and downstream of wetlands in the watershed. While Hg flux was higher from wetland drainage, the Hg flux from the upland site exhibited a greater relative increase to elevated runoff. Hg flux was controlled by discharge; however, Hg species concentrations were not well correlated with discharge, dissolved organic carbon (DOC), or total suspended solids (TSS) through the duration of events. A counter‐clockwise hysteresis response of DOC with increasing runoff contrasted with the clockwise response for total Hg, suggesting different contributions from source areas for these solutes. Correspondence with elevated total K and NO₃^? (α < 0·05) during the rising limb of the hydrograph suggests rapid delivery of throughfall Hg, potentially enhanced by hillslope hollows, to the stream channel. As the watershed saturated, stream Hg appears to be derived from the soil Hg pool. Results suggest that particulate Hg did not contribute substantially to total Hg flux during events (<25%). These results emphasize the role of watershed attributes and storm characteristics in Hg transport and bioavailability. Copyright © 2008 John Wiley & Sons, Ltd.     

鄱阳湖湿地植物灰化薹草(Carex cinerascens)对不同地下水位的生理生态响应

地下水位在非淹水期对湿地植物的生长影响较大,但目前相关研究十分缺乏.本文选择鄱阳湖典型植被灰化薹草(Carex cinerascens)为研究对象,研究不同地下水位(地下水位埋深10、20、40、80和120 cm)对灰化薹草形态指标、地上生物量和生理指标的影响.结果表明,随着地下水位埋深的增加,灰化薹草的株高、叶长和生物量均显著降低,地下水位10 cm处理组的灰化薹草生物量为0.371±0.017 g,为地下水位120 cm处理组(0.084±0.004 g)的4.4倍;处理组间灰化薹草叶片中超氧化物歧化酶活性、过氧化物酶活性、游离脯氨酸含量和叶绿素含量均存在显著差异,其中游离脯氨酸含量由地下水位10 cm处理组的6.29±0.70μg/g增加到地下水位120 cm处理组的8.54±1.37μg/g,表明随着地下水位埋深的增加,灰化薹草面临一定程度的干旱胁迫.灰化薹草的生理生态响应综合表明,地下水位埋深20 cm以内适宜灰化薹草的生长,地下水位埋深80 cm以上的干旱胁迫会阻碍灰化薹草的生长.     

Bedrock erosion due to hoeing as tillage technique in a hilly agricultural landscape,southwest China

Tillage on hillslopes may not only induce severe soil erosion, but may also cause bedrock erosion under certain conditions. Yet, little is known about bedrock erosion by tillage in a hilly agricultural landscape, southwest China. The aim of this study is to quantify the translocation of rock fragments derived from bedrock fragmentation by hoeing under different conditions, including slope gradient, hoeing depth and soil-covered thickness using a gravel tracing method. The reliability of the gravel tracing method was confirmed by the bedrock dyeing tracing method. Hoeing depth is a significant factor affecting the translocation rate of rock fragments (Q_r ). Meanwhile, under the condition of overlying soil layers (0.06−0.10 m thick), the values of Q_r were significantly smaller with a reduction of 20.7−25.6%, compared with rock fragmentation by hoeing for bare bedrock. However, slope gradient was found to have insignificant effects on Q_r . Fractured bedrock moved as individual small fragments, which was mainly controlled by the hitting force of the hoe, while soil moved in the shape of lumps, which was dominated by both drag force of the hoe and gravity. This study suggests that hoeing into soil-covered bedrock can diminish bedrock erosion while providing soil matrix for shallow soil layers. Our work presents a quantitative assessment of bedrock erosion by hoeing and an underlying insight into characteristics of bedrock erosion by tillage operations in hilly agricultural regions with mudstone and shale, southwest China. © 2020 John Wiley & Sons, Ltd.     

Quickflow response to forest harvesting and recovery in a northern hardwood forest landscape

Forest harvesting often increases catchment quickflow (QF, water delivered rapidly to the stream channel), a metric of high‐flow events controlling a catchment's solute and sediment export. Nevertheless, our understanding of QF responses to various silvicultural strategies (e.g., clearcutting, selection harvest, and shelterwood harvest) is incomplete. We present a 31‐year examination of QF delivery from treatment (clearcut, selection harvest, and shelterwood harvest) and control catchments in a deciduous forest landscape in central Ontario, Canada. Growing season root‐zone storage capacity was estimated using a water balance approach to evaluate temporal changes in QF response to precipitation (P) for pretreatment and posttreatment periods. Threshold relationships between QF and P were assessed for control and treatment catchments for pretreatment and posttreatment periods using piecewise regression. Root‐zone storage capacity demarcated shifts in the hydrologic regime arising from forest harvesting and subsequent regeneration. This was particularly pronounced for clearcutting where postharvest decline in root‐zone storage capacity was followed by a rise to preharvest values. Similar pretreatment threshold relationships between QF and P, and near‐identical P thresholds for producing significant QF, reflected similar soil and overburden depths in the catchments. Harvesting effects were indicated by increases in QF/P ratios for relative small P and the number of P events that generated QF, thus changing treatment QF vs. P threshold relationships. Prior to harvesting there was no significant increase in QF with P below a threshold P of 35–45 mm; however, there was a significant QF vs. P relationship below this threshold for all treatments postharvest. Clearcutting increased the number of QF events for the entire postharvest period and the first 9‐year postharvest compared to the other treatments; nevertheless, evidence for intertreatment differences in total QF depth delivered from the catchments during the growing season was inconclusive. Our work suggests that changes in threshold relationships between QF and P, coupled with knowledge of the physical processes underlying them, are useful when evaluating hydrologic responses to forest harvesting.     

洱海湖滨带植被特征及其影响因素分析

2009年5至12月对洱海湖滨带植被进行了3次调查,共鉴定出维管植物47科108属145种,其中乔灌木15种、湿生草本植物75种、挺水植物15种、浮叶和漂浮植物各7种、沉水植物26种;有红柳(Salix cavaleriei)、菰(Zizania latifolia)、菱(Trapa natans)和黄丝草(Potam...     

Fine particle transport dynamics in response to wood additions in a small agricultural stream

Wood additions to streams can slow water velocities and provide depositional areas for bacteria and fine particles (e.g., particulate organic carbon and nutrients sorbed to fine sediment), therefore increasing solute and particle residence times. Thus, wood additions are thought to create biogeochemical hotspots in streams. Added wood is expected to enhance in-stream heterogeneity, result in more complex flow paths, increase natural retention of fine particles and alter the geomorphic characteristics of the stream reach. Our aim was to directly measure the impact of wood additions on fine particle transport and retention processes. We conducted conservative solute and fluorescent fine particle tracer injection studies in a small agricultural stream in the Whatawhata catchment, North Island of New Zealand in two reaches—a control reach and a reach restored 1-year earlier by means of wood additions. Fine particles were quantified in surface water to assess reach-scale (channel thalweg) and habitat-scale (near wood) transport and retention. Following the injection, habitat-scale measurements were taken in biofilms on cobbles and by stirring streambed sediment to measure fine particles available for resuspension. Tracer injection results showed that fine particle retention was greater in the restored compared to the control reach, with increased habitat-scale particle counts and reach-scale particle retention. Particle deposition was positively correlated with cobble biofilm biomass. We also found that the addition of wood enhanced hydraulic complexity and increased the retention of solute and fine particles near the wood, especially near a channel spanning log. Furthermore, particles were more easily remobilized from the control reach. The mean particle size remobilized after stirring the sediments was ~5 μm, a similar size to both fine particulate organic matter and many microorganisms. These results demonstrate that particles in this size range are dynamic and more likely to remobilize and transport further downstream during bed mobilization events.     

Incorporating landscape features to obtain an object‐oriented landscape drainage network representing the connectivity of surface flow pathways over rural catchments

A topological representation of a rural catchment is proposed here in addition to the generally used topographic drainage network. This is an object‐oriented representation based on the identification of the inlets and outlets for surface water flow on each farmer's field (or plot) and their respective contributing areas and relationships. It represents the catchment as a set of independent plot outlet trees reaching the stream, while a given plot outlet tree represents the pattern of surface flow relationships between individual plots. In the present study, we propose to implement functions related to linear and surface elements of the landscape, such as hedges or road networks, or land use, to obtain what we call a landscape drainage network which delineates the effective contributing area to the stream, thus characterizing its topological structure. Landscape elements modify flow pathways and/or favour water infiltration, thus reducing the area contributing to the surface yield and modifying the structure of the plot outlet trees. This method is applied to a 4·4‐km² catchment area comprising 43 955 pixels and 312 plots. While the full set of 164 plot outlet trees, with an average of 7 plots per tree, covers 100% of the total surface area of the catchment, the landscape drainage network comprises no more than 37 plot outlet trees with an average of 2 plots per tree, accounting for 52 and 7% of the catchment surface area, when taking account of linear elements and land use, respectively. This topological representation can be easily adapted to changes in land use and land infrastructure, and provides a simple and functional display for intercomparison of catchments and decision support regarding landscape and water management. Copyright © 2011 John Wiley & Sons, Ltd.     

Relative effects of local and landscape factors on wetland algal biomass over a salinity gradient

Wetlands in south-eastern Australia and other arid regions of the world are experiencing increases in salinity due to dryland salinization and climate change. We investigated changes in wetland ecological function, measured as phytoplankton and benthic algal Chl a, over a large salinity gradient (0.047–226 mS cm⁻¹) and in relation to several local water chemistry variables that may be important predictors of algal biomass. We investigated the relative importance of landscape variables that may affect input pollution and hydrology of wetlands at four spatial scales (100, 500, 1,000 and 5000 m). We explored the strength and form of the relationships between algal biomass and local and landscape predictors with emphasis on the effects of local and landscape salinity. We found local variables were more important than landscape variables in influencing algal biomass. We also found salinity of wetlands was not a good predictor of phytoplankton biomass but it did predict benthic algal biomass.     

Water isotopic composition traces source and dynamics of water supply in a semi-arid agricultural landscape

Changes in seasonality and form of precipitation alter the structure and function of grassland and steppe ecosystems and pose challenges for land management and crop production in regions like the Northern Great Plains, North America. This research uses isotopic composition of water (δ¹⁸O and δ²H) to explore the sources and fate of soil water in lower-elevation agricultural areas of the Judith River watershed, in the headwaters of the Missouri River, USA. Extensive non-irrigated cereal crop production in this area occurs on well-drained soils and depends on careful water management. Our observations indicate that colder precipitation contributes isotopically distinct water to cultivated terrace soils relative to downgradient groundwaters and streams. Riparian waters also exhibit a higher fraction of contributions from colder precipitation relative to terrace groundwaters and streams. Apparent contributions from colder precipitation in terrace and riparian soil waters suggest that snowmelt is a key component of the water supply to these systems. Riparian waters also show evidence of evaporation suggesting that water spends sufficient time in some ponds and open channels in the riparian corridor to reflect fractionation by evaporation. The evolution of water isotopic composition from soils to shallow aquifers to stream corridors indicates source water partitioning as precipitation moves through this semi-arid agricultural landscape. The apparent mixing processes evident in this evolution reveal source water dynamics that are necessary to understand plant transpiration, solute processing, and contaminant leaching processes.     

Decline in the species richness contribution of Echinodermata to the macrobenthos in the shelf seas of China

Echinoderms play crucial roles in the structure of marine macrobenthic communities. They are sensitive to excess absorption of CO₂ by the ocean, which induces ocean acidification and ocean warming. In the shelf seas of China, the mean sea surface temperature has a faster warming rate compared with the mean rate of the global ocean, and the apparent decrease in pH is due not only to the increased CO₂ absorption in seawater, but also eutrophication. However, little is known about the associated changes in the diversity of echinoderms and their roles in macrobenthic communities in the seas of China. In this study, we conducted a meta-analysis of 77 case studies in 51 papers to examine the changes in the contribution of echinoderm species richness to the macrobenthos in the shelf seas of China since the 1980s. The relative species richness (RSR) was considered as the metric to evaluate these changes. Trends analysis revealed significant declines in RSR in the shelf seas of China, the Yellow Sea, and the East China Sea from 1997 to 2009. Compared with the RSR before 1997, no significant changes in mean RSR were found after 1997, except in the Bohai Sea. In addition, relative change in the RSR of echinoderms and species richness of macrobenthos led to more changes (decrease or increase) in their respective biomasses. Our results imply that changes in species richness may alter the macrobenthic productivity of the marine benthic ecosystem.     

全新世以来东北地区沼泽湿地发育过程及其对气候变化的响应

沼泽湿地是陆地生态系统的重要组成部分,在维护区域环境稳定中起着重要作用.随着社会经济的发展,人类活动导致湿地大面积退化和消失,严重影响了区域生态安全;恢复退化湿地已成为各国政府和学者关注的焦点.而了解历史时期沼泽湿地发育过程及影响因素则是建立合理湿地恢复目标的重要前提.东北地区是我国最大的沼泽湿地集中分布区,其中70%的湿地面临不同程度的退化威胁;但由于数据的缺乏,东北地区沼泽湿地发育过程及其与气候变化的关系仍不清楚.基于此,本研究系统分析了全新世以来东北地区沼泽湿地形成发育的动态变化过程,并探讨了东北地区不同区域沼泽湿地的发育规律及其对气候变化的响应机理.研究发现东北地区沼泽湿地约从12 ka（1 ka=1000 cal.）开始发育,在距今8.6 ka以后开始广泛形成,约有35%的沼泽湿地形成于全新世暖湿期（8.0-4.0 ka）;而沼泽湿地发育的高峰期则集中在全新世晚期.这种发育趋势与全球北方主要区域沼泽湿地大规模发育趋势显著不同.古气候重建表明,全新世早期东北地区气候温暖湿润,处在有利于沼泽发育的时期,促进了沼泽湿地的形成;而在全新世晚期,东北地区呈现冷湿的气候组合特征,冷湿的气候条件不利于有机质的分解,进而促进了沼泽湿地的大规模形成和发育.此外,研究结果也表明全新世以来东北地区不同区域沼泽湿地发育的时间和规模呈现显著的空间差异,而温度和降水则是影响不同区域沼泽湿地发育的最重要因素.本研究将为我国东北地区沼泽湿地的保护和恢复提供一定的理论和数据支持.     

Flow network derivation from a high resolution DEM in a low relief,agrarian landscape

Digital flow networks derived from digital elevation models (DEMs) sensitively react to errors due to measurement, data processing and data representation. Since high‐resolution DEMs are increasingly used in geomorphological and hydrological research, automated and semi‐automated procedures to reduce the impact of such errors on flow networks are required. One such technique is stream‐carving, a hydrological conditioning technique to ensure drainage connectivity in DEMs towards the DEM edges. Here we test and modify a state‐of‐the‐art carving algorithm for flow network derivation in a low‐relief, agricultural landscape characterized by a large number of spurious, topographic depressions. Our results show that the investigated algorithm reconstructs a benchmark network insufficiently in terms of carving energy, distance and a topological network measure. The modification to the algorithm that performed best, combines the least‐cost auxiliary topography (LCAT) carving with a constrained breaching algorithm that explicitly takes automatically identified channel locations into account. We applied our methods to a low relief landscape, but the results can be transferred to flow network derivation of DEMs in moderate to mountainous relief in situations where the valley bottom is broad and flat and precise derivations of the flow networks are needed. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of slope angle and aspect on plant cover and species richness in a humid Mediterranean badland

Soil erosion is one of the most severe land degradation processes in the Mediterranean region. Although badlands occupy a relatively small fraction of the Mediterranean area, their erosion rates are very high. Many studies have investigated to what extent vegetation controls soil erosion rates. This study, however, deals with the impact of erosion on vegetation establishment. In semi‐arid badlands of the Mediterranean, soil water availability constitutes the main limiting factor for vegetation development. As a consequence, south‐facing slopes are typically less vegetated due to a very large water stress. However, these findings do not necessarily apply to humid badlands. The main objective of this paper is to determine the topographic thresholds for plant colonization in relation to slope aspect and to assess the spatial patterns of vegetation cover and species richness. We surveyed 179 plots on highly eroded badland slopes in the Central Pyrenees. We defined four aspect classes subdivided into slope angle classes. Colonization success was expressed in terms of vegetation cover and species richness. Slope angle thresholds for plant colonization were identified for each slope aspect class by means of binary logistic regressions. The results show that a critical slope angle exists below which plants colonize the badland slopes. Below this critical slope angle, plant cover and species richness increase with a decreasing slope angle. The largest critical slope angles in humid badlands are observed on south‐facing slopes, which contrasts with the results obtained in semi‐arid badlands. North‐facing slopes however are characterized by a reduced overall vegetation cover and species richness, and lower topographic threshold values. The possible underlying processes responsible for this slope‐aspect discrepancy in vegetation characteristics are discussed in terms of environmental variables that control regolith development, weathering and erosion processes. Moreover, possible restoration strategies through the use of vegetation in highly degraded environments are highlighted. Copyright © 2014 John Wiley & Sons, Ltd.     

Tracing the temporal evolution of soil redistribution rates in an agricultural landscape using 239+240Pu and 10Be

Two principal groups of processes shape mass fluxes from and into a soil: vertical profile development and lateral soil redistribution. Periods having predominantly progressive soil forming processes (soil profile development) alternate with periods having predominantly regressive processes (erosion). As a result, short-term soil redistribution – years to decades – can differ substantially from long-term soil redistribution; i.e. centuries to millennia. However, the quantification of these processes is difficult and consequently their rates are poorly understood. To assess the competing roles of erosion and deposition we determined short- and long-term soil redistribution rates in a formerly glaciated area of the Uckermark, northeast Germany. We compared short-term erosion or accumulation rates using plutonium-239 and -240 (^239+240Pu) and long-term rates using both in situ and meteoric cosmogenic beryllium-10 (¹⁰Be). Three characteristic process domains have been analysed in detail: a flat landscape position having no erosion/deposition, an erosion-dominated mid-slope, and a deposition-dominated lower-slope site. We show that the short-term mass erosion and accumulation rates are about one order of magnitude higher than long-term redistribution rates. Both, in situ and meteoric ¹⁰Be provide comparable results. Depth functions, and therefore not only an average value of the topsoil, give the most meaningful rates. The long-term soil redistribution rates were in the range of −2.1 t ha^-1 yr^-1 (erosion) and +0.26 t ha^-1 yr^-1 (accumulation) whereas the short-term erosion rates indicated strong erosion of up to 25 t ha^-1 yr^-1 and accumulation of 7.6 t ha^-1 yr^-1. Our multi-isotope method identifies periods of erosion and deposition, confirming the ‘time-split approach’ of distinct different phases (progressive/regressive) in soil evolution. With such an approach, temporally-changing processes can be disentangled, which allows the identification of both the dimensions of and the increase in soil erosion due to human influence. © 2019 John Wiley & Sons, Ltd.     

Comparison of artificial neural network models for hydrologic predictions at multiple gauging stations in an agricultural watershed

This paper reports on an evaluation of the use of artificial neural network (ANN) models to forecast daily flows at multiple gauging stations in Eucha Watershed, an agricultural watershed located in north‐west Arkansas and north‐east Oklahoma. Two different neural network models, the multilayer perceptron (MLP) and the radial basis neural network (RBFNN), were developed and their abilities to predict stream flow at four gauging stations were compared. Different scenarios using various combinations of data sets such as rainfall and stream flow at various lags were developed and compared for their ability to make flow predictions at four gauging stations. The input vector selection for both models involved quantification of the statistical properties such as cross‐, auto‐ and partial autocorrelation of the data series that best represented the hydrologic response of the watershed. Measured data with 739 patterns of input–output vector were divided into two sets: 492 patterns for training, and the remaining 247 patterns for testing. The best performance based on the RMSE, R² and CE was achieved by the MLP model with current and antecedent precipitation and antecedent flow as model inputs. The MLP model testing resulted in R² values of 0·86, 0·86, 0·81, and 0·79 at the four gauging stations. Similarly, the testing R² values for the RBFNN model were 0·60, 0·57, 0·58, and 0·56 for the four gauging stations. Both models performed satisfactorily for flow predictions at multiple gauging stations, however, the MLP model outperformed the RBFNN model. The training time was in the range 1–2 min for MLP, and 5–10 s for RBFNN on a Pentium IV processor running at 2·8 GHz with 1 MB of RAM. The difference in model training time occurred because of the clustering methods used in the RBFNN model. The RBFNN uses a fuzzy min‐max network to perform the clustering to construct the neural network which takes considerably less time than the MLP model. Results show that ANN models are useful tools for forecasting the hydrologic response at multiple points of interest in agricultural watersheds. Copyright © 2008 John Wiley & Sons, Ltd.     

Comparative risk assessment of permethrin, chlorothalonil, and diuron to coastal aquatic species

The precise application of risk assessment can lead to different conclusions about risk depending on how species are grouped in the assessment. We compared the use of different risk assessment methods for three different classes of pesticide, the herbicide diuron, the fungicide chlorothalonil, and the insecticide permethrin for marine and estuarine species. Permethrin was the most toxic pesticide to marine and estuarine crustaceans. Diuron was the most toxic pesticide to algae, and chlorothalonil was most toxic to early life stages of molluscs and other invertebrates. Toxicity data (96 h LC50/EC50 values) were analyzed using a probability distribution on the ranked toxicity values and 10th centile values were calculated based on different groups of species and for all species combined. Our results indicate that an assessment of risk based on smaller taxonomic groups can be informative, especially for pesticides of less specific modes of action such as chlorothalonil.