Channel Evolution Models as Predictors of Sediment Yield

This paper recounts our predictions of channel evolution of the Black Vermillion River (BVR) and sediment yields associated with the evolutionary sequence. Channel design parameters allowed for the prediction of stable channel form and coincident sediment yields. Measured erosion rates and basin‐specific bank erosion curves aided in prediction of the stream channel succession time frame. This understanding is critical in determining how and when to mitigate a myriad of instability consequences. The BVR drains approximately 1,062 km² in the glaciated region of Northeast Kansas. Once tallgrass prairie, the basin has been modified extensively for agricultural production. As such, channelization has shortened the river by nearly 26 km from pre‐European dimensions; shortening combined with the construction of numerous flow‐through structures have produced dramatic impacts on discharge and sediment dynamics. Nine stream reaches were established within three main tributaries of the BVR in 2007. Reaches averaged 490 m in length, were surveyed, and assessed for channel stability, while resurveys were conducted annually through 2010 to monitor change. This work illustrates the association of current stream state, in‐channel sediment contributions, and prediction of future erosion rates based on stream evolution informed by multiple models. Our findings suggest greater and more rapid sedimentation of a federal reservoir than has been predicted using standard sediment prediction methods.     

Endosulfan induces changes in spontaneous swimming activity and acetylcholinesterase activity of Jenynsia multidentata (Anablepidae, Cyprinodontiformes)

We assessed changes in spontaneous swimming activity and acetylcholinesterase (AchE) activity of Jenynsia multidentata exposed to Endosulfan (EDS). Females of J. multidentata were exposed to 0.072 and 1.4 μg L⁻¹ EDS. Average speed and movement percentage were recorded during 48 h. We also exposed females to EDS at five concentrations between 0.072 and 1.4 μg L⁻¹ during 24 h, and measured the AchE activity in brain and muscle. At 0.072 μg L⁻¹ EDS swimming motility decreased relative to the control group after 45 h, while at 1.4 μg L⁻¹ EDS swimming motility decreased after 24 h. AchE activity significantly decreased in muscle when J. multidentata were exposed to EDS above 0.072 μg L⁻¹, while no significant changes were observed in brain. Thus, changes in swimming activity and AchE activity in muscle are good biomarkers of exposure to EDS in J. multidentata.     

砂泥岩地基大直径灌注桩竖向承载力试验研究

以某电厂桩基础为工程依托,进行了两试桩竖向静载荷试验,探讨了砂泥岩地基大直径灌注桩的荷载传递机理和竖向承载特性。试验结果表明,砂泥岩地基大直径灌注桩在极限荷载作用达到稳定的情况下,荷载由桩侧阻力与桩端阻力共同承担,但表现出很强的摩擦桩特征,桩侧阻力的发挥取决于桩土相对位移,对于不同的土层,桩侧摩阻力达到极限时所对应的桩土之间相对位移不尽相同。针对试验结果,根据上部结构对基础沉降的要求,以桩顶沉降量来控制桩的竖向承载力,并提出了简化的计算公式,该公式考虑了桩土相对位移对桩侧阻力发挥的影响。     

Developing and applying a soil erosion model in a data-poor context to an island in the rural Philippines

Soil erosion in many parts of the developing world poses a threat to rural livelihoods, to the sustainbility of the agricultural sector, and to the environment. Most erosion prediction models are mechanistic and unsuited to quantify the severity of soil erosion in a data-limited developing world context. The model developed in this paper for Negros Island, in the central Philippines, is based on the Revised Universal Soil Loss Equation, but contains important innovations such as the movement of eroded soil over the landscape, simulating deposition on lower slopes and in waterways. It also includes a term describing farmer strategies to reduce soil erosion, which are typically ignored in erosion prediction models. A two-sample t-test found that model-predicted sediment loading values were not significantly different from field-measured sediment loading values when corrected for watershed size (P = 0.857). The model predicts an annual loss of 2.7 million cubic meters of sediment to waterways such that by 2050 more than 416,000 ha of agricultural land will be rendered unproductive due to erosion. Farmer behavior conserves soil, but on the steepest slopes soil conservation practices are not adequate to prevent erosion. Of two proposed strategies to control soil erosion in the rural Philippines, the model suggests that a complete switch to tree crops would conserve more soil than universal terrace adoption. However, even under these conservation scenarios, erosion threatens the areal extent of upland agriculture on Negros, and hence the sustainability of the island’s food supply.

Climate and land-use changes affecting river sediment and brown trout in alpine countries—a review

Background, aim, and scope

Catch decline of freshwater fish has been recorded in several countries. Among the possible causes, habitat change is discussed. This article focuses on potentially increased levels of fine sediments going to rivers and their effects on gravel-spawning brown trout. Indications of increased erosion rates are evident from land-use change in agriculture, changes in forest management practices, and from climate change. The latter induces an increase in air and river water temperatures, reduction in permafrost, changes in snow dynamics and an increase in heavy rain events. As a result, an increase in river sediment is likely. Suspended sediment may affect fish health and behaviour directly. Furthermore, sediment loads may clog gravel beds impeding fish such as brown trout from spawning and reducing recruitment rates. To assess the potential impact on fine sediments, knowledge of brown trout reproductive needs and the effects of sediment on brown trout health were evaluated.

Approach

We critically reviewed the literature and included results from ongoing studies to answer the following questions, focusing on recent decades and rivers in alpine countries.

Have climate change and land-use change increased erosion and sediment loads in rivers?

Do we have indications of an increase in riverbed clogging?

Are there indications of direct or indirect effects on brown trout from increased suspended sediment concentrations in rivers or from an increase in riverbed clogging?

Results

Rising air temperatures have led to more intensive precipitation in winter months, earlier snow melt in spring, and rising snow lines and hence to increased erosion. Intensification of land use has supported erosion in lowland and pre-alpine areas in the second half of the twentieth century. In the Alps, however, reforestation of abandoned land at high altitudes might reduce the erosion risk while intensification on the lower, more easily accessible slopes increases erosion risk. Data from laboratory experiments show that suspended sediments affect the health and behaviour of fish when available in high amounts. Point measurements in large rivers indicate no common lethal threat and suspended sediment is rarely measured continuously in small rivers. However, effects on fish can be expected under environmentally relevant conditions. River bed clogging impairs the reproductive performance of gravel-spawning fish.

Discussion

Overall, higher erosion and increased levels of fine sediment going into rivers are expected in future. Additionally, sediment loads in rivers are suspected to have considerably impaired gravel bed structure and brown trout spawning is impeded. Timing of discharge is put forward and is now more likely to affect brown trout spawning than in previous decades.

Conclusions

Reports on riverbed clogging from changes in erosion and fine sediment deposition patterns, caused by climate change and land-use change are rare. This review identifies both a risk of increases in climate erosive forces and fine sediment loads in rivers of alpine countries. Increased river discharge and sediment loads in winter and early spring could be especially harmful for brown trout reproduction and development of young life stages. Recently published studies indicate a decline in trout reproduction from riverbed clogging in many rivers in lowlands and alpine regions. However, the multitude of factors in natural complex ecosystems makes it difficult to address a single causative factor.

Recommendations and perspectives

Further investigations into the consequences of climate change and land-use change on river systems are needed. Small rivers, of high importance for the recruitment of gravel-spawning fish, are often neglected. Studies on river bed clogging are rare and the few existing studies are not comparable. Thus, there is a strong need for the development of methods to assess sediment input and river bed clogging. As well, studies on the effects to fish from suspended sediments and consequences of gravel beds clogging under natural conditions are urgently needed.     

Predicting Sustained Fire Spread in Tasmanian Native Grasslands

Fire is widely used in conservation management of native grasslands. Burning is often carried out under conditions that are marginal for sustained fire spread, and therefore it would be useful to be able to predict fire sustainability. There is currently no model allowing such prediction in temperate grasslands. This study aims to identify the environmental variables that determine whether fires will sustain in native grasslands in Tasmania, Australia, and develop a model for predicting fire sustainability in this vegetation. Fuel characteristics and weather conditions were recorded for 111 test fires. Logistic regression modeling identified dead fuel moisture content, fuel load, and percentage dead fuel as predictors of fire sustainability. Classification tree modeling identified dead fuel moisture and fuel load threshold values for sustaining fires. There was also evidence indicating a percentage dead fuel threshold. The logistic regression model and a model combining the results of the classification tree and the percentage dead fuel threshold accurately predicted the outcomes of a small set of experimental fires. These models are likely to have utility in predicting fire sustainability in Tasmanian grasslands and are also likely to be applicable to similar grasslands elsewhere.     

大别山区土壤侵蚀经济损失估值研究

大别山区是土壤侵蚀较为强烈的地区之一,严重的土壤侵蚀不但恶化了自然环境,而且制约着该区域经济社会的可持续发展.在GIS的支持下,通过建立土壤侵蚀数据库获取有关土壤侵蚀量以及土壤侵蚀环境分析所需的基础数据,然后根据环境经济学相关的基本原理和方法对土壤侵蚀进行了货币化估算,以达到土壤侵蚀经济损失估值的目的.     

Lingual and biting responses to prey chemicals by ingestively naive scincid lizards: discrimination from control chemicals,time course,and effect of method of stimulus presentation

Summary. We tested responses to prey chemicals by lizard hatchlings of an oviparous species and neonates of a viviparous species, neither of which had never eaten. Both species responded more strongly to prey chemicals than to odorous and odorless control stimuli presented on cotton swabs. Although only a few species have been examined, all that have been tested have an innate capacity for prey chemical discrimination, suggesting that this innate response to prey chemicals is widespread among lizards that use the lingual-vomeronasal system to locate and identify prey. Innate prey chemical discrimination has the great advantage of permitting lizards lacking prior experience with food to respond appropriately to chemical cues associated with food. Both species discriminated prey chemicals from control substances at age three days, earlier than previously known. Our data hint that Mabuya macularia may be capable of discrimination on its day of birth, but further study is needed to determine the exact onset. A stronger tendency to attack swabs bearing prey chemicals by Scincella lateralis than by M. macularia may be explained by differences in defensiveness near an experimenter or by differences in the importance of visual prey cues for confirmation of chemical cues in the natural habitats of these species. In M. macularia responses to the control stimuli declined over days of testing, suggesting habituation, but responses to prey chemicals did not habituate by the third day of testing, which is interpreted as a possible adaptive response to permit location of food. In the standard method of stimulus presentation, a cotton swab bearing a chemical stimulus is placed anterior to a lizard's snout. We tested a new method in which the swab was placed in continuous contact with the lizard's anterior labial scales. The new method elicited significantly stronger responses from M. macularia. We discuss reasons for this finding and applications for the new method. Received 2 September 1999; accepted 15 December 1999     

湖北省兴山县农业生态环境整治策略

以实地考察材料为基础,分析了兴山县农业生态环境的两大问题——水土流失和土壤质量差。提出了切实可行的整治策略。     

The formation and maintenance of crayfish hierarchies: behavioral and self-structuring properties

Behavioral changes in fighting and the development of dominance relationships were analyzed in groups of juvenile crayfish (Astacus astacus) using quantitative behavioral techniques. When individuals were placed into an aquarium, the number of agonistic challenges, their mean duration, and maximum intensity reached were high initially but then decreased steadily as the hierarchy developed. In all groups, linear hierarchies emerged which became increasingly stable over time. Winning influenced subsequent fighting behavior on two distinct time scales. In the short term, recent winners became progressively less likely to retreat. Second, individuals occupying dominant positions for days became increasingly likely to escalate to higher intensities early in the encounter. Both effects biased the outcome of future interactions such that winning enhanced further success and losing decreased an individual’s subsequent chances for dominance. Received: 11 November 1999 / Revised: 1 March 2000 / Accepted: 3 May 2000