查看更多>>摘要：Roots can stabilise slopes against shallow landslides by mobilising their mechanical strength.Existing analytical models are highly simplified and typically focus on the ultimate limit state only,thus providing little insight into the underlying mechanism of reinforcement mobilisation.A new analytical model('DRAM')was therefore developed to predict mechanical root reinforcement as a function of direct shear displacements.This model accounts for elasto-plastic root behaviour,three-dimensional root orientations,root failure through breakage or slippage,and a dynamically changing shear zone thickness.Comparison to two independent experimental direct shear data sets showed that the model was able to accurately predict the gradual mobilisation of root strength,the magnitude of peak root reinforcement,as well as the presence of significant root reinforcement at large shear displacements,associated with a relatively large quantity of roots slipping out of the surrounding soil.Because the newly developed model more closely resembles the underlying physics of the mobilisation of root reinforcement in direct shear while still being easy to use,it will be a useful tool for the engineering industry,in terms of quantifying root reinforcement distribution for limit analyses at the ultimate limit state,as well as for directing future research into the drivers of mechanical root reinforcement.
查看更多>>摘要：Geotextiles or grain filters are frequently used between technical revetment and subsoil at riverbanks on waterways as erosion control from hydraulic loads.Due to the EU Water Framework Directive of the year 2000(Directive 2000/60/EC)and other EU Directives ecological and near nature hydraulic engineering measures are becoming ever more in demand.That's why more technical-biological bank protection under the use of plants should be applied,for example willow brush mattresses,plant mats,reed gabions.Based on the investigations of the filtration stability of geotextiles used at navigable waterways,a method,and a new test apparatus for verifying the soil retention capability and the mechanical filtration stability of willow brush mattresses and their dense,near-surface root system have been developed.Willow brush mattresses made of white willows(Salix alba L.)or basket willows(Salix viminalis L.)were planted in wooden sample boxes and placed upside down into the test apparatus after a pre-set growing time(0,1,3 and 6 months).By flooding and draining the test apparatus water level drawdown has been simulated.The eroded soil material was collected,weighed after drying until weight constancy,and compared with the dry mass of the retained soil material.The results of this new developed mechanical filtration stability tests for willow brush mattresses show that during the initial phase of six months the willow roots reduced soil erosion.Thus,in long-term plant roots can take over mechanical filter function in near nature bank protection.The basket willow led to significant reductions in soil erosion i.e.,an increase of the soil retention capability after one month and the white willow after three months of growth.
Henrique Vieira de MendonqaMarcelo Henrique OtenioAlice Azevedo Lomeu
8页
查看更多>>摘要：In the present study,a horizontal subsurface flow constructed wetland(HSF-CW)with a surface area of 240 m~2 and HRT of 2 days,was used in the post treatment of a facultative aerated pond.Application rates of 175 kg BOD5 ha~(-1)day~(-1)and 408 kg COD ha~(-1)day~(-1)can be considered admissible for HSF-CW operation following a facultative aerated pond.The system presented values for COD,BOD5 and TSS removal of 88%,98.8% and 99.3%,respectively.The system supported operation at a solids application rate of 23.3 g TSS m~(-2)day~(-1)for two years without clogging.The species grown in the CW(Brachiaria mziziensis)presented a biomass produtivity of between 1.86 and 2.55 kg m~(-2)y~(-1),providing CO2 biofixation of between 3.10 and 3.98 kg m~(-2)y~(-1).The present study,conducted over two years,indicates that the HSF-CW model employed,and the operational parameters proposed,can be used in post treatment for a pond system that is not operating satisfactorily.
查看更多>>摘要：Bioretention has been widely applied to mitigate urban runoff pollution.However,its net nitrogen leaching(outflow nitrogen concentration > inflow nitrogen concentration)frequently occurs and attracts more and more attention.In this paper,the variations of nitrogen leaching under different rainfall-runoff events(overall leaching)from a field bioretention were investigated based on a two-year continuous monitoring effort.The temporal course of leaching during each rainfall-runoff event(phased leaching)was analyzed by dividing the outflow into three phases in accordance with the volumes of residual water stored in the bioretention gravel and soil layers before the rain.The results indicate that:(1)The events with overall net leaching of ammonium(NH_4~+),nitrate(NO_3~-)and dissolved organic nitrogen(DON)account for 8%,46% and 50% of the total monitored events,respectively.Overall net leaching occurs when the event mean concentration in inflow of current rain is lower than that of previous rain and the antecedent dry period(ADP)meets a certain threshold(e.g.,ADP < 70 h for NO_3~-leaching and ADP > 24 h for DON leaching in this study);(2)The nitrogen leaching in the initial and final phase of outflow is respectively affected by the inflow of previous rain and current rain;while the nitrogen leaching in the middle phase is jointly affected by the inflow of previous rain and current rain;in addition,most NO_3~-leaches in the final phase,while most DON leaches in the initial phase;(3)Denitrification and assimilation in the bioretention during drying periods decreases NO_3~-leaching and increases DON leaching in the initial phase of outflow,respectively.This field study thus provides pertinent information that could help accurately assess and efficiently manage the risk of nitrogen leaching from a bioretention system.
查看更多>>摘要：With the aggravation of agricultural pollution and habitat degradation,ecological engineering has been applied to solve those contradictions.One of the effective strategies for agricultural pollution and biodiversity conservation in hilly areas is to build the cascade-pond system.In this project,the cascade-pond system was built as agricultural facilities for sustainable development in Lieshen village of Liangping district,China.In order to analyze the purification effect of aquaculture pollution and the characteristics of the macroinvertebrate assemblages in the cascade-pond system,aquatic macroinvertebrates and environmental variables were sampled at three times in one year.The results showed that the cascade-pond group in the middle reach had lower purification function to the aquaculture pollution from the upstream fish pond,which might be due to the low concentration of sewage from upstream.Higher concentration of nutrients,little macrophytes and plenty of fish in the fish ponds,did harmful to the macroinvertebrate assemblages.Meanwhile,the cascade-pond group in the middle reach with lower concentration of nutrients,abundant macrophytes and less fish could support higher biodiversity of macroinvertebrates.In the cascade-pond group,with the decrease of nutrients,the productivity of macroinvertebrates was limited by oligotrophy condition.In addition to water purification and biodiversity conservation,the system also could provide ecosystem services as hydrological regulation,soil and water conservation,economic production,leisure and entertainment.The study can offer practical model for sustainable development of agriculture in hilly areas and provide data support for the protection of regional biodiversity.
Juan Von ThadenHelen Salazar-ArteagaJavier Laborde
12页
查看更多>>摘要：Agriculture is one of the main drivers of deforestation worldwide,generating highly fragmented landscapes that severely limit the mobility of forest species.Knowledge of the state of previously forested landscapes,taking into account all of its arboreal elements(including isolated trees,living fences,riparian corridors,and others)is a necessary first step to gaining a better understanding of the ecological dynamics of anthropic landscapes,and for designing conservation and management plans that enhance functional connectivity within these landscapes.We used high-resolution images(2.5 m/pixel)to identify all of the arboreal elements-from single tree crowns up to large forest fragments-for 40,000 ha of the Los Tuxtlas Biosphere Reserve.We included isolated trees,usually ignored in most inventories of fragmented landscapes,but which together with the other arboreal elements play an important role as landscape connectors and extra habitat for many species.Using a graph theory approach,we assessed landscape connectivity at six inter-patch distances across open areas(from 50 to 500 m),and propose two strategies for improving landscape connectivity:the creation of woodland islets and the widening of forested riparian corridors in the agricultural matrix.The main arboreal elements that influenced connectivity were old-growth forest fragments and widespread treed living fences,each increasing connectivity by up to 57%(depending on the threshold distance),while riparian corridors and isolated trees contributed 38% and 6%,respectively.Isolated trees in pastures substantially increased the number of effective connections at all distances(>85%).The GIS-simulated restoration proposals to establish circular woodland islets(10 m radius)in the middle of open agricultural areas increased connectivity by 26%,while widening riparian corridors by up to 10 m per riverside increased it by 11%.Increasing the number of arboreal elements within the agricultural matrix at key sites would enhance landscape connectivity considerably,benefiting the organisms that live in forest remnants in the study area without the need to stop agricultural activities.
查看更多>>摘要：Determining the optimal rest grazing period can provide a scientific basis for rest grazing during spring in alpine meadows.Kobresia humilis is one of the main construction species of alpine meadow that is of ecological and economic value.We studied the effects of rest grazing on the reproduction of K.humilis during different periods of spring.The five different rest grazing periods were set based on soil thawing depth and plant re-greening,which included the following:the critical period of soil thawing-plant withering period(PI),the late period of soil thawing-plant withering period(92),the early period of grass regreening-plant withering period(P3),the late period of grass regreening-plant withering period(P4)and the period of local traditional rest grazing-plant withering period(P5).The biomass of each component of K.humilis in P1 was significantly higher than that in other plots,and the corresponding biomass of leaf and stalk + panicle in P1 were 239.6% and 207.1% higher than those of P5.The biomass of each component decreased with the delay of rest grazing time.The seed yield and its components(except the number of seeds per panicle)and seed quality of P1 were higher than those of the other plots.The stalk length and the seed yield of P1 was 416.3% and 142.5% higher than those of P5.The responses of vegetative reproduction indices to different rest grazing periods were varied.The number of leaves in PI was 61.6% higher than that in P5,and the death leaf ratio in P1 was 233.3% lower than that in P5.Finally,rest grazing during the critical period of soil thawing-plant withering period(PI)was inferred to be beneficial to the growth and reproduction of K.humilis using the grey correlation analysis method.Therefore,spring rest grazing in alpine meadows should start from the critical period of soil thawing.
查看更多>>摘要：Over the last 90 years,dry mixed grass prairie across North America has been severely impacted by agriculture,urbanization,and oil and gas operations,presenting significant challenges for land reclamation and range management.This study examined how seed mix and natural recovery revegetation treatments influenced plant community development trends on reclaimed well sites in Alberta,Canada.Three seed mixes,dominant wheatgrass(four species with 95% wheatgrass),non-dominant wheatgrass(five species with 80% non-wheatgrass),and diverse(22 grass and forb species),and natural recovery(unseeded)revegetation treatments were compared to undisturbed mixed grass prairie.Five years after reclamation natural recovery led to a plant community with lesser graminoid and greater forb cover,greater species richness and diversity,and greater bare ground relative to seed mix treatments.Seeded treatments resulted in communities dominated by native wheatgrass species.Multivariate tests revealed community composition of undisturbed prairie and the natural recovery treatment differed from seeded treatments.Indicator species analysis showed the natural recovery treatment was dominated by secondary successional perennial species,while the diverse treatment was dominated by native and non-native early to late successional perennial species.This implies that vegetation recovered more rapidly after disturbance with natural recovery than with a diverse seed mix.Non-native species cover showed a declining trend,and five years after reclamation it was <5% across treatments.Natural recovery revegetation was more effective than seeded treatments;however,a diverse seed mix could be used for mixed grass prairie reclamation.
查看更多>>摘要：The relationships between different ecosystem services are key to regional ecological stability and security,and their trade-offs and synergies are affected by many factors,especially on the Qinghai-Tibet Plateau(QTP),which is susceptible to human activities.Norther Tibet,located on the QTP,has built fences for grazing exclusion in recent years.However,how grazing exclusion affect the ecosystem service variability and their mechanism remains still unclear.Based on the net primary productivity(NPP)quantitative index method,hotspot analysis,geographically weighted regression(GWR)model,this study analyzed the effects of grazing exclusion with fencing on ecosystem services dynamics,trade-offs and synergies.Results showed that the values of biodiversity conservation,water conservation and soil conservation were all higher in the fencing region than in the non-fencing region.Most counties experienced increasing trends in the fencing region with higher biodiversity conservation,water conservation in the fencing region than that in the non-fencing region from 2006 to 2015.Except for the relationship between soil conservation and water conservation in the non-fencing region in Cuoqin county in 2015,the relationships among all ecosystem services were synergistic,and the overall trends were weakening.The county number percentage with higher synergistic relationships in the fencing region than that in the non-fencing region showed gradually increasing trends.Land use intensity,grazing intensity,precipitation and altitude were the main factors that affecting spatial heterogeneity of three ecosystem services in the non-fencing region,while distance to road,distance to town,land use intensity and temperature were the main influencing factors in the fencing region.This study contributes to exploring the effect of grazing exclusion on ecosystem services and their relationships,thus providing guidance for the formulation of grassland restoration measures
查看更多>>摘要：Constructed floating wetlands(CFWs)promote the growth of plants in buoyant structures where nutrients can be assimilated into biomass,and thus offer an alternative treatment that is potentially more economically viable than conventional constructed wetlands(CWs).This study examined the hydroponic growth of native Australian plants including Baumea rubiginosa(BR)and Phragmites australis(PA)in a synthetic water mix representing both stormwater and municipal waste water,and their total nitrogen(TN)and total phosphorus(TP)uptake rate over a 35-week period.With increases in the nutrient levels in synthetic waters,the overall dry weight of both roots and shoots,and the accumulated TN and TP values removed from the system,all increased.For both storm and waste waters,BR was found to have a higher overall shoot weight compared to mat for the PA.In waters with relatively high nutrient levels,BR was found to have a lower overall root weight compared to that for the PA.The %TN accumulated in all plant root tissue was found to be greater than the shoot tissue and consequently the TN removal efficacy by PA(species with a relatively high growth rate of roots)was high in comparison to that by BR(species with a relatively high growth rate of shoots).The TP removal efficacy by BR was higher than that of PA.These results show that CFWs with native plant species could be used to reduce the nutrients levels in both stormwater and wastewater under a Mediterranean climate condition.
NSTL