Effects of thinning and understory removal on water use efficiency of Pinus massoniana:evidence from photosynthetic capacity and stable carbon isotope analyses

Understanding the relationship between forest management and water use efficiency(WUE)is important for evaluating forest adaptability to climate change.However,the effects of thinning and understory removal on WUE and its key controlling processes are not well understood,which limits our comprehension of the physiological mechanisms of various management practices.In this study,four forest management measures(no thinning:NT;understory removal:UR;light thinning:LT;and heavy thinning:HT)were carried out in Pinus massoniana plantations in a subtropical region of China.Photosynthetic capacity and needle stable carbon isotope composition(δ^(13)C)were measured to assess instantaneous water use efficiency(WUE_(inst))and long-term water use efficiency(WUE_(i)).Multiple regression models and structural equation modelling(SEM)identified the effects of soil properties and physiological performances on WUE_(inst)and WUE_(i).The results show that WUE_(inst)values among the four treatments were insignificant.However,compared with the NT stand(35.8μmol·mol^(-1)),WUE_(i)values significantly increased to 41.7μmol·mol^(-1)in the UR,50.1μmol·mol^(-1)in the LT and 46.6μmol·mol^(-1)in HT treatments,largely explained by photosynthetic capacity and soil water content.Understory removal did not change physiological performance(needle water potential and photosynthetic capacity).Thinning increased the net photosynthetic rate(A_n)but not stomatal conductance(g_s)or predawn needle water potential(ψ_(pd)),implying that the improvement in water use efficiency for thinned stands was largely driven by radiation interception than by soil water availability.In general,thinning may be an appropriate management measure to promote P.massoniana WUE to cope with seasonal droughts under future extreme climates.

Sediment Transport Capacity Under the River–Tide Interaction in the Changjiang Estuary

Sediment transport capacity is a fundamental parameter in sediment transport theory and its accurate calculation is important from both theoretical and engineering viewpoints. The capacity of sediment transport has been studied extensively by many researchers in the last decades. Nevertheless, the underlying mechanism behind sediment transport capacity in estuaries remains poorly understood. The current study aims to explore the impact of the river–tide interaction on sediment transport and establish a formula of sediment transport capacity under the river–tide interaction. The impact of the river–tide interaction on the hydrodynamics and sediment dynamics in the Changjiang Estuary was analyzed, a practical method for describing the variation in tide-runoff ratio was established,and a formula of sediment transport capacity considering the impact of river–tide interaction was proposed by introducing the tide-runoff ratio. The new method bridged the gap between two well-known sediment transport capacity methods by considering the variation in the index a for the gravitational term and overcomes the drawback of distinguishing flood/dry season or spring/ebb tide in the calculation of estuarine sediment transport. A large amount of flow and sediment data obtained from the Changjiang Estuary were collected to verify the proposed formula. The effect of salt-fresh water mixture and the morphological evolution on sediment transport capacity of the Changjiang Estuary were discussed.

Removal Effect of Coagulating Sedimentation Method on Polyethylene Microplastics in Water

Microplastic is a new kind of pollutant.It exists widely in the aquatic environment and seriously endangers the aquatic ecosystem.In this study,the coagulating sedimentation method was used to remove microplastics in water.Polyethylene(PE)was selected as the representative of microplastics,polyferric sulfate(PFS),polyaluminum chloride(PAC)and aluminum sulfate(AS)were used as coagulant,and polyacrylamide(PAM)was used as coagulant aid to study the effects of pH,coagulant concentration and sedimentation time on the removal of PE by single and composite coagulant.The results showed that when the dosage of PFS was 0.5 g/L and pH was 5.0,the removal rate could reach 82.14%,which was better than PAC and AS,indicating that PFS had better coagulation and sedimentation performance for PE;the composite coagulant of PFS+PAC+AS(1 g/L+0.2 g/L+0.2 g/L,pH was 5.0)had the highest removal rate of PE,reaching 96.06%;the removal rate of PE increased with the increase in sedimentation time,but considering that the longer sedimentation time has less contribution to the improvement of removal rate,it is recommended that 4 h is appropriate.

Non-capacity transport of non-uniform bed load sediment in alluvial rivers

Rivers often witness non-uniform bed load sedim ent transport. For a long tim e, non-uniform bed load transport has been assum ed to be at capacity regime determined exclusively by local flow. Yet whether the capacity assumption for non-uniform bed load transport is justified remains poorly understood. Here, the relative time scale of non-uniform bed load transport is evaluated and non-capacity and capacity models are compared for both aggradation and degradation cases with observed data. As characterized by its relative time scale, the adaptation of non-uniform bed load to capacity regime should be fulfilled quickly. However, changes in the flow and sedim ent inputs from upstream or tributaries hinder the adaptation. Also, the adaptation to capacity regime is size dependent, the finer the sediment size the slower the adaptation is, and vice versa. It is shown that the capacity model may entail considerable errors compared to the non-capacity model. For modelling of non-uniform bed load, non-capacity modelling is recommended, in which the temporal and spatial scales required for adaptation are explicitly appreciated.

Numerical Analysis of Adaptation-to-capacity Length for Fluvial Sediment Transport

Over the last several decades,various sediment transport capacity formulations have been used by geomorphologists and engineers to calculate fluvial morphological changes.However,it remains poorly understood if the adaptation to capacity could be fulfilled instantly in response to differing inflow discharges and sediment supplies,and thus if the calculation of morphological changes in rivers based on the assumed capacity status is fully justified.Here we present a numerical investigation on this issue.The distance required for sediment transport to adapt to capacity(i.e.,adaptation-to-capacity length) of both bed load and suspended sediment transport is computationally studied using a coupled shallow water hydrodynamic model,in line with varied inlet sediment concentrations.It is found that the adaptation-to-capacity length generally decreases as the Rouse number increases,irrespective of whether the inlet sediment concentration increases or reduces.For cases with vanishing inlet sediment concentration a unified relationship is found between the adaptation-to-capacity length and the Rouse number.Quantitatively,the adaptation-to-capacity length of bed load sediment is limited to tens of times of the flow depth,whilst that of suspended sediment increases substantially with decreasing Rouse number and can be up to hundreds of times of the flow depth.The present finding concurs that bed load sediment transport can adapt to capacity much more rapidly than suspended sediment transport,and it facilitates a quantitative criterion on which the applicability of bed load or suspended sediment transport capacity for natural rivers can be readily assessed.

Aquaculture Environmental Capacity Research of Daiqu Fishery of Zhoushan: The Impact of Cage Culture on Sediment Quality

Impact of LaMmichthys crocea cage culture in Daiqu fishery （Zhoushan, Zhejiang Province） on the chemistry of the sediment was inves- tigated. Sediment samples, in different depths and from three stations at various distances from the cage, were collected, for analyzing total organic matter, total organic carbon, total nitrogen and phosphorus. The results showed a significant increase in all analyzed parameters in station 1, at 5 m from the cage. The difference between reference station （600 m from the cage） and station 2 at 95 m to the cage was insignificant, indicating lo- calized impact of cage farming to the vicinity of cage. The analyzed parameters in various depths did not show a significant difference. The values of analyzed parameters in the perimeter of the cage and their differences with reference stations showed small magnitude and localized impact on the chemistry of sediment. It might be because of deep water and moderate velocity of water current in this fjord. The magnitude of impact may dif- fer durina the summer when biomass and feedina rate would be at the maximum level.

Estimation of CO₂Storage Capacity in the Real Sub-Seabed Sediments by Gas Hydrate

Beyond conventional methods for CO2 capture and storage, a promising technology of sub-seabed CO2 storage in the form of gas hydrate has come into the limelight nowadays. In order to estimate CO2 storage capacity in the real sub-seabed sediments by gas hydrate, a large-scale geological model with the radius of 100 m and the thickness of 160 m was built in this study, and the processes of CO2 injection and CO2 hydrate formation in the sediments with two-phase flow were simulated numerically at three different injection rates of 10 ton/day, 50 ton/day, and 100 ton/day for an injection period of 150 days. Then, the evolutions of CO2 reaction, free CO2, and hydrate formation over time were analyzed quantitatively, and the spatial distributions of the physical properties in the sediments were presented to investigate the behaviors of CO2 hydrate formation in the sediments with two-phase flow. For CO2 storage capacity, a total amount of 15,000-ton CO2 can be stored safely in the sediments at the injection rate of 100 ton/day for 150 days, and a maximum amount of 36,500-ton CO2 could be stored in the sub-seabed sediments per year for a CO2 storage reservoir with the thickness of 100 m. For the practical scenario, an average value of 1 ton/day/m could be used to determine the actual injection rate based on the thickness of the real sub-seabed sediments.

Adsorption Capacity for Phosphorus Comparison among Activated Alumina, Silica Sand and Anthracite Coal

Experimental researches on adsorptive capacity of activated alumina, silica sand and anthracite coal for phosphorus were conducted. Results showed that performances of three filter media were all in line with Langmuir isotherm, and activated alumina adsorptive performance was much better than silica sand and an-thracite coal for phosphorus removal. The adsorptive capacity of activated alumina, silica sand and anthracite coal for phosphorus was 3333μg/g, 49μg/g and 100μg/g respectively. Activated alumina displayed adsorp-tive function well for phosphorus, because its inner porosity, specific surface area and surface isoelectric pH value were all higher than those of other two filter media. While activated alumina was used as filter material in water treatment process, phosphorus would be removed strongly because of adsorptive characteristic of activated alumina.

Channel Evolution of Sandy Reservoir Sediments Following Low-Head Dam Removal, Ottawa River, Northwestern Ohio, U.S.A.

Dozens of low-head dams are removed annually for reasons of obsolescence, financial liability, public safety, or as part of aquatic ecosystem restoration. Prior to removing a dam, hydrologic and sedimentologic studies are used to predict channel changes that would occur after the proposed dam removal. One commonly used predictive approach is a channel evolution model (CEM). However, most CEMs assume that the reservoir has trapped cohesive silts and muds. This study looks at the effects of low-head dam removal on a reservoir in filled with sand-rich sediment. The Secor Dam (2.5 m tall, 17 m wide) was constructed on the Ottawa River in northwestern Ohio (USA) during 1928 and was removed in 2007. High resolution channel cross-sections were measured at 17 locations prior to dam removal and re-measured every approximately 30 days for 6 months following the removal. Sediment sampling, sediment traps, substrate sampling, differential GPS tracking of channel bed forms and sediment coring were also used to characterize the channel sediment response to dam removal. Breaching of the dam produced a diffuse nickzone which was the width of the channel and about 10 m in length. One initial response was downstream migration of a sediment wave at rates up to 0.5 m/hr. The overall effect was erosion of the former reservoir to a distance of 150 m upstream of the former dam. Portions of the former reservoir were incised >1 m. Within the first 6 months after removal, approximately 800 m3 of sand had been mobilized from the former reservoir, transported downstream past the former dam, and had primarily in-filled pre-existing pools within a reach approximately 150 m downstream of the former dam. This behavior significantly differs from the predicted results of current CEMs which anticipate a first flush of suspended sediment and minor deposition of bed load materials in the channel downstream of the former dam.

The rehabilitation of a reservoir: A new methodological approach for calculating the sustainable useful storage capacity

Present work introduces the sustainable useful storage capacity as the minimum storage capacity able to satisfy the water demand for drinkable, industrial and irrigational purposes and necessary in order to overcome water deficit situations which, at least in Central Southern Italy, occur in the summer, when agricultural demand is really high. Sediment volumes to be removed from the reservoir bottom will be calculated as the difference between the current and the sustainable useful storage capacities of the reservoir in study. The calculation methodology of the useful sustainable storage capacity, based on the reservoir water balance between inflows at the reservoir and water demand, has been applied to the Camastra reservoir (Basilicata, Southern Italy), for which numerous reliable data including more than 40 years of inflows and water supplied volumes and data relative to 7 bathymetric surveys are available. Result analysis shows that this methodology, at least in the study case, enables sediment quantities to be removed more sustainably from a technical, economical and environmental point of view.

Experiment of Removing Traces of Phosphorus in Water Using Bottom Sludge of Ise-Bay

Large amounts of sludge has accumulated in the Inner Bay,which is one factor of environmental deterioration.We found that this sludge has an effect of absorbing low concentrations of phosphorus in water.For the purpose of development of water treatment agents and effective utilization of the sludge,phosphorus removal performance was investigated using wet sludge collected in Ise-Bay.A small amount of sludge was added to the test water having a phosphorus concentration of about 1~2 mg/L,and the phosphorus concentration of the filtrate after stirring and filtration was measured.Depending on the sludge conditions,it showed 30% to 80% of phosphorus removal performance.We investigated the relationship between the physical properties of the sludge and the removal performance.

Role of Resuspended Sediments as Sources of Dissolved Inorganic Phosphorus Along Different Dimensions in the Subei Shoal, South Yellow Sea, China

Several studies have documented that during‘green tide’events,comprising green macroalgae blooms in aquatic ecosystems,dissolved inorganic phosphorus(DIP)levels remain relatively steady despite the absorption of a large amount of DIP.In this study,surface sediment samples and a sediment core were extracted using a modified sequential extraction scheme,and water and surface sediment samples were analyzed in April 2017 to better understand phosphorus(P)cycling and replenishment in Subei shoal.We used a simple model on equilibrium of adsorption-desorption to present the buffering capacity of phosphate.The total P(TP)in the surface sediments ranged from 12.2 to 28.4μmol g^(-1)(average 15.5μmol g^(-1))and was dominated by inorganic P.TP,exchangeable P,reactive and reductive Fe/Al bound P,and authigenic apatite P significantly decreased northward and eastward from Subei shoal,contrary to the detrital P and organic P results.Dissolved and particulate inorganic P in the water samples ranged from 0.01 to 0.54μmol L^(-1)(average 0.19μmol L^(-1))and 0.9 to 19.6μmol g^(-1)(average 4.9μmol g^(-1)),respectively.The applied model showed that suspended particulate matter is an important regulator of DIP behavior.Thus,modification of SPM can alter the DIP buffering capacity.The calculated buffering capacity in the surface layer of the sea water was>60 within Subei shoal and always>10 along the path of floating Ulva prolifera,providing a reasonable explanation for the steady concentration of DIP and its replenishment during the blooming of this green macroalgae.

汶川震区山洪灾害场次洪水最大携沙量预测模型

汶川地震后,震区产生了大量松散堆积体,受强降水影响产生了破坏性更强的山洪灾害,加剧了灾害的危险性,增加了灾害防治的困难度,研究震区山洪灾害可为评估灾害的风险性及后续的管理提供依据。本研究以66处历史山洪灾害作为样本数据,进行可量算影响因子的相关性分析,揭示山洪灾害的携沙量影响机制,确定流域面积、主沟长度、相对高差、物源量四个影响因子作为主控因子,基于SPSS进行非线性回归分析,建立了基于场次洪水最大携沙量及最大携沙距离的估算模型,并选取了汶川县和都江堰市的共23处山洪水沙灾害数据进行了模型的验证且与其他模型对比。结果表明,本研究建立的模型可靠性好,精度更高。研究成果有助于预测汶川震区潜在的山洪水沙灾害区域,为山洪水沙灾害的风险评估提供依据。

黄河下游花园口以上河段滞沙能力分析

黄河下游河床调整主要取决于来水来沙和河床边界条件,河床调整沿程不均衡特征明显,花园口以上河段床演变对水沙条件的变化响应尤为突出,泥沙冲淤调整幅度最大。基于河道冲淤及水沙演进特性、滞沙可行性、河槽几何特性等分析,提出了花园口以上河段可作为泥沙天然反调节“库”概念,结合黄河下游实测洪水资料,采用水力计算方法,计算了花园口以上河段的河槽排洪能力及不同河槽规模条件下河槽允许滞沙量,提出了反调“库”滞沙能力,可为小浪底水库排沙指标的确定提供依据,对维持小浪底水库有效库容、弥补后续清水河床沙源不足、改善黄河下游河槽冲淤不均衡现象具有重要意义。

基于磷容量的污水处理厂除磷效能提升控制技术研究

针对污水处理厂回流污泥除磷能力无法准确表征以及除磷药剂使用效率低的问题,首次建立了污泥磷容量的检测方法,研究了除磷药剂种类及用量对污泥磷容量的影响,同时开展了除磷药剂效能提升研究工作。结果表明,使用化学除磷工艺的污水处理厂污泥有不同程度的磷去除能力,即“磷容量”,通过现场实测及拟合计算得到污水处理厂磷容量为0.32~3.25 mg/g(以单位污泥混合液悬浮固体的溶解态活性磷酸盐(sRP)去除量计),折合除磷药剂投加量为0~15.85 mg/L。除磷药剂种类与投加量是影响回流污泥磷容量的关键因素,相同投加量水平下,投加硫酸铝的污泥磷容量较投加聚合氯化铝(PAC)的污泥磷容量高,除磷药剂的预水解程度是导致磷容量差异的主要原因。污泥磷容量与除磷药剂投加量呈正相关。基于污泥磷容量的检测结果,污水处理厂可以采用改变污泥外回流比或将剩余污泥回流到初沉池的方式提高除磷药剂使用效率,可使进水的sRP下降10%以上。此外,剩余污泥回流初沉池可以减少30%的污泥排放量,既强化了除磷效果又实现了污泥的减量化,对污水处理厂绿色发展具有非常重要的指导意义。

含铯废水中亚铁氰化物的粒径分布及组成分析

亚铁氰化物是处理含Cs^(+)离子放射性废水的一种重要方法。为了研究亚铁氰化物处理Cs^(+)离子时的置换机理以及基础性质,本文按照M^(2+)/Fe(CN)64-=1.33的比例投加共沉淀剂(其中M^(2+)代表了Ni^(2+)、Cu^(2+)、Co^(2+)、Cd^(2+)),在不同的模拟水样中制备了亚铁氰化物。利用激光粒度分布仪器考察了M(NO_(3))_(2)与亚铁氰化钾形成共沉淀物的粒径分布。利用高氯酸和加热装置对制备的亚铁氰化物进行溶解以分析其组成。结果表明:共沉淀物的粒径几乎全部处于0.1~10μm;Cs^(+)和Mg^(2+)离子主要取代K^(+)和部分取代M^(2+)离子,Na^(+)离子只取代K^(+)离子;对1.00 mg/L Cs^(+)离子的去除率高于99%;对其吸附容量高达310mg/g以上。总之,亚铁氰化物粒径较小,Na^(+)和Mg^(2+)存在不会影响亚铁氰化物对Cs^(+)离子的去除。

低压浑水管道输沙规律研究及水流挟沙力计算

【目的】确定输水工程适宜运行的水力条件。【方法】以巴音沟河流域输水工程为研究对象,通过数值模拟的方法研究不同泥沙质量浓度、压力条件下浑水管道输沙规律及水流挟沙力特性。【结果】(1)管道断面垂向泥沙质量浓度分布受压力、体积含沙量及管径等因素的影响;当压力及管径较小时,泥沙淤积厚度为6.3~8.0 mm,压力及管径较大时,在Y=-0.07区域以下淤积较多,淤积厚度达到8.6~9.4 mm;(2)同一管径及流速下,随着体积含沙量的增大,该区域流速梯度增大,最大增幅为14%;(3)随着水流速度增大,水流挟沙力增大,悬移质质量浓度也越大,但是悬浮指标逐渐变小。【结论】在低压浑水管道中,管径越大、泥沙质量浓度越大、压力越小,水流挟沙力越小,泥沙越容易淤积。

分散剂对羟基磷灰石除氟剂制备的影响

羟基磷灰石(HAP)是经济高效且安全低碳的除氟剂,其制备时存在反应体系颗粒团聚板结导致产品性能不佳问题。该研究以熟石灰和磷酸为原料,采用加入分散剂的反向滴加化学沉淀法在常温下制备HAP除氟剂,探索分散剂对HAP制备的影响。结果表明:十二烷基苯磺酸钠(SDBS)/乙二醇组合为最佳分散剂,且SDBS、乙二醇和氢氧化钙的最佳质量比为1∶1∶1 000。在优化分散条件下,制得的产品除氟容量达16.56 mg/g,提高了32.90%。反应体系pH值随着氢氧化钙加入而不断升高,在105 min时达到最高值12.96,之后持续降低至8.13。OH-消耗速率与除氟量增加速率的比值先升高后降低,其在180 min时达到最大值4.98,在235 min后低于1.00。颗粒团聚粒径在60 min后持续减小,360 min时产品的d10、d_(50)和d_(90)分别为7.46、15.65和42.41μm,d_(50)和d_(90)较对照组分别降低了56.83%和52.21%。产品中HAP晶体呈纳米级,以团聚形式存在。产品能快速去除水中氟离子,符合拟二级动力学模型。

基于CFD的斜板沉淀池沉淀特性分析

采用欧拉-拉格朗日方法研究了普通斜板沉淀池内水流的流态,利用单向耦合的离散项模型(DPM),计算了普通斜板沉淀池在不同工况条件下颗粒沉积特性及池内流动特性。针对普通斜板沉淀池沉淀效果差,颗粒容易再次上浮,设计了一种改良V型斜板沉淀池,并且结合标准k-ε模型,利用PISO算法,通过北京云超算中心计算了不同颗粒粒径下改良V型斜板沉淀池内颗粒运动的轨迹。结果表明:使用改良V型斜板后,颗粒物的沉降性路径减小,但是涡流强度增加,此时能量耗散更快,有利于固液分离;粒径大的颗粒也更容易沉淀。

耐盐好氧反硝化菌黏质沙雷氏菌HL4的分离鉴定及脱氮性能

【目的】分离鉴定一株耐盐好氧反硝化细菌,以开发高效脱氮菌种,加强海水及咸淡水养殖尾水脱氮技术研究。【方法】采集花鲈(Lateolabrax maculatus)池塘原位底泥,采用稀释涂布法初步分离一株脱氮功能最佳的菌株HL4,通过16s rDNA测序以及生理生化实验鉴定菌株,通过设置不同碳源、碳氮质量比(m_(C)/m_(N))、pH、温度、盐度等条件探明其最适培养条件及脱氮性能。通过攻毒试验[以健康斑马鱼(Danio rerio)为受试生物],检验菌株的环境安全性。【结果】经鉴定,菌株HL4为黏质沙雷氏菌(Serratia marcescens),命名为S.marcescens HL4。以葡萄糖或琥珀酸钠为碳源,菌株HL4在m_(C)/m_(N)=20、pH=6.0~7.0、温度30℃的条件下具有较强脱氮能力,48 h TN去除率为81.83%~87.17%;该菌株在0~30的盐度环境下均可生长,在0~10盐度范围内72 h的总氮(TN)去除率为68.76%~76.59%,在20~30盐度范围内72 h的TN去除率为23.84%~53.94%;在NH_(4)^(+)-N质量浓度为0~100 mg·L^(-1)时,72 h NH_(4)^(+)-N去除率皆在90%以上,在NH_(4)^(+)-N质量浓度为500 mg·L^(-1)时,72 h NH_(4)^(+)-N去除率高达73.52%。健康斑马鱼在含1×10^(6)CFU·mL^(-1)菌株HL4的水体中15 d后,成活率100%。【结论】菌株HL4生物及环境安全性较高,在处理中高浓度铵废水以及治理咸淡水、低盐度海水养殖尾水等领域具有潜在的应用价值。