Effects of phosphorus fertilizer application rate on transformation processes of phosphorus fractions in the purple alluvial soil of a riparian zone

Effects of phosphorus(P)fertilizer application rate on soil transformation processes of P fraction are still unclear in the riparian zone.Purple alluvial soils in the riparian zone of the Three Gorges Reservoir were collected to conduct a 21-day incubation executed by two hydrological environments(drying and flooding)and ten application rates of P fertilizer.Transformation percentages of P fertilizer(TPPF)were calculated as content differences of soil P fractions between fertilizer addition and none fertilizer addition divided by soil total P increases caused by fertilizer addition.TPPF to inorganic P extracted by sodium hydroxide(NaOH-Pi)and hydrochloric acid(HCl-Pi)increase by 20.91%(9.71%)and 24.26%(40.72%)under the drying(flooding)environment.Instead,TPPF to the other fractions decrease.Phosphorus fertilizer input mainly has indirect positive and negative effects on organic P via precipitated P under the drying and flooding environments and finally has indirect positive effects on labile P(p<0.001).Percentage changes of water-soluble inorganic P(H2O-Pi)and HCl-Pi under the flooding environment are higher than that under the drying environment,and percentage changes of organic P extracted by sodium hydrogen carbonate(Na HCO3-Po)and NaOH-Pi show an opposite trend(p<0.01).?(differences in soil P fraction content between flooding and drying incubations)H2O-Pi is negatively correlated with?NaHCO3-Po,and?NaHCO3-Po is positively correlated with?NaOH-Pi(p<0.001).In conclusion,P fertilizer is transformed more into precipitated P than into other P fractions with an application rate increase.Phosphorus fertilizer input mainly increases organic P via precipitated P under the drying environment and decreases organic P via precipitated P under the flooding environment,and organic P is further transformed into labile P.With P fertilizer input,P release caused by flooding is derived from NaHCO3-Po release triggered by NaOH-Pi release.The results can be helpful for the understanding of P fertilizer migration processes from the riparian zone soil to the Three Gorges Reservoir under rain leaching and flooding.

Distribution pattern of rare plants along riparian zone in Shennongjia Area

Due to the importance of riparian zone in maintaining and protecting regional biodiversity, increasingly more ecologists paid their attentions to riparian zone and had been aware of the important effects of riparian zone in basic study and practical management. In this study, 42 sampling belts (10 m?00 m) parallel to the bank of Xiangxi River at different elevations in Shennongjia Area were selected to investigate the riparian vegetation and rare plants. 14 species of rare plants were found distributing in riparian zone, accounting for 42.4% of the total rare plant species in Shennongjia Area. The main distribution range of the 14 rare plant species was the evergreen and deciduous mixed broadleaved forest at elevation of 1200-1800 m, where, species diversity of plant community was the maximum at the moderate elevation. The analysis of TWINSPAN divided the 14 rare species into 3 groups against the elevation, namely low elevation species group, moderate elevation species group, and high elevation species group. The analysis of DCA ordination showed similar results to that of TWINSPAN. In the paper, the authors discussed the reasons forming the distribution pattern of rare plant species, and pointed out that the important function of riparian zone on rare plant species protection.

Shallow groundwater nitrogen responses to different land use managements in the riparian zone of Yuqiao Reservoir in North China

This field study investigated the nitrogen concentrations in the shallow groundwater from an ephemeral stream and four land uses： cropland, two-year restored （2yr） and five-years restored （Syr） woodlands, fishponds, and the nitrogen flux in the riparian zone of Yuqiao Reservoir. The groundwater nitrate-N concentrations in cropland were the highest among the four land uses. Total dissolved nitrogen （TDN） and nitrate-N concentrations in the 2yr woodland were significantly （p 〈 0.05） higher than in 5yr woodland. The lowest nitrogen concentrations were detected in fishponds. Nitrate-N was the main form in cropland and 2yr woodland, whereas both nitrate-N and dissolved organic nitrogen （DON） were the main species in 5yr woodland and fishponds. But, ammonium-N was the main form in the ephemeral stream. During the rainy season, the groundwater flow with dissolved nitrogen drains from upland into the reservoir along the hydraulic gradient. The woodland between the cropland and reservoir could act as a buffer to retain shallow groundwater nitrogen. The dominant form of ammonium-N in the groundwater TDN pool in ephemeral stream indicated that nitrogen from the village and orchard in upland flowed into the reservoir via subsurface flow. The fishpond was not an important pollution source for nitrogen transfer via shallow groundwater.

Influencing factors of sediment deposition and their spatial variability in riparian zone of the Three Gorges Reservoir,China

Many factors can affect the sediment deposition and soil erosion process in riparian zone, including terrain, sediment transport and water level fluctuations. Clarifying the factors influencing sediment deposition process in the riparian zone of the Three Gorges Reservoirs is an important problem to determine the key area of sediment deposition and its trend of development in the study area. In order to reveal the influence of these environmental factors on the sediment deposition in riparian zone of the Three Gorges Reservoir, this study investigated 1） the amount of deposited sediment in different environmental conditions, 2） the potential factors affecting sediment deposition in riparian zone of the Three Gorges Reservoir, 3） the relationship between the deposited sediment amount and these factors previously mentioned using correlation analysis, and 4） the influence of human activities considered as an additional factor. This study found that 1） slope gradient, elevation, inundating duration and human activities were the main factors influencing sedimentation in riparian zone of the Three Gorges Reservoir, and 2） the impact of each factor varied with spaces. Specifically, in the upper reach from Jiangjin to Fuling, human activities such as gravel dredging, bank revetment and ports and wharfs constructing disturbed considerable amounts of deposited sediment, as a result, there was no natural law to dictate the distribution. In the middle reach from Fuling to Fengjie, slope gradient and inundating duration were the controlling factors, and the sediment deposition amount was greater in the areas with a gentler slope or lower elevation. Water flow on gentler slopes generally had lower velocity, resulting in more sediment to deposit. Sites with lower elevations would be drowned by sediment-laden flow with a longer duration resulting from hydrologic regime controlled by the operating strategy of the Three Gorges Reservoir, leading to a larger amount of sediment deposition. In the lower reach from Fengjie to Zigni, slope gradient was similar to the middle reach, performing a primary factor, while other factors showed little relationship with sediment amount.

Soil nutrients in relation to vertical roots distribution in the riparian zone of Three Gorges Reservoir,China

Since the impoundment of the Three Gorges Reservoir(TGR), the riparian zone has been subjected to numerous environmental changes. This study was conducted to recognize the distribution of grass roots and its impacts on soil nutrients in the water level fluctuation zone of TGR. Roots of four predominant herbaceous plants in the study area, specifically, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, and their corresponding relation with soil nutrient contents were investigated. Root surface area density was determined with Win RHIZO, and the relationships of root distribution with soil depths and soil nutrient contents were studied. The results indicates that most roots are distributed in the top soil layer of 0-10 cm. Estimated root surface area density for the selected grass species ranges from 0.16 to 13.44 cm^2/cm^3, and decreases exponentially with an increase in soil depth. Soil organic matter and total nitrogen contents are significantly lower on bare control area than the corresponding values on the grasslands. Total nutrient contents on grasslands of C. dactylon and H. compressa are higher than those of other grass areas. Root length density and root surface area density are significantly correlated with soil organic matter and total nitrogen content for the four grasslands. The present results suggests that plant roots have significant effects on the distribution of soil nutrients in soil profiles in the riparian zone along the TGR. Nevertheless, additional investigations are needed to reveal the specific interactions between plant roots distribution, soil nutrients and water level fluctuations.

Estimation of soil reinforcement by the roots of four postdam prevailing grass species in the riparian zone of Three Gorges Reservoir, China

Soil erosion and bank degradation is a major post-dam concern regarding the riparian zone of the Three Gorges Reservoir. The development and succession of vegetation is a main countermeasure,especially to enhance bank stability and mitigate soil erosion by the root system. In this study, the roots of four prevailing grass species, namely, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, in the riparian zone were investigated in relation to additional soil cohesion. Roots were sampled using a single root auger. Root length density（RLD） and root area ratio（RAR） were measured by using the Win RHIZO image analysis system. Root tensile strength（TR） was performed using a manualdynamometer, and the soil reinforcement caused by the roots was estimated using the simple Wu＇s perpendicular model. Results showed that RLD values of the studied species ranged from 0.24 cm/cm3 to20.89 cm/cm3 at different soil layers, and RLD were significantly greater at 0–10 cm depth in comparison to the deeper soil layers（＆gt;10 cm）. RAR measurements revealed that on average 0.21% of the reference soil area was occupied by grass roots for all the investigated species. The measured root tensile strength was the highest for P. paspaloides（62.26MPa） followed by C. dactylon（51.49 MPa）, H.compressa（50.66 MPa）, and H. altissima（48.81MPa）. Nevertheless, the estimated maximum root reinforcement in this investigation was 22.5 k Pa for H.altissima followed by H. compressa（21.1 k Pa）, P.paspaloides（19.5 k Pa）, and C. dactylon（15.4 k Pa） at0–5 cm depth soil layer. The root cohesion values estimated for all species were generally distributed at the 0–10 cm depth and decreased with the increment of soil depth. The higher root cohesion associated with H. altissima and H. compressa implies their suitability for revegetation purposes to strengthen the shallow soil in the riparian zone of the Three Gorges Reservoir. Although the soil reinforcement induced by roots is only assessed from indirect indicators, the present results still useful for species selection in the framework of implementing and future vegetation recovery actions in the riparian zone of the Three Gorges Reservoir and similar areas in the Yangtze River Basin.

Characteristics,classification and ordination of riparian plant communities in the Three-Gorges areas

Sixteen different vegetation types of grassland and shrubland were selected to study the component and diversity of plant species of riparian plant communities along main channel in the Three-Gorges areas. Species richness (s), Simpson index (D), and Shannon-Weiner index (H) were used to study the biodiversity and the hierarchical classification was carried out by the methods of TWINSPAN and DCA ordination. The results showed that the components of flora were complex and dominated by the temperate type in the riparian plant communities. Species diversity was not different between the communities, but Shannon-Weiner indexes of different layers in some grassland were significantly different. TWINSPAN and DCA indicated that riparian plant communities distributed along the gradient of moisture.

基于土地利用结构的河流岸带生态系统服务簇识别

为识别河流岸带土地利用与生态服务价值的空间结构,从河流岸带保护角度选取水资源保护、净化环境、水文调节、土壤保持、维持养分循环、生物多样性6项生态服务功能,基于遥感影像解译的土地利用数据,运用修正的当量因子法估算得到生态服务价值的空间分布规律,进而进行层次聚类分析识别河流岸带生态服务簇,并应用于太湖流域湖西区溧阳市县级河流——竹箦河作为实例研究。结果表明:(1)竹箦河河岸带6项生态服务价值呈现出显著的空间异质性和聚集性;(2)竹箦河河岸带可划分为5大类生态服务簇,分别为水源涵养型、绿色多元型、经济生态型、生态脆弱型以及耗水污染型;(3)各类服务簇的生态系统服务特点与空间布局分异明显,与岸带实际土地利用结构相协调,揭示了竹箦河河岸带生态服务功能普遍较薄弱的现状。研究结果可为竹箦河及类似平原地区骨干河流岸带功能区划分以及河岸带生态保护与修复方案的制定提供理论参考。

缓冲带植被模式对河岸土壤稳定性的影响

通过10年辽河保护区河岸植被缓冲带工程实施,研究了河岸带不同植被模式对于河岸土壤团聚体组成、结构、土壤稳定性、抗蚀性的影响。结果表明,河岸土壤粒径组成为砂粒质量分数为58%~68%,粉粒质量分数为30%~40%。土壤有机质质量分数为12.0~28.1 g·kg^(-1),与植被种植前相比,灌草、乔草缓冲带河岸土壤有机质含量明显增加。相比于干筛法,湿筛后水稳性团聚体的主要粒径组成为0.25~0.50 mm,占比14%~25%,粒级直径>0.5 mm土壤水稳性团聚体占比明显下降,而粒级直径为0.25~0.50 mm的土壤水稳性团聚体占比明显增加。杞柳缓冲带和水蜡缓冲带土壤结构、团聚体稳定性和抗蚀性高于其他植被带。

黄河中下游过渡区河岸植物多样性与土壤因子的关系

[目的]河岸带物种多样性与土壤因子的关系对维持河岸带生态系统的稳定性十分重要,为揭示黄河中下游河岸带物种多样性与土壤因子的关系,进一步为黄河中下游过渡区河岸生态恢复、保护和高质量发展提供一定的参考与理论指导。[方法]采用样方调查法、试验分析法、CCA排序法等方法,以河南黄河中下游过渡区对植物分布和物种多样性与土壤因子的关系进行研究。[结果](1)黄河中下游过渡区河岸有机质、速效钾及有效磷均属于中等变异程度,土壤含水量、全氮变异系数为强变异性,土壤养分空间分布总体呈现中度不均匀的特征。(2)黄河中下游过渡区河岸植物优势度指数(D)与土壤全氮具有显著负相关关系(P<0.05);土壤pH值、速效钾和有效磷对物种丰富度指数(S)的影响不明显;均匀度指数(E)、香农-威纳指数(H)与6个土壤因子之间均没有达到显著水平。(3)红蓼、头状穗莎草、长芒稗、糠稷、醴肠群落的分布受土壤含水量的影响较大;青蒿、酸枣、毛白杨等的分布主要受全氮的影响较大,在全氮含量较高的区域分布较多;葎草和反枝苋受速效钾影响较大;而狗牙根、苍耳、芦苇、狗尾草、春蓼、绿豆等群落受土壤因子的影响较小。[结论]黄河中下游过渡区河岸带土壤含水量、速效钾及全氮是影响植物分布的主要因子,不同植物对土壤条件的需求存在差异,能够直观反映出植被与土壤环境之间的关系。

黄河兰州段河岸带沉积物氨氮吸附特征及影响因素

通过实验室模拟研究黄河(兰州段)河岸带沉积物对氨氮的吸附特征及影响因素,有助于揭示沉积物在吸附氨氮中“源”与“汇”的特征及天然屏障的作用。研究结果表明:吸附在120 min达到平衡,吸附量达到1200.19 mg/kg。在15、20、25℃下,ENC0分别为4.17、3.12、2.45 mg/L。吸附过为単分子层吸附,在15、20、25℃下,Langmuir模型拟合得到的最大吸附量Qm分别为1868.57、2638.26、3025.18 mg/kg。沉积物在偏酸性条件下对氨氮的吸附效果较好,吸附量最大pH值为5,吸附量为1222.02 mg/kg。沉积物对氨氮的吸附率随扰动频率的增加而变大,扰动频率为0、50、100、150、200 r/min时,吸附率分别为25.5%、43.0%、50.6%、56.2%和74.3%。沉积物对氨氮的吸附率随氨氮的浓度增加先增大后减小,吸附率在浓度为10 mg/L时达到极值73.5%。通过皮尔逊系数相关性分析得到:R扰动频率(0.948)>R温度(0.923)>RpH(-0.862)>R初始浓度(-0.321)。

台州市“一江两溪”河岸带植被分布格局及其环境解释

以浙江省台州市“一江两溪”河岸带湿地植被为研究对象,在环境调查的基础上,首次从区域尺度探讨了影响河岸带湿地植物的物种多样性构成、空间分布的环境梯度因子。结果表明:(1)流域内共调查到的湿地维管植物100种,隶属31科84属,科层面上,以禾本科(Poaceae)(28种)和菊科(Asteraceae)(15种)最为丰富;属层面上,以萹蓄属(Polygonum)(6种)、蔷薇属(Rosa)(3种)、莎草属(Cyperus)(3种)等为代表,单种属(74%)现象非常显著。(2)研究区不同河段植物群落α多样性综合排序为:永安溪>始丰溪>椒江>灵江干流。(3)普通克里格(OK)插值分析显示,各河段河岸带环境因子呈现明显的空间异质性特征。(4)基于ward聚类法,可将所有植物群落样方划分为3个群丛类型,即互花米草(Ass.Spartina alterniflora)+芦苇(Phragmites australis)群丛、乌桕(Ass.Sapiumsebiferum)-芦竹(Arundodonax)群丛和枫杨(Ass.Pterocaryastenoptera)-银叶柳(Salix chienii)+斑茅(Saccharumarundinaceum)+芦竹(Arundodonax)群丛;非度量多尺度(NMDS)排序结果也与聚类结果一致,并表征出自下游至上游植被响应环境梯度的分布格局。(5)冗余分析(RDA)排序结果表明,土壤全钾是影响河岸带植被分布的关键环境限制因子,其中以互花米草和芦苇构成的功能组分布受环境因子梯度影响最为显著。

沙颍河典型河段河岸带土壤理化性质对地下水氮污染的影响

以沙颍河典型河段为研究对象,通过采集果园和农田河岸带的河水、土壤以及地下水样品,并进行理化指标分析,旨在深入探讨土壤理化性质对河岸带地下水氮浓度的影响机制.结果表明:农田河岸带土壤总氮(TN)含量明显高于果园河岸带,达到其TN的1.15倍,并均在距河岸约200m处达到最高值.河岸带地下水与土壤氮含量有一定的响应关系,呈现出相似的空间分布特征.农田河岸带地下水NO_(3)--N浓度(0.56~25.17mg/L)显著高于果园河岸带(0~0.97mg/L);远岸(>200m)地下水NO_(3)--N浓度均高于近岸(<100m).土壤氮素是河岸带地下水氮污染的主要来源之一.土壤中的黏土颗粒含量和施氮量较高,使得土壤颗粒更易于吸附NO_(3)--N,增加了河岸带地下水氮污染的风险.本研究揭示了河岸带土壤理化性质对地下水氮含量的影响机制,为河岸带地下水氮污染防控提供了参考依据.这些发现有助于制定可行的土地管理策略,以减缓或防止地下水氮污染的进一步扩散.

中国河湖岸带草本植物氮磷化学计量学及内稳性特征

河湖岸带是拦截净化氮磷等陆源污染物进入河湖水体的最后屏障,河湖岸带草本植物的稳定性影响着其对污染物的拦截净化能力,研究河湖岸带草本植物生态化学计量学及内稳性,可为河湖岸带草本植物群落恢复和构建提供基础数据。通过对中国河湖岸带草本植物地上部氮(N)、磷(P)含量及土壤或沉积物、水体进行数据收集,分析了植物氮磷化学计量学和内稳性特征及其与环境因子的关系。结果表明:青藏高原湖区草本植物具有较高的N含量(湿生植物:20.51 g·kg^(-1),水生植物:29.81 g·kg^(-1))和较低的P含量(湿生植物:1.39 g·kg^(-1),水生植物:0.99 g·kg^(-1)),N:P>14,表现为P限制,而其他湖区草本植物具有较高的P含量(2.73 g·kg^(-1)),N:P<14,表现为N限制。各湖区植物N、P含量及其比值在空间上具有一定差异,青藏高原湖区水生植物N含量最高,东北平原与山地湖区最低(P<0.05);东北平原与山地湖区湿生和水生植物P含量最高(P<0.05);青藏高原湖区湿生和水生植物N:P最高,东北平原与山地湖区最低(P<0.05)。植物N、P含量及N:P受环境中P含量影响最大,其次是环境中N:P和N含量。内稳性模型表明河湖岸带草本植物属于稳态型,其中湿生植物内稳性指数HN、HP及HN:P大于水生植物,表明水生植物受环境胁迫时响应较大,水生和湿生植物对环境中N、P含量变化响应的差异表明水生和湿生植物对环境中N、P不同的保守利用策略。

黑龙滩水库消落带不同植被恢复模式对土壤物理性质的影响

[目的]探究水库消落带不同植被恢复模式对土壤物理性质的影响,为水库消落带的植被-土壤互馈关系研究与生态重建工作提供科学依据。[方法]以黑龙滩水库消落带自然恢复和人工恢复植被样地为研究对象,采集了不同海拔梯度和土层深度的土壤样品,利用环刀法和干筛法对比分析了土壤容重、总孔隙度、机械稳定性团聚体等物理性质。[结果]人工恢复与自然恢复植被下0—20 cm土层的土壤物理性质差异显著(p<0.05),其中人工恢复植被的土壤容重相较于自然恢复植被低16.97%,而土壤总孔隙度、饱和持水量和含水率相较于自然恢复植被分别增加35.00%,58.45%和117.63%;人工恢复植被下土壤>5 mm机械性团聚体含量显著高于自然恢复植被;多因素方差分析表明,恢复模式与水位高程的交互作用相较于其他交互作用对土壤物理性质的影响更为明显;冗余分析(RDA)和相关性分析表明,恢复模式是黑龙滩水库消落带土壤物理性质空间分异的主控因素。[结论]人工植被恢复能够有效改善土壤物理性质,建议在黑龙滩水库消落带合理开展人工植被恢复,改善土壤质量。

黄河干流生境质量评价研究

河流生境是河流生态系统中的重要组成部分,是维持河流健康的重要因素。为揭示黄河生境质量状况,于2021年和2022年5-7月对黄河源头至下游的26个干流河段开展河流生境现状调查与质量评价.选取河道和河岸10项生境指标开展综合评价.结果显示,黄河干流各河段生境质量综合得分H值介于79~153分,超过69%的河段生境质量介于90~120分,等级为中等.源区、上游、中游和下游生境未表现出显著的区域差异(p>0.05).10项生境指标中,大型木质残体分布在全河段得分最低,介于1~5分,水质状况、河道内人类活动强度、河岸带植被覆盖度和河岸土地利用类型等4项指标在不同区域表现出显著差异(p<0.05).主成分分析结果显示,影响黄河干流生境质量的主要因子有河岸土地利用类型、河道内人类活动强度、水质状况和河岸稳定性等.

河湖岸线保护与利用规划编制关键问题探讨

编制河湖岸线保护与利用规划是河湖长制工作的重要任务以及河湖管理的重要抓手。研究了中国现有岸线保护与利用规划编制成果,采用对照验证、示例说明、理论分析、专家咨询等方法,对规划编制工作中岸线边界线划定、岸线功能区划分、岸线长度统计等关键问题展开了探讨;对照《河湖岸线保护与利用规划编制指南(试行)》相关内容,梳理了各地的做法,分析了各自的优缺点;在此基础上提出了应对上述关键问题的处理原则和解决思路。研究成果表明:为了更好地推动岸线保护与利用规划编制工作,应从法律层面明确河湖岸线的定义,由更高层级机构组织开展编制工作,因地制宜地划分岸线边界线和岸线功能区,同时应注意合理地统计利用岸线长度。

三峡库区城市河岸带草本植物功能性状及群落结构

选择位于三峡库区腹心的重庆主城长江段九龙滩河岸带,研究草本植物功能性状对三峡库区复杂水位变化的响应机理,分析环境胁迫条件下的草本植物CSR策略(竞争型、耐胁迫型、杂草型)及群落构建机制。研究发现,三峡库区城市河岸带内草本植物群落的Shannon-Wiener多样性指数、Simpson优势度指数和Gleason物种丰富度指数随海拔高程升高而增加,而Pielou均匀度指数则呈现出先降低后升高的变化趋势。比叶面积(SLA)和比根长(SRL)与海拔高程呈显著正相关,表明草本植物趋向于随着海拔升高而增加叶面积和根系长度以提高资源获取效率。叶干物质含量(LDMC)与海拔高程呈显著负相关,表明水淹胁迫严重的低海拔消落带区域内的草本植物倾向于形成较厚实的叶片以适应淹水胁迫。植物群落主要展现出耐胁迫型(S)策略,而耐胁迫-杂草型(S/SR)混合策略也广泛存在。S策略植物比例随海拔升高呈现出先减少后增加的趋势,而杂草型(R)策略植物比例则随高程增加先升高后降低;竞争型(C)策略植物比例则最低。结果指出,植物通过调整SLA、SRL和LDMC等功能性状,以及权衡不同海拔高程中这些性状的组合,从而优化其对水位变化的适应能力,并相应调整其CSR策略。本研究初步揭示了三峡库区城市河岸带草本植物对水位变化的响应机制,能够为建立稳定的河岸带草本植物群落和制定三峡库区城市河流景观的可持续管理策略提供重要的理论和实践依据。

平原沙土区河岸带不同植被类型对土壤团聚体稳定性的影响

[目的]明晰不同植被类型对土壤团聚体稳定性及团聚体有机碳含量的影响,为平原沙土区河岸带土壤团聚体稳定性和抗蚀能力提升提供基础数据。[方法]以江苏省平原沙土区丰县复新河河岸带15年生杨树纯林、柳树纯林、杨柳混交林3种植被类型及对照为对象,用湿筛法对0—20 cm, 20—40 cm, 40—60 cm^(3)个层次土壤颗粒进行物理分级,测定了>0.25 mm团聚体含量(R0.25)、平均重量直径(MWD)、几何平均直径(GMD)、分形维数(D)及有机碳等主要指标,并利用线性回归对各指标相关性进行分析。[结果](1)试验地各土层团聚体以<0.25 mm微团聚体为主,占总团聚体含量的50.33%~80.00%。3种植被类型>2 mm和0.25~2 mm粒径团聚体含量高于对照,各土层中杨树纯林>2 mm大团聚体含量最高。(2)与对照相比,3种植被类型R0.25,MWD和GMD分别提高了41.77%~91.28%,29.89%~79.08%和37.60%~94.32%,其中杨树纯林效果最好。杨树纯林和柳树纯林D显著低于对照(p<0.05)。(3)试验地土壤团聚体有机碳含量范围为1.51~6.48 g/kg。与对照相比,3种植被类型下土壤团聚体有机碳含量提高了31.67%~71.68%,杨树纯林团聚体有机碳含量显著高于柳树纯林和杨柳混交林(p<0.05)。杨树纯林在0—20 cm土层各粒径团聚体有机碳含量最高。(4)线性回归分析表明土壤团聚体稳定性与有机碳显著相关,尤其是与大团聚体有机碳含量显著相关。此外,细根生物量、全氮含量、碳氮比和含水率也是影响团聚体稳定性的重要因素。[结论]平原沙土区河岸带杨树纯林更有利于提高土壤团聚体稳定性,增加土壤抗蚀能力。

清水河河岸带土壤重金属源解析及污染风险评价

为探究清水河河岸带土壤重金属的来源及污染状况,于2023年5月对清水河河岸带土壤32个样点中砷(As)、六价铬(Cr)、铅(Pb)、汞(Hg)4种重金属进行采样调查,综合运用描述性统计法、相关分析、聚类分析、APCS-MLR模型以及污染负荷指数(PLI)和潜在生态风险指数(RI)对污染源进行解析与评价。结果表明,清水河河岸带土壤重金属As、Pb元素含量均低于宁夏土壤背景值,Cr元素只在S6(苋麻河)和S9(折死沟)处出现超标现象,为影响土壤状况的风险元素,Hg元素为主要生态超标元素;As、Pb、Hg具有显著相关性和同源性,主要受农业发展、交通运输等人为源和燃料燃烧、酸性废水排放等未知源的影响,As元素还与地质因素有关,Cr元素除受成土母质影响外,还受工业生产的影响;清水河河岸带土壤均处于污染状态,最严重区域为S6(苋麻河)区,属于很强危害区域,最轻区域为S4(冬至河)区,属于轻微危害区域。