Linkages between organic matter mineralization and denitrification in eight riparian wetlands

Denitrification (N₂ production) and oxygen consumption rates were measured at ambient field nitrate concentrations during summer in sediments from eight wetlands (mixed hardwood swamps, cedar swamps, heath dominated shrub wetland, herbaceous peatland, and a wetland lacking live vegetation) and two streams. The study sites included wetlands in undisturbed watersheds and in watersheds with considerable agricultural and/or sewage treatment effluent input. Denitrification rates measured in intact cores of water-saturated sediment ranged from 20 to 260 mol N m^-2 h^-1 among the three undisturbed wetlands and were less variable (180 to 260 mol N M^-2 h^-1) among the four disturbed wetlands. Denitrification rates increased when nitrate concentrations in the overlying water were increased experimentally (1 up to 770 M), indicating that nitrate was an important factor controlling denitrification rates. However, rates of nitrate uptake from the overlying water were not a good predictor of denitrification rates because nitrification in the sediments also supplied nitrate for denitrification. Regardless of the dominant vegetation, pH, or degree of disturbance, denitrification rates were best correlated with sediment oxygen consumption rates (r ² = 0.912) indicating a relationship between denitrification and organic matter mineralization and/or sediment nitrification rates. Rates of denitrification in the wetland sediments were similar to those in adjacent stream sediments. Rates of denitrification in these wetlands were within the range of rates previously reported for water-saturated wetland sediments and flooded soils using whole core¹⁵N techniques that quantify coupled nitrification/denitrification, and were higher than rates reported from aerobic (non-saturated) wetland sediments using acetylene block methods.     

Subsurface denitrification in a forest riparianzone: Interactions between hydrology and supplies ofnitrate and organic carbon

The influence of hydrology andpatterns of supply of electron donors and acceptors onsubsurface denitrification was studied in a forestriparian zone along the Boyne River in southernOntario that received high nitrogen inputs from a sandaquifer. Two hypotheses were tested: (1) subsurfacedenitrification is restricted to localized zones ofhigh activity; (2) denitrification zones occur atsites where groundwater flow paths transportNO₃ ^– to supplies of available organiccarbon. A plume of nitrate-rich groundwater withconcentrations of 10–30 mg N L^–1 flowed laterallyat depths of 1.5–5 m in sands beneath peat for ahorizontal distance of 100–140 m across the riparianzone to within 30–50 m of the river. In situ acetyleneinjections to piezometers revealed that significantdenitrification was restricted to a narrow zone ofsteep NO₃ ^– and N₂O decline at theplume margins. The location of these denitrificationsites in areas with steep gradients of groundwater DOCincrease supported hypothesis 2. Many of thesedenitrification hotspots occurred near interfacesbetween sands and either peats or buried river channeldeposits. Field experiments involving in situadditions of either glucose or NO₃ ^– topiezometers indicated that denitrification wasC-limited in a large subsurface area of the riparianzone, and became N-limited beyond the narrow zone ofNO₃ ^– consumption. These data suggest thatdenitrification may not effectively removeNO₃ ^– from groundwater transported at depththrough permeable riparian sediments unlessinteraction occurs with localized supplies of organicmatter.     

模拟咸水入侵对崇明岛河岸带根际土壤微生物及反硝化作用的影响

通过模拟咸水入侵,研究了其对崇明岛河岸带根际土壤微生物及其反硝化过程的影响.结果表明:模拟咸水入侵后4种不同植被型河岸带土壤根际微生物区系发生显著变化,除放线菌菌群数量稍有增加外,细菌、真菌以及硝化和反硝化细菌数量均出现不同程度下降,特别是反硝化功能细菌数量较对照平均下降51.8％,说明河岸带土壤不同微生物区系对咸水入侵的响应存在显著差异.模拟咸水入侵后,河岸带土壤与氮转换相关的酶活性普遍受到抑制,且抑制作用随酶类型不同而存在差异,亚硝酸还原酶对咸水入侵最敏感,其活性较对照平均下降了43.5％,脲酶活性次之,其降幅为37.4％,而脱氢酶受咸水影响较小,其活性平均下降29.5％.模拟咸水入侵明显削弱了河岸带土壤反硝化作用,其速率平均下降34.9％.不同植被型河岸带土壤微生物对咸水入侵的生态生理响应存在显著差异,与对照相比,茭白根际土壤微生物数量和酶活性受咸水入侵的平均抑制率最大,土壤反硝化速率最小,其次是菖蒲和芦苇.在模拟咸水入侵下,菖蒲与芦苇混合群落根际土壤微生物数量、酶活性和反硝化速率抑制率明显低于单一植物模式,表明混合植被群落根际土壤微生物过程及反硝化作用对咸水入侵具有较好的缓冲性能.     

Soil microbial diversity, community structure and denitrification in a temperate riparian zone

Nitrate (NO ₃ ^– ) removal in riparian zones bordering agricultural areas occurs via plant uptake, microbial immobilisation and bacterial denitrification. Denitrification is a desirable mechanism for removal because the bacterial conversion of NO ₃ ^– to N gases permanently removes NO ₃ ^– from the watershed. A field and laboratory study was conducted in riparian soils adjacent to Carroll Creek, Ontario, Canada, to assess the spatial distribution of denitrification relative to microbial community structure and microbial functional diversity. Soil samples were collected in March, June, and August 1997 at varying soil depths and distances from the stream. Denitrification measurements made using the acetylene block technique on intact soil cores were highly variable and did not show any trends with riparian zone location. Microbial community composition and functional diversity were determined using sole carbon source utilization (SCSU) on Biolog® GN microplates. Substrate richness, evenness and diversity (Shannon index) were greatest within the riparian zone and may also have been influenced by a rhizosphere effect. A threshold relationship between denitrification and measures of microbial community structure implied minimum levels of richness, evenness and diversity were required for denitrification.     

帽儿山地区不同类型河岸带土壤的反硝化效率

以帽儿山地区森林背景下的森林、皆伐、草地河岸带和农田背景下的森林、裸地河岸带土壤为研究对象,采用硝态氮消失法,研究了不同背景下各类型河岸带的反硝化强度及其影响因素．结果表明：各类型河岸带中,农田背景下的森林河岸带土壤反硝化强度最大,其硝态氮消失率的变化范围为46．79％～91．13％,农田背景下的裸地河岸带土壤反硝化强度最小,其硝态氮消失率的变化范围为15．64％～81．84％;森林背景下土壤反硝化强度的大小顺序为皆伐河岸带〉森林河岸带〉草地河岸带,其硝态氮消失率的变化范围依次为42．06％～90．39％、28．24％～85．73％、21．44％～83．11％．研究区河岸带表层土壤的反硝化强度大于底层．河岸带土壤反硝化强度均受可利用碳、硝态氮的限制,各类型河岸带以农田背景下森林河岸带土壤反硝化潜力最大．     

测定潜流人工湿地根系生物量的新方法

设计了一种新方法研究潜流人工湿地植物根系的分布和生物量。采用自制的圆柱形的不锈钢网柱,安放在潜流湿地的碎石基质中,定期分层取出网柱内的碎石,可观察根系的分布特点;收获网柱内的根,可测定根系的生物量和生长量。网柱的直径20cm,高50cm,网孔直径1．80cm,不锈钢丝粗1．38mm。安装时,使网柱垂直,上端达碎石表面,下端靠近湿地床底。安装好后,装入碎石基质,观察测定时,把基质取出,观察完后,再把基质放回。用该方法,对碎石基质的潜流人工湿地中植物根系的分布和生物量进行了1a的实验测定,认为该方法是测定潜流人工湿地根系生长和分布的有效方法,它易于安装、测定方便、准确。7月和12月份两次测定的湿地根系生物量之和为331．8gm^-2,其中分布于0—5cm的根生物量为174．4gm^-2,5～15cm为142．1gm^-2,15cm以下为15．3gm^-2。种问根系生物量的差异很大,根系生物量最大的是美人蕉,为182．4gm^-2,最小的是水鬼蕉,为1．38gm^-2。根生物量似乎呈不同的季节格局,象草7月份根系生物量较大,而其他种12月份的较大。不同种根系生物量的垂直分布也有显著的差异,具根状茎的芦苇和较粗根的水鬼蕉以直径大于1mm的根为主,它们的根分布较深,而浅层根较少;象草、美人蕉和风车草,直径1mm以内的根占根生物量的80％以上甚至100％,它们的根分布较浅。     

Effects of hydrology on spatial patterns of soil development in created riparian wetlands

Surficial soil development was studied in four wetland basins created on the floodplain of the Des Plaines River near Chicago, Illinois, USA. These studies determined changes in the spatial distribution of plant-available nutrients as a result of establishing two different wetland hydrologic regimes. Three wetland basins had mineral soils and one an organic soil. A geostatistical analysis including kriging of collected data indicated that all soil parameters showed significant changes in their spatial structure as a result of the water inputs and unidirectional flows. The degree of spatial variability as indicated by autocorrelation in the soil data (i.e., points closer to one another are more similar than points further apart due to the influence of landscape processes) declined for all parameters except Mg⁺². Temporal changes in the spatial patterns of extractable phosphorus (P) and percent organic carbon (OC) tended to be inverse; P declined in areas where OC increased and vice versa. The spatial pattern of these changes was dissimilar in the mineral soils as compared to the organic soil and was related to patterns of primary productivity. Zones of P uptake and OC accumulation were also related to wetland hydrology and primary productivity. Changes in the distribution of nutrients, particularly P, may be viewed as a result of nutrient spirals within the wetlands. By comparison, the reorganization in the concentrations of K⁺ and Ca⁺² appear to have been mediated by cation exchange processes. The formation of new concentration gradients was strongly related to both flow pathways and the different water inflow rates. The formation of concentration gradients in exchangeable cations was not reflected in the average concentrations within each basin. Mean values changed significantly in only a few instances. Reducing data in this way missed important biogeochemical changes occurring within the experimental wetland basins. This revised version was published online in July 2006 with corrections to the Cover Date.     

滨河湿地不同植被对农业非点源氮污染的控制效果

滨河湿地作为连接河流水体和陆地的一个功能过渡界面区,是河流生态系统与陆地生态系统进行物质、能量、信息交换的一个重要过渡带,也是保护河流水体的最后一道屏障,对水质净化和农业非点源污染控制起着非常重要的作用。以黄河湿地国家自然保护区孟津扣马段为研究对象,采取野外定位观测试验和稳定同位素示踪(人工富集15N源的同位素稀释法)相结合的方法,研究了滨河湿地土壤对农业非点源氮的持留作用、渗漏到地下水中的农业非点源氮和湿地不同植被对滞留在土壤中的农业非点源氮的吸收作用。结果显示:通过地表径流进入滨河湿地的农业非点源氮在3个实验样方的垂向和侧向都发生了渗漏。滨河湿地土壤对农业非点源氮的滞留作用主要发生在0—10cm,相当于一个过滤器的功能。3种受试植被土壤表层的滞留量为芦苇(0.045mg/g)藨草(0.036mg/g)水烛(0.032mg/g),分别占到土壤滞留氮的59.2%、56.3%和56.1%。滞留在土壤中的农业非点源氮污染存在一个相对较长的效应。滨河湿地特殊的氧化还原条件导致强烈的土壤微生物反硝化作用以及滨河湿地植被对氮素的吸收作用,使得0-10cm土层土壤外源氮变化速度最快,1个月后,滞留芦苇、水烛、藨草样方中15N下降了77.8%、68.8%和8.3%;3个月后,芦苇、藨草、水烛样方中的15N下降了93.3%、72.2%和37.5%。滨河湿地复杂的水文过程,使得滞留在土壤表层的农业非点源氮迁移转化更为复杂多变。监测数据显示,在实验设计的浓度和强度范围内农业非点源氮没有对地下水造成影响。不同植被和同一植物的不同生长时期对滞留在土壤中氮的吸收能力差别较大,吸收量依次为芦苇嫩芽(9.731mg/g)老芦苇(4.939mg/g)藨草(0.620mg/g)水烛(0.186mg/g)。通过对生物量计算得出滨河湿地芦苇、水烛和藨草对农业非点源氮的吸收能力分别为氮吸收量96.11、3.76、0.32kg/hm2。可见,滨河湿地作为连接河流与陆地的缓冲带,通过截留、过滤、植物吸收等过程能有效的削减农业非点源氮对临近地表水体污染,对农业非点源氮污染控制起着非常重要的作用。合理的滨河湿地保护与利用模式对河流水环境保护具有重要的意义。     

Seasonal dynamics of denitrification activity in two water meadows

Seasonal variation in denitrification activity was measured in twoflooded water meadows, one on peaty and one on sandy soil, over a three-yearperiod. Measurements were taken during flooded and drained periods, usingthe acetylene-blockage technique, and the rates were compared to massbalance estimates of nitrate removal in the percolating water.Denitrification activity was higher in sandy soil than in peaty soil. Higherwater infiltration rate and thereby higher nitrate load was considered to bethe cause of the higher denitrification in the sandy soil. Floodingsignificantly increased denitrification, and the rates were higher in autumnand winter than in spring. This was considered to be a result of highernitrogen concentration in inflowing stream water during winter. Annualdenitrification was estimated to 430–460 kg N ha^-1yr^-1 in the sandy soil meadow, and 220 kg N ha^-1yr^-1 in the peaty soil meadow. In the sandy soil there was alarge discrepancy between nitrate removal rates and denitrification rates,which can be explained by nitrification of ammonium released from the soil.In the peaty soil nitrate disappearance and denitrification correspondedfairly well.     

河流岸带湿地沉积物重金属分布对植被物种多样性和底栖动物群落特征的影响

河流岸带湿地栖息地完整性对河流水环境、水生态和水文的安全与健康具有重要意义,为探究河流岸带湿地表层沉积物重金属分布特征及其对植被和底栖动物的影响,对滦河干流上中下游河段表层沉积物、植物群落和底栖动物调查分析,采用生物毒性效应系数法和综合潜在生态风险指数法评价沉积物重金属污染特征,采用植被物种多样性指数和底栖动物完整性指数评价滦河植物和底栖动物群落特征,探究岸带湿地沉积物重金属空间分布与植被及底栖动物群落特征之间关系。结果表明,滦河表层沉积物总体呈清洁水平,但不同河段重金属空间分布差异较大,下游重金属生态危害系数和潜在生态风险指数高于上中游。湿地物种调查共识别维管束植物219种,大型无脊椎底栖动物105种,综合评价结果表明下游植物群落物种多样性和底栖动物群落完整性低于上中游。滦河下游岸带湿地沉积物重金属对生物群落具有生物毒性和潜在的生态风险,降低了植被物种多样性和底栖动物群落完整性。大型底栖动物完整性指数能够综合反映底栖动物群落结构特征变化,对河岸带湿地生态健康评价和监测具有重要意义。     

Global trends and uncertainties in terrestrial denitrification and N2O emissions

Soil nitrogen (N) budgets are used in a global, distributed flow-path model with 0.5° × 0.5° resolution, representing denitrification and N₂O emissions from soils, groundwater and riparian zones for the period 1900–2000 and scenarios for the period 2000–2050 based on the Millennium Ecosystem Assessment. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N₂ fixation and atmospheric N deposition increased from 155 to 345 Tg N yr⁻¹ (Tg = teragram; 1 Tg = 10¹² g) between 1900 and 2000. Depending on the scenario, inputs are estimated to further increase to 408–510 Tg N yr⁻¹ by 2050. In the period 1900–2000, the soil N budget surplus (inputs minus withdrawal by plants) increased from 118 to 202 Tg yr⁻¹, and this may remain stable or further increase to 275 Tg yr⁻¹ by 2050, depending on the scenario. N₂ production from denitrification increased from 52 to 96 Tg yr⁻¹ between 1900 and 2000, and N₂O–N emissions from 10 to 12 Tg N yr⁻¹. The scenarios foresee a further increase to 142 Tg N₂–N and 16 Tg N₂O–N yr⁻¹ by 2050. Our results indicate that riparian buffer zones are an important source of N₂O contributing an estimated 0.9 Tg N₂O–N yr⁻¹ in 2000. Soils are key sites for denitrification and are much more important than groundwater and riparian zones in controlling the N flow to rivers and the oceans.     

Nitrate depletion in the riparian zone of a small woodland stream

Field enrichments with nitrate in two spring-fed drainage lines within the riparian zone of a small woodland stream near Toronto, Ontario showed an absence of nitrate depletion. Laboratory experiments with riparian substrates overlain with nitrate enriched solutions revealed a loss of only 5–8% of the nitrate during 48 h incubation at 12°C. However, 22–24% of the initial nitrate was depleted between 24 and 48 h when a second set of substrate cores was incubated at 20°C. Short-term (3 h) incubations of fresh substrates amended with acetylene were used to estimate in situ denitrification potentials which varied from 0.05–3.19 g N g^–1 d^–1 for organic and sandy sediments. Denitrification potentials were highly correlated with initial nitrate content of substrate samples implying that low nitrate levels in ground water and riparian substrates may be an important factor in controlling denitrification rates. The efficiency of nitrate removal in spring-fed drainage lines is also limited by short water residence times of < 1 h within the riparian zone. These data suggest that routes of ground water movement and substrate characteristics are important in determining nitrate depletion within stream riparian areas.     

Nitrogen retention in the riparian zone of catchments underlain by discontinuous permafrost

1. Riparian zones function as important ecotones that reduce nitrate concentration in groundwater and inputs into streams. In the boreal forest of interior Alaska, permafrost confines subsurface flow through the riparian zone to shallow organic horizons, where plant uptake of nitrate and denitrification are typically high. 2. In this study, riparian zone nitrogen retention was examined in a high permafrost catchment (approximately 53% of land area underlain by permafrost) and a low permafrost catchment (approximately 3%). To estimate the contribution of the riparian zone to catchment nitrogen retention, we analysed groundwater chemistry using an end‐member mixing model. 3. Stream nitrate concentration was over twofold greater in the low permafrost catchment than the high permafrost catchment. Riparian groundwater was not significantly different between catchments, averaging 13 μm overall. Nitrogen retention, measured using the end‐member mixing model, averaged 0.75 and 0.22 mmol N m^?2 day^?1 in low and high permafrost catchments, respectively, over the summer. The retention rate of nitrogen in the riparian zone was 10–15% of the export in stream flow. 4. Our results indicate that the riparian zone functions as an important sink for groundwater nitrate and dissolved organic carbon (DOC). However, differences in stream nitrate and DOC concentrations between catchments cannot be explained by solute inputs from riparian groundwater to the stream and differences between streams are probably attributable to deeper groundwater inputs or flows from springs that bypass the riparian zone.     

Effects of fine root decomposition on bacterial community structure of four dominated tree species in Mount Taishan,China

为了理解细菌群落结构和多样性对森林生态系统细根凋落物分解的影响, 该研究以泰山4种主要优势造林树种刺槐(Robinia pseudoacacia)、麻栎(Quercus acutissima)、油松(Pinus tabulaeformis)和赤松(Pinus densiflora)为研究对象, 采用凋落物分解袋法及Illumina Miseq测序平台对细菌16S rDNA V4-V5区扩增产物进行双端测序, 分析了4种树种细根分解对细菌群落结构及多样性的影响。结果表明: (1) 4种植物细根分解速率差异显著, 阔叶树种分解速率显著高于针叶树种, 表现为刺槐>麻栎>油松>赤松。(2) 4个树种细菌序列操作分类单元(OTU)、观测到的物种数、Ace指数和系统发育多样性之间差异显著, 且阔叶树种刺槐和麻栎显著低于针叶树种赤松和油松。4种细根分解的细菌群落结构存在极显著差异。细根初始碳(C)含量、木质素:氮(N)和C:N对细菌群落结构的影响较大。(3)细菌群落相对丰度在5%以上的优势类群是变形菌门、放线菌门、拟杆菌门、酸杆菌门, 且变形菌门、酸杆菌门在4个树种之间差异显著, 特别是阔叶树种变形菌门显著高于针叶树种。在纲水平上, α-变形菌纲、β-变形菌纲、γ-变形菌纲、不明放线菌纲、鞘脂杆菌纲为主要的优势纲, 其中α-变形菌纲、不明放线菌纲在4个树种之间差异显著。(4) Pearson相关性分析表明, 细菌优势门和纲相对丰度受到凋落物初始化学性质的影响, 特别是变形菌门和α-变形菌纲; 变形菌门和α-变形菌纲相对丰度与细根分解速率显著正相关。冗余分析结果也显示, 细根初始N、磷(P)含量和木质素含量对细菌群落结构的影响较大。研究结果有助于理解细菌群落结构和多样性对森林生态系统细根凋落物分解的影响。     

Denitrification Potential, Root Biomass, and Organic Matter in Degraded and Restored Urban Riparian Zones

Hydrologic changes associated with urbanization often lead to lower water tables and drier, more aerobic soils in riparian zones. These changes reduce the potential for denitrification, an anaerobic microbial process that converts nitrate, a common water pollutant, into nitrogen gas. In addition to oxygen, denitrification is controlled by soil organic matter and nitrate. Geomorphic stream restorations are common in urban areas, but their effects on riparian soil conditions and denitrification have not been evaluated. We measured root biomass, soil organic matter, and denitrification potential (anaerobic slurry assay) at four depths in duplicate degraded, restored, and reference riparian zones in the Baltimore, Maryland, U.S.A., metropolitan area. There were three main findings in this study. First, although reference sites were wet and had high soil organic matter, they had low levels of nitrate relative to degraded and restored sites and therefore there were few differences in denitrification potential among sites. Evaluations of riparian restorations that have nitrate removal by denitrification as a goal should consider the complex controls of this process and how they vary between sites. Second, all variables declined markedly with depth in the soil. Restorations that increase riparian water tables will thus foster interaction of groundwater nitrate with near-surface soils with higher denitrification potential. Third, we observed strong positive relationships between root biomass and soil organic matter and between soil organic matter and denitrification potential, which suggest that establishment of deep-rooted vegetation may be particularly important for increasing the depth of the active denitrification zone in restored riparian zones.     

泰山4种优势造林树种细根分解对细菌群落结构的影响

为了理解细菌群落结构和多样性对森林生态系统细根凋落物分解的影响, 该研究以泰山4种主要优势造林树种刺槐(Robinia pseudoacacia)、麻栎(Quercus acutissima)、油松(Pinus tabulaeformis)和赤松(Pinus densiflora)为研究对象, 采用凋落物分解袋法及Illumina Miseq测序平台对细菌16S rDNA V4-V5区扩增产物进行双端测序, 分析了4种树种细根分解对细菌群落结构及多样性的影响。结果表明: (1) 4种植物细根分解速率差异显著, 阔叶树种分解速率显著高于针叶树种, 表现为刺槐>麻栎>油松>赤松。(2) 4个树种细菌序列操作分类单元(OTU)、观测到的物种数、Ace指数和系统发育多样性之间差异显著, 且阔叶树种刺槐和麻栎显著低于针叶树种赤松和油松。4种细根分解的细菌群落结构存在极显著差异。细根初始碳(C)含量、木质素:氮(N)和C:N对细菌群落结构的影响较大。(3)细菌群落相对丰度在5%以上的优势类群是变形菌门、放线菌门、拟杆菌门、酸杆菌门, 且变形菌门、酸杆菌门在4个树种之间差异显著, 特别是阔叶树种变形菌门显著高于针叶树种。在纲水平上, α-变形菌纲、β-变形菌纲、γ-变形菌纲、不明放线菌纲、鞘脂杆菌纲为主要的优势纲, 其中α-变形菌纲、不明放线菌纲在4个树种之间差异显著。(4) Pearson相关性分析表明, 细菌优势门和纲相对丰度受到凋落物初始化学性质的影响, 特别是变形菌门和α-变形菌纲; 变形菌门和α-变形菌纲相对丰度与细根分解速率显著正相关。冗余分析结果也显示, 细根初始N、磷(P)含量和木质素含量对细菌群落结构的影响较大。研究结果有助于理解细菌群落结构和多样性对森林生态系统细根凋落物分解的影响。     

不同温度条件下杉木、桤木和火力楠细根分解对土壤活性有机碳的影响

通过室内培养试验,研究了不同温度(9 ℃、14 ℃、24 ℃和28 ℃)条件下桤木、杉木和火力楠细根分解对土壤活性有机碳的影响.结果表明,不同树种细根的分解率不同,树种间差异显著,大小依次为火力楠>桤木>杉木.细根分解率随着培养温度的增加而增大,随着培养时间的延长而降低.添加细根的种类、培养温度和培养时间均对实验系统中土壤微生物碳和水溶性有机碳的含量产生影响.3个树种细根分解使土壤微生物碳和水溶性有机碳含量显著高于对照,大小依次为火力楠>桤木>杉木>对照; 培养中期以及中等培养温度条件下细根分解对应着较高的土壤微生物碳和水溶性有机碳含量.细根分解对土壤易氧化碳含量无显著影响.     

西太湖河网区恢复与退化河岸带湿地生态及水环境功能比较

对西太湖平原河网区严重退化的河岸带湿地进行恢复的基础上,开展了恢复后湿地和退化湿地内植物群落物种多样性,生物量,植物干物质体内氮、磷含量,湿地水体中悬浮物含量、氮、磷营养物质浓度以及恢复后湿地内反硝化作用等湿地生态和水环境功能方面的比较研究。结果表明:(1)已恢复湿地群落结构趋于完整,物种多样性指数值较高,一般在1.7～3之间,均匀度在0.5～0.9之间波动。退化湿地物种丰富度低,多样性指数值较低,分别在0.3～1.5(H′),0.15～0.65(J)之间波动。在水花生(Alternanthera philoxeroides)入侵的群落内,种类稀少,且分布极不均匀,仅在0.3～1(H′)和0.1～0.3(J)之间波动,群落结构严重退化。(2)在植物生长旺盛期,1m2湿地内的芦苇(Phragmites communis)、香蒲(Typha orientalis)及茭草(Zizania latifolia)分别为42,18株和17株。其在湿地内的生物量分别为:4692,5142kg和2182kg;(3)上述物种单位干物质中的氮、磷平均含量分别达到2.88mg/g和2.09mg/g;沉水植物作为滨岸带湿地群落结构的重要组成部分,不仅具有高的生物量,而且吸收氮磷能力强,单位干物质氮、磷含量分别达到7.27mg/g和4.14mg/g;(4)植物对水体及沉积物中可溶性氮、磷的有效吸收以及颗粒态磷的自然沉降作用,使得上游来水中的总氮浓度流经湿地时,降至0.15～0.89mg/L之间,平均下降了85%;总磷浓度则由进水时的0.248～0.598mg/L,降至出水时的0.002～0.083mg/L;(5)滨岸带湿地对河水中悬浮物的有效拦截、滞留和吸附作用,使得入湖河水中的悬浮物含量降低了90%以上;(6)在高温缺氧的环境中,滨岸带湿地表现出较强的反硝化作用,且由河心向河岸逐渐增强的趋势。近河心处测定的N2O通量为0.034～0.068之间,到河岸处升至0.046～0.089。反硝化作用是削减水体中氮负荷的有效途径。     

美国俄亥俄州人工河滨湿地甲烷排放

2008年11月-2009年10月,在美国俄亥俄州哥伦布市Olentangy河河滨湿地,运用静态箱·气相色谱法对比研究了不同水文模式和植被生长状况下2种植被类型(人工植被和自然植被)淡水河滨恢复湿地甲烷(CH4)排放的时空规律,探讨了湿地土壤温度、水文条件、植被和土壤碳含量等因子对CH4排放的影响.结果表明,人工植被和自然植被湿地CH4排放通量均有明显的季节变化规律,但自然植被的淡水湿地CH4排放量仍明显高于人工植被湿地的排放量,其年排放量分别为68和114gCH4-C· m-2·a-1(P＜0.05),这是由于自然植被湿地相对于人工植被湿地有着更高的累积生产力.在2个实验湿地中,淹没深水区比干湿交替区有更高的CH4排放量,CH4排放通量的中值(平均值)分别为4.7(59.9)和0.09( 1.17)mg·m-2·h-1(P＜0.01),波动的水文相对于静止水文条件可减少CH4排放量.并且,实验湿地CH4排放通量与土壤温度和土壤有机碳含量有一定的相关性.因此,可通过对湿地进行适当的植物配置和水文条件等设计和管理措施有效地减少CH4排放.