Using stable hydrogen and oxygen isotopes to study water movement in soil-plant-atmosphere continuum at Poyang Lake wetland,China

Water movement in the soil-plant-atmosphere continuum (SPAC) has a significant effect on the biogeochemical process in wetlands. This study investigated the water movement in the SPAC in Poyang Lake wetland, which is a protected area with an important ecological function within the Yangtze River basin, under different water-level conditions by analyzing the responses of river, groundwater, soil and plants to precipitation using stable hydrogen and oxygen isotopes. The results show that the stable hydrogen and oxygen isotopic compositions (δ¹⁸O and δD) of soil water decrease with increasing depth due to the near surface evaporation. During the dry season the water-level in Poyang Lake is low, when it rains the influencing depth of precipitation and evaporation on soil water isotopic signatures was 20 cm below the ground surface. The rain water infiltrates into the soil, recharges groundwater and flows to the river. When the water-level in Poyang Lake is low, the Xiu River is recharged by the groundwater, which recharges the soil water by capillary rise. During the flood season, the water-level is high and the water in Poyang Lake reaches or covers the meadows, recharges the groundwater and soil water. In the meantime, the water in Poyang Lake can be recharged by rain water when it rains. During the dry season when it doesn’t rain, plants mainly use groundwater, but soil water is preferred and plants don’t use rainwater directly when it rains. When the lake water-level is extremely low, the plants in Poyang Lake wetland may suffer from water stress, which is harmful for plant growth.     

Isotopic assessment of the hydrologic importance of fog deposition on tall snow tussock grass on southern New Zealand uplands

The stable isotopic composition of rain, fog and groundwater was determined for three sites on the Otago upland snow tussocklands, southeastern South Island, New Zealand, for the snow‐free period of November to June in 1996–1998. The rain and fog were collected concurrently, but the rain was consistently isotopically more depleted than the fog. The compositions of the rain form a line of the equation δD = 8.31δ¹⁸O + 13.6, which is similar to the line of δD = 8.11δ¹⁸O + 13.6 formed by the fog. The groundwater has compositions usually between those of the fog and rain, shows no isotopic evidence of evaporation, and is assumed to be a mixture of the two in sub‐equal proportions. This pattern has been observed previously only in forested regions where the tree crowns act as collection mechanisms for fog water. On the Otago uplands, the only fog collection mechanism is interception gains through fog deposition on the relatively short (0.8–1.2 m) fine wispy foliage of the native tall snow tussock grasses (Chionochloa spp.). These results support earlier but debated claims that interception of fog by the foliage of the dominant tall snow tussock grasses makes a substantial contribution to the water yield from these uplands.     

Fog in the California redwood forest: ecosystem inputs and use by plants

Fog has been viewed as an important source of moisture in many coastal ecosystems, yet its importance for the plants which inhabit these ecosystems is virtually unknown. Here, I report the results of a 3-year investigation of fog inputs and the use of fog water by plants inhabiting the heavily fog inundated coastal redwood (Sequoia sempervirens) forests of northern California. During the study period, 34%, on average, of the annual hydrologic input was from fog drip off the redwood trees themselves (interception input). When trees were absent, the average annual input from fog was only 17%, demonstrating that the trees significantly influence the magnitude of fog water input to the ecosystem. Stable hydrogen and oxygen isotope analyses of water from fog, rain, soil water, and xylem water extracted from the dominant plant species were used to characterize the water sources used by the plants. An isotopic mixing model was employed to then quantify how much fog water each plant used each month during the 3-year study. In summer, when fog was most frequent, ～19% of the water within S.sempervirens, and ～66% of the water within the understory plants came from fog after it had dripped from tree foliage into the soil; for S.sempervirens, this fog water input comprised 13–45% of its annual transpiration. For all plants, there was a significant reliance on fog as a water source, especially in summer when rainfall was absent. Dependence on fog as a moisture source was highest in the year when rainfall was lowest but fog inputs normal. Interestingly, during the mild El Niño year of 1993, when the ratio of rainfall to fog water input was significantly higher and fog inputs were lower, both the proportion and coefficient of variation in how much fog water was used by plants increased. An explanation for this is that while fog inputs were lower than normal in this El Niño year, they came at a time when plant demand for water was highest (summer). Therefore, proportional use of fog water by plants increased. The results presented suggest that fog, as a meteorological factor, plays an important role in the water relations of the plants and in the hydrology of the forest. These results demonstrate the importance of understanding the impacts of climatic factors and their oscillations on the biota. The results have important implications for ecologists, hydrologists, and forest managers interested in fog-inundated ecosystems and the plants which inhabit them.     

黄河三角洲自然保护区湿地植被生物量空间分布及其影响因素

以黄河三角洲自然保护区为研究区域,以野外实测湿地植被地上生物量数据、Landsat-8影像数据和土壤各因子检测数据为数据源,通过分析各遥感因子与实测植被生物量的相关关系,建立生物量模型,进行生物量的定量反演。通过研究生物量与土壤、水环境因子的关系,筛选影响生物量的关键因子,进而分析生物量的空间分布规律。结果表明:湿地植被地上生物量的干重与各遥感因子的相关性较高;以NDVI、EVI、MSAVI、DVI、RVI、Band1、Band2、Band3、Band4、Band6共10个因子作为自变量建立的反演模型最优;反演计算的生物量干重分为5个等级区,最低的1级区和最高的5级区面积较小,为82.23、72.16 km2,分别占研究区湿地植被总面积的13.35%、11.71%。生物量干重适中的2、3、4级区所占面积较大,为211.99、136.39、113.29 km2,分别占研究区湿地植被总面积的34.41%、22.14%、18.39%;在各环境因子中水深对芦苇生物量干重影响最大,土壤含水率对碱蓬生物量干重影响最大,水、盐条件是导致优势种植被生物量干重出现空间分异的主导因素;植被生物量干重呈现由陆向海减小,由黄河河道两岸向外递减的趋势。     

Nutrient status and retention in pristine and disturbed wetlands in Uganda: management implications

Wetlands in Uganda experience different forms of human pressure ranging from drainage for agriculture and industrial development to over harvesting of wetland products. In order to develop sustainable management tools for wetland ecosystems in Uganda and the Lake Victoria Region, water quality analyses were carried out in a rural undisturbed (pristine) wetland (Nabugabo wetland in Masaka) and two urban wetlands that are experiencing human and urban development pressure (the Nakivubo wetland in Kampala and Kirinya wetland in Jinja). The former wetland forms the main inflow into Lake Nabugabo while the other two border the northern shore of Lake Victoria, Uganda. Nabugabo wetland buffers Lake Nabugabo against surface runoff from the catchment, while Nakivubo and Kirinya wetlands provides a water treatment function for wastewater from Kampala City and Jinja town respectively, in addition to buffering Lake Victoria against surface runoff. Water quality was assessed in all the wetland sites, and in addition nutrient content and storage was investigated in the main plant species (papyrus, Phragmites, Miscanthidium and cocoyam) in Nakivubo and Kirinya wetlands. A pilot experiment was also carried out to assess the wastewater treatment potential of both the papyrus vegetation and an important agricultural crop Colocasia esculenta (cocoyam). Low electrical conductivity, ammonium–nitrogen and ortho-phosphate concentrations were recorded at the inflow into Nabugabo wetland (41.5 μS/cm; 0.91 mg/l and 0.42 mg/l respectively) compared to the Nakivubo and Kirinya wetlands (335 μS/cm; 31.68 mg/l and 2.83 mg/l and 502 μS/cm; 10 mg/l and 1.87 mg/l respectively). The papyrus vegetation had higher biomass in Nakivubo and Kirinya wetlands (6.7 kg DW m⁻²; 7.2 kg DW m⁻² respectively), followed by Phragmites (6.5, 6.7), cocoyams (6.4, 6.6) and Miscanthidium (4.0, 4.2). The papyrus vegetation also exhibited a higher wastewater treatment potential than the agricultural crop (cocoyam) during the pilot experiment (maximum removal degree of ammonium–nitrogen being 95% and 67% for papyrus and yams). It was concluded that urbanisation pressure reduces natural wetland functioning either through the discharge of wastewater effluent or the degradation of natural wetland vegetation. It is recommended that wetland vegetation be restored to enhance wetland ecosystem functioning and for wetlands that are not yet under agricultural pressure, efforts should be made to halt any future encroachment.     

Particulate organic and dissolved inorganic carbon stable isotopic compositions in Taylor Valley lakes,Antarctica: the effect of legacy

In perennially ice-covered lakes of Taylor Valley, Antarctica, “legacy”, a carryover of past ecosystem events, has primarily been discussed in terms of nutrient and salinity concentrations and its effect on the current ecology of the lakes. In this study, we determine how residual pools of ancient carbon affect the modern carbon abundance and character in the water columns of Lakes Fryxell, Hoare, and Bonney. We measure the stable carbon isotopic compositions and concentrations of particulate organic carbon (POC) and dissolved inorganic carbon (DIC) in the water column of these lakes over four seasons (1999–2002). These data are presented and compared with all the previously published Taylor Valley lacustrine carbon stable isotopic data. Our results show that the carbon concentrations and isotopic compositions of the upper water columns of those lakes are controlled by modern processes, while the lower water columns are controlled to varying degrees by inherited carbon pools. The water column of the west lobe of Lake Bonney is dominated by exceptionally high concentrations of DIC (55,000–75,000 μmol l⁻¹) reflecting the long period of ice-cover on this lake. The east lobe of Lake Bonney has highly enriched δ¹³C_DIC values resulting from paleo-brine evaporation effects in its bottom waters, while its high DIC concentrations provide geochemical evidence that its middle depth waters are derived from West Lake Bonney during a hydrologically connected past. Although ancient carbon is present in both Lake Hoare and Lake Fryxell, the δ¹³C_DIC values in bottom waters suggest dominance by modern primary productivity-related processes. Anaerobic methanogenesis and methanotrophy are also taking place in the lower water column of Lake Fryxell with enough methane, oxidized anaerobically, to contribute to the DIC pool. We also show how stream proximity and high flood years are only a minor influence on the carbon isotopic values of both POC and DIC. The Taylor Valley lake system is remarkably stable in both inter-lake and intra-lake carbon dynamics. Handling editor: K. Martens     

鄱阳湖南矶湿地优势植物群落及土壤有机质和营养元素分布特征

湿地植物和土壤是承担湿地诸多生态功能的主要基质和载体,相互之间有着强烈的影响。湿地土壤影响植物的种类、数量、生长发育、形态和分布,湿地植物又影响土壤中元素的分布与变化。鄱阳湖湿地的植物和土壤的特征及由他们带来的候鸟栖息地价值都受到他们之间的相互作用以及湖泊水位不同频率和幅度波动的影响。研究鄱阳湖湿地植物和土壤的特征及其形成原因和相互关系。为此,从2010年10月到2011年10月,对鄱阳湖湿地不同水位梯度下分布的芦苇、南荻、苔草、虉草和刚毛荸荠5个优势植物群落中57个定点样方展开了月度植被调查并且对5个不同植物群落下的135个土壤样品进行了实验室分析,研究了鄱阳湖优势植物群落及湿地土壤中有机质、全氮、全磷、全钾含量的分布特征及其相互关系。研究结果表明,鄱阳湖湿地优势植物群落分布特征受湿地土壤元素分布特征、湖面水位波动及植物生长特性和土壤沉积及土壤养分的综合影响,呈现了沿水位和海拔梯度明显的条带状或弧状分布、从湖岸到湖心依次分布为:狗牙根群落、芦苇群落、南荻群落、苔草群落、虉草群落、刚毛荸荠群落,最后是水生植物。同时植物群落的组成和分布特征也随季节性水位涨落的变化而变化;土壤有机质及其他各元素含量特征受植物群落分布、水位波动规律及湿地土壤特性等各种因素的影响,呈现出相对一致的分布规律,在0—20cm土壤层含量较高,20cm层后随土壤深度的增加含量逐渐减小,减小的速度先快后慢直至40cm层后趋于稳定;不同植物群落对土壤有机质、全氮、全磷、全钾的含量及变化具有很大的影响,不同植物群落下同种元素含量差异显著,并且各自随土壤深度和植物群落的变化呈现出层状、带状或弧状富集特征。不同植物群落对土壤养分元素含量影响程度不同,苔草群落对各元素吸收和滞留能力最强、影响最大,刚毛荸荠群落对土壤营养元素影响最弱。湿地植物群落和土壤之间彼此有着强烈的影响,其中植株的重量和土壤的SOC、TN及TP含量有非常显著的负相关关系,与土壤TK含量则有较强的正相关关系,同时,植株的重量和高度与土壤地下水埋深也有微弱的负相关关系。     

Differences in the C age, δC and δO of Holocene tufa and speleothem in the Dinaric Karst

We studied Holocene speleothems and tufa samples collected in numerous caves and rivers in the Dinaric Karst of Croatia, Slovenia, Bosnia and Herzegovina, as well as Serbia and Montenegro. Differences in the formation process of tufa and speleothems are discussed in the context of their isotopic composition (¹⁴C, ¹³C and ¹⁸O), as well as the chemistry of surface water (rivers, lakes) and drip water (in caves). The physical and chemical parameters monitored in the surface water (tufa precipitation) and drip water (speleothem precipitation) show that more stable conditions accompany speleothem rather than tufa formation. This is particularly obvious in the water temperature variations (2-22°C in surface water and 7-12°C in drip water) and in saturation index variation (3-11 in surface water and 1-6 in drip water). The range of ¹⁴C ages recorded by Holocene speleothems (∼12?000 yr) is wider by several thousands years than that of Holocene tufa samples (∼6000 yr). δ¹³C values for tufa samples range from −12‰ to −6‰ and for speleothem samples from −12‰ to +3‰ reflecting higher soil carbon and/or vegetation impact on the process of tufa than on speleothem formation. The differences in δ¹⁸O values of tufa and speleothem samples from different areas reflect different temperature conditions and differing isotopic composition in the water. The study shows that speleothems from the Dinaric Karst can be used as global palaeoclimatic records, whereas tufa records changes in the local palaeoenvironment.     

Dew water isotopic ratios and their relationships to ecosystem water pools and fluxes in a cropland and a grassland in China

Dew formation has the potential to modulate the spatial and temporal variations of isotopic contents of atmospheric water vapor, oxygen and carbon dioxide. The goal of this paper is to improve our understanding of the isotopic interactions between dew water and ecosystem water pools and fluxes through two field experiments in a wheat/maize cropland and in a short steppe grassland in China. Measurements were made during 94 dew events of the D and ¹⁸O compositions of dew, atmospheric vapor, leaf, xylem and soil water, and the whole ecosystem water flux. Our results demonstrate that the equilibrium fractionation played a dominant role over the kinetic fractionation in controlling the dew water isotopic compositions. A significant correlation between the isotopic compositions of leaf water and dew water suggests a large role of top-down exchange with atmospheric vapor controlling the leaf water turnover at night. According to the isotopic labeling, dew water consisted of a downward flux of water vapor from above the canopy (98%) and upward fluxes originated from soil evaporation and transpiration of the leaves in the lower canopy (2%).     

近10年艾比湖湿地不同植物群落土壤水分 盐分 养分变化特征

为研究新疆准噶尔盆地艾比湖湿地不同植物群落近10年土壤水盐及养分的动态变化,以环湖1周160km范围内的典型植被梭梭-柽柳、梭梭、胡杨、芦苇群落为研究对象,分析其在2006和2015年土壤含水量、盐分含量、pH值和有机质含量的变化和空间分布特征。结果表明:(1)近10年艾比湖湿地不同植物群落土壤有机质含量和含水量明显下降且整体水平较低,二者分别下降了24.65%~48%和5.41%~20.16%;土壤含盐量、pH值分别上升81.92%~128.74%和2.99%~4.21%,土壤盐碱程度加强。(2)通过土壤水分-盐分-养分空间分布分析显示,各群落近10年土壤盐渍化增加、养分降低程度大小表现为梭梭-柽柳群落胡杨群落梭梭群落芦苇群落,其中梭梭-柽柳群落土壤达到重度盐化水平,有机质降到6级,而其他群落土壤均为中度盐化,有机质为4级,但芦苇群落土壤退化程度较小。研究发现,近10年艾比湖湿地不同植物群落土壤养分不断下降、水分含量降低、盐渍化程度加剧,土壤处于退化状态;土壤质地、降水和气温暖干化是不同植物群落下土壤退化程度差异的基础,人口、耕地面积和农业用水等人类活动使各群落土壤退化程度的差异更加显著。     

Isotopic indicators of environmental change in a subtropical wetland

The δ¹⁵N and δ¹³C signatures of major organic matter (OM) pools were measured across chemical and hydrologic gradients in a large (58,800 ha) subtropical wetland to evaluate whether stable isotopes were useful indicators of environmental change. Once a rainfall-driven wetland, the Loxahatchee National Wildlife Refuge in the Florida Everglades now receives agricultural and urban drainage that has increased phosphorus (P) and mineral loads around the wetland perimeter. Additionally, water impoundment at the southern end has produced a latitudinal hydrologic gradient, with extended hydroperiods in the south and overdrained conditions in the north.Detritus (?4.8‰ to 8.6‰), floc (?1.4‰ to 3.6‰), and metaphyton (?6.6‰ to +7.4‰) δ¹⁵N declined southward with changes in hydrology as indicated by water depth. This pattern was attributed to higher mineralization rates under shorter hydroperiods. These signatures were also strongly correlated with increased nutrient and mineral loading. Rooted macrophyte δ¹⁵N, by contrast, appeared more responsive to soil nutrient pools. Cattail (?8.9‰ to +7.7‰) was restricted to the wetland perimeter and had the widest δ¹⁵N range, which was positively correlated with soil P. Sawgrass (?5.3‰ to +7.7‰) occurred across most of the wetland, but its δ¹⁵N was not strongly correlated to any gradient. Patterns for δ¹³C were more strongly related to chemical gradients caused by canal intrusion than to latitude or hydrology. Again, metaphyton and detrital signatures were more sensitive to water chemistry changes than macrophytes. This pattern is consistent with their locations at the soil–water (detritus-floc), and air–water (metaphyton) interface. Metaphyton δ¹³C (?36.1‰ to ?21.5‰) which had the broadest range, was affected by DIC source and pool size. In contrast, cattail δ¹³C (?28.7‰ to ?26.4‰) was more closely related to soil P and sawgrass δ¹³C (?30.1‰ to ?24.5‰) was not related to any environmental gradient except latitude. There was no correlation between the two isotopes for any OM pool except cattail.These results indicate that isotopic signatures of microbial (metaphyton and detrital) pools are more responsive to changes in wetland hydrology and water chemistry while those of rooted macrophytes respond only to the extent that soil chemistry is altered. Rooted macrophytes also differ in the sensitivity of their isotopic signatures to environmental change. The selection of OM pools for isotopic analysis will, therefore, affect the sensitivity of the analysis and the resulting patterns. Furthermore, δ¹⁵N may be more robust and interpretable than δ¹³C as an indicator of ecosystem change in wetlands exposed to multiple or complex anthropogenic gradients.     

Relationship between the hydrological conditions and the distribution of vegetation communities within the Poyang Lake National Nature Reserve,China

Hydrological characteristics have been recognized as major driving forces for wetland vegetation. The water cycle and hydrological processes of wetland are increasingly influenced by the ongoing climate change and more intensive human activities, which may in turn affect the distribution and structure of vegetation communities. Poyang Lake, located on the south bank of the lower reach of Yangtze River, receives inflows from five tributaries and discharges to the Yangtze River. The unique hydrological conditions of the Poyang Lake wetland create abundant wetland vegetation communities. As a major national hydraulic project, the Three Gorges Dam across the Yangtze River has changed the water regime of Poyang Lake and hence may affect the vegetation distribution. This work aims to investigate the influences of hydrological properties on vegetation structure at broad spatial and temporal scales. Histograms and sensitivity index are used to link the hydrological processes with the vegetation distribution across the Poyang Lake National Nature Reserve. The results show that different vegetation communities react differently to the hydrological conditions. Specifically, certain communities, e.g. Carex and Eremochloa ophiuroides, are able to survive a wide variety of mean water depth and percent time inundated, while others, like Carex–Polygonum criopolitanum, are found to be relatively sensitive to hydrological conditions. It is suggested that this work provides a new insight for evaluating the impact of hydro-engineering projects on vegetation communities and wetland vegetation restoration.     

The contribution of fog to the water relations of Sequoia sempervirens (D. Don): foliar uptake and prevention of dehydration

Fog is a defining feature of the coastal California redwood forest and fog inputs via canopy drip in summer can constitute 30% or more of the total water input each year. A great deal of occult precipitation (fog and light rain) is retained in redwood canopies, which have some of the largest leaf area indices known (Westman & Whittaker, Journal of Ecology 63, 493–520, 1975). An investigation was carried out to determine whether some fraction of intercepted fog water might be directly absorbed through leaf surfaces and if so, the importance of this to the water relations physiology of coast redwood, Sequoia sempervirens. An array of complimentary techniques were adopted to demonstrate that fog is absorbed directly by S. sempervirens foliage. Xylem sap transport reversed direction during heavy fog, with instantaneous flow rates in the direction of the soil peaking at approximately 5–7% of maximum transpiration rate. Isotopic analyses showed that up to 6% of a leaf's water content could be traced to a previous night's fog deposition, but this amount varied considerably depending on the age and water status of the leaves. Old leaves, which appear most able to absorb fog water were able to absorb distilled water when fully submersed at an average rate of 0.90 mmol m² s^?1, or about 80% of transpiration rates measured at the leaf level in the field. Sequoia sempervirens has poor stomatal control in response to a drying atmosphere, with rates of water loss on very dry nights up to 40% of midday summer values and rates above 10% being extremely common. Owing to this profligate water use behaviour of S. sempervirens, it appears that fog has a greater role in suppressing water loss from leaves, and thereby ameliorating daily water stress, than in providing supplemental water to foliar tissues per se. Although direct foliar absorption from fog inputs represents only a small fraction of the water used each day, fog's in reducing transpiration and rehydrating leaf tissues during the most active growth periods in summer may allow for greater seasonal carbon fixation and thus contribute to the very fast growth rates and great size of this species.     

Summer water use by California coastal prairie grasses: fog,drought, and community composition

Plants in the Mediterranean climate region of California typically experience summer drought conditions, but correlations between zones of frequent coastal fog inundation and certain species’ distributions suggest that water inputs from fog may influence species composition in coastal habitats. We sampled the stable H and O isotope ratios of water in non-photosynthetic plant tissue from a variety of perennial grass species and soil in four sites in northern California in order to determine the proportion of water deriving from winter rains and fog during the summer. The relationship between H and O stable isotopes from our sample sites fell to the right of the local meteoric water line (LMWL) during the summer drought, providing evidence that evaporation of water from the soil had taken place prior to the uptake of water by vegetation. We developed a novel method to infer the isotope values of water before it was subjected to evaporation in which we used experimental data to calculate the slope of the δH versus δO line versus the LMWL. After accounting for evaporation, we then used a two-source mixing model to evaluate plant usage of fog water. The model indicated that 28–66% of the water taken up by plants via roots during the summer drought came from fog rather than residual soil water from winter rain. Fog use decreased as distance from the coast increased, and there were significant differences among species in the use of fog. Rather than consistent differences in fog use by species whose distributions are limited to the coast versus those with broader distributions, species responded individualistically to summer fog. We conclude that fogwater inputs can mitigate the summer drought in coastal California for many species, likely giving an advantage to species that can use it over species that cannot.     

滇西北纳帕海湿地景观格局变化及其对土壤碳库的影响

采用3S技术和In-situ原状土就地取样技术,对滇西北纳帕海湿地26a来的景观格局变化及其驱动下的湿地土壤碳库变化研究表明:纳帕海景观格局变化显著,与1974年相比,景观破碎化程度增强、斑块形状趋于复杂、呈离散分布,湿地景观类型总面积比例呈略有增加(1994年)至大幅减小(2000年)的变化,非湿地景观类型总面积比例则呈略有减小(1994年)至大幅增加(2000年)的变化并取代湿地景观成为基质景观.响应景观类型面积变化,土壤碳储量由1974年的33.46×104 t增至1994年的36.91×l04 t,2000年降至32.92×104 t;随景观类型的转化,1974-1994年土壤碳库积累量为6.08×104 t,择放量为2.63×104 t,1994-2000年积累量为2.01×l04 t,但碳释放量为5.99× 104 t,是前20a的2.28倍.纳帕海湿地景观格局和土壤碳库的变化是自然和人为因素共同作用的结果,在地质、水文和气候等自然因素提供的变化背景上,排水、垦殖、过度放牧、无序旅游、汇水区植被破坏等强烈的人为活动干扰加剧了变化.     

Changes in nitrogen and base cation concentrations in soil water due to the tree cutting in a wetland alder forest in the Kushiro Wetland, northern Japan

As part of the Kushiro Wetland Restoration Project, we evaluated the effect of the tree-cutting (February 2003) on soil water chemistry for 3 years in an alder (Alnus japonica) shrubland on the peat soil in the Kushiro Wetland, the largest wetland in Japan. The alder stand was divided into two types; low stature and high stature stands, mean heights being 1.5 and 2.6 m, respectively. The treatment plot with tree cutting and the reference plot measuring 25 m × 25 m each were established in both stands, and a soil incubation experiment was also conducted by trenching the root zone of wetland vegetation in the treatment plots in both stands in the summer of 2004. The tree cutting did not substantially increase the concentrations of ammonium ion (NH₄ ⁺) and nitrate ion (NO₃ ⁻) in the soil water, although a gradual and slight increase of NO₃ ⁻ concentration was found after the tree-cutting only in the high stature stand (<10 μmol/l). This increase in the NO₃ ⁻ concentration in the high stature stand was probably due to the rhizosphere oxidation of wetland herbaceous vegetation, and was accompanied by the increase of Ca²⁺ concentration. The soil incubation experiment showed no significant change of the nitrogen concentration, suggesting that inorganic nitrogen was immobilized and NO₃ ⁻ was denitrified intensively in this wetland peat soil. The results of this study suggested that this wetland ecosystem had a high potential to stabilize the soil water chemistry.     

基于高通量测序的鄱阳湖典型湿地土壤细菌群落特征分析

采用高通量测序技术分析了鄱阳湖典型湿地土壤细菌群落特征。测序结果表明,不同植被土壤细菌群落丰度与多样性的排序相同:苔草带苔草-虉草带芦苇带泥滩带藜蒿带。沿湖面至坡地,空间位置相近的土壤细菌群落结构具有更大的相似性,苔草-虉草带、苔草带和芦苇带的细菌群落结构相近,泥滩带和藜蒿带的细菌群落结构差异较大。变形菌门(30.0%)是湿地土壤平均相对丰度最高的门,其次为酸杆菌门(16.7%)和绿弯菌门(16.5%);多数门分类细菌相对丰度沿湖面至坡地存在一定变化趋势。硝化螺菌属是第一大属分类水平细菌群落。在土壤化学指标中,与鄱阳湖湿地细菌群落相关性较大的是总磷、铵态氮和有机质含量。以上研究结果表明,鄱阳湖湿地不同植被土壤细菌群落具有结构性差异,但沿湖面至坡地存在规律性变化。     

Connecting carbon and nitrogen storage in rural wetland soil to groundwater abstraction for urban water supply

We investigated whether groundwater abstraction for urban water supply diminishes the storage of carbon (C), nitrogen (N), and organic matter in the soil of rural wetlands. Wetland soil organic matter (SOM) benefits air and water quality by sequestering large masses of C and N. Yet, the accumulation of wetland SOM depends on soil inundation, so we hypothesized that groundwater abstraction would diminish stocks of SOM, C, and N in wetland soils. Predictions of this hypothesis were tested in two types of subtropical, depressional‐basin wetland: forested swamps and herbaceous‐vegetation marshes. In west‐central Florida, >650 ML groundwater day^?1 are abstracted for use primarily in the Tampa Bay metropolis. At higher abstraction volumes, water tables were lower and wetlands had shorter hydroperiods (less time inundated). In turn, wetlands with shorter hydroperiods had 50–60% less SOM, C, and N per kg soil. In swamps, SOM loss caused soil bulk density to double, so areal soil C and N storage per m² through 30.5 cm depth was diminished by 25–30% in short‐hydroperiod swamps. In herbaceous‐vegetation marshes, short hydroperiods caused a sharper decline in N than in C. Soil organic matter, C, and N pools were not correlated with soil texture or with wetland draining‐reflooding frequency. Many years of shortened hydroperiod were probably required to diminish soil organic matter, C, and N pools by the magnitudes we observed. This diminution might have occurred decades ago, but could be maintained contemporarily by the failure each year of chronically drained soils to retain new organic matter inputs. In sum, our study attributes the contraction of hydroperiod and loss of soil organic matter, C, and N from rural wetlands to groundwater abstraction performed largely for urban water supply, revealing teleconnections between rural ecosystem change and urban resource demand.     

鄱阳湖苔草湿地甲烷释放特征

2009年5月-2010年4月在鄱阳湖南矶湿地国家级自然保护区选择以灰化苔草为建群种的洲滩,设置土壤-植物系统(TC)、剪除植物地上部分 (TJ)2个试验处理,利用密闭箱-气相色谱法测定了鄱阳湖典型苔草湿地的甲烷(CH₄)释放通量。结果表明:1)TC、TJ 2个试验处理CH₄释放速率变化范围分别为-0.094-17.75 mg · m^-2 · h^-1、-0.122-19.16 mg · m^-2 · h^-1,均表现出明显的季节变化规律;2)地表未淹水期间,剪草处理CH₄释放显著高于非剪草处理(t=2.69, P<0.05);地表淹水达到15 cm后,剪草处理CH₄释放明显低于非剪草处理。3)土壤5 cm温度、土壤水分与2处理非淹水期间CH₄释放速率均呈显著正相关,是非淹水期间CH₄通量变化的主要控制因子,2因子能够共同解释非淹水期苔草湿地65%-74%的CH₄通量变异;4)试验期间,苔草湿地CH₄释放量约为12.77 gC/m²,相当于同期土壤有机质分解碳排放量的4%,甲烷释放的碳消耗不足苔草湿地年NPP的1%。     

鄱阳湖湿地灰化苔草种群生产力特征及其水文响应

淡水湖泊湿地中,水文条件是影响湿地植物分布和生长发育的关键因素,研究特定湿地植物种群与水文变化之间关系,对于认识湿地植被格局形成及进行湿地生态调控与恢复具有重要意义。选取鄱阳湖湿地洲滩优势植物——灰化苔草(Carex cinerascens)种群作为研究对象,基于野外实地观测数据,研究不同高程带灰化苔草春草种群生产力特征及其对水文变化的响应。结果表明:春草生长季内各高程带灰化苔草种群变化规律基本一致,但其生长发育过程对水文条件产生差异性反应,长期连续水淹和半水淹条件抑制灰化苔草的生长,而间歇性半水淹和未水淹条件则促进灰化苔草伸长生长和生物量积累;生长初期灰化苔草通过储水策略应对水分缺乏形成的干旱胁迫,而生长末期则通过增加干物质含量来应对淹水胁迫;灰化苔草定植与生长发育需要一定的水文条件,淹没期平均水深3.70—2.78 m、淹没频率42.08%—43.17%、平均距湖水面高度-0.23—0.77 m的水文环境更有利于灰化苔草的生长发育。研究结果可为未来鄱阳湖湿地植被保护和湖泊水位调控提供重要参考依据。