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Natural riparian forest wetlands are known to be effective in their ability to remove nitrate by denitrification and sediments with attached phosphorus via sedimentation. On the other hand, litter input and decomposition is a process of crucial importance in cycling of nitrogen and phosphorus in a forest ecosystem.In this study we investigated the amount of nitrogen and phosphorus entering the alder fen ecosystem through leaf litter and its decomposition and the removal capacity of nitrogen and phosphorus by measuring denitrification and sedimentation in the alder fen.We found an average input of leaf litter during fall 1998 of 226 g m−2 yr−1 DW with nutrient concentration of 0.17% P and 1.6% N. This means a yearly input of 0.4 g m−2 yr−1 P and 3.6 g m−2 yr−1 N. The decomposition of leaf litter using litter bags with small and large mesh size resulted in bags with macroinvertebrates (large mesh size) and without macroinvertebrates (small mesh size). After 57 days the litter bags with macroinvertebrates had a decomposition rate of 79%.Denitrification was measured in May and June of 1997 using the acetylene inhibition technique on intact soil cores and slurry-experiments. The average annual denitrification rate was 0.2 g m−2 yr−1 N using data from the core experiments. The denitrification rate was higher after addition of nitrate, indicating that denitrification in the riparian alder fen is mainly controlled by nitrate supply.The sedimentation rate in the investigated alder fen ranged from 0.47 kg m−2 yr−1 DW to 4.46 kg m−2 yr−1 DW in 1998 depending on the study site and method we used. Sedimentation rates were lower in newly designed plate traps than in cylinder traps. The alder fen also showed lower rates than the adjacent creek Briese. Average phosphorus removal rate was 0.33 g m−2 yr−1 P.Input sources for the surface water of the alder fen are sediment mineralization and decomposition of leaf litter; output sources are sedimentation and denitrification. This study showed that a nutrient input of 24.58 kg ha−1 yr−1 N, 8.8 kg ha−1 yr−1 P and 419 kg ha−1 yr−1 DOC into the surface water of the alder fen is possible. Alder fens cannot improve water quality of an adjacent river system. This is only true for a nearly pristine alder fen with the hydrology of 10 months flooded conditions and 2 months non-flooding conditions a year. 相似文献
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地下水-土壤-植被-大气系统(GSPAC)界面水分传输是湿地生态水文过程研究的关键.本文选取鄱阳湖湿地高位滩地的2种典型植被群落:茵陈蒿(Artemisia capillaris)和芦苇(Phragmites australis)群落为研究对象,运用HYDRUS-1D垂向一维数值模拟,量化了湿地GSPAC系统界面水分通量,阐明了典型丰水年(2012年)和枯水年(2013年)鄱阳湖湿地植被群落的蒸腾用水规律和水源组成.结果表明:(1)茵陈蒿和芦苇群落土壤-大气界面的年降水入渗量为1570~1600 mm,主要集中在雨季4-6月,占年总量的60%;植物-大气界面的年蒸腾总量分别为346~470 mm和926~1057 mm,其中7-8月植被生长旺季最大,占年总量的40%~46%;地下水-根区土壤界面的向上补给水量受不同水文年水位变化的影响显著,地下水年补给量分别为15~513 mm和277~616 mm,主要发生在蒸散发作用强烈和地下水埋深较浅的时段.(2)植被蒸腾用水分为生长初期(4-6月)和生长旺季(7-10月)2个阶段,丰水年植被的整个生长期蒸腾用水充足,枯水年植被生长旺季的蒸腾用水受到严重水分胁迫,实际蒸腾量仅为潜在蒸腾量的一半左右.(3)不同水文年湿地植被生长旺季的水源贡献不同:丰水年茵陈蒿群落以地下水补给为主,芦苇群落以湖水和地下水补给为主;枯水年茵陈蒿群落以降水和前期土壤水储量为主,芦苇群落以地下水补给为主.本研究结果有助于揭示湿地植被的水分利用策略,为阐明湖泊水情变化与植被演替的作用机理提供参考依据. 相似文献
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HUANG XiaoFeng YUN Hui GONG ZhaoHeng LI Xiang HE LingYan ZHANG YuanHang HU Min 《中国科学:地球科学(英文版)》2014,57(6):1352-1362
PM2.5 is the key pollutant in atmospheric pollution in China.With new national air quality standards taking effect,PM2.5 has become a major issue for future pollution control.To effectively prevent and control PM2.5,its emission sources must be precisely and thoroughly understood.However,there are few publications reporting comprehensive and systematic results of PM2.5 source apportionment in the country.Based on PM2.5 sampling during 2009 in Shenzhen and follow-up investigation,positive matrix factorization(PMF)analysis has been carried out to understand the major sources and their temporal and spatial variations.The results show that in urban Shenzhen(University Town site),annual mean PM2.5 concentration was 42.2μg m?3,with secondary sulfate,vehicular emission,biomass burning and secondary nitrate as major sources;these contributed30.0%,26.9%,9.8%and 9.3%to total PM2.5,respectively.Other sources included high chloride,heavy oil combustion,sea salt,dust and the metallurgical industry,with contributions between 2%–4%.Spatiotemporal variations of various sources show that vehicular emission was mainly a local source,whereas secondary sulfate and biomass burning were mostly regional.Secondary nitrate had both local and regional sources.Identification of secondary organic aerosol(SOA)has always been difficult in aerosol source apportionment.In this study,the PMF model and organic carbon/elemental carbon(OC/EC)ratio method were combined to estimate SOA in PM2.5.The results show that in urban Shenzhen,annual SOA mass concentration was 7.5μg m?3,accounting for 57%of total organic matter,with precursors emitted from vehicles as the major source.This work can serve as a case study for further in-depth research on PM2.5 pollution and source apportionment in China. 相似文献
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沉水植物在湖泊生态系统中具有重要作用,它不仅是湖泊生态系统食物链中重要的生产者,同时还对湖泊的营养物沉积和循环有着重要的意义,并由此影响着湖泊的富营养化进程.本文以黄河内蒙古段河套灌区湖泊中常见的3种沉水植物篦齿眼子菜(Potamogeton pectinatus)、穿叶眼子菜(Potamogeton perfoliatus)和狐尾藻(Myriophyllum verticillatum)为研究对象,对其种子休眠及萌发特性进行了初步研究.结果表明:狐尾藻种子休眠率较高但休眠易破除,通过切破种皮、低温层积、硝酸钾和赤霉素处理均可显著提高萌发率;篦齿眼子菜种子休眠性较强,低温层积及赤霉素浸泡处理能够显著提高其萌发率;穿叶眼子菜有较深的休眠特性,破除硬实、硝酸钾、赤霉素及低温层积处理均不能有效解除其休眠. 相似文献
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Respiration rates (mg O2 g?1 AFDW h?1) of Leuctra hippopus, Sericostoma personatum, Helodes minuta, Gammarus pulex and Asellus aquaticus were studied across an oxygen gradient at 2.8 and 6.3 °C, corresponding to an expected 3.5 °C increase in Danish winter stream temperature. Species were selected from the Danish Stream Fauna Index (DSFI), representing an expected hierarchy of tolerance towards water quality degradation. We expected that low-ranking, tolerant species (i.e. indicators of bad water quality) would have the capacity to regulate their oxygen uptake relatively independently of oxygen availability (oxy-regulators) and high-ranking, sensitive species (i.e. indicators of good water quality) would be less able to do so (oxy-conformers). For all species respiration rate was higher (although non-significantly) at 6.3 °C. The species’ oxy-regulatory capacity did not consistently reflect their DSFI ranking. As expected, and in accordance with its DSFI ranking, A. aquaticus had the highest oxy-regulatory capacity with the ability to regulate O2 uptake until an oxygen saturation of only 20%, which did not change with increasing temperature, emphasizing the robustness of A. aquaticus towards changes in the environment. S. personatum, H. minuta and G. pulex revealed no oxy-regulatory capacity. In contrast, the plecopteran L. hippopus did display an unexpected oxy-regulatory capacity. Though an increase in temperature changed L. hippopus’ capacity to oxy-regulate (the critical limit increased from 32.5 to 43.5% oxygen), respiration rates did not change significantly in spite of the temperature increase. This result contradicts the general belief that stoneflies, because of their affinity to well oxygenated habitats, are conformers. Our findings call for further studies on the respiratory conformer–regulator concept and its role as an eco-physiological trait for bio-assessment. 相似文献
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《Limnologica》2016
The decomposition of plant litter is an important mechanism in regard to energy and nutrient dynamics of ecosystems. Silicon concentration of plant tissue can affect these processes by changing litter quality, i.e. nutrient stoichiometry and cellulose and phenols content. To determine which group of microbial decomposers benefits from high Si content in plants and how this impacts on animal decomposers, a batch experiment was conducted with reed leaf litter (Phragmites australis) differing in Si content in the presence/absence of invertebrate shredders (Gammarus pulex). Lipid concentration of G. pulex, in reed litter and fine particulate matter (FPOM) were examined. High Si concentration in reed resulted in a decline of gram positive bacteria in the heterotrophic biofilm and of gram negative bacteria in FPOM. The lipid composition in the next trophic level, the decomposer G. pulex, changed too, indicating a diet shift in favor of bacteria and algae with increasing litter Si concentration. Thus, basal decomposers were affected by the Si availability in plant resources, and these effects likely persist along the food chain, as FPOM is a dominant food supply for other groups, e.g. collectors. This impact of Si content on plant substrate quality for decomposer food webs may have global relevance, due to related modifications in carbon and nutrient cycling during litter decomposition. 相似文献
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The effect of density on the growth, recruitment of new ramets, biomass allocation, rhizome spacer length and rhizome branching of the submersed macrophyte Potamogeton perfoliatus L. was experimentally evaluated in a mesocosm with three different initial shoot densities. The findings suggest that the number of primary shoots available in the beginning of the season can strongly influence patterns of growth and clonal reproduction. In contrast to many studies that found decreasing production parameters with plant density, ramet and biomass production of Potamogeton perfoliatus plants were highest at medium plant density. This is probably due to negative feed-back through crowding at high density and unclear negative effects at low density. Shoot allocation tended to increase with density, rhizome allocation tended to decrease with density and root biomass remained unchanged. At low density Potamogeton perfoliatus produced longer rhizome spacers and more branchings than at higher densities. Shorter rhizome spacers at high plant density probably restrict patch expansion and cause discrete patch shapes. A likely mechanism for plastic changes in clonal architecture is increasing competition for light at increasing density, but other density-dependent factors may also contribute.Investigations on propagule numbers of tubers and turions show that self-regulation of ramet number was associated with self-regulation of propagule number in both Potamogeton perfoliatus and Potamogeton pectinatus, with higher densities producing less propagules per plant. 相似文献
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Although 1-alkyl-2,3,6-trimethylbenzenes and a high relative amount of 1,2,3,4-tetramethylbenzene have been detected in marine oils and oil asphaltenes from Tabei uplift in the Tarim Basin, their bio-logical sources are not determined. This paper deals with the molecular characteristics of typical ma-rine oil asphaltenes from Tabei and Tazhong uplift in the Tarim Basin and the stable carbon isotopic signatures of individual compounds in the pyrolysates of these asphaltenes using flash pyrolysis-gas chromatograph-mass spectrometer (PY-GC-MS) and gas chromatograph-stable isotope ratio mass spectrometer (GC-C-IRMS), respectively. Relatively abundant 1,2,3,4-tetramethylbenzene is detected in the pyrolysates of these marine oil asphaltenes from the Tarim Basin. δ 13C values of 1,2,3,4-tetrame-thylbenzene in the pyrolysates of oil asphaltenes vary from-19.6‰ to-24.0‰, while those of n-alkanes in the pyrolysates show a range from-33.2‰ to-35.1‰. The 1,2,3,4-tetramethylbenzene in the pyro-lysates of oil asphaltenes proves to be significantly enriched in 13C relative to n-alkanes in the pyro-lysates and oil asphaltenes by 10.8‰―15.2‰ and 8.4‰―13.4‰, respectively. This result indicates a contribution from photosynthetic green sulfur bacteria Chlorobiaceae to relatively abundant 1,2,3,4-tetramethylbenzene in marine oil asphaltenes from the Tarim Basin. Hence, it can be speculated that the source of most marine oil asphaltenes from the Tarim Basin was formed in a strongly reducing water body enriched in H2S under euxinic conditions. 相似文献
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The effect of El Niño Southern Oscillation cycles on the decadal scale suspended sediment behavior of a coastal dry‐summer subtropical catchment 
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下载免费PDF全文 Andrew B. Gray Gregory B. Pasternack Elizabeth B. Watson Jonathan A. Warrick Miguel A. Goñi 《地球表面变化过程与地形》2015,40(2):272-284
Rivers display temporal dependence in suspended sediment–water discharge relationships. Although most work has focused on multi‐decadal trends, river sediment behavior often displays sub‐decadal scale fluctuations that have received little attention. The objectives of this study were to identify inter‐annual to decadal scale fluctuations in the suspended sediment–discharge relationship of a dry‐summer subtropical river, infer the mechanisms behind these fluctuations, and examine the role of El Niño Southern Oscillation climate cycles. The Salinas River (California) is a moderate sized (11 000 km2), coastal dry‐summer subtropical catchment with a mean discharge (Qmean) of 11.6 m3 s?1. This watershed is located at the northern most extent of the Pacific coastal North America region that experiences increased storm frequency during El Niño years. Event to inter‐annual scale suspended sediment behavior in this system was known to be influenced by antecedent hydrologic conditions, whereby previous hydrologic activity regulates the suspended sediment concentration–water discharge relationship. Fine and sand suspended sediment in the lower Salinas River exhibited persistent, decadal scale periods of positive and negative discharge corrected concentrations. The decadal scale variability in suspended sediment behavior was influenced by inter‐annual to decadal scale fluctuations in hydrologic characteristics, including: elapsed time since small (~0.1 × Qmean), and moderate (~10 × Qmean) threshold discharge values, the number of preceding days that low/no flow occurred, and annual water yield. El Niño climatic activity was found to have little effect on decadal‐scale fluctuations in the fine suspended sediment–discharge relationship due to low or no effect on the frequency of moderate to low discharge magnitudes, annual precipitation, and water yield. However, sand concentrations generally increased in El Niño years due to the increased frequency of moderate to high magnitude discharge events, which generally increase sand supply. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Julien Némery Vincent Mano Alexandra Coynel Henri Etcheber Florentina Moatar Michel Meybeck Philippe Belleudy Alain Poirel 《水文研究》2013,27(17):2498-2508
Carbon and total suspended sediment (TSS) loads were investigated from April 2006 to March 2008 in the mountainous watershed of the Isère River, French Alps (5570 km2). The river bed has been highly impounded for hydroelectricity production during the last century. Hydraulic flushes are managed every year to prevent TSS storage within upstream dams. The Isère River has been instrumented for high‐frequency monitoring of water, TSS by turbidity and carbon (organic, inorganic, dissolved and particulate) in order to evaluate the impact of natural floods and hydraulic flushes on annual loads. Annual TSS load which was estimated between 1.3 and 2.3 MT y?1 (i.e. 233 to 413 T km?2 y?1) highlighted the high erodibility of the Isère watershed. Annual carbon load was estimated between 173 103 T y?1 and 199 103 T y?1 (i.e 31 to 36 T km?2 y?1). About 80% of the annual carbon loads were inorganic. The impact of hydraulic flushes on annual loads appeared limited (less than 3% for annual TSS load and about 1.5% for annual carbon load), whereas the most important natural flood event contributed to 20% of the annual TSS load and 10% of the annual carbon load. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Biological invasions represent a relevant ecological and economic problem of our globalized world. While a few species have been classified as invasive due to their ecological and economic impacts on the invaded ecosystems (e.g., zebra mussel), others show contrasting invasive potential, depending on the invaded ecosystem and/or the traits of the exotic species. This paper reviews the worldwide distribution, ecological impacts and the reasons that explain the invasive success of the aquatic mud snail Potamopyrgus antipodarum Gray (Hydrobiidae, Mollusca), which is native to New Zealand. This review shows that most studies on P. antipodarum distribution have been conducted in Europe, North America and Australia, and few studies in Asia. The distribution of this snail is still unknown in other parts of the world (e.g., Africa, South and Central America). The range of invaded aquatic ecosystems varies from fresh to salt water and from lentic to lotic ecosystems. The ecological impact of this species is due to the fast population growth rate and to the extremely high densities that it can reach, leading to altered C and N cycles in invaded ecosystems. However, at low densities mud snails have been shown to enhance secondary production. Additionally, P. antipodarum has been found to overcome the negative effects of predators and parasites (e.g., it survives the pass through the digestive tracts of fish). This review contributes to assess the magnitude and ecological risk of P. antipodarum invasion throughout the world. 相似文献
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To improve quantitative understanding of mixed‐land‐use impacts on nutrient yields, a nested‐scale experimental watershed study design (n = 5) was applied in a 303(d), clean water act impaired urbanizing watershed of the lower Missouri River Basin, USA. From 2010 to 2013, water samples (n = 858 sample days per site) were analysed for total inorganic nitrogen (TIN‐N), nitrite (NO2–N) nitrate (NO3–N), ammonia (NH3–N), and total phosphorus (TP‐P). Annual, seasonal, and monthly flow‐weighted concentrations (FWCs) and nutrient yields were estimated. Mean nutrient concentrations were highest where agricultural land use comprised 58% of the drainage area (NH3 = 0.111 mg/l; NO2 = 0.045 mg/l; NO3 = 0.684 mg/l, TIN = 0.840 mg/l; TP = 0.127 mg/l). Average TP‐P increased by 15% with 20% increased urban land use area. Highly variable annual precipitation was observed during the study with highest nutrient yields during 2010 (record setting wet year) and lowest nutrient yields during 2012 (extreme drought year). Annual TIN‐N and TP‐P yields exceeded 10.3 and 2.04 kg ha?1 yr?1 from the agricultural dominated headwaters. Mean annual NH3–N, NO2–N, NO3–N, TIN‐N, and TP‐P yields were 0.742, 0.400, 4.24, 5.38, and 0.979 kg ha?1 yr?1, respectively near the watershed outlet. Precipitation accounted for the majority of the explained variance in nutrient yields (R2 values from 0.68 to 0.85). Nutrient yields were also dependent on annual precipitation of the preceding year (R2 values from 0.87 to 0.91) thus enforcing the great complexity of variable mixed‐land‐use mediated source‐sink nutrient yield relationships. Study results better inform land managers and best management practices designed to mitigate nutrient pollution issues in mixed‐land‐use freshwater ecosystems. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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A typical agricultural water reservoir (AWR) of 2400 m2 area and 5 m depth, located in a semi‐arid area (southern Spain), was surveyed on a daily basis for 1 year. The annual evaporation flux was 102·7 W m?2, equivalent to an evaporated water depth of 1310 mm year?1. The heat storage rate G exhibited a clear annual cycle with a peak gain in April (G ～ 45 W m?2) and a peak loss in November (G ～ 40 W m?2), leading to a marked annual hysteretic trend when evaporation (λE) was related to net radiation (Rn). λE was strongly correlated with the available energy A, representing 91% of the annual AWR energy loss. The sensible heat flux H accounted for the remaining 9%, leading to an annual Bowen ratio in the order of 0·10. The equilibrium and advective evaporation terms of the Penman formula represented 76 and 24%, respectively, of the total evaporation, corresponding to a annual value of the Priestley–Taylor (P–T) coefficient (α) of 1·32. The P–T coefficient presented a clear seasonal pattern, with a minimum of 1·23 (July) and a maximum of 1·65 (December), indicating that, during periods of limited available energy, AWR evaporation increased above the potential evaporation as a result of the advection process. Overall, the results stressed that accurate prediction of monthly evaporation by means of the P–T formula requires accounting for both the annual cycle of storage and the advective component. Some alternative approaches to estimating Rn, G and α are proposed and discussed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Elemental carbon and nitrogen levels and isotope ratios were assessed in different biological compartments of a Northwest (NW) Mediterranean bay to trace the various sources of nutrient input from natural (river runoffs) and anthropogenic (harbor outflows, fish farms and urban sewage outfall) sources. Samples from transplanted mussels and natural sea grass communities (Posidonia oceanica leaves and epiphytes) were harvested from different locations throughout the bay during the touristic summer and rainy seasons. The results from the nitrogen analysis revealed that sewage and harbor outflow promote higher nitrogen levels, enrichment of 15N in the tissues, and a higher seasonal variability in sea grass and epiphytes. In mussel tissues, the δ15N was also influenced by sewage and harbor outflow, whereas δ13C was influenced by terrestrial inputs. These results suggest that natural and anthropogenic nutrient inputs have a temporary and localized influence and affect the sensitivity of natural isotopic ratios to changes in hydrologic conditions, especially to rain and tourism. 相似文献
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Intensive measurements of the fluxes of phosphorus (P) and of P retention were carried out in a Danish lowland watershed (Gjern Å) during two hydrological years (June 1987 to May 1989). Seasonal and short-term variations of P concentrations were measured by intensive automatic sampling covering P fluxes from the entire Gjern Å watershed and two subcatchments: the Gelbæk and Lake Søbygård. Moreover, infrequent sampling was performed in all major tributaries of the river system. Transport of P compounds (dissolved and particulate P) exposed a seasonal pattern which was highly affected by flow conditions, instream processes, as well as point and non-point sources. Stormflow P transport during the two study years (1987-8 and 1988-9) constituted 56 and 61% in the Gelbæk, respectively, compared with 25 and 23% in the Gjern Å, respectively. Particulate P transport in the Gelbæk constituted 56 and 75% of annual total P transport during the two years compared with 77 and 75% in the Gjern Å. The magnitude of monthly baseflow and stormflow total P loads was significantly correlated with the mean monthly discharge during baseflow and stormflow in the Gelbæk, whereas only stormflow loads were correlated to discharge in the Gjern Å. In situ measurements of retention showed that the maximum amount of P stored in the Gelbæk during summer (June to August) was 22gPm?2 (1988) compared with 27gPm?2 (1987) in the Gjern Å. Lake Søbygård was a P source during summer but a P sink during winter and on an annual basis the net P released was 810 and 1420 kg, which corresponded to 7 and 20% of the annual P export from the watershed, respectively. Retention constituted about 30% of gross P transport in the Gelbæk during summer compared with 20% in the Gjern Å. Resuspension of retained P during stormflows in September 1987 constituted 94% of the stormflow P transport and 54% of the total P transport. Monthly total P and dissolved reactive P (DRP) mass balances for the main channel of the Gjern Å revealed a significant DRP retention over 17 months (p < 0.05) caused by P adsorption on sediments and biological uptake. On an annual basis the main channel was a sink of DRP (1220 and 1660 kg P) but a source of total P (3440 and 1000 kg P). implying that the channel is an important source of particulate P. Bank erosion proved to be a significant P source in the main channel of Gjern Å, whereas P delivery from soil erosion was possibly of minor importance. The annual non-point P export from two intensively sampled catchments was significantly higher (0.89 and 0.45 kg Pha?1 yr?1) than from the five extensively sampled subbasins (0.43 and 0.17 kg Pha?1 yr?1). No significant relationship could be established between non-point P export and the proportion of arable land and soil type. Only for the wet year of 1987-8 was a significant relationship established between non-point P export and the P load from scattered dwellings outside sewage areas in five subbasins. 相似文献
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Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest in the Changbai Mountains (128°28′E and 42°24′N, Jilin Province, P. R. China) since August 2002. On the data obtained with open-path eddy covariance system and CO2 profile measurement system from Jan. 2003 to Dec. 2004, this paper reports (i) annual and seasonal variation of F NEE, F GPP and R E; (ii) regulation of environmental factors on phase and amplitude of ecosystem CO2 uptake and release Corrections due to storage and friction velocity were applied to the eddy carbon flux.
LAI and soil temperature determined the seasonal and annual dynamics of FGPP and RE separately. VPD and air temperature regulated ecosystem photosynthesis at finer scales in growing seasons. Water condition at the root zone exerted a significant influence on ecosystem maintenance carbon metabolism of this forest in winter.
The forest was a net sink of atmospheric CO2 and sequestered −449 g C·m−2 during the study period; −278 and −171 gC·m−2 for 2003 and 2004 respectively. F GPP and F RE over 2003 and 2004 were −1332, −1294 g C·m−2. and 1054, 1124 g C·m−2 respectively. This study shows that old-growth forest can be a strong net carbon sink of atmospheric CO2.
There was significant seasonal and annual variation in carbon metabolism. In winter, there was weak photosynthesis while the ecosystem emitted CO2. Carbon exchanges were active in spring and fall but contributed little to carbon sequestration on an annual scale. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of F GPP, and 60.4, 62.1% of R E of the entire year.
相似文献19.
污水低碳氮比(C/N)是影响人工湿地氮去除效果限制因素,传统的碳源添加及利用存在成本较高、补充困难的局限性. 本研究契合“就地取材,原位处理”的废物利用原则,选择人工湿地常见的水生植物和农业废弃物(玉米芯、稻草)作为对照,对比了挺水植物(香蒲、美人蕉)、浮叶植物(莲)、沉水植物(菹草)、湿生植物(南荻、短尖苔草)的释碳能力,初步确定了以香蒲、美人蕉、南荻为代表的植物具有较好的释放碳能力,在中国湿地中分布广泛,且均对水体二次污染较小. 以南荻、美人蕉、玉米芯作为碳源添加的模拟人工湿地实验验证表明,在低碳氮比的模拟表流人工湿地投入植物碳源,能有效提高系统的脱氮效率,对照组、南荻组、美人蕉组和玉米芯组的出水总氮浓度分别为(5.24±0.07)、(4.50±0.10)、(3.75±0.17)和(2.97±0.18)mg/L,对应的去除率分别为58%、64%、70%和76%,确定南荻和美人蕉植物残体以及改性材料均残体和改性材料适合作为人工湿地中原位利用的外加碳源. 本研究探索了通过湿地植物配置解决人工湿地水体低C/N比的问题,为提高湿地脱氮效果提供了有意义的新途径. 相似文献
20.
Identifying subsoil sediment sources with carbon and nitrogen stable isotope ratios 总被引：2，自引：0，他引：2 下载免费PDF全文
下载免费PDF全文 J. Patrick Laceby Jon Olley Timothy J. Pietsch Fran Sheldon Stuart E. Bunn 《水文研究》2015,29(8):1956-1971
Increased sediment loads from accelerated catchment erosion significantly degrade waterways worldwide. In the South East Queensland region of Australia, sediment loads are degrading Moreton Bay, a Ramsar listed wetland of international significance. In this region, like most parts of coastal Australia, sediment is predominantly derived from gully and channel bank erosion processes. A novel approach is presented that uses carbon and nitrogen stable isotope ratios and elemental composition to discriminate between these often indistinguishable subsoil sediment sources. The conservativeness of these sediment properties is first tested by examining the effect of particle size separation (testing for consistency during transport) and the effect of sampling at different times (testing for temporal source consistency). The discrimination potential of these sediment properties is then assessed with the conservative properties, based on the particle size and temporal analyses, modelled to determine sediment provenance in three catchments. Nitrogen sediment properties were found to have significant particle size enrichment and high temporal variance indicative of non‐conservative behaviour. Conversely, carbon stable isotopes had very limited particle size and temporal variability highlighting their suitability for sediment tracing. Channel erosion was modelled to be a significant source of sediment (μ 51%, σ 9%) contrasting desktop modelling research that estimated gully erosion is the predominant sediment source. To limit the supply of sediment to Moreton Bay, channel bank and gully erosion must both be targeted by sediment management programs. By distinguishing between subsoil sediment sources, this approach has the potential to enhance the management of sediment loads degrading waterways worldwide. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献