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1.
Jason B. Fellman Eran Hood Robert G. M. Spencer Aron Stubbins Peter A. Raymond 《Ecosystems》2014,17(6):1014-1025
The Coast Mountains of southeast Alaska are currently experiencing some of the highest rates of glacier volume loss on Earth, with unknown implications for proglacial stream biogeochemistry. We analyzed streamwater for δ18O and dissolved organic matter (DOM) biogeochemistry (concentration, δ13C-dissolved organic carbon (DOC), and fluorescence characterization) during the 2012 glacial runoff season from three coastal watersheds in southeast Alaska that ranged in glacier coverage from 0 to 49% and a glacier outflow stream. Our goal was to assess how DOM biogeochemistry may change as receding glaciers are replaced by forests and glaciers contribute less meltwater to streamflow. Discharge and streamwater δ18O varied seasonally reflecting varying contributions of rainfall and snow/icemelt to streamflow over the runoff season. Mean DOC concentrations were lowest in the glacial outflow and highest in the non-glacial stream reflecting an increasing contribution of vascular plant-derived carbon with decreasing watershed glaciation. Fluorescence and δ13C-DOC signatures indicated that DOM shifted from vascular plant-derived, humic-like material in the non-glacial stream toward more δ13C-DOC enriched, glacier-derived DOM in the glacial outflow. Streamwater δ18O was significantly correlated to DOC concentration, δ13C-DOC, and protein-like fluorescence of streamwater DOM (all P < 0.05), demonstrating that changes in the source of streamwater across the glacial watershed continuum have important implications for the amount and quality of stream DOM export. Overall, our findings show that continued glacial recession and subsequent changes in glacial runoff could substantially influence the biogeochemistry of coastal temperature watersheds by altering the timing, magnitude, and chemical signature of DOM delivered to streams. 相似文献
2.
Glacier surfaces are known to harbour abundant and active microbial communities. Phosphorus has been shown to be deficient
in glacial environments, and thus is one of the limits on microbial growth and activity. We quantified the phosphorus pool
in cryoconite debris and the concentration of dissolved phosphorus in supraglacial water on Werenskioldbreen, a Svalbard glacier.
The mean total P content of the cryoconite debris was ~2.2 mg g−1, which is significantly more than would be expected in rock debris from local sources. 57% of this P was present in the fraction
defined as organic P. It may account for the P in excess of the rock debris, and could be explained by allochthonous input
of organic matter. The concentration of total dissolved P in supraglacial water was very low (5.2–8.5 μg l−1), which was probably caused by efficient flushing and re-adsorption onto mineral surfaces. Dissolved organic P (DOP) was
a very important component of the dissolved phosphorus pool on Werenskioldbreen, as concentrations of DOP typically exceeded
those of dissolved inorganic P (or SRP) by more than four times in all the glacial water types. It is very difficult to assess
whether P was limiting in this environment solely on the basis of the N:P ratios in the debris or biomass. There may be some
degree of biological control over the C:N:P ratios in the debris, but the phosphorus cycling in the supraglacial environment
on this glacier seems to be mainly controlled by physical and geochemical processes. 相似文献
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5.
森林生态系统DOM的来源、特性及流动 总被引:18,自引:1,他引:17
可溶性有机物质(Dissolved Organic Matter)是森林生态系统主要的可移动碳库及重要的养分库。系统综述了森林生态系统DOM的来源,组成,性质,季节动态;DOM释放与存留机制及影响因素,森林生态系统DOM的流动及干扰对DOM动态影响等,已有研究表明DOM的森林生态系统C、N、P循环,成土作用,污染物迁移等方面起着重要作用。今后森林生态系统DOM的研究应集中于以几方面:(1)确定森林生态系统中DOM源和汇;(2)评价森林水文条件对DOM释放与存留的调节作用;(3)探讨全球气候变化对森林生态系统DOM的影响;(4)可溶性有机氮(Dissolved Organic Nitrogen),可溶性有机磷(Dissolved Organic Phosphorus)动态与可溶性有碳(Dissolved Organic Carbon)动态的差别。 相似文献
6.
Nicola A. McEnroe Clayton J. Williams Marguerite A. Xenopoulos Petr Porcal Paul C. Frost 《PloS one》2013,8(11)
Urbanization has the potential to dramatically alter the biogeochemistry of receiving freshwater ecosystems. We examined the optical chemistry of dissolved organic matter (DOM) in forty-five urban ponds across southern Ontario, Canada to examine whether optical characteristics in these relatively new ecosystems are distinct from other freshwater systems. Dissolved organic carbon (DOC) concentrations ranged from 2 to 16 mg C L-1 across the ponds with an average value of 5.3 mg C L-1. Excitation-emission matrix (EEM) spectroscopy and parallel factor analysis (PARAFAC) modelling showed urban pond DOM to be characterized by microbial-like and, less importantly, by terrestrial derived humic-like components. The relatively transparent, non-humic DOM in urban ponds was more similar to that found in open water, lake ecosystems than to rivers or wetlands. After irradiation equivalent to 1.7 days of natural solar radiation, DOC concentrations, on average, decreased by 38% and UV absorbance decreased by 25%. Irradiation decreased the relative abundances of terrestrial humic-like components and increased protein-like aspects of the DOM pool. These findings suggest that high internal production and/or prolonged exposure to sunlight exerts a distinct and significant influence on the chemistry of urban pond DOM, which likely reduces its chemical similarity with upstream sources. These properties of urban pond DOM may alter its biogeochemical role in these relatively novel aquatic ecosystems. 相似文献
7.
Microbes in supraglacial ecosystems have been proposed to be significant contributors to regional and possibly global carbon
cycling, and quantifying the biogeochemical cycling of carbon in glacial ecosystems is of great significance for global carbon
flow estimations. Here we present data on microbial abundance and productivity, collected along a transect across the ablation
zone of the Greenland ice sheet (GrIS) in summer 2010. We analyse the relationships between the physical, chemical and biological
variables using multivariate statistical analysis. Concentrations of debris-bound nutrients increased with distance from the
ice sheet margin, as did both cell numbers and activity rates before reaching a peak (photosynthesis) or a plateau (respiration,
abundance) between 10 and 20 km from the margin. The results of productivity measurements suggest an overall net autotrophy
on the GrIS and support the proposed role of ice sheet ecosystems in carbon cycling as regional sinks of CO2 and places of production of organic matter that can be a potential source of nutrients for downstream ecosystems. Principal
component analysis based on chemical and biological data revealed three clusters of sites, corresponding to three ‘glacier
ecological zones’, confirmed by a redundancy analysis (RDA) using physical data as predictors. RDA using data from the largest
‘bare ice zone’ showed that glacier surface slope, a proxy for melt water flow, accounted for most of the variation in the
data. Variation in the chemical data was fully explainable by the determined physical variables. Abundance of phototrophic
microbes and their proportion in the community were identified as significant controls of the carbon cycling-related microbial
processes. 相似文献
8.
The decomposition of dissolved organic matter (DOM) in pelagic ecosystems is mediated primarily by heterotrophic bacteria,
but transformation by short-wave solar radiation may play an important role in surface waters, in particular when humic substances
constitute a substantial fraction of the DOM pool. Most of the studies examining bacterial decomposition and photochemical
transformation of DOM stem from limnetic and coastal marine systems and much less information is available from oceanic environments.
To examine the bacterial decomposition of humic and non-humic DOM in the Southern Ocean we carried out microcosm experiments
in which we measured bacterial growth on isolated fractions of humic and non-humic DOM of the size classes <3 kDa and >3 kDa.
Experiments carried out at the Polar Front showed a preferential bacterial growth on non-humic DOM and in particular on the
size fraction <3 kDa. Bacterial growth, measured as bacterial biomass production, on non-humic DOM accounted for 74% to 88%
of the total growth on all four DOM fractions. In experiments in the Antarctic circumpolar current and the coastal current
under pack ice, bacterial growth was 6× lower than at the Polar Front, and humic and non-humic DOM was consumed to equal amounts.
The size fraction <3 kDa was always preferred. Experiments examining the effect of solar radiation on the release of dissolved
amino acids (DAA) and carbohydrates (DCHO) and their subsequent bacterial utilization showed a stimulating effect on glucose
uptake and the release of DAA at the Polar Front but an inhibition in the eastern Weddell Sea. Ultraviolet-B was the most
effective component of the solar radiation spectrum tested. Effects of UV-B on glucose uptake and release of DAA were positively
correlated with concentrations of humic-bound DAA. The data imply that at low concentrations, e.g., <100 nM (amino acid equivalent),
UV-irradiation reduces, whereas at concentrations >100 nM UV-irradiation stimulates glucose uptake and release of DAA as compared
to dark conditions. 相似文献
9.
Lorena Selak Helena Osterholz Igor Stanković Nikola Hanžek Marija Gligora Udovič Thorsten Dittmar Sandi Orlić 《Environmental microbiology》2022,24(5):2282-2298
In lake ecosystems, changes in eukaryotic and prokaryotic microbes and the concentration and availability of dissolved organic matter (DOM) produced within or supplied to the system by allochthonous sources are components that characterize complex processes in the microbial loop. We address seasonal changes of microbial communities and DOM in the largest Croatian lake, Vrana. This shallow lake is connected to the Adriatic Sea and is impacted by agricultural activity. Microbial community and DOM structure were driven by several environmental stressors, including drought, seawater intrusion and heavy precipitation events. Bacterial composition of different lifestyles (free-living and particle-associated) differed and only a part of the particle-associated bacteria correlated with microbial eukaryotes. Oscillations of cyanobacterial relative abundance along with chlorophyll a revealed a high primary production season characterized by increased levels of autochthonous DOM that promoted bacterial processes of organic matter degradation. From our results, we infer that in coastal freshwater lakes dependent on precipitation-evaporation balance, prolonged dry season coupled with heavy irrigation impact microbial communities at different trophic levels even if salinity increases only slightly and allochthonous DOM inputs decrease. These pressures, if applied more frequently or at higher concentrations, could have the potential to overturn the trophic state of the lake. 相似文献
10.
Travis W. Drake David C. Podgorski Bienvenu Dinga Jeffrey P. Chanton Johan Six Robert G. M. Spencer 《Global Change Biology》2020,26(3):1374-1389
The flux and composition of carbon (C) from land to rivers represents a critical component of the global C cycle as well as a powerful integrator of landscape‐level processes. In the Congo Basin, an expansive network of streams and rivers transport and cycle terrigenous C sourced from the largest swathe of pristine tropical forest on Earth. Increasing rates of deforestation and conversion to agriculture in the Basin are altering the current regime of terrestrial‐to‐aquatic biogeochemical cycling of C. To investigate the role of deforestation on dissolved organic and inorganic C (DOC and DIC, respectively) biogeochemistry in the Congo Basin, six lowland streams that drain catchments of varying forest proportion (12%–77%) were sampled monthly for 1 year. Annual mean concentrations of DOC exhibited an asymptotic response to forest loss, while DIC concentrations increased continuously with forest loss. The isotopic signature of DIC became significantly more enriched with deforestation, indicating a shift in source and processes controlling DIC production. The composition of dissolved organic matter (DOM), as revealed by ultra‐high‐resolution mass spectrometry, indicated that deforested catchments export relatively more aliphatic and heteroatomic DOM sourced from microbial biomass in soils. The DOM compositional results imply that DOM from the deforested sites is more biolabile than DOM from the forest, consistent with the corresponding elevated stream CO2 concentrations. In short, forest loss results in significant and comprehensive shifts in the C biogeochemistry of the associated streams. It is apparent that land‐use conversion has the potential to dramatically affect the C cycle in the Congo Basin by reducing the downstream flux of stable, vascular‐plant derived DOC while increasing the transfer of biolabile soil C to the atmosphere. 相似文献
11.
Spatial and temporal variability of dissolved organic matter quantity and composition in an oligotrophic subtropical coastal wetland 总被引:1,自引:0,他引:1
Dissolved organic matter (DOM) is an essential component of the carbon cycle and a critical driver in controlling variety of biogeochemical and ecological processes in wetlands. The quality of this DOM as it relates to composition and reactivity is directly related to its sources and may vary on temporal and spatial scales. However, large scale, long-term studies of DOM dynamics in wetlands are still scarce in the literature. Here we present a multi-year DOM characterization study for monthly surface water samples collected at 14 sampling stations along two transects within the greater Everglades, a subtropical, oligotrophic, coastal freshwater wetland-mangrove-estuarine ecosystem. In an attempt to assess quantitative and qualitative variations of DOM on both spatial and temporal scales, we determined dissolved organic carbon (DOC) values and DOM optical properties, respectively. DOM quality was assessed using, excitation emission matrix (EEM) fluorescence coupled with parallel factor analysis (PARAFAC). Variations of the PARAFAC components abundance and composition were clearly observed on spatial and seasonal scales. Dry versus wet season DOC concentrations were affected by dry-down and re-wetting processes in the freshwater marshes, while DOM compositional features were controlled by soil and higher plant versus periphyton sources respectively. Peat-soil based freshwater marsh sites could be clearly differentiated from marl-soil based sites based on EEM–PARAFAC data. Freshwater marsh DOM was enriched in higher plant and soil-derived humic-like compounds, compared to estuarine sites which were more controlled by algae- and microbial-derived inputs. DOM from fringe mangrove sites could be differentiated between tidally influenced sites and sites exposed to long inundation periods. As such coastal estuarine sites were significantly controlled by hydrology, while DOM dynamics in Florida Bay were seasonally driven by both primary productivity and hydrology. This study exemplifies the application of long term optical properties monitoring as an effective technique to investigate DOM dynamics in aquatic ecosystems. The work presented here also serves as a pre-restoration condition dataset for DOM in the context of the Comprehensive Everglades Restoration Plan (CERP). 相似文献
12.
The movement of dissolved organic carbon (DOC) through soils is an important process for the transport of carbon within ecosystems
and the formation of soil organic matter. In some cases, DOC fluxes may also contribute to the carbon balance of terrestrial
ecosystems; in most ecosystems, they are an important source of energy, carbon, and nutrient transfers from terrestrial to
aquatic ecosystems. Despite their importance for terrestrial and aquatic biogeochemistry, these fluxes are rarely represented
in conceptual or numerical models of terrestrial biogeochemistry. In part, this is due to the lack of a comprehensive understanding
of the suite of processes that control DOC dynamics in soils. In this article, we synthesize information on the geochemical
and biological factors that control DOC fluxes through soils. We focus on conceptual issues and quantitative evaluations of
key process rates to present a general numerical model of DOC dynamics. We then test the sensitivity of the model to variation
in the controlling parameters to highlight both the significance of DOC fluxes to terrestrial carbon processes and the key
uncertainties that require additional experiments and data. Simulation model results indicate the importance of representing
both root carbon inputs and soluble carbon fluxes to predict the quantity and distribution of soil carbon in soil layers.
For a test case in a temperate forest, DOC contributed 25% of the total soil profile carbon, whereas roots provided the remainder.
The analysis also shows that physical factors—most notably, sorption dynamics and hydrology—play the dominant role in regulating
DOC losses from terrestrial ecosystems but that interactions between hydrology and microbial–DOC relationships are important
in regulating the fluxes of DOC in the litter and surface soil horizons. The model also indicates that DOC fluxes to deeper
soil layers can support a large fraction (up to 30%) of microbial activity below 40 cm.
Received 14 January 2000; accepted 6 September 2000 相似文献
13.
Effect of Native Vegetation Loss on Stream Ecosystem Processes: Dissolved Organic Matter Composition and Export in Agricultural Landscapes 总被引:1,自引:0,他引:1
Darren P. Giling Michael R. Grace James R. Thomson Ralph Mac Nally Ross M. Thompson 《Ecosystems》2014,17(1):82-95
Stream and river ecosystems are dependent on energetic inputs from their watersheds and thus shifts in land use from forest cover to agriculture will affect stream community composition and function. The disruption of forest-aquatic linkages alters the organic matter resources in agricultural streams. Dissolved organic matter (DOM) is the dominant form of organic matter in aquatic ecosystems, and a microbial energy source that is important for stream respiration. The concentrations and characteristics of DOM are regulated by both terrestrial (for example, terrestrial organic matter supply) and in-stream processes (for example, microbial respiration and periphyton production) that are influenced by land management. The effects of watershed land use and topographic, soil and climatic variables on DOM quantity (dissolved organic carbon concentration and load), source (terrestrial or in-stream) and quality (composition and lability) were measured in 14 streams across an agricultural land-use gradient. DOC concentration was positively correlated with watershed pasture cover and negatively correlated with watershed relief. No watershed variables were important correlates of DOC load. Stream DOM was primarily of terrestrial origin, but DOM in agricultural streams had a greater proportion of sources from in-stream sources. This may be due to reduced connection with riparian vegetation and increased in-stream primary production. We suggest that maintaining watershed tree cover greater than 52% and ensuring less than 10% of the length of riparian corridor is cleared for pasture could minimize changes to DOM composition. This is important to avoid flow-on effects for stream ecosystem processes that are mediated by DOM. Long-term DOM monitoring will be valuable for assessing the functional impacts of land-use change. 相似文献
14.
Relationships Between Land Cover and Dissolved Organic Matter Change Along the River to Lake Transition 总被引:1,自引:0,他引:1
James H. Larson Paul C. Frost Marguerite A. Xenopoulos Clayton J. Williams Ana M. Morales-Williams Jon M. Vallazza John C. Nelson William B. Richardson 《Ecosystems》2014,17(8):1413-1425
Dissolved organic matter (DOM) influences the physical, chemical, and biological properties of aquatic ecosystems. We hypothesized that controls over spatial variation in DOM quantity and composition (measured with DOM optical properties) differ based on the source of DOM to aquatic ecosystems. DOM quantity and composition should be better predicted by land cover in aquatic habitats with allochthonous DOM and related more strongly to nutrients in aquatic habitats with autochthonous DOM. Three habitat types [rivers (R), rivermouths (RM), and the nearshore zone (L)] associated with 23 tributaries of the Laurentian Great Lakes were sampled to test this prediction. Evidence from optical indices suggests that DOM in these habitats generally ranged from allochthonous (R sites) to a mix of allochthonous-like and autochthonous-like (L sites). Contrary to expectations, DOM properties such as the fluorescence index, humification index, and spectral slope ratio were only weakly related to land cover or nutrient data (Bayesian R 2 values were indistinguishable from zero). Strongly supported models in all habitat types linked DOM quantity (that is, dissolved organic carbon concentration [DOC]) to both land cover and nutrients (Bayesian R 2 values ranging from 0.55 to 0.72). Strongly supported models predicting DOC changed with habitat type: The most important predictor in R sites was wetlands whereas the most important predictor at L sites was croplands. These results suggest that as the DOM pool becomes more autochthonous-like, croplands become a more important driver of spatial variation in DOC and wetlands become less important. 相似文献
15.
Microbial films play a central role in mediating energy flux in groundwater ecosystems. The activity of these microbes is
likely to be influenced by the availability of resources, especially dissolved organic matter (DOM), and also by consumers,
such as invertebrates that feed on microbial films. We used microcosm experiments to examine how bacterial production and
extracellular enzyme activity on rocks and fine sediments from cave streams responded to amendments of DOM of varying form
and to cave amphipods (Gammarus minus) that feed on microbial films. Glucose and mixtures of DOM extracted from soils and leaves stimulated bacterial production
on rocks by 89–166% relative to unamended controls. In contrast, tannic acid amendment did not influence production. Microbial
films on fine sediment were not consistently responsive to DOM amendment. Glucose amendment led to increased activity of enzymes
associated with C acquisition, but other forms of DOM generally did not alter enzyme activity. DOM amendment led to removal
of nitrate and this was correlated with bacterial production, suggesting microbes can link carbon and nitrogen cycling in
groundwater as is the case in surface systems. Amphipods reduced bacterial production on rocks, but not fine sediments. The
reduction caused by amphipods offset the stimulatory effect of glucose amendment, but there was no interactive effect of DOM
and grazing on bacterial production or enzyme activity. Both resources and consumers play important roles in regulating microbial
activity in groundwater with important implications for higher trophic levels that use microbes for food. 相似文献
16.
Julien Arsenault Julie Talbot Lee E. Brown Manuel Helbig Joseph Holden Jorge Hoyos-Santillan Émilie Jolin Roy Mackenzie Karla Martinez-Cruz Armando Sepulveda-Jauregui Jean-François Lapierre 《Global Change Biology》2023,29(14):4056-4068
Peatland pools are freshwater bodies that are highly dynamic aquatic ecosystems because of their small size and their development in organic-rich sediments. However, our ability to understand and predict their contribution to both local and global biogeochemical cycles under rapidly occurring environmental change is limited because the spatiotemporal drivers of their biogeochemical patterns and processes are poorly understood. We used (1) pool biogeochemical data from 20 peatlands in eastern Canada, the United Kingdom, and southern Patagonia and (2) multi-year data from an undisturbed peatland of eastern Canada, to determine how climate and terrain features drive the production, delivering and processing of carbon (C), nitrogen (N), and phosphorus (P) in peatland pools. Across sites, climate (24%) and terrain (13%) explained distinct portions of the variation in pool biogeochemistry, with climate driving spatial differences in pool dissolved organic C (DOC) concentration and aromaticity. Within the multi-year dataset, DOC, carbon dioxide (CO2), total N concentrations, and DOC aromaticity were highest in the shallowest pools and at the end of the growing seasons, and increased gradually from 2016 to 2021 in relation to a combination of increases in summer precipitation, mean air temperature for the previous fall, and number of extreme summer heat days. Given the contrasting effects of terrain and climate, broad-scale terrain characteristics may offer a baseline for the prediction of small-scale pool biogeochemistry, while broad-scale climate gradients and relatively small year-to-year variations in local climate induce a noticeable response in pool biogeochemistry. These findings emphasize the reactivity of peatland pools to both local and global environmental change and highlight their potential to act as widely distributed climate sentinels within historically relatively stable peatland ecosystems. 相似文献
17.
Human activities cause distinct dissolved organic matter composition across freshwater ecosystems 下载免费PDF全文
Clayton J. Williams Paul C. Frost Ana M. Morales‐Williams James H. Larson William B. Richardson Aisha S. Chiandet Marguerite A. Xenopoulos 《Global Change Biology》2016,22(2):613-626
Dissolved organic matter (DOM) composition in freshwater ecosystems is influenced by the interactions among physical, chemical, and biological processes that are controlled, at one level, by watershed landscape, hydrology, and their connections. Against this environmental template, humans may strongly influence DOM composition. Yet, we lack a comprehensive understanding of DOM composition variation across freshwater ecosystems differentially affected by human activity. Using optical properties, we described DOM variation across five ecosystem groups of the Laurentian Great Lakes region: large lakes, Kawartha Lakes, Experimental Lakes Area, urban stormwater ponds, and rivers (n = 184 sites). We determined how between ecosystem variation in DOM composition related to watershed size, land use and cover, water quality measures (conductivity, dissolved organic carbon (DOC), nutrient concentration, chlorophyll a), and human population density. The five freshwater ecosystem groups had distinctive DOM composition from each other. These significant differences were not explained completely through differences in watershed size nor spatial autocorrelation. Instead, multivariate partial least squares regression showed that DOM composition was related to differences in human impact across freshwater ecosystems. In particular, urban/developed watersheds with higher human population densities had a unique DOM composition with a clear anthropogenic influence that was distinct from DOM composition in natural land cover and/or agricultural watersheds. This nonagricultural, human developed impact on aquatic DOM was most evident through increased levels of a microbial, humic‐like parallel factor analysis component (C6). Lotic and lentic ecosystems with low human population densities had DOM compositions more typical of clear water to humic‐rich freshwater ecosystems but C6 was only present at trace to background levels. Consequently, humans are strongly altering the quality of DOM in waters nearby or flowing through highly populated areas, which may alter carbon cycles in anthropogenically disturbed ecosystems at broad scales. 相似文献
18.
可溶性碳(Dissolved carbon,DC)和颗粒碳(particulate carbon,PC)通量作为森林生态系统碳收支的重要组分,在森林固碳功能的评价和模型预测中具有重要意义,但常因认识不足、测定困难等而在森林碳汇研究中被忽略。综述了森林生态系统DC和PC的组成、作用、相关生态过程及其影响因子,并展望了该领域应该优先考虑的研究问题。森林生态系统DC和PC主要包括可溶性有机碳、可溶性无机碳和颗粒有机碳,主要来源于生态系统的净初级生产量。DC和PC是森林土壤的活性碳库,主要以大气沉降、穿透雨和凋落物的形式输入森林土壤系统,并通过土壤呼吸、侧向运输及渗透流失的方式输出生态系统。从局域尺度看,DC和PC通量受根系分泌、细根分解、微生物周转等生物过程的影响较大;从区域尺度看,它们受土壤和植被特性、生态过程耦联关系、气候因子以及全球变化的综合影响。该领域应该优先考虑:(1)探索不同时空尺度下森林生态系统DC和PC通量的控制因子及其耦联关系,揭示其中的驱动机理;(2)探索DC和PC与其它森林生态系统碳组分的相互关系及转化,阐明DC和PC通量与其它养分之间潜在的生态化学计量关系;(3)探索全球变化,特别是人类活动(如森林经营)和极端干扰事件(如林火、旱涝、冰冻、冻融交替等)对森林生态系统DC和PC通量的影响。 相似文献
19.
C. E. L. Thompson B. Silburn M. E. Williams T. Hull D. Sivyer L. O. Amoudry S. Widdicombe J. Ingels G. Carnovale C. L. McNeill R. Hale C. Laguionie Marchais N. Hicks H. E. K. Smith J. K. Klar J. G. Hiddink J. Kowalik V. Kitidis S. Reynolds E. M. S. Woodward K. Tait W. B. Homoky S. Kröger S. Bolam J. A. Godbold J. Aldridge D. J. Mayor N. M. A. Benoist B. J. Bett K. J. Morris E. R. Parker H. A. Ruhl P. J. Statham M. Solan 《Biogeochemistry》2017,132(1-2):1-22
Headwater streams influence the biogeochemical characteristics of large rivers and play important roles in regional and global carbon budgets. The combined effects of seasonality and land use change on the biogeochemistry of headwater streams, however, are not well understood. In this study we assessed the influence of catchment land use and seasonality on the composition of dissolved organic matter (DOM) and ecosystem metabolism in headwater streams of a Kenyan river. Fifty sites in 34 streams draining a gradient of catchment land use from 100% natural forest to 100% agriculture were sampled to determine temporal and spatial variation in DOM composition. Gross primary production (GPP) and ecosystem respiration (ER) were determined in 10 streams draining primarily forest or agricultural catchments. Absorbance and fluorescence spectrophotometry of DOM reflected notable shifts in composition along the land use gradient and with season. During the dry season, forest streams contained higher molecular weight and terrestrially derived DOM, whereas agricultural streams were dominated by autochthonous production and low molecular weight DOM. During the rainy season, aromaticity and high molecular weight DOM increased in agricultural streams, coinciding with seasonal erosion of soils and inputs of organic matter from farmlands. Most of the streams were heterotrophic. However, GPP and ER were generally greater in agricultural streams, driven by higher dissolved nutrient (mainly TDN) concentrations, light availability (open canopy) and temperature compared with forest streams. There were correlations between freshly and autochthonously produced DOM, GPP and ER during both the dry and wet seasons. This is one of the few studies to link land-use with organic carbon dynamics and DOM composition. Measures of ecosystem metabolism in these streams help to affirm the role of tropical streams and rivers as important components of the global carbon cycle and demonstrate that even semi-intensive, smallholder agriculture can have measurable effects on riverine ecosystem functioning. 相似文献
20.
Abboudi M Jeffrey WH Ghiglione JF Pujo-Pay M Oriol L Sempéré R Charrière B Joux F 《Microbial ecology》2008,55(2):344-357
The effects of phototransformation of dissolved organic matter (DOM) on bacterial growth, production, respiration, growth
efficiency, and diversity were investigated during summer in two lagoons and one oligotrophic coastal water samples from the
Northwestern Mediterranean Sea, differing widely in DOM and chromophoric DOM concentrations. Exposure of 0.2-μm filtered waters
to full sun radiation for 1 d resulted in small changes in optical properties and concentrations of DOM, and no changes in
nitrate, nitrite, and phosphate concentrations. After exposure to sunlight or dark (control) treatments, the water samples
were inoculated with the original bacterial community. Phototransformation of DOM had contrasting effects on bacterial production
and respiration, depending on the water’s origin, resulting in an increase of bacterial growth efficiency for the oligotrophic
coastal water sample (120%) and a decrease for the lagoon waters (20 to 40%) relative to that observed in dark treatments.
We also observed that bacterial growth on DOM irradiated by full sun resulted in changes in community structure of total and
metabolically active bacterial cells for the three locations studied when compared to the bacteria growing on un-irradiated
DOM, and that changes were mainly caused by phototransformation of DOM by UV radiation for the eutrophic lagoon and the oligotrophic
coastal water and by photosynthetically active radiation (PAR) for the mesoeutrophic lagoon. These initial results indicate
that phototransformation of DOM significantly alters both bacterial metabolism and community structure in surface water for
a variety of coastal ecosystems in the Mediterranean Sea. Further studies will be necessary to elucidate a more detailed appreciation
of potential temporal and spatial variations of the effects measured. 相似文献