汉江上游金水河悬浮物及水体碳氮稳定同位素组成特征

金水河位于南水北调中线工程水源地的汉江上游,研究其污染物来源及分布规律对水源地水资源保护尤为重要。研究了不同水文季节金水河中悬浮颗粒物C和N稳定同位素值、水体硝酸盐与铵盐含量及其N稳定同位素特征。结果表明:金水河流域可溶性氮素与悬浮颗粒物的来源具有明显的空间性和季节性差异,并且流域内叶绿素浓度、水体浊度、悬浮物浓度都会对河流碳氮素稳定同位素值造成影响,主要体现在环境因子的变化制约着水体中硝化和反硝化生物对氮素的可利用性。结果显示:1)水体中悬浮颗粒物的碳稳定同位素为-8.03‰-14.57‰,平均值为2.59‰;氮稳定同位素范围为-7.50‰-7.34‰,平均值为:4.33‰,表明悬浮颗粒物的来源主要为外源性土壤有机质与内源性水生植物残体的混合;2)河流水体中铵盐与硝酸盐N-稳定同位素范围分别为-5.86‰-17.20‰,平均值为5.02‰及-1.48‰-15.86‰,平均值为5.75‰;水体可溶性氮素主要来源为大气沉降、河流水生生物以及地表径流所带入的化肥农药等;3)悬浮颗粒物含量不仅随着河流径流量的季节性变化而变化,还随着人为干扰强度的加强而呈递增的趋势,水体悬浮颗粒物含量最高达到(9.883±3.45)mg/L。而NH_4~+及NO_3~-的浓度也呈现出相同的趋势,含量分别为0.07-0.45 mg/L,平均值为0.25 mg/L;0.08-0.44 mg/L,平均值为0.37 mg/L。稳定同位素测定为河流生态系统提供了一个整合时空氮素来源和转移循环过程的综合指标,揭示了环境因子对河流生态系统氮循环的影响过程与机制。     

Dynamic river processes drive variability in particulate organic matter over fine spatiotemporal scales

1. We sampled freshwater suspended particulate organic matter (POM) to determine its carbon and nitrogen stable isotope composition and collected co-located water chemistry data in California's Sacramento—San Joaquin Delta from sites on the Mokelumne and Cosumnes rivers. A 10-km² area was sampled across 12 sites and divided among three habitat types (i.e. riverine, slackwater/slough, and off-channel), 34 times between November 2016 and July 2017. Here, we describe the variability in water quality and POM variables, and assess factors associated with that variability using dimensional reduction and linear modelling within the context of our habitat types.
2. The stable isotope composition of freshwater POM and water chemistry variables differed significantly across small areas (<10 km) and short time frames (weekly). Hydrological connectivity amongst sites was found to be an important factor in the isotopic and elemental composition of POM.
3. During periods of low hydrological connectivity, in situ dynamics were strongly associated with differentiation of POM in different habitats. Discharge (16–433 m³/s) and water temperature (8–30°C) were the variables most associated with variations in the composition of POM. Slackwater sites showed the greatest variability in POM composition, which may be symptomatic of longer water residence times, increased cycling rates of nutrients and organic matter, or a combination of the two.
4. Variability in POM stable isotope composition demonstrates that caution should be exercised when interpreting analyses that assume a static POM stable isotope composition based on two-end member mixing. Unconstrained variability in space or time could confound interpretations of models and data. Moving forward, conceptual and numerical models for river ecosystems that emphasise temporally heterogeneous lateral exchange amongst habitat patches should be prioritised when considering restoration efforts and monitoring outcomes.

     

Isotope variability of particulate organic matter at the PN section in the East China Sea

The source of particulate organic matter at the PN section in the East China Sea has been evaluated using stable carbon and nitrogen isotopes. The results showed that the ¹³C and ¹⁵N compositions varied from –19 to –31 and 0.7–9.5 respectively, and the isotope compositions were statistically distinct, enabling, by use of a simple components mixing equations, assessment of the ability of each tracer to estimate the terrestrial, Kuroshio Water, marine and remineralized sources' contributions. The dominance of terrestrial inputs of the Changjiang could be observed 250 km far from the river mouth in the East China Sea. In the shelf water column, the remineralization of biogenic organic matter becomes an important source except for the terrigenous and marine sources. The estimation of sources recorded by ¹³C data was partly confirmed by equivalent ¹⁵N and C/N compositions that reflected greater control by organic matter diagenesis and biological processing. However, the lighter contribution of ¹³C data of the Kuroshio samples also indicates the alteration of the isotope values by microbial or other processes. The net export flux of POC in the PN section is estimated to be 4.1 kmol C/s and the annual export is 129 Gmol C/yr, which is account for 20% of the East China Sea.     

Temporal shift in contribution of terrestrial organic matter to consumer production in a grassland river

1. We used stable isotopes to study the temporal (early summer versus autumn) pattern of use of terrestrial and aquatic sources of organic carbon by consumers in two bedrock‐confined reaches of a grassland river in New Zealand.
2. The major sources of organic carbon available to primary consumers were expected to be terrestrial leaf‐litter and biofilm from the stream channel. These putative carbon sources showed no significant change in mean δ¹³C between summer and autumn. Leaf litter (mean δ¹³C13C compared to biofilm (mean δ¹³C>?19.92).
3. In contrast to leaf litter and biofilm, the δ¹³C of consumers changed over time, being enriched in ¹³C in the autumn compared with early summer. Both the magnitude (>5‰ in some cases) and rapidity of this shift (< 3 months) was surprising.
4. A two‐source mixing model indicated that, during early summer, terrestrial carbon comprised> 50% of tissue carbon for 15 of the 17 taxa of aquatic consumers analysed. During autumn, terrestrial carbon comprised> 50% of the tissue carbon of only five of 25 taxa. Because the mean δ¹³C of putative food sources was consistent over time, the shift in δ¹³C values for consumers is attributed to a change in relative amounts of terrestrial and aquatic carbon available for consumption.
5. Because seston consists of a mixture of many particles of diverse origin, it may provide an integrated measure of catchment‐wide sources of organic matter entering a stream channel. Like the tissues of most consumers, mean δ¹³C values for seston showed a significant shift toward ¹³C enrichment. This indicated that the relative availability of terrestrial carbon decreased from summer to autumn.
6. The actual quantity of carbon contributed to the stream food‐web by this potential terrestrial–aquatic link is unknown. Although terrestrial carbon may comprise a high proportion of the tissue carbon of consumers prior to summer, the majority of secondary production (and carbon sequestration) probably occurs during early summer as a consequence of rising temperature and high quality food in the form of biofilm.     

Flow and retention of particulate organic matter in riparian fluvial habitats under different climates

The flow and retention of particulate organic matter were compared in two fluvial systems under different climates: the French upper Rhone (temperate climate) and the lower Moulouya in Morocco (Mediterranean climate). In both systems, a breakdown gradient was observed. This gradient was correlated with water motion, oxygen content, richness in hyphomycete species and occurrence of their mycelia and spores on submerged leaves, invertebrate density and consumption by shredders.U.A. CNRS 1451 Ecologie des Eaux Douces et des Grands FleuvesU.A. CNRS 1451 Ecologie des Eaux Douces et des Grands Fleuves     

Nitrogen sedimentation in a lake affected by massive nitrogen inputs: autochthonous versus allochthonous effects

1. Monthly changes to N loadings, in‐lake particulate organic nitrogen (PON), planktonic PON, and PON sedimentary flux were studied in a Spanish flowthrough, seepage lake subject to massive nitrogen inputs from June 2003 to December 2004 when water renewal was very rapid (0.09–0.17 year). 2. The distribution of in‐lake PON did not show a seasonal trend. Total nitrogen input flux ranged from 1.23 to 4.83 g N m^?2 day^?1, 71–76% of which is nitrate while PON represents 6–10%. PON sedimentation rates ranged from 9 to 90 mg N m^?2 day^?1 and fluctuated on a seasonal basis, reaching a minimum in winter and early spring and a maximum after thermal turnover had occurred. 3. This fluctuation was not related to either autochthonous planktonic production or allochthonous inputs. Since charophyte populations in Colgada Lake underwent a seasonal pattern of growth and decomposition, and ¹⁵δN values of settling material peaked at the end of that decomposition process, we suggest that PON sedimentary flux could be partly driven by decomposed charophyte particles. 4. However, the picture of PON sedimentation in this lake was more complex than anticipated because water residence time partly explained PON variability, albeit with a 1 month lag. Water residence time explained 40% of the overall variance of yearly averaged PON sedimentary flux in a meta‐analysis of 13 lakes worldwide. However, the factors such as phytoplankton composition, trophic structure, bottom communities, nutrient loading or productivity levels may also be influential on PON settling dynamics.     

2010年夏季珠江口海域颗粒有机碳的分布特征及其来源

于2010年8月对珠江口海域20个站位的颗粒有机碳(POC)进行采样,分析了POC的空间分布特征,讨论了POC与环境因子之间的关系,并利用碳稳定同位素(δ13C)分析了POC的来源及其贡献率。结果显示,研究区域POC的浓度范围98.5—1929.8μg/L,平均浓度541.9μg/L,空间分布总体呈现自北部海域向中部海域逐渐降低,中部海域至南部海域又逐渐升高,底层大于表层的特点。总悬浮颗粒物、叶绿素a、水动力是影响POC空间分布的重要原因。研究区域总悬浮颗粒物δ13C值的变化范围-27.05‰—-21.03‰,平均为-24.57‰,反映出珠江口海域颗粒有机碳为陆源和水生源混合来源,其分布呈现沿盐度梯度自口门内向口门外逐渐递增,底层高于表层的特点。陆源输入和海洋生物生产是影响δ13C值分布的主要原因。运用二元混合模型计算得知,珠江口北部和中部海域POC以陆源有机碳为主,贡献率平均为64%;南部海域POC以水生源有机碳为主,贡献率平均为68%。与20多年前相比,POC的分布特征与来源已经发生了改变,珠江口海域含沙量减少与营养盐含量增加可能是导致POC组成发生变化的主要原因。     

Allochthonous and autochthonous carbon flows in food webs of tropical forest streams

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Predictability of streamflow and particulate organic matter concentration as indicators of stability in prairie streams

Predictability of stream discharge and particulate organic matter (POM) in the water column was estimated, using Colwell's indices of constancy and contingency, for 6 Texas prairie streams (1 each of 2nd, 3rd, and 4th order with intermittent or perennial discharge). Stream discharge in these 6 prairie streams varied between 0 and 36000 1 s^–1, depending on the stream and season. Predictability (P) of discharge in these streams ranged from 0.45 to 0.62, within the range of values expected for North American streams. Predictability of stream discharge was not significantly different between streams. Particulate organic matter concentrations in these prairie streams are relatively low, ranging from 0.25 to 4.00 mg AFDM 1^–1. Predictability of POM concentration in these streams was high, ranging from 0.75 to 0.85, and was largely the result of constancy of POM concentrations. Within the different POM size classes, Fine POM (FPOM) had the highest predictability (P = 0.89–0.96). In spite of relatively unpredictable stream discharge, POM remained fairly constant providing a measure of habitat predictability and stability.     

The significance of side-arm connectivity for carbon dynamics of the River Danube, Austria

1. Side‐arms connected to the main stem of the river are key areas for biogeochemical cycling in fluvial landscapes, exhibiting high rates of carbon processing. 2. This work focused on quantifying autochthonous and allochthonous carbon pools and, thereby, on comparing transport and transformation processes in a restored side‐arm system of the River Danube (Regelsbrunn). We established a carbon budget and quantified carbon processing from March to September 2003. In addition, data from previous studies during 1997 to 1999 were assessed. 3. Gross primary production (GPP) and community respiration were estimated by diel oxygen time curves and an oxygen mass balance. Plankton primary production was determined to estimate its contribution to GPP under different hydrological conditions. 4. Based on the degree of connectivity, three hydrological phases were differentiated. Most of the organic matter, dominated by allochthonous carbon, was transported in the main channel and through the side‐arm during floods, while at intermediate and low flows (and thus connectivity), transformation processes became more important and autochthonous carbon dominated the carbon pool. The side‐arm system functioned as a sink for particulate matter [total suspended solids and particulate organic carbon (POC)] and a source of dissolved organic carbon (DOC) and chlorophyll‐a. 5. Autochthonous primary production of 4.2 t C day^?1 in the side‐arm was equivalent to about 20% of the allochthonous inputs of 20 t C day^?1 (POC and DOC) entering the area at mean flow (1% of the discharge of the main channel). Pelagic photosynthesis was generally high at mean flow (1.3–3.8 g C m^?2 day^?1), and contributed up to 90% of system productivity. During long stagnant periods at low discharge, the side‐arm was controlled by biological processes and a shift from planktonic to benthic activity occurred (benthic primary production of 0.4–14 g C m^?2 day^?1). 6. The transformation of the organic matter that passes through the side‐arm under different hydrological conditions, points to the importance of these subsystems in contributing autochthonous carbon to the food web of the main channel.     

Terrestrialization alters organic matter dynamics and habitat quality for freshwater mussels (Unionoida) in floodplain backwaters

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Spatial variability in Florida Bay particulate organic matter composition: combining flow cytometry with stable isotope analyses

Long-term management plans for restoration of natural flow conditions through the Everglades increase the importance of understanding potential nutrient impacts of increased freshwater delivery on Florida Bay biogeochemistry. Planktonic communities respond quickly to changes in water quality, thus spatial variability in community composition and relationships to nutrient parameters must be understood in order to evaluate future downstream impacts of modifications to Everglades hydrology. Here we present initial results combining flow cytometry analyses of phytoplankton and bacterial populations (0.1–50 μm size fraction) with measurements of δ¹³C and δ¹⁵N composition and dissolved inorganic nutrient concentrations to explore proxies for planktonic species assemblage compositions and nutrient cycling. Particulate organic material in the 0.1–50 μm size fraction was collected from five stations in Northeastern and Western Florida Bay to characterize spatial variability in species assemblage and stable isotopic composition. A dense bloom of the picocyanobacterium, Synechococcus elongatus, was observed at Western Florida Bay sites. Smaller Synechococcus sp. were present at Northeast sites in much lower abundance. Bacteria and detrital particles were also more abundant at Western Florida Bay stations than in the northeast region. The highest abundance of detritus occurred at Trout Creek, which receives freshwater discharge from the Everglades through Taylor Slough. In terms of nutrient availability and stable isotopic values, the S. elongatus population in the Western bay corresponded to low DIN (0.5 μM NH ₄ ⁺ ; 0.2 μM NO ₃ ⁻ ) concentrations and depleted δ¹⁵N signatures ranging from +0.3 to +0.8‰, suggesting that the bloom supported high productivity levels through N₂-fixation. δ¹⁵N values from the Northeast bay were more enriched (+2.0 to +3.0‰), characteristic of N-recycling. δ¹³C values were similar for all marine Florida Bay stations, ranging from −17.6 to −14.4‰, however were more depleted at the mangrove ecotone station (−25.5 to −22.3‰). The difference in the isotopic values reflects differences in carbon sources. These findings imply that variations in resource availability and nutrient sources exert significant control over planktonic community composition, which is reflected by stable isotopic signatures.     

Importance of soil organic matter for the diversity of microorganisms involved in the degradation of organic pollutants

Many organic pollutants are readily degradable by microorganisms in soil, but the importance of soil organic matter for their transformation by specific microbial taxa is unknown. In this study, sorption and microbial degradation of phenol and 2,4-dichlorophenol (DCP) were characterized in three soil variants, generated by different long-term fertilization regimes. Compared with a non-fertilized control (NIL), a mineral-fertilized NPK variant showed 19% and a farmyard manure treated FYM variant 46% more soil organic carbon (SOC). Phenol sorption declined with overall increasing SOC because of altered affinities to the clay fraction (soil particles <2 mm in diameter). In contrast, DCP sorption correlated positively with particulate soil organic matter (present in the soil particle fractions of 63–2000 μm). Stable isotope probing identified Rhodococcus, Arthrobacter (both Actinobacteria) and Cryptococcus (Basidiomycota) as the main degraders of phenol. Rhodococcus and Cryptococcus were not affected by SOC, but the participation of Arthrobacter declined in NPK and even more in FYM. ¹⁴C-DCP was hardly metabolized in the NIL variant, more efficiently in FYM and most in NPK. In NPK, Burkholderia was the main degrader and in FYM Variovorax. This study demonstrates a strong effect of SOC on the partitioning of organic pollutants to soil particle size fractions and indicates the profound consequences that this process could have for the diversity of bacteria involved in their degradation.     

Biogeochemistry of particulate organic matter transported by the Godavari River,India

The Godavari River, the third largest river of India,has been sampled for Particulate Inorganic and OrganicCarbon (PIC, POC), Particulate Nitrogen (PN), andParticulate Amino Acids (PAA, including 2 hexosamines(HA)). During the dry season Particulate OrganicMatter (POM) in the upper reaches is relatively freshand autochthonous, in the lower reaches it is degradedand inorganic suspended matter content is higher here.In the wet season (wet monsoon) heavy rains cause abasin-wide flushing of humus from entire catchmentarea consequently POM in the river is mainly degradedand allochthonous. Annual transport of the GodavariRiver amounts to 2.81 × 10 6 ton POC, 0.29 × 10 6ton PN and 0.10 × 10 6 tonParticulate Amino Acid Nitrogen. These amounts rank theGodavari River to one of the most important organic carbontransporting rivers in the world.     

Bacterial abundance and production in river sediments as related to the biochemical composition of particulate organic matter (POM)

The major proportion of heterotrophic activity in running waters islocalized on the solid surfaces of sediments in the benthic and hyporheic zoneand is dominated by microorganisms. However, this assertion is based on thestudies of small streams, and little is known about the microbial metabolism oforganic matter in river ecosystems. We therefore explored the relationshipsbetween bacterial abundance and production and the gradients of organic matterquality and quantity in sediments of a sixth-order lowland river (Spree,Germany). We found vertical gradients of detrital variables (particulateorganicmatter (POM), particulate organic carbon (POC), nitrogen (PN), and protein) andof bacterial variables (abundance, production, turnover time, and proportion ofbacterial carbon in total POC) in two different sediment types. These gradientswere steeper in stratified sediments than in the shifting sediments. Detritalvariables correlated strongly with bacterial abundance and production. The bestcorrelation was found for detrital variables indicating substrate quantity andquality (r_S = 0.90 for PN with abundance). Although bacterialbiomasscomprised only 0.7% of the POC (1.9% of PN, 3.4% of the protein) in sediments,the turnover of sedimentary organic carbon was fast (median = 62d), especially in the shifting sediments. Our findings demonstratethat sediment dynamics significantly foster organic carbon metabolism in riversystems. Thus, these sediments, which are typical for lowland rivers, stronglyinfluence the metabolism of the whole ecosystem.     

饶河枯水期主要鱼类营养级位置及其影响因素

稳定同位素技术已经越来越多地被用来研究淡水生态系统的结构与功能。利用氮稳定同位素技术测定了枯水季节饶河鱼类等消费者的营养级位置,比较上、中、下游及入湖口鱼类营养级的空间差异,并分析了影响饶河鱼类营养级位置的主要因素。研究结果表明,饶河鱼类的δ15N值范围为4.7‰—15.6‰,大部分鱼类的δ15N值集中在10‰—14‰之间,其中鄱阳湖间下鱵的δ15N值最大,为(15.6±1.6)‰;乔木湾鲫的δ15N值最小值,为(4.7±0.9)‰。根据δ15N值计算可知,饶河鱼类占有3—4个营养等级。75%的鱼类种类所占的营养级大于3,而营养级小于2的鱼类种类不到10%,可能与枯水期鱼类活动范围受限,种间捕食作用增强,肉食性或饥饿现象增加有关。另外,饶河鱼类的营养级也存在着空间差异,表现为鄱阳湖湖区和入湖口处的鱼类营养级比上、中、下游的鱼类营养级要大。该结果与颗粒有机物POM的δ15N值呈现一致的变化,反映了饶河鱼类的营养级位置主要受到食物来源的影响,与鱼类的个体大小无明显相关。     

Characterisation of the potamal Danube River and the Delta: connectivity determines indicative macrophyte assemblages

The complexity of water bodies in the eu-potamal river corridor and the main delta channels of the Romanian Danube is exemplified by the macrophyte vegetation. Two hypotheses provided the background for our study: (a) is the macrophyte vegetation of large, permanently connected branches significantly separated from that of the main river channel; (b) is the macrophyte composition of the Danube main stem significantly altered when the river divides into the three large navigable Delta channels. Water bodies considered were two contiguous sections of the main river channel, two large branches remaining from the historical floodplain, and the three main Delta channels. We quantified macrophyte diversity and floristic variation. Our data set was prepared from the MIDCC-project data base, in which macrophyte occurrence, abundance and habitat parameters are stored for contiguous survey units of the whole Danube river corridor. Field survey method followed that of Kohler and the European Standard EN14184. Results confirmed our first hypothesis: permanently connected side branches still support significantly different macrophyte assemblages, making them important indicators of floodplain connectivity. The diversion of the Danube into its three large navigable delta channels significantly alters the macrophyte vegetation from the c. 300 km of main stem up-river, substantially supporting our second hypothesis. Our results largely enhance the knowledge on aquatic plant biodiversity in the eu-potamal Danube, forming a solid base for long-term studies. We also discuss the relevance of our results regarding the ecological, as well as the conservational, quality of rivers and their floodplains.     

Allochthonous coarse particulate organic material in forest and pasture reaches of two south-eastern Australian streams

1. Terrestrial plant litter entering two forest and two pasture sites on upland streams in south-eastern Australia was measured over a 2-year period using traps suspended above the streams. Laterally transported terrestrial plant litter was also determined in one stream, but found to be only 10% of the total. 2. Litter accession to traps suspended above the stream was significantly lower at both forested sites than was litter fall in the adjacent riparian vegetation. 3. Litter input was high (600–700g DW m^?2yr^?1) and seasonal, with 30–50% of the annual total entering the stream during December—February (summer). However, seasonality was not as great as that recorded in Northern Hemisphere deciduous forest streams. 4. Leaves comprised the largest litter component, but represented a relatively smaller proportion of the litter than is usually the case in Northern Hemisphere deciduous forest streams; in contrast bark was a relatively large proportion of the litter. 5. At the sites flowing through pasture, litter accession was about two orders of magnitude lower than at the forested sites.     

Seasonal and diel relationships between the isotopic compositions of dissolved and particulate organic matter in freshwater ecosystems

A study of the isotopic composition of organic matter was conducted in a freshwater marsh over seasonal and diel time scales to determine the sources of dissolved organic matter (DOM) and the processes leading to its formation. Bulk C and N isotopic compositions of the bacterial fraction (0.2–0.7 m) and particulate organic matter (POM; 0.7–10 m) were compared on a seasonal basis with the change in ¹³C of DOM. The bulk isotopic data support the idea that DOM was, in part, derived from the breakdown of larger organic matter fractions. The bacterial fraction and POM were compositionally similar throughout the year, based on a comparison of the ¹³C of individual amino acids in each fraction. Annual variation in the ¹³C of amino acids in DOM was greater relative to the variation in larger fractions indicating that microbial reworking was an important factor determining the proteinaceous component of DOM. The ¹³C enrichment of serine and leucine in each organic matter fraction suggested microbial reworking was an important factor determining organic matter composition during the most productive times of year. Changes in the bulk ¹³C of DOM were more significant over daily, relative to seasonal, time scales where values ranged by 6 and followed changes in chlorophyll a concentrations. Although bulk ¹³C values for POM ranged only from –29 to –28 during the same diel period, the ¹³C of alanine in POM ranged from –30 to –22. Alanine is directly synthesized from pyruvate and is therefore a good metabolic indicator. The ¹³C of individual amino acids in DOM revealed the diel change in the importance of autotrophic versus heterotrophic activity in influencing DOM composition. Diel changes in the ¹³C of phenylalanine, synthesized by common pathways in phytoplankton and bacteria, were similar in both DOM and POM. The diel change in ¹³C of isoleucine and valine, synthesized through different pathways in phytoplankton and bacteria, were distinctly different in DOM versus POM. This disparity indicated a decoupling of the POM and DOM pools, which suggests a greater source of bacterial-derived organic matter at night. The results of this study demonstrate the use of the isotopic composition of individual amino acids in determining the importance of microbial reworking and autotrophic versus heterotrophic contributions to DOM over both diel and seasonal time scales.