不同来源有色溶解性有机物光化学/微生物降解过程

城市非点源污染向水生生态系统中输入大量的溶解有机物(DOM),对生态系统健康产生重要影响.有色可溶性有机物(CDOM)是广泛分布于自然水体中的一类成分和结构复杂、含有多种高活性化学官能团的大分子聚合物,是DOM的重要组分,对水生生态系统健康、能量流动及生物地球化学循环有重要影响.光化学反应和微生物代谢过程被认为是控制水体CDOM转化、降解和循环的主要影响因素.然而,对城市化如何影响CDOM组成以及光化学和微生物如何相互作用影响城市水体CDOM动态的理解是不足的.因此,为评估光化学过程和微生物代谢对不同城市水体CDOM降解与转化的贡献,解析不同城市水体CDOM光化学/微生物降解作用机理,本研究在英国伯明翰选择3类具有典型DOM来源的水体样本,通过实验室9 d受控培养实验,对比分析光化学以及微生物影响下CDOM来源和组成的变化.结果表明:(1)城市河流由于接受上游污水排放及较短的水力滞留时间,含有丰富的芳香性碳,其CDOM光化学活性明显高于湖泊,光化学降解率为16.60%;(2)城市湖泊CDOM受人类活动影响,自生源类荧光成分富集,生物活性高,在微生物培养过程中CDOM增加了62.16%,...     

Long-term chemical effects of petroleum in south Louisiana wetlands—I. Organic carbon in sediments and waters

The chemical effects of chronic petroleum input into a shallow water marsh were examined by measuring hydrocarbon levels and dissolved organic carbon content of sediments associated with two active oil fields in south Louisiana. Annual levels of total organic carbon in the surface waters of the oil fields were higher by 1 mg C/l. in the salt marsh and 5 mg C/l. in the fresh marsh than the respective controlsites. Average dissolved organic carbon concentrations in the interstitial waters of cores taken within the oil field environments were 105% higher than the control in the salt marsh and 43% higher than the control in the fresh marsh. Significantly lower ratios of C₁₇ to pristane occurred in both oil field sediments; however, average odd-even predominance values were not indicative of petroleum contaminated sediments. The results indicate that microbial processes are responsible for dissolution of petroleum into dissolved organic carbon and that dissolved organic carbon concentrations may be a more significant measure of chronic petroleum input than hydrocarbon distribution.     

Leaching and microbial degradation of dissolved organic matter from salt marsh plants and seagrasses

Dissolved organic matter (DOM) is outwelled from highly productive salt marshes, but its sources and fates are unclear. To examine common salt marsh plants as sources of coastal DOM, two dominant salt marsh vascular plants Spartina alterniflora and Juncus roemarianus, and two major coastal seagrasses Syringodium filiforme and Halodule wrightii, were collected from a Florida salt marsh and studied using laboratory incubation experiments. We investigated the leaching dynamics of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), and chromophoric dissolved organic matter (CDOM) from these plants, in conjunction with our field investigations of the sources and outwelling of DOM from Florida salt marshes. The leaching of DOM and CDOM from the plants was a rapid process, and leaching rates were 65–288 µM/g dry weight/day for DOC and 3.8–16 µM/g dry weight/day for TDN from different plants in the bacteria-inhibited incubations. DOC was proportional to TDN in the leachates, but the quantity of C and N leached was dependent on the species and growth stage of the plants. At the end of the 25-day experiments, 5.4–23 % and 10–45 % of solid phase C and N were released into DOC and TDN pools, respectively. Bacteria played an important role during the leaching process. The majority of DOC and TDN leached from marsh plants and seagrasses was labile and highly biodegradable with 56–90 % of the leached DOC and 44–72 % of the leached TDN being decomposed at the end of the experiments. The fluorescence measurements of CDOM indicate that organic matter leached from marsh plants and seagrasses contained mainly protein-like DOM which was degraded rapidly by bacteria. Our study suggests that leaching of DOM from salt marsh plants and seagrasses provide not only major sources of DOC, TDN, and CDOM that affect many biogeochemical processes, but also as important food sources to microbial communities in the marsh and adjacent coastal waters.     

Distributions and characteristics of dissolved organic matter in temperate coastal waters (Southern North Sea)

The spatial and temporal distributions of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC) was studied in the East-Frisian Wadden Sea (Southern North Sea) during several cruises between 2002 and 2005. The spatial distribution of CDOM in the German Bight shows a strong gradient towards the coast. Tidal and seasonal variations of dissolved organic matter (DOM) identify freshwater discharge via flood-gates at the coastline and pore water efflux from tidal flat sediments as the most important CDOM sources within the backbarrier area of the Island of Spiekeroog. However, the amount and pattern of CDOM and DOC is strongly affected by various parameters, e.g. changes in the amount of terrestrial run-off, precipitation, evaporation, biological activity and photooxidation. A decoupling of CDOM and DOC, especially during periods of pronounced biological activity (algae blooms and microbial activity), is observed in spring and especially in summer. Mixing of the endmembers freshwater, pore water, and open sea water results in the formation of a coastal transition zone. Whilst an almost conservative behaviour during mixing is observed in winter, summer data point towards non-conservative mixing.     

太湖沿岸水体CDOM吸收光谱特性

有色可溶性有机物(CDOM)吸收光谱特性研究对于水色定量遥感反演具有重要作用.通过2007年6月10日至6月18日太湖沿岸68个CDOM吸收光谱曲线和水质参数实测数据,分析了CDOM吸收光谱曲线特征以及ag(440)、Sg值及其相关关系等,结果表明:太湖沿岸水体CDOM吸收光谱曲线表现为两种类型,贡湖湾CDOM吸收系数明显高于太湖其他沿岸水域,ag(440)最高值即出现在贡湖湾;同时,梅梁湾、贡湖湾、镇湖湾、光富湾等ag(440)高于沿岸水体平均值,而南部3个湖湾皆低于平均值.另外,贡湖湾Sg值较小,且与ag(440)呈现出较好的关系;而沿岸其它水体Sg值与ag(440)虽然呈现负相关,但关系不明显.这对于了解太湖水体CDOM特件以及定量反演有一定的意义和作用.     

Sensitivity analysis of CDOM spectral slope in artificial and natural samples: an application in the central eastern Mediterranean Basin

In the past two decades, optical properties of chromophoric dissolved organic matter (CDOM) in marine environments have been extensively studied. Many of these studies report CDOM properties for the offshore environment where this complex mixture of optically active compounds is strongly diluted. Nevertheless, autochthonous and allochthonous sources have been identified and sinks related to photodegradation and bacterial activity have been demonstrated. The calculation of the spectral slope of the CDOM absorption curve has been proven to be useful and is often reported. However, a rigorous uncertainty analysis of the slope calculation is rarely reported. In this paper, we propose a method to evaluate the uncertainty of CDOM spectral slope calculated between 270 and 400 nm, using both naturally sampled and artificial solutions. We use these results to study the ultra-oligotrophic waters of the Mediterranean Sea (central eastern basin), where little is known about CDOM spatial distribution. We show that dilutions of both artificial and natural samples produce a Gaussian distribution of spectral slopes, indicating that consistent values may be determined, with a typical uncertainty of ±0.0004 nm⁻¹ when absorption at 300 nm was greater then 0.1 m⁻¹ (0.1 m pathlength). Comparing the distribution of spectral slopes from central eastern basin samples to a Gaussian distribution, we show differences between measurements that were significantly different. These values allow us to distinguish possible sources (algal derived CDOM), sinks (e.g. photo-bleaching) at different depths. We propose a subdivision of CDOM compounds into refractory and semilabile/refractory pools and evaluate the CDOM spectral slope of algal derived CDOM released at or near deep chlorophyll maximum.     

Minimal incorporation of Deepwater Horizon oil by estuarine filter feeders

Natural abundance carbon isotope analyses are sensitive tracers for fates and use of oil in aquatic environments. Use of oil carbon in estuarine food webs should lead to isotope values approaching those of oil itself, −27‰ for stable carbon isotopes reflecting oil origins and −1000‰ for carbon-14 reflecting oil age. To test for transfer of oil from the 2010 Deepwater Horizon spill into estuarine food webs, filter-feeding barnacles (Balanus sp.) and marsh mussels (Geukensia demissa) were collected from Louisiana estuaries near the site of the oil spill. Carbon-14 analyses of these animals from open waters and oiled marshes showed that oil use was <1% and near detection limits estimated at 0.3% oil incorporation. Respiration studies showed no evidence for enhanced microbial activity in bay waters. Results are consistent with low dietary impacts of oil for filter feeders and little overall impact on respiration in the productive Louisiana estuarine systems.     

A study of fecal coliform sources at a coastal site using colored dissolved organic matter (CDOM) as a water source tracer

Optical properties of colored dissolved organic matter (CDOM) were measured as a tracer of polluted waters in a Southern California surf-zone with consistently high levels of fecal indicator bacteria. Salinity, temperature, fecal coliform, absorbance (200-700nm) and fluorescence (lambda(excitation)=350nm; lambda(emission)=360-650nm) were measured in the creek and surf-zone during a dry and rain event. Fluorescence to absorption ratios for CDOM were used to distinguish water masses, with two distinct CDOM end-members identified as creek (flu/abs=8.7+/-0.8x10(4)) and coastal (flu/abs=2.2+/-0.3x10(4)). Waters containing the same CDOM end-member had highly variable bacterial levels during the dry event, suggesting intermittent sources of bacteria added to a uniform water source, consistent with marine birds. During the rain event, increased levels of the creek end-member and bacteria indicated a second bacteria source from runoff.     

Effects of crab burrows on pore water flows in salt marshes

Macro-pores such as crab burrows are found commonly distributed in salt marsh sediments. Their disturbance on the soil structure is likely to influence both pore water flows and solute transport in salt marshes; however, the effects of crab burrows are not well understood. Here, a three-dimensional model simulated tidally driven pore water flows subject to the influence of crab burrows in a marsh system. The model, based on Richards’ equation, considered variably saturated flow in the marsh with a two-layer soil configuration, as observed at the Chongming Dongtan wetland (Shanghai, China). The simulation results showed that crab burrows distributed in the upper low-permeability soil layer, acting as preferential flow paths, affected pore water flows in the marsh particularly when the contrast of hydraulic conductivity between the lower high-permeability soil layer and the overlying low-permeability soils was high. The burrows were found to increase the volume of tidally driven water exchange between the marsh soil and the tidal creek. The simulations also showed improvement of soil aeration conditions in the presence of crab burrows. These effects may lead to increased productivity of the marsh ecosystem and enhancement of its material exchange with coastal waters.     

Distribution,characteristics and potential impacts of chromophoric dissolved organic matter (CDOM) in Hudson Strait and Hudson Bay,Canada

The characteristics of chromophoric dissolved organic matter (CDOM) were studied in Hudson Bay and Hudson Strait in the Canadian Arctic. Hudson Bay receives a disproportionately large influx of river runoff. With high dissolved organic matter (DOM) concentrations in Arctic rivers the influence of CDOM on coastal and ocean systems can be significant, yet the distribution, characteristics and potential consequences of CDOM in these waters remain unknown. We collected 470 discrete water samples in offshore, coastal, estuarine and river waters in the region during September and October 2005. Mixing of CDOM appeared conservative with salinity, although regional differences exist due to variable DOM composition in the rivers discharging to the Bay and the presence of sea-ice melt, which has low CDOM concentrations and low salinity. There were higher concentrations of CDOM in Hudson Bay, especially in coastal waters with salinities <28$<28$, due to river runoff. Using CDOM composition of water masses as a tracer for the freshwater components revealed that river runoff is largely constrained to nearshore waters in Hudson Bay, while sea-ice melt is distributed more evenly in the Bay. Strong inshore–offshore gradients in the bio-optical properties of the surface waters in the Hudson Bay cause large variation in penetration of ultraviolet radiation and the photic depth within the bay, potentially controlling the vertical distribution of biomass and occurrence of deep chlorophyll maxima which are prevalent only in the more transparent offshore waters of the bay. The CDOM distribution and associated photoprocesses may influence the thermodynamics and stratification of the coastal waters, through trapping of radiant heating within the top few meters of the water column. Photoproduction of biologically labile substrates from CDOM could potentially stimulate the growth of biomass in Hudson Bay coastal waters. Further studies are needed to investigate the importance of terrestrial DOM in the Hudson Bay region, and the impact of hydroelectric development and climate change on these processes.     

洱海沉积物有色可溶性有机物(CDOM)三维荧光空间分布特性及指示意义

采用荧光光谱区域体积积分法定量研究洱海沉积物有色可溶性有机物（CDOM）三维荧光空间分布特性,结果表明,洱海沉积物CDOM中类腐殖酸组分占比最高（44.5%~74.2%）,其次为溶解性微生物代谢产物（10.7%~20.4%）和类富里酸物质（8.19%~19.7%）,而类蛋白组分占比最低,类腐殖酸占比与H/C和N/C均呈显著负相关;南部湖心平台区域沉积物类富里酸和类蛋白组分占比较高,其CDOM自生源占比较高;北部水生植物分布区溶解性微生物代谢产物占比较高,CDOM陆源性较强;中部深水区及南北湖湾区域类腐殖酸占比较高,随水深增加沉积物CDOM自生源特征增强.随沉积物深度增加类腐殖酸和溶解性微生物代谢产物占比呈下降趋势,类富里酸占比呈上升趋势,CDOM自生源特征增强,脂肪化程度增高.随湖泊富营养化程度增加沉积物CDOM受微生物代谢产物影响增强,陆源性增加,而自生源性降低,湖泊沉积物CDOM具有富营养化指示意义.     

Diel cycles of hydrogen peroxide in marine bathing waters in Southern California, USA: In situ surf zone measurements

Hydrogen peroxide is photochemically produced in natural waters. It has been implicated in the oxidative-induced mortality of fecal indicator bacteria (FIB), a microbial water quality measure. To assess levels and cycling of peroxide in beach waters monitored for FIB, diel studies were carried out in surf zone waters in July 2009 at Crystal Cove State Beach, Southern California, USA. Maximum concentrations of 160–200 nM were obtained within 1 h of solar noon. Levels dropped at night to 20–40 nM, consistent with photochemical production from sunlight. Day-time production and night-time dark loss rates averaged 16 ± 3 nM h⁻¹ and 12 ± 4 nM h⁻¹ respectively. Apparent quantum yields averaged 0.07 ± 0.02. Production was largely dominated by sunlight, with some dependence on chromophoric dissolved organic matter (CDOM) levels in waters with high absorption coefficients. Peroxide levels measured here are sufficient to cause oxidative-stress-induced mortality of bacteria, affect FIB diel cycling and impact microbial water quality in marine bathing waters.     

Distribution and photoreactivity of chromophoric dissolved organic matter in northern Gulf of Mexico shelf waters

The distribution and photoreactivity of chromophoric dissolved organic matter (CDOM) in the northern Gulf of Mexico along the Louisiana coastal shelf were examined during three cruises in summer 2007, fall 2007, and summer 2008. The influence of the Mississippi River plume was clearly evident as CDOM levels (defined as a₃₀₅) and dissolved organic carbon (DOC) concentrations were well-correlated with salinity during all cruises. Elevated CDOM and CDOM:DOC ratios of surface samples collected offshore of Atchafalaya Bay and the Breton-Chandeleur Sound complex indicated emanations of organic-rich waters from coastal wetlands are also an important source to nearshore shelf waters. Generally, CDOM and DOC levels were highest in surface waters and decreased with depth, but during summer 2007 and summer 2008, CDOM levels in near-bottom samples were occasionally higher than at mid-depths without concomitant increases in DOC. CDOM photobleaching was measured during 24 irradiations using a SunTest XLS+ solar simulator with photobleaching rate coefficients (k₃₀₅) ranging from 0.011 to 0.32 h⁻¹. For fall 2007 and summer 2008, higher k₃₀₅ values were generally observed in samples with higher initial CDOM levels. However, samples collected during summer 2007 did not exhibit a similar pattern nor were there differences in photobleaching rates between surface and bottom samples. Spectral slope coefficients (S_275-295 or S_350-400) and DOC levels were largely unchanged after 24 h irradiations. Modeled CDOM photobleaching for northern Gulf of Mexico mid-shelf waters predicts that during the summer when solar irradiance is high and the water column becomes stratified, nearly 90% of the CDOM in the upper 1 m may be lost to photobleaching, with losses up to 20% possible even at 10 m depth.     

氧化还原条件对红枫湖沉积物磷释放影响的微尺度分析

选取贵州红枫湖为研究对象,在实验室条件下模拟了自然、好氧和厌氧条件下沉积物内源磷的释放过程,联合应用微电极技术和沉积物磷形态分析对沉积物—水界面开展了微尺度观测与研究.结果表明,厌氧条件下红枫湖沉积物总磷含量显著降低,且主要是NaOH提取态磷(NaOH-P)和残渣态磷(rest-P)含量降低所致,厌氧条件下沉积物孔隙水中磷酸盐浓度明显升高,而好氧条件下沉积物孔隙水磷酸盐浓度显著降低,反映厌氧条件显著促进了红枫湖沉积物磷释放.厌氧条件下沉积物内部溶解氧浓度下降、硫还原活动增强可能是导致NaOH-P释放的主要原因.O_2浓度的降低加速了沉积物还原作用并产生大量H2S,进而与二价铁离子形成硫化亚铁沉淀,最终导致NaOH-P(Fe-P)释放到孔隙水中.好氧条件向厌氧条件的转换可通过改变沉积物内部pH值分布和微生物活动促使rest-P释放:厌氧条件下,厌氧微生物不仅可以消耗硫酸根产生H_2S,导致pH值降低,还可消耗有机质,将有机磷转变为无机磷.上述研究结果表明,沉积物—水界面氧化还原环境可影响沉积物氧渗透深度、pH值分布、微生物活动、硫循环以及有机质降解过程,进而控制沉积物磷的形态转化与释放.联合应用微电极技术和沉积物磷形态分析对湖泊沉积物—水界面开展微尺度观测研究是揭示沉积物内源磷释放机制与控制因素的有效途径.     

Changes in the spectral and chemical properties of a water mass passing through extensive macrophyte beds in a large fluvial lake (Lake Saint-Pierre, Québec, Canada)

Large fluvial lakes, as part of river corridors, are recognized as spatially heterogeneous ecosystems. Due to their shallowness, the littoral zone of these lakes occupies a large proportion of their surface and is extensively covered by macrophytes that are known to affect their physical, chemical and biological environments in various ways. This study documents the small-scale (5 km) bio-optical variations associated with the longitudinal passage of a water mass through macrophyte beds during their maximal growth season. The utilization of a 2D hydrodynamic model allowed us to establish hydrological connectivity between stations within the beds, and thus to identify longitudinal heterogeneity along the macrophyte beds. Significant changes in the inherent properties of the water were observed along the upstream-downstream gradient. Due to their effects on hydrodynamics, macrophytes were responsible for a decrease in particles and dissolved organic carbon (DOC) resulting in an increasing penetration depth of ultraviolet (UV) and photosynthetically active radiation (PAR). Along the transect, chromophoric dissolved organic matter (CDOM) decreased more rapidly than DOC resulting in a decrease of the CDOM to DOC ratio. The observed changes in the DOC pool may be explained by the constant input of non-chromophoric DOC from macrophyte leachates and exudation within the bed and/or the photochemical and microbial degradation of CDOM. The implication of such small-scale heterogeneity on Lake Saint-Pierre productivity is discussed.     

Hydroclimatic controls on dissolved organic matter (DOM) characteristics and implications for trace metal transport in Hwangryong River Watershed,Korea, during a summer monsoon period

Frequent heavy rainfalls during the East Asian summer monsoon drastically increase water flow and chemical loadings to surface waters. A solid understanding of hydroclimatic controls on watershed biogeochemical processes is crucial for water quality control during the monsoon period. We investigated spatio‐temporal variations in the concentrations and spectroscopic properties of dissolved organic matter (DOM) and the concentrations of trace metals in Hwangryong River, Korea, during a summer period from the relatively dry month of June through the following months with heavy rainfall. DOM and its spectroscopic properties differed spatially along the river, and also depended on storm and flow characteristics around each sampling time. At a headwater stream draining a forested watershed, the concentrations (measured as dissolved organic carbon (DOC)), aromaticity (measured as specific UV absorbance at 254 nm), and fulvic acid‐ and protein‐like fluorescence of DOM were higher in stormflow than in baseflow waters. DOC concentrations and fluorescence intensities increased along the downstream rural and urban sites, in which DOC and fluorescence were not higher in stormflow waters, except for the ‘first flush’ at the urban site. The response of DOM in reservoir waters to monsoon rainfalls differed from that of stream and river waters, as illustrated by storm‐induced increases in DOM aromaticity and fulvic‐like fluorescence, and no significant changes in protein‐like fluorescence. The results suggest that surface water DOM and its spectroscopic properties differentially respond to changes in hydroclimatic conditions, depending on watershed characteristics and the influence of anthropogenic organic matter loadings. DOC concentrations and intensities of spectroscopic parameters were positively correlated with some of the measured trace metals (As, Co, and Fe). Further research will be needed to obtain a better understanding of climate effects on the interaction between DOM and trace metals. Copyright © 2006 John Wiley & Sons, Ltd.