Application of excitation emission matrix fluorescence monitoring in the assessment of spatial and seasonal drivers of dissolved organic matter composition: Sources and physical disturbance controls

The environmental dynamics of dissolved organic matter (DOM) were characterized for a shallow, subtropical, seagrass-dominated estuarine bay, namely Florida Bay, USA. Large spatial and seasonal variations in DOM quantity and quality were assessed using dissolved organic C (DOC) measurements and spectrophotometric properties including excitation emission matrix (EEM) fluorescence with parallel factor analysis (PARAFAC). Surface water samples were collected monthly for 2 years across the bay. DOM characteristics were statistically different across the bay, and the bay was spatially characterized into four basins based on chemical characteristics of DOM as determined by EEM-PARAFAC. Differences between zones were explained based on hydrology, geomorphology, and primary productivity of the local seagrass community. In addition, potential disturbance effects from a very active hurricane season were identified. Although the overall seasonal patterns of DOM variations were not significantly affected on a bay-wide scale by this disturbance, enhanced freshwater delivery and associated P and DOM inputs (both quantity and quality) were suggested as potential drivers for the appearance of algal blooms in high impact areas. The application of EEM-PARAFAC proved to be ideally suited for studies requiring high sample throughput methods to assess spatial and temporal ecological drivers and to determine disturbance-induced impacts in aquatic ecosystems.     

江汉平原高砷地下水中DOM三维荧光特征及其指示意义

水体中溶解性有机质(dissolved organic matter, DOM)是含水层中砷释放的主控因素之一.江汉平原河湖众多、沟渠广布,地表水体与浅层地下水的交互作用使得DOM的组分特征及其强度有显著差异.为查明江汉平原地下水中溶解性有机质在砷迁移转化过程中的作用,对江汉平原地表水和浅层地下水进行三维荧光光谱分析,使用平行因子分析法提取水体中有机质的分子组成、功能特点和荧光特征,并分析各组分相对含量与地下水中砷与铁的关联.江汉平原水体中DOM包括3种主要组分,组分C1、C2为类腐殖质,C2是生物降解过程中产生的小分子,C3为类蛋白物质.地下水DOM以类腐殖质组分C1、C2为主,地表水以类蛋白类物质C3和小分子腐殖质C2为主.高砷地下水中DOM以陆源为主,主要通过两种途径促进As的迁移转化:(1) DOM的腐殖质组分充当微生物群落的电子运输工具,促进微生物作用下的有机质氧化和铁氧化物的还原,并伴随As的释放及大量溶解性有机碳(dissolved organic carbon, DOC)和HCO₃-的产生;(2) As以铁等金属阳离子为桥接物与腐殖质结合,通过形成As-Fe-DOM络合物,导致地下水中砷的迁移.      

贵德盆地三河流域高砷地下水中溶解性有机物三维荧光特性及其指示意义

溶解性有机物(dissolved organic matter, DOM)可以通过多种方式控制含水层中砷的迁移转化。贵德盆地承压含水层地下水砷含量显著高于潜水含水层。为查明承压水中溶解性有机物对砷浓度的影响,对研究区地表水、潜水以及承压水进行吸光度和三维荧光光谱的分析,利用平行因子分析法确定了水样中有机物成分及荧光特征。结果表明,贵德盆地水体中DOM包含陆源类腐殖质(C1)、受人为影响的腐殖质(C2)、类醌化合物(C3)和微生物来源的腐殖质(C4)4种组分。陆源类腐殖质C1可在地下水中富集,占总有机质的40%~55%。相比于地下水,C2和C3则在地表水中占据较高的比例。高砷承压水中C2、C3所占比例高于低砷潜水。其中,C1可以通过络合作用促进溶解性砷浓度的提高,C3作为电子穿梭体可以促进含砷铁氧化物或氢氧化物的还原性溶解从而释放砷。微生物降解有机质生成的HCO-3可以与砷竞争吸附,促进砷的解吸附。此外,还原性溶解产生的Fe(II)与HCO-3形成FeCO3固定一部分的砷。该研究表明,地下水中的天然有机物通过络合作用和作为电子穿梭体促进铁氧化物还原导致地下水砷的富集,为分析黄河上游地区高砷地下水的成因提供理论依据。     

包气带土壤DOM三维荧光表征及对砷污染的指示意义

为了解包气带土壤DOM组成特征, 探索其对砷向地下水中迁移的影响, 对江汉平原高砷区土壤DOM进行了三维荧光光谱分析.结果表明DOM主要为类腐殖质成分, 芳香性官能团的减少导致荧光强度随包气带深度增加而变小, 局部深度荧光信号不规则变化指示非均质土壤剖面上DOM组分或主导官能团的变化.平行因子分析表明, DOM组分可更细致地分解为4种组分, 与微生物源的还原、氧化醌类和陆生的腐殖质富里酸类等相似.砷很可能在DOM腐殖质成分络合作用下与之随水体一起向下迁移, 砷的迁移也可能与微生物源的醌类作用过程有关.三维荧光光谱分析准确、快速地刻画了包气带土壤DOM的组分类别及空间变化特征, 初步揭示了DOM影响砷迁移的可能作用方式, 为进一步的地下水砷污染机制的研究提供了重要的参考信息.      

Groundwater’s significance to changing hydrology, water chemistry, and biological communities of a floodplain ecosystem, Everglades, South Florida, USA

The Everglades (Florida, USA) is one of the world’s larger subtropical peatlands with biological communities adapted to waters low in total dissolved solids and nutrients. Detecting how the pre-drainage hydrological system has been altered is crucial to preserving its functional attributes. However, reliable tools for hindcasting historic conditions in the Everglades are limited. A recent synthesis demonstrates that the proportion of surface-water inflows has increased relative to precipitation, accounting for 33% of total inputs compared with 18% historically. The largest new source of water is canal drainage from areas of former wetlands converted to agriculture. Interactions between groundwater and surface water have also increased, due to increasing vertical hydraulic gradients resulting from topographic and water-level alterations on the otherwise extremely flat landscape. Environmental solute tracer data were used to determine groundwater’s changing role, from a freshwater storage reservoir that sustained the Everglades ecosystem during dry periods to a reservoir of increasingly degraded water quality. Although some of this degradation is attributable to increased discharge of deep saline groundwater, other mineral sources such as fertilizer additives and peat oxidation have made a greater contribution to water-quality changes that are altering mineral-sensitive biological communities.     

Phosphorus and nitrogen inputs to Florida Bay: The importance of the everglades watershed

A large environmental restoration project designed to improve the hydrological conditions of the Florida Everglades and increase freshwater flow to Florida Bay is underway. Here we explore how changing freshwater inflow to the southern Everglades is likely to change the input of nutrients to Florida Bay. We calculated annual inputs of water, total phosphorus (TP), total nitrogen (TN), and dissolved inorganic nitrogen (DIN) to Everglades National Park (ENP) since the early 1980s. We also examined changes in these nutrient concentrations along transects through the wetland to Florida Bay and the Gulf of Mexico. We found that the interannual variability of the water discharge into ENP greatly exceeded the interannual variability of flow-weighted mean nutrient concentrations in this water. Nutrient inputs to ENP were largely determined by discharge volume. These inputs were high in TN and low in TP; for two ENP watersheds TN averaged 1.5 mg l^?1 (0.11 mM) and 0.9 mg l^?1 (0.06 mM) and TP averaged 15 μg l^?1 (0.47 μM) and 9 μg l^?1 (0.28 μM). Both TP and DIN that flowed into ENP wetlands were rapidly removed from the water. Over a 3-km section of Taylor Slough, TP decreased from a flow-weighted mean of 11.6 μg l^?1 (0.37 μM) (0.20 μM) and DIN decreased from 240 μg l^?1 (17μM) to 36 μ l^?1 (2.6 μM). In contrast, TN, which was generally 95% organic N, changed little as it passed through the wetland. This resulted in molar TN:TP ratios exceeding 400 in the wetland. Decreases in TN concentrations only occurred in areas with relatively high P availability, such as the wetlands to the north of ENP and in the mangrove streams of western ENP. Increasing freshwater flow to Florida Bay in an effort to restore the Everglades and Florida Bay ecosystems is thus not likely to increase P inputs from the freshwater Everglades but is likely to increase TN inputs. Based on a nutrient budget of Florida Bay, both N and P inputs from the Gulf of Mexico greatly exceed inputs from the Everglades, as well as inputs from the atmosphere and the Florida Keys. We estimate that the freshwater Everglades contribute <3% of all P inputs and <12% of all N inputs to the bay. Evaluating the effect of ecosystem restoration efforts on Florida Bay requires greater understanding of the interactions of the bay with the Gulf of Mexico and adjacent mangrove ecosystems.     

A Hydrological Budget (2002–2008) for a Large Subtropical Wetland Ecosystem Indicates Marine Groundwater Discharge Accompanies Diminished Freshwater Flow

Water budget parameters are estimated for Shark River Slough (SRS), the main drainage within Everglades National Park (ENP) from 2002 to 2008. Inputs to the water budget include surface water inflows and precipitation while outputs consist of evapotranspiration, discharge to the Gulf of Mexico and seepage losses due to municipal wellfield extraction. The daily change in volume of SRS is equated to the difference between input and outputs yielding a residual term consisting of component errors and net groundwater exchange. Results predict significant net groundwater discharge to the SRS peaking in June and positively correlated with surface water salinity at the mangrove ecotone, lagging by 1 month. Precipitation, the largest input to the SRS, is offset by ET (the largest output); thereby highlighting the importance of increasing fresh water inflows into ENP for maintaining conditions in terrestrial, estuarine, and marine ecosystems of South Florida.     

近岸沉积物再悬浮期间所释放溶解有机物的荧光特征

对采自厦门湾九龙江人海河口的4个沉积物样品进行了室内再悬浮模拟实验,利用荧光激发-发射矩阵光谱(EEMs)研究了再悬浮过程中从沉积物中释放出的有色溶解有机物(CDOM)的荧光特征,同时通过与相应站位沉积物间隙水和底层水的对比分析,探讨了河口近岸海域的沉积物再悬浮作用作为水体中溶解有机物来源之一的可能性.结果表明,对给定站位,CDOM相对荧光强度和溶解有机碳(DOC)含量分布变化非常一致,均为间隙水最高,再悬浮次之,底层水最低;站位之间,底层水和再悬浮水样中CDOM相对荧光强度随盐度的降低而增加,从海端向河端增加的趋势明显.EEMs分析表明,各样品中均存在类腐殖质荧光与类蛋白质荧光团,且模拟实验也表明再悬浮作用可释放类腐殖质与类蛋白质荧光物质到底层水中,表明底质再悬浮将是近岸水体中CDOM的一个重要来源.与相应的底层水相比,间隙水的荧光峰(如峰A/C)的位置发生红移.再悬浮样品中EEMs的荧光团同时表现出相应底层水和间隙水的特征,但是荧光峰(峰A和峰C)的最大激发和发射波长更接近底层水中相应荧光团,与间隙水相比,则发生谱峰位置的蓝移.近海端样品中荧光峰M明显,随着盐度的降低,底层水和再悬浮水样的γ(M/C)值逐渐降低,且海源的峰M由海端向河端逐渐消失,表明峰M属于海洋自生来源.本研究区域DOM的荧光指数在1.61～1.93之间,表明近海端样品DOM主要为生物来源,而近河端样品DOM主要为陆源输入,或者为陆源与生物活动共同作用的结果.     

Using Optical Properties to Quantify Fringe Mangrove Inputs to the Dissolved Organic Matter (DOM) Pool in a Subtropical Estuary

Dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) optical properties were analyzed along two estuarine river transects during the wet and dry seasons to better understand DOM dynamics and quantify mangrove inputs. A tidal study was performed to assess the impacts of tidal pumping on DOM transport. DOM in the estuaries showed non-conservative mixing indicative of mangrove-derived inputs. Similarly, fluorescence data suggest that some terrestrial humic-like components showed non-conservative behavior. An Everglades freshwater-derived fluorescent component, which is associated with soil inputs from the Northern Everglades, behaved conservatively. During the dry season, a protein-like component behaved conservatively until the mid-salinity range when non-conservative behavior due to degradation and/or loss was observed. The tidal study data suggests mangrove porewater inputs to the rivers following low tide. The differences in quantity of DOM exported by the Shark and Harney Rivers imply that geomorphology and tidal hydrology may be a dominant factor controlling the amount of DOM exported from the mangrove ecotone, where up to 21 % of the DOC is mangrove-derived. Additionally, nutrient concentrations and other temporal factors may control DOM export from the mangroves, particularly for the microbially derived fluorescent components, contributing to the seasonal differences. The wet and dry season fluxes of mangrove DOM from the Shark River is estimated as 0.27?×?10⁹ mg C d^?1 and 0.075?×?10⁹ mg C d^?1, respectively, and the Harney River is estimated as 1.9?×?10⁹ mg C d^?1 and 0.20?×?10⁹ mg C d^?1.     

Projected Reorganization of Florida Bay Seagrass Communities in Response to the Increased Freshwater Inflow of Everglades Restoration

Historic changes in water-use management in the Florida Everglades have caused the quantity of freshwater inflow to Florida Bay to decline by approximately 60% while altering its timing and spatial distribution. Two consequences have been (1) increased salinity throughout the bay, including occurrences of hypersalinity, coupled with a decrease in salinity variability, and (2) change in benthic habitat structure. Restoration goals have been proposed to return the salinity climates (salinity and its variability) of Florida Bay to more estuarine conditions through changes in upstream water management, thereby returning seagrass species cover to a more historic state. To assess the potential for meeting those goals, we used two modeling approaches and long-term monitoring data. First, we applied the hydrological mass balance model FATHOM to predict salinity climate changes in sub-basins throughout the bay in response to a broad range of freshwater inflow from the Everglades. Second, because seagrass species exhibit different sensitivities to salinity climates, we used the FATHOM-modeled salinity climates as input to a statistical discriminant function model that associates eight seagrass community types with water quality variables including salinity, salinity variability, total organic carbon, total phosphorus, nitrate, and ammonium, as well as sediment depth and light reaching the benthos. Salinity climates in the western sub-basins bordering the Gulf of Mexico were insensitive to even the largest (5-fold) modeled increases in freshwater inflow. However, the north, northeastern, and eastern sub-basins were highly sensitive to freshwater inflow and responded to comparatively small increases with decreased salinity and increased salinity variability. The discriminant function model predicted increased occurrences of Halodule wrightii communities and decreased occurrences of Thalassia testudinum communities in response to the more estuarine salinity climates. The shift in community composition represents a return to the historically observed state and suggests that restoration goals for Florida Bay can be achieved through restoration of freshwater inflow from the Everglades.     

The American Crocodile in Florida Bay

The American crocodile was declared endangered in the United States in 1975. At that time 75% of the remaining crocodile nests were in Everglades National Park, in Florida Bay. In 1980, the National Park Service established a crocodile sanctuary in northeastern Florida Bay to protect nesting and nursery habitat. In 1985, a monitoring program, focused on nesting, growth, and survival, was established to evaluate the effects of modified water deliveries on crocodiles in Florida Bay. The number and range of crocodile nests increased between 1970 and 1995, but nesting success decreased slightly. Nests on artificial substrates in the Greater Flamingo-Cape Sable area accounted for most of the increase in nests. Nests on artificial substrates were more prone to predation by raccoons. At least 1.5% of marked hatchlings survived for more than 12 mo, and growth rates were variable. Detailed information on growth and survival of crocodiles is still lacking. It is no longer a question of whether crocodiles with survive in Florida Bay, but how ecosystem restoration and management can be applied to improve conditions for crocodiles.     

Source Identification of Florida Bay's Methylmercury Problem: Mainland Runoff Versus Atmospheric Deposition and <Emphasis Type="Italic">In situ</Emphasis> Production

The first advisory to limit consumption of Florida Bay fish due to mercury was issued in 1995. Studies done by others in the late 1990s found elevated water column concentrations of both total Hg (THg) and methylmercury (MeHg) in creeks discharging from the Everglades, which had its own recognized mercury problem. To investigate the significance of allochthonous MeHg discharging from the upstream freshwater Everglades, we collected surface water and sediment along two transects from 2000 to 2002. Concentrations of THg and MeHg, ranging from 0.36 ng THg/L to 5.98 ng THg/L and from <0.02 ng MeHg/L to 1.79 ng MeHg/L, were elevated in the mangrove transition zone when compared both to upstream canals and the open waters of Florida Bay. Sediment concentrations ranged from 5.8 ng THg/g to 145.6 ng THg/g and from 0.05 ng MeHg/g to 5.4 ng MeHg/g, with MeHg as a percentage of THg occasionally elevated in the open bay. Methylation assays indicated that sediments from Florida Bay have the potential to methylate Hg. Assessment of mass loading suggests that canals delivering stormwater from the northern Everglades are not as large a source as direct atmospheric deposition and in situ methylation, especially within the mangrove transition zone.     

The Distribution and Seasonal Variation of Dissolved Trace Metals in Florida Bay and Adjacent Waters

Florida Bay is a shallow carbonate estuary in South Florida. It receives fresh waters from the Everglades that contribute a number of metals to the Bay. The Bay is the largest estuary in Florida with nearly pristine conditions. In this paper we report the first extensive studies of trace metals in the Bay. The seasonal distributions of trace metals (Sc, V, Cr, Co, Cu, Fe, Pb, Mn, Ni and Al) were determined on surface waters in Florida Bay and adjacent waters. The measurements in the Bay were made from May 2000 to May 2001, and the adjacent waters were sampled in September 2000 and May 2002. Most of the dissolved trace metals exhibited their maximum concentrations in summer, except Al and Pb that did not show any seasonal variability. The seasonal variations of the metals are related to the influx of fresh water from rainfall. The lowest concentrations are found during the dry season in the winter and the highest during the wet season in the summer. Several metals (V, Mn, Al, Sc, Fe, Co, Ni and Cr) exhibited their highest concentrations in the western zone of the Bay. These waters from agricultural areas are influenced by Gulf of Mexico waters, which carry metals coming from Barron, Broad and Shark rivers into the Bay. The Shark River always exhibited high concentrations of V, Mn, Al, Sc, Co and Cr. Other possible influences in the western and north-central zone of the Bay are from Flamingo Center, the creeks of Taylor Slough and the mangrove fringe of the Everglades. High concentrations of Al, Co, Ni, Cr, Cu, Fe, and Pb were detected in the eastern zone. The high values found in the northeast are influenced by Taylor Slough runoff and in the southeast by Key Largo, Tavernier Marina and the drainage from the main highway (US1) on Tavernier Key. The minimum concentrations for most of the metals were found in areas near the Key channels that exchange waters between Florida Bay and the Atlantic Ocean (Gulf Stream). The adjacent waters in the Atlantic side including the Gulf Stream waters showed very low concentrations for all the metals studied except for V. In the Bay correlations of V were found: (1) V with salinity and Al and (2) Sc with Si. Most of the other metals did not show any strong correlations with nutrients or salinity. Florida Bay is thus not a typical estuary due to the unique structure of its mud banks and multiple inputs of metals from the mangrove fringe in the north.     

Environmental Controls on Groundwater Chemistry in an Offshore Island Aquifer: Fiesta Key, Florida

A field study was undertaken on the Florida Bay side of Fiesta Key, Florida, to identify the chemical characteristics of a previously unexplored offshore groundwater system and to define the critical parameters affecting groundwater movement and interaction with sediment pore fluids and bedrock. Emphasis was placed on the upper 2 meters of bedrock, where groundwater recharge and discharge potentials are maximized, along a 100 meter transect extending from the island margin. Bedrock cores were used to describe Pleistocene depositional textures, and were sampled at discrete depths to determine the extent of water-rock interaction. Piezometers installed into each core hole were used to monitor surface and ground water tide levels, and for the systematic collection of water samples for a large suite of chemical determinations.Aqueous chemical data indicate that these groundwaters are marine in origin, anoxic, and moderately hypersaline (S = 36–40). Exchange of bedrock pore fluids with overlying Bay waters is restricted by a layer of Holocene sediment and a discontinuous soilstone crust formed at the modern bedrock surface. Groundwater chemistry near the sediment/bedrock interface is marked by elevated concentrations of total alkalinity and Ca2+, and by significant Mg2+ depletion. These waters likely acquired their unusual chemistry by mixing between deeper groundwaters and overlying, early diagenetically altered, sediment porewaters. High alkalinity and calcium concentrations presumably result from the combination of the effects of aerobic metabolism, carbonate dissolution, and sulfate reduction. Mg-depletion most likely resulted from the precipitation of Mg-calcite. These unusual chemistries disappear by 2 m depth in the groundwater system, where Ca2+ and Mg2+ concentrations are similar to those expected for seawater under slightly hypersaline conditions.The Pleistocene bedrock contains low Mg, Sr, F, and P concentrations relative to the overlying unconsolidated Holocene carbonate sediments. This is consistent with the diagenetic recrystallization processes that the bedrock has undergone. Hydraulic conditions favor the net recharge of Florida Bay seawater to the groundwater system, but there are insufficient tide data to identify cyclical water exchange rates or groundwater flow patterns.     

Nutrient Mass Flux between Florida Bay and the Florida Keys National Marine Sanctuary

There is a net discharge of water and nutrients through Long Key Channel from Florida Bay to the Florida Keys National Marine Sanctuary (FKNMS). There has been speculation that this water and its constituents may be contributing to the loss of coral cover on the Florida Keys Reef tract over the past few decades, as well as speculation that changes in freshwater flow in the upstream Everglades ecosystem associated with the Comprehensive Everglades Restoration Plan may exacerbate this phenomenon. The results of this study indicate that although there is a net export of approximately 3,850 (±404) ton N year^?1 and 63 (±7) ton P year^?1, the concentrations of these nutrients flowing out of Florida Bay are the same as those flowing in. This implies that no significant nutrient enrichment is occurring in the waters of the FKNMS in the vicinity of Long Key Channel. Because of the effect of restricted southwestward water flow through Florida Bay by shallow banks and small islands, the volume of relatively high-nutrient water from central and eastern portions of the bay exiting through the channel is small compared to the average tidal exchange. Nutrient loading of relatively enriched bay waters is mediated by tidal exchange and mixing with more ambient concentrations of the western Florida Bay and Hawk Channel. System-wide budgets indicate that the contribution of Florida Bay waters to the inorganic nitrogen pool of the Keys coral reef is small relative to offshore inputs.     

Molecular formulae of marine and terrigenous dissolved organic matter detected by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

The chemical structure of refractory marine dissolved organic matter (DOM) is still largely unknown. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS) was used to resolve the complex mixtures of DOM and provide valuable information on elemental compositions on a molecular scale. We characterized and compared DOM from two sharply contrasting aquatic environments, algal-derived DOM from the Weddell Sea (Antarctica) and terrigenous DOM from pore water of a tropical mangrove area in northern Brazil. Several thousand molecular formulas in the mass range of 300-600 Da were identified and reproduced in element ratio plots. On the basis of molecular elemental composition and double-bond equivalents (DBE) we calculated an average composition for marine DOM. O/C ratios in the marine samples were lower (0.36 ± 0.01) than in the mangrove pore-water sample (0.42). A small proportion of chemical formulas with higher molecular mass in the marine samples were characterized by very low O/C and H/C ratios probably reflecting amphiphilic properties. The average number of unsaturations in the marine samples was surprisingly high (DBE = 9.9; mangrove pore water: DBE = 9.4) most likely due to a significant contribution of carbonyl carbon. There was no significant difference in elemental composition between surface and deep-water DOM in the Weddell Sea. Although there were some molecules with unique marine elemental composition, there was a conspicuous degree of similarity between the terrigenous and algal-derived end members. Approximately one third of the molecular formulas were present in all marine as well as in the mangrove samples. We infer that different forms of microbial degradation ultimately lead to similar structural features that are intrinsically refractory, independent of the source of the organic matter and the environmental conditions where degradation took place.     

Occurrence and distribution of sulfur in peat-forming environments of southern Florida

Cores and surface samples of peats from the Everglades—Mangrove region of Southern Florida were analyzed for total sulfur and pyritic sulfur. These values were compared with the petrographic-botanical components of the peats as determined from point-counts of oriented microtome sections. Pyrite occurs as individual euhedral crystals, loosely packed framboids, and lenses or crusts of minute crystals. Framboids and minute crystals are often associated with organic matter and sometimes with bacteria and fungi. Pyrite tends to selectively occur in void spaces in or between peat tissues. In samples containing very small amounts of pyrite, framboidal pyrite is the prevalent form.Marine to brackish peats contain the highest pyrite and total sulfur contents, with brackish peats generally containing more pyrite than marine peats. Pyrite tends to be lower in all peats within 30 cm of the surface, whether marine or brackish.Burial of freshwater peats beneath marine or brackish peats tends to increase the total sulfur and pyritic sulfur in the underlying peats. Burial beneath brackish-water, clay-rich deposits (such as splays) tends to increase total sulfur and pyritic sulfur in the underlying deposits more than burial beneath less clay-rich deposits.     

Dissolved organic matter tracers reveal contrasting characteristics across high arsenic aquifers in Cambodia:A fluorescence spectroscopy study

Organic matter in the environment is involved in many biogeochemical processes,including the mobilization of geogenic trace elements,such as arsenic,into groundwater.In this paper we present the use of fluorescence spectroscopy to characterize the dissolved organic matter(DOM)pool in heavily arsenicaffected groundwaters in Kandal Province,Cambodia.The fluorescence DOM(fDOM)characteristics between contrasting field areas of differing dominant lithologies were compared and linked to other hydrogeochemical parameters,including arsenic and dissolved methane as well as selected sedimentary characteristics.Absorbance-corrected fluorescence indices were used to characterize depth profiles and compare field areas.Groundwater fDOM was generally dominated by terrestrial humic and fulvic-like components,with relatively small contributions from microbially-derived,tryptophan-like components.Groundwater fDOM from sand-dominated sequences typically contained lower tryptophan-like,lower fulvic-like and lower humic-like components,was less bioavailable,and had higher humification index than clay-dominated sequences.Methane concentrations were strongly correlated with fDOM bioavailability as well as with tryptophan-like components,suggesting that groundwater methane in these arsenic-prone aquifers is likely of biogenic origin.A comparison of fDOM tracers with sedimentary OM tracers is consistent with the hypothesis that external,surface-derived contributions to the aqueous DOM pool are an important control on groundwater hydrogeochemistry.     

Spatial Variation in the Optical Properties of Dissolved Organic Matter (DOM) in Lakes on the Canadian Precambrian Shield and Links to Watershed Characteristics

In the present study, we explored the use of various optical parameters to detect differences in the composition of the dissolved organic matter (DOM) in a set of lakes that are all located on the Canadian Precambrian Shield, but within which Cu and Ni speciation predictions were previously shown to diverge from measured values in some lakes but not in others. Water samples were collected with in situ diffusion samplers in 2007 (N = 18 lakes) and 2008 (N = 8 lakes). Significant differences in DOM quality were identified between the sampling regions (Rouyn-Noranda, Québec and Sudbury, Ontario) and among lakes, based on dissolved organic carbon concentrations ([DOC]), specific UV absorbance (SUVA₂₅₄), fluorescence indices (FI), and excitation–emission matrix (EEM) fluorescence measurements. Parallel factor analysis (PARAFAC) of the EEM spectra revealed four components, two of which (C3, oxidized quinone fluorophore of allochthonous origin, and C4, tryptophan-like protein fluorescence of autochthonous origin) showed the greatest inter-regional variation. The inter-lake differences in DOM quality were consistent with the regional watershed characteristics as determined from satellite imagery (e.g., watershed-to-lake surface area ratios and relative percentages of surface water, rock outcrops vegetative cover and urban development). Source apportionment plots, built upon PARAFAC components ratios calculated for our lakes, were used to discriminate among DOM sources and to compare them to sources identified in the literature. These results have implications for other areas of research, such as quantifying lake-to-lake variations in the influence of organic matter on the speciation of trace elements in natural aquatic environments.     

卤水中溶解性有机质的光谱学性质和光降解行为研究

卤水中溶解性有机质(dissolved organic matter,DOM)会对盐田日晒工艺和产品质量产生不利影响,如盐田卤水的蒸发速率减缓、蒸发度减小以及提取的矿物产品带有刺鼻的气味、浓重的颜色等。因此,对具有资源开发利用价值的卤水体系中DOM结构和性质的研究可以为后续DOM的有效去除或在DOM共存体系中调控无机盐结晶工艺路线提供有效的指导意见。本文以自然界中广泛存在的两种不同类型的卤水体系,即盐湖卤水DOM(SLDOM)和油田卤水DOM(OFDOM)为研究对象,采用溶解性有机碳(dissolved organic carbon,DOC)分析、光谱学分析和平行因子分析等手段对DOM的含量、分子量分布特征、光谱学结构和光降解行为开展了研究。DOC和荧光分析表明SLDOM和OFDOM的DOC含量和生物指数(BIX)值相似;与OFDOM相比,SLDOM的腐质化指数(HIX)值和高分子量组分(HMW)比例偏高;特别吸收光谱(SUVA₂₅₄)和糖类化合物含量检测结果表明,SLDOM和OFDOM的HMW组分中含有的芳香类和糖类化合物所占比例比低分子量组分(LMW)高;三维荧光谱图分析(EEM)结果表明,SLDOM主要以腐殖质类物质为主,而OFDOM以蛋白质类组分为主。此外,DOM的荧光组分在不同分子量中的分布也存在明显差异:对于SLDOM,富里酸主要分布在HMW DOM中,而腐殖酸主要在LMW DOM中;对于OFDOM,芳香胺类蛋白组分主要分布在HMW DOM中,色氨酸和酪氨酸类蛋白组分主要分布在LMM DOM中。在光降解实验中,SLDOM和OFDOM的DOC含量随光照时间增加而逐渐减少,分别下降了29.32%和15.11%。进一步的分析表明,光照过程中两种卤水中糖类化合物均减少,小分子量的DOM优先分解。此外,在光照过程中SLDOM芳香类化合物增加,腐质化程度基本不变;OFDOM芳香类化合物减少,腐质化程度增加。EEM平行因子分析(PARAFAC)结果表明,SLDOM荧光组分在光降解过程中荧光强度增加,而OFDOM荧光强度减少。