Drinking water lakes are threatened globally and therefore in need of protection. To date, few studies have been carried out to investigate how the composition and dynamics of chromophoric dissolved ...organic matter (CDOM) in drinking water lakes are influenced by inflow rate. Such CDOM can lead to unpleasant taste and odor of the water and produce undesirable disinfection byproducts during drinking water treatment. We studied the drinking water Lake Qiandao, China, and found that the concentrations of suspended particulate matter (SPM) in the lake increased significantly with inflow rate (p < 0.001). Similarly, close relationships between inflow rate and the CDOM absorption coefficient at 350 nm a(350) and with terrestrial humic-like fluorescence C3 and a negative relationship between inflow rate and the first principal component (PC1) scores, which, in turn, were negatively related to the concentrations and relative molecular size of CDOM (p < 0.001), i.e. the concentration and molecular size of CDOM entering the lake increased proportionately with inflow rate. Furthermore, stable isotopes (δD and δ18O) were depleted in the upstream river mouth relative to downstream remaining lake regions, substantiating that riverine CDOM entering the lake was probably driven by inflow rate. This was further underpinned by remarkably higher mean chlorophyll-a and in situ measured terrestrial CDOM fluorescence (365/480 nm) and apparent oxygen utilization (AOU), and notably lower mean PC1 and CDOM spectral slope (S275–295) recorded in the upstream river mouth than in the downstream main lake area. Strong negative correlations between inflow rate and a(250):a(365), S275–295, and the spectral slope ratio (SR) implied that CDOM input to the lake in rainy period was dominated by larger organic molecules with a more humic-like character. Rainy period, especially rainstorm events, therefore poses a risk to drinking water safety and requires higher removal efficiency of CDOM during drinking water treatment processes.
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•Both the composition and dynamics of CDOM in Lake Qiandao were driven by inflow rate.•Concentrations of CDOM and humic-like materials increased with increasing inflow rate.•Relative molecular size of CDOM in Lake Qiandao increased with increasing inflow rate.•CDOM in the lake has a more humic-like character in rainy periods than in dry periods.
This review covers historical perspectives, the role of plant inputs, and the nature and dynamics of soil organic matter (SOM), often known as humus. Information on turnover of organic matter ...components, the role of microbial products, and modeling of SOM, and tracer research should help us to anticipate what future research may answer today's challenges. Our globe's most important natural resource is best studied relative to its chemistry, dynamics, matrix interactions, and microbial transformations. Humus has similar, worldwide characteristics, but varies with abiotic controls, soil type, vegetation inputs and composition, and the soil biota. It contains carbohydrates, proteins, lipids, phenol-aromatics, protein-derived and cyclic nitrogenous compounds, and some still unknown compounds. Protection of transformed plant residues and microbial products occurs through spatial inaccessibility-resource availability, aggregation of mineral and organic constituents, and interactions with sesquioxides, cations, silts, and clays. Tracers that became available in the mid-20th century made the study of SOM dynamics possible. Carbon dating identified resistant, often mineral-associated, materials to be thousands of years old, especially at depth in the profile. The 13C associated with C3C4 plant switches characterized slow turnover pools with ages ranging from dozens to hundreds of years. Added tracers, in conjunction with compound-specific product analysis and incubation, identified active pools with fast turnover rates. Physical fractionations of the intra- and inter-aggregate materials, and those associated with silt and clay, showed that all pools contain both old and young materials. Charcoal is old but not inert. The C:N ratio changes from 25 to 70:1 for plant residues to 6 to 9:1 for soil biota and microbial products associated with soil minerals. Active, slow and passive (resistant) pool concepts have been well used in biogeochemical models. The concepts discussed herein have implications for today's challenges in nutrient cycling, biogeochemistry, soil ecosystem functioning, pollution control, feeding the expanding global population and global change.
•The early literature on 13C14C can guide future advances in soil organic matter.•Plant residues are transformed by soil biota and stabilized by the soil matrix.•Humus consists mostly of carbohydrates, N compounds, polyphenols and complex lipids.•Humus ranges in age in the profile from hours to millennia.•Modeling organizes information, test concepts and extrapolates to global scales.
Natural organic matter (NOM) is a complex mixture of biogenic molecules resulting from the deposition and transformation of plant and animal matter. It has long been recognized that NOM plays an ...important role in many geological, geochemical, and environmental processes. Of particular concern is the fate of NOM in response to a warming climate in environments that have historically sequestered carbon (e.g., peatlands and swamps) but may transition to net carbon emitters. In this review, we will highlight developments in the application of high‐field Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) in identifying the individual components of complex NOM mixtures, focusing primarily on the fraction that is dissolved in natural waters (dissolved organic matter or DOM). We will first provide some historical perspective on developments in FTICR technology that made molecular‐level characterizations of DOM possible. A variety of applications of the technique will then be described, followed by our view of the future of high‐field FTICR MS in carbon cycling research, including a particularly exciting metabolomic approach.
•Maize-based organic amendments were examined after seven years of annual application.•All organic amendments increased SOM in bulk soil and all physical fractions.•Biochar exerted the strongest ...positive effect on SOC contents and thermal stability.•The majority of the accumulated C and N occurred in the silt + clay fractions.
Application of organic amendments and N fertilizer can affect C and N sequestration, however, the degree to which diverse organic amendments and optimal N fertilization for matching demand for high crop productivity contributes to soil organic matter (SOM) of Cambisol in the North China Plain is not fully known. The objective was to evaluate the combined effects of annual maize straw-derived organic amendments (straw, manure, compost, biogas residue, or biochar) and in-season mineral N fertilizer amendment on soil organic carbon (SOC) and total N (TN) accumulation and thermal stability in bulk soils and physically isolated soil aggregate fractions in a long-term field experiment on the North China Plain. Application of organic amendments either alone or with N increased the proportion of macroaggregates (+62 to 137 %), aggregate mean weight diameter (+50 to 106 %), SOC (+38 to 206 %) and TN (+13 to 52 %) contents in bulk soil. The organic amendments and N fertilizer additions also increased SOC and TN contents in each of the isolated fractions: macroaggregates (+119 to 851 % for SOC, +109 to 237 % for TN) and microaggregates (+42 to 192 % for SOC and +30 to 145 % for TN), total fine particulate organic matter (T fPOM, +143 to 891 % for T fPOM-SOC, +129 to 549 % for T fPOM-TN) and total silt + clay within aggregates (53–139 % for SOC and 20–106 % for TN). Biochar resulted in the largest increase in SOC contents and improved soil aggregation without N fertilization, but fertilization greatly decreased these responses. The majority of the accumulated C and N occurred in the total silt + clay fractions, making up 50–90 % of total SOC and 79–96 % of total TN. Total fine POM and total silt + clay within aggregates contributed to 40–78 % and 10–56 % of SOC, 28–60 % and 37–71 % of TN increase between soil with and without organic amendments. Our results suggested that C and N retained in T fPOM and silt + clay fractions within aggregates were important mechanisms for C and N stabilization. Substitution of annual above-ground litter with biochar with or without mineral N fertilizer was the most effective way for SOM build up and stabilization under a wheat/maize system in the North China Plain, while manure, compost and biogas residue resulted in little to no increases of SOM in bulk soils and physically isolated aggregate fractions compared to straw amendment. Besides the effects of each amendment type on SOC, the different recovery rates of the various amendments, which determines the total quantity of each amendment that can be produced, should be taken into consideration in decisions about maize residue management at the regional scale in the North China Plain.
Most of Earth's terrestrial surface is made up of sloping landscapes. The lateral distribution of topsoil by erosion controls the availability, stock, and persistence of essential elements in the ...terrestrial ecosystem. Over the last two decades, the role of soil erosion in biogeochemical cycling of essential elements has gained considerable interest from the climate, global change, and biogeochemistry communities after soil erosion and terrestrial sedimentation were found to induce a previously unaccounted terrestrial sink for atmospheric carbon dioxide. More recent studies have highlighted the role of erosion in the persistence of organic matter in soil and in the biogeochemical cycling of elements beyond carbon
.
Here we synthesize available knowledge and data on how erosion serves as a major driver of biogeochemical cycling of essential elements. We address implications of erosion-driven changes in biogeochemical cycles on the availability of essential elements for primary production, on the magnitude of elemental exports downstream, and on the exchange of greenhouse gases from the terrestrial ecosystem to the atmosphere. Furthermore, we explore fates of eroded material and how terrestrial mass movement events play major roles in modifying Earth's climate.
Photochemical transformation of natural organic matter in aquatic environments strongly impacts the environmental behaviors of carbon, nutrients, and pollutants by affecting their solubility, ...toxicity, bioavailability, and mobility. However, the role of particulate organic matter (POM) in environmental photogeochemistry has received much less attention than that of dissolved organic matter (DOM). In this study, a systematic overview was conducted to summarize the photodissolution and photoflocculation of POM in aquatic systems. The photodissolution of various POM, such as resuspended sediments and algal detritus, could be a potential and important source of DOM in the overlying waters, and these photoreleased DOM were dominated by humic-like components. The photogeochemistry of POM is thought to proceed via direct photochemical reactions and reactive radical-dominated indirect processes. Photodissolution can modify the bioavailability of organic matter and influence the biogeochemical cycling of nutrients, heavy metals, and organic pollutants. In addition, the photo-induced flocculation of DOM to POM could also influence the transport and transformation of organic matter and its associated pollutants. The photochemistry of POM can be significantly influenced by several environmental factors, including irradiation wavelength and intensity, organic matter properties, and radical oxygen species. POM photogeochemistry is one of the most important components of the global cycling of natural organic matter. Further studies regarding photogeochemistry should be conducted to overcome the potential problems arising from the concurrent photodegradation of organic matter and to further develop more filed investigations and analytical methods.
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•The photogeochemistry of POM in aquatic systems was systematically overviewed.•The POM photogeochemistry plays an important role in global cycling of organic matter.•Environmental dynamics of pollutants could be affected by POM photogeochemistry.•Photodissolution increases OM bioavailability, while photoflocculation decreases it.
We present a framework for assessing biogeochemical recovery of terrestrial ecosystems from disturbance. We identify three recovery phases. In Phase 1, nitrogen is redistributed from soil organic ...matter to vegetation, but the ecosystem continues to lose nitrogen because the recovering vegetation cannot take up nitrogen as fast as it is released from soil. In Phase 2, the ecosystem begins re-accumulating nitrogen and converges on a quasi-steady state in which vegetation and soil-microbial processes are in balance. In Phase 3, vegetation and soil-microbial processes remain in balance and the ecosystem slowly re-accumulates the remaining nitrogen. Phase 3 follows a balanced-accumulation trajectory along a continuum of quasi-steady states that approaches the true steady state asymptotically. We examine the effects of three ecosystem properties on recovery: openness of the nitrogen cycle, nitrogen distribution in and turnover between vegetation and soils, and the proportion of nitrogen losses that are in a refractory form. Openness exacerbates Phase 1 nitrogen losses but speeds recovery in Phases 2 and 3. A high fraction of ecosystem nitrogen in vegetation, resulting from nitrogen turnover that is slow in vegetation but fast in soil, exacerbates Phase 1 nitrogen losses but speeds recovery in Phases 2 and 3. A high proportion of nitrogen loss in refractory form mitigates Phase 1 nitrogen losses and speeds recovery in Phases 2 and 3. Application of our conceptual framework requires empirical recognition of the continuum of quasi-steady states constituting the balanced-accumulation trajectory and a distinction between the balanced-accumulation trajectory and the true steady state.
Effects of global warming on soil organic carbon (C) can be investigated by comparing sites experiencing different temperatures. However, observations can be affected by covariance of temperature ...with other environmental properties. Here, we studied a thermal gradient in forest soils derived from volcanic materials on Mount Taranaki (New Zealand) to disentangle the effects of temperature and reactive minerals on soil organic C quantity and composition. We collected soils at four depths and four elevations with mean annual temperatures ranging from 7.3 to 10.5 °C. Soil C stocks were not significantly different across sites (average 162 MgC ha
−1
to 85 cm depth,
P
> .05). Neither aluminium (Al)-complexed C, nor mineral-associated C changed significantly (
P
> .05) with temperature. The molecular characterisation of soil organic matter showed that plant-derived C declined with increasing temperature, while microbial-processed C increased. Accompanying these changes, soil short-range order (SRO) constituents (including allophane) generally increased with temperature. Results from structural equation modelling revealed that, although a warmer temperature tended to accelerate soil organic C decomposition as inferred from molecular fingerprints, it also exerted a positive effect on soil total C presumably by enhancing plant C input. Despite a close linkage between mineral-associated C and soil organic C, the increased abundance of reactive minerals at 30–85 cm depth with temperature did not increase soil organic C concentration at that depth. We therefore propose that fresh C inputs, rather than reactive minerals, mediate soil C responses to temperature across the thermal gradient of volcanic soils under humid-temperate climatic conditions.
Permafrost soils in the northern hemisphere are known to harbor large amounts of soil organic matter (SOM). Global climate warming endangers this stable soil organic carbon (SOC) pool by triggering ...permafrost thaw and deepening the active layer, while at the same time progressing soil formation. But depending, e.g., on ice content or drainage, conditions in the degraded permafrost can range from water-saturated/anoxic to dry/oxic, with concomitant shifts in SOM stabilizing mechanisms. In this field study in Interior Alaska, we investigated two sites featuring degraded permafrost, one water-saturated and the other well-drained, alongside a third site with intact permafrost. Soil aggregate- and density fractions highlighted that permafrost thaw promoted macroaggregate formation, amplified by the incorporation of particulate organic matter, in topsoils of both degradation sites, thus potentially counteracting a decrease in topsoil SOC induced by the permafrost thawing. However, the subsoils were found to store notably less SOC than the intact permafrost in all fractions of both degradation sites. Our investigations revealed up to net 75% smaller SOC storage in the upper 100 cm of degraded permafrost soils as compared to the intact one, predominantly related to the subsoils, while differences between soils of wet and dry degraded landscapes were minor. This study provides evidence that the consideration of different permafrost degradation landscapes and the employment of soil fractionation techniques is a useful combination to investigate soil development and SOM stabilization processes in this sensitive ecosystem.
Aquatic dissolved organic matter (DOM) plays an essential role in biogeochemical cycling and transport of organic matter throughout the hydrological continuum. To characterise microbially-derived ...organic matter (OM) from common environmental microorganisms (Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa), excitation-emission matrix (EEM) fluorescence spectroscopy was employed. This work shows that bacterial organisms can produce fluorescent organic matter (FOM) in situ and, furthermore, that the production of FOM differs at a bacterial species level. This production can be attributed to structural biological compounds, specific functional proteins (e.g. pyoverdine production by P. aeruginosa), and/or metabolic by-products. Bacterial growth curve data demonstrates that the production of FOM is fundamentally related to microbial metabolism. For example, the majority of Peak T fluorescence (> 75%) is shown to be intracellular in origin, as a result of the building of proteins for growth and metabolism. This underpins the use of Peak T as a measure of microbial activity, as opposed to bacterial enumeration as has been previously suggested. This study shows that different bacterial species produce a range of FOM that has historically been attributed to high molecular weight allochthonous material or the degradation of terrestrial FOM. We provide definitive evidence that, in fact, it can be produced by microbes within a model system (autochthonous), providing new insights into the possible origin of allochthonous and autochthonous organic material present in aquatic systems.
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•Peak T fluorescence is a proxy for microbial activity rather than enumeration.•Peak T is mainly intracellular material but does exist as extracellular FDOM.•FOM associated with high molecular weight compounds can be autochthonous in origin.•A range of FOM peaks are derived from both allochthonous and autochthonous sources.•Extracellular microbial FDOM is a key source of organic matter in aquatic systems.
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