Laodong Guo

University of Wisconsin–Milwaukee | UWM · School of Freshwater Sciences

There exists increasing evidence supporting the important role of black carbon in global carbon cycles. Particulate black carbon (PBC) is allochthonous and has distinct reactivities compared to the bulk particulate organic carbon (tot-POC) in marine environments. However, the abundance, geochemical behavior of PBC and its importance in oceanic carb...

Dissolved organic matter (DOM) in the ocean, as one of the largest pools of reduced carbon on Earth, plays an important role in the global carbon cycle, yet its chemical structure remains largely unknown. Here we show that high molecular weight DOM (HMW-DOM) contains approximately 10% bonded water (H2O) by weight. The bonded H2O molecules are an in...

Biogenic silica (biogenic Si) is a bioactive component crucial for the biogeochemical cycling of Si in terrestrial and aquatic ecosystems. Its formation and dissolution dynamics are intricately linked to carbon (C) cycling. However, knowledge about the source, composition, and factors controlling the distribution of biogenic Si in coastal wetland s...

Coastal wetlands play a vital role in carbon (C) sequestration, named ‘blue carbon’. The review aims to disentangle the processes and influencing factors, including elevated atmospheric CO2, global climate warming, sea level rise and anthropogenic activities. Firstly, we provided an overview of C processes, including input, output, and deposition,...

Coastal wetlands are key players in mitigating global climate change by sequestering soil organic matter. Soil organic matter consists of less stable particulate organic matter (POM) and more stable mineral-associated organic matter (MAOM). The distribution and drivers of MAOM and POM in coastal wetlands have received little attention, despite the...

Land use change in wetlands leads to significant losses of soil organic matter (SOM). Stable carbon (C) and nitrogen (N) isotopes offer insights into changes in C3/C4 vegetation, SOM sources, and decomposition processes. Yet, predicting the spatial-temporal dynamics of SOM contents and isotopes under land use changes remains challenging. This study...

Paddy fields serve as significant reservoirs of soil organic carbon (SOC) and their potential for terrestrial carbon (C) sequestration is closely associated with changes in SOC pools. However, there has been a dearth of comprehensive studies quantifying changes in SOC pools following extended periods of rice cultivation across a broad geographical...

Aims Silicon (Si) is an essential element for siliceous organisms, including macrophytes, phytoplankton, and diatoms. Coastal wetlands are critical for bridging the river-estuary-ocean continuum to drive the biogeochemical Si cycles. However, it remains unclear about the contents and distribution patterns of bioavailable Si in soils under various s...

As productive and essential ecosystems, coastal wetlands have experienced increased environmental impacts such as saltwater intrusion and eutrophication, resulting in significant shifts in microbially mediated ecosystem functions, such as carbon sequestration and nutrient transformations. The soil microbial respiration, a primary process in the tra...

Variations in molecular weight distributions of dissolved organic matter (DOM) and PARAFAC-derived fluorescent components were investigated along a transect in the seasonally hypereutrophic lower Fox River-Green Bay using the one-sample PARAFAC approach coupling flow field-flow fractionation for size-separation with fluorescence excitation-emission...

Dissolved organic matter (DOM) is closely linked to human activities in drainage basins and plays a crucial role in maintaining ecosystem functioning and reflecting environmental quality. However, the impacts of climate and anthropogenic-induced changes on DOM in riverine systems under increasingly warming conditions still need to be better underst...

Aims Natural stable isotope compositions of carbon (δ¹³C) and nitrogen (δ¹⁵N) can reveal biogeochemical mechanisms that control ecosystem carbon (C) and nitrogen (N) processes. However, little is known about the latitudinal patterns and controlling mechanisms for soil δ¹³C and δ¹⁵N in coastal wetlands based on a large spatial scale. Methods A tota...

Humic acid (HA) and reference natural organic matter (NOM) have been widely used in environmental assessment, biogeochemistry, and ecotoxicity studies. Nevertheless, similarities and differences among the commonly used model/reference NOMs and bulk dissolved organic matter (DOM) have rarely been systematically evaluated. In this study, HA, SNOM (Su...

The occurrence of microplastics (MPs) in aquatic environments has been a global concern because they are toxic and persistent and may serve as a vector for many legacies and emerging pollutants. MPs are discharged to aquatic environments from different sources, especially from wastewater plants (WWPs), causing severe impacts on aquatic organisms. T...

As a major plant‐derived soil organic carbon (SOC) component, lignin phenols are unique biomarkers that reflect biogeochemical characteristics under different vegetation compositions and climatic zones in coastal wetlands. However, the latitudinal patterns of plant‐derived lignin phenols to SOC and their link with the stability and controlling mech...

The complexation of metals with dissolved organic matter (DOM) under different compositions and molecular weights (MWs) will result in different environmental fate and toxicity, but the specific role and impact of DOM MWs remain less well understood. This study explored the metal binding characteristics by DOM with different MWs from different sour...

This study examined the physical and biogeochemical processes that determine the spatial and summer/winter distributions of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) in the Taiwan Strait (TS). The hydrological conditions in the TS varied between early summer and winter because of differences in terrestrial inpu...

As one of the largest reduced carbon pools on earth, it is critical to understand the chemical structures and lability of dissolved organic matter (DOM) in aquatic environments. To achieve a comprehensive view of its composition and reactivity, DOM from both riverine and coastal waters were concurrently extracted via both ultrafiltration and modifi...

Phytoliths are silica biomineralization products within plants and have been considered as a promising material to sequester carbon (C). However, there is considerable uncertainty and controversy regarding the C content in phytoliths due to the lack of detailed information on variation of C under different extraction procedures. Herein, we establis...

Climate change is an existential threat to the vast global permafrost domain. The diverse human cultures, ecological communities, and biogeochemical cycles of this tenth of the planet depend on the persistence of frozen conditions. The complexity, immensity, and remoteness of permafrost ecosystems make it difficult to grasp how quickly things are c...

Soil organic carbon (SOC) in coastal wetlands, also known as ‘blue C’, is an essential component of the global C cycles. To gain a detailed insight into blue C storage and controlling factors, we studied 142 sites across ca. 5000 km of coastal wetlands, covering temperate, subtropical and tropical climates in China. The wetlands represented 6 veget...

Time series water samples were collected monthly between November 2016 and June 2019 from the Lower Changjiang (Yangtze) River at the Xuliujing station, representing the end-member freshwater exported to the ocean, in addition to monthly samples from November 2019 to January 2020 during an extreme drought event. Concentrations of dissolved (DOC) an...

Black carbon (BC) is believed to be refractory and thus affects the timescale of organic carbon conversion into CO2 and the magnitude of the sink of CO2. However, the fate of BC in the oceans remains poorly understood. Here, ²¹⁰Po and ²¹⁰Pb were measured to examine the export of soot in the northeastern South China Sea (SCS). Concentrations of soot...

The major risk of microplastics in marine environments is the bioaccumulation in marine organisms. Plastic ingestion by marine organisms has been investigated and recently more attention has been given to microplastics in seafood. However, it is seldom reported the occurrence of microplastics in marine commercial dried fish products available for h...

Large world rivers and their dissolved organic matter (DOM) fluxes could regulate ecosystem function and biogeochemical processes in coastal marine environments. Knowledge about the seasonal variations in composition and molecular size of DOM remains scarce but is important to a better understanding of the role of river fluxes. Monthly time‐series...

s Understanding of the binding characteristics of wetland dissolved organic matter (DOM) and different metals is important for the quantitative assessment of the environmental behavior of metals in wetlands. In this study, different types of spectroscopy including ultraviolet-visible absorption, Fourier transform infrared, and fluorescence spectros...

Rivers play an important role in global water and carbon cycling, but there are still large uncertainties concerning evaporation and aquatic photosynthesis. Here we combined measurements of water chemistry, isotopic compositions (i.e., Dw, 18Ow, 13CDIC and 14CDIC) and geographic characteristics (i.e., river width) to elucidate in-stream hydrolo...

Arctic rivers are sensitive to climate and environmental change, but the biogeochemical response remains poorly understood. Monthly size‐fractionated dissolved organic matter (DOM) samples from the lower Yukon River were characterized using UV–visible, fluorescence, and Fourier transform‐infrared (FT‐IR) spectroscopy techniques. The EEM‐PARAFAC ana...

Alkaline phosphatase plays an important role in regulating nutrient dynamics and algal blooms in aquatic environments, but the causal relationship between alkaline phosphatase (AP), nutrient status, and chemical speciation of phosphorus (P) in the water column remains elusive. A year-long time series (weekly to biweekly) sampling was conducted to i...

Phosphorus (P) loadings to the Great Lakes have been regulated for decades, but re-eutrophication and seasonal hypoxia have recently been increasingly reported. It is of paramount importance to better understand the fate, transformation, and biogeochemical cycling processes of different P species across the river-lake interface. We report here resu...

Coastal wetlands are among the most productive ecosystems and store large amounts of organic carbon (C) – the so termed “blue carbon”. However, wetlands in the tropics and subtropics have been invaded by smooth cordgrass (Spartina alterniflora) affecting storage of blue C. To understand how S. alterniflora affects SOC stocks, sources, stability, an...

Streams and rivers are critical components of Arctic watersheds, functioning as corridors for the movement of water, carbon, and other solutes from headwater streams to larger rivers, estuaries, and the Arctic Ocean. Recent climate change in the Arctic has altered stream and river discharge, temperature, and biogeochemical processes. In this chapte...

During the 29th Chinese National Antarctic Research Expedition, spatial variations in nitrogen isotopic composition of particulate nitrogen (δ15NPN) and their controlling factors were examined in detail with regard to nitrate drawdown by phytoplankton and particulate nitrogen (PN) remineralization in the Prydz Bay and its adjacent areas. To better...

Despite increasing recognition of the critical role of coastal wetlands in mitigating climate change, sea-level rise and salinity increase, soil organic carbon (SOC) sequestration mechanisms in estuarine wetlands remain poorly understood. Here, we present new results on the source, decomposition and storage of SOC in estuarine wetlands with four ve...

Despite increasing recognition of the critical role of coastal wetlands in mitigating climate change, sea-level rise and salinity increase, soil organic carbon (SOC) sequestration mechanisms in estuarine wetlands remain poorly understood. Here, we present new results on the source, decomposition and storage of SOC in estuarine wetlands with four ve...

Despite increasing recognition of the critical role of coastal wetlands in mitigating climate change, sea‐level rise and salinity increase, soil organic carbon (SOC) sequestration mechanisms in estuarine wetlands remain poorly understood. Here, we present new results on the source, decomposition and storage of SOC in estuarine wetlands with four ve...

Multiple isotope systematics incorporating paired carbon isotopes (δ¹³C and ∆¹⁴C), strontium isotopes (⁸⁷Sr/⁸⁶Sr) and water isotopes (δ²H and δ¹⁸O) are used to investigate the coherent relationships among flow paths, chemical weathering regimes, and Sr export fluxes from the Lower Mississippi River. Monthly water samples were collected at a site ne...

Dissolved organic matter (DOM) is one of the key carbon substrates transported by rivers from land to sea, yet only a small fraction of it has been characterized at the molecular level. Here we characterize high molecular weight DOM (HMW-DOM, >1 kDa) isolated by ultrafiltration from nine North American rivers using thermal slicing ramped pyrolysis...

Silicon (Si) is one of the most abundant elements in the Earth’s crust but its role in governing the biogeochemical cycling of other elements remains poor understood. There is a paucity of information on the role of Si in wetland plants, and how this may alter wetland C production and storage. Therefore, this study investigated Si distribution, nut...

Purpose Phosphorus (P) occurs in different chemical forms in soil and sediment, and they play different ecological and environmental roles. Thus, separation and quantification of different P pools are essential to the understanding of P dynamics in the environment. Over the past decades, different sequential extraction methods have been used concur...

Fluorescence excitation-emission-matrices (EEM) and parallel-factor (PARAFAC) analysis have been widely used in the characterization of dissolved-organic-matter (DOM) in the aquatic continuum. However, large sample-sets are typically needed for establishing a meaningful EEM-PARAFAC model. Applications of the EEM-PARAFAC technique to individual samp...

Improvements in the microalgal harvesting efficiency and separation processes will accelerate cost-effective biomass utilization. Magnetic harvesting is known as a low-cost and environmentally friendly downstream processing technology, but information on optimization of the harvesting procedures is rare. Here, we present optimized harvesting factor...

Arctic terrestrial ecosystems are very sensitive to the global climate change due to the large storage of soil organic carbon and the presence of snow, glacier and permafrost, which respond directly to near surface air temperature that has warmed in the Arctic by almost twice as much as the global average. These ecosystems play a significant role i...

Nutrient pollution and algal blooms in coastal waters have long been a major concern, and understanding the response of algae to nutrient dynamics is thus essential. The minimum concentration under which Ulva prolifera will not grow, estimated from a nutrient-alga coupling model developed in this study, was 6.5 μmol L−1 for nitrate and 0.27 μmol L−...

Understanding the mixing behavior and biogeochemical cycling of heterogeneous dissolved organic matter (DOM) at the land‐ocean interface has been a major challenge, especially in large river‐dominated estuarine and coastal environments with multiple and complex end‐members of riverwater and seawater. Significant correlations and thus an “apparent”...

Dissolved organic matter (DOM) occurs ubiquitously in aquatic environments and plays an intrinsic role in altering the chemical speciation and toxicity of methylmercury (MeHg). However, interactions between MeHg and natural DOM remain poorly understood, especially at the functional group level. We report here the mitigative effects of three natural...

Dissolved organic matter (DOM) occurs ubiquitously in aquatic environments and plays an intrinsic role in altering the chemical speciation and toxicity of methylmercury (MeHg). However, interactions between MeHg and natural DOM remain poorly understood, especially at the functional group level. We report here the mitigative effects of three natural...

Both dissolved and particulate organic materials have been proposed to be important factors in regulating the heterotrophic denitrification in various aquatic environments. However, specific pathways and mechanisms remain elusive. In...

The abundance and fluxes of selected dissolved trace elements (TE), nutrients, and dissolved organic carbon (DOC) were quantified in the Atchafalaya River Basin to better understand its influence on the chemical regime of the Louisiana Shelf, a region where bottom water hypoxia occurs annually during late spring to early fall. Water samples were co...

Phosphorus (P) is an essential nutrient that affects crop yields, soil ecosystems and environmental pollution. The oxygen isotope composition of phosphate (δ¹⁸OP) in soil is mainly controlled by P source, temperature, the δ¹⁸OW of soil water, and biological processes and has been used as a unique tracer for the sources and interconversion of P pool...

Dissolved organic matter (DOM) in aquatic environment significantly influences the behavior and fate of heavy metals via binding, complexation and thus changes the metal speciation; however detailed interfacial processes and mechanisms are still unclear. Here, differential absorbance and fluorescence spectra and two dimensional UV-FTIR heterospectr...

Knowledge of the dynamic changes in molecular size of natural colloidal organic matter (COM) along the aquatic continuum is of vital importance for a better understanding of the environmental fate and ecological role of dissolved organic matter and associated contaminants in aquatic systems. We report here the pH- and cation-dependent size variatio...

Soil organic matter (SOM) in northern high-latitude regions is a major component of the global carbon cycle. However, the yield of soil-dissolved organic matter (DOM) during soil-water interactions and its chemical characteristics and reactivities remain poorly understood. We report here elemental composition and isotopic signatures of bulk-SOM fro...

Water, suspended-particles, and surface-sediment samples were collected from Green Bay, Lake Michigan, for the measurements of phosphorus (P) species, including dissolved/particulate-P, inorganic/organic-P, and five different forms of particulate-P, namely exchangeable- or labile-P (Ex-P), iron-bound-P (Fe-P), biogenic-apatite and/or CaCO3-associat...

Stability of colloidal particles contributes to the turbidity in the water column, which significantly influences water quality and ecological functions in aquatic environments especially shallow lakes. Here we report characterization, origin and aggregation behavior of aquatic colloids, including natural colloidal particles (NCPs) and total inorga...

Effects of photochemical and microbial degradation on variations in composition and molecular-size of dissolved organic matter (DOM) from different sources (algal and soil) and the subsequent influence on Cu(II) binding were investigated using UV-Vis, fluorescence excitation-emission matrices coupled with parallel factor analysis, flow field-flow f...

In order to examine the mixing behavior of dissolved uranium (U) in estuaries under different suspended particulate matter (SPM) regimes, three laboratory-based experiments were conducted by mixing seawater with river water containing different concentrations of SPM. Comparing this study with other field and laboratory-based experiments, dissolved...

Adsorption of natural organic matter (NOM) on nanomaterials (NMs) results in the formation of interfacial area between NMs and the surrounding environment (referred to as NOM-corona), giving rise to NMs’ unique surface identity. This unique surface identity is determined by the ligands and their interactions with NM surfaces. Since the chemical str...

Dissolved organic matter (DOM) is ubiquitous and plays an important role in regulating water quality, ecological function, and the fate and transport of trace elements and pollutants in aquatic environments. Both the colloidal precursors (i.e. <1 kDa) and bulk DOM collected from a freshwater estuary were incubated in the dark for 21 days to examine...

Sediment denitrification is the dominant nitrogen removal pathway in many aquatic habitats and can be regulated by local-, landscape-, and regional-scale factors. However, the mechanisms for how these multiple scale factors and their interactions affect the sediment denitrifying communities remain poorly understood. In this study, we investigated t...

Globally, shallow lakes have suffered from excessive nitrogen (N) loading due to increased human activities in catchments, resulting in water quality degradation and aquatic biodiversity loss. Sediment denitrification, which reduces nitrate (NO3(-)) to N gaseous products, is the most important mechanism for permanent N removal in freshwater lakes....

Dynamic variations in chemical composition and size distribution of dissolved organic matter (DOM) along the river-lake interface in the Fox River plume were investigated using ultrafiltration, flow field-flow fractionation, UV-Vis and fluorescence spectroscopy and parallel factor analysis. On average, ~67% of bulk dissolved organic carbon (DOC) we...

The biological recalcitrance or decomposability of soil organic carbon (SOC) determines its lability and thus C cycling in an ecosystem. Many studies of temperate and tropical soils have reported that SOC from deeper soil is older and more recalcitrant than surface soil. However, it is not clear whether this trend holds for arctic tundra soils. We...