Original ResearchChemical and spectroscopic characterization of humic substances from sediment and riparian soil of a highly polluted urban river (Suquía River, Córdoba, Argentina)
Introduction
Organic matter (OM) is a natural constituent of soil, sediment, and water originating from complex physicochemical transformations of animal-, plant-, and microbial-derived precursors (Paul, 2007, Wetzel, 2001). There is a wide range of constituents encompassing OM mixtures (Prentice & Webb, 2010). Chemically, OM can be conceptualized in terms of biologically active and stable humified pools. Biologically active compounds are aliphatic constituents (i.e. carbohydrates, polysaccharides, phospholipids) of low molecular weight rapidly metabolized by soil microorganisms (Ghani et al., 2003, Marinari et al., 2010). Contrarily, humic substances (HS) are complex aromatic fractions (Vázquez et al., 2016, Vergnoux et al., 2011) derived from decomposing lignocellulosic polymers (Stevenson, 1994).
Humic substances can be separated into different fractions according to their solubility in either an alkaline or acidic pH (Stevenson, 1994). Fulvic acids (FA) are soluble in both alkaline and acidic conditions. Contrarily, humic acids (HA) are extracted from soil or sediment by dilute alkali [0.1 M (sodium hydroxide, NaOH)] but precipitated at a pH of 2 (Vergnoux et al., 2011). These fractions differ in molecular size, with weights being estimated to range from 1000 to 5000 Da, and from 50,000 to 500,000 Da for FA and HA, respectively (McDonald et al., 2004). Accordingly, HA are more polymerized and aromatized than FA (Stevenson, 1994), with the HA/FA ratio being a surrogate of the soil OM maturity degree (Aranda and Oyonarte, 2006, Guimarães et al., 2013).
The chemical nature of HS is governed by the source and origin of humic-like materials, which are either autochthonous OM synthesized in situ; allochthonous OM derived from terrestrial debris of higher plants (D’Andrilli et al., 2013); or anthropogenic OM occurring in wastewaters and sewage outfalls (Gonsior et al., 2011). Techniques commonly applied to characterize the complexity of HS include solid-state 13C (Carbon - 13) nuclear magnetic resonance (NMR) spectroscopy (de Alcantara et al., 2004, Liu et al., 2016), fluorescence excitation-emission matrices (EEMs) spectroscopy coupled with parallel factor (PARAFAC) analysis (Coble et al., 2014), Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (D'Andrilli et al., 2013), Fourier transform infrared (FT-IR) spectroscopy, and ultraviolet–visible (UV–Vis) absorbance spectroscopy (Carletti et al., 2010, Gezici et al., 2012, Guimarães et al., 2013, Mao et al., 2011). FT-IR spectroscopy is a widely used analytical approach that provides relevant information regarding the nature, reactivity, and structural arrangement of HS functional groups (Giovanela et al., 2010, Tivet et al., 2013). The ease of obtaining an IR spectrum with increased energy throughput and a higher signal-to-noise ratio has prompted the use of FT-IR spectroscopy over traditional IR techniques (McDonald et al., 2004). Similarly, UV–Vis absorbance spectroscopy is a fast, non-destructive approach utilized to probe physicochemical features of HS at the bulk level (Giovanela et al., 2010, Morán Vieyra et al., 2009). Previous studies have shown that the ratio of absorbances (Absx, where x is the evaluation size) at 465 and 665 nm (E4/E6) and Δ log K coefficient (log Abs465nm - log Abs665nm) are indicative of HS aromaticity and molecular size, with lower values reflecting a higher degree of OM microbial processing and decomposition (Miralles et al., 2012, Vázquez et al., 2016).
Organic matter is a critical factor modifying the biotic functioning of terrestrial-C, regulating both energy flow and nutrient transfer pathways at the ecosystem level (Williamson et al., 2008). Organic matter may affect food webs either directly by uptake from soil microorganisms, or indirectly by mechanisms such as turbidity, pH, metal chelation, and transport of contaminants (Bolan et al., 2011, Wetzel, 2001). In this regard, HS are important components of polluted environments since they strongly affect the mobility, bioavailability, and fate of different contaminants by a myriad of complexing reactions with heavy metals and organic molecules (Bahemmat et al., 2016, Kulikowska et al., 2015, Parolo et al., 2017).
The Suquía River (Córdoba, Argentina), an endorheic system occupying ∼7700 km2, is currently subjected to a strong anthropogenic impact because it receives an excess of contaminants from various sources, including sewage from the municipal waste water treatment plant (WWTP) located downstream of Córdoba City, as well as agricultural, and industrial effluents from point and non-point pollution sources. Previous studies have reported the negative effect of these activities on the environmental quality of the Suquía River by the combined use of chemical and biological techniques. An extensive monitoring study by Merlo et al. (2011) revealed a strong pollution impact on several reaches and components of the Suquía River, including air, water, riparian soil, sediment, and biota. It was concluded that pollution from Córdoba City, untreated sewage discharges from the WWTP, and pollution from nearby agricultural fields (i) increased the abundance of fecal bacteria (i.e. coliforms, Escherichia coli) in surface water and sediment layers, (ii) depleted dissolved oxygen (DO) concentrations, decreasing local fish total abundance and diversity (iii) exacerbated the accumulation of heavy metals [i.e. copper (Cu), chromium (Cr), nickel (Ni), and lead (Pb)] and a wide range of pesticides (i.e. atrazine, chlorpyrifos and endosulfan) in surface water and sediment layers, and (iv) degraded urban air quality by increasing polyaromatic hydrocarbons (PAHs) (Bonansea et al., 2013, Merlo et al., 2011). Similarly, Monferrán et al. (2011) documented a pollution-dependent response of biomarkers (i.e. detoxification and antioxidant enzymes) measured in Jenynsia multidentata collected close to sewage discharges.
To date, however, no regional studies have addressed changes in the distribution of riverine OM or characterized the chemical nature of associated humic fractions. An adequate knowledge of the structural features that define the reactivity of HS is critical to infer potential interactions with heavy metals, as well as organic and inorganic pollutants. The occurrence of OM along the Suquía River may be variable due to different inputs from anthropogenic-C sources and riparian vegetation. Within this context, some differences in OM composition were expected. The objective of the current study was to characterize the chemical nature of OM following a continuum from minimally disturbed sites, with high plant biomass-C inputs, to more strongly degraded portions of the river, with little or no vegetation coverage. OM and HS from sediment (0–10 cm) and riparian soil (0–20 cm) samples were extracted and further analyzed by means of wet oxidation with potassium dichromate (K2Cr2O7) and bulk optical techniques such as UV–Vis absorbance and FT-IR spectroscopy. It was hypothesized that (i) additional biomass-C inputs at minimally disturbed sites would increase plant-derived OM constituents when compared to more degraded riparian soil and sediment samples (Merlo & Abril, 2014); (ii) such changes would be associated with an increasing maturity degree or processing of HS; and (iii) the influence of riverbank conditions on OM properties would be attenuated from riparian soil to sediment layers (Merlo et al., 2017).
Section snippets
Study area
The study was done in the Suquía River of Córdoba Province (Argentina). This river begins at the San Roque Dam and flows mainly from west to east for about 200 km until reaching the depression of Mar Chiquita Lake (Fig. 1). The watershed is located in a semi-arid region. The mean annual rainfall is in the range of 700–900 mm, with a dry season (from May to November) and a wet season (from December to April) with most of the rainfall occurring in January and February. The mean temperature ranges
Total organic matter and humic substances in riparian soil and sediment
Riparian soil TOM (4.15–50.40 g/kg range) was significantly affected (P < 0.05) by the study sites. Riparian soil TOM was higher at S1 and S2, followed by S5, S3, and S4 (Table 2). Similarly, S1 (9.41 g/kg) and S2 (7.38 g/kg) contained more riparian soil HS than S4 (2.36 g/kg) and S3 (1.70 g/kg) (Table 2). Humic substances accounted for approximately 14–20% of riparian soil TOM at S1, S2, S3, and S5. In contrast, HS accounted for approximately 57% of riparian soil TOM at S4. Humic substances,
Conclusions
The results of the current study supported the hypothesis that changes in OM accretion, as a result of contrasting riverbank conditions, altered the chemical nature of riparian soil TOM. Sites with increased vegetation coverage enhanced the HS pool concentration and compositional diversity. Contrarily, riparian soil HS isolated from highly degraded portions of the river were more humified, reflecting the more decomposed, recalcitrant pool of native OM. Highly heterogeneous sediment samples were
Acknowledgments
This work was supported by the Secretaria de Ciencia y Tecnología - Universidad Nacional de Córdoba, Argentina (SECyT-UNC) and the National Research Council of Argentina (CONICET). The authors acknowledge two anonymous reviewers for providing constructive comments and helpful suggestions that improved the overall quality of this manuscript.
References (69)
- et al.
Realistic soil C sink estimate in dry forests of western Argentina based on humic substance content
Journal of Arid Environments
(2013) - et al.
Organic matter stabilization in soil aggregates and rock fragments as revealed by low-temperature ashing (LTA) oxidation
Soil Biology and Biochemistry
(2008) - et al.
Effect of soil type and management (organic vs. conventional) on soil organic matter quality in olive groves in a semi-arid environment in Sierra Mágina Natural Park (Spain)
Geoderma
(2011) - et al.
Effects of vegetation with different evolution degree on soil organic matter in a semi-arid environment (Cabo de Gata-Níjar Natural Park, SE Spain)
Journal of Arid Environments
(2005) - et al.
Characteristics of organic matter in soil surface horizons derived from calcareous and metamorphic rocks and different vegetation types from the Mediterranean high mountains in SE Spain
European Journal of Soil Biology
(2006) - et al.
Humic substances-enhanced electroremediation of heavy metals contaminated soil
Journal of Hazardous Materials
(2016) - et al.
Dissolved organic matter: Biogeochemistry, dynamics and environmental significance in soils
Advances in Agronomy
(2011) - et al.
Determination of priority pesticides in water samples combining SPE and SPME coupled to GC–MS. A case study: Suquía River basin (Argentina)
Chemosphere
(2013) - et al.
Structural characterization of humic-like substances with conventional and surface-enhanced spectroscopic techniques
Journal of Molecular Structure
(2010) - et al.
Characterization of IHSS Pony Lake fulvic acid dissolved organic matter by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and fluorescence spectroscopy
Organic Geochemistry
(2013)
Carbon and nitrogen in the soil-plant system along rainfall and land-use gradient in southern Africa
Journal of Arid Environments
Assessment of the effects of environmental factors on humification processes by derivative infrared spectroscopy and discriminates analysis
Geoderma
Accumulation and detoxification dynamic of cyanotoxins in the freshwater shrimp Palaemonetes argentinus
Harmful Algae
Subtractive FTIR spectroscopy to characterize organic matter in lignite samples from different depths
Spectrochimica Acta
Hot-water extractable carbón in soils: A sensitive measurement for determining impacts of fertilization, grazing and cultivation
Soil Biology and Biochemistry
Chemical and spectroscopic characterization of humic acids extracted from the bottom sediments of a Brazilian subtropical microbasin
Journal of Molecular Structure
Molecular characterization of effluent organic matter identified by ultrahigh resolution mass spectrometry
Water Research
Soil organic matter pools and carbon fractions in soil under different land uses
Soil and Tillage Research
Characterization of humic acids extracted from the sediments of the various rivers and lakes in China
Journal of Environmental Sciences
The role of DOM sorption to mineral surfaces in the preservation of organic matter in soils
Organic Geochemistry
Humic substances from sewage sludge compost as washing agent effectively remove Cu and Cd from soil
Chemosphere
Cation-induced coagulation of aquatic plant-derived dissolved organic matter: Investigation by EEM-PARAFAC and FT-IR spectroscopy
Environmental Pollution
Characteristics and degradation of carbon and phosphorus from aquatic macrophytes in lakes: Insights from solid-state 13C NMR and solution 31P NMR spectroscopy
The Science of the Total Environment
Characterization of humic substances by advanced solid state NMR spectroscopy: Demonstration of a systematic approach
Organic Geochemistry
Differences of stabilized organic carbon fraction and microbiological activity along Mediterranean vertisols and alfisols profiles
Geoderma
Analytical chemistry of freshwater humic substances
Analytica Chimica Acta
Rewetting and litter addition influence mineralisation and microbial communities in soils from a semi-arid intermittent stream
Soil Biology and Biochemistry
An ultrasound assisted extraction of the available humic substance from marine sediments
Ultrasonics Sonochemistry
Integral assessment of pollution in the Suquía River (Córdoba, Argentina) as a contribution to lotic ecosystem restoration programs
The Science of the Total Environment
Environmental factors associated with heterotrophic nitrogen-fixing bacteria in water, sediment, and riparian soil of Suquía River
Limnologica
Assessment of biogeochemical trends in soil organic matter sequestration in Mediterranean calcimorphic mountain soils (Almería, southern Spain)
Soil Biology and Biochemistry
Surrogate descriptors of C-storage processes on crusted semi-arid ecosystems
Geoderma
Combined UV–Vis absorbance and fluorescence properties of extracted humic substances-like for characterization of composting evolution of domestic solid wastes
Geoderma
Metabolising old soil carbon: Simply a matter of simple organic matter?
Soil Biology and Biochemistry
Cited by (17)
Evaluating river health through respirogram metrics: Insights from the Weihe River basin, China
2024, Science of the Total EnvironmentEntrainment of E. coli and Listeria monocytogenes from sediment in irrigation canal
2022, International Journal of Sediment ResearchCitation Excerpt :Even though the irrigation water was tested free of pathogens, when water flow starts in irrigation seasons, pathogen in sediment can be entrained into the water due to flow velocities and shear stress on bed surface (Zhou et al., 2017). Up to date, some studies have characterized organic matter dynamics and substance spectro-chemical properties (Merlo et al., 2020), while others have related the biofilm effects of natural sediment to the drag coefficient and settling velocity (Shang et al., 2014). Kraemer et al. (2013) quantified bacterial adsorption and affinity in various aggregate sizes of sediments produced by water erosion.
Deciphering the environmental drivers throughout the 20<sup>th</sup> and 21<sup>st</sup> centuries in the paleolimnological record of Laguna del Plata, Laguna Mar Chiquita system, Northern Pampean plain, Argentina
2022, Journal of South American Earth SciencesCitation Excerpt :Before reaching LP, Río Suquía drains Córdoba city (1.3 million inhabitants; INDEC, 2010) where it receives inefficient treated sewage discharges from Córdoba city wastewater treatment plant. During the last 20 years, population, industrialization, and urban expansion, has grown exponentially in Córdoba city with no effective planning, resulting in an increase of effluent discharges into the river (Merlo et al., 2011, 2020; Stupar et al., 2014). Downstream Córdoba City, the Río Suquía basin drains the Pampean plain and receives pollutants from the agricultural activities (Monferrán et al., 2011; Pasquini et al., 2012; Santiago et al., 2015) deteriorating its water quality.
Analysis of biodiversity attributes for extensive vegetated roofs in a semiarid region of central Argentina
2022, Ecological EngineeringCitation Excerpt :The Province is located in the semiarid region of central Argentina, characterized by high thermal seasonal amplitude, with hot and rainy summers (mean temperature 26 °C, with peaks of up to 40 °C) and cold and dry winters (mean temperature 10 °C). The mean annual temperature is 17.4 °C and the mean annual rainfall is in the range of 700 to 900 mm (Derguy et al., 2019; Merlo et al., 2020). According to the Köppen-Geiger climate classification, the region corresponds to a transition between a warm semi-arid climate (type “BSh”) and a humid subtropical climate (type “Cwa”) (Kottek et al., 2006; Susca, 2019).
Evaluation of the sequential coupling of a bacterial treatment with a physicochemical process for the remediation of wastewater containing Cr and organic pollutants
2021, Journal of Hazardous MaterialsCitation Excerpt :In Argentina, years ago, there was an indiscriminate release of pollutants, including PAHs, such as Phe (Rotondo et al., 2021); heavy metals just like Cr(VI) (Ceballos et al., 2021); organochlorine pesticides for instance γ-HCH (Aparicio et al., 2018b); azo dyes, e.g. RB5 (Martorell et al., 2018), among others. In this sense, it is no surprising to find episodes of co-contamination with these pollutants and more (Aparicio et al., 2018b; Biruk et al., 2017; Merlo et al., 2020; Regaldo et al., 2018). Also, others countries have co-contamination problems.