Soils and Sediments

Evolution over years of structural characteristics of humic acids in Black Soil as a function of various fertilization treatments Abstract Purpose Humic substances are the relatively stable and recalcitrant pool of soil organic carbon in the agricultural system. Humic acid (HA) is an active part of soil humic substances. However, little information exists on how structural characteristics of HA evolved with fertilization years in Black Soil. Materials and methods Soil samples were collected in 1997, 2002, 2008, and 2012 from the Long-term Fertilization Station of Black Soil. The methods of 13C-nuclear magnetic resonance spectroscopy, elemental composition analysis, and infrared spectroscopy were employed to analyze the structure of HA. Results and discussion Long-term fertilization had no significant (P > 0.05) effect on the ratio of O and S to C in HA. The ratio of H to C in HA increased with fertilization years after the application of organic manure (M) single or combined with chemical NPK fertilizers. The ratios of aliphatic C to aromatic C, and alkyl C to O-alkyl C in soil HA increased by 7.72% and 20.3%, respectively, in MNPK and M treatments, whereas NPK treatment declined the ratio of aliphatic C to aromatic C by 2.67% compared with CK treatment. Conclusions The HA structure tends to become aliphatic and simplified with years of organic manure combined with NPK fertilizers. To save costs, organic manure was only applied once within the period of crop rotation and was combined with NPK every year to satisfy crop demands for soil nutrients.

Intercropping with sweet corn ( Zea mays L. var. rugosa Bonaf.) expands P acquisition channels of chili pepper ( Capsicum annuum L.) via arbuscular mycorrhizal hyphal networks Abstract Purpose Intercropping of chili pepper (Capsicum annuum L.) with corn (Zea mays L.) is one of the main valuable intercropping patterns. However, the potential contribution of arbuscular mycorrhizal (AM) fungal hyphal networks is still poorly understood. The purpose of this work was to resolve the changes of AM fungal propagation and colonization in the pepper/corn intercropping systems due to the constitution of hyphal networks and the networks’ effects on plant nutrient uptake and interspecific competitive relations. Materials and methods An 18-week pot experiment on an unsterilized soil was carried out to test mycorrhizal performance and P acquisition of chili pepper and sweet corn (Zea mays L. var. rugosa Bonaf.) in two compartments, which were absolutely separated (Sep) by polyvinyl chloride (PVC) layer or semi-separated (Semi-Sep) by nylon mesh (30 μm) screen that only allows the passage of AM fungal hyphae but not plant roots. Root mycorrhizal colonization rates and the biomasses and P concentrations of shoots, roots, and fruits of pepper and corn were all measured. The total P acquisition of each crop per pot and the acquisition ratio of one to two crops were assessed. Soil pH, organic C, total P, available P, AM fungal abundance, and acid phosphatase activity were also tested. Results and discussion In the Sep system, root mycorrhizal colonization, P acquisition amount, shoot biomass, and rhizosphere AM fungal abundance of corn were all higher (P < 0.05) than those of pepper, but soil available P concentration was lower (P < 0.05) in corn compartment than in pepper one. Compared with Sep, Semi-Sep had higher (P < 0.05) mycorrhizal colonization rates with both intercrops and higher (P < 0.05) soil acid phosphatase activity and AM fungal abundance in corn and pepper compartments, respectively. Semi-Sep decreased (P < 0.05) soil available P concentrations with both compartments, but did not narrow the difference of soil available P concentration between compartments, suggesting there was no gradient diffusion of soil available P between compartments. Semi-Sep increased (P < 0.05) the P acquisition ratio and fruit yield of pepper, but not corn. Conclusions Constitution of hyphal networks increased mycorrhizal colonization with both intercrops, and corn supplied part of photosynthetic C for increasing AM fungal propagules in pepper compartment by gradient expansion since AM fungi formed better symbioses with corn. Hyphal networks increased pepper fruit yield via improving P distribution to pepper, but acquired relatively higher P from corn compartment via elevating the soil acid phosphatase activity, suggesting enhanced P competitive ability of pepper against corn upon hyphal networks.

Effects of topography on soil organic carbon stocks in grasslands of a semiarid alpine region, northwestern China Abstract Purpose Soil organic carbon (SOC) in mountainous regions is characterized by strong topography-induced heterogeneity, which may contribute to large uncertainties in regional SOC stock estimation. However, the quantitative effects of topography on SOC stocks in semiarid alpine grasslands are currently not well understood. Therefore, the purpose of this research study is to determine the role of topography in shaping the spatial patterns of SOC stocks. Materials and methods Soils from the summit, shoulder, backslope, footslope, and toeslope positions along nine toposequences within three elevation-dependent grassland types (i.e., montane desert steppe at ~ 2450 m, montane steppe at ~ 2900 m, and subalpine meadow at ~ 3350 m) are sampled at four depths (0–10, 10–20, 20–40, and 40–60 cm). SOC content, bulk density, soil texture, soil water content, and grassland biomass are determined. The general linear model (GLM) is employed to quantify the effects of topography on the SOC stocks. Ordinary least squares regressions are performed to explore the underlying relationships between SOC stocks and the other edaphic factors. Results and discussion In accordance with the present results, the SOC stocks at 0–60 cm show an increasing trend in respect to the elevation zone, with the highest stock being approximately 37.70 g m−2 in the subalpine meadow, about 2.07 and 3.41 times larger than that in the montane steppe and montane desert steppe, respectively. Along the toposequences, it is revealed the SOC stocks are maximal at toeslope, reaching to 14.98, 31.76, and 49.52 kg m−2, which are also significantly larger than those at the shoulder by a factor of 1.38, 2.31, and 1.44, in montane desert steppe, montane steppe, and subalpine meadow, respectively. Topography totally is seen to explain about 84% of the overall variation in SOC stocks, of which 70.61 and 9.74% are attributed to elevation zone and slope position, while the slope aspect and slope gradient are seen to plausibly explain only about 1.84 and 0.01%, respectively. Conclusions The elevation zone and the slope position are seen to markedly shape the spatial patterns of the SOC stocks, and thus, they may be considered as key indicating factors in constructing the optimal SOC estimation model in such semiarid alpine grasslands.

Biodegradation of humic substances by microscopic filamentous fungi: chromatographic and spectroscopic proxies Abstract Purpose The study of interactions between humic substances (HSs) and soil filamentous fungi is the key to understanding the sustainable soil functioning. The present work aims to examine the decomposition of HSs by filamentous dark-pigmented fungus Alternaria alternatа under the laboratory conditions and to determine the effect of easily assimilable organic carbon on this process. Analyzing such polydisperse substances like HSs by a complex integrated methodology makes it possible to explore the data on their decomposition by microorganisms. Materials and methods To achieve the aforementioned goals, we used chromatographic and spectroscopic approaches: low-pressure size-exclusion and hydrophobic interaction chromatography accompanied by absorption and fluorescence spectroscopy. To determine the effect cometabolism conditions produced on HS decomposition, two types of carbon substrates were added to the nutrient media: easily assimilable organic carbon (standard 0.3% or reduced 0.03% sucrose content) and hardly assimilable organic carbon (HSs), as well as their combinations. Five HS samples of different organic matter origin have been inspected: potassium humates (HPs) and humic acids (HAs) from coal, peat, and lignosulfonate. Correlation matrix and principal component analysis (PCA) were calculated for comprehensive data analysis. Results and discussion Transformations of the investigated HSs under fungal cultivation lead to the increase in the low molecular weight fraction, rise of hydrophilic fraction, enlargement of absorbance ratio A250/A365, shortening of the emission wavelength of the humic-type fluorescence, and growth in the fluorescence quantum yield measured with excitation at 355 nm. A positive correlation was observed between the accumulation of fungal biomass and the degree of HS decomposition. PCA analysis confirms that the difference in the results of HS decomposition largely depends on the sucrose content and the nature of HSs. We divided all the HS samples into four groups according to the degree of HS decomposition: original HS solutions, HPs altered using fungal cultivation at 0.03% sucrose, HAs after fungal cultivation at 0.03% sucrose, and finally, HSs (both HPs and HAs) after fungal cultivation at 0.3% sucrose. Conclusions In the laboratory experiments, we showed that (1) the isolated HAs were more effectively degraded than the parent HPs, and this process was more pronounced at a reduced sucrose content, and (2) the decomposition of stable organic compounds (HSs) was activated by the easily assimilable carbon sources (especially 0.3% sucrose) being present. We assume that it is the easily assimilable organic carbon that most likely triggers the HS degradation working as the priming effect in natural environments.

Understanding the mechanisms of soil water repellency from nanoscale to ecosystem scale: a review Abstract Purpose Soil water repellency (SWR) can interrupt water infiltration that may decline plant growth and potentially trigger soil erosion. Until now research has been mainly focused on understanding the mechanisms of SWR at different scales by observation and modelling studies. Materials and methods This review systematically discusses the possible mechanisms at different scales of the occurrence and persistence of SWR from nanoscale to ecosystem scale. Results and discussion Soil characteristics are strongly related to the severity of SWR, particularly in soil organic matter and soil moisture. The presence of a higher amount of hydrophobic organic compounds and lower soil moisture content lead to higher water repellency, suggesting that the interaction at the nanoscale between organic compounds and water molecules primarily determines the persistence of SWR. The repeated alternation of drying-wetting process largely modifies the relationship between water molecules and soil particles that impacts the possibility of SWR from hydrophilic in wet condition to hydrophobic in dry condition. Within ecosystem scale, vegetation and microbes are original sources of SWR-inducing compounds influencing the distribution and prevalence of SWR. Nevertheless, the challenge of global climate change, drought and warming can increase SWR. Extreme SWR induces more serious runoff and overland flow that is enhanced by intensive precipitation. Conclusions We conclude that understanding the interaction of water molecules and organic compounds at soil particle surface is essential to understand SWR at the nanoscale. Expanding the mechanisms of SWR from nanoscale to a larger scale is fundamental to improve the remediation of soil pollution and mitigate global change.

Using 137 Cs and 210 Pb ex measurements to explore the effectiveness of soil conservation measures in semi-arid lands: a case study in the Kouhin region of Iran Abstract Purpose One of the most fragile agro-ecosystems in Iran is represented by dry farming lands on steep hillslopes that occupy ca. 54% of the national agricultural lands. Therefore, in order to reduce loss of fertile soil from these lands, it is important to apply effective soil conservation strategies. This study used cesium-137 (137Cs) and excess lead-210 (210Pbex) measurements to assess the effectiveness of soil conservation practices in controlling soil erosion in Kouhin, Qazvin Province of Iran. Materials and methods Soil samples were collected from two adjacent hillslopes with and without conservation agriculture practices. The managed site benefited from conservation practices, including controlled grazing, terraces, and contour farming for 50 years. The unmanaged site was under cultivation without agricultural conservation practices. At the managed site, both 137Cs and 210Pbex activities were measured. Only 137Cs activity was measured for the unmanaged site. Results and discussion Conservation practices performed at the managed site were effective in minimizing soil erosion, i.e., net soil erosion rates provided by 137Cs measurements were only 4.6 Mg ha−1 year−1 at the managed site, compared to 12 Mg ha−1 year−1 for the unmanaged site. By using the 210Pbex approach, net soil loss and sediment delivery ratio in the managed site were 12.3 Mg ha−1 year−1 and 60%, respectively. Conclusions Soil redistribution magnitudes established from 137Cs inventories are associated with a period extending from 1963 to the time of sampling, while those obtained from 210Pbex measurements are related to the past 100 years. However, 210Pbex measurements are expected to be more sensitive to erosive events that occurred during the last 15 to 20 years and this could reflect the higher estimate of erosion rate provided by this radionuclide for the managed site. The increasing trend seems to suggest a possibility that the higher soil losses estimated by the 210Pbex measurements are a result of increasing climate variability during the last two decades. However, further investigation would be needed to confirm this hypothesis.

Improvement of mining soil properties through the use of a new bio-conditioner prototype: a greenhouse trial Abstract Purpose The effect of a prototype of humic bio-conditioner (H-BC) was assessed on the development of edaphic properties and the growth of maize plants in an edaphic material used as topsoil in the rehabilitation of soils in a coal mine in Colombia. Materials and methods The trial was carried out in a greenhouse, using pots with edaphic material treated with the addition of doses equivalent to 0 (control), 1, 2, and 4 Mg.ha−1 of H-BC; maize seeds were sown and followed up on for 60 days. Plant growth and soil biological, chemical, and physical variables were registered. Results and discussion The 4-Mg.ha−1 treatment maintained a significantly higher enzymatic activity than the control on day 60. The respiration of the soil treated with H-BC increased significantly, with the 4-Mg.ha−1 treatment standing out. The 2-Mg.ha−1 treatment induced the most noticeable changes in soil metabolic activity profiles. Increases in root and leaf development were observed in the treatment with 4 Mg.ha−1; apparently, this dose improved the absorption of Ca, K, and S by plants; the physical and soil aggregation indices increased significantly with 4 Mg.ha−1. Conclusions The results indicate that H-BC can be an alternative as an enhancer of the edaphic material used in soil rehabilitation processes.

Ammonia-oxidizing bacterial and archaeal communities in tropical bioaugmented zero water exchange shrimp production systems Abstract Purpose Ammonia oxidation is an important process in the removal of ammonia generated from feed and metabolic wastes in aquaculture systems. Considering the biogeochemical importance of ammonia oxidation in bioaugmented zero water exchange aquaculture systems, the diversity and abundance of bacterial and archaeal ammonia-oxidizing communities were analyzed in three selected ponds at different time intervals during the culture period, to unravel the key environmental factors influencing their distribution in the system. Materials and methods The diversity and abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in three tropical bioaugmented zero water exchange (ZWE) shrimp culture systems were analyzed using ammonia monooxygenase A (amoA) gene from the sediment metagenome during different phases of culture. The environmental factors associated with the variability in bacterial and archaeal amoA gene abundance and diversity were elucidated using RDA and Pearson correlation analysis. Results and discussion Ammonia-oxidizing archaea (AOA), Nitrosopumilus sp., Nitrosospharea sp., and ammonia-oxidizing bacteria (AOB), Nitrosomonas sp., were the dominant ammonia-oxidizing communities in the ZWE ponds studied. AOA shared 41 OTUs, and the maximum distribution was influenced by dissolved oxygen in the system, whereas AOB shared 4 OTUs. The copy numbers amoA gene determined using qPCR showed that the AOA amoA gene was 10- to 100-fold abundant than AOB amoA gene. Gene abundance of AOA was positively related to total organic carbon (TOC) and salinity of sediments, and the temperature had a negative impact on bacterial amoA gene abundance. The dissolved oxygen and TOC had a negative and redox potential a positive impact on the diversity of AOA, whereas pH had a negative impact on the diversity of AOB. Conclusions The ammonia-oxidizing archaeal communities dominated the bioaugmented zero water exchange aquaculture systems compared to bacteria based on the abundance and diversity analysis using amoA gene sequence-based OTU analysis and gene copy numbers. Dissolved oxygen, total organic carbon, and Eh of the sediments contributed to the distribution and abundance of AOA group in the ZWE ponds. This study points to the importance of environmental management in these culture systems for maintaining ammonia-oxidizing populations for optimal ammonia removal. The relative contribution of the archaea and bacteria to ammonia oxidation in these systems is to be further resolved along with that of anammox and comammox bacteria, which would help to develop appropriate biostimulation or bioaugmentation strategies for the management of these sustainable aquaculture production systems.

Edwin David Ongley (1941–2015)

Chemical patterns in sediments of ancient Theodosius Harbour (Istanbul) Abstract Purpose The use of fossil fuels, cement production and the reduction of forest areas cause a high amount of CO2 emissions to the atmosphere which in turn causes the ocean to be acidified. Acidity of seawater can directly change sediment properties. It is expected that the average pH value of the ocean surface water will decrease between 0.3 and 0.5 pH units according to the projection to year 2100. This study aimed to make a contribution to the understanding of long-term pollution trends. In the study, sediment samples from Neolithic Era, Early Byzantine Era and Byzantine Era from archaeological excavations jointly conducted by Istanbul Archaeological Museums and the Istanbul University Department of Conservation of Underwater Cultural Heritages were investigated. Materials and methods The sediment samples were taken from ancient Theodosius Harbour (5000 BC). Major elements (Si, Al, Fe, Mg, Ca, K, Na, Mn, Ti), rare earth elements (Tb, Yb, Eu, Dy, Tm) and toxic elements (As, Cr, Co, Cu, Ni, Pb and Zn) in sediment samples were determined by X-ray fluorescence spectrometer. The chemical abundance of the ancient sediments was evaluated with the ecological risk factor and geo-accumulation index. Results and discussion The sediment samples from the Neolithic Era reflect the contribution of both parent rock and also anthropogenic pollution. In the Early Byzantine and Byzantine Era, the development of the industry has increased the basic element concentrations in the environment and potential ecological risk and geo-accumulation indices. As, Cu, Cr, Zn, Ni and Co contents of Neolithic Era samples were found to be lower than Early Byzantine and Byzantine Era. Conclusions The obtained the results showed that the toxic elements in the Neolithic Era, which the industry never developed, started to rise and increased concentrations of Ni by about two and a half times, Zn four times, Pb two times, Cr two times, Co six times and As three times in the Early Byzantine and Byzantine Eras. The concentrations of major elements (Al, Ba, Ca, Fe, K, Mg, Mn, Na, Si) did not show any significant difference during these three eras.