Mineralization Rate Of Organic Matter Research Articles

Shifts in bacterial traits under chronic nitrogen deposition align with soil processes in arbuscular, but not ectomycorrhizal-associated trees.

Nitrogen (N) deposition increases soil carbon (C) storage by reducing microbial activity. These effects vary in soil beneath trees that associate with arbuscular (AM) and ectomycorrhizal (ECM) fungi. Variation in carbon C and N uptake traits among microbes may explain differences in soil nutrient cycling between mycorrhizal associations in response to high N loads, a mechanism not previously examined due to methodological limitations. Here, we used quantitative Stable Isotope Probing (qSIP) to measure bacterial C and N assimilation rates from an added organic compound, which we conceptualize as functional traits. As such, we applied a trait-based approach to explore whether variation in assimilation rates of bacterial taxa can inform shifts in soil function under chronic N deposition. We show taxon-specific and community-wide declines of bacterial C and N uptake under chronic N deposition in both AM and ECM soils. N deposition-induced reductions in microbial activity were mirrored by declines in soil organic matter mineralization rates in AM but not ECM soils. Our findings suggest C and N uptake traits of bacterial communities can predict C cycling feedbacks to N deposition in AM soils, but additional data, for instance on the traits of fungi, may be needed to connect microbial traits with soil C and N cycling in ECM systems. Our study also highlights the potential of employing qSIP in conjunction with trait-based analytical approaches to inform how ecological processes of microbial communities influence soil functioning.

Soils and Carbon Pools on the Shungite Rocks of South Karelia under Different Types of Land Use

The azonal organo-accumulative soils (Umbrisols) on shungite rocks and the effect of land use on their properties and ecosystem carbon stock have been studied. The changes in soil profile morphology, main agrochemical and microbiological characteristics of the upper horizons, Corg and Cmic stocks in the 100-cm soil layer, and the structure of carbon pools are analyzed. Pine forest (control), arable land, hayfield, young alder stand, and middle-aged mixed forest are examined. In contrast to zonal soils, a change in land use does not considerably transform the properties of shungite soils. The removal of stones has the greatest effect, leading to the formation of developed arable horizons. The soils are characterized by highly skeletal shallow weakly differentiated profile, low bulk density, and pH close to neutral. A wide range of the Corg content (1.6 to 11.7%) results from a heterogeneous composition of the parent rock. Agricultural development contributes to the accumulation of exchangeable bases and available potassium and phosphorus, the contents of which are initially elevated in shungite soils. Characteristic of all examined sites is a high rate of organic matter mineralization (C/N ratio ≤17). A low Cmic content (84–245 mg C/kg) is recorded in the soils, which is explainable with a low availability of the substrate determined by a lithogenic nature of carbon and increased concentrations of heavy metals and lanthanides in shungite rocks. Soil Corg stock varies in the range of 17–251 t C/ha and Cmic stock, of 6–43 g C/m2. The total ecosystem carbon stock is the highest in hayfield (259 t C/ha) and lowest in young forest (74 t C/ha). The total carbon stock in the arable sites, middle-aged forest stand, and control forest is within 169–211 t C/ha.

Effects of sludge retention time (SRT) on nitrogen and phosphorus removal and the microbial community in an ultrashort-SRT activated sludge system

The ultrashort-sludge retention time activate sludge (USAS) process is considered promising for the recovery of energy and resource from wastewater. In this study, we developed five USAS systems (with sludge retention time (SRT) of 0.5, 1, 2, 3, and 4 d), and investigated the nitrogen and phosphorus removal, as well as the microbial community, in the USAS systems. The results revealed that the activated sludge in the USAS system with a shorter SRT can capture more organic matter from wastewater, with organic matter mineralization, capture, and loss rates of 12.9–45.9, 42.4–62.3, and 18.2–24.8%, respectively. In addition, ammonia oxidization only occurred in the USAS systems with SRTs of 3 and 4 d, and all the USAS systems with different SRTs exhibited phosphorus-removal ability. The microbial community analysis results revealed that the relative abundance of nitrifying and denitrifying bacteria (such as Thauera) increased with an increase in the SRT.

Management of plant nutrient dynamics under alkaline soils through graded application of pressmud and gypsum.

An incubation experiment was conducted to monitor the effect of different organic matter inputs with the graded application of gypsum at different time intervals on soil pH, sodium (Na) content and available plant nutrients like nitrogen (N) and sulphur (S) in alkaline soil. The experiment was formulated with nine treatments, i.e. control (T1), recommended dose of fertilizer (RDF) (T2), RDF+Gyp1 (T3), RDF+FYM5+Gyp2 (T4), RDF+FYM10+Gyp1 (T5), RDF+PM5+Gyp2 (T6), RDF+PM10+Gyp1 (T7), RDF+FYM2.5+PM2.5+Gyp2 (T8), RDF+FYM5+PM5+Gyp1 (T9) with three replications. Periodical soil samples were taken at six and twelve months intervals. Results showed that the addition of organic matter reduced the pH and Na content in the soil. More reduction was observed at one year period as compared to six months. The addition of farmyard manure (FYM) and pressmud (PM) at 10 t/ha with gypsum (1 t/ha) improved available N and available S content as compared to organic inputs (5 t/ha) with gypsum (2 t/ha) in soil. Pressmud application with FYM showed better availability of plant nutrients and a reduction of soil pH (8.39 to 7.79) and Na content from 626 to 391 mEq/L in the soil during the incubation period. During the study, the application of treatment T9 (FYM and PM in equal ratio with 1 t/ha gypsum) showed a better availability of available N (175 to 235 kg/ha) and S (15.44 to 23.24 kg/ha) and reduced the active ion concentration of Na. This study is very useful for the management of sodium toxicity, improving soil health and the mineralization rate of organic matter through the application of organic inputs for sustainable crop production.

Bio-Drying of Municipal Wastewater Sludge: Effects of High Temperature, Low Moisture Content and Volatile Compounds on the Microbial Community

This study examined microbiological processes during the bio-drying of municipal wastewater sludge (WS) from the waste treatment facilities of the Moscow region (Russia). In just 21 days of bio-drying, the moisture content of the mixture of WS and wood chips decreased by 19.7%. It was found that members of the genus Bacillus were the main organic matter destructors. In the period from 7 to 14 days, the rates of organic matter mineralization and moisture loss were the highest, and bacteria of the genus Bacillus dominated, accounting for 43.5 to 84.6% of the bacterial community with a total number of 1.20 (±0.09) × 106 to 6.70 (±0.44) × 105 gene copies µg−1. The maximum number of Amaricoccus was (15.7% of the total bacterial community) in the middle of bio-drying. There was an active accumulation of nitrate nitrogen due to the oxidation of nitrogen-containing substances during the same period of time. Bacteria of the genera Sphingobacterium, Brevundimonas, Brucella, Achromobacter and fungi of the genus Fusarium dominated in the biofilter, which removed volatile compounds from the waste air by 90%. The obtained results allow to model the further intensification of bio-drying, as well as its efficiency and safety.

Soil Nutrient, Salinity, and Alkalinity Responses of Dendrocalamopsis oldhami in High-Latitude Greenhouses Depending on Planting Year and Nitrogen Application

This study explored the viability of greenhouse cultivation of Dendrocalamopsis oldhami under the “South Bamboo North Transplanting” initiative. In this study, the effects of planting year and nitrogen application on changes in soil nutrient levels, salinity, and alkalinity over the plant growth period were explored. After the introduction and planting of bamboo in 2017, a soil layer with a thickness of 0–40 cm was sampled at the end of the shooting stage in the greenhouse between 2017 and 2019 (late August), and the bamboo shoot yield and standing culm density were measured. Following the application of nitrogen to the bamboo groves in 2019, three nitrogen levels were established: no nitrogen (N1:0 g grove−1), medium nitrogen (N2:540 g grove−1), and high nitrogen (N3:1080 g grove−1). Soil layers at depths of 0–20 and 20–40 cm were sampled during the shoot elongation stage (late May) and at the end of the shooting stage (late August). The yield and nutrient content of bamboo shoots under different nitrogen treatments were also investigated. The results showed that Ca2+ and HCO3− were the main salt ions in greenhouse soil. With later planting years, the total number of cations (Ca2+, Na+, Mg2+, and K+) decreased, whereas the total number of anions (HCO3−, SO42−, NO3−, and Cl−) increased, resulting in a decrease in the percentage of exchangeable sodium (ESP), pH, and electrical conductivity (EC). The diameter at breast height, individual weight, and quantity of bamboo shoots increased annually, and the standing culm density increased by 1.4 times. Each year, the total nitrogen content decreased, whereas the alkali-hydrolyzed nitrogen, available phosphorus, and available potassium contents increased. Nitrogen application resulted in a significant decrease in ESP and pH and an increase in the total anion, cation, and EC values. It also reduced soil organic carbon, total nitrogen, total phosphorus, total potassium, available phosphorus, and available potassium. Nitrogen application increased the number of bamboo shoots, total yield, and accumulation of N and P; however, there was no significant difference between N2 and N3. In conclusion, the salinization of calcareous soil was alleviated, and the available nutrients were activated following the introduction of D. oldhami from south to north. The mineralization rates of organic matter and soil fertility increased. Soil acidification and EC decreased at the end of the shoot stage. Nitrogen application acidified the soil, and the yield and soil salt accumulation increased with increasing nitrogen levels. The nutrient uptake efficiencies of nutrients at high nitrogen levels were lower than those at medium nitrogen levels. Therefore, soil salt concentrations with values 0.26 < EC < 0.42 hindered the nutrient uptake of D. oldhami.

Water mass age and dissolved organic matter properties drive the diversity of pelagic prokaryotes in the Western Mediterranean Sea

The deep sea is among the largest, yet still poorly known, ecosystems on Earth. This knowledge gap is particularly evident for the bathypelagic layer (between 1000 and 4000 m) of the deep Mediterranean Sea (MS), characterized by peculiar environmental conditions at meso- and bathypelagic depths, such as the thermal signature of the deep waters, showing temperatures approximately 10 °C higher than any oceanic system at comparable depths. This sustains high rates of prokaryotic activities and fast dissolved organic matter (DOM) mineralization rates, and likely selects for unique microbial assemblages. We collected seawater samples in stations representative of different areas of the Western Mediterranean Sea (Algero-Provençal Basin, Alboran Sea and Gulf of Lion), from the surface to the bathypelagic layer (down to 2680 m) and in different water masses, and described the composition of pelagic prokaryotic communities, along with measurements of the main physical-chemical variables, concentration and optical properties (absorption and fluorescence) of DOM. Remarkable differences in DOM optical properties were observed among water masses, with highest dissolved organic carbon (DOC) values in surface waters and lowest in the oldest water masses represented by the Western Mediterranean Deep Water (WMDW) and the Levantine Intermediate Water (LIW), which were characterized by the highest concentration of recalcitrant DOM. The water mass had a significant partitioning effect on microbial community composition, which showed the highest richness in LIW. DOC, the marine humic-like component of DOM (C1mh) and oxygen were the main drivers of prokaryotic community structure. Changes in quality of DOM were reflected in shifts in community composition, supporting the existence of strong relationships between DOM quality and microbial community composition in the deep MS. Our data shed light on the community composition and diversity patterns of prokaryotic plankton in the deep western MS, helping to elucidate the major microbial players in the DOM cycling, and to progress towards a better comprehension of its future trends in light of changing conditions that are modifying the oceanography of the entire MS basin.

Degradation of refractory organic matter in MBR effluent from treating landfill leachate by the UV-nZVI-H2O2 system.

In this study, nano zero-valent iron (nZVI) was used as the Fe2+ source in the Fenton reaction, and a UV-nZVI-H2O2 system was constructed to efficiently degrade and mineralize refractory organic matter in landfill leachate. The results showed that under the optimal conditions (initial pH = 3, UV = 14W, nZVI = 0.5g/L, and [H2O2] = 30mM), the removal efficiencies of total organic carbon, absorbance at 254nm, and color number were 61.38%, 83.89%, and 85.79%, respectively. Control experiments show that the UV-nZVI-H2O2 system has the highest removal rate and mineralization rate of refractory organic matter. The excellent performance of the UV-nZVI-H2O2 system is related to a higher H2O2 utilization rate. The H2O2 residue in the UV-nZVI-H2O2 system was the lowest, and the effective utilization rate of H2O2 was as high as 98.80%. Alcohol quenching experiments and hydroxyl radical quantitative experiments showed that the dominant reactive oxygen species in the UV-nZVI-H2O2 system was HO• and the yield of HO• was as high as 2007.80μM, which was much higher than that in other systems. The results of spectra analysis showed that the low molecular weight, high fluorescence frequency organic matter, and relatively stable aromatic organic matter were significantly degraded after treatment with the UV-nZVI-H2O2 system and the aromatic degree, humification degree, molecular weight, and molecular polymerization degree of refractory organic matter were also significantly decreased. The mechanism of the UV-nZVI-H2O2 reaction includes homogeneous and heterogeneous Fenton reactions and adsorption and precipitation of organic matter by iron-based colloids. This study can provide theoretical and technical support for the advanced treatment of refractory organic matter in landfill leachate.

Composting Waste from the White Wine Industry

The wine industry generates a large amount of waste, and composting is an alternative for recycling these residues with agronomic and environmental advantages. With this aim, grape marc and grape stalks were composted in static and turned piles, with three and six turns, to investigate the effects of pile conditions during composting in order to improve final compost quality. Thermophilic temperatures were attained soon after pile construction, and the highest maximum temperatures were achieved in the turned piles (70.5–71.8 °C). However, pile moisture content decreased below the recommended values after day 42 in these piles. The extremely high temperatures and low moisture content in the turned piles hampered organic matter mineralization rates and the amount of potentially mineralizable organic matter (OM0) (391–407 g kg−1), whereas the structure of the static pile provided adequate porosity to increase organic matter decomposition and OM0 (568 g kg−1). This study shows that composting grape marc with stalks, for a period of 140 days, resulted in stabilized and matured compost (NH4+-N/NO3–-N < 0.5) with good chemical characteristics for applications as soil organic amendment, without the need for rewetting or turning the piles, thus reducing the agronomic and environmental cost of the composting process.

Application of Heterogeneous Catalytic Ozonation in Wastewater Treatment: An Overview

Catalytic ozonation is a non-selective mineralization technology of organic matter in water by using active free radicals generated by ozone degradation. Catalytic ozonation technology can be divided into homogeneous catalytic reactions using metal ions as catalysts and heterogeneous catalytic reactions using solid catalysts. Homogeneous catalytic ozonation technology has many problems, such as low mineralization rate, secondary pollution caused by the introduction of metal ions and low utilization efficiency of oxidants, which limit its practical application. Compared with homogeneous catalytic ozonation technology, heterogeneous catalytic ozonation technology has the advantages of easy recovery, lower cost of water treatment, higher activity and improved mineralization rate of organic matter. This overview classifies and describes catalysts for heterogeneous catalytic ozonation technology, including the different types of metal oxides, metal-free catalysts, and substrates used to immobilize catalysts. In addition, the heterogeneous catalytic ozonation process involved in the multiphase complex reaction process is discussed. The effects of different parameters on the performance of heterogeneous catalytic ozonation are also discussed.

Climatic controls on stable carbon and nitrogen isotope compositions of temperate grasslands in northern China

The natural abundances of stable carbon (C) and nitrogen (N) isotopes (δ13C and δ15N) are extensively used to indicate the C and N biogeochemical cycles at large spatial scales. However, the spatial patterns of δ13C and δ15N in plant-soil systems of grasslands in northern China and their main driving factors across regional climatic gradient are still not well understood. We measured plant and soil δ13C and δ15N compositions as well as their associated environmental factors across 2000 km climatic gradient (-0.2 to 9 °C; 152 to 502 mm) in grasslands of northern China. The soil δ13C and δ15N values in surface were lower than those in bottom for temperate typical steppe but had no significant differences for temperate meadow steppe and temperate desert steppe. Soil δ13C values declined with increasing soil organic carbon (SOC) but increased as mean annual temperature (MAT). These changes were attributed to the microbial decomposition rate. The δ15N values in soil and plant were negatively correlated with MAT and mean annual precipitation (MAP), which were mainly related to the low soil organic matter mineralization rate and the shift of dominant species from C4 to C3. Our results indicate the spatial patterns and different influencing factors on δ13C and δ15N values along the climatic gradient in grasslands of northern China. The findings will provide scientific references for future research on the C and N biogeochemical cycles of temperate grasslands.

High nutrient loads amplify carbon cycling across California and New York coastal wetlands but with ambiguous effects on marsh integrity and sustainability.

Eutrophic conditions in estuaries are a globally important stressor to coastal ecosystems and have been suggested as a driver of coastal salt marsh loss. Potential mechanisms in marshes include disturbance caused by macroalgae accumulations, enhanced soil sulfide levels linked to high labile carbon inputs, accelerated decomposition, and declines in belowground biomass that contribute to edge instability, erosion, and slumping. However, results of fertilization studies have been mixed, and it is unclear the extent to which local environmental conditions, such as soil composition and nutrient profiles, help shape the response of salt marshes to nutrient exposure. In this study, we characterized belowground productivity and decomposition, organic matter mineralization rates, soil respiration, microbial biomass, soil humification, carbon and nitrogen inventories, nitrogen isotope ratios, and porewater profiles at high and low marsh elevations across eight marshes in four estuaries in California and New York that have strong contrasts in nutrient inputs. The higher nutrient load marshes were characterized by faster carbon turnover, with higher belowground production and decomposition and greater carbon dioxide efflux than lower nutrient load marshes. These patterns were robust across marshes of the Atlantic and Pacific coasts that varied in plant species composition, soil flooding patterns, and soil texture. Although impacts of eutrophic conditions on carbon cycling appeared clear, it was ambiguous whether high nutrient loads are causing negative effects on long-term marsh sustainability in terms of studied metrics. While high nutrient exposure marshes had high rates of decomposition and soil respiration rates, high nutrient exposure was also associated with increased belowground production, and reduced levels of sulfides, which should lead to greater marsh sustainability. While this study does not resolve the extent to which nutrient loads are negatively affecting these salt marshes, we do highlight functional differences between Atlantic and Pacific wetlands which may be useful for understanding coastal marsh health and integrity.

Trend analysis of long-lasting air temperature and precipitation time series in a mountainous fir forest in central Greece. Implications for nitrogen uptake by plants

<p>In the present work meteorological data, concerning temperature and precipitation in a mountainous Bulgarian fir (Abies borisii-regis Mattf.) forest, was analyzed in order to find trends for the period 1973-2019. The results showed that temperature values on annual and seasonal base, especially in summers, showed a significant increasing trend. In addition, the number of days with particularly high temperatures increased together with the daily temperature range. With regard to the rain height an increasing trend was found significant at the 0.1 probability level. The nitrogen concentration in current year needles of the Bulgarian fir measured in the period 1997-2019 showed an increasing trend. This fact could be a sign of increased mineralization rates of organic matter as a response to the temperature increase.</p>

Effect of scleral protein shell amendment on bacterial community succession during the pig manure composting

The impact of scleral protein shell (SPS) amendment on bacterial community succession during pig manure (PM) composting were evaluated in the present work. Five treatments representing different dry weight dosage of SPS [0 % (T1), 2.5 % (T2), 5 % (T3), 7.5 % (T4), 10 % (T5) and 12 % (T6)] were applied with initial mixture of raw materials (Wheat straw along with the PM) and composted for 42 days. Results indicated that the dominant of phyla were Proteobacteria, Actinobacteria, Bacteroidetes and Firmicutes. The relative abundance (RA) of genus un-identified, Ruminofilibacter, Thermovum, Longispora and Pseudomonas were greater among the all treatments but interestingly genus Ruminofilibacter was also higher in control treatment. The network analysis was confirmed that T6 treatment with higher dosage of SPS amendment could enhance the bacterial population and rate of organic matter mineralization. Compared with T1, the T5 has greater potential impact to enhance the bacterial population and significant correlation among the pH and temperature.

An ozone catalytic oxidation system for the degradation of organic compounds in secondary wastewater from refining and chemical processes

ABSTRACT To overcome the low catalytic efficiency, insufficient catalyst strength, and poor ozone circulation in the advanced treatment of secondary wastewater, a hollow cylindrical Fe-Cu-Ce-Mn/Al2O3 catalyst was prepared by the step impregnation method. Compared with the common impregnation method, the step impregnation method produced a more uniform and compact distribution of each metal element, which was more conducive to generating the synergistic effect of various metals; thus, increasing the mineralization rate of organic matter. The hollow cylindrical design ensured the strength of the catalyst and the circulation of ozone. The reduction of the chemical oxygen demand (COD) was compared under different experimental conditions, with the optimal conditions found to be an ozone contact time of 40 min and ozone dosage of 40 mg/L. The average COD, ammonia nitrogen, and ultraviolet absorbance at 254 nm (UV254) removal rates were 36%, 19%, and 20%, respectively. After 3 weeks of continuous experiment, the removal rate was still high. Following analysis by three dimensional fluorescence, GC-MS, and the molecular weight detection of water samples before and after treatment, it was found that the catalyst enhanced the effect of ozone on wastewater treatment, with a significant removal of tryptophan-like aromatic proteins and soluble microbial metabolites, and the removal of most of the small molecular organic matter. In addition, part of the refractory organic matter could be converted into easily degradable organic matter, which greatly improved the biodegradability and mineralization rate of wastewater, and provided good conditions for subsequent treatment.

Positive Effect of Ecological Restoration with Fabaceous Species on Microbial Activities of Former Guyanese Mining Sites.

Understanding ecological trajectories after mine site rehabilitation is essential to develop relevant protocols adapted for gold mining sites. This study describes the influence of a range of mine site rehabilitation and revegetation protocols on soil physicochemical parameters and microbial activities related to carbon, nitrogen and phosphorus cycles. We sampled soil from six rehabilitated mining sites in French Guiana with different plant cover (herbaceous, Cyperaceous, monoculture of Clitoria racemosa and Acacia mangium and association of C. racemosa and A. mangium). We measured the mineralization potential of organic matter by estimating the mineralization of carbon, nitrogen and phosphorus and the microbial catabolic diversity balance. The results showed an improvement in the quality of organic matter on revegetated sites with tree cover. On restored sites with fabaceous species, the microbial biomass is three times higher than non-restored sites, improving the rates of organic matter mineralization and restoring the catabolic diversity to the level of natural Guyanese soils. These results confirm that the establishment of fabaceous species under controlled conditions significantly improves the restoration of microbial communities in mining soils.

Effects of Seasonal Thermal Stratification on Nitrogen Transformation and Diffusion at the Sediment-Water Interface in a Deep Canyon Artificial Reservoir of Wujiang River Basin

Watershed-scale nitrogen pollution in aquatic systems has become a worldwide concern due to its continuous impact on water quality deterioration, while the knowledge of key influencing factors dominating nitrogen transportation and transformation at the sediment-water interface (SWI) remains limited, especially in impounded rivers with an artificial reservoir. Hence, for a better understanding of the effects of thermal stratification on nitrogen transformation, we investigated the nitrogen species and isotopes in the sediment of a deep reservoir in Southwest China. Our results confirmed a significant difference in nitrogen species and isotopic composition in sediment between those in the thermal stratification period and non-thermal stratification period and indicated that the sediment biogeochemical process and transportation were clearly linked to the variations in water temperature and dissolved oxygen dominated by the process of thermal stratification. Significant seasonal differences in NH4+-N and NO3−-N in pore water of the upper layer (0–19 cm) revealed that nitrification exhausted NH4+ in the non-stratified period (NSP), and a potential low mineralization rate appeared when compared with those in the stratified period (SP). Seasonal differences in nitrogen species and isotope fractionation of δ15N-PON (about 2.3‰ in SP) in the upper layer sediment indicated a higher anaerobic mineralization rate of organic matter in SP than that in NSP. The diffusion fluxes of NH4+-N at SWI were 9.48 and 15.66 mg·m−2·d−1 in NSP and SP, respectively, and annual NH4+-N diffusion accounted for 21.8% of total storage in the reservoir. This study demonstrated that the nitrogen cycling processes, especially nitrification, denitrification, and mineralization, have been largely altered along with the changes in dissolved oxygen and that the diffusion of nitrogen species varied with the presence of the oxygen. The results contribute to the future study of watershed nitrogen budget evaluation and suggest that the endogenous nitrogen released from the sediment-water interface should be emphasized when aiming to fulfil water management policies in deep reservoirs.

A Multi-Tracer Study of Fresh Water Sources for a Temperate Urbanized Coastal Bay (Southern Baltic Sea)

Terrestrial surface waters and submarine ground water discharge (SGD) act as a source of dissolved substances for coastal systems. Solute fluxes of SGD depend on the ground water composition and the water-solid-microbe interactions close to the sediment-water interface. Thus, this study aims to characterize and evaluate the hydrogeochemical gradients developing in the fresh-salt water mixing zone of the Wismar Bay (WB), southern Baltic Sea, Germany. Sampling campaigns covering the WB, the fresh-salt water mixing zone at the beach of the WB shoreline, terrestrial surface and ground waters near the WB as well sediments pore water were carried out. In these different waters, the distribution of dissolved inorganic carbon, nutrients, major ions, trace elements, stable isotopes (H, O, C, S), and radium isotopes have been investigated. Enhanced concentrations of radium isotopes together with dissolved manganese, barium in the surface waters of the eastern WB indicated benthic-pelagic coupling via the exchange between pore water and the water column. Salinity, stable isotopes, and major ions in sediment pore water profiles identified the presence of fresh ground water below about 40 cmbsf in the central part of the bay. Geophysical acoustic techniques revealed the local impact of anthropogenic sediment excavation, which reduced the thickness of a sediment layer between the coastal aquifer and the bottom water, causing, therefore, a ground water upward flow close to the top sediments. The fresh impacted pore water stable isotope composition (δ18O, δ2H) plot close to the regional meteoric water line indicating a relatively modern ground water source. The calculated organic matter mineralization rates and the dissolved inorganic carbon sediment-water fluxes were much higher at the fresh impacted site when compared to other unimpacted sediments. Therefore, this study reveals that different fresh water sources contribute to the water balance of WB including a SGD source.

Exploring the Drivers Controlling the Priming Effect and Its Magnitude in Aquatic Systems

AbstractChanges in mineralization rates of stable or persistent organic matter induced by inputs of labile organic matter can alter the organic carbon (C) balance along the terrestrial‐aquatic ecosystem continuum. This phenomenon, also known as the priming effect, is well‐established in terrestrial ecosystems, but has only recently been explored in the domain of aquatic ecology–with widely contrasting responses of stable carbon to the priming effect reported across the literature. Here, we compiled data from experimental studies on C mineralization in aquatic systems that directly or indirectly tested for the priming effect and used a meta‐analytic approach to investigate the physical and chemical drivers behind the differing outcomes reported across studies. We found that the reported heterogeneity could be explained by two main factors: how the priming effect is measured and whether the study was performed in the laboratory or under field conditions. These findings suggest that how the priming effect is tested and measured has strong implications for its detection and magnitude.

Genotypic variation in maize (Zea mays) influences rates of soil organic matter mineralization and gross nitrification.

Agricultural management practices that increase soil organic matter (SOM), such as no-tillage (NT) with crop residue retention, together with crop varieties best able to source nutrients from SOM, may help reverse soil degradation and improve soil nutrient supply and uptake by plants in low-input environments of tropical and subtropical areas. Here, we screened germplasm representing genetic diversity within tropical maize breeding programmes in relation to shaping SOM mineralization. Then we assessed effects of contrasting genotypes on nitrification rates, and genotype-by-management history interactions on these rates. SOM-C mineralization and gross nitrification rates varied under different maize genotypes. Cumulative SOM-C mineralization increased with root diameter but decreased with increasing root length. Strong influences of management history and interaction of maize genotype-by-management history on nitrification were observed. Overall, nitrification rates were higher in NT soil with residue retention. We propose that there is potential to exploit genotypic variation in traits associated with SOM mineralization and nitrification within breeding programmes. Root diameter and length could be used as proxies for root-soil interactions driving these processes. Development of maize varieties with enhanced ability to mineralize SOM combined with NT and residue retention to build/replenish SOM could be key to sustainable production.