total-N Content Research Articles

Nutrient losses over time via surface runoff and subsurface drainage from an agricultural field in northern Sweden.

Nitrogen (N) and phosphorus (P) losses, via both surface runoff and subsurface drainage water, were monitored in an agricultural field in northern Sweden for 32 yr. The objective was to determine losses of N and P in a long-term perspective in relation to meteorological factors and impacts of agricultural land use, with a focus on relative contributions of surface runoff and subsurface drainage water to N and P losses. In order to collect surface runoff water, an embankment was installed on three sides of the field, and the fourth side had an open ditch that drove runoff water to a measuring station. Subsurface water draining from the field was collected in a fishbone-shaped drainage system that terminated at the measuring station. In 50% of years (16/32), mean annual concentration of total N (TN) was significantly higher in subsurface drainage water than in surface runoff water. An opposing trend was seen for total P (TP), with mean annual concentration being significantly higher in surface runoff water than in subsurface drainage water in all but 3 of the 32 yr monitored. Years with a barley crop had higher TN concentration in subsurface drainage water but no difference in surface runoff compared with years with ley. In contrast, years with barley had lower TN concentration in surface runoff than years with ley, with no difference in TP in subsurface drainage water.

Distribution of nitrogen storage in density and size fractions varied with tillage practices and cropping systems with residue return in black soil of Northeast China

AbstractCrop residue return can prevent the degradation of cropland caused by conventional tillage practice in Northeast China. Meanwhile, additional nitrogen (N) input from crop residue inevitably changes soil N pools. Our objectives were to evaluate soil N storage changes in soil physical fractions. The residue return treatments consisted of no‐tillage (NT) and moldboard plow (MP), combined with continuous maize (Zea mays L.) (MM) and maize–soybean [Glycine max (L.) Merr.] rotation (MS) cropping systems, that is, NTMM, NTMS, MPMM, MPMS; conventional tillage (removal of crop residue and deep plow) with continuous maize (CTMM) was included as a control. The concentration of total N (TN) in bulk soil and physical fractions (light fraction [LF], sand, silt, and clay) was measured. In 0‐to‐5‐cm layer, TN content was higher in NT than MP, whereas the result was opposite in 10‐to‐20‐cm layer. Thus, the stratification ratio (SR) of soil TN was greater under NT. The TN content in MM was greater than MS under both tillage practices with residue return. Residue return treatments increased soil N storage by 6.44–24.85% in 0–20 cm compared with CTMM. Continuous maize increased the N storage in all physical fractions, whereas the decrease of silt‐N storage was observed in MS. Overall, it was concluded that residue return could enhance soil N storage, whereas the distribution of N storage changes in LF and sand size fractions was influenced by tillage practice, and the distribution of N storage changes in silt size and clay size fractions was influenced by cropping system.

The Fate and Balance of Nitrogen on a Sloped Peanut Field on Red Soil

To comprehensively evaluate the fate of nitrogen (N) through erosion and leakage, and to reveal the constitution of the whereabouts for fertilizer N on a sloping red soil cultivated with peanut, two treatments with three repetitions of conventional fertilization and no fertilization were set up according to the N-balance method. Lysimetric devices were adopted to observe the output of N in terms of loss, plant use, and residual N under natural rainfall in 2017 and 2018 in De’an, Poyang Lake Basin, China. The results showed that (1) leaching water was the main pathway of N output from runoff (including erosion and leakage), and the TN (total N) concentration of each surface runoff exceeded surface water Class V standard value of 2.0 mg L−1. (2) The fertilizer N use rate, the residual rate, and the apparent loss rate were 25.19–27.87%, 9.92–14.79%, and 60.02–62.21%, respectively. The apparent fertilizer N loss rate caused by soil erosion and leakage was 0.11–5.90% and 4.27–16.27%, respectively. (3) N losses from surface runoff and leakage were higher in the wet year (2017), whereas the amount of residual N in the soil profile was higher in the dry year (2018). This study provides a scientific basis for the adjustment of crop N fertilization in the study area.

KARAKTERISTIK VEGETASI, HARA NITROGEN DAN KARBON ORGANIK TANAH PADA TEGAKAN HUTAN TAMAN NASIONAL GUNUNG-MERBABU DAN TEGALAN (The Characteristics of Vegetation, Soil Nutrients of Nitrogen and Soil Organik Carbon at Forest Stands of Mount-Merbabu National Park and Dry Field)

Java island, which has a wet tropical climate, has a variety of vegetation stands. This study examines the characteristics of vegetation, nutrient levels of N, and soil organic carbon (SOC) under forest stands of Mount-Merbabu National Park (Pine/ Pinus merkusii, Puspa/ Schima noronhae theaceae, Acacia/ Acacia decurren fabaceae, Bintamin/Cupressus sp, and Mixed) and dry field at a soil depth of 0-30 cm (0-10, 10-20, 20-30cm). Observations the characteristics of vegetation were made by Observing Plot Units measuring 50 m x 50 m with 3 replications, while the observations of N nutrients and SOC included: total-N, Organic-C, and bulk density soil with 3 replications as well. The research data were analyzed descriptively, followed by the F-Test and DMRT Test at 5% level. The results showed that the forest stands of Mount-Merbabu National Park has the highest species density value in Puspa forest stand, followed by Mixed, Pine, Acacia, and Bintamin. Soil tota-N and Organic-C content decreased with the increasing soil depth. The highest soil total-N content in the depth of 0-10 cm was in the Puspa forest stand (1.34%), while Acacia is 0.74%, and dry field is 0.34%. The highest of soil organic-C content was in the Puspa forest stand (9.53%), the lowest was Pine (2.85%) and dry field (2.12%). Puspa (Schima noronhae theaceae) can be recommended as a good type of reforestation plant.

Use of Organic Materials to Limit the Potential Negative Effect of Nitrogen on Maize in Different Soils.

This study was launched to test organic materials in the form of humic acids (HA) applied to soil to improve the effect of nitrogen on maize, and to determine an optimal dose of HA, which will be ecologically safe and will counteract potential negative (phytotoxic) influences of excessive nitrogen fertiliser doses, on two soils with different textural composition. The maize plants grown on the loamy sand were characterised by a higher value of the SPAD leaf greenness index, yields, and a lower content of total-N and sulphate sulphur in maize. Urea, and especially UAN, promoted higher SPAD leaf greenness index values during the stem elongation stage and particularly during the tassel emergence stage. The effect of urea on maize yields was positive on both soils, but UAN had a positive effect on this parameter only on the loamy sand. HA tended to increase the SPAD leaf greenness index. The impact of HA on plant height and yields (especially medium dose) was generally positive. However, a negative effect of the interaction of HA with UAN on the plant height and maize yield on the sand was observed. HA caused an increase in the total-N content, and their highest dose also decreased the sulphate sulphur content in maize. The application of HA to soil has a positive influence on the growth and development of plants and can create positive effects by mitigating adverse consequences of intensive agricultural production in the natural environment.

Evaluasi Kemampuan Kesuburan Tanah di Kecamatan Tutur Pasuruan

The aim of this study was to discover soil fertility indicators for coffee cultivation in Tutur District as well as the variables that influence soil fertility levels for coffee cultivation land. A survey method was employed in this investigation. The findings of the chemical characteristics test were utilized as a guide for creating maps of the land fertility potential for coffee plants in Tutur Village. These maps included information on water content, soil pH, C-Organic content, N-total content, Phosphorus content, base saturation, and CEC. According to this study, Tutur District's coffee farming may be classified into three soil fertility status categories: low, medium, and high fertility status. The slope of the land is the factor that has the biggest impact on the soil fertility in the Tutur District's coffee growing region; the steeper the slope, the less fertile the soil is.

Changes in nitrogen and phosphorus within a decade in waters along a major canal and estuary in South Florida.

The West Palm Beach-C51 (WPB-C51) canal connects Lake Okeechobee with Lake Worth Lagoon (LWL) in South Florida. This canal receives discharges from Lake Okeechobee and from agricultural and urbanized areas. The objectives of this research were to determine spatial and temporal differences and trends of N and P forms along the WPB-C51 canal and LWL for 2009-2019. Data were obtained from the South Florida Water Management District. Average total P (TP) and total N (TN) concentrations at studied stations ranged from 55 to 183μg L-1 and from 0.61 to 2.62mg L-1 , respectively. The TP and TN concentrations at LWL inflow were higher than the State of Florida's regulatory criteria (49μg L-1 and 0.66mg L-1 , respectively). The TP and TN concentrations generally declined from Lake Okeechobee to LWL; however, agricultural drainage was highest for soluble reactive P (SRP) and all N forms. Temporal trends showed predominantly increasing trends for concentrations of P forms. Total P and TN load rates increased by 0.005 and 0.032 t yr-1 , respectively, at LWL inflow. Results suggest nutrient assimilation by plants and P precipitation along the WPB-C51 canal. Possible sources of SRP and N are fertilizers, nitrification, and organic matter mineralization. Increasing trends in P concentration are possibly due to legacy P and urbanization, and increases in TP and TN loads can be due to larger Lake Okeechobee discharges and higher nutrient concentrations. Results emphasize the need to implement strategies to minimize nutrient input into LWL to meet its water quality goals.

Comprehensive effects of integrated management on reducing nitrogen and phosphorus loss under legume-rice rotations

Paddy fields-based cropping systems are usually located in areas with dense water networks, so nitrogen (N) and phosphorus (P) losses from rice paddy fields caused by runoff might pose a serious pollution risk to their surrounding water bodies. However, current research over establishing a low fertilizer input paddy-based cropping system with comprehensive management for reducing runoff losses of N and P is insufficient. A five-year field trial was carried out with a rice-fava planting system in the Erhai Lake watershed from 2015 to 2019. Three treatments were designed namely chemical fertilizer plus manure (CMF), reduced chemical fertilizer combined with manure at the same application rate under CMF treatment (RF), and returning straw plus chemical and organic fertilizers at the same rate with RF treatment (RFS). The mean annual runoff losses of total N (TN) and total P (TP) range from 0.99 to 1.39 kg ha −1 yr −1 and 0.09–0.12 kg ha −1 yr −1 . Compared with CMF treatment, RF had lower runoff losses of TN and TP by 20.86% and 23.05%, respectively, but the yields and soil fertility were also reduced. After returning straw, soil organic carbon (SOC), TN, and crop yields were maintained or even increased, and runoff losses of TN and TP were further reduced by 9.48% and 7.41%, respectively, compared with RF. Therefore, the runoff losses of N and P decreased by selecting the rice-fava rotation system and reducing chemical fertilizer input through manure application and straw returning, which greatly reduced the surplus N and P in this system. Moreover, the temporal variation in the concentration of TN and TP, along with the N:P ratio approved the existence of potential risk caused by TN and TP losses to the watershed in the early stage of rice growth. Overall, in addition to taking field measures to reduce the N and P runoff losses from paddy fields, the runoff water with high N and P concentrations in early rice growth stage cannot be ignored. • Rice-fava system with low fertilizer maintained yield and had low environment risk. • Straw returning ensured crop yields under substituting chemical fertilizer by manure. • Combined of straw returning and manure substitution reduced nutrient runoff loss. • Runoff N/P concentration and N:P ratio in early stage of rice may need interception.

Soil nutrient contents and stoichiometry within aggregate size classes varied with tea plantation age and soil depth in southern Guangxi in China

Abstract. Soil ecological stoichiometry offers a tool to explore the distribution, cycling, limitation, and balance of chemical elements in tea plantation ecosystems. This study aimed to explore how soil organic C (OC) and nutrient contents (total N (TN), total P (TP), Ca2+, Mg2+, Fe2+, and Mn2+) as well as their stoichiometric ratios (C/N, C/P, N/P, Ca/Mg, and Fe/Mn) varied with tea plantation age (8, 17, 25, and 43 years) and soil depth (0–10, 10–20, 20–40, and 40–60 cm) within aggregates in southern Guangxi in China. Our results showed that tea plantation age and soil depth significantly affected soil nutrient stoichiometry in different sizes of aggregates. Among different ages of tea plantations, soil OC, TN, and TP contents as well as C/N, C/P, and N/P ratios significantly decreased as the soil depth increased. In addition, soil Ca2+ and Mg2+ contents were significantly lower in the surface soil layer than the deeper soil layer, whereas soil Fe2+ and Mn2+ contents showed opposite trends, and no significant differences were detected in Ca/Mg and Fe/Mn ratios among different soil depths. At the 0–40 cm soil depth, continuous planting of tea corresponded to increases in soil OC, TN, Fe2+, and Mn2+ contents, whereas soil Ca2+ and Mg2+ contents significantly decreased over time. During the process of tea growth, the losses of soil Ca2+ and Mg2+, especially Ca2+ (as indicated by the decrease in the soil Ca/Mg ratio), led to soil acidification, which reduced Fe2+ absorption and enhanced Mn2+ uptake by tea plants (as indicated by the increase in the soil Fe/Mn ratio). In general, tea plantation age affected the variations of soil nutrient contents and stoichiometry, and such effects were more obvious at the 0–40 cm soil depth, in contrast to the 40–60 cm soil depth.

C:N ratios of bulk soils and particle-size fractions: Global trends and major drivers

C:N ratios are the most ancillary and available proxy for soil organic matter (SOM) chemical composition and quality in the literature, but there is surprising little information on how it is affected by environmental factors. To address this knowledge gap, we searched the global literature and gathered information from 74 studies conducted between 1980 and 2019, covering 29 countries and a wide range of variation environmental settings. We compiled data on soil organic carbon (SOC), total N (TN) and C:N ratios in bulk soil and, for the first time, within soil particle-size fractions – sand, silt, and clay. Correlation and random forest statistical analyses showed that SOC and TN contents were mostly controlled by macroscale, climatic drivers, namely temperature and precipitation, whereas soil C:N ratios were more responsive to microscale drivers, e.g. soil particle-size distribution. Specifically, C:N ratios in bulk soil were most strongly correlated with sand contents (r = 0.52; p < 0.001), consistent with the high C:N of sand-sized SOM (median 16.7). Otherwise, clay-sized SOM showed much less variation in C:N ratios (5.0–17.6, median 9.6), regardless of sampling depth and land use. Clay C:N ratios were only consistently lower under arid climate types. Silt-sized SOM showed intermediate C:N ratios (median 13.1) relative to sand and clay-sized fractions. Hence, our results suggest a preferential immobilization of N-enriched SOM onto clay-sized particles coupled to a segregation of N-depleted SOM in sand-sized fractions. Although bulk soil C:N increased with sand contents, the accumulation of N-depleted SOM within sand-sized fractions increased with clay content. Overall, by identifying the complementarity of macro- and microscale factors underpinning soil C and N pools and their C:N ratios, our results contribute to reduce the inherent complexity to model SOM cycling across global to local scales.

Erosion intensity and check dam size affect the horizontal and vertical distribution of soil particles, carbon and nitrogen: Evidence from China’s Loess Plateau

Check dams are effective soil and water conservation structures worldwide that play an important role in preserving sediments containing carbon (C) and nitrogen (N). However, in terms of the depositional characteristics of C and N in check dams, research on the relative effects of erosion intensity and depositional area is limited, hindering our understanding of the fates of eroded C and N. This study compared the horizontal and vertical distributions of soil particles, organic C (OC), and total N (TN) in check dams of various sizes and erosion intensities in the Loess Plateau. The results showed greater variations in the horizontal and vertical patterns of soil particles of smaller check dams and highly serious erosion (erosion modulus = 15040 t km-2 a-1) than those that of larger check dams and strong erosion regions (erosion modulus = 5151 t km-2 a-1). Soil OC and TN contents decreased from the dam body to the gully head, especially in the highly serious erosion region. Notably, the effect of smaller check dam on the vertical distributions of soil OC and TN was more intense than that of the larger check dam in the strong erosion region. In contrast, a minor effect of check dam size was observed in the highly serious erosion region. Moreover, a closer relationship between the distribution of OC and TN with silt content rather than with clay content in check dams was observed, and this relationship was enhanced by an increase in erosion intensity. Overall, the synergistic effects of erosion intensity and check dam size affected the spatial patterns of OC and TN in sediments on the Loess Plateau. Careful consideration of these two factors is beneficial for accurately assessing the C and N fates in depositional areas.

Climatic effects on soil organic nitrogen fractions and amino acid chirality in paddy soils

Soil organic nitrogen (N) accounts for more than 90% of the total N (TN) in paddy soils. An inadequate understanding of the different organic N fractions in paddy soils and their corresponding bioavailability under different climatic conditions has constrained the development of appropriate nutrient management strategies in rice production. Here we apply a modified Bremner method coupled with High Performance Liquid Chromatography (HPLC) to characterize how Soil Organic Nitrogen (SON) fractions and amino acid chirality vary under different climatic conditions by sampling five typical rice production sites along a latitudinal gradient. According to the results, climate had no obvious influence on TN, N form, and individual amino acid concentrations. However, the proportions of various N forms in TN had linear relationships with annual mean temperature, with high correlation coefficients. Amino acid components also exhibited similar trends (with correlation coefficients as high as 0.85). Most notably, consistent linear relationships were observed between the D/L ratios of several amino acids and annual mean temperature in paddy soils (correlation coefficients = 0.18–0.92). The findings of the present study could provide insights on SON and amino acid dynamics in paddy soil systems under intensive production along climate gradients.

Effects of the Preceding Crop on Soil N Availability, Biological Nitrogen Fixation, and Fresh Pod Yield of Organically Grown Faba Bean (Vicia faba L.)

In the current study, the impact of the preceding crops on growth, fresh pod yield, nitrogen fixation efficiency, and nitrogen nutrition of faba bean (Vicia faba L.) was investigated for two years in both organic and conventional crops. As preceding crops served cabbage, pea, and faba bean. The pod number per plant (PN) and the total fresh pod yield (TFPY) were significantly lower with cabbage compared to pea and faba bean as preceding crops in both cropping systems and both experimental years. However, in the organic farming system, pea increased significantly in PN and TFPY compared to faba bean as a preceding crop, while in the conventional system, there was no significant difference between the two legumes. The greater yield performance with the two legumes as preceding crops was associated with higher soil NO3-N and total-N concentrations at the beginning of the subsequent faba bean crop. The higher soil N availability when the preceding crop was a legume resulted partly from the higher biomass of crop residues left by these crops on the field after harvest, compared to cabbage. However, it was also associated with a more extensive nodulation of the faba bean roots by rhizobia and a higher percentage of N derived from atmosphere (%Ndfa) in their plant tissues, as determined through the natural abundance of the 15N isotope, when the preceding crop was a legume. The cropping system had no impact on pod yield, but organic farming increased the %Ndfa in both years.

Variations in Soil C, N, P Stocks and Stoichiometry With Soil Depth and Forest Types in Qilian Mountains of Northwest China

Forests ecosystem plays a significant role in supplying multiple services given the unique properties of forest soils, in which the elements of C, N, and P are essential to support soil fertility and site productivity. However, soil properties at different soil depths between plantation forests (PF) and natural forests (NF) have not been well quantified. Therefore, the current study was carried out in the Qilian Mountains of northwest China to determine the difference between PF and NF in the soil properties, both physical (e.g., bulk density, BD) and chemical (e.g., pH value, the contents, stocks, and stoichiometry of soil organic carbon (SOC), total N (TN), and total P (TP)). Research analyzed soil samples at different depths (0–20, 20–40, 40–60, 60–80, and 80–100 cm). The results showed that the soils’ pH values and BD were significantly higher (p≤ 0.05) in PF than in NF and increased with soil depth. The contents of SOC, TN, and TP decreased considerably with soil depth and then stabilized at the soil depth of 80–100 cm. The NF showed significantly higher (p≤ 0.05) SOC, TN, and TP contents than PF, confirming that the soil quality of PF had not fully recovered yet. The stocks of SOC and TN quickly decreased with soil depth up to 40–60 cm and stabilized gradually. Additionally, the soil stoichiometry of C:P and N:P decreased significantly with rising soil depth, while the C:N ratio remained unchanged. The N:P and C:P ratios were lower in PF than in NF, while the C:N ratio was higher in PF than in NF. In conclusion, the results show that the soils of NF present significantly higher stocks of SOC and TN but lower (or nearly equal) TP stocks than PF (under the same age group and tree species composition). These results imply that maintaining NF and avoiding their replacement by PF can help keep higher soil quality and related ecosystem services.

Limiting Factors of Agronomic Characteristics for Maize Through Nutrient Omission Techniques

The deficiency of primary macronutrients can inhibit the vegetative growth of the plants. The study aimed to obtain the influence of nutrient omission techniques fertilization (NOTF) on the agronomic characteristics, nutrient uptake and to determine the growth limiting factors for maize. This research was located on the farmer field in Padang Bulan, Medan Baru, North Sumatra, Indonesia, from December 2020 to March 2021. This research was applied the Randomized Block Design within the single factor through NOTF that has been converted (urea: superphosphate: KCl = 0.15: 0.10: 0.025 g kg-1). The treatment using F0 = control; F1 = N + P + K; F2 = P + K; F3 = N + K; F4 = N + P within three replications. The parameters were processed using ANOVA and continued by a Duncan Multiple Range Test (DMRT) at P &lt; 0.05. The F1-F4 treatments significantly increased plant height, number of leaves, leaf area, fresh weight of root and shoot, and dry weight of root and shoot for maize. It was found in the highest plant height, the number of leaves, and the dry weight of root at the N + P fertilization. However, the N + P + K fertilization increased leaf area, fresh weight, and dry weight of shoot. It showed the highest concentration and uptake nutrient of total-N, total-P, and total-K. The novelty of this study found the limiting factor that inhibited the maize growth was the non-fertilization of nitrogen.

Nitrogen-fixing bacteria and organic ameliorant for corn growth and yield increment in Inceptisols

Since Inceptisols, in general, contain low soil organic matter and major plant nutrients, inorganic fertilizers are commonly added during corn cultivation. In order to maintain long-term soil health and fertility, bioferilizer and organic ameliorant application are suggested. The addition of nitrogen (N)-fixing bacteria (NFB) can benefit plant growth through the supply of available nitrogen for plant uptake. Organic ameliorants can enhance soil chemical and biological properties. A field trial had been performed to observe the effect of biofertilizer and organic ameliorant on corn growth, N status in soil and plant, and the yield and wasteof corn. The experiment was designed in a Completely Randomized Block Design that consisted of four treatments and six replications. The treatments were 1.2 kg/ha N-fixing mixed biofertilizer, 2 t/ha organic ameliorant, and mixtures of biofertilizer and ameliorant. Control plants received neither biofertilizer nor ameliorant. The experiment results found that N-fixing biofertilizer and ameliorant increased plant height, fully-developed leaves number, soil reaction and N uptake of corn compared to the control. The total-N content was slightly increased after NFB inoculation with and without amelioration over other treatments. Plots treated with biofertilizer and ameliorant produced a higher grain weight compared to the control treatment. Corn wastes such as empty corn cob and husk weight were increased in plants treated with biofertilizer, ameliorant and a combination of both. This study suggested that the combined application of biofertilizer and ameliorant produced 66% more grain yield and 84 % more cob and husk waste compared to untreated plants.

Using dredged sediments to support wetland plant development in a constructed delta lake

Restoration efforts take place at large scales to improve the ecological value of degraded, modified river deltas. To anticipate on the implications of using dredged, estuarine sediment to restore wetlands in river deltas, we studied the development of Typha latifolia (cattail) and Phragmites australis (common reed) on two designated dredged sediments, virgin Holocene clay (clay) and eroded clay (mud), under different water levels (inundated, saturated, and moist) in a mesocosm experiment. The mud sediment contained about two times higher Fe, S, and P content and four times higher N-total content compared to clay sediment. The organic content was comparable for both sediments. Sediment type influenced germination and shoot growth of T. latifolia, which were both higher on clay compared to mud, but did not influence germination and initial growth of P. australis. Water level treatment effects on plant response were limited to inundation conditions only; this condition strongly reduced P. australis seedling and shoot development. Both species developed significantly more above- and belowground biomass when growing in mud compared to clay, however, their nutrient content was comparable on both sediment types. Overall, T. latifolia development was more strongly influenced by sediment composition compared to P. australis, but the latter species is more vulnerable to higher water levels during early stages of development. We conclude that both dredged sediment types are suitable as sediment for developing macrophyte vegetation.

Impact assessment of on-site swine wastewater treatment facilities on spatiotemporal variations of nitrogen loading in an intensive livestock farming watershed.

Excess nitrogen (N) resulting from human activity causes environmental issues, including eutrophication in agricultural watersheds with intensive livestock farming. Among the N sources in Korea, on-site swine wastewater treatment facilities (OSWTFs) tend to be densely distributed in watersheds with intensive livestock farming. Therefore, it is critical to sustainably manage livestock excreta. This study used the Soil and Water Assessment Tool (SWAT) to investigate the effects of various pollution sources, including OSWTFs, on N loads in rivers in the Cheongmi watershed, which is an intensive livestock farming and agricultural area in Korea. The simulated hydrological and water quality outputs were calibrated and validated for 2012-2019 using Sequential Uncertainty Fitting ver. 2 in the SWAT-Calibration and Uncertainty Program. The hydrological simulations agreed with the observations, with a correlation coefficient (R2) of ≥ 0.8 and Nash-Sutcliffe coefficient of 0.67-0.86. The simulated total N (TN) was also strongly correlated with the observed monthly average loading (R2, 0.36-0.73) and annual average concentration (R2 ≥ 0.5), demonstrating the reliability of the model constructed herein. A simulation of management scenarios indicates that, if the permissible N concentration in effluent from OSWTFs was reduced to 60mgN/L, the TN concentrations in rivers would decrease by up to 50%. The findings of this study indicate that more stringent effluent water quality standards are required for OSWTFs to protect water quality and aquatic ecosystems in intensive swine farming watersheds.

Significant Temporal and Spatial Variability in Nutrient Concentrations in a Chinese Eutrophic Shallow Lake and Its Major Tributaries

Sediment nutrients can be released to the surface water when hydraulic disturbance becomes strong in shallow lakes, which contributes to nutrient enrichment and subsequent lake eutrophication in the water column. To explore the seasonal variations and spatial distributions exhibited by nutrients in the water column, surface sediment, and pore water of Lake Yangcheng and its major tributaries, we determined the concentrations of nitrogen (N) and phosphorus (P) throughout the lake in different seasons of 2018. Total N (TN) and total P (TP) concentrations in the connected rivers were much greater than those in the lake, indicating that external loading greatly contributed to the nutrient enrichment. TN concentration in the water column was highest in the winter, whereas TP peaked in the summer. A similar temporal pattern was observed for TN and TP in the sediment with maxima in the winter and minima in the summer; however, nutrients in the pore water were highest in the summer, in contrast to the temporal variation in the sediment. Additionally, high TN values in the water column and high TP in the three compartments were distributed primarily in the west part of the lake, while high TN concentrations in the sediment and pore water were observed mainly in the east portion of the lake. According to the enrichment factor index (an indicator evaluating the nutrient enrichment by comparing the detected contents and standard values), nutrients in the lake sediment were severely enriched with TN and TP averaging 2195.8 mg/kg and 543.0 mg/kg, respectively. The vertical distribution of TN and TP generally exhibited similar decreasing patterns with an increase in sediment depth, suggesting mineralization of TN and TP by microbes and benthic organisms. More attention and research are needed to understand the seasonality of nutrient exchange across the sediment–water interface, especially in eutrophic lakes.

Carbon and nitrogen dynamics as affected by land-use and management change from original rice paddies to orchard, wetland, parking area and uplands in a mountain village located in Shonai region, Northeast Japan

ABSTRACT This study investigated the effect of land-use and management change (LUMC) on carbon (C) and nitrogen (N) dynamics after 15–40 years. LUMC constituted change from rice paddies to chestnut orchard, wetland, and buckwheat upland fields in Shonai region, Yamagata Prefecture, Northeast Japan. Soil samples were collected from the top – (0–15 cm) and sub-layers (15–30 cm) for analysis of soil organic C (SOC) and its δ13C value, total N (TN), and their stocks. C decomposition (Dec-C) and net N mineralization (Net Min-N) were determined according to the production of CO2 and NH4 + + NO3 – by aerobic incubation and CO2 + CH4 and NH4 + by anaerobic incubation, respectively. The results reveal that 40 years after change from rice paddy to orchard and wetland, the SOC and TN contents in the top-layer were not significantly altered. However, in buckwheat upland fields and in the parking area where vegetation was absent, the SOC content decreased significantly. Conversion of rice paddies to amur silver grass wetland altered the soil δ13C the most, leading to an increase of 5.1‰ and 2.9‰ for the top – and sub-layers, respectively. In general, the incubation experiment results revealed that a change to orchard and wetland did not significantly decrease the Dec-C and Net Min-N. Whereas, the change from rice paddies to parking area significantly decreased the Dec-C and Net Min-N in both aerobic and anaerobic conditions. We conclude that LUMC over decades had various effects on the SOC and TN contents and stocks as well as their mineralization potentials.