Nitrogen Distribution Patterns Research Articles

Impact of fertilization depth on sunflower yield and nitrogen utilization: a perspective on soil nutrient and root system compatibility.

The depth of fertilizer application significantly influences soil nitrate concentration (SNC), sunflower root length density (RLD), sunflower nitrogen uptake (SNU), and yield. However, current studies cannot precisely capture subtle nutrient variations between soil layers and their complex relationships with root growth. They also struggle to assess the impact of different fertilizer application depths on sunflower root development and distribution as well as their response to the spatial and temporal distribution of nutrients. The Agricultural Production Systems sIMulator (APSIM) model was employed to explore the spatial and temporal patterns of nitrogen distribution in the soil at three controlled-release fertilizer (CRF) placement depths: 5, 15, and 25 cm. This study investigated the characteristics of the root system regarding nitrogen absorption and utilization and analyzed their correlation with sunflower yield formation. Furthermore, this study introduced the modified Jaccard index (considering the compatibility between soil nitrate and root length density) to analyze soil-root interactions, providing a deeper insight into how changes in CRF placement depth affect crop growth and nitrogen uptake efficiency. The results indicated that a fertilization depth of 15 cm improved the modified Jaccard index by 6.60% and 7.34% compared to 5 cm and 25 cm depths, respectively, maximizing sunflower yield (an increase of 9.44%) and nitrogen absorption rate (an increase of 5.40%). This depth promoted a greater Root Length Density (RLD), with an increases of 11.95% and 16.42% compared those at 5 cm and 25 cm, respectively, enhancing deeper root growth and improving nitrogen uptake. In contrast, shallow fertilization led to higher nitrate concentrations in the topsoil, whereas deeper fertilization increased the nitrate concentrations in the deeper soil layers. These results provide valuable insights for precision agriculture and sustainable soil management, highlighting the importance of optimizing root nitrogen absorption through tailored fertilization strategies to enhance crop production efficiency and minimize environmental impact.

Vertical Distribution Patterns of Nitrogen and Phosphorus in Soil Solution: Insights from a Wetland Trial Site in the Li River Basin

Vertical Distribution Patterns of Nitrogen and Phosphorus in Soil Solution: Insights from a Wetland Trial Site in the Li River Basin

Casein, whey protein and non-protein nitrogen content of milk to identify water, sugar and flour adulterated milk

This study was aimed to assess the potential of using milk's nitrogen distribution pattern, specifically casein, whey protein, and non-protein nitrogen content, as a method for detecting milk adulteration with water, sugar, and flour. Whole milk samples were collected from the Bangladesh Agricultural University Dairy Farm, BAU, Mymensingh, and subjected to adulterations, including 15%, 20%, and 25% water additions and subsequent sugar or flour adjustments to match the fresh milk's specific gravity. The samples were analyzed for specific gravity, fat content, and nitrogen distribution. Results indicated that while specific gravity remained consistent across samples adulterated with sugar or flour, it varied significantly (P<0.05) in those diluted with water. Fat content was significantly (P<0.05) reduced in samples adulterated with water and sugar, particularly at the 25% water addition level. Though total protein, true protein, and casein contents were significantly lower (P<0.05) in the 25% water-added milk compared to fresh milk, they were not significantly different (P>0.05) across the other adulterated samples when compared to fresh milk. Whey protein and non-protein nitrogen levels were statistically consistent (P>0.05) across all the samples. The results indicate that the nitrogen distribution pattern, in its current state, cannot be used to detect milk adulteration effectively. Further research with a larger dataset considering various factors affecting nitrogen distribution in milk is recommended for conclusive results. Bangladesh Journal of Animal Science 53 (1): 23-30, 2024

Differences in sediment nitrogen and phosphorus distribution between riverside and lakeside wetlands in a river-connected lake

The distribution of nutrients in sediments is the result of multiple factors, including hydrological conditions and vegetation regulation, and in wetlands with complex hydrological conditions, this distribution is uncertain. In this study, the spatial distribution patterns of nitrogen and phosphorus in sediments were studied in the riverside and lakeside wetlands of Dongting Lake, a typical river-connected lake. The results showed that the nitrogen and phosphorus concentrations in the surface sediments were higher than those in the subsurface sediments in both the riverside and lakeside wetlands. In addition, the concentration of total nitrogen (TN) of lakeside wetlands in the surface sediments was higher than that of riverside wetlands, whereas the concentration of total phosphorus (TP) did not differ between the two wetland types. In the surface sediments, there were significant positive correlations between the TN and TP concentrations in the riverside wetlands (p < 0.05), but no significant correlation in the lakeside wetlands (p > 0.05). In riverside wetlands, the nitrogen and phosphorus concentrations showed strong spatial dependence. However, in the lakeside wetlands, the spatial dependence of NO3 −-N was strong, that of NH4 +-N was moderate, and that of TN and TP was weak. This study shows that both hydrology and vegetation cause differences in the distribution of nutrients in the sediments. The results obtained from this investigation clarify the differences of sediment nitrogen and phosphorus distributions in the two types of wetlands and provide a technical reference for the management of different wetland types.

Algal Decomposition Accelerates Denitrification as Evidenced by the High-Resolution Distribution of Nitrogen Fractions in the Sediment–Water Interface of Eutrophic Lakes

This study investigates the decomposition process of algal blooms (ABs) in eutrophic lakes and its impact on the labile endogenous nitrogen (N) cycle. In situ techniques such as diffusive gradients in thin films (DGT) and high-resolution dialysis (HR-Peeper) were employed to decipher the vertical distribution of N fractions within the sediment–water interface (SWI) in Taihu, China. Additionally, an annular flume was used to simulate regional differences in lake conditions and understand labile nitrogen transformation during AB decomposition. This study reveals that the NH4+-N fraction exuded from algae is subsequently converted into NO3-N and NO2-N through nitrification, resulting in a significant increase in the concentrations of NO3−-N and NO2−-N at the SWI. The decomposition of algae also induces a significant increase in dissolved organic matter (DOM) concentration, referring to humic acid and humus-like components; a seven-millimeter decrease in dissolved oxygen (DO) penetration depth; as well as a significant decrease in the pH value near the SWI, which consequently promotes denitrification processes in the sediment. Moreover, the decomposition process influences nitrogen distribution patterns and the role conversion of sediments between a “source” and a “sink” of nitrogen. This investigation provides evidence on the migration and/or transformation of N fractions and offers insights into the dynamic processes across the SWI in eutrophic lakes.

Influence of cultivation techniques on dry matter partitioning, nitrogen distribution pattern and yield of super hybrid rice Liangyoupeijiu

Liangyoupeijiu was grown under different crop cultivation techniques viz: conventional tillage and transplanting (CTTP), no tillage and transplanting (NTTP), conventional tillage and direct seeding (CTDS) and no- tillage and direct seeding (NTDS) during 2011 and 2012. Results showed that, CTTP had higher leaf dry weight than NTTP. Maximum leaf dry weight reduced in direct seeded than transplanted rice. Shoot dry weight reduced by 6% both in transplanted and direct seeded rice from heading to 12 days after heading (DAH) in both the years. No tillage and transplanting had higher export percentage of dry matter and transport percentage of dry matter among the cultivation techniques in both the years. At heading, leaf nitrogen concentration (%) and nitrogen uptake (g m-2) were higher in transplanted than direct seeded rice and significantly higher nitrogen uptake was observed under conventional tillage and transplanting in both the years. The physiological nitrogen use efficiency was higher in no-tillage than conventional tillage in both the years. Total nitrogen (kg ha-1) uptake was higher in conventional tillage than no tillage either in transplanted or in direct seeded rice and was higher under conventional tillage and transplanting among the cultivation techniques in both the years. Grain yield was closely associated with uptake of total nitrogen at heading. Although, direct seeded rice had more than 23% higher panicle number than transplanted rice but conventional tillage and transplanting produced higher grain yield due to higher uptake of nitrogen by grain at maturity and bigger sink size. Bangladesh Rice J. 26 (2): 51-62, 2022

Enhancing leaf photosynthesis from altered chlorophyll content requires optimal partitioning of nitrogen

While optimising leaf chlorophyll content ([CHL]) has been proposed as a relevant means to manipulate canopy light penetration and canopy photosynthesis, effects of modifying [CHL] on leaf photosynthesis are yet to be investigated thoroughly. A greenhouse experiment and a field experiment were conducted involving rice genotypes of different genetic backgrounds and their leaf-colour variants. Leaf photosynthesis was more influenced by alteration to yellow-leaf than to stay-green cases. Higher specific leaf area and stomatal conductance were observed in two yellow-leaf variants, while only one yellow-leaf variant showed significantly increased Rubisco carboxylation capacity (Vcmax), maximum electron transport rate (Jmax), and photosynthetic nitrogen-use efficiency (PNUE). Model analysis indicated that reducing leaf [CHL] decreased the energy loss via non-photochemical quenching, but improving Vcmax, Jmax, and PNUE would require an improved nitrogen distribution pattern within the leaf. Label-free quantitative proteomics confirmed that an increased investment of nitrogen in Cyt b6/f and Rubisco was observed in the yellow-leaf variant of the genetic background with improved Vcmax, Jmax, and PNUE, but not in the other background. Our results suggest that reducing [CHL] can improve leaf photosynthesis only if the saved nitrogen is optimally distributed to proteins that are more rate-limiting to photosynthesis.

An exploration into the relationship between mineral elements (nitrogen and phosphorus) and nutritional quality in soil-watermelon (Citrullus lanatus) system

To fundamentally explore the correlation between crop nutritional quality and mineral elements, specific tests and accurate analysis were carried out on all organs and root soil of watermelon (Citrullus lanatus). The results showed that the distribution patterns of nitrogen and phosphorus at watermelon maturity were similar, and the average nitrogen and phosphorus contents were in the orders of leaf and seed > stem, peel, root > pulp > root soil, and peel > seed > root, stem, leaf > root soil > pulp, respectively. From the perspective of element geochemistry, biophile and lithophile elements had the strongest correlation with nitrogen and phosphorus, and watermelon did not antagonize soil nitrogen and phosphorus uptake. The prediction model of nitrogen translocation factor in watermelon organs to total acid was established by partial least squares with R2 = 0.81. Significantly, when the isometric log-ratio of nitrogen to phosphorus in watermelon leaves was 1.97 to 2.19, the watermelon pulp showed better quality with total acid > 0.5%, total sugar > 5% and soluble solids > 10%. Therefore, the characterization of nitrogen and phosphorus in watermelon leaves can serve as a non-destructive analysis to predict watermelon fruit quality.

Temporal variation in distribution pattern of nitrogen in Albizia chinensis (Osb.) Merr. as a function of nitrate reductase and nitrogenase activity

Temporal variation in distribution pattern of nitrogen in Albizia chinensis (Osb.) Merr. as a function of nitrate reductase and nitrogenase activity

Spatio-Temporal Patterns of Nitrogen and Phosphorus Stoichiometry in Cascade Ponds in an Agricultural Small Watershed and Their Influencing Factors

Ecological stoichiometry of nitrogen and phosphorus is an important indicator to characterize the nitrogen and phosphorus trophic status in aquatic ecosystems. The study of the spatio-temporal patterns of nitrogen and phosphorus stoichiometry is beneficial to the nitrogen and phosphorus pollution management in pond ecosystems. In this study, 18 groups (36 in total) of typical cascade ponds were selected as long-term observations to investigate the spatial distribution patterns of nitrogen and phosphorus component ratios (ratio of total nitrogen to phosphorus: TN:TP, ratio of dissolved nitrogen to phosphorus: TDN:TDP, ratio of particulate nitrogen to phosphorus: PN:PP) in water bodies in the tropical agricultural watershed of Jinjing. The results showed that the average values of TN:TP and TDN:TDP in the upstream ponds were 26.4 and 53.4, respectively, and were more than those in the downstream (22.95 and 48.1, respectively). In contrast, the PN:PP (13.78) in the upstream was significantly lower than that of the downstream (30.39). Furthermore, the factors of rainfall, agricultural land use and fish farming influenced the spatio-temporal variability of the N:P ratios. The ratios of TN:TP and TDN:TDP were higher in the wet season and lower in the dry season. Agricultural land use and fish farming reduced the ratios of the above three nitrogen and phosphorus components in cascade ponds in the study area. Our results show that strengthening agricultural land pollution control and aquaculture management could help to improve water quality of pond ecosystems in the study area.

Spatial distribution patterns of nitrogen and phosphorus in water and bed sediment of the Three Gorges Reservoir

Nutrient state in the Three Gorges Reservoir has long been concerned. Mainstream of the reservoir however has received relatively less researchers’ attention compared to tributaries. In 2015–2017, we sampled 40 cross-sections along mainstream and 10 tributaries in flood and dry seasons in order to reveal lateral, vertical, and longitudinal distribution patterns of total nitrogen (TN) and phosphorus (TP) in water and sediment. Concentrations of waterborne TN and TP ranged from 1.48 to 2.33 mg/L and 0.09 to 0.16 mg/L respectively. Laterally, nutrients were well mixed and homogeneously distributed. Vertically, nutrients concentrations in surface water were higher than in bottom water. Longitudinally, TN concentration increased from tail to head of the reservoir due to accumulation of nitrogen imported from riparian zone and tributaries, whereas TP concentration decreased from tail to head because of sediment deposition. TN and TP concentrations in channel bed sediment were 622–949 and 916–950 mg/kg respectively. Neither of them had significant longitudinal trends nor correlations with waterborne nutrient concentrations. This work will help to understand nutrient dynamics in the Three Gorges Reservoir.

Climatic Changes and Anthropogenic Activities Driving the Increase in Nitrogen: Evidence from the South-to-North Water Diversion Project

As one of the most widespread elements, nitrogen has been broadly concerned in water bodies. Understanding variations in nitrogen is of paramount importance to ecosystem stability and human health. The spatiotemporal variations in total nitrogen (TN) and ammonia in the Middle Route of the South-to-North Water Diversion Project (MRP) during the period from 2015 to 2019 were evaluated. The correlation between anthropogenic activities based on quantitative land use cover and nitrogen concentration was addressed. The results indicated that TN increased by 0.072 mg/L from south to north over the period (p &lt; 0.05), but ammonia decreased by 0.018 mg/L (p &lt; 0.05), notably, in five years. In addition, Chl a had the highest concentration in autumn, showing seasonal variation. The linear regression showed that ammonia concentration was significantly negatively correlated with Chl a (p &lt; 0.1). Furthermore, as human activities’ intensity increased by 6‰ from 2015 to 2019, TN increased and ammonia decreased. The rhythm of meteorological conditions could also result in the variation in nitrogen, which affected N concentration in the MRP. The increase in construction land and agricultural land led to TN increase, and algae absorption was one of the reasons leading to the decrease in ammonia. It could be concluded that climatic changes and anthropogenic activities were the driving forces of nitrogen changes in the MRP. Thus, land use changes around the MRP should be the focus of attention to reduce the nitrogen concentration. This study is the first report on the nitrogen distribution pattern in the MRP. It could be useful to authorities for the control and management of nitrogen pollution and better protection of water quality.

Analysis of Non-Point Source Pollution Features of Chao River Basin Based on the CMADS-Driven SWAT Model

By the China Meteorological Assimilation Driving Datasets for the Soil and Water Assessment Tool (SWAT) model (CMADS 1.0), this paper simulated the non-point source (NPS) pollution of Chao River Basin in the upper reach of Miyun Reservoir, and analyzed the spatial-temporal distribution pattern of nitrogen and phosphorus pollutants and the contribution rates of pollution sources. The major findings of the research are as follows. The CMADS V1.0-driven SWAT model shows good applicability to the study area. The simulation of the runoff, nitrogen and phosphorous pollution in the calibration period and the validation period has yielded a Nash-Sutcliffe efficiency (Ens) coefficient at 0.51~0.78, and a coefficient of determination at 0.73~0.88, which meets the model evaluation standards. The total nitrogen (TN) and total phosphorus (TP) pollution load in the flood season is considerably large, and the average inflow of TN and TP into the reservoir accounts for 60.62% and 75.15% the total annual inflow, respectively. The #26 sub-basin marks the biggest TN and TP loads, and it is thus worth more attention from pollution control administrations. Overall, the TN and TP load in the lower reach of the basin are larger than the upper reach. NPS pollution is the major type of pollution caused by human production and life. The livestock and poultry farming as well as fertilizers, which are the main contributors to NPS pollution, are considered the focus of NPS pollution control.

Fencing enclosure alters nitrogen distribution patterns and tradeoff strategies in an alpine meadow on the Qinghai-Tibetan Plateau

The grasslands of Qinghai-Tibetan Plateau have become extremely degraded, resulting in widespread deficiency of soil N. In efforts to restore degraded lands, fencing enclosure has been used extensively. However, the effect of fencing on N allocation patterns and nutritional strategy of alpine plants are equivocal. In this study, we used 15N tracer (CO (15NH2)2, 10 g N m−2) to examine the allocation and distribution of N in plants and soil in grasslands either grazed heavily by livestock or fenced for three years in an alpine meadow of Northern Tibet. The 15N recovery (15Nrec) in shoots of the fenced enclosure increased by 207% in grasses, decreased by 103% in forbs, and did not change in sedges when compared to the grazed meadow. The 15Nrec in shoots accounted for only 1.97% and 4.65% of the total N in the grazed and fenced meadows, respectively. Fencing increased soil 15N content at 0–5 cm depth by 6.9%, but decreased the content at 5–10 cm depth by 11.7%. The results demonstrated that fencing altered the soil N distribution by increasing 15Nrec in top soil and by decreasing 15Nrec in subsurface soil. In addition, fencing had no impact on root 15N storage (33%–39%), 15N losses (9.6%–12.5%) and soil available 15Nrec (NH4+-N, NO3–-N and light fraction organic N), but decreased root:shoot 15Nrec ratio by 49.8% (16.9:1 in grazed and 8.4:1 in fenced grassland). Fencing increased soil organic carbon, total N and NO3–-N concentrations, which indicated that the strategy of the plants was to allocate relatively more N to roots in nutrient-poor soil (grazed) but relatively more N to shoots in nutrient-rich soil (fenced).

Short-term effects of nitrogen deposition on nitrogen spatial and temporal distributions in a Calamagrostis angustifolia wetland of the Sanjiang Plain.

Nitrogen (N) availability is an important factor regulating the feedback mechanisms of global change. This research uses a small Calamagrostis angustifolia wetland i = on the Sanjiang Plain of Northeast China as the research object and 15N tracer technology to study the effects of different nitrogen deposition levels (0 gN/m2, 4 gN/m2, and 8 gN/m2) through in situ controlled field experiments. Temporal and spatial distribution patterns of nitrogen in plants and soils and their short-term effects on nitrous oxide emissions fluxes were studied. The results showed that 1) the nitrogen content in the stems, leaves and roots of C. angustifolia decreased slowly with the growing season. Nitrogen application significantly increased the absorption of tracer nitrogen in the aboveground and underground plant parts (P<0.01), and the more nitrogen applied, the larger the absorption amount was (P<0.01). The absorbed amount accounted for 52%-86% of the total tracer nitrogen. 2) The tracer nitrogen in the soil did not show a significant change; the more nitrogen that was applied, the more nitrogen that was retained in the soil, and the tracer nitrogen adsorbed by the soil was mainly ammonium nitrogen. 3) The variation in the 15N-labeled nitric oxide emissions flux under different nitrogen treatments was consistent; nitrogen application increased the 15N-labeled nitric oxide emissions flux, but the difference between the low-nitrogen and high-nitrogen treatments was not significant (P>0.05).

Carbon and nitrogen distribution pattern in soil profile cultivated with Eucalyptus

ABSTRACT The objective of this study was to evaluate the distribution pattern of total organic carbon (TOC) and total nitrogen (TN) in the native field soil profile and Eucalyptus sp. The study was carried out in native field and in eucalyptus plantations with 20, 44, 180 and 240 months, located in Santa Maria and Manoel Viana, RS, Brazil. The decay rate (k) of the TOC and TN contents up to 1.2 m depth was determined by the graphical, numerical and mathematical method using the third order negative exponential model. The content of TOC and TN deep in the soil showed a third order negative exponential distribution. However, the methods used to estimate the decay rate generate differences in TOC and TN contents along the soil profile.

Groundwater nitrate reduction versus dissolved gas production: A tale of two catchments.

At the catchment scale, a complex mosaic of environmental, hydrogeological and physicochemical characteristics combine to regulate the distribution of groundwater and stream nitrate (NO3-). The efficiency of NO3- removal (via denitrification) versus the ratio of accumulated reaction products, dinitrogen (excess N2) & nitrous oxide (N2O), remains poorly understood. Groundwater was investigated in two well drained agricultural catchments (10km2) in Ireland with contrasting subsurface lithologies (sandstone vs. slate) and landuse. Denitrification capacity was assessed by measuring concentration and distribution patterns of nitrogen (N) species, aquifer hydrogeochemistry, stable isotope signatures and aquifer hydraulic properties. A hierarchy of scale whereby physical factors including agronomy, water table elevation and permeability determined the hydrogeochemical signature of the aquifers was observed. This hydrogeochemical signature acted as the dominant control on denitrification reaction progress. High permeability, aerobic conditions and a lack of bacterial energy sources in the slate catchment resulted in low denitrification reaction progress (0-32%), high NO3- and comparatively low N2O emission factors (EF5g1). In the sandstone catchment denitrification progress ranged from 4 to 94% and was highly dependent on permeability, water table elevation, dissolved oxygen concentration solid phase bacterial energy sources. Denitrification of NO3- to N2 occurred in anaerobic conditions, while at intermediate dissolved oxygen; N2O was the dominant reaction product. EF5g1 (mean: 0.0018) in the denitrifying sandstone catchment was 32% less than the IPCC default. The denitrification observations across catchments were supported by stable isotope signatures. Stream NO3- occurrence was 32% lower in the sandstone catchment even though N loading was substantially higher than the slate catchment.

Light–nitrogen relationships within reproductive wheat canopy are modulated by plant modular organization

Within dense canopies, the spatial distribution of nitrogen between leaves in relation to the local light environment is an important and widely investigated adaptive response of plant carbon and nitrogen economy. However a general picture of how nitrogen distribution in photosynthetic tissues, not only in leaf laminae, is structured at plant scale and is affected by the topology and light environment of plant modules (i.e. lamina, sheath, internode) is missing. We investigated the spatial patterns of nitrogen distribution in relation with plant botanical structure for wheat (Triticum aestivum L.) culms. Nitrogen distribution between and within laminae, sheaths and internodes was quantified at anthesis and during grain filling, for two cultivars with contrasted leaf posture grown in the field under low and high N fertilization. We found that independently of leaf posture, specific nitrogen mass (i.e. nitrogen mass per unit surface area) was homogeneous within individual laminae and sheaths, although they spanned a significant depth in the canopy. Sharp changes in nitrogen specific mass at module boundaries were observed. At the canopy level, vertical nitrogen gradients resulted from a decrease of mean specific nitrogen mass of individual plant modules with their position along the culm, and laminae and sheaths specific nitrogen mass decreased linearly with the distance from the top of the canopy. There was no significant gradient of N concentration on a dry mass basis within and between the enclosed internodes, only the distal part of the ear peduncle, which was exposed to the light, showed a strong N gradient. This study gives important information to better understand the phenotypic plasticity of nitrogen distribution in wheat and to build a process-based model of N distribution within wheat culms during the post-anthesis period. It strongly supports the idea that processes should be formalized at the module scale and that a similar formalization can be used for individual laminae and sheaths.

Spatio-temporal dynamics of nitrogen in river-alluvial aquifer systems affected by diffuse pollution from agricultural sources: Implications for the implementation of the Nitrates Directive

Reducing nitrate pollution from diffuse agricultural sources is the major environmental challenge in the two adjacent catchments of the Oja–Tirón and Zamaca rivers (La Rioja and Castilla y León, northern Spain). For this reason, part of their territory was designated a Nitrate Vulnerable Zone (NVZ) according to the Nitrates Directive. The Oja Alluvial Aquifer, the Tirón Alluvial Aquifer and their associated rivers are particularly vulnerable to nitrogen pollution due to the shallow water table, the high permeability of alluvial deposits, interconnections between the alluvial aquifers and surface waters and pressures from agriculture. To this end, nine sampling campaigns, organised on a semi-annual basis and focused on the rivers and alluvial aquifers of the two catchments, were carried out from April 2005 to April 2009. The main objectives of the study were: (1) to investigate the chemical forms of nitrogen in river-alluvial aquifer systems of the Oja–Tirón and Zamaca catchments, (2) to improve our understanding of the spatio-temporal patterns of nitrogen distribution in the alluvial aquifers and associated rivers by integrating hydrochemical data and hydrogeological and environmental parameters, (3) to estimate the amount of nitrogen exported from the rivers and alluvial aquifers to the River Ebro, and (4) to evaluate the suitability of the current method of designating NVZs in the area. High groundwater flow velocities in the upper alluvial zones favoured the advective transport of nitrate and generated a dilution effect. In these areas, inter-annual variations in nitrate concentrations were observed related to precipitation and N-input from agriculture. However, low flow velocities favoured processes of accumulation in the lower alluvial zones. Our results demonstrated that the entire alluvial surface was highly vulnerable, according to dynamics of the nitrogen in the river-alluvial aquifer systems being studied. The amount of nitrogen exported from these river-alluvial aquifer systems to the River Ebro was estimated at 2.4 ± 0.2 kt year−1. Findings from this investigation highlight the need to include the alluvial area corresponding to the Tirón aquifer as a NVZ, particularly as the Tirón sub-catchment provides more than half of the nitrogen exported from the River Tirón to the River Ebro. Based in these results, at least the entire alluvial surface in the study area should be considered a NVZ in order to address the recovery of water quality.

Spatial and temporal distribution patterns of nitrogen in marsh soils from an inland alkaline wetland – A case study of Fulaowenpao wetland, China

Samples of surface (0–10 cm) and subsurface soils (10–20 cm) were collected using a grid sampling method in July and September in order to study the spatial and temporal distribution patterns of all forms of nitrogen and total nitrogen (TN) and the relationships between nitrogen concentrations and selected soil properties in Fulaowenpao wetland, a typical inland alkaline wetland. Results showed that there existed obvious heterogeneity at spatial and temporal scales. Generally, higher spatial variability for nitrate nitrogen ( NO 3 - –N), ammonium nitrogen ( NH 4 + –N) and available nitrogen (AN) were observed compared to organic nitrogen (Org-N) and TN. At the spatial scale, concentrations of NO 3 - –N, NH 4 + –N and AN in surface soils were higher than those in subsurface soils, but no significant differences were observed between both soil layers ( p < 0.05). However, concentrations of Org-N and TN were significantly higher in surface soils compared to subsurface soils ( p < 0.05), and both of them had similar spatial distribution patterns. At the temporal scale, with the exception of NH 4 + –N in both soil layers and NO 3 - –N in subsurface soils, concentrations of all the other forms of nitrogen and TN were generally higher in September than them in July, while there were no significant differences between both sampling periods ( p < 0.05) except for AN ( p < 0.01) in both soil layers. Correlation analysis showed that AN, Org-N and TN were significantly and positively correlated with soil organic matter, total phosphorous, and clay contents, while they were significantly negatively correlated with soil pH values; NO 3 - –N was also correlated with soil organic matter and total phosphorous, however, NH 4 + –N was only closely lined to water contents.