Dissolved Inorganic Nitrogen Loss Research Articles

Increased Soil Soluble Nitrogen Stocks and Decreased Nitrogen Leaching Loss in Rice Paddy Soil by Replacing Nitrogen Fertilizer with Chinese Milk Vetch

Reducing soil nitrogen leaching losses and improving nitrogen-use efficiency with effective fertilization management strategies are extremely important for sustainable agricultural development. A 2-year field study was executed with the same nitrogen input in a subtropical rice production system in Southeast China, using chemical fertilizers as a control (CK), to study the influences of different application amounts of Chinese milk vetch (CMV), i.e., 15,000 kg hm−2 (CL), 30,000 kg hm−2 (CM), and 45,000 kg hm−2 (CH), on soil soluble nitrogen stock and leaching risks in a clay paddy field. The results showed that the soil stocks of soluble inorganic nitrogen (SIN) and soluble organic nitrogen (SON) in a 0–60 cm soil profile under different application amounts of CMV significantly increased by 12.43–36.03% and 19.43–71.75% compared with CK, respectively, which was more favorable to soil SON accumulation. In the 2-year experiment, the total dissolved nitrogen leaching loss was 23.51–61.88 kg hm−2 under different application rates of CMV, of which 50.08–62.69% was leached by dissolved inorganic nitrogen (DIN), and 37.31–49.92% was leached by dissolved organic nitrogen (DON). CMV application improved soil properties (pH, SOM, and urease/protease), increased SIN and SON stocks, and decreased surface water DIN and DON concentrations, thereby reducing DIN and DON leaching. The leachings of DIN and DON in different application rates of CMV were reduced by 11.37–66.23% and 13.39–52.07% compared with the CK treatment, respectively. Conclusively, nitrogen leaching loss in paddy fields was severe, and the DIN and DON leaching loss in CMV treatments were lower than those in the control under the same nitrogen input. Thus, replacing nitrogen fertilizer with CMV under the same nitrogen input could reduce the risk of nitrogen nonpoint pollution in clay paddy fields.

Ten years of monitoring dissolved inorganic nitrogen in runoff from sugarcane informs development of a modelling algorithm to prioritise organic and inorganic nutrient management

Reducing nitrogen (N) losses from cropping systems to aquatic ecosystems is a global priority. In Australia, N losses from sugarcane production in catchments adjacent to the Great Barrier Reef (GBR) are threatening the health of this World Heritage-listed coral reef ecosystem. N losses from sugarcane can be reduced by improving fertiliser management. However, little is known about the contribution of organic sources of N, such as mill mud. We used more than 10 years of data from two of the main Australian sugarcane regions, a high (Wet Tropics) and moderate (Mackay Whitsundays) rainfall area, to calibrate and validate a model to predict dissolved inorganic nitrogen (DIN) losses in runoff from both inorganic and organic fertilisers. DIN losses in runoff were well simulated (RMSE = 0.37 and 2.0 kg N ha−1 for the Wet Tropics and Mackay Whitsunday regions, respectively). Long-term simulations of rate and fertiliser deductions to account for N from organic sources showed that adopting best management practices for organic fertiliser (applying ≤50 wet t ha−1 mill mud) can significantly reduce DIN in runoff losses compared with applications of 150 wet t ha−1. Simulations of typical farmer practices in relation to fallow management (bare fallow vs. legume fallow) and organic fertiliser placement (buried in a fallow but surface applied to a green cane trash blanket in ratoons) showed that inorganic fertiliser rates need to be adjusted to account for N inputs from both mill mud and legume crops. Rates of application of organic N had a larger impact on DIN runoff losses than placement or timing of application. This work presents a DIN in runoff modelling algorithm that can be coupled with nitrogen models readily available in agricultural models to assess the impact of nutrient management on the quality of water leaving agricultural systems.

Implications of water quality policy on land use: a case study of the approach in New Zealand

Achieving good water quality through output controls is difficult. The New Zealand Government recently proposed enforceable bottom lines to protect ecosystem health of 1mgL–1 dissolved inorganic nitrogen (DIN) and 0.018mgL–1 dissolved reactive phosphorus (DRP), but has now delayed considering them. In examining whether these bottom lines could be met through mitigating DIN and DRP losses from existing land uses, we found that if all known strategies to mitigate N and P loss were implemented by 2035, the proportion of catchments exceeding these bottom lines would be predicted to be 4% for DIN and 9% for DRP. If bottom lines were enforced, land use would likely change, but to change successfully good advice and effective multilevel governance are required. Advice should expand and standardise elements of farm environment plans that spatially isolate critical source areas of N and P loss and apply cost-effective mitigations. Governance should focus on combining these plans with the national bottom lines and technical support to connect practices and land use at the farm scale to meeting water quality bottom line at the catchment scale.

Fertiliser management effects on dissolved inorganic nitrogen in runoff from Australian sugarcane farms

Dissolved inorganic nitrogen (DIN) movement from Australian sugarcane farms is believed to be a major cause of crown-of-thorns starfish outbreaks which have reduced the Great Barrier Reef coral cover by ~21% (1985–2012). We develop a daily model of DIN concentration in runoff based on >200 field monitored runoff events. Runoff DIN concentrations were related to nitrogen fertiliser application rates and decreased after application with time and cumulative rainfall. Runoff after liquid fertiliser applications had higher initial DIN concentrations, though these concentrations diminished more rapidly in comparison to granular fertiliser applications. The model was validated using an independent field dataset and provided reasonable estimates of runoff DIN concentrations based on a number of modelling efficiency score results. The runoff DIN concentration model was combined with a water balance cropping model to investigate temporal aspects of sugarcane fertiliser management. Nitrogen fertiliser application in December (start of wet season) had the highest risk of DIN movement, and this was further exacerbated in years with a climate forecast for ‘wet’ seasonal conditions. The potential utility of a climate forecasting system to predict forthcoming wet months and hence DIN loss risk is demonstrated. Earlier fertiliser application or reducing fertiliser application rates in seasons with a wet climate forecast may markedly reduce runoff DIN loads; however, it is recommended that these findings be tested at a broader scale.

The influence of nutrient loading, climate and water depth on nitrogen and phosphorus loss in shallow lakes: a pan-European mesocosm experiment

Losses of phosphorus (P) and nitrogen (N) have important influences on in-lake concentrations and nutrient loading to downstream ecosystems. We performed a series of mesocosm experiments along a latitudinal gradient from Sweden to Greece to investigate the factors influencing N and P loss under different climatic conditions. In six countries, a standardised mesocosm experiment with two water depths and two nutrient levels was conducted concurrently between May and November 2011. Our results showed external nutrient loading to be of key importance for N and P loss in all countries. Almost all dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) were lost or taken up in biomass in all mesocosms. We found no consistent effect of temperature on DIN and SRP loss but a significant, though weak, negative effect of temperature on total nitrogen (TN) and total phosphorus (TP) loss in the deeper mesocosms, probably related to higher organic N and P accumulation in the water in the warmer countries. In shallow mesocosms, a positive trend in TN and TP loss with increasing temperature was observed, most likely related to macrophyte growth.

Linking seasonal inorganic nitrogen shift to the dynamics of microbial communities in the Chesapeake Bay

Seasonal shifts of dissolved inorganic nitrogen (DIN) and the dynamics of microbial communities for nitrogen transformation were investigated in the water column of Chesapeake Bay. The relative abundance of nitrogen over phosphorus (N) showed a strong seasonal and spatial pattern: gradually decreased from upstream to downstream; high in winter and low in summer. Because the phosphorus concentration remained relatively stable, the spatiotemporal pattern of N implied that a substantial fraction of DIN was removed in the bay, especially in summer. Correlation analyses indicated the functional microbial communities and environmental variables, such as temperature, dissolved oxygen, salinity, played important roles for connecting the seasonal variation of N. Among them, temperature was the trigger factor. High temperature in the summer induced the growth of functional microbes, which subsequently consumed a large portion of DIN inputted from the tributaries and reduced the N. The current study provided the relative importance of microbial communities and environmental variables in driving the DIN loss in the bay.

Conceptual frameworks for estimating the water quality benefits of improved agricultural management practices in large catchments

Chemical and sediment losses from agricultural lands are threatening coastal marine and aquatic ecosystems in many parts of the world. This is an acute problem in Australia, where the condition of Great Barrier Reef (GBR) ecosystems is threatened by increased pollutant loads from agricultural lands, and Governments have enacted policies to reduce pollutant exports. These policies raise the question of how to identify changes in land management that will effectively reduce exports. The scale of the GBR catchments (> 400,000km2) precludes detailed modelling investigations, especially within the time scale of policy implementation. Therefore, we developed conceptual frameworks linking agricultural land management to river pollutant exports for two contrasting agricultural pollutants posing threats to the health of GBR ecosystems; dissolved inorganic nitrogen (DIN) and fine sediment (silt and clay), based on a synthesis of past studies. We argue that nitrogen (N) Surpluses (N inputs relative to crop N off-take), are the primary driver of DIN losses from agricultural land to rivers. Similarly, previous studies in GBR grazing lands and elsewhere have quantitatively defined how sediment losses from hill slopes, gullies and stream banks are related to grazing land condition, ground cover and riparian management, which are products of recent climate and grazing practices. From these frameworks we derive relationships between firstly, estimated N Surplus and DIN exports, and secondly ground cover and river fine sediment exports. Using these relationships we examine how DIN and fine sediment exports to the GBR may respond to a range of management scenarios for reducing N inputs, and increasing ground cover and improving riparian management. We predict that widespread adoption of the most extreme scenarios would approximately meet water quality improvement targets set/implied by governments for these two pollutants. However, it is unlikely that these extreme scenarios will be adopted to the extent needed and in the time frames set by current policy. In particular, the agri-environmental management practices defined in this study for N are generally unproven in GBR cropping systems, the required levels of pasture cover and riparian management are generally beyond current experience, and it can take decades to improve land condition, and so reduce erosion rates after cover increases. We also show that the approach taken is applicable to other pollutants, such as total N, that combine characteristics of the pollutants considered here. For the case of total N, the reductions in pollutant loads are not as great smaller relative to targets than for DIN or fine sediments.

Biogeochemical controls on the oxygen, nitrogen and sulfur distributions in the water column of Golfo Dulce: an anoxic basin on the Pacific coast of Costa Rica revisited

Chemical distributions, respiration rates, and bacterial distributions were measured in 1994 in the water column and sediments of a small, tropical, anoxic basin (Golfo Dulce, Pacific coast of Costa Rica) to examine the biogeochemical controls on anoxia, sulfide, dissolved inorganic nitrogen, and organic carbon consumption. As reported previously, the deepest 100 m of the water column were anoxic, and sulfide concentrations in the bottom waters were less than 7 μM and then only transiently. Both free-swimming sulfide-oxidizing bacteria and Beggiatoa sp. (containing large vacuoles) were observed in the anoxic bottom waters or at the sediment-water interface. Aerobic respiration dominated the decomposition of organic matter in the surface waters and pycnocline, whereas sulfate reduction was principally restricted to the sediments. Bacteria were distributed in discrete zones and exhibited the highest densities where oxygen decreased below 1 μM around 100 m depth, and near the sediment-water interface. The sub-oxic, sub-pycnocline water column was characterized by a dissolved inorganic nitrogen (DIN) deficit of 2.9 mole m-2. With a water residence time of 35 – 57 d, estimated from a salt balance, this deficit corresponded to a DIN loss of 51 – 85 mmol m-2 d-1, comparable to the sub-pycnocline oxygen consumption. Sulfide in the water column was maintained at low concentrations by frequent inputs of oxygenated water from the Pacific Ocean. Sulfide production in the sediments due to bacterial sulfate reduction was scavenged by frequent deposition of iron-rich turbidites. Based on 210Pb distributions, the most recent emplacement of a turbidite in the basin sediments was determined to have occurred between 1989 and 1992. Rev. Biol. Trop. 54 (Suppl. 1): 171-191. Epub 2006 Sept. 30.

TERRESTRIAL C SEQUESTRATION AT ELEVATED CO2AND TEMPERATURE: THE ROLE OF DISSOLVED ORGANIC N LOSS

We used a simple model of carbon–nitrogen (C–N) interactions in terrestrial ecosystems to examine the responses to elevated CO2 and to elevated CO2 plus warming in ecosystems that had the same total nitrogen loss but that differed in the ratio of dissolved organic nitrogen (DON) to dissolved inorganic nitrogen (DIN) loss. We postulate that DIN losses can be curtailed by higher N demand in response to elevated CO2, but that DON losses cannot. We also examined simulations in which DON losses were held constant, were proportional to the amount of soil organic matter, were proportional to the soil C:N ratio, or were proportional to the rate of decomposition. We found that the mode of N loss made little difference to the short-term (<60 years) rate of carbon sequestration by the ecosystem, but high DON losses resulted in much lower carbon sequestration in the long term than did low DON losses. In the short term, C sequestration was fueled by an internal redistribution of N from soils to vegetation and by increases in the C:N ratio of soils and vegetation. This sequestration was about three times larger with elevated CO2 and warming than with elevated CO2 alone. After year 60, C sequestration was fueled by a net accumulation of N in the ecosystem, and the rate of sequestration was about the same with elevated CO2 and warming as with elevated CO2 alone. With high DON losses, the ecosystem either sequestered C slowly after year 60 (when DON losses were constant or proportional to soil organic matter) or lost C (when DON losses were proportional to the soil C:N ratio or to decomposition). We conclude that changes in long-term C sequestration depend not only on the magnitude of N losses, but also on the form of those losses.

Input-Output Budgets of Inorganic Nitrogen for 24 Forest Watersheds in the Northeastern United States: A Review

Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watersheds at 15 locations in the northeastern United States. The study watersheds are completely forested, free of recent physical disturbances, and span a geographical region bounded by West Virginia on the south and west, and Maine on the north and east. Total N budgets are not presented; however, fluxes of inorganic N in precipitation and streamwater dominate inputs and outputs of N at these watersheds. The range in inputs of DIN in wet-only precipitation from nearby National Atmospheric Deposition Program (NADP) sites was 2.7 to 8.1 kg N ha −1 yr −1 (mean = 6.4 kg N ha −1 yr −1 ;m edian =7 .0 kg Nh a −1 yr −1 ). Outputs of DIN in streamwater ranged from 0.1 to 5.7 kg Nh a −1 yr −1 (mean = 2.0 kg N ha −1 yr −1 ;m edian =1 .7 kg Nh a −1 yr −1 ). Precipitation inputs of DIN exceeded outputs in streamwater at all watersheds, with net retention of DIN ranging from 1.2 to 7.3 kg N ha −1 yr −1 (mean = 4.4 kg N ha −1 yr −1 ;m edian =4 .6 kg Nh a −1 yr −1 ). Outputs of DIN in streamwater were predominantly NO3-N (mean = 89%; median = 94%). Wet deposition of DIN was not significantly related to DIN outputs in streamwater for these watersheds. Watershed characteristics such as hydrology, vegetation type, and land-use history affect DIN losses and may mask any relationship between inputs and outputs. Consequently, these factors need to be included in the development of indices and simulation models for predicting 'nitrogen saturation' and other ecological processes.

Inorganic Nitrogen Losses from a Forested Ecosystem in Responseto Physical, Chemical, Biotic,and Climatic Perturbations

Nitrate leaching to streams is a sensitive indicator of the biogeochemical status of forest ecosystems. Two primary theories predicting long-term (decadal) changes in nitrate loss rates (N saturation theory and the nutrient retention hypothesis) both predict increasing dissolved inorganic nitrogen (DIN) losses for watershed 6 (W6), the biogeochemical reference watershed at the Hubbard Brook Experimental Forest (HBEF). Measured values, however, have declined substantially since measurements began in the mid-1960s. Are these theories wrong, or are there other important controls on DIN losses at the annual to decadal time scale that have obscured the tendency toward higher losses over time? We tested the individual and combined effects of several forms of disturbance on DIN loss rates from northern hardwood forests by comparing predictions from a relatively simple model of forest carbon, nitrogen, and water dynamics (PnET-CN) with the long-term record of annual DIN loss from W6 at HBEF. Perturbations tested include interannual climate variation, changes in atmospheric chemistry (CO2, O3, N deposition), and physical and biotic disturbances (two harvests, a hurricane salvage, and a defoliation event). No single disturbance caused changes in DIN losses to mimic measured values. Only when run with all of the disturbances combined did the model-predicted pattern of interannual change in DIN loss approach the measured record. Single-disturbance simulations allow an estimation of the role of each in the total pattern of DIN loss. We conclude that DIN losses from W6 were elevated in the 1960s by a combination of recovery from extreme drought and a significant defoliation event. N deposition alone, in the absence of other disturbances, would have increased DIN losses by 0.35 g N m−2y−1. These findings indicate that predictions of DIN losses must take into account the full spectrum of disturbance events and changes in environmental conditions impacting the systems examined.

Nitrogen regeneration and dissolved organic nitrogen release during spring in a NW Mediterranean coastal zone (Gulf of Lions):implications for the estimation of new production

Nitrogen regeneration fluxes of ammonium (NH 4 + ) and nitrate (NO 3 - ) as well as losses of dissolved organic nitrogen (DON) by phytoplankton were investigated over a 2 mo period (spring 1997) in a NW coastal Mediterranean area (Gulf of Lions) using 15 N-tracer techniques. Profiles of dissolved inorganic nitrogen (DIN) concentrations were almost uniform with values of 600, 150 and 35 nM for NO 3 - , NO 2 - and NH 4 + , respectively, except at the end of the study period when the upper layer became nitrogen-depleted (<50 nM down to 40 m). Chlorophyll (chl) distributions showed a surface maximum (to 0.85 mg m -3 ) and a deep maximum (to 1.25 mg m -3 ) at 40 m. Plankton DIN utilization (net uptake) was most of the time highest at the surface, with rates reaching 62 and 40 nM d -1 for NH 4 + and NO 3 - , respectively. However, a deepening (to 60 m) of maximum NO 3 - uptake rates with a corresponding deepening of the nitracline sometimes occurred during the experiment. Therefore, f-ratio profiles depicted maximum surface values (∼0.40) at the beginning of the experiment and a deep maximum at the end. NH 4 + regeneration rates were 1 order of magnitude higher (up to 220 nM d -1 ) than nitrification and DIN loss (as DON) rates, and could largely sustain more than 100% of the plankton NH 4 + demand. Underestimation of NH 4 + uptake rates due to 15 N isotope dilution had only a small effect on the ∫-ratio calculation (overestimation <5%). Nitrification occurred from the surface (10 to 20 nM d -1 ) down to the base of the euphotic layer (30 nM d -1 ), and corresponded to 90% and »100% of the plankton NO 3 - demand at the surface and in the nitracline, respectively. Consequently, a great part of NO 3 - uptake did not correspond to new production and should be considered as regenerated production, particularly in the NO 3 - depleted surface layer. Profiles of DIN loss (as DON) well paralleled those of DIN net uptake with values highest at surface reaching 35 and 14 nM d -1 for NH 4 + and NO 3 - , respectively. DIN loss rates represented on average ∼23% of gross DIN uptake (gross DIN uptake = DIN losses + DIN net uptake) whatever the substrate was, indicating that (1) DIN loss (as DON) did not depend on the nitrogen source, and (2) DIN uptake was mostly due to phytoplankton and not to bacterioplankton, although the study area tended to be globally nitrogen-depleted and based on regeneration. Failure to account for DIN losses had no significant effect on the computation of ∫-ratios.

Measuring gross uptake of 15N‐labeled nitrogen by marine phytoplankton without particulate matter collection: Evidence of low 15N losses to the dissolved organic nitrogen pool

Present 15N tracer techniques allowing indirect estimates of gross uptake of dissolved inorganic nitrogen (DIN) from measurements of DIN net uptake and DIN loss to the dissolved organic nitrogen (DON) pool (DIN gross uptake = DIN net uptake + DIN loss) require collection by filtration of particulate organic nitrogen (PON). We introduce a simple and reliable method that avoids this filtration step and permits direct determination of DIN gross uptake. The method involves (1) collection after 15N tracer addition and incubation of a 300‐ml sample, (2) removal of initial DIN, (3) conversion of total organic nitrogen (PON + DON) to DIN, (4) recovery of formed DIN, and (5) quantification of mass and 15N enrichment of initial and formed DIN. Gross uptake rates obtained in parallel from experiments without particulate matter collection (WOPMC) and with particulate matter collection (WIPMC) were in good agreement (R2 = 0.99) with values ranging from about 0.2 nM h−1 (open ocean) to 200 nM h−1 (culture). Variation in gross uptake rate in a set of five replicate samples, processed using both the WOPMC and WIPMC methods, was less than 7%. Losses of DIN to the DON pool were found to be negligible in laboratory cultures and represented on average only 15% of gross DIN uptake in the open ocean. Experimental considerations suggest that high DIN losses (≥50% of gross DIN uptake) to the DON pool are unlikely for healthy and actively growing cells and probably are limited to dying cells loosing their organic nitrogen content during postbloom situations (cell lysis) and/or during sloppy feeding by zooplankton (cell rupture).

Effects of land use, climate variation, and N deposition on N cycling and C storage in northern hardwood forests

We hypothesized that much of the variability in dissolved inorganic nitrogen (DIN) loss from forested catchments can be explained by land use history and interannual climatic variation, and that these factors determine the degree to which N deposition results in increased storage of C in forests. We used an existing model of C, N, and water balances in forest ecosystems in conjunction with long‐term climate and N leaching loss data from several northern hardwood forest ecosystems to predict the effects of land use, climate variability and N deposition on C storage and N cycling and loss. Six sites from the White Mountains of New Hampshire with very different land use histories and annual stream DIN losses were used. The only model parameter that varied between sites was land use or disturbance history. Each site was simulated using both mean climate data for each year and actual time series climate data. Vegetation removal resulted in a period of increased DIN leaching, followed by losses below those in control stands for both measured and simulated data. One site with an extreme fire event over 170 years ago still showed reduced N losses in both modeled and measured data. Significant interannual variation in DIN loss is evident in the field data. Model predictions using actual climate time series data captured much of this variation. This high interannual variability along with the slow rate of change in DIN loss predicted by PnET‐CN using mean climate throughout the simulations suggests that statistically significant increases in DIN leaching losses due to long‐term increases in N deposition will not be detectable for several decades, given current rates of N deposition. N deposition increased C storage in all simulations, but the quantity stored was about 50% that predicted by another published model. This difference results from differences in the efficiency with which added N is retained in the ecosystem. The previous model used an 80% retention value, while retention was closer to 50% over most of the time period examined here.