Search

Apportionment of nitrate (NO3-) sources in surface water and classification of monitoring locations according to NO3- polluting activities may help implementation of water quality control measures. In this study, we (i) evaluated a Bayesian isotopic mixing model (stable isotope analysis in R [SIAR]) for NO3- source apportionment using 2 yr of δ15N-NO3- and δ18O-NO3- data from 29 locations within river basins in Flanders (Belgium) and five expert-defined NO3- polluting activities, (ii) used the NO3- source contributions as input to an unsupervised learning algorithm (k-means clustering) to reclassify sampling locations into NO3- polluting activities, and (iii) assessed if a decision tree model of physicochemical data could retrieve the isotope-based and expert-defined classifications. Based on the SIAR and d11B results, manure/sewage was identified as a major NO3- source, whereas soil N, fertilizer NO3-, and NH4+ in fertilizer and rain were intermediate sources and NO3- in precipitation was a minor source. The k-means clustering algorithm allowed classification of NO3- polluting activities that corresponded well to the expert-defined classifications. A decision tree model of physicochemical parameters allowed us to correctly classify 50 to 100% of the sampling locations as compared with the k-means clustering approach. We suggest that NO3- polluting activities can be identified via clustering of NO3- source contributions from samples representing an entire river basin. Classification of future monitoring locations into these classes could use decision tree models based on physicochemical data. The latter approach holds a substantial degree of uncertainty but provides more inherent information for dedicated abatement strategies than monitoring of NO3- concentrations alone. [ABSTRACT FROM AUTHOR]

Old-growth forests of southern Chile represent an important reserve of temperate (rain) forests in the world. Wetter and colder forest ecosystems appear to be more efficient in conserving and recycling N such that mostly non-plant available N species are lost, which could be indicated by more depleted δ 15 N values of the soil and plants. Hydrological N loss from the old-growth forests in southern Chile occurs mainly via dissolved organic nitrogen and not via dissolved inorganic N. Forest disturbances ( e.g . fire, clear-cutting or enhanced N deposition) cause (abrupt) changes in ecosystem N-cycling processes. In this study, we hypothesized that δ 15 N signatures of soil profiles under old-growth forests could be used as an integrator for ecosystem N-cycling, and changes of these δ 15 N profiles could be valuable to assess ecosystem resilience towards disturbances. Six old-growth forests were selected in the phytogeographical region of the Valdivian rain forest in southern Chile. One of the sites has been partly burned in February 2002. First, we observed that ecosystems with higher mean annual precipitation and lower mean annual temperature were relatively more depleted in 15 N. Secondly, we found that a forest fire caused a 100-fold increase of the nitrate export and induced an enrichment of the soil δ 15 N signal in the upper 20 cm. [ABSTRACT FROM AUTHOR]

Strategies used to reduce emissions of N2O and CH4 in rice production normally include irrigation management and fertilization. To date, little information has been published on the measures that can simultaneously reduce both emissions. Effects of application of a urease inhibitor, hydroquinone (HQ), and a nitrification inhibitor, dicyandiamide (DCD) together with urea (U) on N2O and CH4 emission from rice growing were studied in pot experiments. These fertilization treatments were carried out in the presence and absence of wheat straw, applied to the soil surface. Without wheat straw addition, in all treatments with inhibitor(s) the emission of N2O and CH4 was significantly reduced, as compared with the treatment whereby only urea was applied (control). Especially for the U+HQ+DCD treatment, the total emission of N2O and CH4 was about 1/3 and 1/2 of that in the control, respectively. In the presence of wheat straw, the total N2O emission from the U+HQ+DCD treatment was about 1/2 of that from the control. The total CH4 emission was less influenced. Wheat straw addition, however, induced a substantial increase in emissions of N2O and CH4. Hence, simultaneous application of organic materials with a high C/N ratio and N-fertilizer (e.g. urea) is not a suitable method to reduce the N2O and CH4 emission. Application of HQ+DCD together with urea seemed to improve the rice growth and to reduce both emissions. The NO3 −-N content of the rice plants and denitrification of (NO3 −+NO2 −)-N might contribute to the N2O emission from flooded rice fields. [ABSTRACT FROM AUTHOR]

Net N mineralization was studied in three different forest sites (Belgium): a mixed deciduous forest with oak ( Quercus robur L . and Quercus rubra L .) and birch ( Betula pendula Roth) as dominant species, a deciduous stand of silver birch ( Betula pendula) and a coniferous stand of Corsican pine ( Pinus nigra ssp . Laricio). The organic (F + H) layer and mineral soil at different depths (0–10, 10–20 and 20–30 cm) were sampled at three locations in the mixed deciduous forest (GE, GF1, GF2), at one location in the silver birch stand (SB) and one in the Corsican pine stand (CP). All samples were incubated over 10 weeks under controlled temperature and moisture conditions. The net N mineralization rates in the organic and upper mineral layer (0–10 cm) were found to be significantly different from the other layers and accounted for 66–95% of the total mineralization over the first 30 cm. Net N mineralization rates in the organic layer ranged from 4.2 to 27.3 mg N m–2 day–1. Net N mineralization and nitrification rates were positively correlated. For the mineral soil, net N mineralization rates decreased with depth and the upper 10 cm showed significantly higher rates, ranging from 8.9 to 33.5 mg N m–2 day–1. The rates of the 10–20 cm and 20–30 cm sublayers were similar, ranging from 1.2 to 7.4 mg N m–2 day–1. The net N mineralization rates for the total mineral layer (0–30 cm) ranged from 17.4 mg N m–2 day–1 (SB) to 36.1 mg N m–2 day–1 (CP). Both from PCA and multiple regression analysis, we could conclude that net N mineralization rates were closely related to the initial mineral N content (Ninitial). Furthermore, significant correlations were observed between the net N mineralization rate, the total carbon (TC) and NH4 +-N content for the mineral layers and between net N mineralization rate, total nitrogen (TN), hemicellulose content and C/N for the organic layers. [ABSTRACT FROM AUTHOR]

Agricultural practices, soil characteristics and meteorological conditions are responsible for eventual nitrate accumulation in the subsoil. There is a lot of evidence that denitrification occurs in the subsoil and rates up to 60–70 kg ha-1 yr-1 might be possible. It has also been shown that in the presence of Fe2+ (formed through weathering of minerals) and an alkaline pH, nitrate can be chemically reduced. Another possible pathway of disappearance is through the formation of nitrite, which is unstable in acid conditions. With regard to the emission of N2O and N2, it can be stated that all conditions whereby the denitrification process becomes marginal are favourable for N2O formation rather than for N2. Because of its high solubility, however, an important amount of N2O might be transported with drainage water. [ABSTRACT FROM AUTHOR]

In 1995 a working group was assembled at the request of OECD/IPCC/IEA to revise the methodology for N2O from agriculture for the National Greenhouse Gas Inventories Methodology. The basics of the methodology developed to calculate annual country level nitrous oxide (N2O) emissions from agricultural soils is presented herein. Three sources of N2O are distinguished in the new methodology: (i) direct emissions from agricultural soils, (ii) emissions from animal production, and (iii) N2O emissions indirectly induced by agricultural activities. The methodology is a simple approach which requires only input data that are available from FAO databases. The methodology attempts to relate N2O emissions to the agricultural nitrogen (N) cycle and to systems into which N is transported once it leaves agricultural systems. These estimates are made with the realization that increased utilization of crop nutrients, including N, will be required to meet rapidly growing needs for food and fiber production in our immediate future. Anthropogenic N input into agricultural systems include N from synthetic fertilizer, animal wastes, increased biological N-fixation, cultivation of mineral and organic soils through enhanced organic matter mineralization, and mineralization of crop residue returned to the field. Nitrous oxide may be emitted directly to the atmosphere in agricultural fields, animal confinements or pastoral systems or be transported from agricultural systems into ground and surface waters through surface runoff. Nitrate leaching and runoff and food consumption by humans and introduction into sewage systems transport the N ultimately into surface water (rivers and oceans) where additional N2O is produced. Ammonia and oxides of N (NOx) are also emitted from agricultural systems and may be transported off-site and serve to fertilize other systems which leads to enhanced production of N2O. Eventually, all N that moves through the soil system will be either terminally sequestered in buried sediments or denitrified in aquatic systems. We estimated global N2O–N emissions for the year 1989, using midpoint emission factors from our methodology and the FAO data for 1989. Direct emissions from agricultural soils totaled 2.1 Tg N, direct emissions from animal production totaled 2.1 Tg N and indirect emissions resulting from agricultural N input into the atmosphere and aquatic systems totaled 2.1 Tg N2O–N for an annual total of 6.3 Tg N2O–N. The N2O input to the atmosphere from agricultural production as a whole has apparently been previously underestimated. These new estimates suggest that the missing N2O sources discussed in earlier IPCC reports is likely a biogenic (agricultural) one. [ABSTRACT FROM AUTHOR]