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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]

Following mineralization of N-rich crop residues, large amounts of mineral N can be released into the soil. Manipulating N mineralization of crop residues may be an option to reduce NO3- in soil. The potential to manipulate the N release from vegetable crop residues by using organic wastes was tested under field conditions. At the start of the experiment, cauliflower (Brassica oleracea L. var. botrytis L.) residues (~73 Mg fresh matter ha 1) together with an immobilizer waste (~5 Mg C ha-1 of straw, green waste compost, sawdust, or paper sludge) were incorporated into a silt loam soil. After 154 d, a remineralizing waste (~1 Mg C ha-1 of vinasse or dairy sludge) was incorporated. During the field experiment, the mineral N content in the soil was measured at regular time intervals, and net N release, NO3- leaching, and denitrification were simulated using a N mineralization-immobilization model coupled to a N3- leaching model. Straw, green waste compost, and sawdust were able to immobilize between 54 and 68% of the N released by the cauliflower residues and reduced N3- leaching by 56 to 68%. Paper sludge released an extra amount of N due to its low C/N ratio. No consistent remineralization of N could be found in any of the treatments, probably due to an unsuitable composition of the remineralizer wastes. Manipulating N release of N-rich crop residues by using organic wastes may be a suitable method to reduce N3- leaching; however, stimulating remineralization of immobilized N by the start of the following spring may not be easy to achieve. [ABSTRACT FROM AUTHOR]

Examines the relationship of nitrogen emissions to specific components of swine production systems. Accurate ammonia emission factors appropriate for the regional climate geography and production systems; Relation of ammonia emissions to lagoon ammonium concentration, acidity, temperature and wind turbulence; Nitrogen input and output in the production system.

Abstract Evaluations of soil organic carbon (SOC) stocks are often based on assigning a carbon density to each one of a number of ecosystems or soil classes considered, using data from soil profiles within these categories. A better approach, in which the use of classification methods by which extrapolation of SOC data to larger areas is avoided, can only be used if enough data are available at a sufficiently small scale. Over 190 000 SOC measurements (0–24 cm) have been made in the Flemish cropland (the Northern part of Belgium) in the 1989–2000 period. These SOC data were grouped into 3-year periods and as means plus standard deviation per (part of) community (polygons). This large dataset was used to calculate SOC stocks and their evolution with time, without data extrapolation. Using a detailed soil map, larger spatial groups of polygons were created based on soil texture and spatial location. Linear regression analysis showed that in the entire study area, SOC stocks had decreased or at best had remained stable. In total, a yearly decrease of 354 kton OC yr-1 was calculated, which corresponds with a net CO2 emission of 1238 kton CO2 yr-1 . Specific regions with a high carbon sequestration potential were identified, based on SOC losses during the 1989–2000 period and the mean 1999 SOC content, compared to the average SOC content of soils in Flanders with a similar soil texture. When restoring the SOC stocks to their 1990 level, we estimated the carbon sequestration potential of the Flemish cropland soils to be some 300 kton CO2 yr-1 at best, which corresponds to a 40-year restoration period. In conclusion, we can say that in regions where agricultural production is very intense, carbon sequestration in the cropland may make only a very modest contribution to a country's effort to reduce greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Presents a study conducted on factors influencing methane emmission from a freshwater wetland in Belgium. Monitoring of drainage capacity and depth of methane production influence on methane emmision; Statistical analysis of emmision data from March to December, 1997; What sites with bad natural drainage and fairly bad natural drainage showed; Description of field experiment; Results of the study.

Ammonium (NH4+) inhibits the microbial oxidation of methane (CH4), and gives rise to the formation of nitrous oxide (N2O) in aerobic soils. However, the NH4+ concentration in the soil water is not necessarily proportional to the total NH4+ concentration inthe soil, due to cation exchange or fixation phenomena. It was foundthat introducing the concept of ion exchange or fixation in kinetic models on CH4 consumption and N2O formation canincrease our knowledge on these processes in soils. A fit of these kinetic models with experimental data showed a standard deviation of slightly more than 10%. The effects of NH4+ on CH4 oxidation and N2O formation can only be compared in soils with the same cation exchange capacity (CEC). [ABSTRACT FROM AUTHOR]