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Although the use of composts derived from anaerobic digestates as soil amendments is likely to increase in the future, there is little information concerning the fate of their C and N compounds after their incorporation into soil. This work assesses C and N concentrations and the associated changes in δ15N and δ13C during the composting processes of cattle and pig slurry anaerobic digestates. In addition, the compost effect on C and N fractions and plant uptake were studied during a six-month pot experiment with rosemary plants. The results did not show δ13C and δ15N isotopic discrimination during composting, indicating a previous stabilization of cattle manure and pig slurry during the anaerobic digestion. This fact was also confirmed by the low C losses during the composting processes (1.2-fold and 1.05-fold for the composting piles with cattle and pig slurry anaerobic digestates, respectively). After soil addition, the composts augmented N values (from 0.41 g kg−1 to around 0.56 g kg−1 in low dose and 0.68 g kg−1 in high dose compost amended soils) and δ15N soil values (increases in the range of 50%–156%), but showed only slight differences in C and δ13C values compared to unfertilised control and inorganic fertilized soils. Moreover, the rosemary leaves of the plants grown on the compost amended soils presented higher N and δ15N abundance than control and inorganic fertilized plants. We conclude that δ15N abundance of anaerobic digestate composts is useful to discern its N uptake and could thus be a useful tool to detect whether organic or mineral fertiliser types were used for agricultural production. • δ13C and δ15N isotopic discrimination was not observed during composting. • Composts increased δ15N soil values compared to control and mineral fertilized soils. • δ15N abundance of anaerobic digestate compost can be useful to discern its N uptake. [ABSTRACT FROM AUTHOR]

Indian estuaries are hypothesized to export a significant amount of nitrogen nutrients to the coastal waters due to the high use of fertilizers. To examine the possible sources of nitrogen nutrients and their modifications within the estuary, a study was conducted by collecting samples at monthly intervals for a period of a year. The river Godavari is the largest monsoonal estuary in India and is fed by monsoon rainfall. Hence the entire estuary is filled with fresh water from July to September (the wet period) whereas saline water is dominant during the dry period. An order of magnitude increase in nitrate concentrations was observed during the wet due to a peak in discharge compared to the dry period. The isotopic composition of nitrogen in nitrate (δ15N NO3) was lower during the wet than the dry period and displayed a significant linear relationship with Chlorophyll-a (Chl-a), particulate organic nitrogen (PON) and carbon (POC) indicating that biological process modified their composition. The lower δ15N NO3 and higher δ18O NO3 values were noticed during the wet than during the dry period. The δ15N NO3 versus δ18O NO3 plot suggests a possible source of nitrate through the nitrification of soil/sewage-borne nitrogen. The higher δ18O NO3 /δ15N NO3 ratios (>1) were observed during August and September than in other months indicating the occurrence of denitrification during the former months. In contrast, an insignificant change in δ15N NO3 and δ18O NO3 within the estuary suggested that denitrification occurred upstream and not within the estuarine zone. River discharge brought residual nitrate to the estuary leading to less input of nitrate to the coastal Bay of Bengal than hitherto hypothesized. [Display omitted] • δ15N NO3 and δ18O NO3 suggest the occurrence of denitrification during the wet period. • NO3 is contributed by river discharge and marine sources during wet and dry periods. • NO3 by sewage is high during and the least during the peak discharge period. • Contribution of fertilizer accounts for only 10–12% to the Godavari estuary. [ABSTRACT FROM AUTHOR]

The Orgeval watershed (104 km 2 ) is a long-term experimental observatory and research site, representative of rural areas with intensive cereal farming of the temperate world. Since the past few years, we have been carrying out several studies on nitrate source, transformation and transfer of both surface and groundwaters in relation with land use and agriculture practices in order to assess nitrate ( NO3-) leaching, contamination of aquifers, denitrification processes and associated nitrous oxide (N2O) emissions. A synthesis of these studies is presented to establish a quantitative diagnosis of nitrate contamination and N2O emissions at the watershed scale. Taking this watershed as a practical example, we compare curative management measures, such as pond introduction, and preventive measures, namely conversion to organic farming practices, using model simulations. It is concluded that only preventive measures are able to reduce the NO3- contamination level without further increasing N2O emissions, a result providing new insights for future management bringing together water-agro-ecosystems. [ABSTRACT FROM AUTHOR]