Modeling dissolved and particulate organic carbon dynamics at basin and sub-basin scales.

Dissolved organic carbon (DOC) and particulate organic carbon (POC) play a fundamental role in biogeochemical cycles of freshwater ecosystems. However, the lack of readily available distributed models for carbon export has limited the effective management of organic carbon fluxes from soils, through river networks and to receiving marine waters. We develop a spatially semi-distributed mass balance modeling approach to estimate organic carbon flux at a sub-basin and basin scales, using commonly available data, to allow stakeholders to explore the impacts of alternative river basin management scenarios and climate change on riverine DOC and POC dynamics. Data requirements, related to hydrological, land-use, soil and precipitation characteristics are easily retrievable from international and national databases, making it appropriate for data-scarce basins. The model is built as an open-source plugin for QGIS and can be easily integrated with other basin scale decision support models on nutrient and sediment export. We tested the model in Piave river basin, in northeast Italy. Results show that the model reproduces spatial and temporal changes in DOC and POC fluxes in relation to changes in precipitation, basin morphology and land use across different sub-basins. For example, the highest DOC export were associated with both urban and forest land use classes and during months of elevated precipitation. We used the model to evaluate alternative land use scenarios and the impact of climate on basin level carbon export to Mediterranean.

Monitoring nutrients fate after digestate spreading in a short rotation buffer area.

One of the main sources of reactive nitrogen pollution is animal manure. The disposal of digestate (material remaining after the anaerobic digestion of a biodegradable feedstock) in agricultural soils could solve both the problems of soil fertilization and waste removal, but the fate of digestate in the environment must be assessed carefully before its massive utilization. To investigate whether digestate could be safely employed as a soil fertilizer, an agricultural field located in Monastier di Treviso (Northern Italy) and characterized by the presence of low hydraulic conductivity clay soils, was selected to be amended with bovine digestate. The experimental site was intensively monitored by a three-dimensional array of probes recording soil water content, temperature, and electrical conductivity, to solve the water and bulk mass fluxes in the unsaturated zone. High-resolution soil coring allowed the characterization of soil water composition over two hydrological years. Chloride, found in high concentrations in the digestate, was used as environmental tracer to track the fate of the percolating water. The study concluded that digestate could be confidently employed in short rotation buffer areas at an average rate of 195 ± 26 kg-N/ha/year in low hydraulic conductivity soils not affected by diffuse fracturing during dry periods.

Vegetation, soil and hydrology management influence denitrification activity and the composition of nirK-type denitrifier communities in a newly afforested riparian buffer.

Soil microbial community composition and activity could be affected by suitable manipulation of the environment they live in. If correctly applied such an approach could become a very effective way to remediate excess of chemicals. The concentration of nitrogen, especially nitrate deriving from agricultural managements, is generally found to increase in water flow. Therefore, by forcing the water flow through a buffer strip specifically designed and possibly afforested with suitable plant species, may result effective in reducing high nitrogen contents. The management of a riparian buffer may definitely affect the soil microbial activities, including denitrification, as well as the composition of the community. The present study reports on the changes occurred in terms of denitrifying microbial community composition, as compared to that of a neighbouring agricultural area, as a consequence of hydraulic management coupled to the suspension of farming practices and to the development of the woody and herbaceous vegetation. With this aim, denitrification was repeatedly measured and the data obtained were related to those deriving from a specific analysis of bacterial groups involved in denitrification. nirK, encoding for nitrite reductase, an enzyme essential for the conversion of nitrite to nitric oxide and considered the key step in the denitrification process, was chosen as the target gene. The main results obtained indicated that denitrification activity changes in riparian buffer as compared to agricultural soil and it is strongly influenced by carbon availability and soil depth. Although no significant differences on the community composition between superficial (0-15 cm) and medium (40-55 cm) layers were observed, the nirK-type denitrifier community was shown to significantly differ between riparian and agricultural soils in both surface and medium layers.