Near-Infrared Spectroscopy is a cost-effective and environmentally friendly technique that could represent an alternative to conventional soil analysis methods, including total organic carbon (TOC). Soil fertility and quality are usually measured by traditional methods that involve the use of hazardous and strong chemicals. The effects of physical soil characteristics, such as moisture content and particle size, on spectral signals could be of great interest in order to understand and optimize prediction capability and set up a robust and reliable calibration model, with the future perspective of being applied in the field. Spectra of 46 soil samples were collected. Soil samples were divided into three data sets: unprocessed, only dried and dried, ground and sieved, in order to evaluate the effects of moisture and particle size on spectral signals. Both separate and combined normalization methods including standard normal variate (SNV), multiplicative scatter correction (MSC) and normalization by closure (NCL), as well as smoothing using first and second derivatives (DV1 and DV2), were applied to a total of seven cases. Pretreatments for model optimization were designed and compared for each data set. The best combination of pretreatments was achieved by applying SNV and DV2 on partial least squares (PLS) modelling. There were no significant differences between the predictions using the three different data sets (p < 0.05). Finally, a unique database including all three data sets was built to include all the sources of sample variability that were tested and used for final prediction. External validation of TOC was carried out on 16 unknown soil samples to evaluate the predictive ability of the final combined calibration model. Hence, we demonstrate that sample preprocessing has minor influence on the quality of near infrared spectroscopy (NIR) predictions, laying the ground for a direct and fast in situ application of the method. Data can be acquired outside the laboratory since the method is simple and does not need more than a simple band ratio of the spectra.

Nitrate is a major groundwater inorganic contaminant that is mainly due to fertilizer leaching. Compost amendment can increase soils’ organic substances and thus promote denitrification in intensively cultivated soils. In this study, two agricultural plots located in the Padana plain (Ferrara, Italy) were monitored and modeled for a period of 2.7 years. One plot was initially amended with 30 t/ha of compost, not tilled, and amended with standard fertilization practices, while the other one was run with standard fertilization and tillage practices. Monitoring was performed continuously via soil water probes (matric potential) and discontinuously via auger core profiles (major nitrogen species) before and after each cropping season. A HYDRUS-1D numerical model was calibrated and validated versus observed matric potential and nitrate, ammonium, and bromide (used as tracers). Model performance was judged satisfactory and the results provided insights on water and nitrogen balances for the two different agricultural practices tested here. While water balance and retention time in the vadose zone were similar in the two plots, nitrate leaching was less pronounced in the plot amended with compost due to a higher denitrification rate. This study provides clear evidence that compost addition and no-tillage (conservation agriculture) can diminish nitrate leaching to groundwater, with respect to standard agricultural practices.

In the summer of 2022, the Po River Delta (Northern Italy), a eutrophication hotspot, was severely affected by high temperatures, exceptional lack of rainfall and saline water intrusion. The effect of saline intrusion on benthic nitrogen dynamics, and in particular the N removal capacity, was investigated during extreme drought conditions. Laboratory incubations of intact sediment cores were used to determine denitrification and DNRA rates at three sites along a salinity gradient in the Po di Goro, an arm of the Po River Delta. Denitrification was found to be the main process responsible for nitrate reduction in freshwater and slightly saline sites, whereas DNRA predominated in the most saline site, highlighting a switch in N cycling between removal and recycling. These results provide evidence that salinity is a key factor in regulating benthic N metabolism in transitional environments. In a climate change scenario, salinity intrusion, resulting from long periods of low river discharge, may become an unrecognized driver of coastal eutrophication by promoting the dissimilatory nitrate reduction to ammonium and N recycling of bioactive nitrogen within the ecosystem, rather than its permanent removal by denitrification.

Although representing a paramount mechanism against nitrogen excess in agricultural landscapes, soil denitrification is still a largely unknown term in nitrogen balances at the watershed scale. In the present work, a comprehensive investigation of nitrogen sources and sinks in agricultural soils and waters was performed with the aim of gaining insights into the relevance of soil denitrification in a highly farmed sub-basin of the Po River delta (Northern Italy). Agricultural statistics, water quality datasets, and results of laboratory experiments targeting nitrogen fluxes in soils were combined to set up a detailed nitrogen budget along the terrestrial–freshwater continuum. The soil nitrogen budget was not closed, with inputs exceeding outputs by 72 kg N·ha⁻¹·year⁻¹, highlighting a potential high risk of nitrate contamination. However, extensive monitoring showed a general scarcity of mineral nitrogen forms in both shallow aquifers and soils. The present study confirmed the importance of denitrification, representing ~37% of the total nitrogen inputs, as the leading process of nitrate removal in heavily fertilized fine-texture soils prone to waterlogged conditions.

Aquatic vegetation loss caused substantial decrease of ecosystem processes and services during the last decades, particularly for the capacity of these ecosystems to sequester and store carbon from the atmosphere. This study investigated the extent of aquatic emergent vegetation loss for the period 1985–2018 and the consequent effects on carbon sequestration and storage capacity of Valle Santa wetland, a protected freshwater wetland dominated by Phragmites australis located in the Po river delta Park (Northern Italy), as a function of primary productivity and biomass decomposition, assessed by means of satellite images and experimental measures. The results showed an extended loss of aquatic vegetated habitats during the considered period, with 1989 being the year with higher productivity. The mean breakdown rates of P. australis were 0.00532 d⁻¹ and 0.00228 d⁻¹ for leaf and stem carbon content, respectively, leading to a predicted annual decomposition of 64.6% of the total biomass carbon. For 2018 the carbon sequestration capacity was estimated equal to 0.249 kg C m⁻² yr⁻¹, while the carbon storage of the whole wetland was 1.75 × 10³ t C (0.70 kg C m⁻²). Nonetheless, despite the protection efforts over time, the vegetation loss occurred during the last decades significantly decreased carbon sequestration and storage by 51.6%, when comparing 2018 and 1989. No statistically significant effects were found for water descriptors. This study demonstrated that P. australis-dominated wetlands support important ecosystem processes and should be regarded as an important carbon sink under an ecosystem services perspective, with the aim to maximize their capacity to mitigate climate change.