A simple model to assess nitrogen and phosphorus contamination in ungauged surface drainage networks: application to the Massaciuccoli Lake Catchment, Italy

A Spatially Distributed, Physically-Based Modeling Approach for Estimating Agricultural Nitrate Leaching to Groundwater

Nitrogen-nitrate, while being fundamental for crop production, is of particular concern in the agricultural sector, as it can easily leach to the water table, worsening groundwater quality. Numerical models and Geographic Information System may support the estimation of nitrate leaching rates in space and time, to support sustainable agricultural management practices. In this paper, we present a module for the simulation of the processes involved in the nitrogen cycle in the unsaturated zone, including nitrate leaching. This module was developed taking steps from the ANIMO and EPIC model frameworks and coupled to the hydrological models integrated within the FREEWAT platform. As such, the nitrogen cycle module was then included in the FREEWAT platform. The developed module and the coupling approach were tested using a simple synthetic application, where we simulated nitrate leaching through the unsaturated zone for a sunflower crop irrigated district during a dry year. The results of the simulation allow the estimation of daily nitrate concentration values at the water table. These spatially distributed values may then be further used as input concentration in models for simulating solute transport in aquifers.

Spatial Data Management and Numerical Modelling: Demonstrating the Application of the QGIS-Integrated FREEWAT Platform at 13 Case Studies for Tackling Groundwater Resource Management

Because of the spatial nature of groundwater-related data and their time component, effective groundwater management requires the application of methods pertaining to the Information and Communication Technologies sector, such as spatial data management and distributed numerical modelling. The objective of this paper is to demonstrate the effectiveness of the QGIS-integrated FREEWAT platform and an approach combining spatial data management and numerical models to target groundwater management issues. FREEWAT is a free and open source platform integrated in a Geographic Information System environment and embedding tools for pre- and post-processing of spatial data and integrating numerical codes for the simulation of the hydrological cycle, with a main focus on groundwater. To this aim, this paper briefly presents the FREEWAT platform, introduces the FREEWAT approach, and showcases 13 case studies in European and non-European countries where the FREEWAT platform was applied. Application of the FREEWAT platform to real-world case studies is presented for targeting management of coastal aquifers, ground- and surface-water interaction, climate change impacts, management of transboundary aquifers, rural water management and protection of groundwater-dependent ecosystems. In this sense, compared to other existing software suites, FREEWAT allows data analysis and visualization to accomplish each step of the modelling workflow, i.e., from data analytics, to conceptual model definition, to numerical modelling and reporting of results. The presented experiences demonstrate that improved access to data and the portability of models and models’ results can help to promote water sustainability from the local- to the basin-scale. Furthermore, FREEWAT may represent a valuable tool to target the objective of increasing the capabilities of public authorities and private companies to manage groundwater resources by means of up-to-date, robust, well-documented and reliable software, without entailing the need of costly licensing, nowadays seldom affordable by public water authorities. Based on the strengths highlighted, the FREEWAT platform is a powerful tool for groundwater resources management, and for data collection, sharing, implementation and comparison of scenarios, for supporting planning and decision-making.

Assessment of soil buffer capacity on nutrients and pharmaceuticals in nature-based solution applications

The ability of a soil to sustain infiltration rates and to attenuate pollutants is critical for the design and operation of Managed Aquifer Recharge/Soil Aquifer Treatment and phyto-treatment schemes, also referred to as "Blue Infrastructures". We investigated the buffering capacity of a sediment sample and a peat soil sample for nutrients and selected pharmaceutical compounds and its evolution under continuous infiltration of secondary treated wastewater (TWW) in column experiments. Samples were obtained from two blue infrastructures, the Sant'Alessio Induced River Bank Filtration plant and the San Niccolò large-scale phyto-treatment plant in Italy, and were mainly different in their organic carbon contents (0.9 and 48%, respectively). In the column experiments, a constant infiltration rate of about 0.5 L/d was maintained for 6 months. After 4 months of operation, diclofenac and carbamazepine were spiked into the TWW to evaluate their fate. Water quality was monitored by periodic water sampling from the column inflow, at sampling ports along the column length, and at the outflow. Hydraulic conductivity (K) was also monitored. The hydraulic conductivity of the Sant'Alessio sediment decreased by a factor of 10 during the first 10 days of infiltration and then stabilized, while for the San Niccolò K (initially lower) remained constant for 50 days until it decreased following a change of the redox condition in the column. The different redox conditions, due to the two different soils tested, influenced also the concentration and mobility of PO₄^3-, Fe, Mn, and NPOC, and the speciation of the redox sensitive elements (nitrogen and sulfur). NOPC and phosphate were enriched during the filtration through San Niccolò peat soil (from 2 to 4 times, respectively), while they were buffered by the Sant'Alessio sediment (from 0.2 to 0.4 times, respectively). Diclofenac removal (69% and below 20% for San Niccolò and Sant'Alessio, respectively) was related to sorption and degradation processes and it was lower than the removal of carbamazepine in both soils (76 and 35%). The buffer capacity differences between the two soils were higher for diclofenac (62%) than carbamazepine (35%). Nevertheless, since no apparent degradation of carbamazepine was detected in both soils, its persistence in the soil may have a larger impact in case of desorption, posing contamination risk to groundwater. The results highlight the importance of the soils or sediments to be used as medium in such nature-based solutions for their operations. They also offer an approach to, e.g., tailor man-made soil layers in infiltration basins. We strongly suggest that soil characteristics and test duration are carefully considered in designing these infrastructures, when nature-based processes are the choice for dealing with reuse of treated wastewater management issues.

Rewetting in Mediterranean reclaimed peaty soils and its potential for phyto-treatment use

A pilot experimental field combining rewetting of reclaimed peaty soils and water phyto-treatment was set up in the Massaciuccoli Lake basin (Tuscany, Italy) to reduce the water eutrophication and peat degradation caused by almost a century of drainage-based agricultural use. In this paper, we investigated the restoration process occurring consequently to the conversion of a drained area in a natural wetland system (NWS) (the partial top soil removal, the realization of a perimeter levee to contain the waters, the rewetting with the drainage waters coming from the of surrounding cultivated areas) and the capability of the spontaneous vegetation to catch nutrients acting as a vegetation filter. To follow the restoration process over time (2012-2016), we used a mixed approach merging phytosociological surveys with ortophotos taken by an Unmanned Aerial Vehicle (UAV). During the last year of observation (2016), we performed destructive sampling on the most widespread plant communities in the area (Phragmites australis and Myriophyllum aquaticum community) to quantify the biomass production and the uptake of nitrogen and phosphorus. Stands of Phragmites australis (Cav.) Trin. ex Steud. yielded more than Myriophyllum aquaticum (Vell.) Verdc. (4.94 kg m-2 vs 1.08 kg m-2). M. aquaticum showed higher nutrient contents (2.04% of N and 0.35% of P), however P. australis was able to take up more nutrients within the NWS because of its larger cover and productivity. In the perspective of maximizing the plant development and consequently the amount of nutrients extracted from treated waters, the authors suggest 4-5 year-long-harvesting turns, better occurring in spring-summer.

Tracing the sources and cycling of phosphorus in river sediments using oxygen isotopes: Methodological adaptations and first results from a case study in France

An essential aspect of eutrophication studies is to trace the ultimate origin of phosphate ions (P-PO₄) associated with the solid phase of river sediments, as certain processes can make these ions available for algae. However, this is not a straightforward task because of the diversity of allochthonous and autochthonous sources that can supply P-PO₄ to river sediments as well as the existence of in-stream processes that can change the speciation of these inputs and obscure the original sources. Here, we present the results of a study designed to explore the potentials, limitations and conditions for the use of the oxygen isotope composition of phosphate (δ¹⁸Op) extracted from river sediments for this type of tracing. We first tested if the method commonly applied to soils to purify P-PO₄ and to measure their δ¹⁸Op concentrations could be adapted to sediments. We then applied this method to a set of sediments collected in a river along a gradient of anthropogenic pressure and compared their isotopic signatures with those from samples that are representative of the potential P-PO₄ inputs to the river system (soils and riverbank material). The results showed that following some adaptations, the purification method could be successfully transposed to river sediments with a high level of P-PO₄ purification (>97%) and high δ¹⁸Op measurement repeatability and accuracy (<0.4‰). The values for the potential allochthonous sources varied from 11.8 to 18.3‰, while the δ¹⁸Op value for the river sediments ranged from 12.2 to 15.8‰. Moreover, a sharp increase (>3‰) in the sediment δ¹⁸Op value immediately downstream from the discharge point revealed the strong impact of municipal wastewater. The calculation of the theoretical equilibrium δ¹⁸O_p values using the river water temperature and δ¹⁸O_w showed that the downstream sediments were in equilibrium, which was not the case for the upstream sediments. This difference could be related to the contrast between the short residence time of the transfer system in the catchment head, which can preserve the isotopic variability of the source materials, and the longer residence times and higher P bioavailability in the lower catchment, possibly fostering the recycling of P-PO₄ by the biota and the equilibration of the oxygen isotope signature in P-PO₄. These results demonstrate the potential of the isotopic approach to assess the sources and in-stream turnover of sedimentary P in river systems.

Preliminary investigation on the potential use of two C4 turfgrass species to reduce nutrient release in a Mediterranean drained peatland

This study compared dry matter production, nutrient uptake and tissue nutrient concentration of two C4 turfgrass species (Cynodon dactylon × Cynodon transvaalensis Burtt Davy and Paspalum vaginatum Swartz) supplied with three different nutrient solutions in a sand and peat culture. The 8-week experiment was performed in mesocosms and simulated the conditions of an open-field phyto-treatment system located in a Mediterranean drained peatland (Tuscany, Italy). Peat was collected on the site, and one of the solutions mimicked drainage water flowing into it. Three hypotheses were tested: (i) the species chosen efficiently removed nutrients from both the solution and the substrate; (ii) peat contributed to the nutrient load; and (iii) the species chosen were suitable in the open-field system. Both species adapted well to the experimental conditions and demonstrated considerable ability to remove nutrients. P. vaginatum took up nitrogen more efficiently, mainly in conditions of high nutrient availability. We observed supplementary nutrient uptake by plants in the peat treatment. Performances of the two C4 turfgrasses extrapolated to the field scale seemed effective from a phyto-treatment perspective.