Assessing land-ocean connectivity via Submarine Groundwater Discharge (SGD) in the Ria Formosa Lagoon (Portugal): combining radon measurements and stable isotope hydrology

Natural radioactive tracer-based assessments of basin-scale Submarine Groundwater Discharge (SGD) are well developed, but because of the different modes in which SGD takes place and the wide range of spatial and temporal scales under which the flow and discharge mechanisms involved occur, quantifying SGD while discriminating its source functions remains a major challenge. Yet, correctly identifying both the fluid source and composition is critical: when multiple sources of the tracer of interest are present, failure to adequately discriminate between them will lead to inaccurate attribution and the resulting uncertainties will affect the reliability of SGD solute loading estimates. This lack of reliability then extends to the closure of local biogeochemical budgets, confusing measures aiming to mitigate pollution. Here, we report a multi-tracer study to identify the sources of SGD, distinguish its component parts and elucidate the mechanisms of their dispersion throughout the Ria Formosa – a seasonally hypersaline lagoon in Portugal. We combine radon budgets that determine the total SGD (meteoric + recirculated seawater) in the system with stable isotopes in water (2H, 18O), to specifically identify SGD source functions and characterize active hydrological pathways in the catchment. Using this approach, SGD in the Ria Formosa could be separated into a net water input and another involving no net water transfer, i.e. originating in seawater recirculation through permeable sediments. The former SGD mode is present occasionally on a multiannual timescale, while the latter is a permanent feature of the system. In the absence of meteoric SGD inputs, seawater recirculation through beach sediments occurs at a rate of ~ 1.4 × 106 m3 day−1, implying the entire tidal-averaged volume of the lagoon is filtered through local sandy sediments within 100 days, or about 3.5 times a year, driving an estimated nitrogen (N) load of ~ 350 t N yr−1 into the system as NO3−. Land-borne SGD could add a further ~ 61 t N yr−1 to the lagoon. The former source is autochthonous, continuous and responsible for a large fraction (59 %) of the estimated total N inputs into the system via non-point sources, while the latter is an occasional allochthonous source, so more difficult to predict, but capable of driving new production in the system

An integrated assessment of nitrogen source, transformation and fate within an intensive dairy system to inform management change

From an environmental perspective optimised dairy systems, which follow current regulations, still have low nitrogen (N) use efficiency, high N surplus (kg N ha-1) and enable ad-hoc delivery of direct and indirect reactive N losses to water and the atmosphere. The objective of the present study was to divide an intensive dairy farm into N attenuation capacity areas based on this ad-hoc delivery. Historical and current spatial and temporal multi-level datasets (stable isotope and dissolved gas) were combined and interpreted. Results showed that the farm had four distinct attenuation areas: high N attenuation: characterised by ammonium-N (NH4+-N) below 0.23 mg NH4+-N l-1 and nitrate (NO3--N) below 5.65 mg NO3--N l-1 in surface, drainage and groundwater, located on imperfectly to moderately-well drained soils with high denitrification potential and low nitrous oxide (N2O) emissions (av. 0.0032 mg N2O-N l-1); moderate N attenuation: characterised by low NO3--N concentration in drainage water but high N2O production (0.0317 mg N2O-N l-1) and denitrification potential lower than group 1 (av. δ15N-NO3-: 16.4‰, av. δ18O-NO3-: 9.2‰), on well to moderately drained soils; low N attenuation—area 1: characterised by high NO3--N (av. 6.90 mg NO3--N l-1) in drainage water from well to moderately-well drained soils, with low denitrification potential (av. δ15N-NO3-: 9.5‰, av. δ18O-NO3-: 5.9‰) and high N2O emissions (0.0319 mg N2O l-1); and low N attenuation—area 2: characterised by high NH4+-N (av. 3.93 mg NH4+-N l-1 and high N2O emissions (av. 0.0521 mg N2O l-1) from well to imperfectly drained soil. N loads on site should be moved away from low attenuation areas and emissions to air and water should be assessed

The river Po: geochemical fluxes and related insights on weathering processes and erosion rates

The Alps and the Apennines both convey water and sediments to the Po river that is the most important fluvial system of the Italian Peninsula, characterized by a length of 650 Km, an hydrological basin of 74000 km2 and an average discharge of 47 Km3/yr. Major and trace elements, stable isotope composition of water and radiogenic strontium isotopes were used to characterize the sources and fluxes of solutes. Compared with the local meteoric isotopic signature, stable isotopes (delta18O between -10.8 and -9.2; deltaD between -70.0 and -65.4) reveal that most of the recharge occurs in the north-western part of the basin, i.e. conveyed mainly from the highlands. Although subordinate, carbonatic lithologies are preferentially involved in the weathering processes inducing the typical Ca-HCO3 hydrochemical facies and a specific strontium isotopic signature (87Sr/86Sr 0.7090-0.7092) that is intermediate between that of Mesozoic carbonates (0.707-0.708) and felsic igneous and metamorphic rocks (> 0.701). The data also provide insights on the erosion and denudation rates of the orogens bordering the basin. The observed TDS (average and median of 39 measurements are 268 and 292 mg/l, respectively) suggest that a solute flux in the order of 13*105 t/yr is transferred from the Po River toward the Adriatic Sea. A total erosion of 68*106 t/yr is estimated within the Po River drainage basin, assuming that solute represent a fraction (of ca 20%) of the weathering products. This estimation conforms to other recent investigations

The Geochemical composition of Po River Water, with emphasis to the C-N-O-H isotopic signature

The Po river basin, approximately 74,000 km2, covers most part of Northern Italy, about a quarter of the national territory. Over 20 million inhabitants live in this area, which is interested by intense urbanization, industrial and agricultural a ctivities. This in turn means that the River Po is potentially affected bycontaminants that can be transferred toward the Adriatic Sea. It is therefore important to evaluate the quality and to monitor the compositional evolution of its water, taking in consideration major and trace elements as well as isotopic compositions. In the framework of a cooperative project between the Univ. Ferrara and the Helmhotz Center for Environmental Research UFZ of Halle (Germany) we carried out a wide range of different isotopic analyses including: a) 18O/16O and 2H/1H that give indication on the zone where most of the meteoric recharge occurs, and that trace the salinization due to mixing with sea water occurring in the terminal part of the River Po Delta; b) 13C/12C and 15N/14N that give indications on the origin of nutrients th at induce eutrophication processes. In particular, the carbon isotopic analysis provides information on the interaction processes between water and carbon dioxide and, therefore, on the (natural and/or anthropogenic) origin of this component. The isotopic composition (δ13C) of Dissolved Inorganic Carbon (DIC) in the Po River varies, and appears to be different at distinct distance from the River source. We observed a δ13C range of variation between 11,5‰ and 4,4 ‰, with the lower value recorded in the site at the confluence with the Ticino river. Emphasis is also given to the δ15N , and preliminary data using the Denitrifier Method (Sigman et al. 2001; Anal. Chem. 73, 4145 – 4153), show the following δ15N range of variation: 2,2 and +12,1. These data compared with data from the literature (Sacchi et al. 2013 and references therein; Applied Geochemistry), highlight nitrate contamination from several sources, including synthetic fertilizers from agricultural crops, manure from zootechnical activities, as well assewage components

Wasserversorgung und Sulfatbelastung des Grundwassers unter land- und forstwirtschaftlich genutzten Flaechen. Teilprojekt 4: Isotopenanalytische Bewertung des Sulfathaushaltes in landwirtschaftlich genutzten Wassergewinnungsgebieten Abschlussbericht

SIGLEAvailable from TIB Hannover: F03B842+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Anwendung stabiler Umweltisotope zur Bewertung hydrochemischer Zustaende und Prozesse in Folgelandschaften des Braunkohlebergbaus

The investigations were carried out in two abandoned brown coal mining areas, i.e. the Cospuden area in the Central German Brown Coal District and the TRS 111 area in the Niederlausitz Brown Coal District. Each comprised a spoil bank, a mining lake and a region of natural groundwater aquifers. The hydrochemical parameters of groundwater, pore water and surface water were measured, and the stable isotopes of hydrogen and oxygen were analyzed in water, the stable isotopes of sulphur and oxygen in dissolved sulfate, and the stable isotopes of carbon in dissolved inorganic carbon. #delta#"3"4S was measured in sedimentary pyrites and new minerals formed by pyrite oxidation. The measurements were to find out inhhowfar the conditions and processes in the compartment of the investigated areas can be described on the basis of the stable environmental isotopes. On the one hand, new findings were obtained in the isotope studies, while existing model assumptions were validated on the other hand. Further, material balances and hydrological balances were established on the basis of the stable isotopes, and forecasts were made on the development of water quality in abandoned mining areasIn zwei Folgelandschaften des Braunkohlebergbaus, dem Untersuchungsgebiet Cospuden im Mitteldeutschen Braunkohlenrevier und dem Untersuchungsgebiet TRS 111 im Niederlausitzer Braunkohlenrevier, jeweils bestehend aus einer Tagebaukippe, einem Tagebaurestsee und einem Bereich mit gewachsenen Grundwasserleitern, wurden in den vorliegenden Grund-, Poren- und Oberflaechenwaesser die wichtigsten hydrochemischen Parameter bestimmt und Untersuchungen der stabilen Isotope des Wasserstoffs und Sauerstoffs im Wasser, des Schwefels und Sauerstoffs im geloesten Sulfat und des Kohlenstoffs im geloesten anorganischen Kohlenstoff durchgefuehrt. Darueber hinaus erfolgte die #delta#"3"4S-Bestimmung an sedimentaeren Pyriten und Mineralneubildungen der Pyritoxidation. Ziel der Untersuchungen war es herauszufinden, inwieweit sich mit den stabilen Umweltisotopen Zustaende in den Kompartimenten der Untersuchungsgebiete erfassen und Prozesse beschreiben und nachvollziehen lassen. Dabei konnten einerseits neue Erkenntnisse aus den Isotopenuntersuchungen abgeleitet, andererseits bereits bestehende Modellvorstellungen validiert werden. Weiterhin wurden anhand der stabilen Isotope stoffliche und hydrologische Bilanzierungen vorgenommen sowie prognostische Aussagen zur Beschaffenheitsentwicklung der Waesser in den Bergbaufolgelandschaften hergeleitet. (orig.)Available from TIB Hannover: RR 6252(2000,33) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Investigating “net” provenance, N source, transformation and fate within hydrologically isolated grassland plots

Agricultural landscapes contain many different soil types with heterogeneous nitrogen (N) attenuation capacity. Typically, a zone of contribution (ZOC) surrounding a borehole is used to interpret subsurface hydro-biogeochemical functional capacity. This presents a “net” interpretation of source and attenuation within these calculated areas. Herein, we use the concept of ZOC commonly used for borehole screen intervals but for an end-of-pipe location within four hydrologically isolated plots. Water samples from end-of-pipe and piezometer locations are examined for nitrogen (N), biogeochemical, dissolved gas and isotopic viewpoints to elucidate multi-layered “net” water provenance, N source, transformations and fate. Results showed a nitrate (NO¯3-N) plume migrating in shallow groundwater (between 0.39 and 8.07 mg N/L), with low concentrations in the shallow artificial drainage system (below 3.22 mg N/L). Water provenance data showed distinct signatures of: precipitation and deep groundwater at 3–4 m below ground level (bgl) and water entering, migrating and discharging at the end of pipe location. The latter signature was caused by enrichment of δ¹⁸O-H₂O during migration. This means there was disconnectivity on site with no interaction between water migrating through the drainage pipe at 1 m and deeper groundwater migrating at 3–4 m depth. The analysis of NO¯3-N concentration and its isotopic signature (δ¹⁵N-NO₃¯ and δ¹⁸O-NO₃) identified further connections between screen interval depths and an up-gradient organic point source with elevated NO¯3-N migrating at this depth and different transformation processes occurring at different depths. Temporally NO¯3-N concentrations at this depth have decreased over time. Fenton et al. documented an average of 7.5 (±4.5) mg N/L whereas Ibrahim et al. documented an average of 6.8 (±3.7) mg N/L at this depth. The point source was removed in 2006 and NO¯3-N concentration in the present study have further reduced to an average of 3.9 (±2.8) mg N/L. End-of-pipe data at 1 m bgl highlighted connectivity with the overlying plot and showed different water attenuation functionality than the deeper system. End-of-pipe locations clustered together along the denitrification line. This highlighted a consistency of signals across the four plots in terms of what occurs in the soil profile above the drain installation depth of 1 m. At 3–4 m bgl however, samples varied spatially showing inconsistency between the end-of-pipe locations and plots indicating the occurrence of different processes. A fuller characterisation of dairy farm N sustainability can be deemed using the “net” provenance, N source, N transformation and fate methodology presented. Future work should investigate how drainage design (shallow and groundwater) affects N transformation and the “net” concept developed herein should be rolled out to rank dairy farms in terms of their N attenuation capacity

Investigating “net” provenance, N source, transformation and fate within hydrologically isolated grassland plots

Agricultural landscapes contain many different soil types with heterogeneous nitrogen (N) attenuation capacity. Typically, a zone of contribution (ZOC) surrounding a borehole is used to interpret subsurface hydro-biogeochemical functional capacity. This presents a “net” interpretation of source and attenuation within these calculated areas. Herein, we use the concept of ZOC commonly used for borehole screen intervals but for an end-of-pipe location within four hydrologically isolated plots. Water samples from end-of-pipe and piezometer locations are examined for nitrogen (N), biogeochemical, dissolved gas and isotopic viewpoints to elucidate multi-layered “net” water provenance, N source, transformations and fate. Results showed a nitrate (NO 3 − -N) plume migrating in shallow groundwater (between 0.39 and 8.07 mg N/L), with low concentrations in the shallow artificial drainage system (below 3.22 mg N/L). Water provenance data showed distinct signatures of: precipitation and deep groundwater at 3–4 m below ground level (bgl) and water entering, migrating and discharging at the end of pipe location. The latter signature was caused by enrichment of δ 18 O-H 2 O during migration. This means there was disconnectivity on site with no interaction bet ween water migrating through the drainage pipe at 1 m and deeper groundwater migrating at 3–4 m depth. The analysis of NO 3 − -N concentration and its isotopic signature (δ 15 N-NO 3 − and δ 18 O-NO 3 ) identified further connections between screen interval depths and an up-gradient organic point source with elevated NO 3 − -N migrating at this depth and different transformation processes occurring at different depths. Temporally NO 3 − -N concentrations at this depth have decreased over time. Fenton et al. documented an average of 7.5 (±4.5) mg N/L whereas Ibrahim et al. documented an average of 6.8 (±3.7) mg N/L at this depth. The point source was removed in 2006 and NO 3 − -N concentration in the present study have further reduced to an average of 3.9 (±2.8) mg N/L. End-of-pipe data at 1 m bgl highlighted connectivity with the overlying plot and showed different water attenuation functionality than the deeper system. End-of-pipe locations clustered together along the denitrification line. This highlighted a consistency of signals across the four plots in terms of what occurs in the soil profile above the drain installation depth of 1 m. At 3–4 m bgl however, samples varied spatially showing inconsistency between the end-of-pipe locations and plots indicating the occurrence of different processes. A fuller characterisation of dairy farm N sustainability can be deemed using the “net” provenance, N source, N transformation and fate methodology presented. Future work should investigate how drainage design (shallow and groundwater) affects N transformation and the “net” concept developed herein should be rolled out to rank dairy farms in terms of their N attenuation capacity