Natural potential sources of nitrate contamination involve decaying of organic matter, bacterial production, atmospheric deposition, and soil N. The study presents the first results of nitrate ...distribution and migration through soil horizons of the Eutric Cambisols, one of the most common soils developed in the area of the Zagreb aquifer and situated in an area without potential anthropogenic sources of nitrate (first sanitary protection zone of the Velika Gorica well field). A total of 16 parameters of soil water and 16 parameters of soil were used to conduct statistical techniques and analyse associated factors within the soil zone. The results indicate that in the deepest soil horizon, nitrogen is present mostly as nitrate due to nitrification under aerobic conditions which promote stability and the potential for nitrate transport. It was found that nitrate concentrations are the result of soil N nitrification, caused by a NO3−/Cl− molar ratio higher than 1 and the absence of precipitation isotopic signature. The results also show that within the coarse-grained Eutric Cambisols N primarily migrates to deeper parts of unsaturated zone in the form of nitrate and nitrite.
This study demonstrates an approach to estimate the background value of nitrate as a basis for better groundwater management and protection in areas under long-term human impact. The aim was to ...determine the ambient background value (ABV) of nitrate in the catchment area of the Velika Gorica well field, a hydrogeologically homogeneous area within the Zagreb aquifer. ABVs are determined using four well-known model-based objective methods (the iterative 2-σ technique, IT; the calculated distribution function, CDF; the cumulative frequency curve, CFC; and the probability plot, PP), while simultaneously testing the reliability of the results of each method. If the results are not statistically significant, data selection is performed. The results show that using data without selection can lead to statistically non-significant ABVs, but with the additional selection of data, a statistically non-significant result became a statistically significant one. In summary, all final ABVs must be statistically significant and determined using as large a data set as possible. Reducing the size of the data set is acceptable only in the case of a statistically non-significant result.
AbstractThe unsaturated zone plays a crucial role in the hydrological cycle and is a key factor in modeling and understanding hydrological processes. It regulates water transfer from the land surface ...to the groundwater while providing protection, transfer, and attenuation of potential groundwater contaminants. This research presents the first results of continuous in situ monitoring of all soil horizons of the Eutric Cambisols and the remaining unsaturated zone of the Zagreb aquifer (Velika Gorica well field). The Zagreb aquifer is the main source of potable water for the inhabitants of the City of Zagreb and Zagreb County, which is protected by the Republic of Croatia. Cross-correlation analysis and water stable isotopes (δ2H and δ18O) were used to investigate whether there is a hydraulic connection between precipitation and groundwater, the approximate duration of percolation, and whether there are indicators that suggest the presence of preferential flow or processes such as water mixing and/or evaporation. The cross-correlation analysis showed and confirmed the assumption of the presence of preferential flow with average lag times ranging from 1.59 up to 3.63 h. The results also indicate that low organic matter content may contribute to higher lag times associated with precipitation infiltration. It was found that only high-intensity precipitation events allow effective infiltration, and that the amount of infiltration depends on the water content of the soil at the beginning of each precipitation event. The isotopic results showed that the isotopic composition of the soil water in the first three soil horizons follows the one of precipitation, while deuterium excess confirmed that the sampled water is mobile water and that an evaporation process is possible in the A horizon. The results also show that suction cups can be used to determine the isotopic signature of both bulk and mobile water, depending mainly on the granulometric composition of the material in which they are installed.
Practical ApplicationsIntensive and growing groundwater extraction in past decades now challenges humans to maintain the resource, especially in regions where climate is drying. Knowing which factor and to what extent drives the process of resource replenishment is the key to maintaining and securing the resource and thus sustainable water supply. Knowing what we can measure, and which methodologies we can use for processing the data we have measured, is of value to practitioners and water supply managers. An original combination of well-known methodologies (water stable isotopes analysis and cross-correlation analysis) as presented in this article suggests how can we process measured precipitation data in order to obtain the knowledge of the processes that drive resource replenishment. In addition, it suggests what kind of data we should measure and what kind of equipment we need for such a task.
The diversity of processes taking place in hillslope agro-ecosystems makes the estimation of vadose zone dynamics rather challenging. This paper presents the first insight into the research of ...volumetric water content, granulometric composition, meteorological data, precipitation and soil-water isotopic composition conducted within the SUPREHILL project at its vadose zone observatory. The main goals of this research are related to the evaluation of soil-water origin at the hillslope vineyard, but also to the estimation of depths until which precipitation infiltrates and where the occurrence of preferential flow is possible. For that purpose, hydrometeorological data, granulometric composition and stable isotopesof hydrogen (δ2H) and oxygen (δ18O) from precipitation and sampled soil water have been used. The results indicate the existence of a different isotopic signature in soil water, which suggests different infiltration patterns in the investigated area. Also, the results point out that surface runoff, subsurface runoff, and most of the passive wick lysimeters respond to precipitation, while the response of suction probes located at deeper depth is not that evident. This corresponds to the results related to the variation of water content at different depths. All the results indicate the possible existence of a low permeable layer at an approximate depth of 60 cm. Furthermore, preferential flow, if it exists, can be expected from the shallowest depths of the vineyard to a maximum depth of 80 cm. It is expected that an established long-term monitoring network at the SUPREHILL Observatory will give a more precise definition of soil-water behaviour and the existence of preferential flow.
Raznolikost procesa koji se odvijaju unutar vadozne zone pri padinskim agroekosustavima čini procjenu dinamike vode izazovnom. Ovaj rad predstavlja prvi uvid u rezultate volumetrijskoga sadržaja ...vode, granulometrijskoga sastava tla, meteoroloških podataka te izotopni sastav oborina i vode u tlu istraživanih u sklopu projekta SUPREHILL, to jest njegova opservatorija. Glavni ciljevi ovoga rada vezani su za procjenu podrijetla vode u tlu padinskoga vinograda, ali i za procjenu dubine do koje se oborine infiltriraju te gdje je moguća pojava preferencijalnoga toka. Za navedenu svrhu korišteni su hidrometeorološki podatci, granulometrijski sastav tla te stabilni izotopi vodika (δ2H) i kisika (δ18O) iz oborina te iz uzorkovane vode iz tla. Rezultati upućuju na postojanje različitoga izotopnog potpisa u vodi u tlu, što sugerira različite obrasce infiltracije na istraživanome području. Također, rezultati pokazuju da sustavi za površinsko i podzemno otjecanje te većina pasivnih lizimetara reagiraju na oborine, dok odaziv usisnih sondi instaliranih na većim dubinama nije očit. Navedeno odgovara rezultatima koji se odnose na varijaciju sadržaja vode u tlu na različitim dubinama. Svi rezultati upućuju na mogućnost postojanja slabije propusnoga sloja na približno 60 cm dubine. Nadalje, preferencijalni tok vode, ako postoji, prema ovim saznanjima može se očekivati do dubine od 80 cm. Očekuje se da će dugoročno praćenje podataka putem uspostavljene senzorske mreže u SUPREHILL opservatoriju preciznije definirati ponašanje vode u tlu i postojanje preferencijalnoga toka vode.
