Towards the understanding of antibiotic occurrence and transport in groundwater: Findings from the Baix Fluvià alluvial aquifer (NE Catalonia, Spain).

Antibiotics are an increasing focus of interest due to their high detection frequency in the environment. However, their presence in water bodies is not regulated by environmental policies. This field study investigates, for the first time, the occurrence, behavior and fate of a selection of 53 antibiotics, including up to 10 chemical groups, in an alluvial aquifer originated from manure application in an agricultural region using hydrogeological, hydrochemical and isotopic approaches. Up to 11 antibiotics were found in groundwater corresponding to 4 different chemical groups: fluoroquinolones, macrolides, quinolones and sulfonamides. In surface water, only 5 different antibiotics from 2 chemical groups: fluoroquinolones and sulfonamides, were quantified. The most frequent antibiotics were sulfamethoxazole and ciprofloxacin. Concentrations of antibiotics were in the order of ng/L, with maximum concentrations of 300ng/L in groundwater. Hydrochemistry and isotopic data and geostatistics confirmed the spatial trend observed for nitrates, where nitrate concentrations tend to be higher in the margin areas of the study area, and lower concentrations are found nearby the river. On the other hand, no clear continuous spatial concentration trend of antibiotics was observed in the aquifer, supported by the short spatial correlation found in the variograms. This indicates that the physical-chemical properties and processes of each antibiotic (mainly, sorption and degradation), and other environmental issues, such as a patchy diffuse input and the manure antibiotic content itself, play an important role in their spatial distribution in groundwater. A discussion on the estimation of the antibiotic sorption parameter reveals the difficulties of describing such phenomena. Furthermore, retardation factors will extend over several orders of magnitude, which highly affects the movement of individual antibiotics within the aquifer. To summarize, this study points out the difficulties associated with antibiotic research in groundwater in order to define water resources quality management strategies and environmental regulations.

Identifying the effects of human pressure on groundwater quality to support water management strategies in coastal regions: a multi-tracer and statistical approach (Bou-Areg region, Morocco).

Groundwater pollution from anthropogenic sources is a serious concern affecting several coastal aquifers worldwide. Increasing groundwater exploitation, coupled with point and non-point pollution sources, are the main anthropogenic impacts on coastal environments and are responsible for severe health and food security issues. Adequate management strategies to protect groundwater from contamination and overexploitation are of paramount importance, especially in arid prone regions, where coastal aquifers often represent the main freshwater resource to sustain human needs. The Bou-Areg Aquifer (Morocco) is a perfect example of a coastal aquifer constantly exposed to all the negative externalities associated with groundwater use for agricultural purposes, which lead to a general increase in aquifer salinization. In this study data on 61 water samples, collected in June and November 2010, were used to: (i) track groundwater composition changes related to the use of irrigation water from different sources, (ii) highlight seasonal variations to assess aquifer vulnerability, and (iii) present a reproducible example of multi-tracer approach for groundwater management in rural coastal areas. Hydrogeochemical results show that Bou-Areg groundwater is characterized by - high salinity, associated with a remarkable increase in bicarbonate content in the crop growing season, due to more intense biological activity in irrigated soils. The coupled multi-tracer and statistical analysis confirms the strong dependency on irrigation activities as well as a clear identification of the processes governing the aquifer's hydrochemistry in the different seasons. Water Rock Interaction (WRI) dominates the composition of most of groundwater samples in the Low Irrigation season (L-IR) and Agricultural Return Flow (ARF) mainly affects groundwater salinization in the High Irrigation season (H-IR) in the same areas naturally affected by WRI. In the central part of the plain River Recharge (RR) from the Selouane River is responsible for the high groundwater salinity whilst Mixing Processes (MIX) occur in absence of irrigation activities.

Nitrogen inputs to a river course in a heavily impacted watershed: a combined hydrochemical and isotopic evaluation (Oglio River Basin, N Italy).

This study aims at evaluating sources and processes affecting NO3(-) concentrations in the Oglio River. Five sampling campaigns considered the main watercourse, tributaries, point pollution sources, springs, and groundwater. Physico-chemical parameters, N forms, B, Sr(2+), stable isotopes (δ(2)HH2O, δ(18)OH2O, δ(15)NNO3, δ(18)ONO3, δ(11)B) and discharge were measured. Hydrological modelling was performed using mass balance and End Member Mixing Analysis equations. During the irrigation period, in the upstream reach, up to 90% of the natural river flow is diverted for irrigation and industrial purposes; excess water drained from agricultural fields is returned to river in the downstream reach. Results evidenced, in the middle reach, a large input of NO3(-)-rich groundwater which could be quantified using hydrological modelling. Groundwater inputs are responsible for the sharp, tenfold increase in NO3(-) in the river water, from 2.2-4.4 up to 33.5 mgL(-1), and are more evident in summer, when discharge is lower. Nevertheless, river water preserves its natural B isotopic composition, indicating that the two tracers do not have a common origin and are not co-migrant. In the lower plain, surface-groundwater interconnections and human disturbances in the water cycle favour the recycling of the compounds in the environment, and lead to a similarity in composition of the different water bodies (Oglio River, tributaries and groundwater). The long lasting agronomical practices have profoundly modified the surface-groundwater equilibrium and chemical characteristics, resulting in a highly buffered system. Infiltrating irrigation water leaches down NO3(-) which is subsequently denitrified; when returned to the Oglio River, groundwater modifies the river water composition by dilution, in the case of NO3(-), or by addition, for other constituents (e.g. Cl(-), B). The results of this study indicate that, in order to reduce the NO3(-) transport towards the Adriatic Sea, groundwater contamination should be addressed first, with expected long recovery times.

Modeling of natural organic matter transport processes in groundwater.

A forced-gradient tracer test was conducted at the Georgetown site to study the transport of natural organic matter (NOM) in groundwater. In particular, the goal of this experiment was to investigate the interactions between NOM and the aquifer matrix. A detailed three-dimensional characterization of the hydrologic conductivity heterogeneity of the site was obtained using slug tests. The transport of a conservative tracer (chloride) was successfully reproduced using these conductivity data. Despite the good simulation of the flow field, NOM breakthrough curves could not be reproduced using a two-site sorption model with spatially constant parameters. Preliminary results suggest that different mechanisms for the adsorption/desorption processes, as well as their spatial variability, may significantly affect the transport and fate of NOM.