Critical Analysis of the Methodology Used by Barba-Briosco et al. in Their Study of Pollutants in the Huelva Estuary, Spain

Introduction This paper provides a critical analysis of the methodology used by Barba-Brioso et al. (2010) in their study about water pollution from multiple sources in the Huelva Estuary, Spain. It discusses the extent to which this methodology has enabled the authors to achieve their aims and objectives, focusing on whether one could be confident with the quality of the data provided. It also tackles whether there are any areas in which the methodology could be improved. Barba-Brioso et al. (2010) studied major ions, nutrients, pesticides, etc. in human development-impacted coastal wetland of Huelva Estuary. The hydrodynamics of the area has been modified by previous land use, which led to the division of the ecosystem into a tideland and an artificial freshwater basin. The Huelva Estuary, which is polluted by mine, causes the flooding of the tideland stretch, which occurs twice a day. Acid discharges are also collected in the tidal channel from industrial point sources that play a part in metal enhancement. The tidal situation in Huelva Estuary has an important contribution to the transport of pollutants except for the artificial basin exhibiting cyclic mineralisation pattern. Barba-Brioso et al.’s Methodology The authors initially adopted sampling of the tideland zone in order to take into account the impacts of tidal regimes, in which nine samples were taken for high tide and twelve for low tide. A Zodiac boat was used to access the sampling site. The cyclic freshwater variations were examined by taking water samples of 1-20 cm in lacustrine zone whereby five were collected during winter and three during summer. Additionally, the study collected three samples of running water in summer and five in winter which were taken from open pipes and tributary streams. Field constraints caused an imbalance to the sampling design. The methodology also adopted several specific studies for the reference of general procedures in taking the water samples, which is considered the strength of the methodology since it sought evidence-based practice to utilising the selected procedure. Ion chromatography was also used to determine sulfate, nitrate, and bromide concentrations, amongst others. Critical Analysis of the Methodology The measurement used in Barba-Brioso et al.’s study is rather intricate and highly systematic, as the research itself is objective, quantitative, and is assumed to be statistically valid, as quantitative research must be (Bamberger, 2000; Bower, 2005). The methodology is able to address the primary objective of ascertaining how the concentration of pollutants is influenced by tidal and cyclical regimes in Huelva Estuary. This is demonstrated in the manner by which sampling was chosen, specifically the 9 samples for high tide and twelve for low tide, so that the impacts of tidal regime may be considered. The same was done for the cyclical regimes, in which the same sampling pattern for water was collected. This paved the way to addressing the research objective being mentioned. The adoption of intricate methods for the data in Barba-Brioso et al.’s (2010) study is similar in extent as other studies citing it, such as Zhang et al. (2011) and Guillen et al. (2012). The adoption of the experimental method in Barba-Brioso et al.’s study to examine the research problem is harmonious with its use of basic descriptive statistics of element concentrations and other elements in the wetland. The use of Merck 1000 ppm and bicarbonate determination indicate its pursuit for accurate generation of results relating to water and wastewater examination. The objectivity of the study is also shown in its triplicate measurement of the samples, with the representative value (mean) having achieved specific percentage accuracy. Barba- Brioso and colleagues also cited other authors in their calculation of the instrumental detection limit, which is suggestive of their stance to provide evidence to the relevance and applicability of the method to their study. It only means that the authors wanted to back up their use of such method through other studies utilising the same. Moreover, the objective of detecting anthropogenic inputs through hydrochemical irregularities was addressed in the study by tackling hydrochemical parameters, amongst others, in basic descriptive statistics organised based on tidal and cyclical conditions that took place at the time when sampling was carried out. This allowed the analysis of the estuarine waters to find slight alkaline content alongside local recording of acidic values at the rim of the tidal channel during low tide periods. The objective of detecting anthropogenic inputs through hydrochemical irregularities was also addressed by an identification of the wide variation in the mean pH values in the lacustrine wetland, which is higher during winter (8.4) than during summer (7.5). In addition, the methodology used a Piper diagram to plot the hydrochemical data, bearing dissolved prime cations and anions, which then exhibited two major water types in the wetland, specifically sodium chloride sulfate and a mixture of cal cium, magnesium, and sulfate-chloride. The Piper diagram has been used also in other studies depicting similar direction as that of this study, such as in the studies of Adams et al. (2001), Cloutier et al. (2008), and Van den Boogaart and Tolosana-Delgado (2008). The procedure in Barba-Brioso et al. (2010) revealed greater concentrations of nitrate distribution during low tide, which increases in the upstream route as well as detected the highest levels of nitrate and phosphate in small streams. It may thus be inferred that these data emanating from the methodology, enabled Barba- Brioso et al. to address the second objective, which again is to detect anthropogenic inputs through hydrochemical irregularities. Such objective was also addressed by the methodology’s stance to determine Ca and Mg concentrations through atomic absorption spectroscopy as well as atomic emission spectroscopy to determine K and NA. The application of SPE and HPLC procedures in quantifying all the studied pesticides was also congruent with the objective of identifying the various sources of pollution by apportionment procedures. In the same manner, the methods being carried out alongside this (e.g. use of water and methanol to condition the cartridge, etc.) app arently supported the study’s intention to tackle the objective of identifying anthropogenic inputs through hydrochemical irregularities. Furthermore, to determine trace elements, the methodology used measurements of iron elevated contents at the convergence of the Tinto River and the Tidal channel. Citing the methodology In the study of Guillen et al. (2012), the authors did not use the same methods as Barba-Brioso et al. (2010) in their (Guillen et al., 2012) attempt to find out trace elements’ mobility through the modified BCR sequential extraction method. Rather, atomic absorption spectroscopy and atomic emission spectroscopy were utilised by Barba- Brioso et al. (2010). Mass spectroscopy with plasma of inductive couple carried out the analyses of dissolved trace elements in Barba- Brioso and colleagues’ study. The pursuit of the method to derive the expected precision was seen in an attempt to correct for any drift during the analysis through the measurement of certified reference material, thereby producing the range of a specific mean precision for all the analyses and a particular detection limit optimisation for all the trace elements being analysed.The apportionment methods also allowed different potentially toxic elements to be distributed on a closely parallel manner with the pattern of major cations and anions, in which a declining upstream trend was depicted during both high and low tides. The method used enabled the study to determine the sources of pollution in the Domingo Rubio wetland in Tideland area and overall wetland. The manner of data collection was highly scientific and accuracy-specific, as the study intended to investigate the major ions and trace elements as well as the pesticide distribution in the coastal wetland. The passing of the replicates of water sample through the equivalent cartridges at a specific flow rate was also indicative of an aim to ascertain pesticide distribution, which was linked to an objective of identifying the various sources of pollution in Domingo Rubio. It may also be observed that the analytical methods concerning anions and nutrients in which Merck 1000 ppm and Standard Methods were used to examine water and wastewater were parallel to the objectives of determining hydrochemical anomalies and various sources of pollution in the wetland. It may therefore be claimed that the extent to which the methodology has enabled the investigators to meet the stated aims and objectives is sufficient enough. Further, the quality of the data being provided was something to be confident about. The authors enumerated the analytical methods and procedures one by one, strongly focusing on the details of these procedures, including the elements being examined. They also used a table on which to organise the data, clear enough for the reader to understand them. The high confidence level of the data being presented is indicative of how they were analysed in the results section, in which the parameters of water quality were summarised and compared, alongside the samples’ chemical composition. In this regard, the study is able to pinpoint that the tidal channel is characterised by slight alkaline content, describing its pH mean values during low tide and high tide, and that there is the presence of acidic values at the rim of the tidal channel during low tide. This specific analysis was enabled by the kind of data being gathered and the manner through which to analyse them. In addition, the methodology paved the way for the result to conclude that the water samples being examined were oxidising. Similarly, it was able to point out that the most acidic water had the higher Eh values, leading to a deviation from the common pattern demonstrated by the dominant waters in the wetland. The results also revealed the existence of the effect of tidal interaction through the way the data were used to examine the gradual decline of the electrical conductivity in the upstream route. The data also allowed identifying the period when the maximum value was recorded. The study’s depiction of dissolved oxygen concentrations in the draining streams across the agricultural areas is parallel to its objective to find out the influence of tidal and cyclical conditions on the concentrations of pollutants. An interesting point to mention is the fact that Barba-Brioso et al.’s (2010) study was cited by Haarstad et al. (2011) in their investigation of pollutants in natural wetla nds and the latter also used the experimental design, enabling the authors to identify the pesticides found and identify toxic heavy metals. An experimental design – with a different statistical approach – was also utilised in Barba-Brioso et al.’s (2010) study on the application of the life cycle impact assessment to the Domingo Rubio tidal structure. With the above discussion, it is thereby concluded that there are no more areas in which the methodology could be improved as it was able to cover all the necessary aspects deemed to be achieved by the objectives. Conclusion This paper has been focused on analysing critically the methodology adopted in the study of Barba-Brioso et al. (2010), which is about water pollution from multiple sources in the Huelva Estuary. This work is able to pinpoint the extent to which the methodology has allowed the aims and objectives to be addressed in their entirety. Sampling for both high tide and low tide was utilised in Barba-Brioso et al.’s study to consider the impacts of tidal regimes, in which water samples were taken during winter and summer. A highly systematic and intricate methodology was adopted, considering that the study itself was quantitative where objectivity and statistical validity were highly considered. The study’s adoption of the experimental method is consistent with the use of basic descriptive statistics that allowed examining the concentrations of elements in the wetland. It also utilised hydrochemical parameters, amongst others, as a way to contribute to addressing its objective to identify hydrochemical irregularities. With the study’s identification of dissolved oxygen concentrations in the draining streams, it likewise tackled the objective of recognising the influence of tidal and cyclical conditions on the concentrations of pollutants. 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