Geochemical classification of groundwater using multivariate statistical analysis in Latvia

Abstract

Multivariate statistical methodsprincipal component analysis (PCA) and hierarchical cluster analysis (HCA)are applied to identify geochemically distinct groundwater groups in the territory of Latvia. The main processes observed to be responsible for groundwater chemical composition are carbonate and gypsum dissolution, fresh and saltwater mixing and ion exchange. On the basis of major ion concentrations, eight clusters (C1-C8) are identified. C6 is interpreted as recharge water not in equilibrium with most sediment forming minerals. Water table aquifers affected by diffuse agricultural influences are found in C3. Groundwater in C4 reflects brine or seawater admixture and gypsum dissolution in C5. C7 and C2 belong to typical bicarbonate groundwater resulting from calcite and dolomite weathering. Extremely low Cl À and SO 4 2À are observed in C8 and described as preindustrial groundwater or a solely carbonate weathering result. Finally, C1 seems to be a poorly defined subgroup resulting from mixing between other groups. This research demonstrates the validity of applying multivariate statistical methods (PCA and HCA) on major ion chemistry to distribute characteristic trace elements in each cluster even when incomplete records of trace elements are present. Key words | groundwater chemistry, hierarchical cluster analysis, principal component analysis, trace elements Riga region. A noticeable increase of salinity in fresh groundwater around the city of Riga has been observed (Levins ). Coastal groundwater aquifers sometimes are affected by seawater intrusion, in particular if large cities are using them 799

Springs ecosystem classification

“…In addition, dissolved or gaseous methane, sulfides, and hydrogen can be important indicators in subaqueous freshwater springs. Many studies have used springs geochemistry to describe karstic or deep‐aquifer springs sourcing (e.g., Shuster and White 1971, Huntoon 2000, Crossey et al 2009, Hershey et al 2010, Springer et al 2017), and multivariate statistical techniques have revealed spatial and anthropogenic impacts, including as seawater intrusion into coastal aquifers (e.g., Yidana 2010, Retike et al 2016). However, while essential to understanding springs aquifer sourcing, ecosystem ecology, and utility for human use, like other aquifer and groundwater metrics, springs geochemistry does not readily or unambiguously distinguish springs ecosystems and thus remains of secondary importance in classification.…”

New Data on Seawater Intrusion in Liepāja (Latvia) and Methodology for Establishing Background Levels and Threshold Values in Groundwater Body at Risk F5

“…Data preprocessing included: (1) removal of historical samples which reported sodium and potassium as a sum (NaK) (an additional criterion); (2) removal of samples with ionic balances error greater than ± 10% as suggested by Müller et al (2006) and 3where such information was available samples with nitrate content exceeding 4 mg/l were removed as potentially affected by human activities. Much stricter criterion than suggested 10 mg/l by Müller et al 2006 was chosen based on most recent study about geochemical composition of groundwater in Latvia (Retike et al 2016).…”

“…Much stricter criteria were used, and value of the inflection point for chloride was set 18 mg/l. Results were compared with values obtained by Retike et al (2016). Next, BL for chloride ion was determined as 90 th percentile of all freshwater samples below the inflection point value according to BRIDGE methodology (Müller et al 2006).…”

“…Next, BL for chloride ion was determined as 90 th percentile of all freshwater samples below the inflection point value according to BRIDGE methodology (Müller et al 2006). This step was accomplished for two reasons: (1) the validation results from previous study suggested that 18 mg/l for chloride might be too high (Retike et al 2016) and (2) visual observation of the inflection point is subjective and may hold some uncertainty. Similarly, BL were set for sulphate and sodium.…”

Avotu ūdeņu kvalitāte Latvijā

“…Aptuveni pusē avotu ir pārsniegts pieļaujamais dzelzs, divos avotos sulfātjonu saturs, tomēr šo parametru pārsniegums nerada draudus cilvēka veselībai (Veselības inspekcija 2016). Divos avotos ir pārsniegta pieļaujamā amonija vai nitrātu koncentrācija, novērots, ka vismaz pusē paraugu ir pazemes ūdeņiem neraksturīgi augsta nitrātjonu vērtība (Retike et al 2016). Tas liecina, ka avota ūdens kopumā ir relatīvi vāji aizsargāts pret iespējamu virszemes piesārņojumu un tajā varētu būt pārsniegta arī līdz šim neanalizētu parametru pieļaujamā vērtība.…”