Subsurface chemical discharge in Lithuanian area

Abstract

An assessment of groundwater chemical leakage under the Lithuanian hydrogeological conditions, using the classic method of hydrogeological/ hydrograph division and linking it with the chemical leakage. Subsurface chemical discharge is the amount of salts flown by the rivers due to their draining impact on the subsurface. The chemical runoff is determined by two key factors: groundwater runoff yield and total content of dissolved solids (TDS). The value of the groundwater runoff module (the yield from 1 km²) in the river basins of Lithuania ranges from 0.4 to 5.0 l/s km². TDS values in shallow groundwater drained by the rivers range from 180 to 800 mg/l. The modules of subsurface chemical runoff in the area of Lithuania range from 3–9 to 54 t/year from 1 km² with the highest values observed in the Baltija uplands and Dainava Plain. During the last decade, the chemical runoff has stabilised due to decline in technogenic load. If compared to the dissolved solids drained by the rivers the subsurface chemical discharge can make up 7–45%. The chemical runoff out for all area of Lithuania, as assessed by the hydrological/hydrogeological technique according to the minimum long‐term runoff and TDS content in the river water of that period, reaches 2.2 mln. t/year of mineral material, about 90% of which come from the Nemunas River basin. To restrict the influence of technogenic pollution on the results of the assessment of underground chemical runoff, only observations done upstream the pollution sources (mainly urban) have been used. The qualitative assessment of the changes in groundwater chemical discharge and flow fluctuations due to technogenic impact has been carried out by applying graphical analysis of the underground chemical runoff module.

Santrauka

Darbo tikslas – ivertinti požemini chemini nuoteki Lietuvos hidrogeologinemis salygomis, taikant klasikine hidrologohidrogeologine hidrografo skaidymo metodika. Požeminis cheminis nuotekis – tai drusku kiekis, nutekantis upemis del drenažinio poveikio. Chemini nuoteki lemia du pagrindiniai veiksniai – požeminio nuotekio debitas ir vandens bendroji mineralizacija. Požeminio nuotekio modulio dydis (debitas iš 1 km²) Lietuvos teritorijos upiu baseinuose kinta nuo 0,4 iki 5,0 l/s km². I upes požemiu nutekančio gruntinio vandens bendroji mineralizacija – nuo 180 iki 800 mg/l. Požeminio cheminio nuotekio Lietuvos teritorijoje moduliai yra nuo 3–9 iki 54 t/metus iš 1 km². Didžiausias požeminis cheminis nuotekis Baltijos aukštumose bei Dainavos lygumoje. Pastaraji dešimtmeti cheminis nuotekis stabilizavosi del sumažejusios technogenines apkrovos. Palyginti su bendru mineraliniu medžiagu kiekiu, nutekančiu upemis, požeminis cheminis nuotekis gali sudaryti 7–45 %. Visas požeminis cheminis nuotekis Lietuvos teritorijoje, ivertintas pagal minimalu daugiameti nuoteki ir to periodo upiu vandens mineralizacija, siekia 2,2 mln. t/metus mineraliniu medžiagu, kuriu apie 90 % išplukdoma iš Nemuno baseino. Technogeninio užterštumo itakai požeminio cheminio nuotekio vertinimo rezultatams riboti naudoti tik stebejimu duomenys aukščiau taršos šaltiniu (daugiausia miestu). Požeminio vandens cheminio nuotekio, kuri lemia technogeninis poveikis, pokyčiu kokybinis ivertinimas atliktas nuotekio moduliu grafoanalizes pagrindu.

Keywords:

• groundwater runoff modulus
• total dissolved solids
• subsurface chemical discharge modulus
• environmental conditions

Reikšminiai žodžiai:

• požeminio nuotekio modulis
• bendroji mineralizacija
• požeminio cheminio nuotekio modulis
• gamtines salygos