**2. Geology of the North Lithuanian karst region**

The total area of Lithuania is 65,300 km<sup>2</sup> and is situated along the south‐eastern shore of the Baltic Sea [8]. The karst region is located in North Lithuania (mainly in Biržai and Pasvalys administrative districts) and borders with the karst territories of the neighbouring South Latvia (**Figure 1**).

The karst processes highly active are related to Upper Devonian gypsum and dolomites that occur beneath the Quaternary cover (**Table 1**). Mainly of Quaternary deposits consist of loam and sandy loam, sand, gravely sand, gravel clay and silt; in some places, karstified rocks are overlain by the Pamūšis Formation (dolomitic marl, clay and other) and the Istras Formation (dolomite) of Upper Devonian [4, 7, 9].

Karst in the North Lithuania is matured not only at the land surface (sinkholes, karst shafts and dolines) but also in the subsurface (cavities and caves). In the region of active gypsum, karst (the area of 400 km<sup>2</sup> ) is counted more than 8500 different size and shape sinkholes [4, 7, 9].

The thickness of the cover of the karst rocks in the area varies from parts of the first metre up to 70 m and has a common tendency to increase southwards and especially westwards. Investigation of Water Quality in the Agricultural Area of Lithuanian Karst Region http://dx.doi.org/10.5772/intechopen.68536 101

occurs in contact with water and this causes subsidence problems. In agriculture land, these phenomena are inconvenient, but in urban area, they constitute a geological hazard that can

The rate of chemical denudation of soluble rocks is one of the main factors determining the intensity of karst process. Gypsum denudation is mainly predetermined by water balance, which depends on meteorological conditions (precipitation and evaporation). The highest intensity of gypsum denudation is during the spring flood and the lowest in the dry period.

The main human activities influencing karst development are groundwater extraction and

Karst region is densely populated. The two districts (Biržai and Pasvalys) with more than 53,000 of inhabitants [6] are located in it. Soils are fertile; agriculture has been a tradi‐ tional activity on these soils. Precipitation water dissolves not only natural salts from soils but also nutrient surplus from agriculture areas where unbalanced fertilisation rate was applied. Problems are caused by filtration of the water which is rich in salts and which pollutes groundwater. The major amount of precipitation infiltrates into the karst aquifer through Quaternary sediments, however, infiltration takes place through karst sinkholes as well [3, 7]. Karst groundwater becomes polluted frequently and in shorter time periods

The purpose of this chapter is to present a short review of the research finding on water (drainage, stream, groundwater and sinkhole) quality in agricultural area of North Lithuanian

Baltic Sea [8]. The karst region is located in North Lithuania (mainly in Biržai and Pasvalys administrative districts) and borders with the karst territories of the neighbouring South

The karst processes highly active are related to Upper Devonian gypsum and dolomites that occur beneath the Quaternary cover (**Table 1**). Mainly of Quaternary deposits consist of loam and sandy loam, sand, gravely sand, gravel clay and silt; in some places, karstified rocks are overlain by the Pamūšis Formation (dolomitic marl, clay and other) and the Istras Formation

Karst in the North Lithuania is matured not only at the land surface (sinkholes, karst shafts and dolines) but also in the subsurface (cavities and caves). In the region of active gypsum,

The thickness of the cover of the karst rocks in the area varies from parts of the first metre up to 70 m and has a common tendency to increase southwards and especially westwards.

) is counted more than 8500 different size and shape sinkholes [4, 7, 9].

and is situated along the south‐eastern shore of the

Since 1978, the intensity of karst denudation has been increased by 30% [2, 3].

seriously affect development and human safety [2].

agriculture [4, 5].

100 Cave Investigation

karst region.

Latvia (**Figure 1**).

karst (the area of 400 km<sup>2</sup>

than water in non‐karstic aquifers [1].

The total area of Lithuania is 65,300 km<sup>2</sup>

(dolomite) of Upper Devonian [4, 7, 9].

**2. Geology of the North Lithuanian karst region**

**Figure 1.** Location of Lithuanian karst area: (1) Pre‐quaternary carbonates; (2) area of intensive karst in North Lithuania (according to literature [2, 3]).


**Table 1.** Stratigraphy of the Middle‐Upper Devonian sediments in the North Lithuania [4].

Sinkholes are located in the areas with the cover thickness less than 25 m. In the areas where the cover thickness is up to 5 m, new sinkholes are forming intensively [9, 10].
