Characterization of Salinity in The River Neretva Delta Using Landsat TM5 and in situ Data

Salinization greatly affects the ecosystems, crop production and the economy. Source of salinity can be generally categorized as primary or naturally occurring and secondary or human induced salinity. Primary salinity stems from atmospheric effects on the rocks containing primary minerals for thousands of years, discharged ions are then combined in various salts which are later naturally distributed to remote geographical areas. Improper management of natural resources which results in soil and water salt build-up applies to secondary salinity. The area being analyzed in this paper is the alluvial river Neretva delta. Today, this area is used for intensive agricultural production of fruits and vegetables, from which citrus orchards are being most present. Agronomic production in the river Neretva delta poses substantial economic importance at a local and a national level as well. Lately, the sustainability of this production has become threatened by the increase in the salinity of groundwater and surface waters. Climate, hydrological and hydrogeological processes, including the engineering structures dictate the salinity fluctuation in the delta. There are two main directions of salt water penetration in the river Neretva delta: sea water intrusion through the riverbed and from deep underground layers where groundwater is already salinized because of direct connection with the sea through porous aquifer. Intensive agriculture demands high water levels, particularly in semi-arid climate, which then culminates with the rising of salty groundwater table. Furthermore, drop in quality of water used for irrigation due to reduced precipitation and extensive use of fertilizers and herbicides add to the total salinity in the river Neretva delta. Soil or water salinity is often depicted by measurements of electrical conductivity which is expressed in deciSiemens per meter (dS/m). This paper describes the interrelationship between in situ measurements of electrical conductivity in open watercourses with Landsat TM5 data in the period between May 2009 and October 2011. Water electrical conductivity was measured once per month on the 13 locations mostly placed in the melioration canals and near the pumping stations. Satellite data was firstly corrected for radiometric and atmospheric effects, afterwards the intensity, salinity, and vegetation indices were calculated. A total of 37 satellite images were analyzed in this study, where 23 of them are placed in the path 30 and row 188, while remaining 14 are placed in the same path but in the row 187 of the Worldwide Reference System. These images needed to be analyzed separately since pixel footprint of Landsat TM5 equals to 900 square meters. Pixel misalignment between these two groups of images and spectral mixing of classes at the pixel level, resulted in considerable differences in spectra at a given point for the two substantial images from different rows. In near vicinity of in situ sampling points, pixels classified as cultivated and uncultivated areas were selected. Correlation analysis of the original Landsat bands, their ratios and spectral indices with the electrical conductivity values was performed and accomplished correlation values were discussed.