The goal of the LoTSS sky survey is to observe the whole North sky with the LOFAR telescope at very low radio frequencies (approximately 150 MHz). At low frequencies, most of the polarized emission of the Milky Way is synchrotron radiation produced by high energy electrons. Faraday rotation changes the angle of polarization when the radiation passes through magnetized interstellar medium. Faraday rotation is proportional to the square of the wavelength of radiation. Therefore, we can use Faraday tomography and rotation measure (RM) synthesis method to disentangle the observed emission over the range of Faraday depths. Faraday depth gives us the distribution of ionised interstellar medium and magnetic field along the line of sight. In this work we combined 186 single LoTSS observations into a mosaic which covers approximately 1400 square degrees of the sky at South Galactic latitudes. We calculated the Faraday moments. The zero moment represents the total intensity of radiation over the whole Faraday spectrum. The first moment is the average Faraday depth weighted by intensity. The second moment is a half of the weighted width of the Faraday spectrum. The most significant feature of the mosaic is a gradient of intensity over multiple Faraday depths which covers the field of view from west to east. At the steepest part of the gradient the emission moves on average 4⁰ on the sky when the Faraday depth changes by 1 rad m-2. We compared our results to the Galactic Faraday rotation sky map and concluded that the emission observed in the LoTSS survey is produced at distances closer to us compared to the size of the whole galaxy.