Geochemical dataset of the Danube Delta sediments

We present geochemical analyses (major, such as CaCO3, TOC, Fe2O3, and minors such as MnO and TiO2) and trace elements, as well as some trace elements with genetic significance (Rb, Sr, Zr) or toxic and potentially affected by anthropic influences (Cu, pb, Zn, Cd, Cr, V, Ni, Co) of the superficial bed sediments of the St. George distributary which is the most sinuous and morphologically dynamic branch of the Danube River. Bed sediment samples were collected onboard of R.V. Istros, in June 2017. The dataset is useful to evaluate the distribution of the sediment along the fluvial channel, the present ecological state of the environment and, the effects of artificial intervention on the fluvial channel (the cutoff of the natural channels by navigational canals between 1984 and 1988). The data are presented as tabular format.


Specifications
Geochemistry Specific subject area Geochemical analyses of the superficial bed sediments Type of data Table  Chart Figure How data were acquired Surface sediment samples were collected with a grab sampler "Van Veen" type. Sediments were oven dried and homogenized using a mortar grinder RM 200 (Retsch, Germany) and sieved with a 250-μm stainless steel sieve. The total organic carbon (TOC) and CaCO 3 concentrations were determined in accordance with WakleyBlack titration method modified by Black [1] and Gaudette et al. [2] , respectively. Fe 2 O 3 (total), TiO 2 , Rb, Sr, Zr and V have been analyzed by X-ray fluorescence spectroscopy, using a VRA-30 sequential spectrometer, on compacted powders; Mn, Co, Ni, Cu, Zn, Cr and Pb have been determined by flame, AAS and Cdby graphite furnace AAS on an ATI UNICAM 939E AA spectrometer, after digestion of the samples with boiling HNO 3

Value of the Data
• Geochemistry of river sediments are controlled by the physical and chemical weathering of parent rocks, but also by factors such as climatic, hydrological, morphological and anthropogenic pressures in the basin. • The presented data could be used by hydrologists, sedimentologists and geochemists for the research planning, sediment sampling, and specific analyses protocol. • Evaluating post effects of the anthropogenic pressures in a natural environment can provide important comprehension of other similar cases worldwide. • The data advance knowledge about actual ecological state of the Danube Delta sediments.

Data Description
This data presented consists of geochemical data acquired along the St. George branch in June 2017. The spatial distribution of the geochemical sampling stations is presented in Fig. 1 . The sediments were sampled in medium to high water stage, at a daily discharge of 2170 m 3 .s −1 (measured at the entrance in the study reach, A1) ( Fig. 1 ). Surface sediment samples were collected with a grab sampler from 17 locations distributed along the branch, on the main channel  and former meanders (Mahmudia, Dunav ȃ ¸t de Sus (Upper) and Dunav ȃ ¸t de Jos (Lower)). Information on the sampling stations (coordinates, water depth and site characteristics are provided in Table 1 . Order 161/2006 [3] sets Romanian quality criteria for a number of chemical compounds, organic and inorganic, in sediments: these include a number of heavy metals analysed in sediment samples ( Table 2 ). The geochemical parameters analysed on bed sediments of the three studied meanders during the field campaign from June 2017 are shown in Table 3 .
The Table 4 show the descriptive statistics for the concentrations of the studied variables. Table 5 present the correlation matrix (Pearson) for the major constituents, minor constituents and heavy metals.
The linear regression analysis and the calculation of the prediction interval for the relationship

Experimental Design, Materials and Methods
Prior to geochemical analysis the sediment samples were oven dried (24-48 h/105 °C), ground, and homogenized using a mortar grinder RM 200 (Retsch, Germany) and sieved with a 250-μm stainless steel sieve. The total organic carbon (TOC) and CaCO 3 concentrations were determined in accordance with WakleyBlack titration method modified by [1] and [2] , respectively. The concentrations of Fe 2 O 3 , TiO 2 , MnO, Zr, Cr, V, Zn, Cu, Ni, As, and Pb were measured Table 3 Results of geochemical analyses on bed sediments of the three studied meanders during the field campaign from June 2017 to estimate the geochemical properties of bottom sediments and characterize the variation of major and trace elements.

Ethics Statement
None.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships which have or could be perceived to have influenced the work reported in this article.