DOI: 10.34810/data2486
title: Tracing chemical diversity in dissolved organic matter from freshwaters to marine environments

description: This dataset provides detailed measurements of the chemical composition and proton-binding properties of dissolved organic matter (DOM) collected along the Ebro River continuum, from its headwaters to the Mediterranean Sea. Samples were collected across different seasons to capture spatial and temporal variability. The dataset includes quantified concentrations of low- and high-affinity DOM binding groups (expressed in mmol·mol C⁻¹), estimates of the organic contribution to total alkalinity (μmol binding groups·L⁻¹), and metadata on sampling locations, environmental conditions, and physicochemical parameters.
The data enable exploration of seasonal shifts and spatial gradients in DOM reactivity, with particular attention to the influence of riverine processes, such as groundwater inputs, terrestrial runoff, and in-river degradation. Researchers can use this dataset to examine DOM's role in micronutrient cycling, carbon transport, and buffer capacity in aquatic systems.
description: This dataset comprises chemical, physical, and geospatial data collected from water samples at various locations, designated as P1, P2, P3, and P4, during both winter and summer seasons (e.g., P1_W and P1_S). The sampling points P1 to P3 are located along the Ebro River, while P4 is situated in the Mediterranean Sea, capturing the transition from freshwater to coastal marine environments. These locations were selected to represent a gradient of land use and cover conditions, including forested, agricultural, and urbanized areas, as detailed in the “Land Use_Cover” sheet.

The dataset encompasses ancillary water quality parameters such as pH, temperature, salinity, and dissolved organic carbon (DOC), which provide environmental context for interpreting the chemical behavior of dissolved organic matter (DOM). Additional sheets provide acid-base titration results and model-derived parameters that describe the DOM’s functional group content and its proton-binding behavior. Specifically, intrinsic and conditional acid-base constants (log K) are presented in the “AS_Intrisec” and “AS_Condicional” sheets, reflecting how DOM interacts with protons under varying pH and ionic strength conditions.

The dataset also includes parameters obtained through the NICA-Donnan model, such as Qmax (maximum site density), logKH (proton affinity constants), and m1/m2 (site heterogeneity factors), which are crucial for understanding DOM reactivity. These parameters were determined using computational routines developed in MATLAB, which are provided as part of this repository for reproducibility and further modeling applications. In addition, a table with the experimental charge vs. pH curves under different ionic strength conditions is included, offering transparency into the raw data that supported model fitting.

The sheets “Alkalinity_Contribution_pH3_8” and “Alkalinity_Contribution_pH3_10” quantify the contribution of DOM to alkalinity across specific pH ranges, while the “%_Unprotonated” sheet estimates the proportion of binding sites that remain unprotonated at environmental pH—important for predicting complexation with metals and nutrients.

This dataset is suitable for research involving DOM characterization, water quality assessments, geochemical modeling, and the influence of land use on aquatic biogeochemistry. Users are encouraged to consider contextual variables—especially pH, ionic strength, and site-specific characteristics—when comparing or reapplying the data.
description: Microsoft Excel, null