A Dataset on Dissolved Organic Matter Nutrients and Biodegradability in Surface Water and Soil Porewater from a Boreal Peatland with 13-Year Nitrogen Addition

The experiment employed a randomized block design with four nitrogen addition levels: control (0 g N·m⁻²·yr⁻¹), low nitrogen (3 g N·m⁻²·yr⁻¹), medium nitrogen (6 g N·m⁻²·yr⁻¹), and high nitrogen (12 g N·m⁻²·yr⁻¹). Each treatment consisted of four replicates, resulting in a total of 16 plots (4 m × 4 m). A 2 m buffer zone was established between plots, and stainless steel plates were buried to a depth of approximately 40 cm around each plot to prevent lateral nutrient diffusion.

Nitrogen fertilizer, in the form of urea solution, was evenly applied from May to July each year, while control plots received an equivalent amount of purified water. In early August 2024, surface water samples were collected from three randomly selected hollows within each plot. Meanwhile, soil porewater at a depth of 15 cm was extracted using a manual pump from two randomly selected hummocks and two hollows within each plot.

Water samples from the same plot were pooled and filtered through glass fiber filters (Whatman GF/F, 0.7 μm). The filtrates were used for the determination of dissolved organic matter (DOM) properties and biodegradability. Measured parameters included the concentrations of dissolved organic carbon (DOC), dissolved total nitrogen (DTN), and dissolved total phosphorus (DTP).

DOC and DTN were determined using a TOC analyzer (multi N/C 2100S, Jena, Germany), while DTP was measured using the persulfate oxidation-molybdenum antimony anti-colorimetric method [25]. DOM aromaticity was assessed using SUVA254 (L·mg⁻¹·m⁻¹), calculated by dividing the UV absorbance at 254 nm, measured with a UV-Vis spectrophotometer (UV600SC, Shanghai Jinghua Technology Instrument Co., Ltd.), by the DOC concentration.

Fluorescence excitation-emission matrix (EEM) spectra of DOM were obtained using a fluorescence spectrophotometer (F-7000, Hitachi, Japan), with excitation wavelengths ranging from 200 to 700 nm and emission wavelengths from 250 to 700 nm, at a scanning interval of 5 nm and a scan speed of 6000 nm·min⁻¹. The instrument performed automatic internal calibration. To eliminate interference from Rayleigh and Raman scattering, the methods of Bahrame et al. [27] were applied for data removal and interpolation.

Based on the fluorescence regional integration (FRI) method proposed by Chen et al. [28], the EEM spectra were divided into five fluorescence regions (Region I: tyrosine-like proteins; Region II: tryptophan-like proteins; Region III: fulvic acid-like substances; Region IV: soluble microbial byproduct-like substances; and Region V: humic acid-like substances). The normalized fluorescence area (Ui) and fluorescence contribution ratio (ρi) were calculated for each region.

The dataset is stored in tabular format, comprising 16 records corresponding to the 16 plots. Each row represents the comprehensive observational data for a single plot. Column labels include treatment type (control/low/medium/high nitrogen), DOC, DTN, and DTP concentrations (in mg·L⁻¹) for surface water and soil porewater separately, DOC:DTN, DOC:DTP, and DTN:DTP stoichiometric ratios, SUVA254 values (L·mg⁻¹·m⁻¹), normalized fluorescence area (Ui), and fluorescence contribution ratios (ρi, %) for each fluorescence region.

This dataset does not involve time-series observations; all samples were collected in August 2024. The spatial extent is confined to 16 fixed plots within a single study site (52.94°N, 122.86°E). All data are measured values, with each measurement repeated three times and averaged before entry.

All instruments were calibrated with standard curves, ensuring data quality and reliability. The data file is saved in Excel (.xlsx) format, which can be opened with commonly available office software.