Physicochemical properties of water bodies in the East and West Streams in Southeast China

Physicochemical properties of the Dongxi River in southeastern China, including data on nutrients and pollutants in the river water during the wet and dry seasons.Site positioning was conducted with a Magellan eXplorist 500 GPS device, and flow velocity was captured using a Decatur SVR2 handheld anemometer. The linear distance from each sampling point to the corresponding catchment outlet was computed using Google Earth Pro (v7.3.3). A WTW Multi 3620 IDS multi-parameter instrument was deployed for the in-situ determination of key water parameters, including dissolved oxygen (DO), pH, temperature, electrical conductivity (EC), and total dissolved solids (TDS). Subsequent laboratory testing comprised the measurement of turbidity with a HANNA HI98703 instrument; chlorophyll-a (Chl-a) quantification via spectrophotometry following the HJ 897-2017 protocol; assessment of dissolved nutrient levels (NO₃⁻-N, NO₂⁻-N, NH₄⁺-N, PO₄³⁻-P) using a SEAL AA3 continuous flow analyzer after 0.45-μm membrane filtration; total N determination through alkaline persulfate digestion combined with ultraviolet spectrophotometry; total P analysis by ammonium molybdate spectrometry; computation of dissolved inorganic N (DIN) as the summation of its inorganic constituents; dissolved organic C (DOC) concentration measured by high-temperature catalytic oxidation on a Shimadzu TOC-VCPH analyzer; derivation of the C:N ratio from DOC and DIN values; evaluation of the permanganate index (COD_Mn) via the potassium permanganate oxidation method; total suspended solids content quantification by gravimetric analysis after filtration (0.45 μm) and drying at 103–105 °C; five-day biochemical oxygen demand (BOD₅) tested according to standard procedures; and chemical oxygen demand (COD_Cr) analyzed by HACH DR2800 colorimetry following digestion with a DRB200 reactor. The concentrations of heavy metal elements (Cu, Ni, and As) were measured in triplicate samples using inductively coupled plasma mass spectrometry (ICP-MS, X Series II, Thermo Fisher Scientific, USA). Blank samples were concurrently analyzed to ensure that the data were reliable.