Data for: Hydrological connectivity regulates nitrogen transformation within a meandering driven hyporheic zone under contrasting hydrological conditions
Description
This dataset is the original data of the paper “Hydrological connectivity regulates nitrogen transformation within a meandering driven hyporheic zone under contrasting hydrological conditions”. The dataset includes water level data and water chemistry data during the rainy season of a wet year 2021 and a normal year 2022. All the water level and concentration data were obtained by in situ monitoring in a meandering river bend in the upstream Xilin River, which is located in the central Inner Mongolia, China (43°37′11.2″N, 116°42′23.6″E). The water chemistry data include the concentration of Dissolved Organic Nitrogen (DON), DIN species (NO3-, NO2-, NH4+) and Dissolved Oxygen (DO). High-resolution groundwater level was collected in the riparian zone. Five lateral transects (T1-T5) were set up along the meander reach to investigate the hyporheic exchange flow (Fig. 1). Along each transect, three monitoring points were installed, with one in the middle of river channel, and one on each bank 2 m away from the river edge. For each instream point at C1 (inlet), C3 (apex) and C5 (outlet), three PVC piezometers with 5 cm diameter were installed to depths of 20 cm, 50 cm and 100 cm below the riverbed surface to observe groundwater heads at multiple depths. For the instream points at C2 and C4, one PVC piezometer was installed at the depth of 100 cm below the riverbed surface. For the monitoring points on each bank, one piezometer was installed to 150 cm depth below the ground surface. Along the transect at the meander apex (T3), we established two more piezometers in the inner bank of the meander, located 6 m and 10 m away from the river edge.
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Water level observations and water sampling were carried out from 7 July to 13 August, 2021 and from 17 July to 25 August, 2022. The river stage was observed by reading a water level gauge attached to the external surface of the instream piezometers. The groundwater levels were manually measured by steel tape once a day during the study periods. The water levels were then converted to absolute elevations based on a datum point measured by GPS-RTK systems on the riverbank. We collected both river water and pore water samples every 3 days over the study periods in 2021 and 2022. River water samples were collected by first triple-rinsing bottles with river water and then filling them directly. Pore water samples were collected from all instream piezometers open at 20 cm, 50 cm and 100 cm depths below the riverbed surface and all the piezometers on the river banks at 150 cm below the ground surface. Each well was purged prior to pore water sample collection in order to remove stagnant water. To collect the pore water samples, 20 mL water was slowly drawn into a syringe attached to the sampler tubing with an inlet at the bottom of each well. After discarding the rinse water, another 100 mL water were drawn. All the sampled water was filtered through 0.45 μm filters for measurement of N concentrations. The collected water was immediately partitioned into 50 mL transparent polyethylene bottles for NO3-, NO2- and NH4+ concentration analysis, and 50 mL brown glass bottles for DON concentration analysis. All the water samples were stored in a refrigerator (4 °C) and transported to the laboratory for analysis immediately on arrival. The concentrations of DIN species, i.e., NO3-, NO2- and NH4+ were determined by the spectrophotometric method. NO3- concentration was analyzed by using Shimadzu UV-2600 reader spectrophotometer at wavelengths of 220 nm and 275 nm. The calibration curve (NO3- concentration versus absorbance) was plotted by measuring the UV-vis absorbance at 220 nm and 275 nm of a series reference solutions of known concentrations of potassium nitrate. Concentrations of calibration standard solution were 0, 0.5, 1, 2, 5 and 10 mg L-1. The calibration curve related concentration to the difference between absorbance at 220 nm and 275 nm. Similar procedures were applied for measuring the concentrations of NH4+ and NO2-. DON concentration was determined by alkaline potassium persulfate digestion followed by the UV spectrophotometric method. The Dissolved Oxygen (DO) concentration of river water and pore water were measured using a multi parameter portable meter (WTW Multi 3630 IDS SETG).
Institutions
- Inner Mongolia UniversityInner Mongolia, Hohhot