Using Dual Isotopes of Nitrate to Identify the Source of Nitrogen Pollution in the Songhua River Basin, Northeast China

Nitrogen pollution is a severe problem in the Songhua River Basin (SHR) in China. Samples were collected from 36 sections of the SHR during the high, low, and flat seasons of the river, and the main sources of nitrogen in the water were qualitatively analyzed with isotope data for nitrogen and oxygen of nitrate. The contribution rates of each major pollution source were quantitatively analyzed using the Iso Source mass balance model. The results from these experiments indicate that the values for δ15N-NO3 and δ18O-NO3 in the flat flow season range from 1.52‰ to 14.55‰ and −14.26‰ to 2.03‰, respectively. The values for δ15N-NO3 and δ18O-NO3 in the low flow season range from 6.66‰ to 15.46‰ and −5.82‰ to 65.70‰, respectively. In the low flow season, nitrogen comes from the input of domestic and manure sewage (53%) and soil organic N (45%). The values of δ15N-NO3 and δ18O-NO3 in the high flow season range from 2.07‰ to 14.24‰ and −3.99‰ to 8.03‰, respectively. In the high flow season, nitrogen comes from soil organic nitrogen (41%), domestic and manure sewage (32%), and nitrogen fertilizer (27%), which are the main sources of nitrogen pollution in the SHR. The conclusions from the qualitative and quantitative analysis of nitrogen sources in the SHR can provide a scientific basis for the source control and treatment of nitrogen pollution.

Investigation of spatial and temporal variability of river ice phenology and thickness across Songhua River Basin, northeast China

The regional role and trends of freshwater ice are critical factors for aquatic ecosystems, climate variability, and human activities. The ice regime has been scarcely investigated in the Songhua River Basin of northeast China. Using daily ice records of 156 hydrological stations across the region, we examined the spatial variability in the river ice phenology and river ice thickness from 2010 to 2015 and explored the role of snow depth and air temperature on the ice thickness. The river ice phenology showed a latitudinal distribution and a changing direction from southeast to northwest. We identified two spatial clusters based on Moran's I spatial autocorrelation, and results showed that the completely frozen duration with high values clustered in the Xiao Hinggan Range and that with low values clustered in the Changbai Mountains at the 95 % confidence level. The maximum ice thickness over 125 cm was distributed along the ridge of the Da Hinggan Range and Changbai Mountains, and the maximum ice thickness occurred most often in February and March. In three subbasins of the Songhua River Basin, we developed six Bayesian regression models to predict ice thickness from air temperature and snow depth. The goodness of the fit (R2) for these regression models ranged from 0.80 to 0.95, and the root mean square errors ranged from 0.08 to 0.18 m. Results showed significant and positive correlations between snow cover and ice thickness when freshwater was completely frozen. Ice thickness was influenced by the cumulative air temperature of freezing through the heat loss of ice formation and decay instead of just air temperature.

Different runoff patterns determined by stable isotopes and multi-time runoff responses to precipitation in a seasonal frost area: a case study in the Songhua River basin, northeast China

Runoff patterns are crucial to determine the hydrological response to climate change, especially in a seasonal frost area. In this study, multi-time runoff responses to meteoric precipitation for the period from July 2014 to June 2016 and the period from 1955 to 2010 were obtained to identify different runoff patterns in the Songhua River basin, northeast China, based on six stations. Two distinctly different runoff responses are exhibited: a periodic one in response to precipitation in the Nen River and a constant one in the Second Songhua River under different scales. Stable isotopes in the plain with diverse characteristics also supported these runoff patterns. What is more, gradual runoff relatively less sensitive to precipitation in the Second Songhua Rive was attributed to upstream dam constructions. Furthermore, the Second Songhua River contributes more water to the main stream during January to March at the seasonal scale and in the 2000s at the annual scale, with low precipitation during those periods. This study could have implications for water management in the Songhua River basin.

The Research on Temporal–Spatial Distribution and Morphological Characteristics of Ancient Settlements in the Songhua River Basin

Settlements have a high cultural and historical value in regions as indicators of human habitation and culture. The Songhua River Basin is on the edge of a traditional cultural center, which has scattered ecological elements, a special culture, and historical faults. Because of the superposition of traces of different ethnic activities in different periods, the Songhua River has a special and diversified cultural foundation and heritage, which is of high research value. However, the ancient settlements in this region have not been given sufficient attention and as a result it is difficult to achieve a complete and systematic study. In order to promote the cultural value of this historical region and the development of a regional and cultural industry, this paper seeks to study the ancient settlements of Songhua River Basin. With the help of GIS technology, archeological excavations, and the concept of ethnic pedigree in ethnology, this study analyzes the temporal–spatial distribution and morphological characteristics of ancient settlements in the Songhua River Basin, in order to determine how the heritage value of these settlements can be sustainably protected.