Improving surface water quality of the Yellow River Basin due to anthropogenic changes

Response of stream water quality to the vegetation patterns on arid slope: a case study of Huangshui River basin

Vegetation patterns on slopes strongly affect the water cycle processes in a basin, especially the water yield and confluence in arid areas. Quantifying and evaluating the effects of hydrological change on the migration and transformation of pollutants are challenging. Based on 4-year stream water quality data of 13 monitoring sites in the Huangshui River basin, a typical arid watershed of the Chinese Loess Plateau, the redundancy analysis (RDA) and structural equation modeling (SEM) analysis tools were used to quantify its relationship with vegetation patterns. In the study, land use and the enhanced vegetation index (EVI) were used as a metric of vegetation patterns; accordingly, the 13 catchments were divided into three groups via the cluster analysis, including large (over 80%), medium (70 ~ 80%), and small (below 70%) proportion vegetation patterns (LVP, MVP, SVP). The results of the LVP group showed that vegetation patterns negatively affected the contamination of total phosphorus (TP), ammonia nitrogen (NH3-N), permanganate index (CODMn), and biochemical oxygen demand (BOD5) in the stream water, and the contribution rates were - 0.57. While the proportion of urban area positively correlated with stream water quality in the groups of MVP and SVP, the contribution rates were 0.46 and 0.36, respectively. Moreover, the precipitation in the groups of MVP and SVP negatively correlated with pollutants (- 0.24 and - 0.26). Those results revealed the response of stream water quality to vegetation patterns on the slope with the consideration of precipitation, land use, and socio-economic factors for the regional water and land resource allocation. This study has important management implications for vegetation patterns on slope of fragile ecosystems in arid areas.

Identifying the water quality variation characteristics and their main driving factors from 2008 to 2020 in the Yellow River Basin, China

Understanding of the water quality dynamics and their main influence factors is crucial for sustainable water environment management especially in the sensitive ecosystem area. Here, the spatiotemporal dynamic of water quality in the Yellow River Basin from 2008 to 2020 and its relationship with physical geography, human activities, and meteorology were studied by using Pearson correlation test, and a generalized linear model. The results showed that water quality was significantly improved since 2008, which was reflected from the decreasing trend of the permanganate index (COD_Mn) and ammonia nitrogen (NH₃-N), and increasing trend of the dissolved oxygen (DO). However, the total nitrogen (TN) remained severely polluted with average annual concentration inferior to level V. Spatially speaking, the water quality in the upper and lower reaches was better than that of the middle reaches. The whole basin was severely contaminated by TN with 2.62 ± 1.52, 3.91 ± 1.71, and 2.91 ± 1.20 mg L^-1 from upper, middle, and lower reaches, respectively. Thus, TN should be paid much attention in the water quality management of the Yellow River Basin. The water quality improvement could be attributed to the reduction of pollution discharges and ecological restoration. Further analysis found the variation of water consumption and increase of forest and wetland area contributed 39.90% and 47.49% for COD_Mn and 58.92% and 30.87% for NH₃-N, respectively. Meteorological variables and total water resources contributed slightly. This study is expected to provide in-depth insights for the water quality dynamics and their response to human activities and natural factors in the Yellow River Basin, which could provide theoretical references for water quality protection and management.

Anthropogenic Land Use and Land Cover Change as Potential Drivers of Sediment Sources in the Upper Crocodile River, North West Province, South Africa

In this study, we investigated the accelerating pace of anthropogenic land use and land cover change (LULCC) disturbance, which has generated enormous impacts on the Crocodile River. Spot images from 1996, 2009 and 2022 were used to generate the land use maps and quantify the changes. A supervised classification with the maximum likelihood classifier was used to classify the images. Sediment sources were classified into two sources, revealed by erosional characteristics in the catchment. A gamma spectrometry detector, high-purity germanium (HPGe) "Well" detector by Canberra and inductively coupled plasma mass spectrometry (ICP-MS) were used for the analysis of the samples. The results revealed that from 1996-2022, built-up areas, bare land and water bodies increased by 3.48%, 2.47% and 1.90%, respectively. All the LULCC classes increased annually from 1996-2022, except for grassland, which shrunk. The results of the radionuclides analysis showed that ²¹⁰Pb_ex was found to be a more effective tracer than ¹³⁷Cs. The mass balance model revealed that subsurface sources contributed 60%, while surface sources contributed 40%, of the sediment load in the river. This research provides valuable information necessary for integrated catchment management policies for future LULCC and soil erosion to be adopted.

The Effect of Rainfall on Aquatic Nitrogen and Phosphorus in a Semi-Humid Area Catchment, Northern China

The impact of rainfall on water quality may be more important in semi-arid regions, where rainfall is concentrated over a couple of months. To explore the impact of rainfall changes on water quality, e.g., nitrogen (TN) and phosphorous (TP), the diversion from Luan River to Tianjin Watershed in the northern semi-humid area was selected as the study area. TN and TP concentrations in rivers and the Yuqiao Reservoir during the three-year high-flow season (2019-2021) were analyzed. The response relationship and influencing factors among the watershed's biogeochemical process, rainfall, and water quality were clarified. The results showed that rainfall in the high flow season mainly controlled the river flow. The concentration of TN and TP in the inflow rivers is regulated by rainfall/flow, while the concentration of TN and TP in the water diversion river has different variation characteristics in the water diversion period and other periods. The lowest annual concentrations of TN and TP were observed in the normal year, while the highest annual concentration was observed in the wet year, indicating that the hydrological process drove the nutrient transport in the watershed. For the tributaries, the Li River catchment contributed a large amount of N and P to the aquatic environment. For the reservoir, the extreme TN concentrations were the same as the tributaries, while the extremes of TP concentrations decreased from the dry year to wet year, which was in contrast to the tributaries. The spatial variation of TN and TP concentrations in the reservoir showed that the concentration decreased following the flow direction from the river estuary to the reservoir outlet. Considering climate change, with the increase of rainfall in North China in the future, the TN and TP transport fluxes in the watershed may continue to increase, leading to the nitrogen and phosphorus load of the downstream reservoir. To ensure the impact of the increase of potential N and P output fluxes in the watershed on the water quality of the reservoir area, it is necessary to strengthen the effective prevention and control of non-point source pollution in the watershed.