Investigation of the Impact of the Guangzhou-Lechang Expressway Segment at the Pajiang River Detention Basin to Its Normal Flood Prevention Operation

Based on the existing relevant information, the paper investigates the occupation situation of the segment of the Guangzhou-Lechang expressway in the Pajiang River detention basin and analyzes the relationship of the water conservancy facility construction to the planning of the detention basin. One-dimensional and two-dimensional mathematical models are established to evaluate the construction effect on flood control in the detention basin under the normal use condition of the Pajiang River. The results show that the construction occupies 0.09% regulation and storage volume of the detention basin, which leads to the following impacts to its flood prevention operation: the starting time of the detention basin delayed 3~12 minutes, the average discharge of the Jiangkouxun section in the main river of the Beijiang River increased 12m3/s, and the average discharges of the Tiechuang-ao section of the Pajiang River and the Changbu section of the Yuantan River in the detention basin decreased 14 m³/s and 13 m³/s, respectively. Meanwhile, the highest water level of the Jiangkouxu Station and the peak discharge of the Shijiao Station remain almost the same. Therefore, as the conclusion, the engineering construction of the expressway segment only produces a minor impact on flood control of the Beijiang River. This investigation provides the technical basis for evaluation of the impact to flood prevention by highway construction for similar projects and will be useful for decision-making of the relevant planning agencies.

Vegetation influences soil properties along riparian zones of the Beijiang River in Southern China

Riparian soils and vegetation are important factors influencing the biodiversity and biogeochemical processes of river ecosystems. Riparian soils and vegetation form the foundation for multiple ecosystem services provided by river ecosystems. However, it remains poorly understood how riparian soils and vegetation interact with one another to maintain these services. In this study, we sampled four common types of riparian vegetation associated with the Beijiang River in South China. These included forestland, bamboo forest, mixed forest, and grassland ecosystems. Specifically, we analyzed the spatial distribution of riparian soils and their response to environmental factors (i.e., coverage and height of trees, shrubs and grass, distance to river, and altitude). Our results indicate that soil properties in riparian zones were affected significantly by vegetation type. In particular, clay content, soil organic carbon, and nitrate nitrogen content were significantly correlated with vegetation type. In contrast, changes in soil total nitrogen, total phosphorus, and available phosphorus content were not associated with vegetation type. Moreover, soil physical and chemical properties interacted with one an other, as well as with vegetation characteristics. This was indicated by the significant correlation observed between soil organic carbon, total nitrogen, total phosphorus, and soil texture, with structural characteristics of the four vegetation types. We also found that height and cover of trees and shrubs were significantly correlated with soil chemical properties. However, the effects of topographic variables such as altitude and distance to river were not significant. Results from this study can thus provide a basis for the ecological restoration and land management of degraded iparian zones.

Reservoir-Induced Hydrological Alterations Using Ecologically Related Hydrologic Metrics: Case Study in the Beijiang River, China

Anthropogenic activities have a tremendous impact on water ecosystems worldwide, especially in China. To quantitatively evaluate the hydrological alteration connected with aquatic lives and river ecological risks, we took the Beijiang River located in South China as the case study and used ecosurplus (defined as ecological carrying capacity exceeding ecological consumption)/ecodeficit (defined as ecological consumption exceeding carrying capacity) and Indicators of Hydrological Alterations to evaluate hydrological changes. The Ecologically Relevant Hydrologic Indicators were employed to select the key indices of Indicators of Hydrological Alterations, and the eco-environmental water demand calculation provide an effective way for the reservoir operation. Results showed that: (1) High flows contributed more to the ecodeficit, while low flows contributed more to the ecosurplus; (2) the ecodeficit in some parts of the river basin might exceed the ecosurplus after reservoir construction, especially along the main stream; and (3) the determination of eco-environmental water demand is a feasible way for improving the environment by controlling reservoirs. The current study can help guide the optimization of hydrological operation in the basin toward making the ecosystem healthier and has potential to further provide a reference for other basins in terms of hydrological alterations driven by anthropogenic activities.

Temporary and net sinks of atmospheric CO₂ due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology

The study provides the major ion chemistry, chemical weathering rates and temporary and net CO2 sinks in the Beijiang River, which was characterized as hyperactive region with high chemical weathering rates, carbonate and silicate mixing lithology and abundant sulfuric acid chemical weathering agent with acid deposition and AMD origins. The total chemical weathering rate of 85.46 t km−2 a−1 was comparable to other rivers in the hyperactive zones between the latitude 0–30°. Carbonate weathering rates of 61.15 t km−2 a−1 contributed to about 70 % of the total. The lithology, runoff and geomorphology had significant influence on the chemical weathering rate. The proportion of carbonate outcrops had significant positive correlation with the chemical weathering rate. Due to the interaction between dilution and compensation effect, significant positive linear relationship was detected between runoff and total, carbonate and silicate weathering rates. The geomorphology factors such as catchment area, average slope and hypsometric integral value (HI) had non-linear correlation on chemical weathering rate and showed significant scale effect, which revealed the complexity in chemical weathering processes. DIC-apportionment showed that CCW (Carbonate weathering by CO2) was the dominant origin of DIC (35 %–87 %) and that SCW (Carbonate weathering by H2SO4) (3 %–15 %) and CSW (Silicate weathering by CO2) (7 %–59 %) were non-negligible processes. The temporary CO2 sink was 823.41 103 mol km−2 a−1. Compared with the temporary sink, the net sink of CO2 for the Beijiang River was approximately 23.18 × 103 mol km−2 a−1 of CO2 and was about 2.82 % of the temporary CO2 sink. Human activities (sulfur acid deposition and AMD) dramatically decreased the CO2 net sink and even make chemical weathering a CO2 source to the atmosphere.