Abstract The pH value of lake water varies with the lake environment, which has an effect on the form of phosphorus in sediment, and then the release of sediment phosphorus. The form of phosphorus in sediments was analyzed using field sampling. The environmental conditions with pH values of 4.0, 7.0 and 10.0 were simulated indoors to estimate the effects of pH on phosphorus release from sediments and the content change of various forms of phosphorus was studied. The results showed that in Wuliangsuhai Lake, Ca-P accounted for 54.3%, which was the largest portion of the TP. Phosphorus release was favored under acidic and alkaline conditions, and the alkaline condition was more favorable. The proportion of Fe/Mn-P and Fe/Al-P in the TP decreased with an increase in the pH, while the proportion of Ca-P in the TP increased with an increase in the pH. Under the alkaline condition (pH = 10), Ca-P in the sediment increased significantly, with an increase of 22.5%. However, Fe/Mn-P and Fe/Al-P decreased significantly, with drops of 37.3% and 44.9%, respectively. Under the acidic condition (pH = 4), Fe/Mn-P and Fe/Al-P in the sediment increased significantly, and the increases were 63.1% and 37.1%, respectively. However, Ca-P decreased significantly, with a drop of 39.2%. In general, low pH promoted the release of Ca-P, and a high pH promoted the release of Fe/Mn-P and Fe/Al-P. Wuliangsuhai Lake water is characterized by weak alkaline characteristics throughout the year, and biological available phosphorus accounts for 13.3%–20.9% of the TP, with Fe/Mn-P being the dominant form. This study revealed that the risk of phosphorus release from sediments to the overlying water was greater under alkaline conditions.
Nutrients may be eliminated from ice when liquid water is freezing, resulting in enhanced concentrations in the unfrozen water. The nutrients diluted from the ice may contribute to accumulated concentrations in sediment during winter and an increased risk of algae blooms during the following spring and summer. The objective of this study was to evaluate the influence of ice cover on nitrogen (N) and phosphorus (P) concentrations in the water and sediment of a shallow lake, through an examination of Ulansuhai Lake, northern China, from the period of open water to ice season in 2011-2013. The N and P concentrations were between two and five times higher, and between two and eight times higher, than in unfrozen lakes, respectively. As the ice thickness grew, contents of total N and total P showed C-shaped profiles in the ice, and were lower in the middle layer and higher in the bottom and surface layers. Most of the nutrients were released from the ice to liquid water. The results confirm that ice can cause the nutrient concentrations in water and sediment during winter to increase dramatically, thereby significantly impacting on processes in the water environment of shallow lakes.
Energy is a fundamental driver that causes material movement. It is important to discover changes in energy by studying the internal mechanism of pollutant migration between system components during the freezing process. To explore the migration mechanism of heavy metal ions (HMIs) from ice to water in a lake, we carried out a laboratory freezing experiment and simulated the distribution and migration of HMIs (Fe, Cu, Mn, Zn, Pb, Cd, and Hg) under different conditions. Then, we analyzed the use of energy by first-principle calculations. The results showed that HMIs are more stable in an aqueous environment than in an ice environment. For the same HMI, the binding energy in water is smaller than that in ice. Hence, the HMIs migrated from ice to water as the lake was freezing. The ability of different kinds of heavy metals to migrate from ice to water is related to their binding energy in ice. The concentrations of HMIs in ice are positively correlated with their binding energies. This study investigated the migration characteristics and mechanisms of HMIs in the process of lake freezing.
The present study aims to get a better understanding of the spectral characteristics and sources of dissolved organic matter (DOM) in water and ice sheet of a eutrophic shallow lake during the freezing period. The results of UV-Vis showed that DOMs in the lake had a low degree of humification. The DOMs were mainly small molecular weight DOMs and the concentration of colored DOM in the waterbody was significantly higher than that in the ice sheet. Three fluorescent components were detected through both PARAFAC and FRI approaches - C1 (fulvic acid-like compounds), C2 (microbial humus) and C3 (tyrosine) respectively. The proportions of humic-like components (C1 + C2 = 48.9%) and protein-like components (C3 = 51.1%) in the waterbody were almost similar. However, the content of protein-like components in the ice was significantly higher than that of humus-like ones, accounting for 83.53% of the total fluorescence intensity. The results of correlation analysis and PCA showed that the main controlling factors of DOM in the waterbody were dissolved inorganic nitrogen and dissolved organic carbon. The photo-degradation behavior of DOM in the waterbody was found to be inhibited due to the buffering effect of the ice sheet. On the other hand, the main controlling factors of DOM in the ice were observed to be nutrients (N, P) and salinity. Overall, the results showed that the concentration of DOM in Ulansuhai decreased spatially from the northwest to southeast areas. This may be attributed to the influence of the inlets location and the special distribution of dense growth area of reeds. The study concluded that the exogeneous pollutants mainly came from the farmland drainage, domestic sewage and industrial wastewater collected by the drainage system of Hetao Irrigation District. The endogenous pollutants mainly came from the decomposition of hydrophytes, algae and other residues through microbial metabolism.
Parks are important carriers of urban blue-green space and cultural services, which are vital to beautify the city and improve the quality of life of residents. Constructing a questionnaire system for cultural services in blue-green spaces is of great significance for evaluating and studying the supply of regional cultural services and quantifying residents' cultural needs. In this paper, we take Zhengzhou city park as the evaluation object, and based on AliCloud server ECS and WebGIS technology, combined with drone orthophoto and real-life three-dimensional model, we make the questionnaire survey system of blue-green space cultural service to collect residents' social value preference and suggestions for the park. Respondents enter the system through any device with internet access, browse park pictures and profiles, and participate in the online questionnaire survey, and the collected data on residents' value preferences can be used to assess the value of the park's cultural services by methods such as the SolVES model. The system solves the shortcomings such as heavy workload and low response rate of distributing questionnaires in the field. The system integrates a variety of digital technologies and improves the questionnaire survey method, which can effectively improve the efficiency and quality of the questionnaire survey and analyze the problems and deficiencies of the park with the opinions of the respondents, so as to provide the management with references for optimization and standardization, and to promote the enhancement of the quality of cultural services.
Deposition is the main migration process of low-density microplastic aggregation in lakes. In order to explore the deposition law of low-density microplastic aggregation in Wuliangsu Lake, a microplastic trap was designed and applied to examine the deposition process based on the similarities and differences between microplastics and naturally occurring suspended solids. The deposition processes of different sizes and shapes of low-density microplastic aggregation were quantified in Wuliangsu Lake. The results showed that the deposition fluxes of all types of low-density microplastic aggregation increased with wind speed. The deposition of flux of low-density microplastic aggregations with a similar shape of fiber and with a size ranging from 0.05-0.5, 0.5-2, and 2-5 mm had better correlation with wind speed. The correlation coefficient changed from 0.218 to 0.836. The deposition of flux of low-density microplastic aggregations with a similar shape of fiber, fragment, grain, and film and with size ranging from 0.05-0.5, 0.5-2, and 2-5 mm under different wind speeds at different experiment sites changed from 0-(1458±284), 0-(368±144), 0-(71±37), and 0-(85±65)n·(m2·d)-1, respectively. Furthermore, we found that, when shape was held constant, larger low-density microplastic aggregations were more likely to be deposited, whereas smaller low-density microplastic aggregations were more likely to be transported. When size was held constant, fragmentary low-density microplastic aggregations were more likely to be deposited than fibrous and film microplastic.
Hetao Oasis is located in a typical piedmont alluvial plain bounded by the Langshan Mountain Range in the north, desert in the west, and the Yellow River in the south. Agricultural activities within the oasis significantly impact the hydrological cycle and water quality in downstream locations. The research uses the Soil and Water Assessment Tool (SWAT) for a piedmont plain by defining the watershed boundary as coinciding with the natural mountain ridge, the border between the oasis and the desert, and the Yellow River. The model simulates water discharge with coefficient of determination and a Nash–Sutcliffe model efficiency of 0.78 and 0.62 during model calibration, and 0.75 and 0.69 during model validation, suggesting that delineation of the watershed as carried out in this research is suitable for piedmont plain topography. From the results, the mountains contribute 28.4% to the water discharge at the outlet of the watershed, and water-use efficiency of irrigated water is about 40%, which is consistent with field-based measurements. Methodologies used in delineating watershed boundaries and parameterizing SWAT provide a solid foundation for water balance studies in other regions of the world with similar topography.
Overlying water and sediment samples were collected from 11 locations in Ulansuhai Lake in June of 2012 to determine the concentration of dissolved inorganic phosphorus (DIP) in the interstitial water, overlying water and sediment and to estimate the diffusion flux of DIP at the sediment–water interface. The DIP levels in overlying water were 0.004–0.185 mg/L (average = 0.062 mg/L), while they were 0.05–0.25 mg/L (average = 0.124 mg/L) in the interstitial water in the 0–2 cm surface sediment. Moreover, the annual mean exchange flux of DIP in the sediment was between −0.092 mg/m2·d and 0.053 mg/m2·d, and this occurred via internal source action in most areas. After area weighting, it is estimated that the exchange capacity of DIP at the sediment–water interface of the Ulansuhai Lake is 1.30 t/a. These findings indicate internal loading of phosphorus in sediment of the Ulansuhai Lake; thus, the diffusion of DIP in the interstitial water has effects on the lake, with a degree of influence of 2.7% to 81.5%.
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