Influenced by high-strength agricultural activities, climate and so on, the system of groundwater resources has gained more characters of complex system in Sanjiang Plain. Take Jiansanjiang Bureau for example, the approximate entropy is adopted to analyze the complexity of groundwater depth series in 7 production teams. The results show the complexity order from big to small as follows: 4th production team of Qianjin Farm, 69th production team of Qixing Farm, 22th production team of Qianjin Farm, 1th production team of 859 Farm, 26th production team of 859 Farm, 11th production team of Qianjin Farm, 21th production team of 859 Farm. We can see that the groundwater exploitation is the key factor in groundwater dynamic variation. The results reveal the essence of complex dynamic system, providing a basis for decision-making in managing groundwater resources scientifically in Jiansanjiang Bureau and even the Sanjiang Plain.
Understanding the spatial patterns and driving mechanisms of net primary productivity (NPP) and precipitation utilization efficiency (PUE) is crucial for assessing ecosystem services. This study analyzed the variations in NPP and PUE in Heilongjiang Province from 2001 to 2020, using MOD17A3 NPP products and meteorological, topographic, and land use data. The distribution of the NPP and PUE of seven land use categories was determined in the study, namely, cropland, forest, grassland, water, barren, impervious and wetland. The multi-year spatial averages for NPP and PUE were 428.96 gC·m−2·a−1 and 0.74 gC·m−2·mm−1, respectively, with forests showing the highest values and barren lands the lowest. During the study period, 91.4% of the NPP increased at an average rate of 3.36 gC·m−2·a−1, while PUE exhibited a polarized trend. Changes in land use, especially conversions involving cropland and forest, along with climatic factors such as rising precipitation and temperature, significantly influenced NPP and PUE dynamics. These findings provide a scientific basis for ecological restoration and the assessment of ecosystem function under changing climatic conditions.
Irrigation water use efficiency is a primary evaluation index that links economic production development with the efficient use of water resources. Canal water conveyance is an important part of irrigation, and the distribution characteristics of canal systems have an important influence on irrigation water use efficiency. In this paper, 75 irrigated districts in Heilongjiang Province in 2015 were selected as the study objects. The main, branch, lateral, and sublateral canals were graded into first-, second-, third-, and fourth-order classes, respectively. The irrigation districts were divided into three classes, that is, four-order, three-order, and two-order, according to the canal orders that the irrigation districts contained. The canal system framework was described by Horton’s law. The fractal dimension of the canal system was calculated based on the bifurcation ratio and length ratio of the canals. The relationships between fractal dimensions and irrigation water use efficiency were evaluated. The results showed that the irrigation water use efficiency of the four-order and three-order irrigation districts initially increased and then decreased with increases in the fractal dimension (D). In the irrigation districts, an irrigation water use efficiency of more than 10 × 103 hm2 and less than 0.67 × 103 hm2 was proportional to the increase in the fractal dimension, whereas the opposite result was found for districts with (0.67–10) × 103 hm2. The irrigation water use efficiency of the four-order and two-order irrigation districts with less than 3.3 × 103 hm2 had the greatest potential to increase the water use efficiency. Therefore, canal system reconstruction suggestions for different irrigation districts were provided. The results have important theoretical significance and practical value for the improvement of irrigation construction and the promotion of irrigation water efficiency planning.
In order to study the multi-level time scale structure and localized characteristics of monthly precipitation in Chahayang irrigation district in time region,the wavelet analysis theory is adapted.This paper carries out wavelet transform through Mexican Hat wavelet function and analyzes the multiple time scale characteristics of precipitation,and then reveals the wavelet transform time-frequency features of precipitation at different time scales and interchanged periodic law between the rainfall period and the rainless period.The results show that from the larger scale of 80~120 months,there may be about 30 year periodic variation in the monthly precipitation of irrigation district,and furthermore,it will be still in the low period in the next five years.However,with the reduction of scale,the catastrophe points will increase and the cycle will become small,and furthermore,the precipitation will change quickly from the low period to the high period.
Excessive heavy metal content in soil can seriously hinder plant physiological metabolism and growth. This study, with soybean, examined how drip irrigation reduced heavy metal toxicity. The drip irrigation experiments with four irrigation frequencies were conducted by controlling the lower limit of the soil matric potential (D1: −10 kPa; D2: −20 kPa; D3: −30 kPa; D4: −40 kPa). Through comparison with traditional surface irrigation, the effects of drip irrigation on heavy metal distribution, soybean growth status, physiological metabolism and transcriptome under Cd, Pb and Cr(VI) composite pollution were comprehensively analyzed. The results show that (i) The Cd, Pb and Cr(IV) in soil migrated away from the plant under drip irrigation, thereby reducing the inhibition of heavy metal stress on soybean growth at the root, among which D1 had the best improvement effect on soybean growth. (ii) Drip irrigation improved the resistance of soybean to heavy metal stress, and promoted the transport and fixation of free Cd2+, Pb2+ and Cr6+ in cells, thereby reducing the damage of oxidative stress and heavy metal ions to cell structure. (iii) Drip irrigation was conducive to the energy supply and protein stability of cell physiological metabolism, which helped the improvement of soybean physiological activity. Overall, compared with surface irrigation, drip irrigation reduced the toxicity of heavy metals to soybeans by moving heavy metals out of the root zone and enhancing physiological activity. The results of this study can provide a theoretical basis for the application of drip irrigation technology in the prevention and control of heavy metal pollution, and provide a new strategy for the safe production of agriculture.
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