Water conservation pattern of Fangcheng River Basin in Beibu Gulf and its response to precipitation.

Assessing the spatiotemporal patterns of watershed water conservation under the influence of the South Asian monsoon climate and its response to precipitation is essential for revealing the evolving patterns of water conservation under different temporal scales. Following the principles of water balance and using the Soil and Water Assessment Tool (SWAT) model, we investigated the spatiotemporal patterns of water conservation and its response to precipitation in the Fangcheng River Basin of Beibu Gulf. The results showed that water conservation in Fangcheng River Basin calculated by SWAT model were 1637.4 mm·a-1, accounting for 50.7% of the mean annual precipitation. The variation of water conservation in different sub-basins was obviously different. Sub-basins with high forest coverage and steep slopes exhibited higher water conservation, while sub-basins with other land use types (such as cropland and grassland), gentle slopes, and intense human activities showed lower water conservation. At the monthly scale, both water conservation and its variation showed similar response characteristics to precipitation in the basin. The response of water conservation variation to sub-precipitation events could be classified into two types. For the short-term rainfall events (duration≤2 days), water conservation variation showed a linear relationship. For the medium to long-term rainfall events (2 days

[C and N Transport Flux and Associated Changes of Water Quality Parameters from a Multiscale Subtropical Watershed in the Poyang Lake Area].

In this study, a connected waterflow watershed system in the Poyang Lake area was selected as the study site, which ranged from the primary tributary to the lake area (Xiangxi River Jiazhu River Ganjiang River Poyang Lake). The aims of the study were to monitor different forms of C and N and evaluate the transport flux of C and N, and then, the transport mechanisms of C and N and the variation characteristics of water quality parameters in Poyang Lake were discussed, with the intent of providing a scientific basis for the comprehensive management of watershed health within the Poyang Lake Basin ecosystem. The main results were as follows. ① The concentrations of C and N in the Poyang Lake watershed exhibited significant seasonal changes, wherein the TIC, TOC, and TC concentrations in the Poyang Lake Basin were higher in the wet season than those in the dry season, and the NO3--N and DTN concentrations were higher in the dry season than those in the wet season. The main reason for the increase of TC in the wet season was the increase of TIC. Most of the TN in the wet season was transported by non-dissolved forms of N, while the TN in the dry period mostly was transported by DTN, and the DTN was mostly in the form of NO3--N. ② The C and N transport fluxes in the Poyang Lake watershed also showed significant seasonal variation. The C transport flux of Xiangxi River was lower during the wet season than that during the dry season, and the C transport flux of Jiazhu River and Ganjiang River was higher during the wet season than that during the dry season. The various forms of N transport flux in Xiangxi River, Jiazhu River, and Ganjiang River watershed were higher in the wet season than those in the dry season. There was a very significant positive correlation between the flux and runoff at the 99% confidence level. ③ The COND, TDS, and pH in the Poyang Lake watershed were lower during the wet season than those during the dry season, while the ORP in the wet season was higher than that in the dry season.

[Ecohydrologic separation of the mixing process between precipitation and soil water: A review.] / é™æ°´ä¸ŽåœŸå£¤æ°´æ··åˆè¿‡ç¨‹çš„ç”Ÿæ€æ°´æ–‡åˆ†ç¦»çŽ°è±¡åŠå ¶ç ”ç©¶è¿›å±•.

Within the framework of traditional translatory flow, infiltrating precipitation and water at any soil depth is firstly well mixed and eventually enters the stream. Based on the dual stable isotope approach (δD and δ18O), recent studies showed that ecohydrologic separation occurs during the mixing process between precipitation and soil water. Namely, soil water has two pools: soil bound water which includes unavailable and available water used by plants, and soil mobile water entering the stream. The partial mixing of both water pools is defined as hydrologic connectivity. In this review, the concept and meaning of ecohydrologic separation are explained systematically. We described the mixing process between precipitation and soil water, and water isotopes (δD and δ18O) of soil bound water and mobile water in detail. We summarized the advantages and disadvantages of the direct and substitute methods to measure δD and δ18O in soil water, bound water, and mobile water. We reviewed the researches on hydrologic separation and connectivity of soil bound water and mobile water in runoff plot and watershed, including the qualitative research based on the direct and substitute methods, and the quantitative research using the models and control experiments. At last, we proposed that further studies should strengthen the research on the qualitative and quantitative methods of ecohydrological separation, and their influences on traditional ecohydrology models.

[Effect of Montmorillonite on Fractions and Availability of Phosphorus in Soils Applied with Organic Fertilizer].

An incubation experiment was carried out to study the effect of montmorillonite on pH, the fractions and availability of phosphorus in a sandy yellow soil (SY) and a mineral flavicant soil (MF) applied with biogas residues of swine manure (BSR). The rates of montmorillonite applied were 0%, 5%, 7.5% and 10%, respectively. The results indicated that soil pH was not affected by BSR, but was significantly increased by montmorillonite. In both soils, application of BSR caused an increase in the content and proportion of Al-P during the incubation, and an increase in the content but a slight decrease in the proportion of Fe-P in later period of incubation. The concentration of O-P was not markedly changed, but its proportion was decreased by applying BSR in both soils. The changes of Ca-P varied with soils. BSR had no significant influence on Ca-P content, but decreased the proportion of Ca-P in SY, meanwhile, it increased both Ca-P content and proportion in MF. Addition of montmorillonite in soils applied with BSR decreased the contents and proportions of Al-P and O-P, and the proportion of Fe-P did not change the contents of Fe-P, but increased the content and proportion of Ca-P in SY. In MF, montmorillonite could decrease the contents and proportions of Fe-P and O-P, and the proportion of Al-P did not affect the content of Al-P, but increased the contents and proportions of Ca-P greatly. The contents of available phosphorus (A-P) were enhanced by 17.9%-38.0% and 17.1%-33.7% in SY and MF respectively, and the phosphorus activation coefficient (PVC) was significantly improved in both soils by applying BSR. The contents of A-P were reduced by 8.8%-35.5% and 1.1%-11.6% in SY and MF respectively. Correlation analysis showed that montmorillonite reduced the availability of phosphorus through increasing pH and contents of Ca-P, decreasing the content of Al-P in SY, and through increasing pH and decreasing content of Fe-P in MF. The availability of phosphorus in SY was influenced more obviously than that in MF by montmorillonite.