Role of the Branched PEG‑<i>b</i>‑PLLA Block Chain in Stereocomplex Crystallization and Crystallization Kinetics for PDLA/MPEG‑<i>b</i>‑PLLA‑<i>g</i>‑glucose Blends with Different Architectures

The isothermal crystallization behavior and corresponding morphology evolution of poly(d-lactic acid) (PDLA) blends with PLLA6.7k or MPEG-b-PLLA6.7k-g-glucose with different architectures and different PLLA-grafted copolymer contents were investigated. The formation of stereocomplexes (SCs) in between the chain branched structure of MPEG-b-PLLA6.7k-g-glucose and PDLA chains acting as the physical crosslinking points slows down the motion of PDLA chains, but the SCs could act as a heterogeneous nucleating agent for the late formation of homocrystals (HCs) in the blend system, accelerating the crystallization kinetics of HCs through enhancing the nucleation density. For PDLA/MPEG-b-PLLA6.7k-g-glucose blends, the mobility of SCs in the blend system and the nucleation density of SCs in the blends exhibit oppositional behavior during the isothermal crystallization at a Tc of 130 °C. The evolution of the crystal growth and structure during the isothermal crystallization process by rheometry has revealed the interesting role of the branched chains of MPEG-b-PLLA6.7k-g-glucose in the mechanism of the crystallization in PDLA blends

Image2_The buffering of a riverine carbonate system under the input of acid mine drainage: Example from a small karst watershed, southwest China.JPEG

In a karstic area affected by acid mine drainage (AMD), hydrochemical conditions, such as temperature, salinity, alkalinity, DIC, dissolved oxygen, and nutrients, may affect the buffering capacity of carbonate systems in freshwater systems. The resulting pH fluctuation is larger than that of a marine system. Therefore, this study focuses on the buffering of a riverine carbonate system under the input of AMD and discusses the variations in a series of buffering factors, including the Revelle factor, γDIC, γAlk βDIC, βAlk, ωDIC, and ωAlk. The results revealed that the Revelle factor could reflect the buffering process effectively; in addition, the maximum value of the Revelle factor appeared at pH = 8.5. The data points for pH greater than this value indicated that the Huatan River had the ability to absorb atmospheric CO2 in spring. Conversely, the data for pH less than this value reflected the buffering of H+ during CO2 degassing in summer and autumn. In winter, the data were around the maximum value, indicating the weakest buffering capacity. As a result, the dynamics of the carbonate system caused the most sensitive response to pH. In addition, the maximum Revelle factor value did not always indicate the carbonate system had reached equilibrium; the presence of strong CO2 degassing was still a possibility. Under acidic conditions, as CO2(aq) increased, the absolute values of γDIC, βDIC, ωDIC, and γAlk increased correspondingly, indicating the enhanced buffering capacity of H+ during CO2 degassing. Under the four Representative Concentration Pathways scenarios (RCPs) included in the IPCC’s fifth assessment report, the degassing rate of the Huatan River would decrease by 5%, 15%, 26%, or 48%, depending on the scenario. Even though the Huatan River revealed CO2 degassing characteristics in winter and spring under current conditions, it will eventually become a sink for atmospheric CO2 as atmospheric CO2 concentration increases. In this light, the carbon sink effect in karst areas will become increasingly important.</p

Table1_The buffering of a riverine carbonate system under the input of acid mine drainage: Example from a small karst watershed, southwest China.DOCX

In a karstic area affected by acid mine drainage (AMD), hydrochemical conditions, such as temperature, salinity, alkalinity, DIC, dissolved oxygen, and nutrients, may affect the buffering capacity of carbonate systems in freshwater systems. The resulting pH fluctuation is larger than that of a marine system. Therefore, this study focuses on the buffering of a riverine carbonate system under the input of AMD and discusses the variations in a series of buffering factors, including the Revelle factor, γDIC, γAlk βDIC, βAlk, ωDIC, and ωAlk. The results revealed that the Revelle factor could reflect the buffering process effectively; in addition, the maximum value of the Revelle factor appeared at pH = 8.5. The data points for pH greater than this value indicated that the Huatan River had the ability to absorb atmospheric CO2 in spring. Conversely, the data for pH less than this value reflected the buffering of H+ during CO2 degassing in summer and autumn. In winter, the data were around the maximum value, indicating the weakest buffering capacity. As a result, the dynamics of the carbonate system caused the most sensitive response to pH. In addition, the maximum Revelle factor value did not always indicate the carbonate system had reached equilibrium; the presence of strong CO2 degassing was still a possibility. Under acidic conditions, as CO2(aq) increased, the absolute values of γDIC, βDIC, ωDIC, and γAlk increased correspondingly, indicating the enhanced buffering capacity of H+ during CO2 degassing. Under the four Representative Concentration Pathways scenarios (RCPs) included in the IPCC’s fifth assessment report, the degassing rate of the Huatan River would decrease by 5%, 15%, 26%, or 48%, depending on the scenario. Even though the Huatan River revealed CO2 degassing characteristics in winter and spring under current conditions, it will eventually become a sink for atmospheric CO2 as atmospheric CO2 concentration increases. In this light, the carbon sink effect in karst areas will become increasingly important.</p

Impoundment-induced nitrogen–phosphorus imbalance in cascade reservoirs alleviated by input of anthropogenic nutrients

<p>The ratio of nitrogen to phosphorus (N:P) is an important variable that has a close relationship with the ecological problems of nuisance algal blooms and eutrophication in aquatic environments in terms of nutrient limitation. Reservoirs generally have much higher retention efficiency for P than for N. This inherent dissimilarity in the N and P biogeochemical cycles likely results in N–P stoichiometric imbalance in downstream rivers and reservoirs, consequently causing an increase in the N:P ratio and aggravating P limitation. Here we determined the total N (TN) and total P (TP) concentrations in the cascade reservoirs of the Wujiang River and Lancangjiang River basins. The results show that TN:TP ratios in these 2 basins exhibited a common inverted V-shaped (∧) pattern downstream. We found that P is not only retained by reservoirs more efficiently than N but is also replenished at faster rates than N given anthropogenic impacts; consequently, the N–P imbalance caused by these impoundments is alleviated within a short distance downstream because of inputs of anthropogenic nutrients. Our research suggests that construction of cascade reservoirs does not necessarily lead to strict P deficiency and anomalously high N:P ratios downstream.</p