Identify nitrogen transport paths and sources contribution in karst valley depression area using isotopic approach.

Karst groundwater provides drinking water for a quarter of Earth's population. However, in intensive agricultural regions worldwide, karst water is commonly polluted by nitrate (NO3-), particularly in the valley depression areas with well hydrological connectivity. The valley depression aquifers are particularly vulnerable to anthropogenic pollution because their pipes and sinkholes respond quickly to rainfall events and anthropogenic inputs. Identifying nitrate sources and transport paths in the valley depression areas is key to understanding the nitrogen cycle and effectively preventing and controlling NO3- pollution. This study collected high-resolution samples at four sites including one surface stream-SS, two sinkholes-SH and reservoir-Re, during the wet season in the headwater sub-catchment. The chemical component concentrations and stable isotopes (δ15N-NO3- and δ18O-NO3-) were analyzed. The stable isotope analysis model in R language (SIAR) was used to quantitatively analyze the contribution rate of NO3- sources. The results showed that the down section site (Re) has the highest [NO3--N], followed by SH and the lowest SS. The sources calculation of SIAR demonstrated that, during the non-rainfall period, soil organic nitrogen was the primary source of the down section site, followed by fertilizer and the upper reaches sinkholes. During the rainfall period, fertilizer was the primary source of the down section site, followed by soil organic nitrogen and from upper reaches sinkholes. Rainfall events accelerated fertilizer-leaching into the groundwater. Slight denitrification may have occurred at the sampling sites but the assimilation of Re and SH could not occur. In conclusion, agricultural activities were still the primary influencing factor of [NO3--N] in the study area. Therefore, the focus of NO3- prevention and control in the valley depression areas should consider the methods and timing of fertilization and the spatial distribution of sinkholes. To reduce nitrogen flux in the valley depression area, effective management policy should consider, e.g., prolongation of water residence time by wetland, and blocking nitrogen loss paths by sinkholes.

The effect of reservoir expansion from underground karst cave to surface reservoir on water quality in southwestern China.

Due to the excessive exploitation of traditional energy sources, the attention paid to water energy has increased in recent years. As an important means to effectively utilize water energy, reservoirs play an important role in drinking water, irrigation, flood control, and drought resistance. However, utilizing reservoirs often led to water quality issues resulting from the interaction of nutrients and hydrological conditions, especially due to the special structure of karst areas. Because of the change of hydrological conditions by the effect of dam construction, the dynamic of water quality will be more obvious in karst areas with a fast exchange of water and contaminants between underground and surface streams. In the present study, the change in water quality of a karst reservoir, the Muzhu Reservoir in the Houzhai Catchment, was studied. Long-term monitored datasets (1981-2002) and water quality datasets of more recent years were used to assess the effect on the water quality of reservoir expansion from the underground reservoir to the surface reservoir in a karst area. Long-term series datasets had shown that the hydro-chemistry type had been changed from HCO3-·SO42--Ca2+·Mg2+ type to HCO3--Ca2+ type in the short term after the reservoir's expansion. The chemical components of water originating from a rock background reduced markedly after the reservoir's expansion, whereas the content of the anthropogenic contribution in the water decreased after the expansion, except in April and May. Isotopic characteristics showed that δ15N-NO3- and δ18O-NO3- values were positively correlated before and after the reservoir expansion, but the slope of the linear regression before the expansion was 0.34, while the slope of the linear regression before the expansion was close to 0.7. This indicated that although denitrification and assimilation may occur simultaneously after the reservoir's expansion, the role of denitrification on nitrate removal decreased, which resulted in nitrate accumulation in the karst reservoir. The results highlighted that nitrate accumulation in karst reservoirs should be monitored to decrease nitrate concentration in the future.

Cortistatin Improves Cardiac Function After Acute Myocardial Infarction in Rats by Suppressing Myocardial Apoptosis and Endoplasmic Reticulum Stress.

OBJECTIVES:: The endoplasmic reticulum (ER) stress-induced apoptotic pathway is associated with the development of acute myocardial infarction (AMI). Cortistatin (CST) is a novel bioactive peptide that inhibits apoptosis-related injury. Therefore, we investigated the cardioprotective effects and potential mechanisms of CST in a rat model of AMI. METHODS:: Male Wistar rats were randomly divided into sham, AMI, and AMI + CST groups. Cardiac function and the degree of infarction were evaluated by echocardiography, cardiac troponin I activity, and 2,3,5-triphenyl-2H-tetrazolium chloride staining after 7 days. The expression of CST, ER stress markers, and apoptotic markers was examined using immunohistochemistry and Western blotting. RESULTS:: Compared to the AMI group, the AMI + CST group exhibited markedly better cardiac function and a lower degree of infarction. Electron microscopy and terminal deoxynucleotidyl transferase dUTP nick end labeling confirmed that myocardial apoptosis occurred after AMI. Cortistatin treatment reduced the expression of caspase 3, cleaved caspase 3, and Bax (proapoptotic proteins) and promoted the expression of Bcl-2 (antiapoptotic protein). In addition, the reduced expression of glucose-regulated protein 94 (GRP94), glucose-regulated protein 78 (GRP78), CCAAT/enhancer-binding proteins homologous protein, and caspase 12 indicated that ER stress and the apoptotic pathway associated with ER stress were suppressed. CONCLUSIONS:: Exogenous CST has a notable cardioprotective effect after AMI in a rat model in that it improves cardiac function by suppressing ER stress and myocardial apoptosis.