Water quality assessment of benthic diatom communities for water quality in the subalpine karstic lakes of Jiuzhaigou,a world heritage site in China

Jiuzhaigou, characterized by its magnificent waterscapes and subalpine karstic features, is both a World Heritage Site and a World Biosphere Reserve in southwestern China. In recent years, this unique ecosystem has shown signs of stress due to increasing tourism activities within the reserve. The various routine methods, which monitor physical and chemical properties, do not fully reflect water quality in the subalpine and alpine lakes, while the indicators using aquatic organisms to evaluate the water quality or status of the subalpine lakes are poorly reported. Thus, in this study, benthic diatoms from multiple habitats in Jiuzhaigou were sampled and assessed for water quality monitoring. Canonical Correspondence Analysis(CCA) showed that the canonical coefficients for elevation, water temperature and total nitrogen on the first Canonical Correspondence Analysis axis were-0.84, 0.78 and-0.53, respectively, environmental variables associated with the distribution patterns of benthic diatoms. The dominance of diatom taxa indicative of nutrient enrichment indicates a clear trend toward eutrophication in the Pearl Shoal and Colorful Lake, two of the sites mostly visited by tourists. It was observed that the effect of the type of substratum on diatom community composition is not significant in subalpine lakes. The most dominant species in Jiuzhaigou lakes are the genera Achnanthes, Fragilaria, Cymbella, Cocconeis, Diatoma and Denticula. In combination with dominant and sensitive species in the benthic diatom communities, CCA and CA methods can be used to evaluate the impact of human activities on subalpine karstic lakes. The dominance of diatom taxa is indicative of nutrient enrichment and the results of CCA and CA indicate a clear trend toward eutrophication in the Pearl Shoal and Colorful Lake, two of the sites mostly visited by tourists.

Surface Ozone in Jiuzhaigou National Park, Eastern Rim of the Qinghai-Tibet Plateau, China

Located in southwestern China, Jiuzhaigou National Park is one of the most popular tourism destinations in China, famous for its unique aquatic ecosystems and beautiful forests. However, plants in the park may be at high ozone risk as a result of the intensive use of diesel tour buses in the park. In addition, Jiuzhaigou is close to a region with relatively high regional anthropogenic NO x emissions. During the growing season, also the peak season of tourism, we measured ozone concentration at two sites within the Park and these were: Jiuzhaigou Bureau (JB) and Long Lake (LL). The results indicate that ozone concentrations were not high enough to cause foliar injury during the monitoring period, although the risk of ozone to plants was higher in spring than in summer and autumn. Diurnal ozone cycles at JB and LL displayed significantly higher ozone concentrations in the daytime than in the nighttime, suggesting photochemical production of ozone during the day and ozone deposition during the night as a result of the nocturnal boundary layer. In parallel with the seasonal change of background surface ozone in the Northern Hemisphere, maximum daily 8-h average ozone concentration (MDA8) and daily ozone concentration decreased from spring to autumn at the two sites. This temporal variation in Jiuzhaigou was most likely associated with the downward mixing of ozone-rich air from the free troposphere, because all the high-ozone events (MDA8 > 70.0 ppb) were observed in spring and ozone-rich air from the free troposphere was the dominant cause. In summary, our data suggest that ozone concentrations in Jiuzhaigou were more affected by the regional-scale of background pattern in air quality and meteorological conditions than by local tourist activities.

Diurnal Variation in Relative Photosynthetic Performance of Marestail (Hippuris vulgaris Linn.) Across a Water Temperature Gradient using PAM Fluorometry in Jiuzhaigou National Nature Reserve,Sichuan Province,China

This paper reports the first photosynthetic study of marestail in Jiuzhaigou.In this work,we used PAM fluorometry to examine photosynthetic rates of submerged and emerged marestail in three lakes.Three lakes were studied across a gradient of water temperature,with low water temperature conditions in Grass Lake and Arrow Bamboo Lake,and higher water temperature in Five Colored Lake.In the field,electron transport rates (ETRmax) were measured as rapid light curves (RLCs) by in situ yield measurements.Submerged and emerged marestail showed higher photosynthetic activity in Five Colored Lake compared to the other lakes,a response consistent with the adaptation of marestail in Five Colored Lake to high water temperature.The optimal temperature for photosynthesis of submerged marestail in Jiuzhaigou was about 12 °C.Non-photochemical quenching (NPQ) of submerged and emerged marestail increased with increasing water temperature.Maximum quantum yield (Fv/Fm) of submerged marestail in Five Colored Lake showed full recovery at 1700 h due to higher NPQ.Further,the chlorophyll a for submerged marestail was the highest in Grass Lake and the lowest in Five Colored Lake.These results indicate that in different lakes the function of these aquatic plants is associated with a diversity of place-dependent environmental conditions,especially water temperature that leads to pronounced differences in the plant's ecophysiological reactions.

Influence of surface roughness on the development of moss-dominated biocrusts on mountainous rock-cut slopes in West Sichuan, China

Since natural restoration combined with artificial auxiliary measures may achieve a relatively rapid restoration effect at a lower cost, it has become an essential measure for the ecological restoration of rock slopes. Previous studies have focused heavily on the relationship between substrate nutrients and water conditions and the development of mosses on the rock surface, but quantitative characterization of substantial effect of rock surface texture(e.g., microrelief) on moss growth is absent. The undulating microrelief on the rock surface can increase the heterogeneity of the microhabitat, which may be an important factor affecting the development of mossdominated biocrusts. In this study, the roughness of rock surfaces, moss coverage and biomass, weight and major nutrient contents of soils within the biocrusts were measured in the western mountainous area of Sichuan Province, Southwest China to further examine the role of rock surface microrelief in the biocrusts. The results showed that three main factors affecting the development of the biocrusts were bryophyte emergence, soil accumulation, and lithology. The presence of moss accelerates soil formation on rock surfaces and lead to the accumulation of nutrients so that all parts of the moss-dominated biocrusts system can develop synergistically. It was found that a microrelief structure with a roughness between 1.5 and 2.5 could gather soil and bryophyte propagules effectively, which may have a strong relationship with the angle of repose. When the roughness is 1.5, the corresponding undulation angle is very close to the theoretical minimum value of the undulation angle calculated according to the relationships between the undulation angle of the protrusion, slope and angle of repose.

The role of NiFe_(2)O_(4)nanoparticle in the anaerobic digestion(AD)of waste activated sludge(WAS)

Anaerobic digestion(AD)is a promising technology for the treatment of waste activated sludge(WAS)with energy recovery.However,the low methane yield and slow methanogenesis limit its broad application.In this study,the NiFe_(2)O_(4)nanoparticles(NPs)were fabricated and applied as a conductive material to enhance the AD via promoting the direct interspecies electron transfer(DIET).The crystal structure,specific surface area,morphology and elemental composition of the as-prepared NiFe_(2)O_(4)NPs were characterized by X-ray diffraction(XRD),Brunauer-Emmett-Teller(BET),scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).The biochemical methane potential(BMP)test was performed(lasting for 35 days)to evaluate the energy recovery in AD with the addition of the NiFe_(2)O_(4)NPs.The results illustrate that NiFe_(2)O_(4)NPs could accelerate both the hydrolysis,acidogenesis and methanogenesis,i.e.,the cumulative methane production and daily methane yield increased from 96.76±1.70 mL/gVS and 8.24±1.26 mL gVS^(-1)d^(-1)in the absence of NiFe_(2)O_(4)NPs(Group A)to 123.69±3.20 mL/gVS and 9.71±0.77 mL gVS^(-1)d^(-1)in the presence of NiFe_(2)O_(4)NPs(Group B).The model simulation results showed that both the first-order kinetic model and the modified Gompertz model can well simulate the experimental results.The hydrolysis rate constant k increased from 0.04±0.01 d^(-1)in Group A to 0.06±0.01 d^(-1)in Group B.And the maximum methane production potential and activity were both improved after adding NiFe_(2)O_(4).The microbial community analysis revealed that the microorganisms associated with hydrolysis and acidogenesis were more abundant in the presence of NiFe_(2)O_(4).And the methanogenic archaea were enriched to a larger extent,resulted in the higher methanogenesis activities via dosing NiFe_(2)O_(4).