Anti-Inflammatory and α-Glucosidase Inhibitory Triterpenoid with Diverse Carbon Skeletons from the Fruits of Rosa roxburghii.

The fruits of Rosa roxburghii Tratt. are edible nutritional food with high medicinal value and have been traditionally used as Chinese folk medicine for a long time. In this study, 26 triterpenoids including four new pentacyclic triterpenoids, roxbuterpenes A-D (1, 4, 5, and 24), along with 22 known analogues (2, 3, 6-23, 25, and 26), were isolated from the fruits of R. roxburghii. Their chemical structures were determined on the basis of extensive spectroscopic analyses (including IR, HRESIMS and NMR spectroscopy). The absolute configuration of roxbuterpene A (1) was determined by an X-ray crystallographic analysis. This is the first report of the crystal structure of 5/6/6/6/6-fused system pentacyclic triterpenoid. Notably, roxbuterpenes A and B (1 and 4) possessed the A-ring contracted triterpenoid and nortriterpenoid skeletons with a rare 5/6/6/6/6-fused system, respectively. Compounds 1-7, 11, 13-15, 18-20, 24, and 25 exhibited moderate or potent inhibitory activities against α-glucosidase. Compounds 2, 4, 6, 11, and 14 showed strong activities against α-glucosidase with IC50 values of 8.4 ± 1.6, 7.3 ± 2.2, 13.6 ± 1.4, 0.9 ± 0.4, and 12.5 ± 2.4 µM, respectively (positive control acarbose, 10.1 ± 0.8 µM). Compounds 13, 14, and 16 moderately inhibited the release of NO (nitric oxide) with IC50 values ranging from 25.1 ± 2.0 to 51.4 ± 3.1 µM. Furthermore, the expressions of TNF-α (tumor necrosis factor-α) and IL-6 (interleukin-6) were detected by ELISA (enzyme-linked immunosorbent assay), and compounds 13, 14, and 16 exhibited moderate inhibitory effects on TNF-α and IL-6 release in a dose-dependent manner ranging from 12.5 to 50 µM.

Construction and assessment of an indicator system of stream conditions in a typical mountain landscape in Northeast China.

Stream ecosystem health assessments are crucial for the effective management of aquatic ecosystem service functions and the assessment of anthropogenic and climatic impacts on aquatic ecosystems. However, there is still a lack of comprehensive assessment methods based on complete ecosystem structures. This study improved an ecological health assessment system, which consists of 13 indicators based on ecosystem structure. The assessment system was applied to 30 streams on Changbai Mountain. The results showed that the comprehensive index of stream health (ISH) in Changbai Mountain was relatively high, and the ISH increased with the elevation gradient. The dominant factors controlling the ecosystem health level were water pH, water flow, vegetation coverage, total phosphorus (TP), and vegetation diversity index. All these results indicated that the damage caused by excessive deforestation and farmland occupation in recent years has not been fully reversed and that human disturbance from tourism may be the main reason for the low stream health at lower elevations. Our results suggest that the key to future work is to increase quantitative research on disturbance sensitivity and to develop economically viable restoration measures.

How internal nutrient loading forms in shallow lakes: Insights from benthic organic matter mineralization.

Internal nutrient loading in shallow lakes has long been known as a key driver of eutrophication, especially after external loading reductions. Earlier efforts have been made to quantity the size and potential release of internal nutrient pools in lakes. Yet, links among substrates, microbial processes, and the size and actual release of internal nutrient pools remain largely unclear. To assess the links, sediment organic matter in Lake Taihu, China, was characterized by combining optical measurements, and lake-wide sediment gross nitrogen (N) transformations were measured using the stable isotope (15N) dilution technique. Meanwhile, respirations and nutrient fluxes across the sediment-water interface (SWI) were measured by conducting intact core continuous-flow incubations. The cause-effect relationships among sediment physicochemical parameters (especially organic matter properties), gross N transformations, extractable nutrient concentrations, and nutrient fluxes across the SWI were revealed by partial least square path models. Results showed that environmental controls on the N transformation rates at different seasons varied, with sediment-derived dissolved organic matter abundance being more important than other variables in driving the rates during summer blooms. This study put a step toward revealing the significant positive effects of sediment organic matter mineralization on porewater nutrient concentrations and then on nutrient fluxes across the SWI at late season. The significant positive correlation between the gross N mineralization rates and ammonium fluxes across the SWI and the estimated considerable volume of net N mineralization in summer further suggested that algal blooms can get substantial inorganic N from sediment N mineralization during the lake N limitation period. Overall, this paper presents new insights into the substrates- and microbial process-driven internal nutrient loading of shallow lakes, which is the fundamental driving force of internal nutrient loading formation.

Screening saikosaponin d (SSd)-producing endophytic fungi from Bupleurum scorzonerifolium Willd.

Saikosaponin d (SSd) is an important bioactive compound of traditional Chinese medicinal plant Bupleurum scorzonerifolium Willd. and exhibits many effects, such as anti-tumor, anti-inflammation and immunomodulatory. Since endophytic fungi possess the natural capacity to produce the similar secondary metabolite to that of their host plants, they are promising as alternative sources of plant bioactive natural products. In this study, in order to search for SSd-producing strains, endophytes were isolated from B. scorzonerifolium and were authenticated by the ITS sequence and the translation elongation factor-1alpha gene (TEF-1α) sequence analysis. The profile of metabolites present in the crude exacts was carried out by ultra performance liquid chromatography time-of-flight mass spectrometry (UPLC/Q-TOF-MS) analysis. The results showed that two strains, CHS2 and CHS3 from B. scorzonerifolium could produce SSd by UPLC/Q-TOF-MS analysis, and the amount of SSd produced by strain CHS2 and CHS3 were about 2.17 and 2.40 µg/mL, respectively. CHS2 and CHS3 showed a close phylogenetic relationship to Fusarium oxysporum and Fusarium acuminatum, respectively. According to our concern, no endophytic fungi capable of producing SSd from B. scorzonerifolium have been found before. Our clear intention was to isolate and identify these endophytic fungi that produce important active secondary metabolites, and then study the strains that produce this compound on a large scale through fermentation or even genetic study, to provide a feasible and more convenient way for the production of SSd.

Biological Activities and Secondary Metabolites from Sophora tonkinensis and Its Endophytic Fungi.

The roots of Sophora tonkinensis Gagnep., a traditional Chinese medicine, is known as Shan Dou Gen in the Miao ethnopharmacy. A large number of previous studies have suggested the usage of S. tonkinensis in the folk treatment of lung, stomach, and throat diseases, and the roots of S. tonkinensis have been produced as Chinese patent medicines to treat related diseases. Existing phytochemical works reported more than 300 compounds from different parts and the endophytic fungi of S. tonkinensis. Some of the isolated extracts and monomer compounds from S. tonkinensis have been proved to exhibit diverse biological activities, including anti-tumor, anti-inflammatory, antibacterial, antiviral, and so on. The research progress on the phytochemistry and pharmacological activities of S. tonkinensis have been systematically summarized, which may be useful for its further research.

Two New Phenolic Glycosides with Lactone Structural Units from Leaves of Ardisia crenata Sims with Antibacterial and Anti-Inflammatory Activities.

Two new lactones, named Ardisicreolides A-B (1-2), together with four known flavonoids, Quercetin (3), Myricetrin (4), Quercitrin (5), Tamarixetin 3-O-rhamnoside (6), were isolated from the ethyl acetate portion of 70% ethanol extracts of dried leaves from Ardisia crenata Sims. These compounds were identified from Ardisia crenata Sims for the first time. The structures of 1-6 were elucidated according to 1D and 2D-NMR methods and together with the published literature. All of the isolated compounds were evaluated for in vitro anti-microbial effect against Escherichia coli, Pseudomonas aeuroginosa, Enterococcus faecalis, Proteus vulgaris, Staphylococcus aureus, and Bacillus subtilis. In addition, compounds 1-2 were assessed for anti-inflammatory activity by acting on LPS-induced RAW 264.7 macrophage cells in vitro. The results showed that only compound 2 exhibited moderate antibacterial activity on Bacillus subtilis. Moreover, compounds 1 and 2 were found to significantly inhibit the production of nitric oxide (NO) and reduce the release of tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), interleukin-4 (IL-4), and interleukin-10 (IL-10) in LPS-induced RAW 264.7 macrophage cells. The present data suggest that lactones from the leaves of A. crenata Sims might be used as a potential source of natural anti-inflammatory agents.

Antirheumatoid Arthritic Effects of Sabia parviflora Wall. Leaf Extracts via the NF-κB Pathway and Transient Receptor Potential Protein Family.

As an important traditional medicine of Buyi and Miao ethnic groups in Guizhou, Sabia parviflora Wall. provides antiviral properties against hepatitis, eliminates wind and dampness, and exhibits anti-inflammatory and pain relief properties. It has also been shown to treat rheumatoid arthritis (RA) and other diseases. However, the pharmacodynamic mechanism of S. parviflora Wall. for RA has not been reported. In this study, we identified the effective compounds of S. parviflora Wall. leaves against RA and discussed the mechanism against complete Freund's adjuvant-induced arthritis (AIA) based on inflammatory proteins and transient receptor potential (TRP) proteins. S. parviflora Wall. leaf extracts (0.64 g/kg, 0.32 g/kg, and 0.16 g/kg, once daily) were given orally for 21 days. On the 15th day of complete Freund's adjuvant-induced RA, the effects of this medicine on RA rats were investigated. S. parviflora Wall. extracts increased body weight, decreased foot swelling, and reduced thymus and spleen indices in model rats. Most of pannus in the synovial tissue of RA rats disappeared upon treatment, and the local inflammatory cells were greatly reduced when given the fraction of n-butanol (0.64 g/kg/d, 0.32 g/kg/d, and 0.16 g/kg/d) of 70% alcohol-soluble fraction of S. parviflora Wall. leaves. In addition, the release of inflammatory factors such as tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-15 (IL-15), and vascular endothelial growth factor (VEGF) in the RA rat serum was inhibited. The active compounds inhibited the expression of TNF-α, IL-1ß, IL-6, IL-10, IL-15 and nuclear factor kappa-Bp65 (NF-κBp65) inflammatory protein and TRP protein transient receptor potential melastatin-5 (TRPM-5) and transient receptor potential channel-6 (TRPC-6), to reduce the expression of VEGF in synovial tissue of RA rats and relieve redness and edema. High-performance liquid chromatography identified six flavonoids and three triterpenoid saponins as active compounds. These findings suggest S. parviflora Wall. leaves may play a role in RA treatment by inhibiting the release of inflammatory factors as well as participating in the inflammatory protein expression in the NF-κB pathway and TRP protein family.

Six decades of field observations reveal how anthropogenic pressure changes the coverage and community of submerged aquatic vegetation in a eutrophic lake.

Six decades field observation data series on submerged aquatic vegetation (SAV), water level and water quality from Lake Taihu were compiled to reveal the dynamics in coverage and species composition of SAV and their anthropogenic drivers. We found that both SAV species composition and coverage area declined significantly in Lake Taihu during the period, and the increasing nutrient levels and water level as well as decreasing water clarity were responsible for these change trends. Specifically, the decrease in species richness could be particularly well predicted by total nitrogen (TN) and the ratio of water clarity (i.e., Secchi disk depth (SDD)) to water level (WL), contributing 47.3 % and 32.3 %, respectively, while the coverage of macrophytes was most strongly related to the water level, accounting for 70.1 % of the variation. A classification tree analysis revealed a threshold of TN of 3.2 mg/L and SDD/WL of 0.14 that caused a shift to a eutrophic low-macrophyte dominated state. Our results highlight that SDD/WL must be improved for SAV recolonization, rather than merely reducing nutrient input and regulating water level. Our findings provide scientific information for lake managers to prevent plant degradation in macrophyte-dominant lakes and facilitate a shift to a macrophyte-dominant state in eutrophic lakes.

Cytotoxic 13,28 Epoxy Bridged Oleanane-Type Triterpenoid Saponins from the Roots of Ardisia crispa.

Ardisiacrispin D-F (1-3), three new 13,28 epoxy bridged oleanane-type triterpenoid saponins, together with four known analogues (4-7) were isolated from the roots of Ardisia crispa. The structures of 1-7 were elucidated based on 1D and 2D-NMR experiments and by comparing their spectroscopic data with values from the published literatures. Ardisiacrispin D-F (1-3) are first examples that the monosaccharide directly linked to aglycone C-3 of triterpenoid saponins in genus Ardisia are non-arabinopyranose. In the present paper, all compounds are evaluated for the cytotoxicity against three cancer cell lines (HeLa, HepG2 and U87 MG) in vitro. The results show that compounds 1, 4 and 6 exhibited significant cytotoxicity against Hela and U87 MG cells with IC50 values in the range of 2.2 ± 0.6 to 9.5 ± 1.8 µM. The present investigation suggests that roots of A. crispa could be a potential source of natural anti-tumor agents and their triterpenoid saponins might be responsible for cytotoxicity.

A new ent-kaurane diterpenoid from the pericarps of Datura metel.

A new ent-kaurane diterpenoid, named kaurane daturoside A (1), was isolated from the 70%-EtOH extract of dried pericarps of Datura metel L., along with six known terpenoids, 16α,17-dihydroxy-ent-kauran-19-diglycoside (2), cyclosieversioside F (3), astragaloside II (4), ginsenoside Rg1 (5), astrojanoside A (6), celerioside E (7). The isolated structures were elucidated by means of spectroscopic analyses, and the compounds 2, 3, 7 were separated from Solanaceae for the first time. Meanwhile, among isolates, compounds 2 and 5 exhibited anti-inflammatory activities against LPS-activated RAW264.7 cells (IC50<11.00 µM).

New use of old medicine: Nifedipine acts on the TRP family and inflammatory proteins in the treatment of chilblain.

As a calcium antagonist, the mechanism of nifedipine for treating chilblain has not been reported. In the present study, we established the chilblain model by using -20 ℃ 95% ethanol to freeze the right back foot of SD rats, and investigated the effects of this drug. Hematoxylin-eosin (HE) examination indicated most of pannus in the skin tissue of chilblain rats had disappeared, and the local inflammatory cells were also greatly reduced when given nifedipine at 15.0 mg/kg/d. The enzyme-linked immunosorbent assay (ELISA) revealed that nifedipine inhibited release of inflammatory factors TNF-α, IL-6, IL-1ß and VEGF in serum. The RT-PCR analysis showed that nifedipine down regulated mRNA levels of TRPC-6 and VEGF in skin tissue. Furthermore, immunohistochemical examination showed nifedipine inhibited expression of IL-1ß, IL-6, and TNF-α inflammatory protein and further inhibited expression of TRP (transient receptor potential) family proteins TRPM-7, TRPC-1, TRPC-3 and TRPC-6 and reduced expression of VEGF in skin and relieved erythema and oedema. This study demonstrated that nifedipine as an old medicine can be new use for the treatment of chilblain by acting on TRPs family and inflammatory proteins.

Emodin-Induced Oxidative Inhibition of Mitochondrial Function Assists BiP/IRE1α/CHOP Signaling-Mediated ER-Related Apoptosis.

Cassiae Semen is a widely used herbal medicine and a popular edible variety in many dietary or health beverage. Emerging evidence disclosed that improper administration of Cassiae Semen could induce obvious liver injury, which is possibly attributed to emodin, one of the bioactive anthraquinone compounds in Cassiae Semen, which caused hepatotoxicity, but the underlying mechanisms are not completely understood. Hence, the present study firstly explored the possible role of oxidative stress-mediated mitochondrial dysfunction and ER stress in emodin-cause apoptosis of L02 cells, aiming to elaborate possible toxic mechanisms involved in emodin-induced hepatotoxicity. Our results showed that emodin-induced ROS activated ER stress and the UPR via the BiP/IRE1α/CHOP signaling pathway, followed by ER Ca2+ release and cytoplasmic Ca2+ overloading. At the same time, emodin-caused redox imbalance increased mtROS while decreased MMP and mitochondrial function, resulting in the leaks of mitochondrial-related proapoptotic factors. Interestingly, blocking Ca2+ release from ER by 2-APB could inhibit emodin-induced apoptosis of L02, but the restored mitochondrial function did not reduce the apoptosis rates of emodin-treated cells. Besides, tunicamycin (TM) and doxorubicin (DOX) were used to activate ER stress and mitochondrial injury at a dosage where obvious apoptosis was not observed, respectively. We found that cotreatment with TM and DOX significantly induced apoptosis of L02 cells. Thus, all the results indicated that emodin-induced excessive ROS generation and redox imbalance promoted apoptosis, which was mainly associated with BiP/IRE1α/CHOP signaling-mediated ER stress and would be enhanced by oxidative stress-mediated mitochondrial dysfunction. Altogether, this finding has implicated that redox imbalance-mediated ER stress could be an alternative target for the treatment of Cassiae Semen or other medicine-food homologous varieties containing emodin-induced liver injury.

Response of community composition and biomass of submerged macrophytes to variation in underwater light, wind and trophic status in a large eutrophic shallow lake.

Light climate is of key importance for the growth, community composition of submerged macrophytes in lakes and, they, in turn, are affected by lake depth and the degree of eutrophication. To test the relationships between submerged macrophyte presence and the ratio of Secchi disk depth (SDD) to water depth, i.e. SDD/depth, nutrients and wind, we conducted an extensive sampling campaign in a macrophyte-dominated area of the eastern region (n = 36) in 2016 in Lake Taihu, China, and combined the data gathered with results from extensive physico-chemical monitoring data from the entire lake. We confirmed that SDD/Depth is the primary factor controlling the community composition of macrophytes and showed that plant abundance increased with increasing SDD/Depth ratio (p < 0.01), but that only SDD/Depth > 0.4 ensured growth of submerged macrophytes. Total phosphorus and total nitrogen also influenced the growth and community composition of macrophytes (p < 0.01), while Chla was an indirectly affecting factor by reducing underwater light penetration. Wave height significantly influenced plant abundance (p < 0.01), whereas it had little effect on the biomass (p > 0.05). The key to restore the macrophyte beds in the lake is to reduce the nutrient loading. A decrease of the water level may contribute as well in the shallow bays but will not bring plants back in the main part of the lake. As the tolerance of shade and nutrients varied among the species studied, this should be taken into account in the restoration of lakes by addition of plants.

Genus Alangium - A review on its traditional uses, phytochemistry and pharmacological activities.

The species from Alangium have been used as folk medicine to treat rheumatism, skin diseases, diabetes by the people of Southeast Asia. Previous phytochemical studies have shown this genus are rich sources of alkaloids, glycosides, and terpenoids, which have attracted considerable attention of many researchers due to their markedly diverse and complex architecture. The crude extracts as well as the monomeric compounds from the title genus possess anti-tumor, anti-inflammatory, antibacterial, anti-oxidant pharmacological activities. Besides, some isolates from Alangium exhibited the effects on skeletal, smooth muscle and the nervous system. As a large genus of medicinal plants, the medicinal value of Alangium has been widely reported, but there is no review that provide a systematic summary towards its chemical constituents and pharmacological activities, to our knowledge. This work aims to present a comprehensive overview on the traditional uses, phytochemistry, and pharmacological activities of medicinal plants in the genus Alangium, and to explore the evidence supporting its ethnopharmacological effectiveness.

Emerging role of dissolved organic nitrogen in supporting algal bloom persistence in Lake Taihu, China: Emphasis on internal transformations.

Dissolved organic nitrogen (DON) accounts for a significant fraction of the dissolved nitrogen (N) pool in eutrophic lakes, and substantial components of DON are available for phytoplankton. However, long-term changes in DON concentrations in eutrophic lakes have been poorly documented, and the particulate-related internal cycling of DON at the molecular level remains unclear. In this study, changes in the concentration of DON during the past 14 years of Lake Taihu, China were analyzed. Algae and sediment suspensions were incubated under summer sunlight to examine transformations of DON (e.g., photodissolution) at the bulk concentration and molecular level. Concentrations of DON in Lake Taihu ranged from 0 to 4.59 mg L-1, with a mean of 0.82 ± 0.60 mg L-1 (n = 3360). Although annual averages of the concentration of DON (n = 240) showed no significant linear variation from 2005 to 2018, the percentage of DON in total dissolved nitrogen (TDN) increased linearly (p < .05) and was maintained at >50% after 2015. Seasonally, DON concentrations were highest in spring (1.10 ± 0.56 mg L-1), followed by winter (0.87 ± 0.58 mg L-1) and summer (0.54 ± 0.37 mg L-1) concentrations, and lowest in autumn (0.44 ± 0.38 mg L-1). Outdoor incubation experiments suggest that both algae and sediment suspensions contribute to significant increases of DON concentrations but contribute to decreases of inorganic N concentrations at the end of incubations. Moreover, the production of DON by algae suspensions differed from that of sediment suspensions, with more labile components released from algae (e.g., proteins and amino acids), while more refractory components were released from sediment suspensions (e.g., lignin with low H/C and O/C). Taken together, these results emphasize the increasing percentage of DON in TDN during 2009-2018 and the different patterns of algae- and sediment-dominated internal DON transformations in Lake Taihu.

A bibliometric review of nitrogen research in eutrophic lakes and reservoirs.

The global application of nitrogen is far greater than phosphorus, and it is widely involved in the eutrophication of lakes and reservoirs. We used a bibliometric method to quantitatively and qualitatively evaluate nitrogen research in eutrophic lakes and reservoirs to reveal research developments, current research hotspots, and emerging trends in this area. A total of 2695 articles in the past 25years from the online database of the Scientific Citation Index Expended (SCI-Expanded) were analyzed. Articles in this area increased exponentially from 1991 to 2015. Although the USA was the most productive country over the past 25years, China achieved the top position in terms of yearly publications after 2010. The most active keywords related to nitrogen in the past 25years included phosphorus, nutrients, sediment, chlorophyll-a, carbon, phytoplankton, cyanobacteria, water quality, modeling, and stable isotopes, based on analysis within 5-year intervals from 1991 to 2015 as well as the entire past 25years. In addition, researchers have drawn increasing attention to denitrification, climate change, and internal loading. Future trends in this area should focus on: (1) nutrient amounts, ratios, and major nitrogen sources leading to eutrophication; (2) nitrogen transformation and the bioavailability of different nitrogen forms; (3) nitrogen budget, mass balance model, control, and management; (4) ecosystem responses to nitrogen enrichment and reduction, as well as the relationships between these responses; and (5) interactions between nitrogen and other stressors (e.g., light intensity, carbon, phosphorus, toxic contaminants, climate change, and hydrological variations) in terms of eutrophication.

Optical properties and composition changes in chromophoric dissolved organic matter along trophic gradients: Implications for monitoring and assessing lake eutrophication.

Chromophoric dissolved organic matter (CDOM) is an important optically active substance in aquatic environments and plays a key role in light attenuation and in the carbon, nitrogen and phosphorus biogeochemical cycles. Although the optical properties, abundance, sources, cycles, compositions and remote sensing estimations of CDOM have been widely reported in different aquatic environments, little is known about the optical properties and composition changes in CDOM along trophic gradients. Therefore, we collected 821 samples from 22 lakes along a trophic gradient (oligotrophic to eutrophic) in China from 2004 to 2015 and determined the CDOM spectral absorption and nutrient concentrations. The total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chla) concentrations and the Secchi disk depth (SDD) ranged from 0.02 to 24.75 mg/L, 0.002-3.471 mg/L, 0.03-882.66 µg/L, and 0.05-17.30 m, respectively. The trophic state index (TSI) ranged from 1.55 to 98.91 and covered different trophic states, from oligotrophic to hyper-eutrophic. The CDOM absorption coefficient at 254 nm (a(254)) ranged from 1.68 to 92.65 m-1. Additionally, the CDOM sources and composition parameters, including the spectral slope and relative molecular size value, exhibited a substantial variability from the oligotrophic level to other trophic levels. The natural logarithm value of the CDOM absorption, lna(254), is highly linearly correlated with the TSI (r2 = 0.92, p < .001, n = 821). Oligotrophic lakes are distinguished by a(254)<4 m-1, and mesotrophic and eutrophic lakes are classified as 4 ≤ a(254)≤10 and a(254)>10 m-1, respectively. The results suggested that the CDOM absorption coefficient a(254) might be a more sensitive single indicator of the trophic state than TN, TP, Chla and SDD. Therefore, we proposed a CDOM absorption coefficient and determined the threshold for defining the trophic state of a lake. Several advantages of measuring and estimating CDOM, including rapid experimental measurements, potential in situ optical sensor measurements and large-spatial-scale remote sensing estimations, make it superior to traditional TSI techniques for the rapid monitoring and assessment of lake trophic states.

Spatiotemporal dynamics of chlorophyll-a in a large reservoir as derived from Landsat 8 OLI data: understanding its driving and restrictive factors.

Chlorophyll-a (Chla) is an important indicator of water quality and eutrophication status. Monitoring Chla concentration (C Chla ) and understanding the interactions between C Chla and related environmental factors (hydrological and meteorological conditions, nutrients enrichment, etc.) are necessary for assessing and managing water quality and eutrophication. An acceptable Landsat 8 OLI-based empirical algorithm for C Chla has been developed and validated, with a mean absolute percentage error of 14.05% and a root mean square error of 1.10 µg L-1. A time series of remotely estimated C Chla was developed from 2013 to 2015 and examined the relationship of C Chla to inflow rate, rainfall, temperature, and sunshine duration. Spatially, C Chla values in the riverine zone were higher than in the transition and lacustrine zones. Temporally, mean C Chla value were ranked as spring > summer > autumn > winter. A significant positive correlation [Pearson correlation coefficient (r) = 0.88, p < 0.001] was observed between the inflow rate and mean C Chla in the northwest segment of the Xin'anjiang Reservoir. However, no significant relation was observed between mean C Chla and meteorological conditions. Mean (± standard deviation) value for the ratio of total nitrogen concentration to total phosphorus concentration in our in situ dataset is 75.75 ± 55.72. This result supports that phosphorus is the restrictive factor to algal growth in Xin'anjiang Reservoir. In addition, the response of nutrients to Chla has spatial variabilities. Current results show the potential of Landsat 8 OLI data for estimating Chla in slight turbid reservoir and indicate that external pollution loading is an important driving force for the Chla spatiotemporal variability.

Long-term MODIS observations of cyanobacterial dynamics in Lake Taihu: Responses to nutrient enrichment and meteorological factors.

We developed and validated an empirical model for estimating chlorophyll a concentrations (Chla) in Lake Taihu to generate a long-term Chla and algal bloom area time series from MODIS-Aqua observations for 2003 to 2013. Then, based on the long-term time series data, we quantified the responses of cyanobacterial dynamics to nutrient enrichment and climatic conditions. Chla showed substantial spatial and temporal variability. In addition, the annual mean cyanobacterial surface bloom area exhibited an increasing trend across the entire lake from 2003 to 2013, with the exception of 2006 and 2007. High air temperature and phosphorus levels in the spring can prompt cyanobacterial growth, and low wind speeds and low atmospheric pressure levels favor cyanobacterial surface bloom formation. The sensitivity of cyanobacterial dynamics to climatic conditions was found to vary by region. Our results indicate that temperature is the most important factor controlling Chla inter-annual variability followed by phosphorus and that air pressure is the most important factor controlling cyanobacterial surface bloom formation followed by wind speeds in Lake Taihu.