Mean Chlorophyll Concentration Research Articles

Long-term responses of phytoplankton biomass to the ocean surface variables in the central parts of the Arabian Sea and the Bay of Bengal

The northern Indian Ocean has been warming steadily for over a half-century, especially the north-western Indian Ocean. It is widely reported that the increasing sea surface temperature in the global oceans decreases phytoplankton biomass and productivity. The impacts of long-term variations in the sea surface properties on the phytoplankton biomass (chlorophyll a) are least studied in the northern Indian Ocean. In this study, we have retrieved satellite, model, and ARGO float data sets to investigate the long-term variations in the distributions and trends of major oceanic variables for a better understanding of the respective changes that occurred in chlorophyll a concentration in the central regions of the Arabian Sea (AS) and the Bay of Bengal (BB). We have selected variables such as sea surface temperature (SST), sea surface salinity (SSS), photosynthetically available radiation (PAR), euphotic depth (ZEU), mixed layer depth (MLD), wind speed, mean sea level anomaly (MSLA), surface currents, etc., to relate with chlorophyll a. We found significant increasing trends in SST and positive-MSLA in both basins, and the chlorophyll a was decreased in the AS but contrastingly increased in the BB. Further data analysis revealed the possible reasons, such as seasonal changes in mean sea level anomaly and meridional currents, for the increasing trend of chlorophyll a in the central Bay of Bengal. The northward flow of the meridional currents during the southwest monsoon (SWM), transports the nutrient-rich water from the coastal upwelling zone of the southwest coast of India to the southern and central BB, and enhances chlorophyll a. Contrastingly, the southward flow of low-saline and nutrient-depleted Bay of Bengal water reduces the chlorophyll a. In addition, the large area of cold-core eddies found during the NEM enhanced the chlorophyll a in the central BB. Though contrasting trends between both basins in chlorophyll a distribution were found, the mean concentration of chlorophyll a in the northern Indian Ocean decreases. The present study signifies the importance of monsoon currents and eddies in regulating the chlorophyll a biomass and primary productivity in the AS and BB.

Evaluating the Performance of Alternate Wetting and Drying Irrigation Technology: An On-farm Rice Case Study in An Giang Province, the Mekong Delta of Vietnam

Alternate wetting and drying irrigation (AWD) is a promising technique that has been tried across Southeast Asia to reduce water consumption and methane emissions in irrigated rice cultivation. The study conducted in the upper Vietnamese Mekong Delta compared the effectiveness of plant growth, yield components, and yield under three different water application regimes: the treatments of community AWD (AWD_C), household individually (AWD_H), and continuous flooding (CF) with the expectation to explore the ability to use water effectively in rice cultivation. The results showed no significant difference in water use between the three treatments. However, there was a considerable difference in coefficient of variation value (CV); the CV value of the water column in the AWD_C (1.32%) was a significant difference from that of AWD_H (0.87%) and CF (0.89%). The mean chlorophyll content, the yield, and the weight of 1,000 grains of the AWD_H treatment were significantly higher than that of the other two treatments. In another aspect, the water productivity of the AWD_H treatment was the highest (0.66 kg/m3), a statistically significant difference compared to the AWD_C and CF (0.37; 0.33 kg/m3). In conclusion, the AWD_H shows efficiency in leaf chlorophyll content, 1,000-grain weight, yield, and water productivity. The AWD_C is inferior to the AWD_H due to the large variation of field elevation. It is noted that field elevation is critical to the technique’s success in being applied on a large scale.

Long-Range Transport of a Dust Event and Impact on Marine Chlorophyll-a Concentration in April 2023

Dust aerosols serve as a crucial nutrient source to the oceans and profoundly influence marine ecosystems. This study used satellite and ground observations to explore a strong dust event on 9–13 April 2023, emanating from the Gobi Desert, shared by Mongolia and China’s Inner Mongolia region. We investigated the deposition of dust particles and their effects on marine phytoplankton communities. Our findings revealed that the dust event was intense, enduring, and expansive, illustrated by hourly PM10 concentrations peaking at 5055 µg/m3 near the source and consistently exceeding 1000 µg/m3, even at considerable distances. The dust traveled along two different trajectories and was deposited in the same area of the Northwest Pacific. Total dust deposition in the study area (37°N–42°N, 145°E–165°E) was 79.88 mg/m2 from 13 to 18 April, much higher than the 2019–2022 average deposition of 33.03 mg/m2 for the same period. With dust deposition, the observed mean chlorophyll-a concentrations in the area increased to 2.78 mg/m3 on 14 April, an extraordinary 692% increase above the long-term average. These results highlight the profound impact of dust on the productivity of marine phytoplankton communities by inputting more nutrients into the ocean through different pathways.

Evaluation of metrics and thresholds for use in national-scale river harmful algal bloom assessments

The spatiotemporal distribution of harmful algal blooms (HABs) in rivers remains poorly understood, and there is an urgent need to develop a consistent set of metrics to better document HAB occurrences and forecast future events. Using data from seven sites in the Illinois River Basin, we computed metrics focused on HAB conditions related to excess algal growth and hypoxia. Daily mean chlorophyll and dissolved oxygen (DO) concentrations, gross primary productivity (GPP), and net ecosystem productivity (NEP) rates, focused on water quality status, identifying the timing of the transition from a clear-water to an algal dominated state. Early warning indicators (EWIs), the first-order autoregressive process (Ar1) and standard deviation (SD) of chlorophyll concentrations, focused on future events, forecasting blooms. Metrics were compared to either literature-derived or statistical-based thresholds and were normalized by total number of daily samples for an exceedance rate. Exceedances of a daily mean chlorophyll concentration averaged 50 % across all sites using a 10 µg L−1 threshold but increasing the threshold to 50 μg L−1 reduced the average exceedance rate to 5 %. The average exceedance rate for GPP (∼8 g O2 m2d−1 threshold) was 15 %, similar to the daily amplitude DO concentration (∼3 mg L−1 threshold), but the average for NEP (0 g O2 m2 d−1 threshold) was higher, at 28 %. The number of days with at least 1 continuous DO concentration below the threshold of 5, 3, or 2 mg L−1, had basin wide exceedance rates of 9 %, 3 %, and 2 %, respectively. Thresholds for EWIs, Ar1 and SD, were exceeded at 5 of the 7 sites with high chlorophyll concentrations and GPP rates. The correlation between proxies for algal biomass (chlorophyll concentration) and productivity (GPP) was strongest for sites in the middle region of the basin, with R2 values between 0.54 and 0.74. Although, cyanotoxin concentrations are the most commonly used metrics by states to define an inland water HAB, there is a paucity of publicly available data. The wider availability of chlorophyll and oxygen data combined with the results from this study suggest that biomass and productivity state and event-based metrics may be a promising way to assess and predict the vulnerability of rivers to some of the deleterious effects of HABs at broad spatial scales.

Environmental predictors for the restoration of a critically endangered coral, Acropora palmata, along the Florida reef tract.

The population decline and lack of natural recovery of multiple coral species along the Florida reef tract have instigated the expanding application of coral restoration and conservation efforts. Few studies, however, have determined the optimal locations for the survival of outplanted coral colonies from restoration nurseries. This study predicts the optimal locations for Acropora palmata colonies along the Florida reef tract using a boosted-regression-tree model to examine the relationships between the occurrence of wild A. palmata and ten environmental variables. Our model results predicted A. palmata was most likely to occur in shallow reef habitats with (i) generally low mean chlorophyll-a concentrations (< 1 mg m-3), (ii) moderate fetch (3 kJ m-2), (iii) salinities between 20 and 37.5 ppt, (iv) temperatures between 20 and 32°C, (vi) low mean concentrations of total nitrogen (0.16 ppm), and (iv) irradiance between 26.5 and 53.5 mol m-2 s-1. The most suitable habitats for A. palmata were disproportionately allocated to reefs in Biscayne Bay, the Upper Keys, the western-lower Florida Keys, the Marquesas, and the Dry Tortugas. The middle Florida Keys had unfavorable environmental conditions for A. palmata habitat. Results from this study inform where A. palmata, outplanted as part of restoration and conservation efforts, would have suitable environmental conditions to persist over time. This study also provides decision-making support for management focused on the conservation and restoration of the endangered species A. palmata along the Florida reef tract.

Algal Biological Features Viewed in Satellite Observations: A Case Study of the Bohai Sea

Algal cell abundance weakly depends on inherent optical properties and chlorophyll-a concentration in the Bohai Sea, so it is very hard to derive algal cell abundance (ACA) from ocean color data using a simple bio-optical model. To obtain ACA for biological communication at large scale, a neural network model has been developed and then applied for investigating the changing monthly trend of ACA, intracellular chlorophyll-a concentration, and cell size in the Bohai Sea using MODIS data from 2002 to 2015. The results showed that the neural network model could provide an accurate log-transformed value of algal cell abundance (LACA) from ocean color images whose retrieval uncertainty did not exceed 9%. Furthermore, when the model was applied to map the monthly mean LACA and then further convert it to cell size in the Bohai Sea, the results showed that the satellite-derived monthly mean cell size varied from 4.81 to 15.29 μm. The decreasing monthly mean algal cell abundance and increasing monthly mean chlorophyll-a concentration imply that the monthly mean intracellular chlorophyll-a concentration from 2002 to 2015 increased, which indicates that the waters in the Bohai Sea became more eutrophic over those 14 years. Moreover, due to seasonal variations in vertical mixing or other physical forcing factors, the ACA and cell size exhibited significant seasonal variations. Although further tests are required to validate the model’s robustness, these preliminary results indicate that the neural network model is an encouraging approach to exploiting more novel biological parameters such as the LACA from ocean color satellites for oceanic communication.

The relationship between the infestation of Whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) and the chlorophyll content in different Eggplant varieties

The sweet potato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), is one of the most important pests in vegetables. Although the host plant Solanum melongena, is considered the most preferred, the whiteflies have preferences for particular varieties of eggplant. In this study, we evaluated three eggplant varieties in choice feeding tests. We found that the varieties of Zomorrod and Barcelona were the most preferred with the highest numbers of whitefly nymphs, which were 312 and 300 per leaf, respectively, on the last week of May. In comparison, the nymph average was 171.8 per leaf on the last week of May on the kareema. Chlorophyll concentration has been negatively affected by the infestation of B. tabaci. The investigation of the chlorophyll content ratio between the uninfested and infested eggplant leaves showed a decrease in chlorophyll content at 13.95 and 6.60 11 mg/L of the Zumorrod variety for the uninfested and infested leaves, respectively, with 52.67% chlorophyll reduction. At the same time, the mean chlorophyll content for uninfested and infested eggplant leaves of the Barcelona variety was 12.74 and 4.95 mg/L, respectively, with 61.14% chlorophyll reduction. At the same time, the Kareema variety was recorded at 17.49 and 4.95 mg/L for the uninfested and infested leaves, respectively, with 72.39% chlorophyll reduction. Furthermore, feeding by B. tabaci reduced leaf photosynthesis in eggplant by restricting gas exchange through stomata and reducing chlorophyll's content and photosynthetic capacity. Keywords: population density; piercing pest; Bemisia tabaci; Solanum melongena; host preference; plant pigments

Effect of Inorganic Fertilizers (NPK) with Organic Sources (Biomix and Humic Acid) on the Bulb Quality and Storage Quality of Onions (Allium cepa L.)

An investigation entitled "Effect of different levels of fertilizers with organic sources on growth, yield and quality of onion (Allium cepa L.)" was undertaken at the experimental farm, Department of Horticulture, VNMKV, Parbhani, Maharashtra, in the late Kharif season of 2020–21 and 2021–22. The present investigation was laid out in a factorial randomized block design (FRBD) with three different levels of recommended dose of fertilizers (RDF): F1: RDF 80% (80:40:40 NPK kg/ha), F2: RDF 100% (100:50:50 NPK kg/ha) and F3: RDF 120% (120:60:60 NPK kg/ha) with six levels of organic sources, namely, S0 : Control, S1 : Biomix 10 kg/ha, S2 : Biomix 12.5 kg/ha, S3 : Biomix 15 kg/ha, S4 : Humic acid 05 kg/ha and S5 : Humic acid 10 kg/ha comprising eighteen treatments and replicated thrice. The aim of this work is to study the effect of different levels of RDF and organic sources on the bulb quality and storage quality of onions (Allium cepa L.). The onion bulb produced under 120% RDF has recorded the higher mean values of the quality parameters, viz., chlorophyll content (63.44 SPAD value), ascorbic acid content (11.71 mg/100 g), total soluble solids (12.23%), reducing sugar (2.33%), non-reducing sugar (5.27%) and total sugar (7.60%). Among the organic sources, humic acid at 10 kg/ha had the highest mean chlorophyll content (59.66 SPAD value), total soluble solids (11.91%), reducing sugar (2.29%), non-reducing sugar (5.03%), and total sugar (7.32%), with the exception of ascorbic acid (10.89 mg/100 g), which was highest at biomix 15 kg/ha. In five months of storage studies, the mean minimum physiological loss in weight (18.47%) at ambient storage was observed under 80:40:40 NPK kg/ha, and the maximum total soluble solids (%) were recorded at 120:60:60 NPK kg/ha. During a five-month storage study, the mean minimum PLW (18.55%) at ambient storage was recorded under biomix at 15 kg/ha. The mean maximum total soluble solids were found after humic acid treatment (10 kg/ha) in the fifth month of storage.

The Importance of Spatial and Temporal Scales in Understanding Chlorophyll Variability in the Southern Ocean

Polar regions are undergoing dramatic, rapid, and possibly irreversible changes. Substantial shifts in patterns of sea ice extent and thickness have cascading effects on polar ecosystems (including phytoplankton), with implications for carbon cycling and global climate. Phytoplankton growth is closely tied to environmental variables such as light and nutrient availability, which are sensitive to climate-induced changes in upper ocean circulation, stratification, and sea ice cover. Recently, Prend et al. (2022, https://doi.org/10.1029/2022GB007329) investigated temporal and spatial scales of chlorophyll (a proxy for phytoplankton biomass) variability in the Southern Ocean. They demonstrated that the dominant temporal scale of variability is sub-seasonal (∼0.5–3 months). The implications of this are two-fold: first, climate oscillations (such as the Southern Annular Mode) are not major drivers of year-to-year variation in chlorophyll; second, intermittent bursts of chlorophyll, generated by small-scale processes such as storms and eddies, dictate the annual mean chlorophyll concentration. Additionally, spatial autocorrelation for chlorophyll concentration varied by time scale: seasonal chlorophyll variability was correlated over much larger areas than were variations in year-to-year chlorophyll concentration. Based on Prend et al. (2022, https://doi.org/10.1029/2022GB007329), future work should be cognizant of (a) the spatio-temporal scales over which chlorophyll is averaged and (b) the need to focus on small-scale, sub-seasonal events (rather than large-scale climate oscillations) to mechanistically explain chlorophyll variability.

Primary productivity measurements in the Ross Sea, Antarctica: a regional synthesis

Abstract. Polar systems are undersampled due to the difficulty of sampling remote and challenging environments; however, these systems are critical components of global biogeochemical cycles. Measurements on primary productivity in specific areas can quantify the input of organic matter to food webs and so are of critical ecological importance as well. However, long-term measurements using the same methodology are available only for a few polar systems. Primary productivity measurements using 14C-uptake incubations from the Ross Sea, Antarctica, are synthesized, along with chlorophyll concentrations at the same depths and locations. A total of 19 independent cruises were completed and 449 stations occupied where measurements of primary productivity (each with seven depths) were completed. The incubations used the same basic simulated in situ methodology for all. Integrated water column productivity for all stations averaged 1.10 ± 1.20 g C m−2 d−1, and the maximum was 13.1 g C m−2 d−1. Annual productivity calculated from the means throughout the growing season equalled 146 g C m−2 yr−1. The mean chlorophyll concentration in the euphotic zone (the 1 % irradiance level) was 2.85 ± 2.68 mg m−3 (maximum observed concentration was 19.1 mg m−3). Maximum photosynthetic rates above the 30 % isolume (normalized to chlorophyll) averaged 0.98 ± 0.71 mg C (mg chl)−1 h−1, similar to the maximum rate found in photosynthesis–irradiance measurements. Productivity measurements are consistent with the temporal patterns of biomass found previously, with biomass and productivity peaking in late December; mixed layers were at a minimum at this time as well. Estimates of plankton composition also suggest that pre-January productivity was largely driven by the haptophyte Phaeocystis antarctica and summer productivity by diatoms. The data set (https://doi.org/10.26008/1912/bco-dmo.863815.2, Smith, 2021) will be useful for a comparison to other Antarctic regions and provide a basis for refined bio-optical models of regional primary productivity and biogeochemical models for the Southern Ocean.

Environmental predictors of phytoplankton chlorophyll-a in Great Lakes coastal wetlands

Coastal wetlands of the Laurentian Great Lakes are diverse and productive ecosystems that provide many ecosystem services, but are threatened by anthropogenic factors, including nutrient input, land-use change, invasive species, and climate change. In this study, we examined one component of wetland ecosystem structure – phytoplankton biomass – using the proxy metric of water column chlorophyll-a measured in 514 coastal wetlands across all five Great Lakes as part of the Great Lakes Coastal Wetland Monitoring Program. Mean chlorophyll-a concentrations increased from north-to-south from Lake Superior to Lake Erie, but concentrations varied among sites within lakes. To predict chlorophyll-a concentrations, we developed two random forest models for each lake – one using variables that may directly relate to phytoplankton biomass (“proximate” variables; e.g., dissolved nutrients, temperature, pH) and another using variables with potentially indirect effects on phytoplankton growth (“distal” variables; e.g., land use, fetch). Proximate and distal variable models explained 16–43% and 19–48% of variation in chlorophyll-a, respectively, with models developed for lakes Erie and Michigan having the highest amount of explanatory power and models developed for lakes Ontario, Superior, and Huron having the lowest. Land-use variables were important distal predictors of chlorophyll-a concentrations across all lakes. We found multiple proximate predictors of chlorophyll-a, but there was little consistency among lakes, suggesting that, while chlorophyll-a may be broadly influenced by distal factors such as land use, individual lakes and wetlands have unique characteristics that affect chlorophyll-a concentrations. Our results highlight the importance of responsible land-use planning and watershed-level management for protecting coastal wetlands.

Automated soybean mapping based on canopy water content and chlorophyll content using Sentinel-2 images

Accurate and timely spatiotemporal distribution information of soybean is vital for sustainable agriculture development. However, it is challenging to establish a phenology-based automated crops mapping algorithm at large spatial domains by simply applying vegetation index temporal profile. This study developed a Phenology-based automatic Soybean mapping algorithm through combined Canopy water and Chlorophyll variations (PSCC). Three phenology-based indices were designed: the ratio of change magnitudes of vegetation index to water stress index during the late growth stage (T1), the mean concentration of chlorophyll during the whole growth period (T2), and the accumulated variations of chlorophyll before and after heading date (T3). Soybean was distinguished by lower T1 and T3 and higher T1 due to higher senescence water loss and chlorophyll content. The PSCC method was validated in Northeast China from 2017 to 2021 and in four states (Missouri, Illinois, Indiana, and Ohio) of the United States (US) in 2020 using Sentinel-2 datasets. Soybean planting areas obtained by PSCC were consistent with the corresponding agricultural statistical area (R2 > 0.83). The soybean maps were evaluated using 5702 reference data, and the overall accuracy and kappa coefficient were 91.99% and 0.8338, respectively. The overall accuracy for soybean mapping was improved by 16.07% compared with using only canopy water variation. The result showed that our method could be applied to large spatial domains and multi-years without retraining. The soybean planting area in Northeast China expanded substantially 25,867 km2 (by 89.10%) during the period 2015–2020 and decreased slightly 7,535 km2 (by 13.73%) from 2020 to 2021. Soybean expansion occurred mainly in ever-planted regions. Northeast China contributed about 60% to the national soybean revitalization goal in 2020. This study provided information on the soybean spatiotemporal changes in Northeast China, which was significant for agricultural policymakers to formulate soybean production plans to achieve national soybean revitalization.

Evaluation of shade tolerance of one annual and five perennial Medicago species under different artificial shade levels

ABSTRACT The objective of this study was to evaluate the shade tolerance of one annual and five perennial Medicago genotypes under different artificial shade levels and determine the shade tolerant candidates for an intercropping system. The results showed that shade significantly affected branch number and plant dry weight, but not plant height and leaf area. The mean branch number and dry weight plant−1 (g) across the tested genotypes were 42.5 and 2.2 under non-shade condition, decreased to 39.5 and 2.0 at 25% shade level, and were further reduced to 17.2 and 0.4 at 75% shade level, respectively. The mean chlorophyll content (mg g−1) and maximum quantum yield of Photosystem II (Fv/Fm) across the tested genotypes at 75% shade level (38.8; 0.6) were significantly lower than other shade levels (46.6–47.3; 0.69–0.70). Antioxidant enzyme activity and malondialdehyde production in Medicago leaves increased concomitantly with increased shade levels compared to non-shade control. The evaluation showed that annual M. polymorpha ‘Jinhuacai’ (range of mean: 0.97–5.97 g) significantly out-yielded those perennials (range of mean: 0.26–2.57 g) by a wide margin at all shade levels. This study would provide baseline information on shade tolerance of Medicago species for the selection of intercropped candidates in an intercropping system.

Seagrass in a Changing Estuary, the Indian River Lagoon, Florida, United States

Seagrass is a major structural habitat in the Indian River Lagoon. Maps documented locations and areal extents of beds periodically since the 1940s, and surveys of fixed transects yielded changes in percent cover and depths at the end of the canopy since 1994. Areal extent increased by ∼7,000 ha from 1994 to 2009, mean percent cover within beds decreased from ∼40 to 20%, and mean percent cover standardized to maximum transect length remained near 20%. Thus, conditions supported a consistent biomass because cover decreased as areal extent increased. Between 2011 and 2019, ∼19,000 ha or ∼58% of seagrasses were lost, with offshore ends of canopies moving shoreward and shallower, and standardized mean percent cover decreased to ∼4%. These changes coincided with blooms of phytoplankton, and ≤ 27% of incident subsurface irradiance at 0.9 m was stressful. Decreases in mean percent cover per month of stress became larger when initial mean cover per transect was &amp;lt; 20%, which suggested that the ratio of aboveground to belowground tissues in the expanded and sparser beds led to respiratory demand that was not met by photosynthesis. Despite intermittent improvements in light penetration, widespread recovery of seagrasses has not occurred potentially due to detrimental feedbacks. For example, loss of seagrass exposed sediments to waves, and the resulting disturbance may have hampered recruitment of new shoots. The same decreases also made 58–88% of the carbon, nitrogen, and phosphorus in seagrass tissue available to other primary producers. These nutrients did not enhance growth of epiphytes, whose biomass decreased by ∼42%, but they apparently fueled blooms of phytoplankton, with mean chlorophyll-a concentrations increasing by &amp;gt; 900%. Such intense blooms increased shading and loss of seagrasses. Fortunately, data showed that patches of seagrasses at depths of 0.5–0.9 m persisted for 22–24 years, which suggested that this depth zone could hold the key to recovery. Nevertheless, optimistic estimates predict recovery could take 12–17 years. Such a long-term, widespread loss of a key structural habitat may generate multiple adverse effects in the system, and mitigating such effects may entail planting seagrasses to accelerate recovery.

Effect of Gamma Irradiation on Chlorophyll Content in the Cowpea (Vigna unguiculata (L.) Walp)

The experiment was conducted to study the mutagenic effect of gamma rays on chlorophyll content at three different physiological stages in the cowpea: pre-flowering, flowering and post-flowering. Five sets of cowpea seeds were subjected to individual doses of gamma rays: 400 Gy, 450 Gy, 500 Gy, 600 Gy and 0 Gy. The seeds were sown to raise the M1 generation. The M1 generation seeds were collected and sown in the next season to raise the M2 generation. Leaf chlorophyll content was measured for M2 generation plants. Mean chlorophyll content for pre-flowering stage ranged between 38.9 ± 8.17 (control) and 64.2 ± 6.16 (400 Gy). Flowering stage mean chlorophyll content ranged from 48.3 ± 14.4 (600 Gy) to 99.4 ± 6.22 (450 Gy). Post-harvest chlorophyll mean content ranged between 13.1 ±0.98 (600 Gy) and 38.0 ±1.90 (400 Gy). There were significant differences in treatment effects for pre-flowering (P = 0.021), flowering (P = 0.005) and harvest (P = 0.000). At pre-flowering treatment, treatment 400 Gy scored a significant increase of 64 percent (P = 0.02) above the control. The optimum dose for useful induced mutation for increases in chlorophyll concentration in the cowpea was 400 Gy.

Linking Chlorophyll Concentration and Wind Patterns Using Satellite Data in the Central and Northern California Current System

The California Current System (CCS) is a highly productive region because of wind-driven upwelling, which supplies nutrients to the euphotic zone. Numerous studies of the relationship between phytoplankton productivity and wind patterns suggest that an intermediate wind speed yields the most productivity on the shelf. However, few studies have considered the productivity-wind relationship across the entire CCS, including the Northern CCS (north of 42˚N), an unusually productive region with highly variable upwelling- and downwelling-favorable winds. Using satellite chlorophyll concentration from GlobColour together with QuikSCAT and ASCAT winds, we examine the relationship between shelf (shallower than the 150 m isobath) chlorophyll concentration and wind patterns in the Central and Northern CCS. Results from this analysis suggest that while there is a dome-shaped relationship between mean chlorophyll concentration and wind stress for the whole system, the Central CCS and Northern CCS have significantly different relationships, which is evident in the separation between their mean chlorophyll concentration-wind stress curves. The Northern CCS also supports high chlorophyll concentration during downwelling-favorable winds. To understand this difference in chlorophyll concentration-wind stress relationships, results from particle tracking experiments using a ROMS model of the Northern CCS are used to map shelf retention times with respect to wind patterns. These results suggest that on the 1˚-latitude scale, the effect of wind intermittency on retention is minimal in the Northern CCS; however, this result does not disqualify the influence of more complex controls on retention like wind intermittency on smaller spatial scales. Lastly, we present a revised hypothesis to describe the relationship between chlorophyll concentration and wind stress in the CCS that includes the influence of non-upwelling-derived nutrients in the Northern CCS.

The seasonal dissipation of Ulva prolifera and its effects on environmental factors: based on remote sensing images and field monitoring data

Ulva prolifera blooms have occurred every summer in the South Yellow Sea since 2008. U. prolifera blooms appeared in the area near the Jiangsu shoal and then were driven to the Shandong Peninsula by the prevailing summer winds. The blooms covered a maximum area of more than 50000 km2 and had an aggregate estimated biomass of 3.64 × 105 tons. Large number of U. prolifera dissipation in the natural degradation and this cause a serious impact on the marine environment. We used MODIS, HJ-1A/B and GF-1 remote sensing image data to conduct large-scale monitoring of U. prolifera. Combined with sea surface monitoring station data from Haiyang city, Shandong province, we analyzed the impact of U. prolifera death on the coastal sea environment of Haiyang city from 2012 to 2016 using multiple regression analysis. It showed that chlorophyll-a concentration was related to sea surface temperature (SST), salinity, dissolved inorganic nitrogen (DIN) and phosphate (R2 = 0.50, P < 0.001). Among these, DIN and phosphate were important factors affecting chlorophyll-a concentration. There was a significant positive correlation between chlorophyll-a concentration and DIN, but a significant negative correlation between chlorophyll-a concentration and phosphate. The nutrients released by the decomposition of U. prolifera enhanced the growth of planktonic microalgae, and increased the mean chlorophyll-a concentration from 1.398 μmol/L to 2.819 μmol/L during May to August in the study area. This increased the Level of eutrophication in the coastal area and contributed to blooms of secondary algae such as red tides.

Comparison of water level and eutrophication indicators during the wet and dry period in a eutrophic urban lake

Eutrophication modifies lakes' ecological balances and threatens its viability. To date, eutrophication management strategies have been related to nutrient reduction in the lakes' water column. However, nutrient reduction strategies are complicated by the variations of the lake's water level, nutrient concentration, and eutrophication symptom, which are primarily known to be influenced by the local rainfall patterns. Therefore, this study aimed to compare the variability of water level, total phosphorus, and total chlorophyll-a concentrations in Slim River Lake during wet and dry seasons. In this study, water sampling and depth measurements were carried out from six sampling points for 1 year. Water samples were used to quantify total phosphorus and total chlorophyll-a. Our results showed that mean water levels in the studied lake ranged from 1.36 m to 5.46 m in the wet season and from 1.31 m to 5.41 m in the dry season, which implicated no significant difference (p > .05) between seasons in most sampling points. Total phosphorus present at concentrations exceeding 10 mg/L and showed small variations between wet and dry seasons. Mean total phosphorus concentrations varied from 10.55 mg/L to 26.66 mg/L in the wet season and 10.77 mg/L to 21.76 mg/L in the dry season and showed no significant difference between seasons. In addition, mean chlorophyll-a concentrations ranged from 14.35 mg/m3 to 180.13 mg/m3 and from 14.15 mg/m3 to 39.27 mg/m3 in wet and dry seasons, respectively. Chlorophyll-a concentrations showed significant differences (p < .05) between seasons in the deepest sampling points in the lake. The observed seasonal variations in total chlorophyll-a suggest the importance of algae monitoring during the wet season even when no apparent surge of phosphorus concentration is detected.

Variation in Chemical Constituents of Siyez Wheat (Triticum monococcum L.) in Response to Some Abiotic Stress Factors

Main aim of this study was to determine the effects of different salt contents (75 mM, 150 mM and 225 mM NaCl), heavy metal (0.2 mg/L FeCl3, NiCl2, ZnCl2), lime (2 mg/L CaCO3), drought (50%) and pollution (0.2 mg/L dust of factories) on photosynthetic pigments, malondialdehyde (MDA), hydrogen peroxide (H2O2) levels, the ascorbate peroxidase (APX), catalase (CAT), guaiacol peroxidase (GPOX) and superoxide dismutase (SOD) in Siyez wheat (Triticum monococcum L.). All experiments were carried out under laboratory conditions with 16 hour-day and 8 hour-night photoperiod in an incubator at 23 ± 1°C. Results showed that mean chlorophyll-a concentration was highest in the siyez seedlings treated with the pollution, while both mean chlorophyll-b and total chlorophyll concentrations were highest with 75 mM salt application. Mean total carotenoid was, however, highest with the drought treatment and mean relative water content was highest with NiCl2 application. Mean MDA and H2O2 contents were found to be highest in the siyez seedlings treated with 225 mM salt, whereas they were lowest with NiCl2 treatment. Mean proline content was highest with the NiCl2 treatment compared to the lowest concentration in the control siyez seedlings (82 µmol/g). Mean APX, CAT and GPOX activities were noted to be highest in the siyez seedlings treated with NiCl2. In general, the siyez seedlings showed high tolerance to the pollution, NiCl2 and drought with having highest photosynthetic pigments, proline, protein content and enzymes activities. Among all treatments, 225 mM NaCl and CaCO3 negatively influenced chemical compounds of the siyez seedling. When all data are taken into consideration, it can be said that higher photosynthetic pigments, proline contents, antioxidant enzymes activities and lower MDA and H2O2 levels play an important role in the resistance of siyez seedlings against abiotic stress conditions.

Effects of macroconsumers on benthic communities across a gradient of vegetation loss in tropical karst streams

Though many studies have demonstrated top-down control by macroconsumers on benthic communities and ecosystem processes in tropical streams, few have simultaneously addressed such effects across a gradient of riparian vegetation loss. Here, we investigated if potential top-down effects induced by macroconsumers interact with native vegetation changes of tropical karst streams in Brazil. We experimentally excluded macroconsumers (e.g., fish and shrimp) from benthic habitats of seven streams with a range of forest cover from 20% to 100% and examined the effects on benthic invertebrate and periphyton communities. Across sites, the absence of macroconsumers had no effects on mean chlorophyll-a concentrations, total dry mass or abundance of benthic invertebrates. However, the periphyton community significantly differed between control and treatment replicates. Overall, experimental exclusion of macroconsumers resulted in weak or negligible effect on benthic communities, which contrasts a significant proportion of related literature conducted elsewhere. Such top-down effects have been poorly studied in tropical karstic streams to date.