scholarly journals Identification of Regime Shifts and Their Potential Drivers in the Shallow Eutrophic Lake Yilong, Southwest China

2020 ◽  
Vol 12 (9) ◽  
pp. 3704
Author(s):  
Lei Zhao ◽  
Mingguo Wang ◽  
Zhongyao Liang ◽  
Qichao Zhou
Keyword(s):  
Regime Shift ◽  
Eutrophic Lake ◽  
Regime Shifts ◽  
Nutrient Reduction ◽  
Eutrophic Lakes ◽  
Test Analysis ◽  
Key Drivers ◽  
High Possibility ◽  
Cage Fish

Regime shifts in shallow lakes can lead to great changes in ecosystem structures and functions, making ecosystem management more complicated. Lake Yilong, located in Yunnan Province, is one of the most eutrophic lakes in China. Although there is a high possibility that this lake has undergone regime shift one or more times, the presence of regime shifts and their drivers remain unknown. Here, we employed the sequential t-test analysis of regime shifts to detect the regime shifts based on the long-term (1989–2018) dataset of the lake. We further determined their potential drivers, and explored the nutrient thresholds of regime shifts and hysteresis. The results showed that during the testing period, three regime shifts occurred in 1996 (restorative type), 2009 (catastrophic type) and 2014 (restorative type). The potential key drivers for the first two regime shifts (1996 and 2009) were both related to aquaculture. The abolition of cage fish culture may have led to the restorative regime shift in 1996, and the stocking of crabs and excessive premature releasing of fry possibly caused the catastrophic regime shift in 2009. However, the third regime shift, which occurred in 2014, was possibly related to the drought and succedent hydration. These results indicate that adjustments of aquaculture strategy and hydrological conditions are critical for the lake ecosystem’s recovery. Moreover, the total phosphorus thresholds were identified to be lower than 0.046 mg/L (restorative type) and higher than 0.105 mg/L (catastrophic type), respectively. In addition, an obvious hysteresis was observed after 2014, suggesting that nutrient reduction is important for this lake’s management in the future.

Application of a sequential regime shift detection method to the Bering Sea ecosystem

2005 ◽  
Vol 62 (3) ◽  
pp. 328-332 ◽  
Author(s):  
Sergei Rodionov ◽  
James E. Overland
Keyword(s):  
Bering Sea ◽  
Regime Shift ◽  
Poor Performance ◽  
Regime Shifts ◽  
Test Analysis ◽  
Eastern Bering Sea ◽  
Time Signals ◽  
Shift Detection ◽  
Changes Over Time ◽  
The Bering Sea

Abstract A common problem of existing methods for regime shift detection is their poor performance at the ends of time-series. Consequently, shifts in environmental and biological indices are usually detected long after their actual appearance. A recently introduced method based on sequential t-test analysis of regime shifts (STARS) treats all incoming data in real time, signals the possibility of a regime shift as soon as possible, then monitors how perception of the magnitude of the shift changes over time. Results of a STARS application to the eastern Bering Sea ecosystem show how the 1989 and 1998 regime shifts manifest themselves in biotic and abiotic indices in comparison with the 1977 shift.

scholarly journals A Remote Sensing Algorithm of Column-Integrated Algal Biomass Covering Algal Bloom Conditions in a Shallow Eutrophic Lake

2018 ◽  
Vol 7 (12) ◽  
pp. 466 ◽  
Author(s):  
Jing Li ◽  
Ronghua Ma ◽  
Kun Xue ◽  
Yuchao Zhang ◽  
Steven Loiselle
Keyword(s):  
Remote Sensing ◽  
Water Column ◽  
Algal Biomass ◽  
Water Surface ◽  
Algal Bloom ◽  
Eutrophic Lake ◽  
Retrieval Algorithm ◽  
Temporal Consistency ◽  
Eutrophic Lakes

Column integrated algal biomass provides a robust indicator for eutrophication evaluation because it considers the vertical variability of phytoplankton. However, most remote sensing-based inversion algorithms of column algal biomass assume a homogenous distribution of phytoplankton within the water column. This study proposes a new remote sensing-based algorithm to estimate column integrated algal biomass incorporating different possible vertical profiles. The field sampling was based on five surveys in Lake Chaohu, a large eutrophic shallow lake in China. Field measurements revealed a significant variation in phytoplankton profiles in the water column during algal bloom conditions. The column integrated algal biomass retrieval algorithm developed in the present study is shown to effectively describe the vertical variation of algal biomass in shallow eutrophic water. The Baseline Normalized Difference Bloom Index (BNDBI) was adopted to estimate algal biomass integrated from the water surface to 40 cm. Then the relationship between 40 cm integrated algal biomass and the whole column algal biomass at various depths was built taking into consideration the hydrological and bathymetry data of each site. The algorithm was able to accurately estimate integrated algal biomass with R2 = 0.89, RMSE = 45.94 and URMSE = 28.58%. High accuracy was observed in the temporal consistency of satellite images (with the maximum MAPE = 7.41%). Sensitivity analysis demonstrated that the estimated algal biomass integrated from the water surface to 40 cm has the greatest influence on the estimated column integrated algal biomass. This algorithm can be used to explore the long-term variation of algal biomass to improve long-term analysis and management of eutrophic lakes.

scholarly journals Boomerang hiring: Strategy for sustainable development in COVID-19 era

2021 ◽  
pp. 1-6
Author(s):  
Penumadu V. Raveendra ◽  
Yellappa M. Satish
Keyword(s):  
Sustainable Development ◽  
Organization Culture ◽  
Human Beings ◽  
Hiring Process ◽  
Positive Growth ◽  
The World ◽  
Key Drivers ◽  
Hr Managers ◽  
The Right

BACKGROUND: Many companies are forced to restructure themselves by right sizing due to unexpected fall in demand for their products and services created by the COVID-19 pandemic. COVID 19 not only affected the health of human beings but also their wealth across the world. Global economic parameters are showing a sign of positive growth with decreased number of COVID 19 cases across the world. Many companies are in a dilemma to rehire their former employees or to hire the new candidates to meet the increased demand. OBJECTIVES: The objectives of study are i) to analyze the key drivers for boomerang hiring and ii) to develop a conceptual process for boomerang hiring. METHODS: An exploratory methodology was designed to identify the key drivers of boomerang hiring by studying the various successful stories of those companies which had rehired their former employees. Various papers were reviewed to develop the process for boomerang hiring. RESULTS: Study showed that knowledge about the culture of the company, cost of hiring, morale booster for the existing employees, and customer retention, are the key drivers for boomerang hiring. This hiring process requires special skills from HR Managers, as this decision will impact long term success of the company. CONCLUSION: The process of boomerang hiring cannot be standardized as each organization culture is different and companies cannot have the same strategy for each candidate as every individual is different. Boomerang hiring will work as the right strategy during pandemic situation as former employees would have built relations with the customers. The customers will be happy to see the former employees who had served them better.

scholarly journals Ecological Degradation of the Yangtze and Nile Delta-Estuaries in Response to Dam Construction with Special Reference to Monsoonal and Arid Climate Settings

Water ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1145
Author(s):  
Zhongyuan Chen ◽  
Hao Xu ◽  
Yanna Wang
Keyword(s):  
Regime Shift ◽  
Yangtze Estuary ◽  
Anthropogenic Sources ◽  
Arid Climate ◽  
Dam Construction ◽  
Nutrient Inputs ◽  
The Yangtze Estuary ◽  
Ecological Degradation ◽  
Phytoplankton Communities

This study reviews the monsoonal Yangtze and the arid Nile deltas with the objective of understanding how the process–response between river-basin modifications and delta-estuary ecological degradation are interrelated under contrasting hydroclimate dynamics. Our analysis shows that the Yangtze River had a long-term stepwise reduction in sediment and silicate fluxes to estuary due to dam construction since the 1960s, especially after the Three Gorges Dam (TGD) closed in 2003. By contrast, the Nile had a drastic reduction of sediment, freshwater, and silicate fluxes immediately after the construction of the Aswan High Dam (AHD) in 1964. Seasonal rainfall in the mid-lower Yangtze basin (below TGD) complemented riverine materials to its estuary, but little was available to the Nile coast below the AHD in the hyper-arid climate setting. Nitrogen (N) and phosphate (P) fluxes in both river basins have increased because of the overuse of N- and P-fertilizer, land-use changes, urbanization, and industrialization. Nutrient ratios (N:P:Si) in both delta-estuaries was greatly altered, i.e., Yangtze case: 75:1:946 (1960s–1970s), 86:1:272 (1980s–1990s) and 102:1:75 (2000s–2010s); and Nile case: 6:1:32 (1960s–1970s), 8:1:9 (1980s–1990s), and 45:1:22 (2013), in the context of the optimum of Redfield ratio (N:P:Si = 16:1:16). This led to an ecological regime shift evidenced by a long-term change in phytoplankton communities in the Yangtze estuary, where silicious algae tended to lose dominance since the end of the 1990s, when more toxic dinoflagellates began to emerge. In the Nile estuary, such a regime shift was indicated by the post-dam dramatic reduction in zooplankton standing crop and fish landings until the early 2000s when biological recovery occurred due to nutrient inputs from anthropogenic sources. Although the Yangtze had higher human impacts than the Nile in terms of population, industrialization, and fertilizer application, N concentrations in the Nile estuarine waters surpassed the Yangtze in recent decades. However, eutrophication in the Yangtze estuary is much more intensive than in the Nile, leading to the likelihood of its estuarine water becoming more acidic than ever before. Therefore, ecological degradation in both delta-estuaries does not follow a linear trajectory, due not only to different climate dynamics but also to human forcings. The comparative insights of this study should be incorporated into future integrated coastal management of these two important systems.

scholarly journals A long-term multi-proxy record of varved sediments highlights climate-induced mixing-regime shift in a large hard-water lake ~5000 years ago

2014 ◽  
Vol 73 (2) ◽  
Author(s):  
Walter Finsinger ◽  
Thierry Fonville ◽  
Emiliya Kirilova ◽  
Andrea Lami ◽  
Piero Guilizzoni ◽  
...  
Keyword(s):  
Regime Shift ◽  
Hard Water ◽  
Proxy Record ◽  
Varved Sediments ◽  
Water Lake ◽  
Mixing Regime

scholarly journals Spatially varying constraints of human-caused fire occurrence in British Columbia, Canada

2017 ◽  
Vol 26 (3) ◽  
pp. 219 ◽  
Author(s):  
Philip E. Camp ◽  
Meg A. Krawchuk
Keyword(s):  
British Columbia ◽  
Spatial Patterns ◽  
Fire Management ◽  
Fire Occurrence ◽  
Explanatory Variables ◽  
Human Footprint ◽  
Key Factor ◽  
Key Drivers ◽  
Spatially Varying

Human-caused wildfires are controlled by human and natural influences, and determining their key drivers is critical for understanding spatial patterns of wildfire and implementing effective fire management. We examined an array of explanatory variables that account for spatial controls of human-caused fire occurrence from 1990 to 2013 among six ecosystem zones that vary in human footprint and environmental characteristics in British Columbia, Canada. We found that long-term patterns of human-caused fire in ecosystem zones with a larger human footprint were strongly controlled by biophysical variables explaining conditions conducive to burning, whereas fire occurrence in remote ecosystem zones was controlled by various metrics of human activity. A metric representing the wildland–urban interface was a key factor explaining human-caused fire occurrence regardless of ecosystem zone. Our results contribute to the growing body of research on the varying constraints of spatial patterns of fire occurrence by explicitly examining human-caused fire and the heterogeneity of constraints based on human development.

scholarly journals Genetic Diversity of Small Eukaryotes in Lakes Differing by Their Trophic Status

2005 ◽  
Vol 71 (10) ◽  
pp. 5935-5942 ◽  
Author(s):  
Marie Lefranc ◽  
Aurélie Thénot ◽  
Cécile Lepère ◽  
Didier Debroas
Keyword(s):  
Trophic Status ◽  
Eutrophic Lake ◽  
Rrna Genes ◽  
Eutrophic Lakes ◽  
Massif Central ◽  
Operational Taxonomic Units ◽  
Single Clone ◽  
18S Rrna Genes ◽  
Lake Pavin ◽  
Environmental Sequences

ABSTRACT Small eukaryotes, cells with a diameter of less than 5 μm, are fundamental components of lacustrine planktonic systems. In this study, small-eukaryote diversity was determined by sequencing cloned 18S rRNA genes in three libraries from lakes of differing trophic status in the Massif Central, France: the oligotrophic Lake Godivelle, the oligomesotrophic Lake Pavin, and the eutrophic Lake Aydat. This analysis shows that the least diversified library was in the eutrophic lake (12 operational taxonomic units [OTUs]) and the most diversified was in the oligomesotrophic lake (26 OTUs). Certain groups were present in at least two ecosystems, while the others were specific to one lake on the sampling date. Cryptophyta, Chrysophyceae, and the strictly heterotrophic eukaryotes, Ciliophora and fungi, were identified in the three libraries. Among the small eukaryotes found only in two lakes, Choanoflagellida and environmental sequences (LKM11) were not detected in the eutrophic system whereas Cercozoa were confined to the oligomesotrophic and eutrophic lakes. Three OTUs, linked to the Perkinsozoa, were detected only in the Aydat library, where they represented 60% of the clones of the library. Chlorophyta and Haptophyta lineages were represented by a single clone and were present only in Godivelle and Pavin, respectively. Of the 127 clones studied, classical pigmented organisms (autotrophs and mixotrophs) represented only a low proportion regardless of the library's origin. This study shows that the small-eukaryote community composition may differ as a function of trophic status; certain lineages could be detected only in a single ecosystem.

scholarly journals Earth observation for monitoring and mapping of cyanobacteria blooms. Case studies on five Italian lakes

2016 ◽  
Vol 76 (s1) ◽  
Author(s):  
Mariano Bresciani ◽  
Claudia Giardino ◽  
Rosaria Lauceri ◽  
Erica Matta ◽  
Ilaria Cazzaniga ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Algal Blooms ◽  
Remote Sensing Data ◽  
Late Summer ◽  
Eutrophic Lake ◽  
Cyanobacterial Blooms ◽  
Landsat 8 ◽  
Negative Effects ◽  
Eutrophic Lakes ◽  
Chl A

Cyanobacterial blooms occur in many parts of the world as a result of entirely natural causes or human activity. Due to their negative effects on water resources, efforts are made to monitor cyanobacteria dynamics. This study discusses the contribution of remote sensing methods for mapping cyanobacterial blooms in lakes in northern Italy. Semi-empirical approaches were used to flag scum and cyanobacteria and spectral inversion of bio-optical models was adopted to retrieve chlorophyll-a (Chl-a) concentrations. Landsat-8 OLI data provided us both the spatial distribution of Chl-a concentrations in a small eutrophic lake and the patchy distribution of scum in Lake Como. ENVISAT MERIS time series collected from 2003 to 2011 enabled the identification of dates when cyanobacterial blooms affected water quality in three small meso-eutrophic lakes in the same region. On average, algal blooms occurred in the three lakes for about 5 days a year, typically in late summer and early autumn. A suite of hyperspectral sensors on air- and space-borne platforms was used to map Chl-a concentrations in the productive waters of the Mantua lakes, finding values in the range of 20 to 100 mgm-3. The present findings were obtained by applying state of the art of methods applied to remote sensing data. Further research will focus on improving the accuracy of cyanobacteria mapping and adapting the algorithms to the new-generation of satellite sensors.

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