Ecological shift and resilience in China's lake systems during the last two centuries
- Authors: Zhang, Ke , Dong, Xuhui , Yang, Xiangdong , Kattel, Giri , Zhao, Yanjie , Wang, Rong
- Date: 2018
- Type: Text , Journal article , Review
- Relation: Global and Planetary Change Vol. 165, no. (2018), p. 147-159
- Full Text: false
- Reviewed:
- Description: The worldwide decline of wetland ecosystems calls for an urgent reassessment of their current status from a resilience perspective. Understanding the trajectories of changes that have produced the current situation is fundamental for assessing system resilience. Here, we examine long-term dynamics of wetland ecosystem change by reviewing paleoecological records from 11 representative lakes in China. We identify unprecedented change in alga communities in the context of last two centuries. Striking ecological shifts have occurred in all lakes, yet with spatial and temporal differences. The long-term trajectories of change in diatom species composition and structure indicate gradually eroded system resilience. These ecological shifts were shaped by socio-economic activities as China transformed from a rural agricultural to an industrialized society within the last several decades, during which multiple drivers have accumulated and acted synergistically. The balance between ecosystem and society, which appeared to exist for thousands of years, was broken by increasing population, new technology, and urbanization since the 1980s. The consequences are the emergence of new positive feedbacks with the potential to drive the coupled systems into undesirable states. By linking long-term social and ecological change at a regional scale, our study provides a novel contribution to the understanding of lake ecosystems resilience in present-day China. We argue that sustaining wetland ecosystems requires integrated approaches that incorporate a deeper understanding of social-ecological dynamics over decadal-centennial timescales to address the complex underlying mechanisms leading to the current degradation.
Assessing change in floodplain wetland condition in the Murray Darling Basin, Australia
- Authors: Gell, Peter , Reid, Michael
- Date: 2014
- Type: Text , Journal article
- Relation: Anthropocene Vol. 8, no. (2014), p. 39-45
- Full Text: false
- Reviewed:
- Description: Lowland Australian rivers and floodplains have been affected by agriculture and flow regulation for more than a century. Our capacity to understand the complex causes of ecosystem change is limited by the lack of historical records of ecosystem condition. Records of change over this critical period are available through analysis of sedimentary records. These provide benchmarks of the range of natural conditions and, by providing a long time series of conditions, trends and trajectories of change. Over recent decades, 51 sediment records from billabongs and lagoons throughout the southern Murray Darling Basin have been subject to palaeoecological analysis. The picture that emerges from this synthesis is that ecosystems have undergone substantial ecological change in response to human activities. Diatom assemblages preserved in wetland sediments attest to salinisation in 34% of sites and increased nutrient concentrations in 48%. More extensive is the impact of increased sediment flux with evidence for increased sedimentation rate, turbidity or macrophyte loss in 80% of sites. Intriguing differences exist in the timing and nature of change experienced by aquatic ecosystems in different parts of the Basin. These patterns of ecosystem response suggest underlying differences in the resilience of these ecosystems to different anthropogenic stressors, which may result from contrasting hydrologic, geomorphologic and climatic contexts. This systematic compilation of the palaeoecological evidence of change in the aquatic ecosystems of the Basin sheds light on what are the principal drivers of change across the region and provides guidance as to how these systems can be best restored. © 2014 Elsevier Ltd. All rights reserved.
Ecological response to hydrological variability and catchment development : Insights from a shallow oxbow lake in Lower Mississippi Valley, Arkansas
- Authors: Bhattacharya, Ruchi , Hausmann, Sonja , Hubeny, J. Bradford , Gell, Peter , Black, Jessica
- Date: 2016
- Type: Text , Journal article
- Relation: Science of the Total Environment Vol. 569-570, no. (2016), p. 1087-1097
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- Description: The ecological response of shallow oxbow lakes to variability in hydrology and catchment development in large river floodplain ecosystems (RFE) in Arkansas remains largely unknown. Investigating these responses will advance our understanding of ecological evolution of oxbow lakes in response to the major environmental drivers, which will establish baseline conditions required to develop effective management practices for RFE. In this pilot study, we examined the potential of using a dated surface sediment core from Adams Bayou, a floodplain lake located within the Cache-Lower White River Ramsar site in SE Arkansas. Stratigraphic records of diatoms and sediment geochemistry were used to ascertain variation in Adams Bayou's ecological condition. During 1968–2008, in response to hydrological and anthropogenic changes, Adams Bayou's diatom assemblages progressed from predominantly benthic (Gomphonema parvulum and Meridion circulare) to primarily planktonic assemblage (Aulacoseira granulata and Cyclotella meneghiniana), along with a decrease in magnetic susceptibility (k) and % silt. Statistical analyses reveled that during 1968–2000, higher hydrological connectivity and catchment alterations drove Adams Bayou's ecosystem. After 2000, lower hydrological connectivity and increase in cultivation were the major drivers. The potential impact of increasing air temperature was also noted. The shift in Adams Bayou from a connected, clear, mesotrophic state to a relatively isolated, turbid and nutrient enriched state is consistent with regime shift models and highlights its sensitivity to a combination of environmental stresses prevalent in the catchment. Although fluvial systems pose challenges in establishing clear chronologies, oxbow lake sediments can be a effective paleoecological archives. Our work provides clear evidence for the change in the ecological character of this wetland of international significance and flags the need for a wider assessment of water bodies across this site under obligations to the Ramsar Convention.
- Description: The ecological response of shallow oxbow lakes to variability in hydrology and catchment development in large river floodplain ecosystems (RFE) in Arkansas remains largely unknown. Investigating these responses will advance our understanding of ecological evolution of oxbow lakes in response to the major environmental drivers, which will establish baseline conditions required to develop effective management practices for RFE. In this pilot study, we examined the potential of using a dated surface sediment core from Adams Bayou, a floodplain lake located within the Cache-Lower White River Ramsar site in SE Arkansas. Stratigraphic records of diatoms and sediment geochemistry were used to ascertain variation in Adams Bayou's ecological condition. During 1968–2008, in response to hydrological and anthropogenic changes, Adams Bayou's diatom assemblages progressed from predominantly benthic (Gomphonema parvulum and Meridion circulare) to primarily planktonic assemblage (Aulacoseira granulata and Cyclotella meneghiniana), along with a decrease in magnetic susceptibility (k) and % silt. Statistical analyses reveled that during 1968–2000, higher hydrological connectivity and catchment alterations drove Adams Bayou's ecosystem. After 2000, lower hydrological connectivity and increase in cultivation were the major drivers. The potential impact of increasing air temperature was also noted. The shift in Adams Bayou from a connected, clear, mesotrophic state to a relatively isolated, turbid and nutrient enriched state is consistent with regime shift models and highlights its sensitivity to a combination of environmental stresses prevalent in the catchment. Although fluvial systems pose challenges in establishing clear chronologies, oxbow lake sediments can be a effective paleoecological archives. Our work provides clear evidence for the change in the ecological character of this wetland of international significance and flags the need for a wider assessment of water bodies across this site under obligations to the Ramsar Convention. © 2016 Elsevier B.V.
Assessing change in floodplain wetland condition in the Murray Darling Basin
- Authors: Gell, Peter , Reid, Michael
- Date: 2014
- Type: Text , Conference paper
- Relation: Symposium on Australia-China Wetland Network Research Partnership; Nanjing Institute of Geography and Limnology Chinese Academy of Sciences (NIGLAS) Nanjing, China; 23rd-28th December 2014 p. 27-35
- Full Text:
- Reviewed:
- Description: Lowland Australian rivers and their floodplains have been affected by the progressive introduction of agriculture, flow regulation and invasive exotic species for more than a century. In the context of this complex suite of stressors, our capacity to understand and mitigate the causes of ecosystem change is limited by the lack of historical records of the condition of ecosystems over the past 200 to 300 years. However, records of change over this critical time period can be established through analysis of sedimentary records. Such records can be used to provide benchmarks of the range of natural conditions prior to European settlement and, by providing a long time series of conditions, enhanced capacity to detect trends and trajectories of change. Over the past two decades, more than 50 sediment records from billabongs, lagoons and waterholes throughout the Murray-Darling Basin have been subject to palaeoecological analysis. The picture that emerges from these studies is of ecosystems that have undergone substantial ecological change in response to human activities; however, there are also intriguing differences in the timing and nature of change experienced by aquatic ecosystems in different parts of the Murray-Darling Basin. These patterns of ecosystem response appear to reflect underlying differences in the resilience of these ecosystems in relation to different anthropogenic stressors, which, in turn, may result in contrasting hydrologic, geomorphologic and climatic contexts. This paper presents an attempt to systematically compile and summarise the palaeoecological evidence of change in the aquatic ecosystems of the Murray-Darling Basin and, in so doing, shed light on what the principal drivers of change are in floodplain wetlands across the basin, and hence provide guidance as to how these systems can be best preserved and restored.
Are freshwater systems in lower mekong basin (Southeast asia) resilient? a synthesis of social-ecological system
- Authors: Kattel, Giri
- Date: 2020
- Type: Text , Journal article
- Relation: Environmental Research Communications Vol. 2, no. 11 (2020), p.
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- Description: Social-ecological resilience of freshwater systems in lower Mekong basin in southeast Asia is largely unknown. Over the recent past, the freshwater ecosystems in the region have gone through severe environmental stress. Climate change, sea level rise, over-extraction of water and eutrophication together have increased vulnerability to regime shifts of ecosystems in the region. Regime shifts can have long-lasting effects on social-ecological resilience. Response diversity plays a central role in linking ecological, social, and financial systems and enhances resilience. Documenting regime shifts and associated feedbacks as well as the role of response diversity in social-ecological resilience and ecosystem goods and services in the region is essential for future sustainability. In this study, primarily, I have described mechanisms behind emergence of feedback loops at a time of regime shifts and its impacts on ecological resilience. Secondly, I have developed a framework for social-ecological resilience of freshwater ecosystems for southeast Asian region. Thirdly, I have provided current contexts of social-ecological resilience of two of the most productive freshwater ecosystems in the lower Mekong basin of southeast Asia: the Tonle Sap Lake (Cambodia) and the Vietnamese Mekong Delta. Finally, in conclusion, I have outlined the key roles response diversity plays in showing the effects of environmental stress and maintaining social-ecological resilience in the region. © 2020 The Author(s). Published by IOP Publishing Ltd.