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.
Description:
Within-lake spatio-temporal variability of remains of cladocerans and diatoms were examined, using trap and surficial sediment sampling approaches in Lugu Lake, one of the deep mountain lakes in the subtropical region of southwest China, to understand the response to recent environmental change. Seasonality played a strong role in the distribution patterns of both cladocerans and diatoms, but their responses to seasonal change varied. The rich resources of food supported a cladoceran population peak during summer, while increased mixing and higher nutrient triggered diatom blooms in spring. The summer also witnessed increased grazing effects of primary consumers on diatoms when the water column was nutrient-enriched. In particular, Ceriodaphnia intensified grazing on small diatoms (Cyclotella ocellata), consequently affecting community patterns during summer, while increased wind activity during spring induced turbulence, remixing, transportation and depositional processes of remains of littoral Alona guttata and benthic diatoms. The distribution pattern of cladocerans in surface sediments was similar to that of diatoms. Seasonal community patterns and trophic interactions between cladocerans and diatoms in trap and surface sediments of differential depth gradients provide evidence that high-resolution sampling of multi-proxy biological remains in deep mountain lakes of southwest China can help reduce biases in paleoenvironmental reconstructions.
Description:
Evaluation of visual quality is essentially a multi-dimensional and multi-sensory experience of landscape assessment. Visual quality refers to the character, condition and quality of lakes/wetlands. It involves perceiving, preferring and valuing the visual quality by the public. Visual quality is an outcome of the perceptual, cognitive and emotional processes in response to visual stimuli of a lake environment. Visual quality therefore is dependent upon the perceptual and structural aspects of perceived scenes of wetlands. Visual assessment, an evaluating process of gaining non-material or intangible benefits by people from ecosystems, through spiritual enrichment, cognitive development, self-reflection, recreation, and aesthetic experiences, has now become one of significant research areas under cultural components of ecosystem services. Public perception in such studies is composed from both the objective and subjective elements of human–landscape interactions. However, it is still a matter of debate whether subjective–objective realities are dichotomous or supplementary to enhancing the quality of human experiences in natural settings. In fact, much research considers them as inseparable and integral parts of landscape perception, despite the tendency for disintegrating landscapes into their constituent components. There is a fundamental theoretical divergence of opinions over the question whether a landscape has an intrinsic or ‘objective’ beauty, which may be in some ways measurable or comparable, or whether beauty is a value that can be only attributed subjectively to an area or a specific landscape.
Description:
Evaluation of visual quality is essentially a multi-dimensional and multi-sensory experience of landscape assessment. Visual quality refers to the character, condition and quality of lakes/wetlands. It involves perceiving, preferring and valuing the visual quality by the public. Visual quality is an outcome of the perceptual, cognitive and emotional processes in response to visual stimuli of a lake environment. Visual quality therefore is dependent upon the perceptual and structural aspects of perceived scenes of wetlands. Visual assessment, an evaluating process of gaining non-material or intangible benefits by people from ecosystems, through spiritual enrichment, cognitive development, self-reflection, recreation, and aesthetic experiences, has now become one of significant research areas under cultural components of ecosystem services. Public perception in such studies is composed from both the objective and subjective elements of human–landscape interactions. However, it is still a matter of debate whether subjective–objective realities are dichotomous or supplementary to enhancing the quality of human experiences in natural settings. In fact, much research considers them as inseparable and integral parts of landscape perception, despite the tendency for disintegrating landscapes into their constituent components. There is a fundamental theoretical divergence of opinions over the question whether a landscape has an intrinsic or ‘objective’ beauty, which may be in some ways measurable or comparable, or whether beauty is a value that can be only attributed subjectively to an area or a specific landscape.
Cladoceran-inferred ecological and hydrological changes of two floodplain wetlands in two large river systems, the Murray (Australia) and Yangtze Rivers (China)
Description:
The landscapes of two of the world’s large river basins, the Murray and Yangtze Rivers of Australia and China, have been intensively developed for the provision of food and water resources. Long term archives of change, reveal that man-made infrastructures in the river and catchment modifications for agricultural and industrial developments have reduced the resilience of wetlands ecosystem structure and functions in recent decades. The river regulations imposed during the 20th centuries in the Murray and Yangtze Rivers have transformed hydrology and ecology of the river and associated wetlands. High resolution, subfossil cladoceran assemblages retrieved from Kings Billabong and Zhangdu Lake of the Murray and Yangtze Rivers, have strongly responded to human disturbances in the past. Ratios of littoral to planktonic (L:P) assemblages of subfossil cladocerans and the number of ephippial remains in Kings Billabong indicated the shift in hydrology and ecology of Kings Billabong, and ecological stress as a result of changes in naturally occurring dry-wet cycles following river regulation (1927 AD). Similarly, the subfossil cladoceran assemblages and their ephippia in Zhangdu Lake also reflected the impacts of the construction of the Three Gorges Dam (1954) in the Yangtze River on hydrology and ecology of the wetland.
Description:
The landscapes of two of the world’s large river basins, the Murray and Yangtze Rivers of Australia and China, have been intensively developed for the provision of food and water resources. Long term archives of change, reveal that man-made infrastructures in the river and catchment modifications for agricultural and industrial developments have reduced the resilience of wetlands ecosystem structure and functions in recent decades. The river regulations imposed during the 20th centuries in the Murray and Yangtze Rivers have transformed hydrology and ecology of the river and associated wetlands. High resolution, subfossil cladoceran assemblages retrieved from Kings Billabong and Zhangdu Lake of the Murray and Yangtze Rivers, have strongly responded to human disturbances in the past. Ratios of littoral to planktonic (L:P) assemblages of subfossil cladocerans and the number of ephippial remains in Kings Billabong indicated the shift in hydrology and ecology of Kings Billabong, and ecological stress as a result of changes in naturally occurring dry-wet cycles following river regulation (1927 AD). Similarly, the subfossil cladoceran assemblages and their ephippia in Zhangdu Lake also reflected the impacts of the construction of the Three Gorges Dam (1954) in the Yangtze River on hydrology and ecology of the wetland.
Description:
Global environmental change has affected aquatic ecosystems of the southeast Tibetan Plateau during the past 200 years, altering the composition and biomass of primary producers (e.g. algae). However, the response of primary consumers (e.g. cladocerans) to this recent environmental forcing is not well documented. Samples of cladoceran remains from sediment traps (1-year deployment), surface sediments covering a range of water depths and a short 22.5-cm sediment core were analysed in a small, remote alpine lake (Moon Lake) in Sichuan Province (SW China). Littoral forms, notably Chydorus sphaericus and Acroperus harpae, together with Daphnia pulex dominated the cladoceran community. Remains of these cladocerans were well represented in the sediment core assemblages as indicated by their relative abundance in the surface sample. There was a marked increase in the abundance of D. pulex and total cladoceran fluxes in the sediment core from ca. 1880 AD, coinciding with the changes in diatom assemblages and pigments. Analysis of the multi-proxy data (cladocerans, diatom, pigment, total organic carbon, C/N ratio, air temperature and atmospheric NO3 (-) records) suggests that both direct and indirect climatic forcing, coupled with enhanced nutrient supply (e.g. NO3 (-) deposition) effects on primary producers have changed cladoceran community dynamics in Moon Lake over the last similar to 200 years.