Using palaeolimnological data and historical records to assess long-term dynamics of ecosystem services in typical Yangtze shallow lakes (China)

Interactive effects of climate-atmospheric cycling on aquatic communities and ecosystem shifts in mountain lakes of southeastern Tibetan Plateau

Recent climate warming and atmospheric reactive nitrogen (Nr) deposition are affecting a broad spectrum of physical, ecological and human systems that may be irreversible on a century time scale and have the potential to cause regime shifts in ecological systems. These changes may alter the limnological conditions with important but still unclear effects on lake ecosystems. We present changes in cladoceran with comparisons to diatom assemblages over the past ~200 years from high-resolution, well-dated sediment cores retrieved from six high mountain lakes in the southeastern (SE) margin of the Tibetan Plateau. Our findings suggest that warming and the exponential increase of atmospheric Nr deposition are the major drivers of ecological regime changes. Shifts in cladoceran and diatom communities in high alpine lakes began over a century ago and intensified since 1950 CE, indicating a regional-scale response to anthropogenic climate warming. Zooplankton in the forest lakes showed asynchronous trajectories, with increased Nr deposition as a significant explanatory factor. Forest lakes with higher dissolved organic carbon (DOC) concentrations partially buffered the impacts of Nr deposition with little structural change, while lakes with low DOC display symptoms of resilience loss related to Nr deposition. Biological community compositional turnover in subalpine lakes has shown marked shifts, equivalent to those of low-elevation lakes strongly affected by direct human impacts. This suggests that local effects override climatic forcing and that lake basin features modified by anthropogenic activity act as basin-specific filters of common forcing. Our results indicate that snow and glacial meltwaters along with nutrient enrichment related to climate warming and atmospheric Nr deposition, represent major threats for lake ecosystems, even in remote areas. We reveal that climate and atmospheric contaminants will further impact ecological conditions and alter aquatic food webs in higher altitude biomes if climate and anthropogenic forcing continue.

Determining critical thresholds of ecological restoration based on ecosystem service index: A case study in the Pingjiang catchment in southern China

Considering that the degradation of ecological systems is an urgent environmental challenge, promoting multiple ecosystem services (ES) through ecological restoration has recently become more critical. However, the complicated interactions among multiple ES are not fully considered in ecological restoration planning and management, which prevents simultaneous improvements to environmental and human welfare. In this study, the spatio-temporal variations of multiple ES and their interactions were investigated in the Pingjiang catchment, which used to suffer severe soil erosion and has been the target of the ecological restoration projects. The results showed that five individual ES were heterogeneously distributed, and each individual ES and their overall benefits have increased with the implementation of ecological restoration (except for water yield). However, significantly negative correlations existed in over half of ten ES pairs, and the trade-offs among the five individual ES also increased. Through redundancy analysis, the forest proportion (FP) was identified as the major socio-ecological factor that determines multiple ES patterns; therefore, determining the appropriate FP for restoration areas is important for regulating the supply of ES. The constraint effects of FP on each ES and their overall benefits and trade-offs were examined, and inconsistent thresholds were detected for some relationships. Thus, a comprehensive index (ES index) that incorporates the overall trade-offs was proposed to reflect the complicated interactions among multiple ES and the preferences of different stakeholder groups. The constraint effect of FP on the ES index was explored, and the threshold values detected in the hump-shaped curve of the constraint lines provided references for determining the appropriate FP. This study established an integrated land use management framework by proposing a comprehensive ES index and determining its critical thresholds through the constraint line method. The results provide insights for the better planning and targeting of ecological restoration and land use management projects worldwide.

Regime shifts in a shallow lake over 12 years: consequences for taxonomic and functional diversity, and ecosystem multifunctionality

Under increasing nutrient loading, shallow lakes may shift from a state of clear water dominated by submerged macrophytes to a turbid state dominated by phytoplankton or a shaded state dominated by floating macrophytes. How such regime shifts mediate the relationship between taxonomic and functional diversity and lake multifunctionality is poorly understood. We employed a detailed database describing a shallow lake over a 12-year period during which the lake has displayed all the three states (clear, turbid, and shaded) to investigate how species richness, functional diversity of fish and zooplankton, ecosystem multifunctionality, and five individual ecosystem functions (nitrogen and phosphorus concentrations, standing fish biomass, algae production, and light availability) differ among states. We also evaluated how the relationship between biodiversity (species richness and functional diversity) and multifunctionality is affected by regime shifts. We showed that species richness and the functional diversity of fish and zooplankton were highest during the clear state. The clear state also maintained the highest values of multifunctionality as well as standing fish biomass production, algae biomass, and light availability, whereas the turbid and shaded states had higher nutrient concentrations. Functional diversity was the best predictor of multifunctionality. The relationship between functional diversity and multifunctionality was strongly positive during the clear state, but such relationship became flatter after the shift to the turbid or shaded state. Our findings illustrate that focusing on functional traits may provide a more mechanistic understanding of how regime shifts affect biodiversity and the consequences for ecosystem functioning. Regime shifts towards a turbid or shaded state negatively affect the taxonomic and functional diversity of fish and zooplankton, which in turn impairs the multifunctionality of shallow lakes.

Evaluation of Ecosystem Services in the Dongting Lake Wetland

The Aeronautical Reconnaissance Coverage Geographic Information System (ArcGIS) 10.2 and Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model are used to comprehensively evaluate ecosystem services in the Dongting Lake Wetland, focusing on water yield, soil conservation, carbon storage, and snail control and schistosomiasis prevention. The spatial and temporal variations of these services, as well as their variations between different land use types in a period of 10 years from 2005 to 2015, are investigated, and the value of such services is then estimated and analyzed. The results of this study show various temporal and spatial trends in the ecosystem services, such as (1) the overall increase of all these services during the study period (although significant in some services, such as schistosomiasis patient reduction, by 86.8%; and, very slight in some others such as soil conservation, only by 0.02%); (2) different orders of the services values that are based on different land use types; and, (3) the temporal changes in the proportion of the values of different ecosystem services with respect to the total services value. Besides, it is concluded that the evaluation of ecosystem services of a certain wetland is heavily dependent on the characteristics of the area where the wetland is located, and the assessment indicators and methods should be selected based on such characteristics through the analysis of the results and a comparison with the findings of literature.

A palaeolimnological perspective to understand regime-shift dynamics in two Yangtze-basin lakes

Natural and human disturbances have caused widespread regime shifts in shallow lakes of the lower Yangtze basin (LYB, China) resulting in a severe decline of ecosystem services. Improved understanding of the relationship between environmental forcing and ecosystem response, and the mechanisms behind regime shifts has significant implications for management. However, the patterns of these regime shifts and the underlying internal mechanisms are less known. In this study, two typical lakes (Chaohu and Zhangdu) from the LYB were selected to determine the trajectories of ecological regime shifts, both of which transitioned from vegetation- to plankton-dominated states several decades ago. Ecological trajectories since the 1900s in both lakes were reconstructed using palaeolimnological proxies, mainly diatom assemblages. Although results show that regime shifts occurred in both lakes in the 1970s and the 1950s, respectively, their inherent mechanisms were different. In Lake Zhangdu, altered hydrological conditions pushed the ecosystem across an ecological threshold, providing an example of a driver-mediated regime shift. In Lake Chaohu, ongoing nutrient loading influenced ecosystem processes and drove the lake to an alternative stable state, potentially presenting an example of a critical transition after a loss of resilience. This research indicates that palaeolimnological perspectives can provide insights into regime shift changes, as well as important information regarding which restoration methods should be tailored to individual lakes.

Integrating long-term dynamics of ecosystem services into restoration and management of large shallow lakes

Adequately understanding the dynamics of ecosystem services (ES), a practical framework for analyzing social-ecological systems (SES), is crucial for sustainable environmental management and decision-making. However, the interactions among multiple ES at multi-decadal scales are less explored, and many challenges remain to integrate long-term dynamics of ES into ecological restoration and management. Here, we combined socioeconomic data with synthesized paleolimnological records to assess the dynamics of 12 critical ES and regional SES in the Taihu Lake Basin (China) over the past century. Our results indicated that multiple provisioning services showed upwards trends while major regulating services in terms of water, sediment, soil and air regulation had sustained downwards trends since the 1950s, and reached dangerous status after the 1980s. This dynamic trade-off was mainly attributed to the effects of continued socioeconomic transitions including agriculture intensification, industrialization and urbanization. Anthropogenic land use change, pollution input, and climate changes are considered as major drivers of long-term environmental degradation. Regulating services exhibited various dynamical properties including different linear and nonlinear trends, and abrupt changes, which underlined the comprehensive consideration of legacy effects, ecological baseline, thresholds, and resilience into lake management. Environmental Kuznets curve analyses suggested that the regional SES started significant disorder from the 1970s driven by the transition between ES and non-ES (socioeconomic) supply, and then underpinned a gradual shift to reorganization stage after the 1990s. Our study highlights the significance of ES assessment from historical perspective to understand the major processes and underlying mechanisms of lake SES. With adaptive policy interventions on pollution control, efficient resource-use, and targeted environmental investment, the sustainability of regional SES can be expected.

Analyzing ecosystem services of freshwater lakes and their driving forces: the case of Erhai Lake, China

Freshwater lakes provide critical ecological services to the local ecosystem. However, many of them are facing serious challenges, such as ecosystem degradation and water contamination, due to irrational water utilization and a lack of effective management. Under such a circumstance, it is crucial to examine the ecosystem services of freshwater lakes and uncover the driving forces so that appropriate protection policies can be raised. This study aims to fill such a research gap by employing an emergy accounting method. A case study of Erhai Lake (the second largest freshwater lake in Yunnan province, southwest China) was conducted for the period of 2001-2015. Driving forces that affect ecosystem services were analyzed by using Logarithmic Mean Divisia Index (LMDI). Results show that the total ecosystem services of Erhai Lake were reduced from 334.03E + 18 sej in 2001 to 274.37E + 18 sej in 2015. This was caused by the obvious decline of regulating services and supporting services, far exceeding the increase of provisioning services and cultural services. In 2015, two types of increased services that benefit human life in the market became the primary services of Erhai Lake. And their proportions were far beyond the two reduced ones that were overlooked due to their public and free attributes. The key driving forces include economic scale factor (∆E_ES), the fast and intensive economic activities. This development was at the cost of environmental degradation based upon the analysis of emergy benefit factor (∆E_EB). Finally, several suggestions are presented. This study provides valuable insights to understand ecosystem services of freshwater lakes so that a sustainable development pathway can be found to protect such freshwater lakes.

Understand the resilience and regime shift of the wetland ecosystem after human disturbances

Wetland protection and restoration are important for human's sustainable development, and assess the resilience and regime shift of wetland ecosystem under human disturbances is necessary for this purpose. Geochemical records, including nitrogen (N), phosphorus (P), heavy metals and polycyclic aromatic hydrocarbons (PAHs) from seven wetland cores dated by ²¹⁰Pb and ¹³⁷Cs analysis were used to identify the historical background of human disturbances on wetlands in the Sanjiang Plain. We also carried out paleoecological analysis (including plant macrofossils and diatoms) in one core (Honghe wetland) to reconstruct the successions of wetland ecological communities. The resilience and regime shift of ecosystem were evaluated based on autocorrelation and the Sequential t-test analysis of regime-shifts algorithm. Our results show that enrichment factors (EFs) of N, P and heavy metals (Cu, Zn, Pb etc.), and the concentrations of PAHs experienced slight increases from the 1920s but dramatic increases from the late 1970s. The dominant species of plant community began to change from Drepanocladus aduncus to Carex lasiocarpa from the late 1970s, and the diatoms began to change from wet-indicator to dry-indicator species from the 1950s in Honghe wetland. The regime shift of the wetland ecosystem occurred around 1990 CE, which due to a drop in water level caused by human activities, such as wetland drainage for the reclamation and the excessive use of groundwater for irrigation purpose, rather than climate moisture variations. There is a time gap between the severe disturbances and regime shift due to the stronger resilience of wetland ecosystem. The ecological characteristics (e.g. water level, biological compositions, and EFs of nutrient elements and heavy metals) of Honghe wetland before the late 1970s (release phase) were used as reference conditions for wetland restoration.

Ecosystem services trade-offs and determinants in China's Yangtze River Economic Belt from 2000 to 2015

Ecosystem services (ES) play an important role in sustaining ecological security, sustainable development and human well-being. This study investigates spatio-temporal changes in five key ES in the Yangtze River Economic Belt of China in 2000-2015-water conservation (WC), soil retention (SR), carbon sequestration (CS), biodiversity conservation (BC) and food supply (FS), by applying three ecological models (InVEST, RUSLE, CASA). Employing scenario simulations, the study quantifies distinct effects of significant factors on ES changes. Using spatial overlapping and Spearman's rank correlation respectively, the study distinguishes spatial patterns of synergies and trade-offs between five ES at the grid and city-scales. The results show that CS, FS, WC and SR presented an overall upward trend, increasing by 22.7%, 16.9%, 6.4% and 4.7%, respectively, while BC remained steady with a marginal degradation. Change in these five ES exhibited dramatic spatial heterogeneity. Across 131 cities, 98.5% of which increased in CS, 87.7% in WC, 68.5% in FS, and 53.1% in SR, while more than half experienced slight degradation in BC. There is high heterogeneity and a great diversity among spatial distributions of ES synergies and trade-offs, which is largely dependent on ES pairs and spatial patterns of land use. Land use/land cover change was the dominant force driving changes in SR, BC and CS, while meteorological factors exhibited a greater effect on WS change than land use/land cover change. The paper examines the synergies between WC-SR, CS-BC and BC-FS on the city level, while WC-BC exhibits significant trade-offs, and no significant relationships for other ES pairs. It is imperative that ES trade-offs at different scales are incorporated to strengthen ecological protection and management policies in project implementation, maintaining ES within vital regions in China. More sophisticated methods and more ES indicators need to be incorporated to enhance the robustness and completeness of assessment.

Evaluating indirect and direct effects of eco-restoration policy on soil conservation service in Yangtze River Basin

The conservation impacts of policies that promote large-scale ecological restoration of ecosystem services and socio-economic development are well documented around the world. However, the effect of socio-economic development resulting from such policies on ecosystem services is rarely analysed, although it is important to do so if these policies are to be sustainable. We analysed the socio-economic impacts of soil conservation services from 2000 to 2015 in the Yangtze River Basin under the Grain to Green Programme (GTGP). Also we assessed the driving forces behind the programme: conservation policies, urbanization, agricultural development, and population growth. Our results show that during 2000-2015, cultivated area decreased by 7.5%, urban area increased by 67.5%, forest area increased by 2.1%, and soil erosion was reduced by 19.5%. The programme not only contributed significantly to an improvement in soil conservation services but also enhanced them significantly through faster urbanization. Furthermore, vegetation cover and crop yields increased synergistically, mainly due to high-efficiency agriculture that reduced the negative effect of the GTGP on agricultural production. Overall determining the indirect and direct effects of the GTGP on soil conservation and agricultural production are important for furthering our understanding of the long-term effects of ecological restoration policies, and the present study offers practical insights for ecological restoration of other watersheds.