Ecosystem health assessment of the plant-dominated Baiyangdian Lake based on eco-exergy

Occurrence and influencing factors of antibiotics and antibiotic resistance genes in sediments of the largest multi-habitat lakes in Northern China

Baiyangdian Lake is a typical and largest multi-habitat lake in the North plain of China. To understand the generation and transmission of antibiotics resistance genes (ARGs) in multi-habitat lakes, the contents of nutrients (TC, TOC, TN, TP and TS), heavy metals (Zn, Cr, Ni, Cu, Pb, As, Cd and Hg), 22 antibiotics, 16S-rRNA(16S), Class I integron (intI1) and 20 ARGs were determined. Samples were taken from the Fuhe river, river estuaries, reed marshes, living area, fish ponds and open water of Baiyangdian Lake. The results showed that quinolones were the main pollutants in six habitats, and the content range was ND-104.94 ng/g. Thereinto, aac (6') -IB, blaTEM-1, ermF, qnrA, qnrD, tetG, sul1, sul2 and tetM were detected in all the analyzed samples. The absolute abundance of sul1 was the highest (5.25 × 10⁵ copies/g-6.21 × 10⁷ copies/g) in most of the samples. In these different habitats, the abundance of antibiotics and ARGs in river estuary was the highest, and that in reed marshes was the lowest. There was a significant positive correlation between the abundance of heavy metals (Cu, Pb, Zn, Ni, Cd, Hg) and the absolute abundance of 11 ARGs (P < 0.01). Redundancy analysis showed that Cu, Zn, intI1, TP and macrolides were the important factors affecting the distribution of ARGs. Our finding provides a more likely driving and influencing factor for the transmission of ARGs in lakes with complex and diverse habitats.

Enrichment differences and source apportionment of nutrients, stable isotopes, and trace metal elements in sediments of complex and fragmented wetland systems

Anthropogenic activities significantly influence the lake environment and are reflected by the element contents in sediments/soils. The lake fragmentation provides a unique opportunity for comparing the influences of natural/anthropogenic activities of different wetlands systems. In this study, a complex and fragmented lake was investigated, and sediment/soil samples were collected from different systems. The nutrient contents (C, N, and P), stable isotopic compositions (δ¹³C and δ¹⁵N), and trace metal contents (As, Cd, Cr, Cu, Ni, Pb, and Zn) in the sediments/soils were measured to determine the natural and anthropogenic influences and pollution sources. Lake fragmentation was caused by insufficient water input and long-term agricultural and aquacultural activities of local residents. Due to the effect of anthropogenic activities, the enrichment conditions of various elements differed significantly for different wetland systems. Industrial, agricultural, and biological sources significantly influenced the element enrichment in different systems. The results demonstrated that the anthropogenic activities significantly influenced the sediments/soils in wetland systems, and the lake fragmentation reduced the diffusion of the contaminants. These results provide accurate reference information for pollution control, lake management, and ecological restoration.

Assessing the safe operating space of aquatic macrophyte biomass to control the terrestrialization of a grass-type shallow lake in China

As an important type of aquatic ecosystem, lake ecosystems play an irreplaceable role in providing water resources, controlling floods, regulating the regional climate, and maintaining the regional ecological balance. However, multiple lake ecosystems have been threatened by the expansion of aquatic macrophytes and the resulting bioaccumulation, which accelerates the process of lake terrestrialization. Therefore, it is necessary to identify the safe operating space of macrophyte biomass in order to control the terrestrialization of shallow lakes. In this study, we investigated the biomasses of dominant species and community types at different growth stages in different terrestrialized zones for a typical shallow lake in North China. Then, we developed a suitable method for estimating the safe operating space for the aquatic macrophyte biomass in different terrestrialization stages. Our results showed that the aquatic macrophyte biomass generally increased with the increasing terrestrialization stage. In addition, the biomass in September was lower than that in May. On the community scale, the biomass of Phragmites australis, Phragmites australis - Ceratophyllum demersum, and Nelumbo nucifera - Ceratophyllum demersum - Typha orientalis communities was significantly higher than that of Potamogeton pectinatus and Potamogeton pectinatus - Nelumbo nucifera communities. Terrestrialization exhibited lower impacts on plant biomass in May, whereas a greater impact of terrestrialization was observed in September. Generally, single-species communities had higher plant biomass than mixed communities. The target management years for different terrestrialized zones were established to calculate the safe operating space of macrophyte biomass. The current biomass values were much higher than those calculated for the safe operating space, especially in September and for the P. australis and P. australis - C. demersum communities, indicating that there is high pressure to manage these communities. The approach proposed in the study provides a scientific reference for macrophyte management to control the terrestrialization status of grass-type shallow lakes.

Chemical fractions, diffusion flux and risk assessment of potentially toxic elements in sediments of Baiyangdian Lake, China

The pollution of potentially toxic elements (PTEs) in Baiyangdian Lake (BYDL), the largest shallow lake in northern China, has been focused on since the construction of the Xiong'an New Area. However, research on the bioavailability and diffusive flux of PTEs in BYDL sediments has been still limited. Herein, sediment samples were collected from BYDL to systematically evaluate the pollution risk, bioavailability, and diffusion flux of PTEs using multiple methods, including the pollution indexes, risk assessment code, bioavailable metal index, the sequential extraction, and diffusive gradients in thin-films (DGT). The results showed that the average concentrations of PTEs (except for Cd) were similar to the local background. The spatial distribution of PTEs showed that their contents were higher in northern sediments than in southern sediments, and risk assessment results suggest that Cd is the priority pollutant in the BYDL. Most PTEs in the sediments were mainly present in the residue fractions; however, Cd was mainly present in the non-residue fraction. Further analysis of the Cd content and chemical fraction showed that Cd was not only abundant in the northern sediments, but also that the non-residual fraction of Cd was significantly higher than in the southern sediments. The diffusive fluxes of PTEs in the northern sediments were also investigated in comparison with their chemical fractions. Results suggest that Cd has the potential to diffuse from the sediment into the overlying water. Additionally, upon combining the DGT and chemical fractions analyses, it was found that the PTEs which mainly in non-residual fraction tend to diffuse upwards into the overlying water. But, the release tendency of PTEs does not fully depend on their non-residual content. Overall, PTEs did not significantly contaminate BYDL sediments; nevertheless, the potential ecological risk of Cd should be considered.

Health Evaluation and Risk Factor Identification of Urban Lakes—A Case Study of Lianshi Lake

Health assessment and risk factor identification represent the premise and foundation of scientific management and ecological restoration of urban lakes. Based on in-depth understanding of the nature–society duality of urban lakes, a framework for evaluating urban lake health was constructed, including four modules, namely, establishing an index system; determining the index weight; identifying risk factors; and a comprehensive lake health evaluation. Employing this framework, we evaluated Lianshi Lake, Beijing, classifying the lake condition as “sub-healthy”. Based on the evaluation data, we identified the health risk factors of the lake. We applied standard difference rate (SDR) and risk degree (Rd) (safe degree (Sd)) concepts, and classified the indices of risk areas employing the Pareto analysis method. Finally, we identified the lake residence period, landscape connectivity, and eutrophication as the major risk factors in Lianshi Lake. Three factors constitute the basis of ecosystem health and are key targets of ecological restoration: the lake residence period represents the hydrological and hydrodynamic characteristics of the lake; landscape connectivity is described from an ecological perspective, and represents the integrity of the lake ecosystem; and the eutrophication states describe the water quality characteristics and represent the availability of lake water. The results contribute to decision-making for comprehensive urban lake management.

Distribution, ecological risk and source identification of heavy metals in sediments from the Baiyangdian Lake, Northern China

Baiyangdian Lake (BYDL) is the largest plant-dominated freshwater wetland in the North China Plain. It plays an important role in supporting the construction of Xiongan New Area. Heavy metals contents (As, Cd, Cu, Cr, Ni, Pb, and Zn) in the sediments from BYDL are investigated to determine their spatial distribution and potential ecological risk in this study. Then the relationship and sources of contaminants were analyzed using a multivariate visual statistical analysis. The risk assessment results reveal that the surface sediments of BYDL are moderately to highly polluted by heavy metals, and the primary contaminants are Cd, Pb, and Zn. The spatial distribution of high potential risk regions mainly concentrate in the stream corridor between the east and west of the lake, and the distribution of high potential risk level of Cd, Pb, and Zn occur in a similar region. Additionally, exogenetic heavy metals are accumulated in the sediment cores within a depth of 16 cm, and their contents and risk decreased sharply with the increasing of depth. Furthermore, the results of statistical analysis implied that the Cd, Pb, and Zn in sediments are derived from industrial sources, the As and Cr from the geological process and the nutrients are from the nonpoint agricultural pollution. Overall, this study gives more information about the ecological risk distribution and pollution sources of BYDL, which is essential for the strategic design of future pollution control and environmental remediation.

Dredging project caused short-term positive effects on lake ecosystem health: A five-year follow-up study at the integrated lake ecosystem level

Sediment dredging is a controversial technology for lake eutrophication control. A lengthy and holistic assessment is important to understand the effects of a dredging project on a lake ecosystem. In this study, a dredging project was followed for 5 years. To understand the variations of lake ecosystems before, during and after the project, water quality, phytoplankton, zooplankton and benthic animal biomass were monitored; Four subindicators, including eco-exergy (Ex), structural eco-exergy (Ex_st), buffer capacity of total phosphorus for phytoplankton (β_(TP)(phyto)) and trophic level index (TLI) were calculated and developed to an integrated ecosystem health indicator (EHI). The monitoring results showed that the dredging project caused many short-term positive effects such as decreased total nitrogen, total phosphorus, permanganate index and phytoplankton biomass throughout the entire lake water, increased Secchi disk depth in the whole lake and increased benthonic animal biomass in the nondredged regions. However, these positive effects disappeared overtime. Water chemistry and biomass returned to the initial state before dredging. EHI showed that the dredging project caused negative effects on the lake health in the dredged region at first. Subsequently, the health status of the entire lake, including the dredged and nondredged regions, improved until 1-2 years after the project finished. Because of the lack of other timely ecological restoration measures, the lake gradually returned to its initial health status. However, the health status in the dredged regions was only slightly better than before dredging and often worse than that of the nondredged regions. Our study suggested that dredging projects may only cause short-term positive effects on lake ecosystem health. The external interception and dredging ratio were important. A dredging project should be combined with other ecological lake restoration measures when the project has caused positive effects in a lake.

Eco-exergy and emergy based self-organization of three forest plantations in lower subtropical China

The bio-thermodynamic structures of a mixed native species plantation, a conifer plantation and an Acacia mangium plantation in Southern China were quantified over a period of 15 years based on eco-exergy methods. The efficiencies of structural development and maintenance were quantified through an integrated application of eco-exergy and emergy methods. The results showed that the storage of eco-exergy increased over 3 times in all three plantations, as predicted by the maximum eco-exergy principle. This trend was primarily seen due to the accumulation of biomass, instead of an increase in the specific eco-exergy (eco-exergy per unit biomass), although species richness did increase. The eco-exergy to emergy and eco-exergy to empower ratios of the three plantations generally increased during the study period, but the rate of increase slowed down after 20 years. The dominant trees are the largest contributors to the eco-exergy stored in the plantations, and thus, the introduction of suitable indigenous tree species should be considered after the existing trees pass through their period of most rapid growth or around 20 years after planting. The combined application of C-values and suggested weighting factors in the eco-exergy calculation can imply opposite results, but may also supply useful information for forest management.

Chlorophyll a simulation in a lake ecosystem using a model with wavelet analysis and artificial neural network

Accurate and reliable forecasting is important for the sustainable management of ecosystems. Chlorophyll a (Chl a) simulation and forecasting can provide early warning information and enable managers to make appropriate decisions for protecting lake ecosystems. In this study, we proposed a method for Chl a simulation in a lake that coupled the wavelet analysis and the artificial neural networks (WA-ANN). The proposed method had the advantage of data preprocessing, which reduced noise and managed nonstationary data. Fourteen variables were included in the developed and validated model, relating to hydrologic, ecological and meteorologic time series data from January 2000 to December 2009 at the Lake Baiyangdian study area, North China. The performance of the proposed WA-ANN model for monthly Chl a simulation in the lake ecosystem was compared with a multiple stepwise linear regression (MSLR) model, an autoregressive integrated moving average (ARIMA) model and a regular ANN model. The results showed that the WA-ANN model was suitable for Chl a simulation providing a more accurate performance than the MSLR, ARIMA, and ANN models. We recommend that the proposed method be widely applied to further facilitate the development and implementation of lake ecosystem management.