Pollution characteristics of persistent and toxic organic substances in lakes of Tanzania
Due to the inadequate control of Persistent and Toxic Organic Substances (PTOS) in Tanzania, they are still many ways to transport into the lake environment, to threaten the lake ecology safety and human health.
To understand the status of PTOS pollution in Tanzanian lakes, Prof. Zhang Lu from the Joint Research Station for East African Great Lakes and Urban Ecology (affiliated to Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences) led a joint group with Tafiri scientiest in early 2020 to conduct a field survey on PTOS pollution in East African lakes.
The study of 18 lakes in Tanzania shows that the distribution of PTOS has large spatial variations. Among the lakes, the PTOS level in Lake Jipe, Mabayani Reservoir, Lake Duluti and Lake Hombolo was relatively higher, while was relatively lower in Lake Chala, Lake Small Momela, Lake Babati, Lake Singida and Lake Kindai. Overall, the pollution levels of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs) in Tanzania lakes are relatively lighter compared to lakes worldwide.
Among the four major types of PTOS pollutants in Tanzania lakes, phthalate esters (PAEs) pollution is the more worthy of attention. Source identification shows that phthalate esters (PAEs), PAHs, HCHs and Methoxychlor have obvious watershed input characteristics. A multi-index comprehensive scoring method based on the measured concentrations of pollutants, the inherent properties of compounds (lipophilicity and hydrophobicity, structure-activity relationship), and lake ecological risks and health risks was proposed. Based on this method, a list of precedent-controlled PTOS pollutants (8PAEs,6 PAHs, 7 OCPs and 5 PCBs) for Tanzania lakes was built.
It was concluded that PAEs were the priority pollutants for drinking water safety and ecosystem health for Tanzania lakes. Therefore, Tanzania should control the production, use and emission of PAEs, especially around the lake areas, in order to reduce the impact of PTOS on lake water ecology.
A list of precedent-controlled PTOS pollutants (8PAEs,6 PAHs, 7 OCPs and 5 PCBs) for Tanzania lakes
Tackling harmful cyanobacterial blooms with Chinese colleagues: we’re all in the same boat
Harmful cyanobacterial blooms (CyanoHABs) are a rapidly proliferating global problem, threatening the use and sustainability of our freshwater resources. In recent decades, the United States, China, and other developed and developing countries threatened by CyanoHAB expansion have established collaborative efforts aimed at mitigating and managing this environmental and human health problem. However, an escalating negative political climate and restrictive policies on scientific exchange threaten these efforts. In this Perspective, I point to progress that has been made to counter the CyanoHAB problem on U.S.–Chinese fronts through our collaborations, which have been mutually beneficial from research and academic perspectives. Much like global efforts now needed to control pandemics, we are all “in the same boat” when to comes to countering the threat CyanoHABs pose for drinkable, swimmable, and fishable freshwater supplies and human health.
FIG. (A) Hans Paerl collecting surface algal bloom sample at Lake Taihu, China. (B) Prof. Guangwei Xu and Hans Paerl collecting plankton samples at Lake Erhai, Yunnan Province, China. (C) Prof. Guangwei Xu and Hans Paerl, preparing nutrient addition bioassays near Lake Taihu. (D) Chinese Graduate Students and Hans Paerl filling bioassays with lake Taihu water. (E and F) U.S. and Chinese students working at the experimental mesocosm site located on the shore of Lake Taihu. (G) Hans Paerl and collaborators at the International Society of Limnology (SIL) meetings, held in Nanjing, China, August, 2018. (H) Prof, Yiping Li and Hans Paerl at a Graduate Student Symposium, Hohai University, Nanjing.
Hans W. Paerl. 2020. JOURNAL OF PHYCOLOGY.DOI: 10.1111/jpy.13058
Radiation dimming and decreasing water clarity fuel underwater darkening in lakes
Long-term decreases in the incident total radiation and water clarity might substantially affect the underwater light environment in aquatic ecosystems. However, the underlying mechanism and relative contributions of radiation dimming and decreasing water clarity to the underwater light environment on a national or global scale remains largely unknown. Here, we present a comprehensive dataset of unprecedented scale in China’s lakes to address the combined effects of radiation dimming and decreasing water clarity on underwater darkening. Long-term total radiation and sunshine duration showed 5.8% and 7.9% decreases, respectively, after 2000 compared to 1961–1970, resulting in net radiation dimming. An in situ Secchi disk depth (SDD) dataset in 170 lakes showed that the mean SDD significantly decreased from 1.80 ± 2.19 m before 1995 to 1.28 ± 1.82 m after 2005. SDD remote sensing estimations for 641 lakes with areas ≥ 10 km2 showed that SDD markedly decreased from 1.26 ± 0.62 m during 1985–1990 to 1.14 ± 0.66 m during 2005–2010. Radiation dimming and decreasing water clarity jointly caused an approximately 10% decrease in the average available photosynthetically active radiation (PAR) in the euphotic layer. Our results revealed a more important role of decreasing water clarity in underwater darkening than radiation dimming. A meta-analysis of long-term SDD observation data from 61 various waters further elucidated a global extensive underwater darkening. Underwater darkening implies a decrease in water quality for potable water supplies, recession in macrophytes and benthic algae, and decreases in benthic primary production, fishery production, and biodiversity.
Spatial distribution of SDD differences during 2005–2016 compared to the 1960s–1995 (a), comparison of SDDs before 1995 to after 2005 according to the five geographic lake zones and the Hu Huanyong Line (b and c) for the dataset of 170 lakes.
All: all lakes; EPL: Eastern Plain Lake zone; YGPL; Yunnan-Guizhou Plateau Lake zone; NPL: Northeast Plain Lake zone; IMXL: Inner Mongolia-Xinjiang Lake zone; TPL: Tibetan Plateau Lake zone; NW and SE represent results for lakes in the northwestern and southeastern regions of the Hu Huanyong Line.
Yunlin Zhang, Boqiang Qin, Kun Shi, Yibo Zhang, Jianming Deng, Martin Wild et al., 2020. Science Bulletin. DOI: https://doi.org/10.1016/j.scib.2020.06.016
Climate mediates continental scale patterns of stream microbial functional diversity
Understanding the large-scale patterns of microbial functional diversity is essential for anticipating climate change impacts on ecosystems worldwide. However, studies of functional biogeography remain scarce for microorganisms, especially in freshwater ecosystems. Here we study 15,289 functional genes of stream biofilm microbes along three elevational gradients in Norway, Spain and China.
We find that alpha diversity declines towards high elevations and assemblage composition shows increasing turnover with greater elevational distances. These elevational patterns are highly consistent across mountains, kingdoms and functional categories and exhibit the strongest trends in China due to its largest environmental gradients. Across mountains, functional gene assemblages differ in alpha diversity and composition between the mountains in Europe and Asia. Climate, such as mean temperature of the warmest quarter or mean precipitation of the coldest quarter, is the best predictor of alpha diversity and assemblage composition at both mountain and continental scales, with local non-climatic predictors gaining more importance at mountain scale. Under future climate, we project substantial variations in alpha diversity and assemblage composition across the Eurasian river network, primarily occurring in northern and central regions, respectively.
We conclude that climate controls microbial functional gene diversity in streams at large spatial scales; therefore, the underlying ecosystem processes are highly sensitive to climate variations, especially at high latitudes. This biogeographical framework for microbial functional diversity serves as a baseline to anticipate ecosystem responses and biogeochemical feedback to ongoing climate change.
Félix Picazo, Annika Vilmi, Juha Aalto, Janne Soininen, Emilio O. Casamayor, Yongqin Liu, Qinglong Wu, Lijuan Ren, Jizhong Zhou, Ji Shen & Jianjun Wang*. Microbiome. 2020. DOI:10.1186/s40168-020-00873-2