Changing temporal and spatial patterns of methane emission from rivers by reservoir dams: a review

Dams built on rivers can bring economic benefits to local production and are considered to be environmentally friendly. However, in recent years, many researchers found that the establishment of dams has created excellent conditions for the production of methane (CH₄) in rivers, making it change from a "weak source" of rivers to a "strong source" of dams. In particular, reservoir dams have a great impact on CH₄ emission in rivers within their regions in terms of time and space. Spatially, the sedimentary layer and water level fluctuation zone of reservoirs are the main direct and indirect causes of CH₄ production. Temporally, the synergetic effect between water level adjustment of the reservoir dam and environmental factors leads to large changes in the substances of the water body, impacts on the production and transport of CH₄. Finally, the generated CH₄ is emitted into the atmosphere through several important emission modes: molecular diffusion, bubbling, and degassing. The contribution of CH₄ emitted from reservoir dams to the global greenhouse effect cannot be ignored.

Sources, Migration, Transformation, and Environmental Effects of Organic Carbon in Eutrophic Lakes: A Critical Review

Organic carbon (OC) plays a leading role in the carbon cycle of lakes and is crucial to carbon balances at regional and even global scales. In eutrophic lakes, in addition to external river inputs, the decomposition of endogenous grass and algae is a major source of organic carbon. Outbreaks of algal blooms (algal eutrophication) and the rapid growth of aquatic grasses (grass eutrophication) can lead to the accumulation and decay of large amounts of algae and aquatic grass debris, which increases the intensity of the carbon cycle of lakes and greatly impacts aquatic environments and ecosystems. The structures, decomposition processes, and distribution characteristics of algae and higher aquatic plant debris in eutrophic lakes are different from mesotrophic and oligotrophic lakes. Studying their accumulation dynamics and driving mechanisms is key to further understanding lake carbon cycles and their many interdependent pathways. This paper focuses on the carbon sources, tracing technologies, migration and transformation processes, and environmental effects of OC in eutrophic lakes. Based on the existing knowledge, we further combed the literature to identify the most important knowledge gaps preventing an in-depth understanding of the processes and driving mechanisms of the organic carbon cycle in eutrophic lakes.

Assessment and management of lake eutrophication: A case study in Lake Erhai, China

Some wastewater sources, such as agricultural waste and runoff, and industrial sewage, can degrade water quality. This study summarises the sources and corresponding mechanisms that trigger eutrophication in lakes. Additionally, the trophic status index and water quality index (WQI) which are effective tools for evaluating the degree of eutrophication of lakes, have been discussed. This study also explores the main nutrients (nitrogen and phosphorus) driving transformations in the water body and sediment. Lake Erhai was used as a case study, and it was found to be in a mesotrophic state, with N and P co-limitation before 2006, and only P limitation since 2006. Finally, effective measures to maintain sustainable development in the watershed are proposed, along with a framework for an early warning system adopting the latest technologies (geographic information systems (GIS), remote sensing (RS)) for preventing eutrophication.