Dear Colleagues,

Freshwater reservoirs, as with all inland aquatic systems, are a well-known source of greenhouse gas (GHG; CO₂, CH₄, and N₂O) to the atmosphere, but their quantitative measurement and importance are still loosely constrained. This is mainly due to a lack of clear methodology for GHG quantification, unavailability of datasets for medium- to long-term prediction, and model availability. Freshwater bodies (e.g., rivers, lakes, and reservoirs) are actual sites of carbon processing and transport. They receive carbon (C) in various forms (inorganic and organic forms, labile organic carbon, autochthonous and allochthonous); the maximum part of which is released into the atmosphere and partially buried more or less in their sediments and transferred downstream. Since the 1990s (after the pre-industrial era), freshwater has contributed a significant amount of GHG emissions into the atmosphere. Furthermore, it plays an important role in regional and/or global carbon budgeting. The GHG emissions are mainly due to the degradation of organic matter (resulting mainly from the catchments and reaching the freshwater ecosystem through runoffs), occuring aerobically and/or anaerobically in benthic sediment. This quantification (maximum/minimum) is mainly due to the availability of nutrients (particularly carbon and nitrogen), climatic condition, depth, availability of dissolved oxygen, stratification, temperature of water column, etc. In general, tropical eco-regions are hotspots of emissions compared to temperate and sub-tropical regions. Given the worldwide importance of natural ecosystems, questioning man-made reservoirs as to their own carbon footprints is to be expected. There is vast uncertainty surrounding GHG inventory, although part of this uncertainty is the result of the complex biogeochemical processes involved and a lack of clear methodology to assess their GHG footprint.

This Special Issue accepts critical reviews, monographs, mini research articles, and research papers that analyze and discuss GHG emissions from freshwater ecosystems. Special emphasis is placed on (i) the quantification of GHG from rivers, lakes, reservoirs; (ii) their impact on regional and/or global carbon budgeting; (iii) modeling and measurement; (iv) factors affecting emissions; v) carbon budgeting; vi) carbon dynamics and their climate change implications; (vii) the mitigation strategies and/or regulatory policies.

Prof. Dr. Amit Kumar
Prof. Dr. Zhiguo Yu
Guest Editors

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• Greenhouse gas emissions
• River
• Lake
• Peatlands
• Hydropower reservoir
• Freshwater bodies
• CO₂, CH₄, and N₂O
• Climate and soil environmental factors
• Carbon dynamics
• Modeling and measurement
• Water quality assessment
• Carbon budgeting
• Soil carbon sequestration
• Carbon sources and sink
• Eco-hydrology
• GHG footprint
• C burial

Title: Methane and carbon dioxide emissions from ponds: A comprehensive review of processes, mechanism and their driving factors
Authors: Sandeep K. Malyan¹; Amit Kumar²; Ram Kishor Fagodiya³; Smita S. Kumar⁴; Amit Kumar⁵*; Zhiguo Yu⁵; Devendra Kumar⁶
Affiliation:
1 Research Management and Outreach Division, National Institute of Hydrology, Jalvigyan Bhawan, Roorkee, Uttarakhand-247667, India; [email protected]
2 Central Muga Eri Research and Training Institute, Central Silk Board, Jorhat, Assam 785000, India; [email protected]
3 Division of Irrigation and Drainage Engineering, ICAR-Central Soil Salinity Research Institute, Karnal, Haryana 132001, India; [email protected]
4 Department of Environmental Sciences, J.C. Bose University of Science and Technology YMCA Faridabad, India; [email protected]
5 School of Hydrology and Water Resources, Nanjing University of Information Science and Technology, Nanjing, China; [email protected] 6 Amity Institute of Environmental Toxicology, Safety and Management, Amity University Noida, Uttar Pradesh-201301, India; [email protected] *Corresponding author: [email protected] (A.K)
Abstract: Inland water bodies (particularly, ponds) emit a significant amount of methane (CH4) and carbon dioxide (CO2) to the atmosphere. In recent decades, ponds (<10000 m2) probably account for about 1/3rd of the global lake perimeter and are considered hotspots for greenhouse gas (GHGs; especially, CH4 and CO2) emission. High nutrients and waterlogged conditions provide an ideal environment for CH4 production and emission. The rate of emissions was differed according to climatic regions and is influenced by several biotic and abiotic factors like temperature, water nutrients, pH, dissolved oxygen, sediments, water depth, etc. Further, higher CO2 fluxes were associated with calcium, silicon, while higher CH4 fluxes were associated with total organic carbon and total phosphorus. Micro and macro plankton play a significant role in CO2 and CH4 emissions from ponds systems. There were several other factors and mechanism which significantly affect the CH4 and CO2 rate from ponds and need a comprehensive evaluation. This study aims to develop a decisive understanding of GHGs emission mechanism, processes from ponds, along with their key factors affecting emissions rate. Besides, uncertainty & limitation of GHG measurements, and future directions have also been discussed. This review will be highly useful for the environmentalist, policymakers, and water resources planners & managers to take suitable mitigation measures in advance so that its climatic impacts could be reduced in the future.

Title: Eco-hydrological Appraisal with Environmental Quality of Freshwater Ecosystems
Authors: Ramachandra T V^1,2,3**, Vinay S^1,4, Asulabha K S1, Sincy V¹, Bharath H Aithal^1,4
Affiliation:
1.Energy & Wetlands Research Group, Centre for Ecological Sciences (CES), Indian Institute of Science
2 Centre for Sustainable Technologies (astra), Indian Institute of Science (IISc)
3. Centre for infrastructure, Sustainable Transportation and Urban Planning (CiSTUP), IISc
4. Ranbir and Chitra Gupta School of Infrastructure Design and Management (RCG SIDM), IIT-Kharagpur, Web URL: http://ces.iisc.ernet.in/energy;
http://ces.iisc.ernet.in/foss http://orcid.org/0000-0001-5528-1565
*Corresponding Author: [email protected]; [email protected]
Abstract: Rivers are important source of freshwater that cater needs of society. The burgeoning population and the consequent land use changes have been altering the biophysical and chemical integrity, flow characteristics, etc. This necessitates understanding land use dynamics, flow dynamics, hydrologic regime and water quality of riverine ecosystems. Assessment of land use dynamics in the Aghanashini river basin reveal the decline of vegetation cover from 86.06% (1973) to 50.78% (2018). Computation of Eco-Hydrological Indices (EHI) highlights that the sub-watersheds with native vegetation had higher infiltration (and storage) compared to the water loss due to evapotranspiration and meet the societal demand. Computation of Water Quality Index helped to assess overall water quality across seasons. The study provides insights of hydrology linkages with the catchment landscape dynamics to the hydrologists and land use managers for the prudent management of river basins to address the issues of water stress through watershed treatment involving afforestation, appropriate cropping, soil conservation measures, etc.