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Carbon Dioxide Availability in Inlands Rivers Is Driven by Dissolved Organic Carbon, Not Warming: A Case Study of Tigris River




DOC, CO2, Climate change, Warming, Carbon mineralization, Brownification


Rivers became supersaturated with carbon dioxide (CO2), so they play an essential role in the global carbon budgets. To increase our understanding of the source of CO2 availability in rivers, we studied the role of climate-changed drivers of CO2 availability, which are ‘‘dissolved organic carbon (DOC), and warming’’. We sampled 45 locations of 3 parts within the Tigris River in Baghdad during autumn and winter. The results showed that all the studied variables (water temperature, pH, DOC, CO2) changed over time. The variations in CO2 availability are associated with changes in DOC concentration, not with water temperature. Overall, our results suggest that elevated CO2 in rivers could result from increased DOC inputs. Therefore, we can conclude that increased DOC concentration in rivers was required for microbial respiration and photo-mineralization, which are the primary sources of CO2 in river ecosystems.


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Xiao K, Abbt-Braun G, Horn H. Changes in the characteristics of dissolved organic matter during sludge treatment: A critical review. Water Res. 2020; 187: 116441.

Tiwari AK, Pal DB. Nutrients contamination and eutrophication in the river ecosystem. Ecological Significance of River Ecosystems: Elsevier Sci. 2022: 203-16.

Wei M, Gao C, Zhou Y, Duan P, Li M. Variation in spectral characteristics of dissolved organic matter in inland rivers in various trophic states, and their relationship with phytoplankton. Ecol Indic 2019; 104: 321-32.

Liu S, Feng W, Song F, Li T, Guo W, Wang B, et al. Photodegradation of algae and macrophyte-derived dissolved organic matter: A multi-method assessment of DOM transformation. Limnologica. 2019; 77: 125683.

Liu S, He Z, Tang Z, Liu L, Hou J, Li T, et al. Linking the molecular composition of autochthonous dissolved organic matter to source identification for freshwater lake ecosystems by combination of optical spectroscopy and FT-ICR-MS analysis. Sci Total Environ. 2020; 703: 134764.

Powers LC, Del Vecchio R, Blough NV, McDonald N, Schmitt-Kopplin P, Gonsior M. Optical properties and photochemical transformation of the dissolved organic matter released by Sargassum. Front Mar Sci. 2020;7:588287.

Wild B, Andersson A, Bröder L, Vonk J, Hugelius G, McClelland JW, et al. Rivers across the Siberian Arctic unearth the patterns of carbon release from thawing permafrost. Proc Natl Acad Sci. 2019; 116(21): 10280-5.

Sterner RW, Reinl KL, Lafrancois BM, Brovold S, Miller TR. A first assessment of cyanobacterial blooms in oligotrophic Lake Superior. Limnol Oceanogr. 2020; 65(12): 2984-98.

Kritzberg ES, Hasselquist EM, Škerlep M, Löfgren S, Olsson O, Stadmark J, et al. Browning of freshwaters: Consequences to ecosystem services, underlying drivers, and potential mitigation measures. Ambio. 2020; 49: 375-90.

Mackay E, Feuchtmayr H, De Ville M, Thackeray S, Callaghan N, Marshall M, et al. Dissolved organic nutrient uptake by riverine phytoplankton varies along a gradient of nutrient enrichment. Sci Total Environ. 2020; 722: 137837.

Liu F, Wang D, Zhang B, Huang J. Concentration and biodegradability of dissolved organic carbon derived from soils: A global perspective. Sci Total Environ. 2021; 754: 142378.

Hamdan M, Karlsson J, Byström P, Al‐Haidarey MJ, Ask J. Carbon dioxide limitation of benthic primary production in a boreal lake. Freshw Biol. 2022; 67(10): 1752-60.

Chaplot V, Mutema M. Sources and main controls of dissolved organic and inorganic carbon in river basins: A worldwide meta-analysis. J Hydroly. 2021; 603: 126941.

Chen J, Li H, Zhang Z, He C, Shi Q, Jiao N, et al. DOC dynamics and bacterial community succession during long-term degradation of Ulva prolifera and their implications for the legacy effect of green tides on refractory DOC pool in seawater. Water Res. 2020; 185: 116268.

Ni W, Li M, Ross AC, Najjar RG. Large projected decline in dissolved oxygen in a eutrophic estuary due to climate change. J Geophys Res: Oceans. 2019; 124(11): 8271-89.

Deeds J, Amirbahman A, Norton SA, Suitor DG, Bacon LC. Predicting anoxia in low‐nutrient temperate lakes. Ecol Appl. 2021; 31(6): e02361.

Carrick HJ, Marble C, Tian YQ. Differential responses for stream algal assemblages exposed to factorial N and P enrichment along an in situ DOC gradient. Front Environ Sci.. 2023; 11: 416.

Isles PD, Creed IF, Jonsson A, Bergström A-K. Trade-offs between light and nutrient availability across gradients of dissolved organic carbon lead to spatially and temporally variable responses of lake phytoplankton biomass to browning. Ecosystems. 2021: 1-16.

Al-Ani R, Al Obaidy A, Hassan F. Multivariate analysis for evaluation the water quality of Tigris River within Baghdad City in Iraq. iraqi J Agric Sci. 2019; 50(1): 331-42.

El-Amier YA, Al-Hadithy ON, Kadhim OG, El-Alfy M. Evaluation of Water and Sediment Quality of the Tigris River, Baghdad City, Iraq. Am J Environ Sci 2018; 1(1): 10-9.

Jabar SS, Hassan FM. Monitoring the Water Quality of Tigris River by Applied Overall Index of Pollution. IOP Conf Ser : Environ Earth Sci. 2022: IOP Publishing.

Majeed OS, Al-Azawi AJ, Nashaat MR. The Effect of Tharthar-Tigris Canal on the Environmental Properties of the Tigris River Northern Baghdad, Iraq. Baghdad Sci J. 2022; 19(6): 1177-1109.

Mustafa MH, Jankeer MH. Quality Difference Between Two Location on Tigris River Within Mosul City. Rafidain J Sci. 2007; 1 (18) 111-124. (in Arabic).

Saad MA, Antoine SE. Limnological studies on the River Tigris, Iraq. II. Seasonal variations of nutrients. Int Rev Hydrobiol. 1978; 63(5): 705-19.

Yasin S S. A Study of Monthly Changes in some Physical, Chemical, and Phytosanitary parameters in Tigris River at Salah Din Governorate SK Yasin. Tikrit J Agri Sci. 2018; 18(4): 131-141.

Khadim HJ, Oleiwi HO, editors. Assessment of Water Quality in Tigris River of AL-Kut City, Iraq by Using GIS. E3S Web of Conferences; 2021; 2(1): 155-163: EDP Sciences.

Enad HY, Jaeel AJ, editors. Water quality index of Tigris River on Waist Governorate for aquatic life. IOP Conf Ser : Mater Sci Eng 2019: 12(3): 101-112. IOP Publishing.

Al-Sudani IM. Water quality assessment of Tigris River using overall index of pollution (OIP). Baghdad Sci J. 2021; 18(2): 1099-100.

Weiss LC, Pötter L, Steiger A, Kruppert S, Frost U, Tollrian R. Rising pCO2 in freshwater ecosystems has the potential to negatively affect predator-induced defenses in Daphnia. Curr Biol. 2018; 28(2): 327-32. e3.

APHA APHA. Standard Methods for the Examination of Water and Wastewater, 21st Ed Washington, DC.22621. pp .2005.

Hadi RAM. Algae studies on the River Univ.College, Cardiff,UK; 1981.

Golterman HL, Clymo R S, Ohnstad M A M. Methods for Physical and Chemical Analysis of Fresh Waters. 2nd ed. Oxford: Blackwell Scientific Publications; 1978.

Williams CJ, Yamashita Y, Wilson HF, Jaffé R, Xenopoulos MA. Unraveling the role of land use and microbial activity in shaping dissolved organic matter characteristics in stream ecosystems. Limnol Oceanogr. 2010; 55(3): 1159-71.

Henard CA, Wu C, Xiong W, Henard JM, Davidheiser-Kroll B, Orata FD, et al. Ribulose-1, 5-bisphosphate carboxylase/oxygenase (RubisCO) is essential for growth of the methanotroph Methylococcus capsulatus strain Bath. Appl Environ. 2021; 87(18): e00881-21.

Hassan FM, El-Sheekh MM, Wahhab TA. Environmental factors drive phytoplankton primary productivity in a shallow Lake. Egypt J Aquat Bio Fish. 2023; 27(2): 1-12.

Shatilla NJ, Carey SK. Assessing inter-annual and seasonal patterns of DOC and DOM quality across a complex alpine watershed underlain by discontinuous permafrost in Yukon, Canada. Hydrol Ear Syst Sci. 2019; 23(9): 3571-91.

Backlund P. Degradation of aquatic humic material by ultraviolet light. Chemosphere. 1992; 25(12): 1869-78.

Paine ER, Schmid M, Boyd PW, Diaz‐Pulido G, Hurd CL. Rate and fate of dissolved organic carbon release by seaweeds: A missing link in the coastal ocean carbon cycle. J Phycol. 2021; 57(5): 1375-91.

Van Puijenbroek P, Beusen A, Bouwman A. Global nitrogen and phosphorus in urban waste water based on the Shared Socio-economic pathways. J Environ Manag. 2019; 231: 446-56.

Allesson L, Andersen T, Dörsch P, Eiler A, Wei J, Hessen DO. Phosphorus availability promotes bacterial DOC-mineralization, but not cumulative CO2-production. Front Microbiol. 2020; 11: 569879.

Liu J, Han G. Controlling factors of riverine CO2 partial pressure and CO2 outgassing in a large karst river under base flow condition. J Hydrol. 2021; 59(3): 125-132.

Sang L, Liu X, Sun D, Yang Y, Yang J, Wang Z, et al. Effect of tidal hydrology on soil anaerobic CO2 production of freshwater marsh in the Yellow River estuary wetland, China. Ecol Indic. 2022; 145: 109747.

Hamdan M, Byström P, Hotchkiss ER, Al-Haidarey MJ, Ask J, Karlsson J. Carbon dioxide stimulates lake primary production. Sci Rep. 2018; 8(1): 1-5.

Rasmusson LM, Buapet P, George R, Gullström M, Gunnarsson PC, Björk M. Effects of temperature and hypoxia on respiration, photorespiration, and photosynthesis of seagrass leaves from contrasting temperature regimes. ICES J Mar Sci. 2020; 77(6): 2056-65.

Huertas IE, Rouco M, Lopez-Rodas V, Costas E. Warming will affect phytoplankton differently: evidence through a mechanistic approach. Proceedings of the Royal Society B: Biol sci. 2011; 278(1724): 3534-43.