Spatio-temporal variability in the sources of particulate organic carbon and nitrogen in a tropical Godavari estuary

Gawade, L.; Krishna, M. S.; Sarma, V. V. S. S.; Hemalatha, K.; Rao, Y. Venkateshwara

doi:10.1016/j.ecss.2018.10.004

Cited by 16 publications

(4 citation statements)

References 62 publications

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“…5c, S3), suggesting mixing of freshwater and estuarine/marine phytoplankton in the delta, where the latter has typically less negative δ 13 C org values (i.e. −22.8 ‰ to −24.4 ‰; Dehairs et al, 2000;Krishna et al, 2015;Gawade et al, 2018). This observation is consistent with changes in electrical conductivity and water isotopic values (δ 18 O) that showed seawater intrusion in the delta in the dry season (Kirkels et al, 2020b).…”

Section: Suspended Particulate Mattersupporting

confidence: 59%

Carbon isotopic ratios of modern C₃ and C₄ vegetation on the Indian peninsula and changes along the plant–soil–river continuum – implications for vegetation reconstructions

et al. 2022

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Abstract. The large difference in the fractionation of stable carbon isotopes between C3 and C4 plants is widely used in vegetation reconstructions, where the predominance of C3 plants suggests wetter and that of C4 plants drier conditions. The stable carbon isotopic composition of organic carbon (OC) preserved in soils or sediments may be a valuable (paleo-)environmental indicator, based on the assumption that plant-derived material retains the stable carbon isotopic value of its photosynthetic pathway during transfer from plant to sediment. In this study, we investigated the bulk carbon isotopic values of C3 and C4 plants (δ13C) and of organic carbon (δ13Corg) in soils, river suspended particulate matter (SPM) and riverbed sediments to gain insight into the control of precipitation on C3 and C4 plant δ13C values and to assess changes in δ13Corg values along the plant–soil–river continuum. This information allows us to elucidate the implications of different δ13C end-members on C3 / C4 vegetation reconstructions. Our analysis was performed in the Godavari River basin, located in the core monsoon zone in peninsular India, a region that integrates the hydroclimatic and vegetation changes caused by variation in monsoonal strength. The basin has distinct wet and dry seasons and is characterised by natural gradients in soil type (from clay-rich to sandy), precipitation (∼ 500 to 1500 mm yr−1) and vegetation type (from mixed C3 / C4 to primarily C3) from the upper to the lower basin. The δ13C values of Godavari C3 plants were strongly controlled by mean annual precipitation (MAP), showing an isotopic enrichment of ∼ 2.2 ‰ from ∼ 1500 to 500 mm yr−1. Tracing δ13Corg values from plant to soils and rivers revealed that soils and riverbed sediments reflected the transition from mixed C3 and C4 vegetation in the dry upper basin to more C3 vegetation in the humid lower basin. Soil degradation and stabilisation processes and hydrodynamic sorting within the river altered the plant-derived δ13C signal. Phytoplankton dominated the δ13Corg signal carried by SPM in the dry season and year-round in the upper basin. Application of a linear mixing model showed that the %C4 plants in the different subbasins was ∼ 7 %–15 % higher using plant end-members based on measurement of the Godavari vegetation and tailored to local moisture availability than using those derived from data compilations of global vegetation. Including a correction for the 13C enrichment in Godavari C3 plants due to drought resulted in maximally 6 % lower estimated C4 plant cover. Our results from the Godavari basin underline the importance of making informed choices about the plant δ13C end-members for vegetation reconstructions, considering characteristics of the regional vegetation and environmental factors such as MAP in monsoonal regions.

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Section: Suspended Particulate Mattersupporting

confidence: 59%

Carbon isotopic ratios of modern C₃ and C₄ vegetation on the Indian peninsula and changes along the plant–soil–river continuum – implications for vegetation reconstructions

et al. 2022

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“…Interestingly, δ 13 C org values of dry season SPM became less negative near the Godavari's outflows into the Bay of Bengal (Fig. 5c, S3), suggesting mixing of 440 freshwater and estuarine/marine phytoplankton in the delta, where the latter has typically less negative δ 13 C org values (i.e., -22.8 to -24.4 ‰;Dehairs et al, 2000;Krishna et al, 2015;Gawade et al, 2018). This result is also consistent with changes in electrical conductivity and water isotopic signature (δ 18 O) that showed seawater intrusion in the delta in the dry season (Kirkels et al, 2020b).…”

Section: Suspended Particulate Mattermentioning

confidence: 97%

Carbon isotopic ratios of modern C3 and C4 vegetation on the Indian Peninsula and changes along the plant–soil–river continuum; implications for (paleo-)vegetation reconstructions

Kirkels

Boer

Hernández

et al. 2022

Preprint

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Abstract. The large difference in the fractionation of stable carbon isotopes between C3 and C4 plants is widely used in vegetation reconstructions, where the predominance of C3 plants suggests wetter and that of C4 plants drier conditions. The isotopic composition of organic carbon (OC) preserved in soils or sediments may be a valuable (paleo-)environmental indicator, based on the assumption that plant-derived material retains the carbon isotopic signature of its photosynthetic pathway during transfer from plant to sediment. In this study, we investigated the carbon isotopic signature of C3 and C4 plants (δ13C) and of organic carbon (δ13Corg) in soils, river Suspended Particulate Matter (SPM) and riverbed sediments, to gain insight in the control of precipitation on C3 and C4 plant δ13C values and to assess changes in δ13Corg values along the plant–soil–river continuum. This information allows us to elucidate the implications of different δ13C end-members on C3/C4 vegetation reconstructions. Our analysis was performed in the Godavari River basin, which has mixed C3 and C4 vegetation and is situated in the Core Monsoon Zone in peninsular India, a region that integrates the hydroclimatic and vegetation changes caused by variation in monsoonal strength. The Godavari C3 and C4 plants revealed more negative δ13C values than global average vegetation values, suggesting region-specific plant δ13C signatures. Godavari C3 plants confirmed a strong control by Mean Annual Precipitation (MAP) on their δ13C values, with an isotopic enrichment of ~2.2 ‰ for the interval between ~500 and 1500 mm y-1. Tracing δ13Corg values from plant to soils and rivers revealed that soils and riverbed sediments reflected the transition from mixed C3 and C4 vegetation in the dry upper basin to more C3 vegetation in the humid lower basin. Soil degradation and stabilisation processes and hydrodynamic sorting within the river altered the plant-derived δ13C signal. Phytoplankton dominated the δ13Corg signal carried by SPM in the dry season and year-round in the upper basin. Our analysis revealed that the reconstructed C3/C4 vegetation composition was sensitive to the plant δ13C end-members used as mixing model input. The %C4 plants in the different subbasins was ~10–19 % higher using Godavari-specific end-members than using global averages, and including a correction for drought enrichment in Godavari C3 plants resulted in a 2–10 % lower estimated C4 plant cover. Hence, incorporating region-specific plant δ13C end-members and drought correction of the C3 end-member in mixing models need to be considered to determine C3 and C4 distributions of modern- and paleo-vegetation in monsoonal regions.

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“…Studies on the anthropogenic impact on water quality in estuaries by biogeochemical models are mainly available in temperate estuaries of industrialized countries (Gawade et al, 2018;Regnier et al, 2013). The Carbon Generic Estuarine Model (C-GEM) is a generic onedimensional, reactive-transport model that takes advantage of the relationship between estuarine geometry and hydrodynamics to minimize data requirements (Volta et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…Vipindas et al, 2018 suggested that nitrification rate can increase 10-40 folds when encountering a low flushing rate of tropical estuary during pre-monsoon. Similarly, oxidation rate of organic matter would not be significantly affected by temperature, but by the river discharge magnitude (Gawade et al, 2018;Wu et al, 2013). Therefore, the factors controlling the intensity of biogeochemical processes will differ between the temperate and tropical systems.…”

Section: Introductionmentioning

confidence: 99%

Biogeochemical functioning of an urbanized tropical estuary: Implementing the generic C-GEM (reactive transport) model

Nguyen

Némery

Gratiot

et al. 2021

Science of The Total Environment

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Estuaries are amongst the most productive ecosystems of the land ocean continuum, but they are also under high anthropic pressures due to coastal urbanization. Too sparse observations have hindered the understanding of complex interactions between water quality and estuarine hydrodynamics and biogeochemical transformations. Until now, estuarine modelling studies have mainly focused on temperate estuarine systems in industrialized countries. This study investigates the responses of a tropical estuary to pollution load from a megacity (Ho Chi Minh City, Southern Vietnam) by applying a one-dimensional, biogeochemical estuarine model (C-GEM). The Saigon River Estuary flows through the megacity of Ho Chi Minh (HCMC) and is subject to episodic hypoxia events due to wastewater inputs from urban discharges. Good agreements are found between simulation outputs and observations for tidal propagation, salinity, total suspended sediment, and water quality variables in dry season in Saigon River Estuary. C-GEM reproduces the increases in ammonium, total organic carbon, phytoplankton and dissolved oxygen depletion in the urban section of the Saigon River as an impact of untreated wastewaters from HCMC. The steadystate version of C-GEM also reveals the formation of a pollutant cloud (30-km stretch) resulting from the combined effects of tidal fluctuation and low flushing capacity during the dry season. Furthermore, the quantification of the reaction fluxes simulated by the model demonstrates that nitrification is the main process removing NH 4 + from the Saigon River. For the first time in such a type of environment, our study demonstrates the effectiveness of C-GEM at unraveling the complex interplay between biogeochemical reactions and transport in a tropical estuary with a minimized data requirement. This is significant for tropical estuaries in developing countries, where intensive monitoring programs are rare and have thus been rarely the object of modelling investigations.

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Spatio-temporal variability in the sources of particulate organic carbon and nitrogen in a tropical Godavari estuary

Cited by 16 publications

References 62 publications

Carbon isotopic ratios of modern C₃ and C₄ vegetation on the Indian peninsula and changes along the plant–soil–river continuum – implications for vegetation reconstructions

Carbon isotopic ratios of modern C₃ and C₄ vegetation on the Indian peninsula and changes along the plant–soil–river continuum – implications for vegetation reconstructions

Carbon isotopic ratios of modern C3 and C4 vegetation on the Indian Peninsula and changes along the plant–soil–river continuum; implications for (paleo-)vegetation reconstructions

Biogeochemical functioning of an urbanized tropical estuary: Implementing the generic C-GEM (reactive transport) model

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Spatio-temporal variability in the sources of particulate organic carbon and nitrogen in a tropical Godavari estuary

Cited by 16 publications

References 62 publications

Carbon isotopic ratios of modern C3 and C4 vegetation on the Indian peninsula and changes along the plant–soil–river continuum – implications for vegetation reconstructions

Carbon isotopic ratios of modern C3 and C4 vegetation on the Indian peninsula and changes along the plant–soil–river continuum – implications for vegetation reconstructions

Carbon isotopic ratios of modern C3 and C4 vegetation on the Indian Peninsula and changes along the plant–soil–river continuum; implications for (paleo-)vegetation reconstructions

Biogeochemical functioning of an urbanized tropical estuary: Implementing the generic C-GEM (reactive transport) model

Contact Info

Product

Resources

About

Carbon isotopic ratios of modern C₃ and C₄ vegetation on the Indian peninsula and changes along the plant–soil–river continuum – implications for vegetation reconstructions

Carbon isotopic ratios of modern C₃ and C₄ vegetation on the Indian peninsula and changes along the plant–soil–river continuum – implications for vegetation reconstructions