Dual carbon isotope (δ13C-Δ14C) characteristics and carbon footprint in the spring-pond systems at the Puding Karst Water-Carbon Cycle Test Site

doi:10.13745/j.esf.sf.2022.1.35

Abstract

Abstract:

The dissolved inorganic carbon (DIC) and organic carbon (OC) transported to the ocean by rivers are affected by natural and anthropogenic factors. Understanding the influence of these factors on the age, source, and transformation of DIC and OC can help constrain global carbon budget and improve the assessments of natural and human impacts on the riverine carbon cycle. The present study uses dual carbon isotopes (δ¹³C-Δ¹⁴C) of DIC, particulate organic carbon (POC), and aquatic plants with traditional hydrogeochemical characteristics in the spring (groundwater) and spring-fed pond (surface water) systems at the Puding Karst Water-Carbon Cycle Test Site to identify the relavent carbon sources and carbon transformation processes. The results showed that (1) the Δ¹⁴C of DIC and POC in the spring-pond systems displayed the same trend, that is, the Δ¹⁴C value is lower in the spring water than in the pond water, indicating likely a younger CO₂ invasion of the pond system. (2) The changes in water chemistry and carbon isotope of pond water were controlled by different land use and aquatic plants. (3) The OC concentrations were significantly higher in pond water than in spring water, and the Δ¹⁴C values of POC were close to those of submerged plants and DIC (apparent ages of 3200-900 years). Such finding indicates that the POC in the pond water was mainly derived from aquatic photosynthesis, which involved old carbon (DIC)—produced by the weathering of carbonate rocks—as carbon source to generate new autochthonous OC (AOC) with negative Δ¹⁴C values and “old” apparent age. (4) The contribution percentage of AOC to POC in surface water was more than 75%. Meanwhile, the AOC flux in the spring-pond systems was between 250-656 t C km^-2 a^-1, and the surface water system of grassland contributed the most AOC and had the highest AOC flux relative to other land use. Such finding indicates the important role of primary production in the organic carbon cycle in shallow water controlled by submerged plants. Overall, the regulation of aquatic plant communities through land use adjustment in karst areas can have major impact on the increasing of carbon sink capacity in these areas.

Key words: dissolved inorganic carbon, particulate organic carbon, autochthonous organic carbon, dual carbon isotopes, carbon footprint, the Puding Karst Water-Carbon Cycle Test Site

CLC Number:

LI Dong, ZHAO Min, LIU Zaihua, CHEN Bo. Dual carbon isotope (δ13C-Δ14C) characteristics and carbon footprint in the spring-pond systems at the Puding Karst Water-Carbon Cycle Test Site[J]. Earth Science Frontiers, 2022, 29(3): 155-166.

Figures/Tables 8

Fig.1 Geographic location and layout of the Shawan Karst Water-Carbon Cycle Test Site, Puding, Guizhou. Basemap from China online national standard map service.

Table 1 Hydrochemical properties of spring and spring fed pond systems at the study sites (16:00,20th, Jul, 2015)

Table 2 Carbon isotopic compositions of DIC and POC in spring and spring fed systems under five land uses

Fig.2 Comparisons of Δ14C-δ13C characteristics between spring and spring-fed pond systems under different land uses. (a)δ13CDIC comparison; (b) δ13CPOC comparison; (c) Δ14CDIC comparison;(d) Δ14CPOC comparison

Fig.3 Relationships between Δ14Cplant, Δ14CPOC and Δ14CDIC in spring and sping-fed pond systems under different land uses

Table 3 Isotopic composition of aquatic plants in four experimental ponds

监测池	水生植物	δ¹³C_植物/‰	Δ¹⁴ $C D I C 泉水$ /‰	Δ¹⁴ $C D I C 池水$ /‰	Δ¹⁴C_植物/‰	植物年龄/a BP
P2	轮藻(Hydrilla verticillata)	-16.47	-358±2	-297±4	-293±3	2 897
P2	水绵(Spirogyra)	-8.14	-358±2		-298±2	2 963
P3	轮藻(Hydrilla verticillata)	-10.58	-359±3	-316±6	-317±3	3 261
P3	金鱼藻(Hornwort)	-13.44	-359±3		-314±3	3 220
P4	轮藻(Hydrilla verticillata)	-16.36	-124±1	-59±3	-120±1	935
P4	水绵(Spirogyra)	-6.72	-124±1		-118±1	903
P5	轮藻(Hydrilla verticillata)	-22.93	-291±2	-266±2	-264±2	2 544
P5	金鱼藻(Hornwort)	-16.34	-291±2		-267±2	2 570

Table 3 Isotopic composition of aquatic plants in four experimental ponds

监测池	水生植物	δ¹³C_植物/‰	Δ¹⁴ $C D I C 泉水$ /‰	Δ¹⁴ $C D I C 池水$ /‰	Δ¹⁴C_植物/‰	植物年龄/a BP
P2	轮藻(Hydrilla verticillata)	-16.47	-358±2	-297±4	-293±3	2 897
P2	水绵(Spirogyra)	-8.14	-358±2		-298±2	2 963
P3	轮藻(Hydrilla verticillata)	-10.58	-359±3	-316±6	-317±3	3 261
P3	金鱼藻(Hornwort)	-13.44	-359±3		-314±3	3 220
P4	轮藻(Hydrilla verticillata)	-16.36	-124±1	-59±3	-120±1	935
P4	水绵(Spirogyra)	-6.72	-124±1		-118±1	903
P5	轮藻(Hydrilla verticillata)	-22.93	-291±2	-266±2	-264±2	2 544
P5	金鱼藻(Hornwort)	-16.34	-291±2		-267±2	2 570

Fig.4 The autochthonous and allochthonous contribution percentages of organic carbon in the five experimental ponds under different land uses

Fig.5 The growth status of aquatic plants in the five experimental ponds under different land uses

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