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- Title
Agricultural Land‐Use Increases Carbon Yields in Lowland Streams of the Congo Basin.
- Authors
Drake, Travis W.; Baumgartner, Simon; Barthel, Matti; Bauters, Marijn; Alebadwa, Serge; Akoko, Nadine Bahizire; Haghipour, Negar; Eglinton, Timothy; Van Oost, Kristof; Boeckx, Pascal; Six, Johan
- Abstract
As the dominant mode of deforestation in the Congo Basin, shifting agriculture is expected to increase with the projected four‐fold population growth for the region by 2,100. To assess how this land‐use change will affect the export of carbon (C) to rivers in a typical lowland forest ecosystem, we studied paired watersheds near Kisangani, Democratic Republic of the Congo. Two streams, one draining an intact forest (Forest) and one draining an agricultural landscape (Ag), were gauged, equipped with sensors, and sampled fortnightly for one year. Annual average specific discharge was 1.4 mm d−1 (+76%) higher in the Ag compared to the Forest. Average annual dissolved organic C (DOC) and particulate organic C (POC) concentrations were 5.2 mg L−1 (+163%) and 1.3 mg L−1 (+81%) higher in the Ag stream, which, along with the higher discharge, resulted in 8.3 (+410%) and 2.4 g C m−2 yr−1 (+97%) larger C yields, respectively. Baseflow dissolved inorganic carbon, carbon dioxide, and methane yields were also higher in the Ag stream. Despite the higher yields of organic C (OC), the composition of OC did not differ significantly. Carbon to nitrogen ratios, along with isotopic signatures, revealed that both streams contained young, semi‐degraded organic matter derived from C3 vegetation. Correspondingly, biodegradable DOC (BDOC) proportions did not differ between the streams, although the Ag stream yielded more total BDOC. These results show that agricultural land‐use likely exports a greater proportion of Net Primary Productivity (NPP) to aquatic ecosystems, which may affect both C storage in soils and the proportion of gross PP that is ultimately respired. Plain Language Summary: Shifting agriculture, which is the main way forests are cleared in the Congo Basin, is expected to increase as the population grows. To see how this type of deforestation affects the amount of carbon that ends up in rivers, we studied two types of watersheds: one with only forest and one with mostly farms. We measured the water flow and carbon levels in streams draining these watersheds for a year. We found that the stream draining the farmed area had more water and more carbon compared to the forest stream. This means that more carbon from plants and soil was being washed into the farm stream. The carbon in both streams came from similar sources: partially broken‐down plants and topsoil that were recently grown or formed, respectively. The farm stream had a bit more carbon that could break down further once it entered the stream. These findings tell us that farming sends more plant matter and carbon into rivers. This could affect how much carbon is stored in the soil and how much goes back into the air. Key Points: Streams draining agricultural land‐use in Congo lowlands exhibited higher water and organic carbon yieldsThe composition and inferred sources of organic carbon did not differ between forest and agricultural streamsLow intensity shifting agriculture in Congo lowlands thus exports a high proportion of net primary productivity downstream
- Subjects
CONGO River Watershed; CONGO (Democratic Republic); AGRICULTURE; SHIFTING cultivation; WATERSHEDS; ISOTOPIC signatures; CARBON; PLANT-soil relationships; WATERSHED management
- Publication
Journal of Geophysical Research. Biogeosciences, 2024, Vol 129, Issue 3, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2023JG007751