Terrestrial Organic Matter Inputs Modulate Methane Emissions from a Mega-Reservoir.

Reservoirs are hotspots for methane (CH) emissions. However, to date, the effects of terrestrial organic matter (OM) input and degradation on CH emissions from large reservoirs remain largely unknown. From May 2020 to April 2021, we conducted monthly sampling campaigns at 100 sites in Lake Qiandao (580 km), a mega-reservoir in China, and made monthly vertical profile observations from March to September 2023.

Inflow-modulated inputs of dissolved organic matter fuel carbon dioxide emissions from a large hyper-eutrophic lake.

Terrestrial dissolved organic matter (DOM) is potentially reactive and, upon entering lake ecosystems, can be readily degraded to low-molecular-weight organic matter and dissolved CO. However, to date, there has been limited research on the links between long-term variation in the composition of DOM and CO emissions from lakes. Lake Taihu is a large, shallow, and hyper-eutrophic lake where DOM composition is strongly influenced by inputs from the rivers draining cultivated and urbanized landscapes.

Low NO and variable CH fluxes from tropical forest soils of the Congo Basin.

Globally, tropical forests are assumed to be an important source of atmospheric nitrous oxide (NO) and sink for methane (CH). Yet, although the Congo Basin comprises the second largest tropical forest and is considered the most pristine large basin left on Earth, in situ NO and CH flux measurements are scarce. Here, we provide multi-year data derived from on-ground soil flux (n = 1558) and riverine dissolved gas concentration (n = 332) measurements spanning montane, swamp, and lowland forests.

Fire-derived phosphorus fertilization of African tropical forests.

Central African tropical forests face increasing anthropogenic pressures, particularly in the form of deforestation and land-use conversion to agriculture. The long-term effects of this transformation of pristine forests to fallow-based agroecosystems and secondary forests on biogeochemical cycles that drive forest functioning are poorly understood. Here, we show that biomass burning on the African continent results in high phosphorus (P) deposition on an equatorial forest via fire-derived atmospheric emissions.

In-depth analysis of NO fluxes in tropical forest soils of the Congo Basin combining isotope and functional gene analysis.

Primary tropical forests generally exhibit large gaseous nitrogen (N) losses, occurring as nitric oxide (NO), nitrous oxide (NO) or elemental nitrogen (N). The release of NO is of particular concern due to its high global warming potential and destruction of stratospheric ozone. Tropical forest soils are predicted to be among the largest natural sources of NO; however, despite being the world's second-largest rainforest, measurements of gaseous N-losses from forest soils of the Congo Basin are scarce.

Century-long apparent decrease in intrinsic water-use efficiency with no evidence of progressive nutrient limitation in African tropical forests.

Forests exhibit leaf- and ecosystem-level responses to environmental changes. Specifically, rising carbon dioxide (CO ) levels over the past century are expected to have increased the intrinsic water-use efficiency (iWUE) of tropical trees while the ecosystem is gradually pushed into progressive nutrient limitation. Due to the long-term character of these changes, however, observational datasets to validate both paradigms are limited in space and time.

Land-use controls on carbon biogeochemistry in lowland streams of the Congo Basin.

The flux and composition of carbon (C) from land to rivers represents a critical component of the global C cycle as well as a powerful integrator of landscape-level processes. In the Congo Basin, an expansive network of streams and rivers transport and cycle terrigenous C sourced from the largest swathe of pristine tropical forest on Earth. Increasing rates of deforestation and conversion to agriculture in the Basin are altering the current regime of terrestrial-to-aquatic biogeochemical cycling of C.

Mobilization of aged and biolabile soil carbon by tropical deforestation.

In the mostly pristine Congo Basin, agricultural land-use change has intensified in recent years. One potential and understudied consequence of this deforestation and conversion to agriculture is the mobilization and loss of organic matter from soils to rivers as dissolved organic matter. Here, we quantify and characterize dissolved organic matter sampled from 19 catchments of varying deforestation extent near Lake Kivu over a two-week period during the wet season.

Increasing Alkalinity Export from Large Russian Arctic Rivers.

Riverine carbonate alkalinity (HCO and CO) sourced from chemical weathering represents a significant sink for atmospheric CO. Alkalinity flux from Arctic rivers is partly determined by precipitation, permafrost extent, groundwater flow paths, and surface vegetation, all of which are changing under a warming climate. Here we show that over the past three and half decades, the export of alkalinity from the Yenisei and Ob' Rivers increased from 225 to 642 Geq yr (+185%) and from 201 to 470 Geq yr (+134%); an average rate of 11.

High fire-derived nitrogen deposition on central African forests.

Atmospheric nitrogen (N) deposition is an important determinant of N availability for natural ecosystems worldwide. Increased anthropogenic N deposition shifts the stoichiometric equilibrium of ecosystems, with direct and indirect impacts on ecosystem functioning and biogeochemical cycles. Current simulation data suggest that remote tropical forests still receive low atmospheric N deposition due to a lack of proximate industry, low rates of fossil fuel combustion, and absence of intensive agriculture.

Ancient low-molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw.

Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere.