Re-evaluation of Wetland Carbon Sink Mitigation
A new review of coastal and inland wetland carbon sink services reveals current mitigation concepts for greenhouse gas emissions and measurements are not what they seem. Accumulation of buried organic carbon is not a measure of carbon sequestration; stable organic carbon inputs require subtraction and are undervalued; and carbon mitigation from wetland restoration is less than their preservation.
The study was published in the journal Wetlands as a flagship Mark Brison Review, from Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (NIGLAS) in collaboration with Borneo Marine Research Institute (BMRI) Universiti Malaysia Sabah (UMS), and lead by the Institute for Marine and Antarctic Studies (IMAS) University of Tasmania (UTAS).
Associate Reseacher Dr John Barry Gallagher (IMAS) said that the sediment organic carbon accumulation down inland and coastal wetlands has always been regarded as a convenient means of measuring trends and average rates of sequestration over climatic scales. Wetlands, however, are open to organic inputs from catchments and adjacent water bodies. These can be labile and easily consumed or decomposed, and recalcitrant outside the carbon loop that is not consumed or decomposed.
Consequently, what is required from the sediment record is not the total organic burial, but the burial rate of what remains of the wetlands plant production from the amount of the labile organics inputs consumed, and the remains of those recalcitrants inputs, largely black or pyrogenic carbon. To estimate this we modified a general decomposition model to hindcast the original input rate and to project what remains for all organic sources after 100 years of burial.
For a mangrove and a seagrass ecosystem, we found that carbon accumulation was on average 33.5 and 7.2 times greater than their respective sequestration rates. We also noted that sequestration relative to its non-canopy replacement or alternative stable state is not included for voluntary or compliance carbon markets, instead, only the rate of loss and gain of organic stocks for wetlands likely be disturbed or restored. This limitation would otherwise undervalue the wetlands systems mitigation potential with one caveat: the rate of gain in sediment stocks for a restored system is similarly constrained as a mitigation service by consumption and decomposition of those external organic inputs.
Dr Gallagher says that the review is important from two standpoints. Firstly, natural carbon sequestration solutions require re-evaluation. This is required to avoid GHG emissions above their capacity or indeed reduce the ability to fulfil Nations’emission targets, as set by COP26. Secondly, the model provides a new Paleoecological tool. It has the potential to measure and predict how wetlands' ability to function as a carbon sink can change with both climate and catchment agricultural and industrial development from changes to government policy.
Paper link: https://link.springer.com/article/10.1007/s13157-022-01539-5
Estimating seasonal water budgets in global lakes by using multi-source remote sensing measurements
The seasonal change in lake water storage (LWSsc) reflect periodic fluctuations of the basin-scale water balance. However, the role of LWSsc in regulating the water budget at the global scale has not yet been investigated based on straight-forward observations. Quantifying LWSsc is necessary, especially under the context of global change. Available in-situ measurements of lake water levels and volumes are still scarce. Therefore, the Global Surface Water datasets of Joint Research Centre and multi-source satellite altimetry datasets through mathematical statistics methods are used in this study to address this issue. We estimate the LWSsc of 463 lakes and reservoirs worldwide with areas greater than 10 km2, which represent nearly 64% of the total global lake area and 93% of the total lake volume capacity. Results show that the global seasonal water storage variation of these examined water bodies is 1390.91 ± 78.91 km3, comprising 869.44 ± 67.35 km3 from lakes and 521.46 ± 41.11 km3 from reservoirs. The relatively large estimates of LWSsc are concentrated in North American and African basins. Among the watersheds, the seasonal fluctuations of lakes in the North American Lawrence basin make up the most substantial magnitude of 10.76% of the global LWSsc. The latitudinal direction zonality of LWSsc is relatively significant. The LWSsc is concentrated between 30° N and 60° N in the northern hemisphere and between the equator and 30° S in the southern hemisphere. Considering the geographic similarity and climatological zonality, the global LWSsc estimates are also extrapolated to other lakes without direct satellite altimetry observations on the basis of the average rate of the examined lakes distributed in the same Koppen-Geiger Climate Classification zones. The LWSsc is calculated with a consequence of 488.23 ± 14.72 km3 for these extrapolated lakes, indicating an estimate of 1357.67 ± 68.94 km3 for the LWSsc of the global natural lakes (>10 km2). This initial estimation of LWSsc at a global scale will greatly help the improvement of our understanding of the seasonal behavior of lakes and reservoirs in regulating global and regional water cycles and the contribution of terrestrial water storage to sea level rise.
CHEN Tan, SONG Chunqiao, KE Linghong et al. Journal of Hydrology.doi.org/10.1016/j.jhydrol.2020.125781
Data construction and spatiotemporal trend attribution of runoff over the African Continent (1981–2016)
Due to global climate change, coupled with the increase in population, growth in water withdrawals, expansion of farmland area and reduction of forest, the surface runoff process in Africa has undergone major changes and extreme hydrological events have been occurred frequently, which has caused greater impact on the production and life of the people.
In order to systematically understand the response of runoff trends to climate change and human activities, the research team of Researcher Prof. Liu Yuanbo from the Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences (CAS) constructed improved monthly runoff data for the African continent from 1981 to 2016 based on the river discharge data from 535 gauging stations using a revised runoff curve number, downscaling and interpolation statistical methods. Then, monthly and annual runoff data, climate data (precipitation and temperature) and human activities (farmland expansion and water withdrawal) were used to assess runoff trend responses to climate change and human activities in Africa during 1981–2016. Related results were published in the Journal of Hydrometeorology.
Analysis of runoff trend responses to climate change and human activities revealed that land cover changes contributed more (72% a-1) to the observed net runoff change (0.30% a-1) than continental climate change (28% a-1). These contributions were results of cropland expansion rate of 0.46% a-1 and precipitation increase of 0.07% a-1. The annual runoff trends were 0.21% a-1 in the tropical region, 0.16% a-1 in the temperate region and 0.91% a-1 in the arid region. The runoff increase in the tropical region was fully caused by human activities, with a contribution to net runoff increase of 160% a-1 due to cropland expansion by 0.53% a-1. Climate change was responsible for an increased runoff in the temperate and arid regions, with contributions of 102% a-1 and 117% a-1, respectively.
Land cover change was the dominant cause of increased annual runoff, with trends ranging from 0.06% a-1 to 1.38 % a-1 in 7 of the 25 major river basins, including the Africa–Indian Ocean Coast, Limpopo, Shebelle–Juba, Volta, Gulf of Guinea, Africa–East Central Coast and Madagascar due to cropland expansion trends (0.02% a-1 – 1.03% a-1). The Orange, Namibia–Coast, Africa–Red Sea–Gulf of Aden Coast and Zambezi basins experienced runoff reduction (-0.15% – -1.88%) due to the increase in water withdrawal (1.80% a-1 – 3.23% a-1).
Climate change was the dominant factor that induced annual runoff change in 14 of the 25 major basins, where 11 basins (Africa–South Interior, Africa–West Coast, Nile, Angola–Coast, Rift Valley, Africa–North West Coast, Niger, Mediterranean South Coast, Africa–North Interior, Lake Chad and Senegal) had runoff increase (0.08% a-1 – 1.76% a-1) due to precipitation increase (0.15% a-1 – 0.73% a-1). Three basins (South Africa–West Coast, South Africa–South Coast and Congo) experienced runoff reduction (-0.89% a-1 – -0.02% a-1) due to precipitation decrease (-0.11% a-1 – -0.55% a-1) and temperature rise (0.07% a-1 – 0.17% a-1).
The performance and simplicity of the statistical methods used in this study could be useful for improving runoff estimations in other regions with limited streamflow data. The results of the current study could be important to natural resource managers and decision makers in terms of raising awareness of climate change adaptation strategies and agricultural land-use policies in Africa.
Pollution characteristics of persistent and toxic organic substances in lakes of Tanzania
Due to the inadequate control of Persistent and Toxic Organic Substances (PTOS) in Tanzania, they are still many ways to transport into the lake environment, to threaten the lake ecology safety and human health.
To understand the status of PTOS pollution in Tanzanian lakes, Prof. Zhang Lu from the Joint Research Station for East African Great Lakes and Urban Ecology (affiliated to Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences) led a joint group with Tafiri scientiest in early 2020 to conduct a field survey on PTOS pollution in East African lakes.
The study of 18 lakes in Tanzania shows that the distribution of PTOS has large spatial variations. Among the lakes, the PTOS level in Lake Jipe, Mabayani Reservoir, Lake Duluti and Lake Hombolo was relatively higher, while was relatively lower in Lake Chala, Lake Small Momela, Lake Babati, Lake Singida and Lake Kindai. Overall, the pollution levels of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs) in Tanzania lakes are relatively lighter compared to lakes worldwide.
Among the four major types of PTOS pollutants in Tanzania lakes, phthalate esters (PAEs) pollution is the more worthy of attention. Source identification shows that phthalate esters (PAEs), PAHs, HCHs and Methoxychlor have obvious watershed input characteristics. A multi-index comprehensive scoring method based on the measured concentrations of pollutants, the inherent properties of compounds (lipophilicity and hydrophobicity, structure-activity relationship), and lake ecological risks and health risks was proposed. Based on this method, a list of precedent-controlled PTOS pollutants (8PAEs,6 PAHs, 7 OCPs and 5 PCBs) for Tanzania lakes was built.
It was concluded that PAEs were the priority pollutants for drinking water safety and ecosystem health for Tanzania lakes. Therefore, Tanzania should control the production, use and emission of PAEs, especially around the lake areas, in order to reduce the impact of PTOS on lake water ecology.
A list of precedent-controlled PTOS pollutants (8PAEs,6 PAHs, 7 OCPs and 5 PCBs) for Tanzania lakes