A new global water chemistry database and long-term time series of carbon fluxes
Contact: Gibran Romero-Mujalli, Mingyang Tian, Jens Hartmann
Rivers transport matter from land to the ocean, act as an important link between terrestrial and marine ecosystems and play a significant role in the biogeochemical cycle of elements. River biogeochemistry is susceptible to human and natural perturbations and each watershed has characteristics that can be specific for its region. Previous studies attempted to quantify total nutrient loads from the biggest rivers. The temporal variability, however, was not included in these global budgets. Moreover, the contribution of small rivers and groundwaters remained to be quantified. The lack of a homogeneous river chemistry dataset makes it difficult to quantify biogeochemical budgets and to validate global river models. This is partly because the monitoring of water chemistry of most rivers is still a challenging task and current global datasets have limitations on reporting only one water type, the amount of variables considered, or the way the data is organized. To overcome these challenges, we developed the GLOWACHEM (Global Water Chemistry) database to provide an accessible and consistent archive for water quality and water quantity (e.g. water levels) data for different water types (rivers, groundwaters, lakes, springs, estuaries, etc.). It consists of an integration of current global datasets, like GLORICH and GEMStat (Hartmann et al., 2014; UN Environment Programme, 2017), national datasets and data from publications. All information is spatially and temporally tagged. Currently, the data contains more than 100,000 river stations distributed in 96 countries, representing the biggest water chemistry dataset built at the moment.
We implemented the GLOWACHEM database to study the Elbe catchment to understand the temporal and spatial change of carbon fluxes, and to determine the human impact through the parameters of nitrogen and phosphorus, etc. In this study, we conclude that the riverine CO2 emission is decreased with the improvement of water qualities since 1990s. This is because changes in wastewater treatment have largely reduced nutrient loads, impacted the quality of transported carbon to the ocean and changed the CO2 evasion from the surface water to the atmosphere. Riverine processes affecting the internal carbon cycle were changed by water management decisions. In the context of global carbon mitigation, our research in the Elbe River basin provides a new idea to reduce riverine CO2 emissions by strengthening water quality governance especially in highly polluted rivers today.
References:
Hartmann, J., Lauerwald, R., Moosdorf, N. (2014). A brief overview of the GLObal RIver CHemistry Database, GLORICH. Procedia Earth and Planetary Science, 10, 23–27.
United Nations Environment Programme (2017). GEMStat database of the Global Environment Monitoring System for freshwater (GEMS/Water) Programme. International Centre for Water Resources and Global Change, Koblenz. Accessed 5 December 2019. Available upon request from GEMS/Water Data Centre: gemstat.org