1. Water sampling campaigns and laboratory analysis (Dr. Duong TT; Dr. Ho TC; BSc Nguyen TBN; BSc Vu DA and MSc Nguyen TMH):
River water quality and carbon contents
Due to the lack of a complete water quality data base of the Red River basin, monthly field campaigns have been organized at ten gauging stations Yen Bai, Vu Quang, Hoa Binh, Son Tay, Hanoi, Gian Khau, Nam Dinh, Truc Phuong, Ba Lat, Quyet Chien gauging stations of the Red River system from August 2012 to December 2014.
Figure: Sampling sites for water quality of the Red River
Water samples are immediately filtered through 47-mm Whatman GF/F filters (0.7µm pore size) and stored at 40C when transporting back to the laboratory. Chlorophyll a, phytoplankton and periphytic diatoms, coliforms are determined at the IET laboratory. Major ions (K+, Na+, Ca2+, Mg2+) are measured by atomic absorption spectroscopy (AAS) method. Various carbon species (mainly DIC, DOC and POC) and nutrients (N, P and Si) are determined at the INPC laboratory by the APHA methods (APHA, 1995). CH4 and CO2 concentrations are measured by using a gas chromatograph (GC, Agilent) equipped with a flame ionization detector (FID) and with a thermal conductivity detector (TCD), respectively (Figure)
Figure : In situ measurement and laboratory analysis
Point and non-point sources
More than 100 agricultural and industrial wastewater samples in both dry and rainy season were taken and analyzed for the variables as presented above.
Some first results of the water quality of the Red River system and of channel irrigation in an agricultural region in Hanoi were analyzed for the Journal of Vietnamese Environment (Germany), Vietnam Journal of Biology and the Vietnam Agriculture and Rural development. These results are also used for modeling approach About 100 agricultural and industrial wastewater samples in both dry and rainy season have been taken and analyzed.
Figure Industrial and agricultural wastewater sampling.
2. Measurement of carbon exchange/emission (Dr. Cyril Marchand; Dr. Le TPQ; Dr. Ho TC; MSc Nguyen TK; BSc Nguyen TBN and BSc Vu DA):
A new participant, Dr Cyril Marchand from IRD, who is an expert in carbon cycling, contributed to measurements at five sites selected from the Red River upstream to downstream in wet and dry seasons in 2014, by different methods: calculation of CO2 fluxes either using a floating chamber connected to an IRGA, or determining pCO2 within the water column using an equilibrator (Figure 4). In both methods, the first results show that CO2 flux from the Red river network is characterized by significant spatial and seasonal variations. In the wet season (September 2014) the higher CO2 fluxes were observed than the dry season (November 2014). The final results of these measurements are synthesized for a peer-reviewed paper.
Figure : Measurement of carbon exchange at the water-air interface
3. Collection of available dataset from different sources (Prof Zhou Y., Dr Lu XX, Dr Le TPQ, Mrs Tran TBN, MSc Nguyen TMH):
The long-term discrete existing data (since the 1960s) of the Red River, including water quality, land use, population, agricultural and industrial development, hydrological management, and meteorological data have been collected from different sources, such as previous scientific research project, data published in the national books, reports or data from different official agencies …
+ To collect and synthesize the long-term discrete existent data (since the 1960s) of the water quality, industrial and agricultural wastewater, meteorology, hydrology, population and landuse of the whole Red River system in both China and Vietnam terrain;
+ To collect the data for prospective scenarios: climatic data (air temperature and rainfall); new reservoirs implementation, land use with intensive agricultural practices, industrial activities, population and urbanization increase of the basin in the 2050 horizon.
The data collection are used for
- modeling validation for describing the carbon transfer and carbon emission under the pressure of human activities and natural conditions in the Red River basin in the past, present and perspective scenarios
- calculating carbon emission and flux from the Red River.
4. Modeling application:
Assess the river water quality, to estimate C emission from the Red River; to characterize and identify the variables (geology, rainfall, reservoirs, land use, agriculture, population,…) controlling C fluxes and emission from this river (Dr. Duong TT; MSc Nguyen TMH; Dr. Le TPQ, Dr Lu XX; Dr Ho TC; Prof. Zhou Y).
In order to make use of the SENEQUE/RIVERSTRAHLER model for calculating faecal contamination at the scale of the whole Red River drainage network, data available in small rivers draining small watersheds with different land use were gathered and allowed to define the diffuse sources to surface water. Also, data on wastewater, with different levels of treatment, were used to characterize point sources. These constraints together with results from laboratory experiments (e.g. faecal bacterial mortality, proportion of attached vs. free bacteria, …) are used for the implementation of the model. The first results of the model show a reasonable agreement between the calculated and observed values at the monitored stations. The final results of these measurements and modelling approach is published for two peer-reviewed papers.
Figure: Organic matter input the SENEQUE/RIVERSTRAHLER Model
A similar approach is conducted in parallel to monitor and model dissolved (DOC) and particulate (POC) organic carbon. The application of the model provides also consistent results compared with the measurements at the monitored stations.
We continue to apply of the SENEQUE/RIVERSTRAHLER model for water quality of the Red River system focusing on the concept of autotrophy/heterotrophy as an indicator of CO2 budget in the Red River drainage network. In particular, the measurements of CO2 emissions in the different sectors of the river system might be compared with the budget of production and consumption of organic carbon as represented by the model. Such a dual approach of the ‘boundless carbon cycle’ in a large drainage network (modeling of in-stream carbon cycle related microbial activities and measurement of CO2 emission) would be a first achievement in this very timely field of research.
The simulation by the model of the current distribution of major forms of the carbon (form dissolved to particulate, from organic to inorganic) has been validated for the present situation, then, the past and prospective scenarios is explored.
The final results of these measurements and modelling approach is submitted for a peer-reviewed paper in Bioeochemistry Journal.