Anh Duo, Trinh

Leng, Melanie

McGowan, Suzanne

Panizzo, Virginia

Roberts, Lucy

Salgado, Jorge

Smith, Andi

Thu Nga, Do

Vane, Christopher

NERC Open Research Archive

RESEARCH SUMMARYWater quality in riversof the Red River DeltaSuzanne McGowan, Do Thu Nga, Trinh Anh Duc,Virginia Panizzo, Jorge Salgado, Lucy Roberts,Melanie Leng, Andi Smith, Christopher VaneHANOICovers anestimated14,300km2Home to23% ofVietnam’spopulationHong (Red) RiverDay RiverIn the Red River Delta depletion andpollution of groundwater resources isincreasing future reliance on surfacewaters from rivers. Good river waterquality is vital for regional watersecurity and for safeguarding foodproduction in the “rice-bowl”of northern Vietnam.Since 2018, researchers from Vietnamand the UK have been collaborating toinvestigate water quality in rivers acrossthe Red River Delta. The findings identifyhydrological characteristics, pollutionhotspots and help to understandhow water quality links withgreenhouse gas production.Rice farming is widespreadacross the deltaIncludes the city of Hanoiwhich is growing rapidlyRiver water quality monitoringhas been conducted for 20 yearsThac Ba (in 1963) and Hoa Binh (in 1988) damscreated reservoirs upstream of the deltaDrainage patterns heavily modified byagriculture and infrastructure developmentVIETNAMLAOSCHINAAssessment of water qualityWater quality assessment involves the measurement ofphysical, chemical and biological features of waters to allow theircomparison with standards defined by regulatory bodies. For theRed River Delta, this is benchmarked by the National technicalregulation on surface water quality (QCVN 08-MT:2015/BTNMT ).Dissolved oxygen (DO) is a key measure of water health;without oxygen nothing can live in rivers and low levels mayindicate organic pollution issues. DO measured each month in2018 and 2019 at 21 sites along the Red and Day Rivers fromthe reservoirs in the uplands to the coast were mostly in classB2 (moderately poor) or lower when assessed by theVietnamese DO standards. Some sites in the heavily urbanizedarea around Hanoi had very lower water quality (below classB2). Only 13% of samples achieved Class A for DO.Monthly measurements of DO across the Day andRed Rivers illustrate the difficulty in interpreting single watermeasurements. Seasonal variability in DO means that thetiming of sampling could have a major impact on how thewater is classified. Water quality would be classified as betterduring the wet than the dry season. Regular monitoringidentifies periods when water quality issues are mostprevalent, and identifies times when low DO could havedetrimental implications e.g. for aquatic life or for changingthe cycling of metals and nutrients.For other chemical variables between 2018 and 2019, theVietnamese limits for nitrite were exceeded in more than halfof the samples, and one third were placed in class B2 orlower for ammonium. In contrast, 99% and 95% of samplesfor nitrate and phosphate respectively achieved good (A class)status. 37% of nitrogen is present in the reduced form ofammonium and nitrite, but the oxidized form (nitrate) isdominant in most samples.Recommendation: Water quality should be conducted atleast monthly over the annual water cycle. Seasonal variabilitycan provide important information for hydrology and waterquality management. The most polluted river sites aroundHanoi should be a priority for water quality improvement.Stable isotopes for tracing theRed River water cycleThe flat relief and intensive water regulation via dams, sluicesand dikes poses a challenge for hydrological monitoring usingconventional methods. Stable isotopes can offer a rapid andcost-effective way to evaluate regional hydrology.Rainwater falling on the Red River Delta has a stable isotopesignature that varies seasonally, dependent on source,temperature and amount of rainfall. This distinctive seasonalpattern can be used to calculate the proportion of rainwatersupplying the main river waters during different seasons.In the Day River, stable isotope calculations indicate thataround 50% of the water derives from “young rainfall” i.e.rainfall no more than 3 months old (Trinh et al 2020). This ismuch higher than the global average of one-third and reflectsa catchment that is mostly saturated, where water passage isaccelerated by artificial flow paths such as rice paddy, dikes,and hard urban surfaces.In the Red River, only 20% of the river water is classified as“young” (Nguyen et al 2021). The presence of reservoirs in thecatchment slows down the water residence time, meaningthat it takes longer for water to pass through the catchment.Due to the larger contribution of young water in the Day River,the river water supply could be more susceptible to changesin rainfall delivery; both tropical storms and droughts arepredicted to increase in the future. Longer water residencetimes in the Red River could mean that dilution of pollutants ismore limited in this river.Recommendation: The Day River drainage system shouldbe upgraded to allow faster water release during stormsand infrastructure for water storage put in place to mitigateagainst flooding.Stable isotopes in waterWater consists of one oxygen and twohydrogen atoms. Isotopes are a form of anelement with one or more extra neutrons.Stable isotopes do not decay (they are notradioactive). Distinctive isotope signals canbe incorporated into water depending on theabundance of the heavier isotopes, wetherefore have a tracer of water if wemeasure the isotope ratios of water.OH1H1OH21816H2GULF OFTONKINIntroductionWATER QUALITY IN THE RED RIVER DELTA 3DAY RIVER50% YOUNG 20% YOUNG 33% YOUNGRED RIVER GLOBAL AVERAGE%Water from 'young' rainfallProject supported by:Authors: Suzanne McGowan, Do Thu Nga, Trinh Anh Duc, Virginia Panizzo,Jorge Salgado, Lucy Roberts, Melanie Leng, Andi Smith, Christopher VaneUPSTREAM(Thac Ba / Hoa Binh)Dissolved oxygenHIGH QUALITYWATER STANDARDSA2A1B1B2LOW QUALITYWATER STANDARDSDOWNSTREAM(Nhu Tân / Ba Lat)Identifying sources ofnitrogen pollutionDissolved nitrate contains both oxygen and nitrogen isotopes.Distinctive isotope signatures can be found in nitratedepending on its provenance, we can therefore find thesource of nitrate pollution. We demonstrate the effectivenessof applying stable isotope approaches from nitrate.In the Day River oxygen and nitrogen isotopes act as a tracerwhich enables the assessment of provenance of the nitratepollution (Luu et al 2020). The nitrate isotope data show howbiological activities drive the isotopic compositions and thesechange along the Day River course. Inorganic urea fertilizer isa major source of nitrate, along with urban sewage, showing aclear impact especially the downstream sections especiallyafter the confluence with the Nhue River, the main riverdelivering water from Hanoi City. Further down the river afterthe confluence with the Nhue River, the proportion of naturalinputs (soil/ground and upstream Red River inflow sources) ofnitrate contribute < 50% of the pollution nitrate load. The highproportion of nitrate from anthropogenic activities in the DayRiver is apparent.Recommendation: The application of inorganic fertilizers topaddy fields in the Day River area should be re-evaluated tomoderate application when this is an option. This isparticularly important when fertilization practices are takingplace in the rainy season, where rapid and large scale deliveryof nitrate is demonstrated.Nitrogen use efficiency in theRed River DeltaAgriculture accounted for 14.85% of Vietnam’s grossdomestic product (GDP) in 2021. The Red River Delta (RRD)is the second biggest rice bowl in Vietnam. About 47% oflanduse is agricultural and aquacultural land, of this, 90% isused for annual crops. About 80% of the delta dwellers areengaged in the agricultural sector. Pollution of water sourceswith nitrogen from chemical fertilizers is a major threat toenvironmental and human health in the delta.Recommendation: Improvement of nitrogen useefficiency is needed.Our project developed a Material Flow Analysis model (MFA)model to quantify loads of nitrogen (N) pathways from humansto the environment in the RRD and then identify potentialpollution sources or intervention points (Do et al 2019).The MFA model will, therefore, provide interdisciplinaryevidence to support decision-making.The MFA model can quantify loads of nitrogen (N) pathwaysfrom humans to the environment in the RRD and identifypotential pollution sources or intervention points (Do et al 2019).RRD farmers use animal manure together with chemical fertilizersin rice production. More than half of the N load to the paddy fieldis from chemical fertilizers. Most rice farmers apply chemicalfertilizers above the recommended rates with the hope ofincreased crop yield. However, fertilizer use efficiency is low ataround 60% for N. Excess fertilizer enters soils and waters bypercolation and runoff, causing air, water, and soil pollution.Changes in environmental policy and farming practice, forinstance reductions in applied chemical fertilizers, the reuse ofanimal manure for producing biogas and bio-slurry, and thereuse of sludge from aquaculture and onsite sanitation systemscan be explored with the MFA model to predict their effects onnitrogen pathways and loads in the RRD.Recommendation: The MFA model is a useful platformto quantitatively determine how changes in agriculturaland domestic practices will change the flows of nitrogenin the environment. Scenarios from the MFA can help todevelop policies on environmental management, raiseawareness and change the behaviors of the local deltadwellers on resource efficiency.Pollutants in the suspendedsediments of riversMeasurements in the Red River Delta show that there has beena long-term decline in suspended sediment of the rivers sincethe installation of dams to create reservoirs at Thac Ba and HoaBinh in the late 1980s. Suspended sediment can be importantin influencing transport and deposition of pollutants becausesome elements, including metals, bind easily to suspendedmaterial carried in river clays, silts and organic matter.Analysis of suspended matter in sediments of the Day and RedRivers shows high pollution by chromium (Cr) and arsenic (As)which exceed the recommended Vietnamese limits (QCVN43:2017/BTNMT) in most sites across the Red River Delta.Cr and As concentrations of suspended sediments are higherduring the wet season and further emphasized during periodsof intensive rainfall and storms such as in 2018. This indicatesthat transport of polluted sediment from the catchment to theriver is a source of As and Cr contamination and that thiscould get worse as storms intensify in the future.Other pollution hotspots occurred around Hanoi where waste-waters entering the Day River via the Nhue River led to highconcentrations of phosphorus, copper, chromium and arsenic.Flux calculations indicate that a significant proportion ofmetal elements are deposited within the delta environment,highlighting the role of the delta in protecting coastal watersfrom contamination. However, this accumulation over thelonger term means that deltaic sediments could poseincreasing environmental and health risks in the future.Salinisation of waters due to sea level rise and changes in theorganic matter concentration of river waters can strengthen thebinding of metals to sediments, adding another factor to considerin understanding metal transport from the land to coastal areas.Recommendation: The elemental composition of suspendedsolids in the RRD should be monitored, with a focus onelements such as Cr and As that exceed current regulatorylimits. Further research into how these metals pass betweendissolved and particulate forms in this river delta is necessary.How and why do carbon dioxideconcentrations vary in RRD waters?Large tropical rivers are dynamic and shifting CO2 sources.They receive large quantities of terrestrial organic carbon,which often can be degraded and respired elevating thepartial pressure of CO2 (pCO2) in waters. We calculated thepCO2 of river waters along the Day and Red Rivers upstreamand downstream of Hanoi City.In densely populated areas around Hanoi City the partialpressure of CO2 in river waters was higher than in other partsof the river. This was due to the receipt of sewage wastes intothe water containing organic matter which produces CO2when it decomposes. Channelisation and water demands ofrivers in urban areas lead to more stagnant waters which,together with sewage-derived nutrient inputs create theconditions for cyanobacteria to bloom. Blooms ofcyanobacteria produce more organic matter and reinforce thecycle for CO2 production. Cyanobacteria blooms can alsoproduce toxins- a “harmful algal bloom” (HAB), furtherdegrading water quality and posing risks for water users.In the future, increases in water demands to support urbandevelopment could intensify stagnant waters in urban rivers,which will likely strengthen the riverine CO2 capacities of theRRD and the risk of potential associated HABs.Recommendations: Increases in pCO2 and HABsrisks could be mitigated through active watermanagement to increase water flows in urbanrivers during dry periods.WATER QUALITY IN THE RED RIVER DELTA 5Developing analytical capacity in VietnamThe isotope analysis described above were conducted atthe British Geological Survey in the UK and the VietnamAtomic Energy Institute (VINATOM) in Hanoi. VINATOM hasa suit of laboratories equipped for water isotope analysesvia Isotope Ratio Mass Spectrometey (IRMS), it also has anElemental Analyser Isotope Ratio Mass Spectrometer(EA-IRMS) for carbon and nitrogen isotope analysis and isprocuring a Gas Chromatrographic- Isotope Ratio MassSpectrometer (GC-IRMS) for compound specific stableisotope analysis. With the help of the International AtomicEnergy Agency (IAEA) VINATOM is setting up a standardstorage facility providing working standards samples forwater isotope analysis.WATER QUALITY IN THE RED RIVER DELTA4Above limits for bothfresh and brackish waterAbove thelower limitWithin 10mg/Kg(or 1 mg/Kg for Cd)Below limits for bothfresh and brackish waterBelow analyticaldetection limitNo dataARSENIC CONCENTRATIONDRYDay RiverSeasonRed RiverDRYWETWETURBANIncreased pCO2, HABsand nutrients in urban areasDAMDAMO2 declines inurban areasRURALRiver Soil / GroundwaterMarketOnsite sanitation systemBiogas PitLatrineSepticTankLivestockPig Poultry CattleAtmosphereRice FieldFish pondGreywater, ExcretaFoodCommercialfeedsCommercialfeedsMeat, eggsChemical fertilizersRunoffRunoffIrrigationManureManureManureLeachateBlackwaterRiceSludgeHouseholdsOrganic pollutionThe sediment quality of the Red River and associated urbanwaterways of Hanoi have been evaluated by comparingorganic pollutants in surface samples from soils, bank andchannel and shallow sediment cores.Emerging contaminants such as antibiotics, anti-epileptics,anti-inflammatories and hormones were 3 to 15 times higherin samples from urban rivers compared to those from theRed River. The anti-inflammatory, ibuprofen was the mostabundant emerging contaminant and was present at higherconcentrations than many other Vietnamese Rivers.Environmental forensics using fecal steroid sewage markercompounds, revealed that urban waterways containappreciable amounts of untreated sewage which couldimpact environmental health. Conversely, banned legacypolychlorinated biphenyls (PCBs) were below internationalsediment quality criteria and therefore not a likely to harmbiota or humans. Fossil fuel hydrocarbons derived polyaromatichydrocarbons (PAH) and petroleum hydrocarbons were presentat moderate concentrations but distributed across the entireRed River system. Sediments from the urban waterways ofHanoi contained appreciable amounts of alkylated-PAH whichindicated manufactured oil/crude oil inputs (e.g. mopedengines) whereas those from main Red River were mainlydominated by parent forms originating from vehicular exhaustor soot from power stations. Microtox solid-phase test bioassaysuggested that out of 149 sediments evaluated 4 were acutelytoxic, 11 moderately toxic and 134 non-toxic.Recommendation: Increasing emerging contaminants(pharmaceuticals) and sewage could be mitigatedthrough greater waste treatment processing.Hydrocarbon pollution requires greater controlon urban run-off into waterways and rivers.Sediment retention and water qualityin Hoa Binh reservoirHoa Binh Reservoir is located in the upper reaches of theRed River Delta and was established by damming in 1989.Sediment trapping in this site and other reservoirs has beenimplicated as being important for reductions in sedimentsupply to the delta and in modifying nutrient availability bytrapping phosphorus in the sediments. Two sediment coreswere collected from the centre of the reservoir to betterunderstand how this 9 billion m3 water body functions andchanges the waters downstream.Dating of the reservoir sediments using radioactive lead isotopesindicates a rapid sedimentation rate of around 2 g/cm-2 yr-1.Carbon content of the sediments is mostly between 1.5% to2.5%, which suggests that a large amount of carbon ismineralized before it reaches the sediments. The C:N ratioswhich are all lower than 10 suggest the organic matter in thesediments derives mostly from algae produced in the reservoir.Therefore, we can infer that the reservoir is probably not a sink forcarbon delivered from the upstream catchment since much ofthis is mineralized before it is trapped in the sediments.Down-core measurements indicate a possible increase in lakeproductivity over the past decade. This is indicated by a shiftin the composition of carbon stable isotopes, and indicationsthat the types of algae have changed. For example, remainsof diatoms (silica-cased-algae) show a shift towards thenutrient-loving Aulacoseira granulata in recent sediments,and chlorophyll and carotenoid pigments from a range ofalgae increased. There is also an increase in microcystintoxins that derive from cyanobacteria. Together, thesechanges indicate that the reservoir has probably becomemore productive over the past 10 years.Recommendation: The rate of sediment infilling doesnot pose a short-term concern for infilling of the reservoir,but monitoring of the reservoir should be conducted toassess eutrophication.ReferencesTrinh, A.D., Do, T.N., Panizzo, V.N., McGowan, S. and Leng, M.J. (2020). Usingstable isotopes to estimate young water fractions in a heavily regulated, tropicallowland river basin. Hydrological Processes, 34(22), pp.4239–4250.Duong TT, Nguyen HY, Le TPQ, Nguyen TK, Tran TTH, Le ND, Dang DK, Vu TN,Panizzo V, McGowan S (2019) Transitions in diatom assemblages and pigmentsthrough dry and wet season conditions in the Red River, Hanoi (Vietnam). PlantEcology and Evolution 152(2): 163-177.Do TN, Tran VB, Trinh AD, Nishida K. Quantification of nitrogen load in a regulatedriver system in Vietnam by material flow analysis. Journal of Material Cycles andWaste Management. 2019 Jul;21(4):974-83.Luu, T.N.M., Do, T.N., Matiatos, I., Panizzo, V.N. and Trinh, A.D., 2020. Stableisotopes as an effective tool for N nutrient source identification in a heavilyurbanized and agriculturally intensive tropical lowlandbasin. Biogeochemistry, 149(1), pp.17-35.This work was funded by RCUK/ UKRI-NAFOSTED grant numbers NE/P014577/1] including investigators Do Thu Nga, Trinh Anh Duc, Luu Thi NguyetMinh, Le Thi Phuong Quynh (Vietnam Academy of Science and Technology), TranMinh Tien (Vietnam Academy of Agricultural Sciences), Virginia Panizzo, MelanieLeng, Chris Vane (Centre for Environmental Geochemistry, University ofNottingham-British Geological Survey).WATER QUALITY IN THE RED RIVER DELTA6

Water quality in rivers of the Red River Delta

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Water quality in rivers of the Red River Delta

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