Changing Land Use and Population Density Are Degrading Water Quality in the Lower Mekong Basin

Establishing reference conditions in rivers is important to understand environmental change and protect ecosystem integrity. Ranked third globally for fish biodiversity, the Mekong River has the world’s largest inland fishery providing livelihoods, food security, and protein to the local population. It is therefore of paramount importance to maintain the water quality and biotic integrity of this ecosystem. We analyzed land use impacts on water quality constituents (TSS, TN, TP, DO, NO3−, NH4+, PO43−) in the Lower Mekong Basin. We then used a best-model regression approach with anthropogenic land-use as independent variables and water quality parameters as the dependent variables, to define reference conditions in the absence of human activities (corresponding to the intercept value). From 2000–2017, the population and the percentage of crop, rice, and plantation land cover increased, while there was a decrease in upland forest and flooded forest. Agriculture, urbanization, and population density were associated with decreasing water quality health in the Lower Mekong Basin. In several sites, Thailand and Laos had higher TN, NO3−, and NH4+ concentrations compared to reference conditions, while Cambodia had higher TP values than reference conditions, showing water quality degradation. TSS was higher than reference conditions in the dry season in Cambodia, but was lower than reference values in the wet season in Thailand and Laos. This study shows how deforestation from agriculture conversion and increasing urbanization pressure causes water quality decline in the Lower Mekong Basin, and provides a first characterization of reference water quality conditions for the Lower Mekong River and its tributaries.

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River Discharge and Water Level Changes in the Mekong River: Droughts in an Era of Mega-Dams

10.22541/au.161189206.60684509/v1 ◽

2021 ◽

Author(s):

XiXi Lu ◽

Samuel Chua

Keyword(s):

Water Level ◽

Water Discharge ◽

Dry Season ◽

Water Levels ◽

Mekong River ◽

Wet Season ◽

Discharge Data ◽

Mekong Basin ◽

Lower Mekong Basin ◽

Dry Conditions

While 1992 marked the first major dam – Manwan – on the main stem of the Mekong River, the post-2010 era has seen the construction and operationalisation of mega dams such as Xiaowan (started operations in 2010) and Nuozhadu (started operations in 2014) that were much larger than any dams built before. The scale of these projects implies that their operations will likely have significant ecological and hydrological impacts from the Upper Mekong Basin to the Vietnamese Delta and beyond. Historical water level and water discharge data from 1960 to 2020 were analysed to examine the changes to streamflow conditions across three time periods: 1960-1991 (pre-dam), 1992-2009 (growth) and 2010-2020 (mega-dam). At Chiang Saen, the nearest station to the China border, monthly water discharge in the mega-dam period has increased by up to 98% during the dry season and decreased up as much as -35% during the wet season when compared to pre-dam records. Similarly, monthly water levels also rose by up to +1.16m during the dry season and dropped by up to -1.55m during the wet season. This pattern of hydrological alterations is observed further downstream to at least Stung Treng (Cambodia) in our study, showing that Mekong streamflow characteristics have shifted substantially in the post-2010 era. In light of such changes, the 2019-2020 drought – the most severe one in the recent history in the Lower Mekong Basin – was a consequent of constructed dams reducing the amount of water during the wet season. This reduction of water was exacerbated by the decreased monsoon precipitation in 2019. Concurrently, the untimely operationalisation of the newly opened Xayaburi dam in Laos coincided with the peak of the 2019-2020 drought and could have aggravated the dry conditions downstream. Thus, the mega-dam era (post-2010) may signal the start of a new normal of wet-season droughts.

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Developing Land Use Land Cover Maps for the Lower Mekong Basin to Aid Hydrologic Modeling and Basin Planning

Remote Sensing ◽

10.3390/rs10121910 ◽

2018 ◽

Vol 10 (12) ◽

pp. 1910 ◽

Cited By ~ 3

Author(s):

Joseph Spruce ◽

John Bolten ◽

Raghavan Srinivasan ◽

Venkat Lakshmi

Keyword(s):

Land Use ◽

Land Cover ◽

Satellite Data ◽

Reference Data ◽

Assessment Tool ◽

Deciduous Forest ◽

Land Use Land Cover ◽

Modis Ndvi ◽

Mekong Basin ◽

Lower Mekong Basin

This paper discusses research methodology to develop Land Use Land Cover (LULC) maps for the Lower Mekong Basin (LMB) for basin planning, using both MODIS and Landsat satellite data. The 2010 MODIS MOD09 and MYD09 8-day reflectance data was processed into monthly NDVI maps with the Time Series Product Tool software package and then used to classify regionally common forest and agricultural LULC types. Dry season circa 2010 Landsat top of atmosphere reflectance mosaics were classified to map locally common LULC types. Unsupervised ISODATA clustering was used to derive most LULC classifications. MODIS and Landsat classifications were combined with GIS methods to derive final 250-m LULC maps for Sub-basins (SBs) 1–8 of the LMB. The SB 7 LULC map with 14 classes was assessed for accuracy. This assessment compared random locations for sampled types on the SB 7 LULC map to geospatial reference data such as Landsat RGBs, MODIS NDVI phenologic profiles, high resolution satellite data, and Mekong River Commission data (e.g., crop calendars). The SB 7 LULC map showed an overall agreement to reference data of ~81%. By grouping three deciduous forest classes into one, the overall agreement improved to ~87%. The project enabled updated regional LULC maps that included more detailed agriculture LULC types. LULC maps were supplied to project partners to improve use of Soil and Water Assessment Tool for modeling hydrology and water use, plus enhance LMB water and disaster management in a region vulnerable to flooding, droughts, and anthropogenic change as part of basin planning and assessment.

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Development and application of GIS-based assessment of land-use impacts on water quality: A case study of the Kharaa River Basin

AMBIO ◽

10.1007/s13280-018-1123-y ◽

2018 ◽

Vol 48 (10) ◽

pp. 1154-1168 ◽

Cited By ~ 5

Author(s):

Gunsmaa Batbayar ◽

Martin Pfeiffer ◽

Martin Kappas ◽

Daniel Karthe

Keyword(s):

Water Quality ◽

Land Use ◽

River Basin ◽

Land Use Impacts ◽

Application Of Gis

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The Chao Phraya River Basin: water quality and anthropogenic influences

Water Science & Technology Water Supply ◽

10.2166/ws.2018.167 ◽

2018 ◽

Vol 19 (5) ◽

pp. 1287-1294 ◽

Cited By ~ 2

Author(s):

Nuanchan Singkran ◽

Pitchaya Anantawong ◽

Naree Intharawichian ◽

Karika Kunta

Keyword(s):

Water Quality ◽

Land Use ◽

River Basin ◽

River Mouth ◽

Oxygen Demand ◽

Quality Parameters ◽

Paddy Fields ◽

Coliform Bacteria ◽

Wet Season ◽

Chao Phraya River

Abstract Land use influences and trends in water quality parameters were determined for the Chao Phraya River, Thailand. Dissolved oxygen (DO), biochemical oxygen demand (BOD), and nitrate-nitrogen (NO3-N) showed significant trends (R2 ≥ 0.5) across the year, while total phosphorus (TP) and faecal coliform bacteria (FCB) showed significant trends only in the wet season. DO increased, but BOD, NO3-N, and TP decreased, from the lower section (river kilometres (rkm) 7–58 from the river mouth) through the middle section (rkm 58–143) to the upper section (rkm 143–379) of the river. Lead and mercury showed weak/no trends (R2 < 0.5). Based on the river section, major land use groups were a combination of urban and built-up areas (43%) and aquaculture (21%) in the lower river basin, paddy fields (56%) and urban and built-up areas (21%) in the middle river basin, and paddy fields (44%) and other agricultural areas (34%) in the upper river basin. Most water quality and land use attributes had significantly positive or negative correlations (at P ≤ 0.05) among each other. The river was in crisis because of high FCB concentrations. Serious measures are suggested to manage FCB and relevant human activities in the river basin.

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Interacting land use and soil surface dynamics control groundwater outflow in a montane catchment of the lower Mekong basin

Agriculture Ecosystems & Environment ◽

10.1016/j.agee.2018.09.005 ◽

2018 ◽

Vol 268 ◽

pp. 90-102 ◽

Cited By ~ 6

Author(s):

Olivier Ribolzi ◽

Guillaume Lacombe ◽

Alain Pierret ◽

Henri Robain ◽

Phabvilay Sounyafong ◽

...

Keyword(s):

Land Use ◽

Soil Surface ◽

Surface Dynamics ◽

Mekong Basin ◽

Lower Mekong Basin ◽

Groundwater Outflow

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Impacts of Mainstream Hydropower Dams on Fisheries and Agriculture in Lower Mekong Basin

Sustainability ◽

10.3390/su12062408 ◽

2020 ◽

Vol 12 (6) ◽

pp. 2408 ◽

Cited By ~ 13

Author(s):

Yuichiro Yoshida ◽

Han Soo Lee ◽

Bui Huy Trung ◽

Hoang-Dung Tran ◽

Mahrjan Keshlav Lall ◽

...

Keyword(s):

Developing Countries ◽

Electricity Generation ◽

Lao Pdr ◽

Mekong River ◽

Environmental Damage ◽

Dam Construction ◽

Mekong Basin ◽

Hydropower Potential ◽

Hydropower Dams ◽

Lower Mekong Basin

The riverine ecosystems of the Mekong River Basin possess the world’s most productive inland fishery and provide highly productive food crops for millions of people annually. The development of hydropower potential in the Mekong River has long been of interest to governments in the region. Among the existing 64 dams, 46 dams have been built in the Lower Mekong Basin (LMB) to produce up to 8650 MW of electricity. Additionally, of the 123 proposed built hydropower dams, eleven hydropower plants have been nominated for the river mainstream and are expected to install a total of 13,000 MW in the LMB countries. However, serious concerns have intensified over the potential negative economic consequences, especially on fisheries and agriculture in Cambodia and Vietnam. To date, most of the concerns have concentrated on the impacts on hydrology, environment, livelihood, and diversity in the LMB attributed to hydropower development. This paper, however, discusses the fishery and agricultural sectors of the LMB and focuses on the downstream floodplains of Cambodia and Vietnam. The dam construction has caused greater losses of biodiversity and fisheries than climate change in the LMB. The reduction of 276,847 and 178,169 t of fish, 3.7% and 2.3% of rice, 21.0% and 10.0% of maize will contribute to a decrease of 3.7% and 0.3% of the GDP of Cambodia and Vietnam, respectively. Lao PDR may benefit the most revenue from electricity generation than the other country in the LMB, as most of the proposed dams are projected in the country. Cambodia burdens 3/4 of the reduction of total capture fishery destruction, whilst Lao PDR, Thailand, and Vietnam endure the remaining 1/3 losses. The tradeoff analyses reveal that losses of capture fisheries, sediment or nutrients, and social mitigation costs are greater than the benefits from electricity generation, improved irrigation, and flood control of the LMB region. The socioeconomic and environmental damage caused by hydropower dams in developing countries, including the Mekong, is greater than the early costs in North America and Europe. It is proposed that dam construction for hydropower in the Mekong River, as well as other rivers in developing countries, should be gradually removed and shifted toward solar, wind, and other renewable resources.

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Relationship between water quality and macro-scale parameters (land use, erosion, geology, and population density) in the Siminehrood River Basin

The Science of The Total Environment ◽

10.1016/j.scitotenv.2018.05.244 ◽

2018 ◽

Vol 639 ◽

pp. 1588-1600 ◽

Cited By ~ 16

Author(s):

Farshid Bostanmaneshrad ◽

Sadegh Partani ◽

Roohollah Noori ◽

Hans-Peter Nachtnebel ◽

Ronny Berndtsson ◽

...

Keyword(s):

Water Quality ◽

Land Use ◽

Population Density ◽

River Basin ◽

Scale Parameters ◽

Macro Scale

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Linking Changes in Land Cover and Land Use of the Lower Mekong Basin to Instream Nitrate and Total Suspended Solids Variations

Sustainability ◽

10.3390/su12072992 ◽

2020 ◽

Vol 12 (7) ◽

pp. 2992 ◽

Cited By ~ 2

Author(s):

Kongmeng Ly ◽

Graciela Metternicht ◽

Lucy Marshall

Keyword(s):

Water Quality ◽

Land Use ◽

Land Cover ◽

Suspended Solids ◽

Total Suspended Solids ◽

Mekong River ◽

Forest Land ◽

Lulc Changes ◽

Correlation Analyses ◽

Forest Land Cover

Population growth and economic development are driving changes in land use/land cover (LULC) of the transboundary Lower Mekong River Basin (LMB), posing a serious threat to the integrity of the river system. Using data collected on a monthly basis over 30 years (1985–2015) at 14 stations located along the Lower Mekong river, this study explores whether spatiotemporal relationships exist between LULC changes and instream concentrations of total suspended solids (TSS) and nitrate—as proxies of water quality. The results show seasonal influences where temporal patterns of instream TSS and nitrate concentrations mirror patterns detected for discharge. Changes in LULC influenced instream TSS and nitrate levels differently over time and space. The seasonal Mann–Kendall (SMK) confirmed significant reduction of instream TSS concentrations at six stations (p < 0.05), while nitrate levels increased at five stations (p < 0.05), predominantly in stations located in the upper section of the basin where forest areas and mountainous topography dominate the landscape. Temporal correlation analyses point to the conversion of grassland (r = −0.61, p < 0.01) to paddy fields (r = 0.63, p < 0.01) and urban areas (r = 0.44, p < 0.05) as the changes in LULC that mostly impact instream nitrate contents. The reduction of TSS appears influenced by increased forest land cover (r = −0.72, p < 0.01) and by the development and operation of hydropower projects in the upper Mekong River. Spatial correlation analyses showed positive associations between forest land cover and instream concentrations of TSS (r = 0.64, p = 0.01) and nitrate (r = 0.54, p < 0.05), indicating that this type of LULC was heavily disturbed and harvested, resulting in soil erosion and runoff of nitrate rich sediment during the Wet season. Our results show that enhanced understanding of how LULC changes influence instream water quality at spatial and temporal scales is vital for assessing potential impacts of future land and water resource development on freshwater resources of the LMB.

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