@article{BauerBoersigPhametal.2022,
  author    = {Bauer, Jonas and B{\"o}rsig, Nicolas and Pham, Van Cam and Hoan, Tran Viet and Nguyen, Ha Thi and Norra, Stefan},
  title     = {Geochemistry and evolution of groundwater resources in the context of salinization and freshening in the southernmost Mekong Delta, Vietnam},
  series = {Journal of Hydrology: Regional Studies},
  volume    = {40},
  journal   = {Journal of Hydrology: Regional Studies},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {2214-5818},
  doi       = {10.1016/j.ejrh.2022.101010},
  pages     = {17},
  year      = {2022},
  abstract  = {Study region: Ca Mau Province (CMP), Mekong Delta (MD), Vietnam. Study focus: Groundwater from deep aquifers is the most reliable source of freshwater in the MD but extensive overexploitation in the last decades led to the drop of hydraulic heads and negative environmental impacts. Therefore, a comprehensive groundwater investigation was conducted to evaluate its composition in the context of Quaternary marine transgression and regression cycles, geochemical processes as well as groundwater extraction. New hydrological insights for the region: The abundance of groundwater of Na-HCO3 type and distinct ion ratios, such as Na+/Cl-, indicate extensive freshwater intrusion in an initially saline hydrogeological system, with decreasing intensity from upper Pleistocene to deeper Miocene aquifers, most likely during the last marine regression phase 60-12 ka BP. Deviations from the conservative mixing line between the two endmembers seawater and freshwater are attributed to ion-exchange processes on mineral surfaces, making ion ratios in combination with a customized water type analysis a useful tool to distinguish between salinization and freshening processes. Elevated salinity in some areas is attributed to HCO3- generation by organic matter decomposition in marine sediments rather than to seawater intrusion. Nevertheless, a few randomly distributed locations show strong evidence of recent salinization in an early stage, which may be caused by the downwards migration of saline Holocene groundwater through natural and anthropogenic pathways into deep aquifers.},
  language  = {en}
}
@article{WilhelmsBoersigYangetal.2022,
  author    = {Wilhelms, Andre and B{\"o}rsig, Nicolas and Yang, Jingwei and Holbach, Andreas and Norra, Stefan},
  title     = {Insights into phytoplankton dynamics and water quality monitoring with the BIOFISH at the Elbe River, Germany},
  series = {Water},
  volume    = {14},
  journal   = {Water},
  number    = {13},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2073-4441},
  doi       = {10.3390/w14132078},
  pages     = {20},
  year      = {2022},
  abstract  = {Understanding the key factors influencing the water quality of large river systems forms an important basis for the assessment and protection of cross-regional ecosystems and the implementation of adapted water management concepts. However, identifying these factors requires in-depth comprehension of the unique environmental systems, which can only be achieved by detailed water quality monitoring. Within the scope of the joint science and sports event "Elbschwimmstaffel" (swimming relay on the river Elbe) in June/July 2017 organized by the German Ministry of Education and Research, water quality data were acquired along a 550 km long stretch of the Elbe River in Germany. During the survey, eight physiochemical water quality parameters were recorded in high spatial and temporal resolution with the BIOFISH multisensor system. Multivariate statistical methods were applied to identify and delineate processes influencing the water quality. The BIOFISH dataset revealed that phytoplankton activity has a major impact on the water quality of the Elbe River in the summer months. The results suggest that phytoplankton biomass constitutes a substantial proportion of the suspended particles and that photosynthetic activity of phytoplankton is closely related to significant temporal changes in pH and oxygen saturation. An evaluation of the BIOFISH data based on the combination of statistical analysis with weather and discharge data shows that the hydrological and meteorological history of the sampled water body was the main driver of phytoplankton dynamics. This study demonstrates the capacity of longitudinal river surveys with the BIOFISH or similar systems for water quality assessment, the identification of pollution sources and their utilization for online in situ monitoring of rivers.},
  language  = {en}
}
@article{HoanRichterBorsigetal.2022,
  author    = {Hoan, Tran Viet and Richter, Karl-Gerd and Borsig, Nicolas and Bauer, Jonas and Ha, Nguyen Thi and Norra, Stefan},
  title     = {An improved groundwater model framework for aquifer structures of the quaternary-formed sediment body in the southernmost parts of the Mekong Delta, Vietnam},
  series = {Hydrology : open access journal},
  volume    = {9},
  journal   = {Hydrology : open access journal},
  number    = {4},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2306-5338},
  doi       = {10.3390/hydrology9040061},
  pages     = {20},
  year      = {2022},
  abstract  = {The Ca Mau peninsula (CMP) is a key economic region in southern Vietnam. In recent decades, the high demand for water has increased the exploitation of groundwater, thus lowering the groundwater level and leading to risks of degradation, depletion, and land subsidence, as well as salinity intrusion in the groundwater of the whole Mekong Delta region. By using a finite element groundwater model with boundary expansion to the sea, we updated the latest data on hydrogeological profiles, groundwater levels, and exploitation. The basic model setup covers seven aquifers and seven aquitards. It is determined that the inflow along the coastline to the mainland is 39\% of the total inflow. The exploitation of the study area in 2019 was 567,364 m(3)/day. The most exploited aquifers are the upper-middle Pleistocene (qp(2-3)) and the middle Pliocene (n(2)(2)), accounting for 63.7\% and 24.6\%, respectively; the least exploited aquifers are the upper Pleistocene and the upper Miocene, accounting for 0.35\% and 0.02\%, respectively. In the deeper aquifers, qp(2-3) and n(2)(2), the change in storage is negative due to the high exploitation rate, leading to a decline in the reserves of these aquifers. These groundwater model results are the calculations of groundwater reserves from the coast to the mainland in the entire system of aquifers in the CMP. This makes groundwater decision managers, stakeholders, and others more efficient in sustainable water resources planning in the CMP and Mekong Delta (MKD).},
  language  = {en}
}