Open access peer-reviewed chapter

Recharge and Turnover of Groundwater in Coastal Aquifers with Emphasis on Hydrochemistry and Isotopes

Written By

Gunnar Jacks and Satheesachandran Thambi

Submitted: 15 May 2017 Reviewed: 20 December 2017 Published: 06 February 2018

DOI: 10.5772/intechopen.73301

From the Edited Volume

Aquifers - Matrix and Fluids

Edited by Muhammad Salik Javaid and Shaukat Ali Khan

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Abstract

Coastal aquifers are globally subject to considerable stress. The population density is often high in coastal areas, and in addition, the coastal plains often have good agricultural soils demanding irrigation. While a portion of the irrigation can be provided by rivers, local groundwater is also used adding to the water requirement. Many coastal aquifers are large with a slow turnover of the groundwater and recharge is difficult to assess. This review is aimed at giving an overview of the hydrochemistry with an emphasis of giving insight into the groundwater recharge and the sustainability of the groundwater quality. The past climate history has given an imprint of hydrochemistry of especially coastal aquifers.

Keywords

  • groundwater
  • aquifer
  • coastal
  • recharge
  • hydrochemistry
  • isotopes

1. Introduction

About 1 billion out of 7 billion people in the world live in coastal areas and rely on coastal aquifers for their water supply and irrigation [1]. A simple calculation of the water requirement can be done by assessing that the population density is 2000/km2, a figure taken from the Kerala coast in SW India. With the proposed population density, each person has an area of 500 m2 to reside on. The water need is dominated by the water requirement for food production and varies from 2500 l/day and person in developing countries to 5000 l/day in industrialized countries [2]. The water use in households is in the order of less than 200 l/day and person. If using the figure 2700 litres per day and person for total water demand, then this would be equal to a water requirement of around 2000 mm/year or of the same order as the yearly rainfall in the actual area. Thus, even in rather rainfall-rich areas, coastal aquifers are subject to a considerable stress.

Coastal plains are often underlain by thick sediments, and they are complex intercalations of finer and coarser sediments formed under different climatic conditions. Looking back on the recent past climatic history, just a few thousands of years back, there have been large variations in sea level and locally, there have been considerable tectonic movements.

This review will be focused on using the hydrochemistry of the groundwater and isotopes to decipher the groundwater exchange in coastal aquifers. This approach is especially useful in coastal aquifers where salt water intrusion could complicate the picture. In view of the authors’ experience, there will be a focus on South and Southeast Asia, however, with some examples from other regions such as Europe.

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2. Groundwater recharge

Groundwater recharge can occur in different ways:

  • recharged locally by rainwater

  • recharged from coastal plain rivers

  • being a mixture of intruded saltwater and freshwater

Local groundwater is in many places not sufficient to recharge the aquifers. There are many aquifers in semiarid areas that are overused. Examples are common in S and SE Asia. Megacities with groundwater supply have in several places salinity problems resulting from land subsidence like in Bangkok and Jakarta [3]. In view of the climate change foreseen, there will be increase in sea levels that will affect the balance between groundwater and seawater. Ericson et al. [4] have evaluated 40 deltas regarding the effective sea level rise (ESLR), which in their evaluation is a combined effect of sea level rise and subsidence of the deltas. The Bengal delta in Bangladesh and India is experiencing an ESLR rate as high as 25 mm/year, while the Mississippi delta in USA has a rate of around 10 mm/year. The sea level rise as such is in the order of 3.3 mm/year, and the rate is expected to increase in the coming decades [5]. Ericson et al. [4] estimate that by 2050, about 8.6 M people are at risk due to ESLR. Local conditions such as tectonic movements and land subsidence due to excessive groundwater extraction thus play a large role in the risk of saline intrusion into costal aquifers in coming years [3]. The shoreline displacements may have a variety of reasons such as neo-tectonic movements but also anthropogenic activities such as deforestation and increased erosion [6].

Fog water condensation is a rare mechanism of groundwater recharge, but it may play a limited role under specific conditions. An example is the Al-Qara Mountain behind the Salalah Plain in Oman [7]. The browsing of a large population of camels has caused the degradation of mountain forest and decrease in recharge. The local precipitation is 100 mm, and the fog collection now adds just 10 mm to the recharge.

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3. Groundwater recharged from rivers

This is a common case. To trace the river water into the aquifer is of interest to assess the recharge. In this case, isotope investigations may be of good use. In some cases, the river water has a specific composition not only regarding water chemistry but also regarding isotopes of some elements. This could be traced in the aquifer mirroring where the river is recharging the aquifer.

With a past history of saline groundwater being refreshed by recharge, there are cases with elevated chloride ratio that could be interpreted as salt water intrusion. If the recharge occurs in a located area giving kind of a piston flow, a sequence of defined water types could be observed. These water types range from a typical fresh water of Ca-HCO3 type via a Na-HCO3 type to a brackish mixed type of water. The Na-HCO3 type is formed by ion exchange, the Na-saturated aquifer material from the saline period, picks up calcium from the fresh recharged water and releases sodium into the groundwater. This is observed in a Tertiary aquifer on the Kerala coast in India [8] and in the Tertiary and Cretaceous aquifers in Tamil Nadu [9] (Figure 1).

Figure 1.

Water types in the Kerala Tertiary coastal aquifer resulting from flushing by recharge before the Last Glacial Maximum. The Precambrian, under-laying the Tertiary strata, are faulted in the SE-NW direction, which also guides the recharge in the same direction.

If the recharge area is scattered, not creating piston flow of recharge, mixtures of water types are found [10, 11].

Elevated chloride levels in the local Kerala Tertiary aquifer [8] were in places caused by diffusion of chloride from intercalated clay beds. Drilling and sampling of sediments, sand, and intercalated clay showed that the pore water in the clay contained elevated salinity with chloride that diffused into the surrounding coarser sediments (Figure 2).

Figure 2.

Residual pore water chloride in a clay layer dating back from a previous saline period was found in the Kerala coastal aquifers. The pore water was extracted from the core in the center of the clay layer.

This could also be seen by plotting the δ18Ο ratio in the water versus chloride. There was no mixing line toward sea water composition, but the δ18O ratios remained constant irrespective of the chloride concentration (Figure 3) (Table 1).

Figure 3.

δ18O ratios in groundwater plotted versus chloride. Data from Kerala coastal aquifers. There is no mixing in of sea water, but the increase of chloride above about 80–100 mg/l is likely to come from pore water in clay layers as is seen in Figure 2.

SampleδD (‰)δ18O (‰)Chloride (mg/l)
1−44.20−7.464.9
2−43.85−7.1410.0
3−44.52−7.36146
4−44.83−7.83995
5−48.12−7.0476
6−47.12−7.7560.1
7−43.10−9.301220
8−46.15−8.35392
9−44.82−8.22819
10−44.32−8.46191
SMOW0.000.0019,345

Table 1.

δD and δ18O in groundwater in Mati Plain in Albania have no relationship with chloride concentration showing that sea water intrusion is not the source of chloride.

The groundwater in Mati coastal plain in the northern Albania serves as water source for about 400,000 people, and there was a concern that this pumping rate may cause salt water intrusion [12]. In the catchment, there are several abandoned and active copper mines and the sulfate in river has an isotopic ratio typical of sulfides. This could be traced over large areas of plain showing that the recharge from the river is good. Close to the seaside, there were elevated chloride and sulfate levels that could be of old sea water origin. The δ34S ratio was 24‰, thus well over the sea water ratio at 21‰. This can be explained by sulfate reduction in the intercalated clay layers (Figures 4 and 5). Thus, sea water intrusion is not a current threat.

Figure 4.

Cross section of the Mati Plain aquifer in Albania with δ34S ratios in groundwater [12]. In the plain, the δ34S ratios are mirroring recharge from river Mati, which has a δ34S ratio mirroring sulfide oxidation in mining areas in the catchment. The left well, close to the seaside, has a δ34S ratio above the sea water, likely to be caused by sulfate reduction in clay layers.

Figure 5.

Staple diagram with δ34S ratios in groundwater indicating recharge from the river Mati with sulfate having sulfide origin from oxidation of waste rock from copper mines [12]. The high δ34S ratios in sea near wells are above the sea water ratio (21‰), which indicates sulfate reduction in intercalated clay layers. The black bars are samples from copper mine waste in the catchment.

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4. Measures to halt sea water intrusion

Where sea water intrusion is already a fact, there are measures to halt it. First of all, groundwater extraction should be diminished. While there are no visible signs of sea water intrusion in the Kerala Tertiary aquifers, there is a gradual development of surface water utilization for the larger towns in the coastal plain, which is a good measure to protect the coastal aquifers. On the Indian east coast, this is more difficult as the river flows are lesser there. Ballykraya and Ravi [13] describe the creation of a barrier by artificial recharge near the coast. A similar measure has been taken in the Salalah plain by well recharge of treated waste water along the coast line [14, 15]. A new approach, which could be more efficient, is when fresh water recharge into the nonsaline part of the coastal aquifer is combined with pumping of saline water near the shoreline [16].

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5. Effects of past climate change

The last glaciation has implied large variations in sea level, in the order of 125 m. Several areas that were under the sea level in preglacial time were drained from the sea during the Last Glacial Maximum (LGM).

This could enhance the recharge with fresh water. A Tertiary aquifer on the Kerala coast in SW India has groundwater dates varying between 23 and 34 kA BP (kA BP = kilo-annum, thousands of years before present) [8] and should thus have been recharged just before LGM. This is reasonable as the head for recharge was large, 60–80 m. However, just before LGM, the recharge has obviously been interrupted. In this case, the paleoclimatic conditions seem to have promoted the recharge during a wet SW monsoon which just before LGM was interrupted by a dry monsoon (Figure 6).

Figure 6.

Sea water levels during the last glacial period. The SW monsoon had, as per the abundant paleoclimatological data published, a wet period before LGM followed by a dry period after the LGM.

Other aquifers on the Indian east coast has groundwater of a similar age and the same period and mechanisms of recharge may apply [9, 17]. The paleoclimatic data from India are abundant from both marine sediments as well as local pockets on current land illustrating the variations in the strength of the SW monsoon [18, 19, 20, 21, 22, 23].

The past climate change has, in several aquifers near sea, formed a sequence of Ca-HCO3 → Na-HCO3 → Na-Ca-Cl types of groundwater formed by flushing of an initially formed saline/brackish aquifer by fresh water [24, 25]. This could be seen laterally in Kerala (Figure 1). The direction of the recharge flow is from SE toward NW directed by the topography of the underlying Precambrian, which is likely to be intersected by faults in the same direction. The same zonation is seen depth-wise for instance in the Mekong river delta and in the Red River delta in Vietnam [26].

A secondary effect of flushing is that the softening effect of the process creates Na-HCO3 type of groundwater (Figure 7) which tends to mobilize fluoride [27, 28, 29, 30]. Where the recharge is less of a “piston flow” process, there will be more mixed forms of groundwater types. This is often the case on the Indian SE coast where the sedimentology is more intricate [10, 11].

Figure 7.

Na/Cl ratios versus chloride, showing the mobilization of sodium during the late stage of fresh water flushing. When the fresh water stage is approached, there is mobilization of sodium creating a Na-HCO3 type of water often with elevated levels of fluoride.

Another effect of the last glaciation is the common occurrence of arsenic in groundwater in Holocene sediment, for instance not only in the Bengal delta [31, 32, 33, 34, 35, 36] but also in other coastal plains in S and SE Asia [37, 38, 39] like in the Mekong river delta, the Red River delta, and the Irrawaddy river delta. When the sea level was lowered before Last Glacial Maximum (LGM) at around 18 kA before present, the sediments were subject to erosion and redeposition and this lowered the organic matter content [39]. Contrarily, after LGM, the sea level rose and created abundant wetlands rich in organic matter [40]. These sediments become easily anoxic with reduction of ferric oxyhydroxides and mobilization of arsenic into groundwater [41].

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6. Conclusions and summary

Coastal aquifers and their recharge is a crucial issue for approximately 1 billion people who are living on coastal plains globally. Due to high population density and high water demand for domestic and more so for food production, there is a high stress on the water resources. There are modeling tools that can be used to assess the sustainability of the groundwater in coastal aquifers, but in addition, hydrochemistry and isotopes may be a substantial help in the assessment, especially in costal aquifers where a possible sea water intrusion adds to the complexity. Dating, mostly by 14C methodologies gives reliable results adding to the assessments of the groundwater turnover [42]. For aquifers that that have a past memory of salinity, there may be a good relationship between age and chloride levels, chloride which is retained in parts of the aquifer where groundwater turnover is slower (Figure 8). Chloride in this case, as is shown in Figure 2, is not derived from salt water intrusion. For shorter turnover rates, tritium is used especially after the bomb tests in the 1960s has faded out [43].

Figure 8.

Age of groundwater in the Mati plain aquifer related to the chloride levels [12]. The slow turnover rate has left portion of the aquifer with elevated chloride levels.

Elevated salt content in coastal aquifers could have many sources in addition to salt water intrusion. A common case is found in coastal aquifers that consist of sand and gravel intercalated with clay layers. As the groundwater turnover is slow, often in the range of thousands of years, there might still be more or less saline pore water in the clay layers that continue to diffuse into the coarser material (Figure 8). In some, there is sulfate reduction in the clay due to elevated organic matter content and this is mirrored as elevated δ34S ratios.

The often intricate mixtures of water and dissolved salt in coastal aquifers could be interpreted by suitable isotopes such as δD, δ18O, δ34S, if different sources of the isotope ratios can be traced back to the source of the water. A good example is δ34S on a coastal aquifer in Albania where there were two main sources, sulfide-related sulfate from mines and sulfate in the groundwater formed by sulfate reduction in intercalated clay layers in the aquifer. A common feature often formed by flushing in postglacial time of formerly saline aquifers is the appearance of specific water such as NaHCO3 formed by ion exchange. At the end of the flushing period, there is a pronounced increase in the Na/Cl ratio formed by the uptake of calcium in the fresh water recharge and release of sodium at adsorption sites from the saline period.

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Abbreviations

18O18O/16O for oxygen isotopes
ESLREffective sea level rise
ka BPThousands of years before present
LGMLast Glacial Maximum
SMOWSurface mean ocean water
SW monsoonSouthwest monsoon
δ34S34S/32S ratio for sulfur isotopes
δDIsotopic ratio for hydrogen isotopes (2H/H or deuterium/common hydrogen)

References

  1. 1. Walton B. Here comes the sea: The struggle to keep the ocean out of California’s coastal aquifers. http://www.circleofblue.org/2015/world/here-comes-the-sea-the-struggle-to-keep
  2. 2. Chapagain AK, Hoekstra AY. Water footprints of nations. UNESCO-IHE, Inst. for water education. Main report. Vol. 1. 75 pp
  3. 3. Onodera S, Saito M, Sawano M, Hosono T, Taniguchi M, Shimada J, Umezawa Y, Lubis RF, Buapeng S, Delinom R. Effects of intensive urbanization on the intrusion of shallow groundwater into deep groundwater: Examples from Bangkok and Jakarta. Science of the Total Environment. 2008;404:401-410
  4. 4. Ericson JP, Vörösmarty CJ, Dingman SL, Ward LG, Meybeck M. Effective sea-level rise and deltas: Causes of change and human dimension implications. Global and Planetary Change. 2006;50:63-82
  5. 5. Chen X, Zhang X, Church JA, Watson CS, King MA, Monselesan D, Legresy B, Harig C. The increasing rate of global mean sea-level rise during 1993-2014. Nature Climate Change. 2017;7:492-495
  6. 6. Fouache E, Vella C, Dimo L, Gruda G, Mugnier J-L, Denèfle M, Monnier O, Hortyat M, Huth E. Shoreline displacement since Middle Holocene in the vicinity of the ancient city Apollonia (Albania, Seman and Vjosa deltas). Quaternary International. 2010;216:118-128
  7. 7. Shammas M. Impact of the AlQara mountain fogwater forest on groundwater recharge in the Salalah paain. Sultanate of Oman. Ecohydrology and Hydrobiology. 2007;7(1):37-49
  8. 8. Jacks G, Thambi DSC. Hydrochemistry of the Kerala coastal aquifers. In: A. Mukherjee, editor. Groundwater in Asia. Berlin: Springer Verlag; 2018. in print
  9. 9. Sukhija BS, Varma VN, Nagabushanam P, Venkat Reddy D. Differentiation of palaeomarine and modern seawater intruded in coastal groundwaters of Karaikal and Tanjavur, India based on inorganic chemistry organic biomarker fingerprints and radioactive dating. Journal of Hydrology. 1996;174:173-201
  10. 10. Thilagavathi R, Chidambaram S, Prasanna MV, Thivya C, Singaraja C. A study on groundwater geochemistry and water quality in layered aquifer systems of Pondicherry region, Southeast India. Applied Water Science. 2012;2:253-269
  11. 11. Sonkamble S, Chandra S, Ahmed S, Rangarajan R. Source speciation resolving hydrochemical complexity of coastal aquifers. Marine Pollution Bulletin. 2014;78:118-129
  12. 12. Kumanova X, Marku S, Fröjdö S, Jacks G. Recharge and sustainability of a coastal aquifer in northern Albania. Hydrogeology Journal. 2013;22:883-892
  13. 13. Ballykraya PN, Ravi R. Natural fresh-water ridge as barrier against sea-water intrusion in Chennai city. Journal of the Geological Society of India. 1998;52(3):279-286
  14. 14. Shammas M, Jacks G. Seawater intrusion in the Salalah plain aquifer, Oman. Environmental Geology. 2007;53(3):575-587
  15. 15. Shammas M. The effectiveness of artificial recharge in combatting seawater intrusion in Salalah coastal aquifer, Oman. Environmental Geology. 2008;55:191-204
  16. 16. Abdoulhalik A, Ahmed A, Hamill GA. A new physical barrier system for seawater intrusion control. Journal of Hydrology. 2017;549:416-427
  17. 17. Sukhija BS, Venkat Reddy D, Nagabushanam P. Isotopic finger prints of palaeoclimates during the last 30 000 years in deep confined groundwater of southern India. Quaternary Research. 1998;50:252-260
  18. 18. Jayalahshmi K, Nair KM, Kumar H, Santosh M. Late Pleistocene-Holocene palaeoclimate history of the southern Kerala basin, southwest India. Gondwana Research. 2004;7(2):585-594
  19. 19. Juyal N, Chamyal IS, Bhandari S, Bhushan R, Singhvi AK. Continental record of the southwest monsoon during the last 130 kA: Evidence from the southern margin of the Thar desert, India. Quaternary Science Reviews. 2006;25:2632-2650
  20. 20. Juyal N, Pant RK, Basaviah N, Bhushan R, Saini NK, Yadava MG, Singhvi AK. Reconstruction of the Last Glacial to early Holocene monsoon variability from relict lake sediments of the Higher Central Himalya, Uttarakhand, India. Journal of Asian Earth Sciences. 2009;34:437-449
  21. 21. Agrawal S, Sanyal P, Sarkar A, Jaiswal MK, Dutta K. Variability of Indian monsoonal rainfall over past 100 kA and its implication for C3-C4 vegetational change. Quaternary Research. 2012;77:159-170
  22. 22. Kumaran KPN, Limaye RB, Punekar SA, Rajaguru SN, Jashi SV, Karlekar SN. Vegetation response to South Asian Monsoon variations in Konkan, western India during late Quaternary: Evidence from fluvio-lacustrine archives. Quaternary International. 2013;286:3-18
  23. 23. Huang C, Wei G, Ma J, Liu Y. Evolution of the Indian summer monsoon during the interval 32.7-11.4 kA BP: Evidence from the Baoxiu peat, southwest China. Journal of Asian Earth Sciences. 2016;131:72-80
  24. 24. Agerstrand T, Hansson G, Jacks G. Effect on groundwater composition of sequential flushing with fresh and saline water. In: Proc. of the 7th Salt Water Intrusion Meeting, Uppsala, Sweden 1981. http://www.swim.site.nl/pdf.swim07html
  25. 25. Mercado A. The use of hydrogeological patterns in carbonate sand and sandstone aquifers to identify intrusion and flushing of saline water. Ground Water. 1985;23(5):635-645
  26. 26. Kim J, Kim K, Thao NT, Batsaikhan B, Yun S. Hydrochemical assessment of freshening saline groundwater using multiple end members model: A study of the Red River aquifer, Vietnam. Journal of Hydrology. 2017;549:703-714
  27. 27. Jacks G, Bhattacharya P, Chaudhary V, Singh KP. Controls on the genesis of some high-fluoride groundwaters in India. Applied Geochemistry. 2005;20:221-228
  28. 28. Dhaniya Raj, Shaji E. Fluoride contamination in groundwater resources of Alleppey, southern India. Geoscience Frontiers. 2016. DOI: http://dx.doi.org/10.1016/j.gsf.2016.01.002
  29. 29. Berger T, Mathurin FA, Drake H, Åström M. Fluoride abundance and controls in fresh groundwater and bedrock fractures in an area with fluoride rich granitoid rocks. Science of the Total Environment. 2016;560-570:948-960
  30. 30. Jacks G. Chapter 15 in Four Decades of Groundwater Research in India. In: Thangarajan M. editor. Fluoride in Groundwater—Mobilization, Trends and Remediation. UK, England: CRC Press
  31. 31. Ghosh D, Routh J, Dario M, Bhadury P. Elemental biomarkers characteristics in a Pleistocene aquifer vulnerable to arsenic contamination in the Bengal Delta Plain, India. Applied Geochemistry. 2015;62:87-98
  32. 32. Acharyya SK, Lahiri S, Raymahashay BC, Bhowmik A. Arsenic toxicity of groundwater in parts of the Bengal basin and Bangladesh. The role of Quaternary stratigraphy and Holocene sea-level fluctuation. Environmental Geology. 2000;39:1127-1137
  33. 33. Acharyya SK. Arsenic levels in groundwater from Quaternary alluvium in the Ganga Plain and the Bengal Basin, Indian Subcontinent: Insights into influence of statigraphy. Gondwana Research. 2005;8(1):55-66
  34. 34. Al Lawati WM, Rizoulis A, Eiche E, Boothman C, Polya D, Lloyd JR, Berg M, Vasquez-Aguilar P, van Dongen BE. Characterization of organic matter and microbial communities in contrasting arsenicrich Holocene and arsenic-poor Pleistocene aquifers, Red River Delta, Vietnam. Applied Geochemistry. 2012;27:315-325
  35. 35. Hossein M, Bhattacharya P, Frape SK, Jacks G, Islam MM, Rahman MM, von Brömssen M, Hasan MA, Ahmed KM. Sediment colour tool for targeting arsenic-safe aquifers for the installation of shallow drinking water tubewells. Science of the Total Environment. 2014;493:615-625
  36. 36. Kulkarni HV, Mladenov N, Johanneson KH, Datta S. Contrasting dissolved organic matter quality in groundwater in Holocene and Pleistocene aquifers and implications for influencing arsenic mobility. Applied Geochemistry. 2017;77:195-205
  37. 37. Hoang TH, Bang S, Kim K-W, Nguyen MH, Dang DM. Arsenic in groundwater and sediment in the Mekong river delta, Vietnam. Environmental Pollution. 2010;158:2648-2658
  38. 38. Norrman J, Sparrenbom C, Berg M, Nguyen MH, Dang DM. Arsenic in groundwater and sediments in the Mekong river delta, Vietnam. Applied Geochemistry. 2015;61:248-258
  39. 39. Stuckey JW, Sparks DL, Fendorf S. Delineating the convergence of biogeochemical factors responsible for arsenic release to groundwater in South and Southest Asia. Advances in Agronomy. 2016;140:43-74
  40. 40. Jacks G, Thambi DSC. Groundwater memories of past climate change—Examples from India and the Nordic countries. Advances in Agronomy. 2017;3:49-57
  41. 41. Bhattacharya P, Chatterjee D, Jacks G. Occurrence of arsenic in groundwater in alluvial aquifers from delta pklains, eastern India: Options for safe drinking water supply. International Journal of Water Resources Development. 1997;13:79-92
  42. 42. Pearson FJ, Hanshaw BB. Sources of dissolved carbonate species in groundwater and their effects on carbon 14 dating. In: Isoptope Hydrology. Vienna: IAEA. 1970. pp. 271-285
  43. 43. Kralik M. How to estimate mean residence times for groundwater. Progress in Earth and Planetary Science. 2015;13:301-306

Written By

Gunnar Jacks and Satheesachandran Thambi

Submitted: 15 May 2017 Reviewed: 20 December 2017 Published: 06 February 2018