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Shedding light on the invisible: addressing potential groundwater contamination by plastic microfibers

Shedding light on the invisible: addressing potential groundwater contamination by plastic microfibers

Post by Viviana Re, researcher at the University of Pisa in Italy. You can follow Viviana on Twitter at @biralnas.


Until recently, the topic of plastic pollution was relatively unknown to the general public, although the problem was already under everyone’s very eyes.

Indeed, plastic pollution has become one of the most debated issues over the last few years, in some cases even overshadowing the concerns about climate change, and with particular concern about the effects of microplastic (i.e. plastic particles smaller than 5 mm in length) in the natural environment.

First reported in the early 1970s in the Sargasso Sea of the North Atlantic, microplastics have since become a ubiquitous pollutant found in fish and marine animals, table salt, beer, and even drinking water.

Screenshot of LITTERBASE’s Online Portal of Marine Litter (https://litterbase.awi.de/litter).

In parallel with raising awareness (and concern), this emerging issue prompted the scientific community to advance the understanding of the presence and potential effects of microplastics on natural ecosystems and human health.

As a result, the number of studies addressing microplastic pollution in surface water is rapidly increasing, ranging from case studies assessing the presence of these particles in a specific surface water body, to investigations on their possible toxicity, to proposed methodology regarding qualitative and quantitative assessment of their occurrence.

However, despite this growing body of literature, there is a component of the water cycle that remains less considered: groundwater. In fact, so far, only a few studies targeting microplastic occurrence in groundwater have been published (e.g. Bouwman et al. 2018; Mintenig et al. 2019; Panno et al. 2019). Further, only recently was the presence of microscopic plastic fibers in tap water from underground sources revealed. Thus, a great challenge for the international hydrogeological community lies in addressing the potential for groundwater contamination by plastic microfibers. In particular, the key challenges to be addressed are:

  1. The determination of microplastic occurrence in groundwater and, if present, to assess transport mechanisms in different aquifers.
  2. An assessment of the role of microplastics as carriers of contaminants within aquifers.
  3. To define a standardized procedure for microfiber sampling and monitoring in groundwater.

 

In order to complement the existing knowledge on microplastic contamination of aquatic environments, all issues should be tackled in collaboration with surface hydrologists, biologists and scientists already active in the filed.

Additionally, while doing so, we should also engage firsthand and be part of the solution, hence reducing as much as we can the production and release of plastic and microplastic. Don’t know how to start? Consider joining the recently concluded (but annually run) Plastic Free July challenge!

This post is based on a recently published paper:

Re (2019). Shedding light on the invisible: addressing the potential for groundwater contamination by plastic microfibers. Hydrogeology Journal. Open access

A do-it-yourself Jupyter notebook to constrain sediment permeability

A do-it-yourself Jupyter notebook to constrain sediment permeability

Post by Elco Luijendijk, Junior lecturer in the Department of Structural Geology and Geodynamics at Georg-August-Universität Göttingen and WaterUnderground founder Tom Gleeson (@water_undergrnd), Associate Professor in the Department of Civil Engineering at the University of Victoria.


Most of the groundwater on our planet is located in sedimentary rocks. This is why it is important to know how easy or hard it is for water to flow through pores in sediments, which is governed by permeability. Unfortunately, permeability is extremely variable. Wouldn’t it be great if we could estimate permeability based on sediment types (for which a decent amount of data exist)?

Enter the 150+ year challenge to estimate the permeability of sediments with universal equations. Most of the equations work well for one sediment type, such as pure sands or clay. For instance, the Kozeny-Carman equation from the 1920s tends to work well for most granular materials such as sand or silt. However, pure sands or clays are rare, and most of what’s out there are mixtures.

Evaluating how well existing and new equations work for mixed sediments is tricky business. Searching high and wide only three datasets with 78 samples were found that contained all the required information (grain size distribution, clay mineralogy). Needless to say, more data are needed to improve the predictive equations. In a paper published a few years ago we found that in most cases, the permeability of the sediments could be estimated in a two-step process:

  • calculate the permeability of clay and granular (sand/silt) components, and
  • calculate the permeability of the mixed sediment by taking the geometric mean of the two components weighed by the clay content of the sediment.

The resulting workflow was published as a series of equations that are not particularly easy to work with. That is why we recently decided to take advantage of the general awesomeness of Jupyter notebooks to publish a do-it-yourself notebook to calculate permeability on GitHub (https://github.com/ElcoLuijendijk/permeability_notebooks). For those of you new to Jupyter notebooks: these are documents that contain a readable mix of text, code, data and figures and can be used to publish studies in such a way that you can reproduce the analysis and make the figures yourself (much like R Markdown).

The Jupyter notebooks to calculate permeability consist of a main notebook and additional notebooks to calculate the specific surface area of sediments. Also included are all the calibration datasets Jthat were compiled for the publication. You can use the data to evaluate how well the permeability equations match these datasets, or you can set up a new spreadsheet with data from your own study area which can then be used by the notebook to calculate permeability. The notebook automatically generates several figures like the one below (Figure 1).

There is also an additional notebook that calculates first-order estimates of permeability from well log data collected by geophysical tools that map the density or water content of sediments. Such well log data can be more widely available than detailed sediment records and may help estimate permeability for the deeper subsurface (>100s of m), where permeability data are generally scarcer than at the surface.

Comparing these datasets and equations with the Jupyter notebooks highlight the gaps in quantifying permeability. These notebooks and datasets are out there for the world, so join the effort to make more accurate predictions of permeability (and groundwater flow) in sediments!

Figure 1: Figure produced by the Jupyter notebook showing measured vs calculated permeability using an example dataset of mixed natural sediments.

 

Quest for Sustainability of Heavily Stressed Aquifers at Regional to Global Scales: Upcoming Chapman Conference

Quest for Sustainability of Heavily Stressed Aquifers at Regional to Global Scales: Upcoming Chapman Conference

Abstracts are due soon (July 10th) for the upcoming Chapman conference on groundwater sustainability on Oct 21-24, 2019 in Valencia, Spain. Hopefully this will be a rare opportunity where many of the leading people on groundwater sustainability will gather with a shared intention to share, discuss and debate scientific advances and encourage a pivot towards groundwater sustainability.

A range of prestigious invited speakers will provide diverse perspectives on groundwater sustainability. We have limited travel funding from the NSF – priority will be given to US-based students and early career researchers (pre-tenure faculty and postdoctoral fellows). Please pencil this in the conference date and submit an abstract here, and pass this along to anyone who might be interested!

WaterUnderground founder Tom Gleeson is part of the Chapman conference organizing committee and is leading an effort to draft ‘The Valencia Statement and Action Agenda on Global Groundwater Sustainability’. Please get in touch with Tom  if you are interested in contributing!

 

Doing Hydrogeology in R

Doing Hydrogeology in R

Post by Sam Zipper (@ZipperSam), current Postdoctoral Fellow at the University of Victoria and soon-to-be research scientist with the Kansas Geological Survey at the University of Kansas.


Using programming languages to interact with, analyze, and visualize data is an increasingly important skill for hydrogeologists to have. Coding-based science makes it easier to process and visualize large amounts of data and increase the reproducibility of your work, both for yourself and others. 

There are many programming languages out there; anecdotally, the most commonly used languages in the hydrogeology community are Python, MATLAB, and R. Kevin previously wrote a post highlighting Python’s role in the hydrogeology toolbox, in particular the excellent FloPy package for creating and interacting with MODFLOW models. 

In this post, we’ll focus on R to explore some of the tools that can be used for hydrogeology. R uses ‘packages’, which are collections of functions related to a similar task. There are thousands of R packages; recently, two colleagues and I compiled a ‘Hydrology Task View’ which compiles and describes a large number of water-related packages. We found that water-related R packages can be broadly categorized into data retrieval, data analysis, and modelling applications. Though packages related to surface water and meteorological data constitute the bulk of the package, there are many groundwater-relevant packages for each step of a typical workflow.

Here, I’ll focus on some of the packages I use most frequently. 

Data Retrieval:

Instead of downloading data as a CSV file and reading it into R, many packages exist to directly interface with online water data portals. For instance, dataRetrieval and waterData connect to the US Geological Survey water information service, tidyhydat to the Canadian streamflow monitoring network, and rnrfa for the UK National River Flow Archive.

Data Analysis:

Many common data analysis tasks are contained in various R packages. hydroTSM and zoo are excellent for working with timeseries data, and lfstat calculates various low-flow statistics. The EcoHydRology package contains an automated digital filter for baseflow separation from streamflow data.

Modelling:

While R does not have an interface to MODFLOW, there are many other models that can be run within R. The boussinesq package, unsurprisingly, contains functions to solve the 1D Boussinesq equation, and the kwb.hantush package models groundwater mounding beneath an infiltration basin. The first and only package I’ve ever made, streamDepletr, contains analytical models for estimating streamflow depletion due to groundwater pumping. To evaluate your model, check out the hydroGOF package which calculated many common goodness-of-fit metrics.

How do I get and learn R?

R is an open-source software program, available here. RStudio is a user-friendly interface for working with R. RStudio has also compiled a number of tutorials to help you get started!

Other Useful Resources

Louise Slater and many co-authors currently have a paper under discussion about ‘Using R in Hydrology’ which has many excellent resources.

While not hydrogeology-specific, there are many packages for generic data analysis and visualization that will be of use to hydrogeologists. In particular, the Tidyverse has a number of packages for reading, tidying, and visualizing data such as dplyr and ggplot2.

Claus Wilke’s Fundamentals of Data Visualization book (free online) was written entirely within R and shows examples of the many ways that R can be used to make beautiful graphs.

Data sharing: an update on new and existing initiatives

Data sharing: an update on new and existing initiatives

Post by Anne Van Loon, Gemma Coxon, and Bentje Brauns.


Last year, Anne Van Loon wrote about data sharing initiatives in hydrology (“Data drought or data flood? 28 May 2018). This post gives an update on existing and new initiatives.

CAMELS (Catchment Attributes and MEteorology for Large-sample Studies) 

The CAMELS datasets are expanding: from the United States and Chile to Great Britain and Australia.  The CAMELS-GB dataset will consist of hydro-meteorological timeseries and catchment attributes for 671 catchments across Great Britain and is expected to be released on the Environmental Information Data Centre later this year.

The Groundwater Drought Initiative

The Groundwater Drought Initiative is collecting more and more groundwater level data and groundwater drought impacts. The Initiative is very happy to welcome new partners and supporters from as far East as Ukraine and as far South as Albania, increasing the number of participating countries and countries currently considering to participate to 23 (see map). Additionally, a first getting-to-know-each-other & info meeting was held at EGU19 with participants from Austria, Belgium, Canada, Estonia, Germany, Latvia, Luxembourg, Netherlands, Norway, UK, Ukraine, and Switzerland. If you are from Bulgaria, Greece, Hungary, Italy, Romania, Slovakia or any of the other yellow countries on the map below and you have groundwater data (or contacts in organisations who could help) or you are interested in groundwater drought, please contact Bentje Brauns (benaun@bgs.ac.uk).

The IAHS Panta Rhei Working Group on Large Sample Hydrology

The IAHS Panta Rhei focus on efforts to facilitate the production and exchange of datasets worldwide.  This year at EGU, the group organised a splinter meeting to discuss the generation of large sample catchment datasets in the cloud and a session (HS2.5.2 Large-sample hydrology: characterising and understanding hydrological diversity) that showcased several recent data- and model-based efforts on large-sample hydrology from new global datasets to large multi-model ensembles.  If you are interested in being updated on the activities of the group then please contact Gemma Coxon (gemma.coxon@bristol.ac.uk) to be added to the mailing list.

There seems to be a lot going on in the world of hydrological data sharing! To share your own story or initiative, please leave a reply below.



Anne Van Loon (website | @AnneVanLoon) is a Senior Lecturer in Physical Geography  in the School of Geography, Earth and Environmental Sciences at the University of Birmingham.

Gemma Coxon (website) is a Postdoctoral Research Associate and Lecturer in Hydrology in the School of Geographical Sciences at the University of Bristol.

Bentje Brauns (website) is a Hydrogeologist at the British Geological Survey.

Video: Linking water planetary boundaries and UN Sustainable Development Goals

Video: Linking water planetary boundaries and UN Sustainable Development Goals

Water Underground creator Tom Gleeson prepared this quick research video (with no more than a toothbrush, a file holder, and a doughnut, in one take!) for the Ripples project meeting at the Stockholm Resilience Centre, that was held in April. In this video, he talks about using doughnut economics for linking water planetary boundaries and UN Sustainable Development Goals.

 


Curious about why a toothbrush features in the video? For the answer, you’ll need to watch Tom’s previous research video from last summer (see below), on “Revisiting the planetary boundary for water”.

Dowsing for interesting water science – what’s exciting at EGU 2019?

Dowsing for interesting water science – what’s exciting at EGU 2019?

Joint post by Sam Zipper (an EGU first-timer) and Anne Van Loon (an EGU veteran).


Every April, the European Geophysical Union (EGU) holds an annual meeting in Vienna. With thousands of presentations spread out over a full week, it can feel like you’re surrounded by a deluge of water-related options – particularly since the conference center is on an island!  To help narrow down the schedule! Here, we present a few water-related sessions and events each day that caught our attention. Feel free to suggest more highlights on Twitter (using #EGU19) or in the comments section!


Monday 8 April

Using R in Hydrology (SC1.44)

  • Short course 16:15-18:00.
  • This short course will cover R packages and tools for hydrology with both newcomers and experienced users in mind.

Innovative sensing techniques for water monitoring, modelling, and management: Satellites, gauges, and citizens (HS3.3).

  • Posters 16:15-18:00.
  • Curious about new approaches to hydrological science? This session features citizen science, crowdsourcing, and other new data collection techniques.

Plastics in the Hydrosphere: An urgent problem requiring global action


Tuesday 9 April

Nature-based solutions for hydrological extremes and water-resources management (HS5.1.2)

  • Posters 08:30-10:15Orals 10:45-12:30
  • Nature-based solutions are meant to be ‘living’ approaches to address water management challenges – this session will explore how they are used in both urban and rural areas.

HS Division meeting: If you want to know more about the organisation of the Hydrological Sciences Division of EGU (and you like free lunch) check this out!

Plinius Medal Lecture by Philip J. Ward: Global water risk dynamics


Wednesday 10 April

Large-sample hydrology: characterising and understanding hydrological diversity (HS2.5.2)

Sustainability and adaptive management of groundwater resources in a changing environment (HS8.2.1)

  • Posters 10:45-12:30, Orals 16:15-18:00.
  • This session features examples of groundwater sustainability (and challenges) all over the world, with a particular focus on Integrated Water Resources Management.

HS Division Outstanding ECS Lecture by Serena Ceola: Human-impacted rivers: new perspectives from global high-resolution monitoring

Geoscience Game Night (SCA1)


Thursday 11 April

How can Earth, Planetary, and Space scientists contribute to the UN SDGs? (ITS3.5)

  • PICOs 16:15-18:00.
  • Check out the fun PICO format – a combination of posters and talks – and help figure out what the role of earth science is in meeting the United Nations Sustainable Development Goals.

Urban groundwater: A strategic resource (HS8.2.7)

  • PICOs 10:45-12:30.
  • Urban groundwater is understudied relative to groundwater in agricultural areas – what do we know about urban groundwater, and what remains to be learned?

Henry Darcy Medal Lecture by Petra Döll: Understanding and communicating the global freshwater system


Friday 12 April

Innovative methods to facilitate open science and data analysis in hydrology (HS1.2.7)

  • PICOs 08:30-12:30
  • Learn about how you can make your science more open, whether you are an open science beginner or a long-time data sharer!

History of Hydrology (HS1.2.3)

Social Science methods for natural scientists (SC1.48)

  • Short course 14:00–15:45
  • This short course is for everyone who has some dealings with people in their research, such as stakeholders, citizen science, The aim of the session is to demystify Social Science and give practical tips & tricks.

Other Resources

Several other groups and blogs have also compiled water-relevant sessions. Make sure to check out their recommendations, as well!


Cover image source: https://cdn.pixabay.com/photo/2015/09/09/21/33/vienna-933500_960_720.jpg

 

Have you ever wondered if groundwater is connected to climate?

Have you ever wondered if groundwater is connected to climate?

Post by Tom Gleeson Assistant Professor in Civil Engineering at the University of Victoria.


‘Groundwater-surface water interactions’ has become standard hydrologic lexicon and a perennial favorite session title at various conferences… but how often do you hear the phrase ‘groundwater-climate interactions’?

A group of hydrologists, hydrogeologists, atmospheric scientists and geodesists that met in Taiwan this week would say ‘not enough!’ We met to discuss how groundwater, the slow-moving grandparent of the hydrologic cycle interacts with the atmosphere, the fast-moving toddler. The 2nd international workshop on Impacts of Groundwater in Earth system Models (IGEM), was a follow-up of a 2016 workshop in Paris in 2016 (and part of a the bilateral French-Taiwanese IGEM project).

Sessions were focused around a few themes:

  • Groundwater use and its impacts
  • Groundwater representation, assimilation and evaluation in climate models
  • Remote Sensing and in-situ observations on groundwater
  • Groundwater-climate interactions with a special focus on Nebraska

 

And in the afternoons we convened discussion groups focused on ‘groundwater representation in continental to global hydrologic models’ and ‘groundwater-climate interactions’ and arguably just as importantly we ate lots of great food including an awesome fusion dinner and dumplings at the famous Din Tai Fung.

I would love to say that we could provide you with a simple, robust answer to the leading question of how and where groundwater is connected to climate – a holy grail of Earth System science. But like all good questions, the answer at least right now is ‘a little bit in some places, and it depends how you look at it’. We discussed the first enticing but preliminary results of potential hotspots of groundwater-climate interactions, expounded on the importance to water sustainability and dissected vadose zone parameterizations in land surface models but the quest for this holy grail goes on… We plan to meet again in a few years in Saskatchewan and maybe have a few more answers. Do you want to join us on this holy grail quest, and maybe end up making ‘groundwater-climate interactions’ more standard lexicon?

P.S. Thanks to Min-Hui Lo and his group at National Taiwan University for the excellent hospitality and organization!

P.S.S. Just in case it goes viral, the term ‘baddest-ass model’ was first used by Jay Famiglietti (see below).

Celestial groundwater – the subsurface plumbing for extraterrestrial life support

Celestial groundwater – the subsurface plumbing for extraterrestrial life support

Post by Kevin Befus Assistant Professor in Civil and Architectural Engineering at the University of Wyoming.


Have you ever taken a walk on the beach during a lowering (ebbing) tide and see mini-rivers grow and create beautiful drainage patterns before your eyes? These short-lived groundwater seepage features (Fig. 1A) are tiny (and fast) analogs of how groundwater has shaped some parts of Mars! It appears that groundwater loosening sediments can lead to all sorts of scales of erosion on both Earth and Mars.

Figure 1. A) Beach drainage pattern on the order of 1 meter (Source: https://epod.usra.edu/blog/2017/01/beach-drainage.html), B) Martian “alcoves” suggesting groundwater seepage [1].

Mars is not currently a friendly place for water to exist at the surface or even the subsurface, but an abundance of photographic and topographic evidence point to there having been the right conditions for active groundwater flow on Mars.

But isn’t Mars too cold for liquid water? The answer is generally a strong yes for the past few billion years, but amazingly enough, there appears to have been some local places where groundwater discharged to the Martian surface and left behind telltale signs.

Because Mars is cold at its land surface (mean surface temperature of -50 C with daily swings from 0 C to -100 C) with a thinner atmosphere than Earth’s, water on the Martian surface can exist as ice (as in the polar ice cap), but sublimation and evaporation would quickly wick any water near the surface. So, liquid water on Mars needs both more pressure and a good bit of heat for mobile groundwater based on the phase diagram below (circle with M shows the present day Martian surface conditions).

Figure 2. Phase diagram showing average conditions at the planetary surface for Earth (E) near the triple point, and atmospheric conditions for the frozen Mars (M) and vapor-rich Venus (V). source: http://www1.lsbu.ac.uk/water/water_phase_diagram.html#intr2; License: https://creativecommons.org/licenses/by-nc-nd/2.0/uk/)

It turns out that the most expansive evidence of liquid groundwater on Mars comes from deep at the bottom of craters (…deeper than 5 km!), where the Martian geothermal gradient (~10 C/km [Michalski et al.2013]) heats up to the point where groundwater systems, probably made up of brines, can seep across the crater walls. Without the craters, the groundwater wouldn’t have anywhere to discharge, but extraterrestrial hydrogeologists (really based on the geomorphology, but using E.T. hydrogeology principles) have identified numerous craters with groundwater seepage erosional patterns (Figure 1). The question remains open on how connected the Martian “aquifers” could be, or if the craters represent only local flow systems.

With liquid groundwater transporting the chemical-rich waters from deeper geothermal areas, the conditions could be right for supporting a deep Martian biosphere. Buried in under the Martian ice, soil, and rock microbial life could have evolved in the subterranean shelter from cosmic radiation. Groundwater flow, potentially related to geothermal conditions, could then have served as the conveyor belt for energy-rich molecules to feed microbial life in the subsurface (and still could?).

So far, Earth is the only celestial body in our solar system with an active water-hydrologic cycle, making us the lucky green planet. But, there could be a methane-based hydrologic cycle on Titan with “methanifers” as methane aquifers! For more information on extraterrestrial hydrogeology, Baker et al. (2005) provides a great overview of the planetary, lunar, and exo-planetary potential for water and groundwater, loosely summarized in this table.

At the moment, Earthlings don’t know that much yet about the paleo-hydrologic processes on Mars. But with new boots…I mean wheels…on the ground in two water-focused locations, new clues could start rolling in on Martian groundwater. The recently-arrived InSight lander will probe the Martian subsurface by drilling 5 m deep and listen for acoustic signals for even more information on the interior of Mars. The next Mars Rover is scheduled to take flight in 2020 for the Jezero Crater, where a river delta could help unravel the water-life story of Mars. And could have some groundwater surprises! At only about 1 km deep, the focus in mainly on tracking down signs of life and unravelling surface hydrologic and erosional processes on Mars, but a long list of expected outcomes does show the mission will keep an eye out for evidence of groundwater activities. Keep your feet grounded, eyes in the sky, and visions of Martian groundwater flying high and drilling low!

References
[1] Malin, M. C., and K. S. Edgett (2000), Evidence for Recent Groundwater Seepage and Surface Runoff on Mars, Science, 288(5475), 2330–2335, doi:10.1126/science.288.5475.2330.
[2] Michalski, J. R., J. Cuadros, P. B. Niles, J. Parnell, A. Deanne Rogers, and S. P. Wright (2013), Groundwater activity on Mars and implications for a deep biosphere, Nat. Geosci., 6(2), 133–138, doi:10.1038/ngeo1706.
[3] Stofan, E. R. et al. (2007), The lakes of Titan, Nature, 445(7123), 61–64, doi:10.1038/nature05438.
[4] Baker, V. R., J. M. Dohm, A. G. Fairén, T. P. A. Ferré, J. C. Ferris, H. Miyamoto, and D. Schulze-Makuch (2005), Extraterrestrial hydrogeology, Hydrogeol. J., 13(1), 51–68, doi:10.1007/s10040-004-0433-2.
[5] Robinson, K. L., and G. J. Taylor (2014), Heterogeneous distribution of water in the Moon, Nat. Geosci., 7(6), 401–408, doi:10.1038/ngeo2173.
[6] Jurac, S., M. A. McGrath, R. E. Johnson, J. D. Richardson, V. M. Vasyliunas, and A. Eviatar (2002), Saturn: Search for a missing water source, Geophys. Res. Lett., 29(24), 25-1-25–4, doi:10.1029/2002GL015855.

Kevin Befus leads the groundwater hydrology group in the Civil and Architectural Engineering Department at the University of Wyoming. With his research group, he studies how groundwater systems respond to hydrologic conditions over glacial timescales and in mountainous and coastal environments.  You can follow along with Kevin’s research through any of the links below:

Personal Webpage | Twitter Research Group Page | UW Faculty Page

 

 

 

 

 


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Of Karst! – short episodes about karst

Of Karst! – short episodes about karst

Post by Andreas Hartmann Assistant Professor in Hydrological Modeling and Water Resources at the University of Freiburg.


Episode 4 – Karst Groundwater: quick and slow at the same time?

We often associate groundwater with large water storage and very slow water movement for instance compared to rivers. But is it possible that groundwater flow can be as quick as stream flow and, at the same aquifer, flow for several months or years before it is reaching the surface again? Of karst, it is possible! When chemical weathering is able dissolve carbonate rock, cracks and fissures may grow to a subsurface channel system that can take vast amounts of water flow (see Of Karst! – episode 2).

The schematic figure below shows how this affects water flow in a karst system. At the surface, water may flow for some distance (external runoff towards the recharge area or internal runoff within the recharge area), before it reaches a dissolution widened vertical crack or fissure. On its way, part of it may slowly infiltrate into the soil but the stronger the rainfall event, the more water will infiltrate quickly into cracks and fissures after being redistributed laterally. Consequently, slow and quick infiltration will be followed by slow and quick vertical flow through the vadose zone. The former through the carbonate rock matrix, the latter through the interconnected system of dissolution caves. Finally, recharge and groundwater flow take place, again quickly through the caves and slowly through the matrix.  When passing the system through the cave network, water can enter and leave the system within several hours. When taking the slow and diffuse path, the transit through the system may take months to years.

Because of this behavior, hydrogeologists often speak about the Duality of Karstic Groundwater Flow and storage, although it is known that there is a wide range of dynamics between quick flow through the caves and slow flow through the matrix and that lateral redistribution between the interconnected caves and the matrix takes place at almost every part of the system.

Figure 1: Schematic description of karstic groundwater flow and storage (Hartmann et al., 2014; modified)

A rather uncomfortable lesson on quick flow processes in karst was learned by a group of school students on a trip through a karstic cave in Thailand. Due to the quick recharge processes explained above, the groundwater tables could quickly rise blocking the return path of the group and resulting in a dramatic rescue mission:

In order to predict the impact of interplay of quick and slow karstic groundwater processes on cave water levels or water resources in general, karst-specific simulation models are necessary. If you are interested in those, follow the Water Underground blog’s postings and wait for Of Karst! Episode 5, which will introduce karstic groundwater modelling.


Andreas Hartmann is an Assistant Professor in Hydrological Modeling and Water Resources at the University of Freiburg. His primary field of interest is karst hydrology and hydrological modelling. Find out more at his personal webpage www.subsurface-heterogeneity.com  

Further reading: Hartmann, A., Goldscheider, N., Wagener, T., Lange, J., Weiler, M., 2014. Karst water resources in a changing world: Review of hydrological modeling approaches. Rev. Geophys. 52, 218–242. doi:10.1002/2013rg000443

 

 


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