Water and chemical budgets of gravel pit lakes: Case studies of fluvial gravel pit lakes along the Meuse River (The Netherlands) and coastal gravel pit lakes along the Adriatic Sea (Ravenna, Italy)

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Water and chemical budgets of

gravel pit lakes

Case studies of fluvial gravel pit lakes along the Meuse

River (the Netherlands) and coastal gravel pit lakes

along the Adriatic Sea (Ravenna, Italy)

Pauline N. Mollema

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Water and chemical budgets of gravel pit lakes.

Case studies of fluvial gravel pit lakes along the Meuse River (The Netherlands) and coastal gravel pit lakes along the Adriatic Sea (Ravenna, Italy).

(PhD thesis, Technische Universiteit Delft)

Keywords: hydrology, hydrochemistry, gravel pit lakes, Italy,

This research was funded in part by WML Limburgs Drinkwater (Maastricht, Netherlands) and by The University of Bologna. Work was carr

Biological, Geological and Environmental Sciences, at the VU University Amsterdam and at the Technical University Delft.

Reuse of the knowledge and information in this publ due credit is given to the source.

Contact: pmollema@gmail.com Cover photographs: Google Earth ISBN: 978-94-6233-214-0

Lay-out front page and printing: Gildeprint Drukkerijen Water and chemical budgets of gravel pit lakes.

(PhD thesis, Technische Universiteit Delft)

: hydrology, hydrochemistry, gravel pit lakes, Italy, the Netherlands

This research was funded in part by WML Limburgs Drinkwater (Maastricht, Netherlands) and by Work was carried out at The University of Bologna, Department of Biological, Geological and Environmental Sciences, at the VU University Amsterdam and at the

Reuse of the knowledge and information in this publication is welcomed on the understanding that

Cover photographs: Google EarthTM_{and Pauline N. Mollema}

out front page and printing: Gildeprint Drukkerijen www.gildeprint.nl

Case studies of fluvial gravel pit lakes along the Meuse River (The Netherlands) and coastal gravel

Netherlands

This research was funded in part by WML Limburgs Drinkwater (Maastricht, Netherlands) and by ied out at The University of Bologna, Department of Biological, Geological and Environmental Sciences, at the VU University Amsterdam and at the

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Water and chemical budgets of gravel pit lakes.

Proefschrift

ter verkrijging van de graad van doctor aan de Technische Universiteit Delft,

op gezag van de Rector Magnificus prof. ir. K.C.A.M. Luyben, voorzitter van het College voor Promoties,

in het openbaar te verdedigen op vrijdag 12 februari 2016 om 12:30 uur.

door

Pauline Nella MOLLEMA

Master of Science Stanford University 1994 and Master of Science Utrecht University 1992, geboren te ’s Gravenhage, Nederland op 28 juni 1968

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Dit proefschrift is goedgekeurd door: Promotor: Prof.dr. P.J. Stuyfzand Copromotor: Dr. M. Antonellini

Samenstelling promotiecommissie: Rector magnificus Voorzitter

Prof.dr. P.J. Stuyfzand Technische Universiteit Delft, promotor Dr. M. Antonellini Università di Bologna, copromotor

Onafhankelijke leden:

Prof. dr. Th. Hofmann Universität Wien Prof. dr. K. Walraevens Universiteit Gent

Prof. dr. ir. H.H.G. Savenije Technische Universiteit Delft Prof. dr. ir. T.J. Heimovaara Technische Universiteit Delft Dr. N. Hartog KWR en Universiteit Utrecht

This research was funded in part by WML Limburgs Drinkwater (Maastricht, Netherlands) and by The University of Bologna. Work was carried out at The University of Bologna, Department of Biological, Geological and Environmental Sciences, at the Faculty of Earth and Life Sciences, VU University Amsterdam and at the Technical University Delft.

ISBN: 978-94-6233-214-0

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Appendix 2A ... 149 Appendix 2b ... 153 Appendix 2C ... 154 Appendix 3A ... 155 Appendix 3B ... 157 Appendix 3C ... 161 Appendix 4A ... 162 Appendix 4B ... 162 Appendix 5A ... 163 Appendix 5B ... 170 Appendix 5C ... 171 Appendix 5D ... 173 Appendix 5E ... 175 Bibliography ... 176 Acknowledgements ... 200

About the author ... 201

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1

SUMMARY

Gravel pit lakes form when gravel is excavated from below the water table of a phreatic or shallow confined aquifer. Typically many of these lakes are concentrated along naturally occurring sedimentary gravel deposits in areas where gravel is needed for construction. Most gravel pit lakes are relatively young features: most are less than 50 years old. The subject of this PhD thesis is to determine how gravel pit lakes change the hydrology and hydrochemistry of an aquifer, a watershed or a drainage basin. Hereto I studied gravel pit lakes in a fluvial freshwater setting of the Meuse Valley (the Netherlands) and gravel pit lakes excavated in ancient beach deposits, filled with brackish water along in the Adriatic coastal zone near Ravenna (Italy). One of the Dutch lakes is used for artificial recharge and drinking water production (DLV Lake) while some other gravel pit lakes are used for recreational purposes (swimming, sailing, scuba diving). The surface water of the lakes and other surface waters (wetlands, rivers) as well as groundwater up and downstream of the lakes was sampled and analyzed for major ion chemistry, trace elements and stable water isotopes. Chemical and water budgets were calculated. The excavation of many gravel pit lakes adds a large surface water area to a watershed. In the Dutch study site 71 lakes between the towns of Maastricht and Asselt add 20 km2_{of surface water which is}

0.26 % percent of the Dutch part of the Meuse watershed. In the Italian drainage basin thirteen lakes with a total surface of 684 hectares cover 6.6% % of the drainage basin. This increase causes a loss of freshwater since surface water evaporation rates in temperate and Mediterranean climates are usually higher than evapotranspiration rates of the pre-existing grassland and forest. The drainage pattern of a watershed changes in presence of gravel pit lakes causing fluctuations of the water table over a large area. In a low lying coastal zone, as the Italian study area, these fluctuations and the fact that the lakes form a constant head surface below sea level enhance salt water intrusion into the aquifer. Gravel pit lakes can be flow-through lakes where groundwater moves through the lake downstream towards a river or other draining feature (for instance a well field) or, alternatively, they may be in direct connection with a river. The gravel pit lakes that I studied in detail have in common that the water budget of the lakes is strongly determined by artificial drainage. In the Dutch DLV Lake, the artificial drainage is caused by pumping wells that extract water for drinking water production downstream of the lake. In the Italian case, the artificial drainage is induced by the land reclamation works that protect the low-lying land from flooding.

Watersheds with multiple gravel pit lakes are more sensitive to changes in climate than watersheds without gravel pit lakes because surface water evaporation rates are more sensitive to changes in climate than evapotranspiration. Especially in groundwater fed gravel pit lakes, evaporated water is replaced by groundwater. Instead evapotranspiration of soil moisture in a watershed without gravel pit lakes, can increase only to certain extend as soil moisture is only fed by precipitation and not by groundwater flow.

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Water budget and conservative tracer modeling showed that because artificial drainage plays such a large role that changes in pumping rates needed to prevent flooding due to higher sea levels (The Italian study site) will affect evapo-concentration more than changes in surface water evaporation caused by climate change. Precipitation on the Italian gravel pit lakes is immediately mixed with brackish gravel pit lake water and can no longer recharge the fresh-brackish rainwater lenses in the upper part of the aquifer. Both the Dutch and the Italian gravel pit lake water has a high alkalinity, a high pH, and metal and trace element concentrations that differ from the groundwater in their respective watersheds. Differences do exist among the specific trace element concentrations, and their budgets in the lakes and the respective watersheds. This stems from the influence of sea water in the Italian case study and the specific soil chemistry of both settings. As and Ba, for example, show up in high concentrations in groundwater and gravel pit lake water in Italy but not in the Netherlands, where Ni, Zn and Al are more important. Differences in chemistry (Fe, SO4, HCO3, Ni etc. and pH) between gravel pit lake water and groundwater

and variations along flow lines show that redox reactions in the soil near the gravel pit lakes occurred in both study sites. These reactions, enhanced by fluctuating water tables and/or denitrification of fertilized soils, have mobilized metals including Fe, Zn, and Ni and other elements such as Al and As. In part, these elements have been adsorbed again by the soil, as is the case for As in the Dutch site, in part they reach the gravel pit lakes where they precipitate on the lake bottom (for example, Fe, Zn, Ni, Al) and some elements remain (partly) in solution in the gravel pit lake water (e.g. As in the Italian lakes).

The gravel pit lakes are strongly influenced by the land use and climate of their watershed. If circumstances change that would lead to less available oxygen either as DO or in NO3 or

that would lead to a lower pH of the lake water, then the reactions that initially caused the deposition of the metals and trace elements on the lake bottom may be reversed. Metals and trace elements could go again into solution, possibly creating a toxic environment for plants, animals, and humans. These changes may be brought about by a change in land use, for example a reduction in the use of fertilizers, or a change in climate (less recharge of the aquifer), or slow leaching processes such as decalcification of the soil. On the other hand, an increasing eutrophication and primary production stimulated by high temperatures or less lake water circulation, would cause an increase in organic and fine grained material deposition to the lake bottom, which would help to fix the metals and trace elements in the lake bottom sediments.

The rate of these processes may change over time since gravel pit lakes have formed only recently while land use and climate change play a role in their current and future evolution. The fixation of metals, C, nutrients and other elements in gravel pit lakes changes also the hydrochemistry of the estuary downstream of the lakes by preventing discharge of dissolved chemical elements into rivers and the sea. In order to assess and evaluate a watershed with gravel pit lakes for its safe use, it is necessary to monitor not only the lake water but also the groundwater, the water budget and the evolution of hydrochemical processes as climate and land use change.

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SAMENVATTING

Tijdens zand en grindwinning in gebieden met een ondiepe water spiegel, vullen de uitgravingen zich met grondwater en vormen meren en (diepe) plassen. In bepaalde gebieden komen deze zandwinputten in grote aantallen voor, geconcentreerd langs natuurlijke sedimentaire grind afzettingen in gebieden waar grind nodig is voor de bouw. De meeste zandwinputten zijn relatief jong: minder dan 50 jaar oud. Het onderwerp van dit proefschrift is de studie naar de veranderingen die zandwinputten teweeg brengen in de hydrologie en hydrochemie van een watervoerend pakket, een rivierbekken of een polder. Daartoe heb ik zandwinputten in het rivierdal van de Maas bestudeerd waar de plassen met zoetwater zijn gevuld en ook zandwinputten gevuld met brak water, in oude strandafzettingen bij Ravenna (Italie) langs de Adriatische kust . Eèn van de bestudeerde Nederlandse zandwinputten (De Lange Vlieter bij Heel) wordt gebruikt voor kunstmatige infiltratie van rivierwater terwijl de andere plassen worden gebruikt voor recreative doeleinden als zwemmen, duiken en zeilen. Het oppervlakte water in de zandwinputten en van andere wateren als rivieren en vennen en ook het grondwater boven en benedenstrooms van de zandwinputten is bemonsterd. Het water is daarna geanalyseerd op de belangrijkste chemische elementen, anionen en kat-ionen, sporenelementen en stabiele isotope van water. De waterbalans en ook divere chemische balansen van de zandwinputten zijn berekend.

Het uitgraven van veel zandwinputten dicht bijelkaar zorgt voor een toevoeging van oppervlakte water. In het Nederlandse studie gebied de Maasplassen zorgen 71 plassen tussen Maastricht en Asselt voor een toevoeging van 20 km2_{oppervlakte water , gelijk aan}

0.26% van het nederlandse deel van het stroomgebied van de Maas. In de Italiaanse polder is de totale oppervlakte van 13 zandwinputten 684 hectare die samen 7 % van de oppervlakte van de ‘Quinto Basin polder’ innemen. Dit extra oppervlaktewater zorgt voor een verlies aan zoetwater omdat oppervlaktewaterverdamping in een gematigd en mediterraans klimaat als van de studiegebieden, doorgaans groter is dan evapotranspiratie van grasland of bos. Ook het afwateringspatroon van een rivierbekken veranderd in de aanwezigheid van zandwinputten omdat ze zorgen voor fluctuaties in de waterspiegel over een grote afstand. In laag gelegen kustgebieden als in het Italiaanse studie gebied, zorgen deze fluctuaties en de plassen die een equipotentiaal vlak onder zeeniveau vormen, voor verzilting van het grondwater.

Als grondwater aan de ene kant de zandwinput instroomt en aan de andere kant eruit en de grond weer in, dan noemt men het ‘door-stroom’ of ‘flow-through’ plassen. Zandwinputten kunnen ook in open verbinding met een rivier staan. De zandwinputten die ik in detail heb bestudeerd hebben gemeen dat hun waterbalans voor een groot deel bepaald wordt door kunstmatige drainage. In de Nederlandse De Lange Vlieter (DLV) is de drainage veroorzaakt door grondwater ontrekking met behulp van pomp putten

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benedenstrooms van de plas. In de Italiaanse plassen is de drainage veroorzaakt door het polder gemaal dat er voor zorgt dat het laaggelegen land niet onderstroomt.

Rivierbekkens of polders met meerdere zandwinputten zijn gevoeliger voor klimaats veranderingen dan die zonder zandwinputten omdat de verdamping van oppervlaktewater gevoeliger is voor klimaats veranderingen dan evapotranspiratie van grass of bos land dat door de zandwinputten vervangen is. In zandwinputten die gevoed worden door grondwater of rivier water, wordt het verdampte water vervangen waardoor een grotere verdamping mogelijk is. Evapotranspiratie van bodemvocht in een bekken of polder zonder zandwinputten kan maar toenemen tot in zekere mate.

Het modelleren van de waterbalans met chloride als conservatieve element laat zien, dat veranderingen in pomp debiet, nodig om overstromingen te voorkomen vanwege hoger zee niveau (Italië) een grotere invloed zal hebben op het process van evapoconcentratie dan veranderingen in de verdampings snelheid door klimaats veranderingen. Neerslag op de Italiaanse zandwinputten mengt zich onmiddelijk met het brakke water in de plas en draagt zo niet langer bij aan devorming van zoet-brakke regen-lensen in de grond.

Zowel de Nederlandse als de Italiaanse zandwinputten bevatten water met een hoge alkaliniteit, een hoge pH en concentraties van metalen en sporen elementen die anders zijn dan die in het nabije grondwater. Er zijn verschillen in de specifieke sporenelementen concentraties en hun balans tussen de twee studie gebieden. Dat is vanwege de invloed van zeewater in het Italiaanse geval en de specifieke bodem chemie in beide studie gebieden. Arsenicum en Barium bijvoorbeeld komen voor in hoge concentraties in grondwater en in de zandwinputten in Italie maar niet in Nederland waar Nikkel, Zink and Aluminium belangrijker zijn. Verschillen in chemie (Fe, SO4, HCO3, Ni etc. and pH) tussen

zandwinput water en groundwater en variaties langs stroomlijnen demonstreren dat redox reacties optreden in de bodem van beide studie gebieden. Deze reacties aangemoedigd door fluctuerende waterspiegels en /of door de de-nitrificatie van (kunst) mest hebben metalen als Fe, Zn, en Ni en andere elementen als Al and As gemobiliseerd. Deze elementen zijn deels weer geadsorbeerd door de bodem zoals in het geval van As in het nederlandse studie gebied maar deels komen ze met het grondwater in de zandwinputten terecht waar ze neerslaan op de bodem (bijvoorbeld, Fe, Zn, Ni, Al) en sommige elementen blijven deels in oplossing in het water van de zandwinput (bijvoorbeeld As in de italiaanse meren).

De waterkwaliteit in de zandwinputten wordt sterk beinvloed door het gebruik van het land en door het klimaat van het rivierbekken of polder. Als er in de toekomst minder zuurstof beschikbaar zou zijn als DO of NO3 of als de pH van het zandwinput water lager zou

worden, dan zouden de reacties die eerst zorgden voor het neerslaan van metalen en sporen elementen op de bodem van de plassen, omgedraaid kunnen worden. Metalen en sporenelementen zouden weer kunnen oplossen en daarbij zouden ze een giftige omgeving kunnen creeren voor planten, beesten en mensen.

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Deze veranderingen zouden kunnen worden veroorzaakt door bijvoorbeeld een afname in het gebruik van bemesting, of door een verandering in het klimaat met bijvoorbeeld minder infiltratie van water in de bodem, of door langzame uitlogings processen in de bodem als bijvoorbeeld decalcificatie die leidt tot verzuring van de bodem. Aan de andere kant zou een grotere eutrophicatie en primaire productie gestimuleerd door hogere temperatuur of minder circulatie in het water, een grotere sedimentie van organisch material tot gevolg hebben. Dit zou helpen om de concentratie van metalen in bodem sedimenten te verdunnen en de metalen en sporen elementen vast te leggen.

De snelheid waarmee deze processen optreden kan ook veranderen aangezien zandwinputten pas korte tijd bestaan terwijl veranderingen in de bestemming van het land en het klimaat een rol spelen in hun huidige en toekomstige evolutie. Het vastleggen van metalen, C, nutrienten en andere elementen in zandwinputten verandert ook de hydrochemie van de riviermond aan zee. Minder opgeloste metalen en sporenelementen bereiken de rivier en uiteindelijk de zee. Om het veilig gebruik van zandwinputten te kunnen evalueren moet niet alleen het water en sedimenten van de zandwinput zelf maar ook het groudwater, de waterbalans en de evolutie van hydrochemische processen en van het klimaat en ruimtelijke inrichting geobserveerd worden.

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7

RIASSUNTO

I laghi di cava si formano quando lo scavo per l’estrazione di ghiaia e sabbia grossolana avviene sotto la tavola d’acqua dell’acquifero superficiale. In zone, dove c’è una grande richiesta di materiale inerte, tanti laghi di cava sono localizzati lungo depositi naturali di ghaia e sabbia. La maggior parte dei laghi di cava sono elementi geomorfologici giovani che hanno meno di cinquanta anni. Questo dottorato di ricerca vuole determinare come i laghi di cava cambino l’idrologia e l’idrochimica di un acquifero, di un bacino di drenaggio naturale o di un bacino drenato artificialmente (polder). Ho studiato i laghi di cava con acqua dolce in un ambiente fluviale lungo il fiume Mosa (Paesi Bassi) e laghi di cava riempiti con acqua salmastra e scavati in depositi di spiaggia Olocenici lungo la costa Adriatica vicino a Ravenna (Italia). Uno dei laghi Olandesi (lago DLV) è attualmente usato per la ricarica artificiale e la produzione di acqua potabile mentre gli altri laghi sono usati per fini ricreativi: nuoto, barca a vela, sub immersioni subacquee. Sia l’acqua superficiale dei laghi e dei fiumi che l’acqua di falda intorno ai laghi è stata campionata e analizzata per anioni, cationi, oligo-elementi e gli isotopi stabili di ossigeno e idrogeno. Il bilancio idrico e diversi bilanci chimici sono stati calcolati. La creazione di tanti laghi aggiunge una superficie d’acqua notevole a un bacino idrografico: nell’area di studio Olandese 71 laghi fra le città di Maastricht e Asselt, aggiungono 20 km2_{di acque superficiali equivalenti allo}

0.26 % della parte Olandese del bacino idrografico della Mosa. Nel sito Italiano i laghi di cava aggiungono 684 ettari che sono il 6.6 % della superficie del Quinto bacino che è il bacino drenato artificialmente in cui si trovano i laghi.

L’aumento delle acque superficiali nel bacino idrografico causa una perdita d’acqua dolce, perché l’evaporazione superficiale dalle superfici libere in un clima temperato e Mediterraneo dell’area di studio italiana è generalmente più grande dell’evapotraspirazione del terreno pre-esistente con erba o bosco.

Il drenaggio di un bacino cambia in presenza di laghi di cava causando fluttuazioni della tavola d’acqua su una grande area. Nei bacini costieri di bassa pianura, come quello Italiano, queste fluttuazioni aggiunte al fatto che i laghi formano una superficie equipotenziale idraulica sotto il livello del mare, causano un aumento dell’intrusione salina. I laghi di cava si definiscono flow-through lakes quando l’acqua di falda entra da un lato laghi del lago e suolo rientra l’acquifero sul lato opposto. I Laghi di cava possono anche essere in connessione aperta con un fiume. I laghi di cava studiati hanno in comune il fatto che i loro bilanci idrologici sono determinati in una gran parte dal drenaggio artificiale. Nel caso olandese (lago DLV), il drenaggio artificiale è controllato dai pozzi d’estrazione che prelevano l’acqua in acquifero per produrre acqua potabile mentre nel caso Italiano, il drenaggio artificiale è causato dalla stazione di pompaggio del consorzio di bonifica che lavora per tenere il terreno asciutto. I bacini con più laghi di cava sono più sensibili ai cambiamenti climatici che i bacini senza laghi, perché il tasso di evaporazione dell’acqua

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superficiale è più sensibile ai cambiamenti climatici che l’evapotraspirazione dell’umidità nel suolo. L’acqua evaporato dai i laghi di cava è completato da acqua di falda o del fiume. Invece l’evapotraspirazione in un bacino senza laghi può aumentare solo fino ad un certo punto: l’umidità nel suolo, infatti, non è infinita. La modellazione che ho fatto del bilancio idrologico con un tracciante conservativo (Cl) ha incluso anche cambiamenti nella velocità di drenaggio per la necessità d’acqua potabile (caso Olandese) o per prevenire allagamenti causati dall’aumento del livello marino (caso Italiano). I risultati indicano che i cambiamenti nel drenaggio artificiale hanno un’influenza maggiore sulla concentrazione del tracciante che i cambiamenti nel tasso di evaporazione causati dai cambiamenti climatici. Le precipitazioni sui laghi di cava Italiani sono mescolate immediatamente con l’acqua salmastra dei laghi e non possono infiltrarsi nel suolo per ricaricare le lenti di acqua dolce-salmastra presenti nell’acquifero.

Sia i laghi Olandesi che quelli italiani hanno un’alcalinità e un pH alti con concentrazioni di metalli e oligo elementi diversi da quelli dell’acqua di falda bacini circostante la zona delle cave. Ci sono differenze fra la concentrazione di elementi specifici e i loro bilanci di massa sia nei laghi che nelle loro falde. Questa osservazione si spiega col fatto che nell’area di studio Italiana c’è l’influenza dell’acqua di mare e in tutte e due i casi la chimica specifica del suolo è diversa. Per esempio, As e Ba occorrono in concentrazioni alte nei laghi Italiani ma non nei laghi Olandesi, dove Ni, Zn e Al sono più importanti. Le differenze nell’idrochimica (Fe, SO4, HCO3, Ni etc. e pH) fra l’acqua nei laghi e l’acqua di falda,

nonché le loro variazioni lungo le linee di flusso, mostrano che delle reazioni redox avvengono nel suolo vicino ai laghi in tutte e due le aree di studio. Queste reazioni, stimolate dalle fluttuazioni della tavola d’acqua e/o dalla denitrificazione dei fertilizzanti, hanno mobilizzato metalli come Fe, Zn, Ni e altri elementi come Al e As. Una parte di questi elementi sono adsorbiti di nuovo nel suolo, ma una parte raggiunge i laghi di cava, dove precipitano sul fondo (per esempio, Fe, Zn, Ni, Al). Altri elementi ancora rimangono, almeno in parte, in soluzione nell’acqua dei laghi come per esempio l’As nei laghi Italiani. I laghi di cava sono influenzati fortemente dall’uso del suolo e dal clima del bacino. Se le circostanze cambiano, in modo da far diminuire l’ossigeno disciolto o il DO o l’NO3 o se

ancora il pH diventasse più basso, allorale reazioni che all’inizio causavano la deposizione di metalli ed elementi oligo-elementi sul fondo del lago potrebbero essere invertite. In tal modo, metalli e oligo-elementi andranno di nuovo in soluzione e creeranno un ambiente potenzialmente tossico per le piante, gli animali e gli esseri umani. Questi cambiamenti potrebbero essere causati da un diverso uso del suolo, per esempio una riduzione nell’uso di fertilizzanti o un cambiamento nel clima (meno ricarica della falda) o da processi lenti nel suolo per esempio la decalcificazione della zona vadosa che può far aumentare l’acidità nel suolo. Dall’altro lato, un’eutrofizzazione più intensa con produzione primaria aumentata da temperature più alte o meno circolazione nei laghi, aumenterebbe la deposizione di materiale organico e fine al fondo del lago il che aiuterebbe a diluire e fissare i metalli e oligo elementi ai sedimenti di fondo.

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La velocità di questi processi può cambiare col tempo, perché I laghi di cava sono ancora giovani e i cambiamenti nell’uso del suolo e nel clima fanno parte della loro evoluzione attuale e futura. La fissazione dei metalli, carbonio, nutrienti e altri elementi nei laghi di cava cambia anche l’idrochemica nella foce dei fiumi e lungo la costa dato che vi è una riduzione degli elementi in soluzione che raggiungono il mare insieme all’acqua di falda o dei fiumi. Per valutare un bacino con laghi di cava e l’uso sicuro di questi laghi, è importante monitorare non solo l’acqua dei laghi ma anche l’acqua della falda, il bilancio idrologico e l’evoluzione dei processi chimici insieme con i cambiamenti nell’uso del suolo e del clima.

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CHAPTER 1 Introduction

1.1 WHY STUDYING GRAVEL PIT LAKES?

Our modern society uses an enormous amount of sand and gravel to construct buildings, highways and anything made of concrete. According to the USGS (2013) the world produces a total of 140 *106_{metric tons of sand and gravel per year, where the USA; Italy,}

and Germany are the three main producers. Gravel typically is produced from natural gravel deposits such as streambeds, beach deposits or alluvial fans. Where the gravel pits are excavated at or below the water table, they fill up with groundwater and become artificial lakes. Since gravel pit lakes follow sub-horizontal geologic layers, there are often many gravel pit lakes close to one another completely changing the landscape and hydrology of a region. In the Netherlands, for example, 500 gravel pit lakes give this country the highest worldwide production per unit surface of 0.4 [thousand tonnes per km2_{]. Similarly in Italy, the gravel pit lakes along the coast near Ravenna increased the}

open water surface in the watershed by 7% from 1972 to 2012 and the excavation is still ongoing (Mollema et al. 2012).

Seekell et al. 2013 showed that lakes, including small lakes, cover a much greater portion of the Earth’s land surface (~3%) than previously believed. This has an influence on all chemical and hydrological budgets: lakes store substantial amounts of carbon in their sediments and greenhouse gas emissions from lakes may almost completely offset the terrestrial carbon sink (e.g., Bastviken et al., 2011; Marcé et al. 2014). Lakes play an important role in the (trace) metal budgets of soils in the watershed (Mollema et al. 2015). Research demonstrates the sensitivity of lakes to climate and shows that physical, chemical, and biological lake properties respond rapidly to climate-related changes (ACIA 2004; Rosenzweig et al. 2007; Adrian et al. 2009).

Lakes in general, however, are not mentioned in the latest reports on climate change (IPCC 2013) and gravel pit lakes do not (yet) appear in databases of lakes (ILEC 2014). Pit lakes and gravel pit lakes, as one particular type, are a relatively new environmental phenomenon and little work has been done to investigate long-term environmental concerns (Fang et al. 2009).

This Doctoral study is on gravel pit lakes in two different watersheds of two different hydrogeological and climatic settings. One study site is in The Netherlands where more than 70 gravel pit lakes have been excavated along the Meuse River. Even though the

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Netherlands do not often suffer droughts since it has a humid temperate climate, the continuous supply of freshwater for industrial, agricultural and civilian use is becoming more and more a challenge. The Netherlands are a very small country with a high population density (407 persons km2_{; CBS 2014), so that there is little space to store}

water. Large parts of the soil and aquifers in the low-lying coastal and fluvial plain of The Netherlands are threatened by salinization, which is only going to worsen under pressures driven by climate change and sea level rise (e.g. Griffioen et al. 2013; Oude Essink, 2010). At the same time there is a fear for river floods due to increasing amounts of rainfall during cloud bursts. Seaward drainage and discharge, therefore, have to be effective. In view of all this, alternative techniques have been designed and applied to store and supply drinking, rain or surface water; some examples are storage of freshwater in a brackish aquifer (Zuurbier et al. 2013), artificial recharge in coastal dunes (Stuyfzand 1993; Karlsen et al. 2012), and river bank filtration (Stuyfand et al. 2006). One gravel pit lake near Roermond in the Southern Netherlands is of particular interest because it is situated within the fluvial plain of the Meuse River and it is being used for artificial recharge and production of drinking water by WML Limburg. That is why this lake was selected as one of the two detailed study sites.

The other study site is in Italy along the Adriatic coast near the city of Ravenna. Gravel excavation along a Holocene coastal gravel deposit has formed a series of lakes parallel to the coast of the Emilia-Romagna region, south of the Po River. The area needs to be drained very efficiently since the surface is below sea level. Furthermore, groundwater of the shallow aquifer and most surface waters are brackish. A detailed hydrochemical study (Chapter 3; Mollema et al. 2013) has helped to understand the differences between the water quality in the various environments and the effects of the gravel pit lakes on the aquifers’ hydrology and hydrochemistry. The groundwater in this area is not used for drinking water supply, but water from the aquifer system is intensively used for agriculture, wetlands and recreation such as fishing and watersports (e.g. Mollema et al. 2012; Vandenbohede et al. 2014).

1.2 THESIS OBJECTIVES AND RESEARCH QUESTIONS

The general objective of this doctoral thesis is to understand the impact of a gravel pit lake and/or multiple gravel pit lakes on the hydrology and hydrochemistry of a watershed. In addition, I aim to investigate the interaction between groundwater and lake water in two different hydrogeologic and climate settings. These are respectively: an alluvial environment in a temperate climate of The Netherlands and a coastal environment in the Mediterranean climate of Northern Italy.

In particular the following questions were addressed:

 How and to what extent does a gravel pit lake or a series of gravel pit lakes influence the water budget of a watershed?

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 How does a gravel pit lake or a series of gravel pit lakes influence the chemical cycle and budget of a watershed, in particular the budget of metals and trace elements and salts?

 How does the resulting hydrochemistry of gravel pit lake water differ from that of natural lakes and other surface and groundwater?

 What is the effect of changes in land use and climate on a watershed with multiple gravel pit lakes?

 How does (artificial) drainage influence groundwater and gravel pit lake hydrology and hydrochemistry?

 What are the implications of all this for the use of gravel pit lakes as a place for artificial recharge and water production, recreation or as natural areas?

In part these questions have been addressed by the undertaking of new field studies presented in this thesis, and in part by using data collected during previous field studies, comparison with existing research publications, calculations and modeling.

1.3. RESEARCH APPROACH

We investigated the gravel pit lakes by mapping the spatial distribution of water types and solute concentrations in ground and surface waters in both the Dutch and Italian study sites. For the Italian study site this was done at first on a fairly large scale in order to distinguish between the characteristics of water in gravel pit lakes and water in other (coastal) environments. To this end, groundwater was sampled from monitoring wells, and lake water was sampled with a vertical Van Doorn-type water sampling bottle from a boat. Water samples were subsequently analyzed for major ion chemistry as well as trace elements and stable isotopes. Water budget calculations were carried out based on climate and stable hydrogen and oxygen isotopes data, and on estimates of evaporation and evapotranspiration. In the Dutch area, a fen near the gravel pit lakes was used as a natural evaporation pan for water budget calculations. Google Earth was used to quantify the surface water area that is added to a watershed by the excavation of gravel pit lakes. A detailed literature study was undertaken to be able to compare the results of the new field studies with previous hydrochemical observations of the composition of ground and surface water, in particular the comparison between gravel pit lakes and natural lakes. Data collection for the Italian study site was in part carried out within the framework of (i) the Waterknow (CIRCLEMED) project funded by the European Union and (ii) the Coastal Salt Water Intrusion (CSI) project of the University of Bologna (IGRG, Ravenna campus). The new data for the Dutch study site was collected in collaboration with WML Limburg, the water utility in the southernmost province of the Netherlands. WML also supplied all existing hydrological, hydro- and geochemical of gravel pit lake De Lange Vlieter.

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14 1.4 THESIS OUTLINE

Chapter 2 gives background information on gravel pit lakes and their environment. A review of geologic and hydrologic settings in which gravel pit lakes occur is presented. The hydrochemistry of gravel pit lake water is compared with other types of surface water and with groundwater, and an overview of hydrochemical and biochemical processes occurring in and around gravel pit lakes is given. The material presented in this review chapter includes data collected in the two study areas for this doctoral study as well as previously published data on natural lake water, river water, and more. A comparison of the water budget of gravel pit lakes in two different settings is included. This chapter is submitted as a review paper. Parts of this chapter were used to write the introduction, summary and conclusion of this thesis (chapters 1 and 6).

Chapter 3 presents a detailed hydrochemical study of gravel pit lakes in an alluvial setting along the river Meuse in the south of the Netherlands. One of these lakes, De Lange Vlieter lake (DLV), is used for the artificial recharge of Meuse River water for the production of drinking water by the ‘NV Waterleiding Maatschappij Limburg’ or in short the ‘WML’. Hydrochemical and stable hydrogen and oxygen isotope data from ground en surface water samples were collected during the summer of 2012. This data and geochemical data of lake bottom sediments collected in the course of multiple years by WML, showed how dissolved metals released by redox reactions in the aquifer upstream from the lakes end up in the bottom sediments. This chapter was published in the Journal of Geochemical Exploration. DOI: 10.1016/j.gexplo.2014.12.004.

In Chapter 4 a large scale hydrochemical study on various coastal environments near Ravenna (Italy) is presented. The following environments were addressed: rivers, drainage channels, lagoons, coastal dunes, paleo dunes, agricultural fields, and gravel pit lakes. The spatial distribution of groundwater bodies with similar hydrochemistry was based on major cation and anion concentrations, stable isotopes and ratios such as SO42-/Cl- and

δ18_O/Cl-_{. Emphasis was put on geochemical conditions and processes that occur and their}

implications for freshwater availability in the various brackish/saline coastal environments. This chapter was published as an article in the journal of Applied Geochemistry (2013). DOI: 10.1016/j.apgeochem.2013.03.017.

Chapter 5 presents a detailed hydrologic and hydrochemical study for the water and chemical budgets of flow-through, saline, gravel pit lakes along the Adriatic coast, including the effect of evaporation and groundwater flow into the lake. Groundwater flow is in part driven by the intense drainage system that is needed to keep the low-lying reclaimed land from inundating. Hydrochemical data is presented along a profile perpendicular to the coast to illustrate the differences between groundwater and gravel pit lake water composition. The influence of groundwater flow and evaporation on the concentration of a conservative tracer such as Cl is modeled using stable isotope data of water in combination with water balance modeling. This chapter is in press by Limnology and Oceanography (Wiley).

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Chapter 6 provides a summary of the findings of this doctoral research and includes an overview of the type of information one would like to have to be able to use gravel pit lakes after excavation in a sustainable and safe manner. The existing policies and regulations regarding water- and (aquatic) soil quality are briefly described, and this chapter ends with suggestions for further research on gravel pit lakes and their watersheds.

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CHAPTER 2 Watersheds with gravel pit lakes under a changing climate

and land use: an introduction and review

.

ABSTRACT

Our modern society uses an enormous amount of sand and gravel to construct buildings. Gravel typically is produced from natural gravel deposits such as streambeds, beach deposits or alluvial fans. Where the gravel pits are excavated at or below the water table, they fill up with groundwater and become artificial lakes. There are often many (tens) gravel pit lakes close to one another changing the landscape and hydrology including the drainage pattern of a watershed. In this review, we provide a synthesis of past research on the hydrology and hydrochemistry of gravel pit lake systems. Furthermore, we illustrate the paper with examples from one fluvial freshwater gravel pit lake system and one coastal brackish system. Calculations show that surface water evaporation is larger in temperate and Mediterranean climates than the actual evapotranspiration of grass land, forests, and wetlands that were replaced by the gravel pit lakes. The lakes cause a loss of freshwater and make the watersheds more sensitive to changes in climate. The creation of water surfaces allows algae and other flora and fauna to develop and an exchange of gases with the atmosphere including CO2 and CH4. The gravel pit lakes influence the transport of

major cation ions and anions (e.g. Ca, HCO3, SO4), dissolved metals (e.g. Fe, Mn, AL),

trace elements (e.g. As, Ni, Zn), nutrients (N and P) in the hydrological cycle. The comparison of hydrochemical data of precipitation, rivers, natural lakes, gravel pit lakes and oceans shows that the gravel pit lakes studied in detail have (among others) a relatively high pH and alkalinity and low dissolved metal concentrations. The hydrochemical and biochemical cycles in gravel pit lakes are accelerated by certain land uses such as agriculture. Water quality in gravel pits will keep changing because they are relatively young but also due to climate and change in land use and gravel pit lake -use. If gravel pit lakes are to be used as nature reserves, recreational areas or as drinking water basins, they need to be monitored over long periods of time and in relation to climate and waterquality in all of the watershed. There are promises for major advances in this research field in the coming years thanks to the becoming available of longer time series for water quality data of gravel pit lakes and surrounding aquifers.

This chapter is submitted to Earth Science Reviews as: Mollema, P. N. and Antonellini, M. The impact of gravel pit lakes on hydrology and hydrochemistry: a review and outlook.

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18 2.1 INTRODUCTION

Our modern society uses an enormous amount of sand and gravel to construct buildings, highways and anything made of concrete. According to the USGS (2013) the world produces a total of 1.4 *108 metric tons of sand and gravel per year (Table 2.1) where the USA, Italy, and Germany are the three main producers. Gravel typically is produced from natural gravel deposits such as streambeds, beach deposits or alluvial fans. Where the gravel pits are excavated at or below the water table, they fill up with groundwater and become artificial lakes. Since gravel pit lakes follow geologic layers, there are often many gravel pit lakes close to one another completely changing the landscape and hydrology of a region. For example in Maine USA, 34 active and former gravel pits cover 26% of the aquifer surface (Peckenham et al. 2009) and in the Netherlands 500 gravel pit lakes give this country the highest production of gravel and sand per surface of 0.4 thousand tonnes per km2 (Table 1). In Italy, the gravel pit lakes along the coast near Ravenna increased the open water surface in the watershed by 6 % from 1972 to 2012 and the excavation has not finished yet (Mollema et al. 2012).

Verpoorter et al. 2014 , Seekell et al. 2013, and McDonald et al. 2012 showed that lakes, including small lakes, cover a much greater portion of the Earth’s land surface (~3.7 %) than previously believed. This has an influence on all chemical and hydrological budgets: lakes store substantial amounts of carbon in their sediments and greenhouse gas (CO2

and methane) emissions from lakes may almost completely offset the terrestrial carbon sink (e.g., Bastviken et al., 2011; Downing, 2010; Tranvik et al., 2009; Wetzel, 1990). Lakes play an important role in the (trace) metal budgets of soils in the watershed (Mollema et al. 2015a). Research demonstrates the sensitivity of lakes to climate and shows that physical, chemical, and biological lake properties respond rapidly to climate-related changes (ACIA 2004; Rosenzweig et al. 2007) and, for this reason, they are sometimes called ‘sentinels’ of climate change (Adrian et al. 2009).

Lakes in general, however, are not mentioned in the latest reports on climate change (IPCC 2013) and gravel pit lakes do not (yet) appear in databases of lakes (ILEC 2014). Pit lakes in general and gravel pit lakes as one particular type, are a relatively new environmental phenomenon, and little work has been done to investigate long-term environmental concerns (Fang et al. 2009; 2010; Miller et al., 1996; Shevenell, 2000). Although the recycling of concrete, has become common (CMRA 2014), still new gravel pits are dug. Because of new uses for gravel and sand, as for example for proppant in hydraulic fracturing, the demand in the USA for sand has increased (USGS 2013).

In this review, we present a synthesis of past research on the role of gravel pit lakes in the water budget and hydrochemistry of watersheds and discuss current perspectives for research in this field. With the term gravel pit lakes we indicate artificial lakes that formed due to excavation of gravel or coarse sand. We evaluate the effect of climate and land use change on the water budget and specific hydrochemical processes occurring in gravel

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pit lakes. We give examples of values for hydrological and hydrochemical properties for gravel pit lake systems in temperate and Mediterranean climate zones, from a case study in the Netherlands (Mollema et al. 2015a) and Italy (Mollema et al. 2015b). We compare the hydrochemical characteristics with published hydrochemistry data on different types of natural lakes and other types of surface waters and groundwater to study the effect of gravel pit lake systems on the natural properties of water in various parts of the hydrological cycle. The fact that hydrochemical studies are published in an enormous spread of scientific journals in the fields of hydrology, environmental sciences, geochemistry, hydrogeology, ecology, and biology and the fact that many different units of measurements are used to express concentration of chemical elements makes it time consuming to compare the hydrochemistry of gravel pit lakes to natural lakes or other types of water. By presenting a hydrochemical summary in comparable units, we hope to contribute to an understanding of the hydrochemistry of gravel pit lake and other types of water.

Table 2.1: Sand and Gravel production data from selected countries and the WORLD Source * USGS 2013 **Production of sand and gravel 2006, Rijkswaterstaat, 2006. Surface area of countries from http://data.worldbank.org/indicator/AG.SRF.TOTL.K2, consulted on 16/07/2014

Production 2012

[thousand tonnes] * Production per land surface area [thousand

tonnes per km2_] USA 49500 0.005 Italy 19800 0.066 Germany 7770 0.022 Australia 5600 0.001 France 5000 0.009 United Kingdom 3800 0.015 The Netherlands 18000 ** 0.433 World (rounded) 140 000 0.001

2.2. CHARACTERISTICS AND HYDRO-GEOLOGICAL SETTINGS OF GRAVEL PIT LAKES

2.2.1 GRAVEL PIT LAKES VERSUS NATURAL LAKES

An important difference with natural lakes is that gravel pit lakes abruptly dissect the geological layering. Gravel and sand deposits are very permeable and so a gravel pit is an open door to the aquifer. Natural lakes typically have a relative depth to surface area

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generally less than 5%, whereas gravel pit lakes commonly have relative depths to surface area ranging between 10 and 40% (Wetzel and Likens, 1991; Doyle and Runnels, 1997). The most common annual lake bottom sedimentation rates range from 1 to 5 mm/year. Natural lakes with a depth between 10 and 500 m can be expected to possess a life span between 104_{and 10}5_{years (Loffler, 2003) and are filled up by sand, clay and gravel}

brought by rivers, atmospheric deposition and transport of chemicals with groundwater and organic detritus depositing on the bottom. Reservoirs tend to fill up by sediments that are trapped behind dams with rates that typically vary from 0.03 to 1 mm yr-1 (e.g. De Vente et al. 2005; Minear and Kondolf, 2009). Many gravel pit lakes are isolated from rivers and may fill up by atmospheric deposition and influx of minerals with groundwater and precipitation of organic material and metal oxides on the bottom and occasional slumping of steep edges. Older gravel pit lakes have typically steeper edges than natural lakes. Often gravel pit lakes are in relatively flat flood plains, so there is limited inwash of water and material compared to natural lakes with steeper catchments. The inflow of metals in gravel pit lakes with groundwater can be up to 1000's of kg/year (Mollema et al. 2015a) but this results in sedimentation rates of only 2 x10-9_{mm yr}-1_{. This suggests that the}

sedimentation rate into isolated gravel pit lakes is relatively small and this type of gravel pit lakes is likely to last at least thousands of years. Most gravel pit lakes are between 3 and 50 m deep and do not reach depths of hundreds of meters as some natural lakes do. The residence time of water in a large lake as Titicaca (850 km3) is 1343 yr while it is 0.4 yr for a small pond (0.013 km3) (Löffler, 2003) and that of gravel pit lakes documented so far, ranges from 0.03-0.04 years for river connected gravel pit lakes (Cross et al. 2014) and 0.1 to 2 years for groundwater fed – or flow-through gravel pit lakes (Löffler, 2003; Mollema et al. 2015a, b; Weilhartner et al. 2012).

2.2.2 USE OF GRAVEL PIT LAKES

Gravel pit lakes can be used for canoeing, fishing (Zhao et al. 2015) and other aquatic sports as for example long distance swimming as in the Standiano Lake, Ravenna, Italy (Iastour, 2014). However many older gravel pit lakes are unsafe to use in this way because of the steep edges, irregular bottom topography and upwelling of deep cold water and people have drowned in them (e.g. Neilson, 2013). Swimming may be dangerous also because of eutrophication that can affect water quality in a negative way with blooms of cyanobacteria (Codd, 2000). In the tropics, open water bodies often are places where diseases are transmitted, for example schistosomiasis (also called bilharzia, snail fever, and Katayama fever) which have part of their lifecycle in water; or malaria with water-related vectors (WHO, 2014). Creating lakes where there used to be an aquifer may increase the risk of occurrence of these water-borne illnesses. Gravel pit lakes may become a nature reserve as the Attenborough Nature Reserve in Nottinghamshire, Derbyshire, UK that was listed as one of the ten eco destinations in the world (BBC 2007). More water surface is created by digging gravel pits which offers living space for water plants, animals, and migrating birds. The artificial lakes offer also the possibility for building waterfront houses as for example in the Cotswold Waterpark, Gloucesteshire, UK

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(Waterpark, 2014). Gravel pits have been used or considered for use as a place to dispose of wastewater or dredging sludge (in Michigan, Blener 1979; Switzerland, Lemann 2008; The Netherlands, Deskundigen Commissie Zandwinputten, 2009: Implementatieteam besluit Bodemkwaliteit 2010; Delleur 2010) or debris from land clearing and even salt (Peckenham et al., 2009). Gravel pit lakes may be used for artificial recharge and recovery of drinking water as has been done in The Netherlands (Mollema et al. 2015a) and considered in the USA (Fang et al. 2009; 2010). They may serve as flood retention areas where particulate matter settles (Cross et al. 2014). With the fast technological development of alternative energy sources such as solar energy, the need for (seasonal) storage of heat is rising and gravel pit lakes may be one of the places to consider for heat storage (Novo et al. 2010). Each of the post excavation uses of gravel pit lakes brings its own consequences and gravel pit lakes, therefore, need to be used, monitored and managed carefully.

2.2.3 GEOLOGIC SETTING OF GRAVEL PIT LAKES.

Alluvial fans are one type of geologic deposit that is mined for its gravel and sand consisting of a fan- or cone-shaped deposit of sediment crossed and built up by streams (Boggs, 1987). Because of the steep topographic gradients in current alluvial fans, lakes typically do not form when the gravel is mined. Gravel in current fluvial deposits often occurs in different morphological parts of rivers including streambeds, stream terraces and floodplains (Boggs, 1987). All of these are mined and often form gravel pit lakes (Fig. 2.1) e.g along the river Meuse, Netherlands (Mollema et al. 2015a) : along Donau River (Weilhartener et al. 2013).

In north Europe (Van Balen and Busschers, 2010; Waterpark 2014), in North America (Maine, Peckenham et al. 2009), and in Canada thick accumulations of sand and gravel were deposited in front of advancing glaciers during the ice ages (Boulton, 1986). The gravel was or still is being accumulated in glacial terraces, outwash plains, eskers, and kame terraces (Boulton, 1986) that may form gravel pit lakes when excavated (Fig. 2.1c). Also currently new gravel deposits are being formed at the margins of glaciers (e.g. Shugar and Clague, 2011) but these deposits are usually above the water table. Both current and fossil (raised) beach deposits may contain gravel (Bluck, 2011) and are mined with gravel pits for example along the coast of the north Adriatic in Italy (Fig. 2.1, Mollema 2013; 2015b). Weathered bedrock is found to be a source of sand and gravel in Australia (Stubbs and Smith, 1997). Gravel deposits are also found and mined offshore (Cattaneo et al. 2003; Kubicki et al. 2007).

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22 12 km

West East

Gravel pit lakes

- 10 masl

-20 masl 0 masl

AdriaticSea

Dune and beach deposits (sand) Along shore deposits (coarse sand - gravel)

Alluvial plain deposits (Clay- sand)

Marsh and swamp deposits (Clay- fine sand)

Alluvial plain deposits (Clay- sand) Pro-delta deposits (loam-silt-sand) a 40 30 20 10 0 ct ct ct fp ft ug st st st _st st ug ftGravel pit lake Gravel pit lake

River b Meter Small stream River Gravel pit lake 50 30 10 70 90 110 Meter

Sand and gravel aquifers Clay and silt Bedrock Water table Direction of groundwaterflow

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Fig. 2.1a Holocene beach gravel deposits near Ravenna, Italy, deposited by along-shore now excavated to form gravel pit lakes, about 7 km from the current shoreline. B. Hypothetical valley cross-section illustrating a complex sequence terraces and deposits (upland gravels). The location of gravel pit lakes that would form if the gravel is excavated is indicated in blue. Only the original water table is indicated. Note ct = cut terraces, ft = fill terraces, ft(b) = buried fill terrace, fp = active floodplain, st = strath terrace, and ug = upland gravels. c. Example of a gravel pit lake excavated in a glacier deposits in a bedrock-valley. Modified from Spieker (1968).

2.3. THE EFFECTS OF GRAVEL PIT LAKES ON THE HYDROLOGY OF AN AREA. 2.3.1 CHANGES IN DRAINAGE PATTERN

Gravel mining along the streambed of rivers disrupts the continuity of sediment transport by rivers and changes the river morphology by creating local areas of deposition and erosion (Kondolf, 1997) and changing the natural morphology into a anthropocene landscape with different incision rates (e.g. Florsheim et al. 2013). The presence of gravel pit lakes changes the hydraulic gradients in the surrounding aquifer, especially if the lakes are created in a sloping area or in a low lying plain. The lakes themselves are by definition a surface of equipotential head. Because the drainage pattern of the area changes (Figs 2.2 and 2.3), a gravel pit lake may cause the rise or the lowering of the water table over a large area (Mas-Pla et al. 1999). If the gravel pit lakes are in a coastal plain, the presence of the new water surface needs to be maintained constant by drainage. This can enhance salt water intrusion up to several kilometers inland as observed by Mas-Pla et al. (1999) and confirmed by modeling studies (Werner et al. 2013; Mollema et al. 2010) especially if sea level is rising.

Gravel pit lakes may intersect abruptly geologic formations such as a confining clay layer or buried paleo-channels. This will enhance the transport of water and its solutes and may disrupt the original stratification of groundwater types. Permeability of the aquifer, especially near the lake may actually change over time due to clogging reactions. The initially (enhanced) groundwater flow transports chemical elements into the lake that may precipitate and clog the bottom or the downstream bank of the lake (Weilhartner et al. 2013). Clogging mechanisms are usually classified into physical, chemical and biological or a combination thereof (Baveye et al., 1998). They include the accumulation of suspended solids, precipitates, the formation of gas bubbles and sediment compaction as well as biological clogging due to microorganisms and the excretion of extracellular polymeric substances (Weilhartner et al. 2013; Hoffmann and Gunkel, 2011 and references therein). The occurrence of redox reactions, in the aquifer system downstream of gravel pit lakes trigger a chemical clogging process when (sub)oxic lake water and anoxic groundwater mix (Bustos-Medina et al. 2013; De la Loma Gonzalez 2013) as it does in regular river bank filtration (Schlieker et al. 2001; Hiscock and Grischek 2001). In contrast to river bank and bed sediments, periodic de-colmation due to floods does not occur naturally in low land lakes and flow-regulated lowland rivers (Gunkel and Hoffmann, 2009) or in isolated gravel pit lakes, so the clogging in banks of gravel pit lakes may be permanent.

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We can distinguish several types of gravel pit lakes depending on the hydrogeologic setting (Figs. 2.2 and 2.3): In a river basin, there may be excavations that create a lake in contact with the river instream (Kondolf, 1997; Cross et al. 2014; Bayram and Önsoy 2015), in a meander, or an old gravel bar (Fig. 2.2). A lake may have formed in an abandoned meander (Fig. 2.3d) or gravel pit lakes may be topographically higher than the stream and not directly connected to the river (Fig. 2.3c). If groundwater infiltrates on one side of such an isolated lake and ex-filtrates on the other sides, we call it a “flow-through lake”. A flow-through lake may also form under the influence of an artificial drainage network as is the case in the gravel pit lakes excavated along the coast of the Adriatic Sea (Mollema et al. 2015b). Whether or not gravel pit lakes are isolated or connected to a river, influences the chemical composition of the lake water including the nutrient supply. Together with the steepness of the lake banks this influences the growth of water plants (Cross et al. 2014) which in turn has effect on the rest of the ecosystem structure of these lakes (Jeppesen et al. 2000, Pokorný and Květ, 2004).

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a. b.

a.

Fig. 2.2 a Google earth image of part of the Meuse Valley, south Netherlands that contains about 70 gravel pit lakes. The following types of lakes are indicated: 1. Flow-through gravel pit lake, separated from river 2.Gravel pit lakes in active and abandoned meanders. 3. Gravel pit lake in open connection to a river. b. Google earth image of gravel pit lakes along the Adriatic coast (Italy). The lakes are aligned along ancient beach deposits parallel to the current coast line, 5-7 km inland, indicated by a yellow outline. C. Google earth image of gravel pit lakes in glacier deposits with new housing developments (Gloucestershire; Cotswold Waterpark). A few lakes are outlined by a yellow line.

River Maas 3 km 1 2 3 Hydraulic gradient Hydraulic gradient

N

2.0 km 1.5 km

N

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Gravel pit lake is to all effects an ‘outcrop’ of the water table. Gravel pit lake formed where the floor of the pit lies below the water table on groundwater divide or in impervious rock. Thereis no lateral flow.

Ground water inflow Ground water out flow Gravel pit lake

Drainage into and out of a gravel pit lake by lateral groundwater flow, flow through lake.

Terminal gravel pit lake: water flows from all sides into the gravel pit lake

a

b

c

Ground water inflow Ground water to river Gravel pit lake River

Drainage into gravel pit lake and river, open connection between gravel pit lake and river.

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Fig. 2.3a. Cross sectional and map view of different types of gravel pit lakes with groundwater flow indicated by arrows. a. Gravel pit lake intersects the water table. b. Terminal pit lake (uncommon for gravel pits) c. Flow-through gravel pit lake. d. In stream gravel pit lake. e. Gravel pit lake in valley bottom. f. Gravel pit lake in an artificially drained basin. g. Artificially recharged gravel pit lake in artificially drained basin. Modified in part from Gandy et al 2004, Younger and Robins, 2002, Gammons et al. 2009, Mollema et al. 2015a.

Ground water inflow Ground water to river Gravel pit lake

Drainage into gravel pit lake and river, flow between gravel pit lake and river. Gravel pit lake could be an oxbow lake.

Ground water between river and gravel pit lake

River

e

f

Ground water

inflow

Ground water out flow towards pumping station or well.

Gravel pit lake

Drainage into and out of a gravel pit lake by lateral groundwater flow, flow through lake driven by artificial drainage or pumping.

Pumping wells or Drainage system

Drainage into and out of a gravel pit lake by lateral groundwater flow, artificial recharge throughpipe system, flow through lake driven by artificial drainageor pumping.

g

Ground water inflow

Ground water out flow towards pumping station or well.

Gravel

pit lake Pumpingwells or

Drainage system

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2.3.2 LAKE AND GROUNDWATER TEMPERATURE

Gravel pit lakes, if they are deep enough, may be thermally stratified as observed in the Boschmolen lake (The Netherlands) (Fig. 4) similar to natural lakes (Imboden and Wuest, 1995). Salinity stratification may potentially occur if the lake water is brackish and the more saline and denser water sinks to the bottom. Destratification by air pumps may occur in gravel pit lakes used for drinking water production (Mollema et al. 2015a).

As far as we know, no observations on increasing water temperatures for gravel pit lakes in particular have been published but Scheffer et al. (2001) reported increasing shallow lake water temperatures in the Netherlands (2001), Schneider and Hook (2010) observed rapid surface warming of all inland water bodies since 1985 and Schmidt and Wuest (2014) found that the lake surface equilibrium temperatures are predicted to increase by 70 to 85 % of the increase in air temperatures as a response to climate change. The maximum difference between surface and bottom water temperatures in stratified lakes is projected to increase by 1 to 2 °C with a local maximum of 3.2 °C due to climate warming (Fang and Stefan, 1999). Climate change may force more prolonged stratification in deep lakes or temporary stratification in shallow lakes (Jensen and Andersen, 1992; Sondergaard et al., 2003). Changes of temperature with depth in lakes will affect also the timing and presence of the clearwater phase with consequences for the life cycle of individual species, and the dynamics of entire food webs (Scheffer et al. 2001). Higher lake temperatures change also the solubility of minerals, their reaction kinetics and the resulting chemical profiles (Fang and Stefan, 2009 Loffler 2003; Yu et al. 2010).

Fig.2.4. Summer temperature profiles in gravel pit lake De Lange Vlieter (The Netherlands) with river water infiltration and air blowers and in the Boschmolen lake without artificial mixing, The Netherlands (Modified from Mollema et al. 2015a).

0

10

20

30

40

0

10

20

30 De

pt

h [

m

]

Temperature [°C]

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Many gravel pit lakes are flow-through lakes fed by groundwater. As a result, a change in temperature of in-flowing groundwater will affect the gravel pit lake water which in turn will affect the groundwater temperature downstream. Increasing air temperatures as predicted by climate change will affect groundwater which may also cause a change in water quality. However changes in temperature due to changes in air temperature are much smaller than changes due to, for example, geothermal heat pumps, so that their effect is likely to be unnoticed (Bonte et al. 2013).

2.3.3 CHANGE IN WATER BUDGETS

The excavation of gravel pits creates surface water where surface water evaporation occurs where previously, evapotranspiration took place on vegetated soil. Evaporation depends on many different climate variables: wind velocity, the relative humidity of air, and vapor pressure deficit, (e.g. Mohammed et al. 2012; Van Heerwaarden et al. 2010 a, b) while the actual evapotranspiration from a vegetated piece of land also depends on the physiologic characteristics of the vegetation (radiation properties and physical resistances in the plant internal pathway), the proportion of the area covered by vegetation and by bare soil as well as the soil water potential in the root zone (Mohamed et al. 2012). In most settings, surface water evaporation is larger than the evapotranspiration of a piece of land since the resistance to evaporation is smaller without vegetation or soil (Penman 1948; Maidment, 1992; Mohamed et al. 2012). In groundwater fed gravel pit lakes, typically only the available energy of the sun limits evaporation since inflowing groundwater replaces the evaporated water.

Fig.2.5. Components of the water budget for an area with a gravel pit lake. The water budget of forest, grassland, and wetland include transpiration while the water budget of a gravel pit lake only includes surface water evaporation, which is usually larger than the pre-existing evapotranspiration.

Surface water evaporation Crop evapotranspiration Evapotranspiration of natural vegetation

Unsaturated zone with soil moisture storage. Precipitation

Water and chemical budgets of gravel pit lakes: Case studies of fluvial gravel pit lakes along the Meuse River (The Netherlands) and coastal gravel pit lakes along the Adriatic Sea (Ravenna, Italy)