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ogeochemistry and biodiversity in a network ofline–alkaline lakes: Implications of ecohydrologicalnnectivity in the Kenyan Rift Valley

fano Fazi a,*, Andrea Butturini b, Franco Tassi c,d, Stefano Amalfitano a,fania Venturi c,d, Eusebi Vazquez b, Martha Clokie e, Silas W. Wanjala f,

c Pacini g, David M. Harper h

ter Research Institute, National Research Council (IRSA-CNR), Roma, Italy

partment of Evolutionary Biology, Ecology and Environmental Sciences, University of Barcelona, Barcelona, Spain

partment of Earth Sciences, University of Florence, Firenze, Italy

titute of Geosciences and Earth Resources, National Research Council (IGG-CNR), Firenze, Italy

partment of Infection, Immunity and Inflammation, University of Leicester, UK

e Naivasha Riparian Association, Kenya

partment of Environmental and Chemical Engineering, University of Calabria, Rende CS, Italy

uatic Ecosystem Services, Ltd., Drabblegate, Aylsham, Norfolk, United Kingdom

T I C L E I N F O

le history:

ived 6 June 2017

pted 25 September 2017

lable online xxx

ords:

e-alkaline lakes

Valley

eochemistry

eria

ogical connectivity

A B S T R A C T

The volcanic and tectonic lakes of the eastern branch of the African Great Rift Valley are

exposed to multiple stressors and characterised by different levels of hydrological

connectivity. Past volcanic activity generated endorheic basins, in which the nature of the

bedrock, its connection with groundwater, and local climatic conditions, favoured the

formation of highly alkaline soda waters. While little is known about their nutrient

dynamics, most lakes in this area experience considerable microbial blooms and harbour

diverse and specifically adapted microbial populations, some of which could embody novel

biotechnological potential.

Here we review the geochemical and (micro)biological features of a cluster of lakes

distributed within the East African Rift, ranging from fresh to hypersaline, under different

levels of hydrological connectivity. Possibly no other location on Earth has a comparable

range of lake types in close proximity to each other and representing such a remarkable

microbial biodiversity. Environmental heterogeneity and habitat connectivity among

adjacent aquatic ecosystems may have positive implications in terms of regional

environmental stability by enhancing the overall carrying capacity, i.e. the resilience to

various forms of impact, contributing to biodiversity protection.

Within these ecosystems, microbial processes encompass the entire basis of their primary

production, in particular those driven by cyanobacteria. Combining a multi-disciplinary

ecohydrological approach with a biogeochemical investigation of the principles underlying

their functioning, our study can contribute to the development of appropriate environmental

protection measures to effectively maintain their natural capital.

� 2017 European Regional Centre for Ecohydrology of the Polish Academy of Sciences.

Published by Elsevier Sp. z o.o. All rights reserved.

Corresponding author at: Water Research Institute, National Research Council of Italy (IRSA – CNR), Via Salaria, km 29.300, Monterotondo, Roma 00015, Italy.

E-mail address: [email protected] (S. FaZi).

Contents lists available at ScienceDirect

Ecohydrology & Hydrobiology

jo u rn al h om ep age: w ww.els evier .c o m/lo c ate /ec oh yd

://dx.doi.org/10.1016/j.ecohyd.2017.09.003

ease cite this article in press as: Fazi, S., et al., Biogeochemistry and biodiversity in a network of saline–alkaline lakes:plications of ecohydrological connectivity in the Kenyan Rift Valley. Ecohydrol. Hydrobiol. (2017), http://dx.doi.org/

0.1016/j.ecohyd.2017.09.003

2-3593/� 2017 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier Sp. z o.o. All rights reserved.

http://dx.doi.org/10.1016/j.ecohyd.2017.09.003

mailto:<ce:e-address id=



http://www.sciencedirect.com/science/journal/16423593


S. Fazi et al. / Ecohydrology & Hydrobiology xxx (2016) xxx–xxx2

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1. Introduction

The interaction among bedrock, surface and groundwaters, in aquifers and within deep lake sediments, is amajor driver of ecosystem dynamics in lakes worldwide,and particularly in lakes affected by geogenic water inputswith high mineral content (Borch et al., 2009; Christensonet al., 2015). Water–bedrock interactions are furtherintensified in tropical areas, owing to high average annualtemperatures, intense weathering, and frequent hydrolog-ical extremes (floods and droughts), which fundamentallycontribute to environmental variability. In semi-arid andsub-humid tropical regions, aquatic ecosystems arethreatened by intense anthropogenic impact because ofurban waste disposal, discharge of industrial effluents,intensive agricultural practices employing fertilizers andpesticides, water abstraction for irrigation and humanuses, and hydroelectric energy production. The combinedand interacting influence of geogenic and anthropogenicdrivers results in biodiversity decline and habitat reduc-tion (Dudgeon et al., 2006); this situation has been recentlyexacerbated by climate change and demographic growth.

Understanding lake biogeochemical dynamics is essen-tial for interpreting the specificity of human impact and foridentifying adequate conservation measures (Vitouseket al., 1997); this is of great relevance for alkaline lakeswhere biogeochemical conditions represent a strongenvironmental filter in the selection of resident lakecommunities of micro-organisms (prokaryotes as well asalgae and micro-crustaceans, Schagerl, 2016). Variabledegrees of connectivity (defined as ‘‘the strength ofinteractions across ecotones’’, Ward et al., 1999) betweenseparate wetlands bear a significant influence on thecomposition of fish communities (Bouvier et al., 2009) aswell as on aquatic bacteria (Peter and Sommaruga, 2016),thus impacting onto regional biodiversity. We propose thatconnectivity among adjacent environmentally heteroge-neous aquatic ecosystems may have positive implicationsin terms of contributing to biodiversity protection and toresilience towards various forms of impact, thus enhancingregional environmental stability and overall carryingcapacity. This reflects the urgency of collecting scientificdata from water bodies at different levels of ecohydrolo-gical connectivity. It will support the understanding ofecosystem features and the design of adequate lakemanagement tools for restoring biodiversity, improvingwater quality and enhancing ecosystem services for thebenefit of lake-dependent communities.

Following the concept of ecohydrology, defined on thebasis of the mutual interaction between hydrologicaldrivers and biotic processes (sensu Zalewski, 2000), thispaper reviews existing links between ecohydrologicalfeatures, hydrological connectivity, and carrying capacitywithin a lake network. Overall, this review illustrates howenvironmental variability among lakes can support systemstability and biodiversity dynamics at regional scale.

We focused on a cluster of lakes aligned from North toSouth within the Kenyan portion of the East African Rift;they are subject to different levels of hydrologicalconnectivity and represent a discontinuous gradient ofwater bodies, stretching from freshwater to hypersaline

conditions (Schagerl, 2016). Knowledge of these lakes islimited to few accessible ones and research activities thatwere carried out typically achieved a lifespan no longerthan a PhD thesis. Limited long-term studies exist exceptthose few based on satellite image analysis (lake levels andchlorophyll concentrations; Tebbs et al., 2011, 2013) andthose on cyanobacteria mass development over a 12-yearperiod (Krienitz et al., 2013a,b,c) and a 15-year period(Krienitz et al., 2016a). This despite the fact that some lakesare under protected area management and could beregularly monitored by conservation management agen-cies. The harsh biogeochemical setting created conditionsfor the development of highly selected and diversifiedmicrobial communities; very few fish species persist, inparticular some cichlids remarkably adapted to alkalineconditions. The target lake network offers a series ofstepping stones for migratory birds as well as habitats forsedentary endemic populations, thus retaining a relevantvalue in terms of regional avian biodiversity.

2. Lakes in the Kenyan portion of the East African RiftValley

The major 30 volcanic and tectonic lakes of the easternbranch of the African Great Rift Valley are characterised bydifferent ranges of hydrological connectivity and areexposed to multiple natural and anthropogenic stressors.Within the Rift, all catchments, except that of Ewaso Ng’iroNorth (receiving tributaries from the Nyandarua moun-tains and from Mt. Kenya) have developed endorheicbasins lacking surface outflow. All the lakes are situated insub-humid to semi-arid savannahs (300–600 mm year�1)subject to high potential evaporation rates (1300–2000 mm year�1) and are fed by drainage from mountainblocks on either side of the Rift Valley. Drastic hydrologicalchanges are rather frequent in the Rift Valley, owing tocapricious precipitation patterns originating in distantgeographical regions, which are dependent on the variableposition of the Inter Tropical Convergence Zone, on thestrength of the monsoons and on the temperature of theIndian Ocean. Lake water levels depend upon the balancebetween water output (e.g. evaporation) and input,controlled by the rate of rainfall that occurs in forestedupland portions of the lake catchments. Water levels mayvary also under the influence of groundwater pressure,which is connected to tectonic movements below the earthcrust and to pressure forces that arise within the mantle.Unusual changes in the water levels of wells are consideredcommon signs of volcanic activity (Tilling, 1989). DeCarolis and Patricelli (2003) report that water level in wellshad risen in occasion of the Vesuvius volcanic eruption ofDecember 1631; similarly, water levels rose in Taal craterlake in the Philippines just before an eruption (Smith,2013). Ephemeral streams, from lower altitudes of thecatchments and underground springs at the bases of themountains, can constitute a small proportion of the inflowssignificantly contributing to the water chemistry. Since2010, most East African lakes are at high water leveldespite lacking evidence of an increase in rainfall (Odongoet al., 2015). Upper catchment deforestation and land coverdegradation could be an important contributing factor, but

Please cite this article in press as: Fazi, S., et al., Biogeochemistry and biodiversity in a network of saline–alkaline lakes:Implications of ecohydrological connectivity in the Kenyan Rift Valley. Ecohydrol. Hydrobiol. (2017), http://dx.doi.org/10.1016/j.ecohyd.2017.09.003



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S. Fazi et al. / Ecohydrology & Hydrobiology xxx (2016) xxx–xxx 3

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re is no clear understanding of the complex hydrologyhis Region, where hydrological records disagree withC climate change predictions based upon popular globalulation models, according to which higher rainfalluld be expected (Klein et al., 2016; Odongo et al., 2015).A cluster of these lakes (Table 1 and Fig. 1) forms aontinuous gradient of water bodies, from freshwater

ringo and Naivasha) to hypersaline (Bogoria, Nakuru,menteita, Sonachi, Natron). The latter are evaporitictems (pH from 9.0 to 12.0) representing extremeditions, characterised by high salinity, high alkalinity

high primary productivity under constant highperatures. While Nakuru is protected as a National

k, Lake Bogoria is a National Reserve (managed by thenty of Baringo), and Lake Elementeita, a Wildlifectuary, is largely within Soysambu Conservancy, aate conservation charity.

Most lakes are primarily of tectonic origin, havingeloped along linear faults stretching across a geologi-y ancient volcanic landscape reshaped by recentcanic activity. Others, such as Sonachi Crater Lake,

entirely within a volcanic caldera and Naivasha, itself atonic lake, includes a number of in-filled volcanicters. Early hydrological studies using stable isotopeshlighted deep water connections below the Rift Valleyr able to transfer groundwater over great distancesgster, 1970). In this way, it could be ascertained thatter from Lake Naivasha reaches as far as Suswa and up toe Magadi, over 100 km South. Recent monitoring of thetical profile in Lake Sonachi showed a distinct increaseemperature and alkalinity with depth (Pacini, unpub-ed), indicating that lake level increase in late 2016ring a dry season) was due to feeding by undergroundaline springs. In some lakes, such as Nasikie Engida ande Magadi in southern Kenya, hot spring provide most of

recharge; in other lake basins, thermal springs areor but sometimes important contributors (Schagerl

Renaut, 2016).No two lakes have the same limnological characteristics

to their different histories and degrees of hydrologicalnection within their catchment, and no one lake isle enough to maintain a consistently high primary

duction. The most studied lakes have been: Naivashanology, ecology, management), Magadi (microbiology

geochemistry) and Nakuru (ecology and manage-nt), whereas Bogoria, Sonachi, Elementeita and Oloidienes have been poorly investigated (Table 2).Kenya’s saline–alkaline lakes offer highly prized cul-al ecosystem services. They are renowned spots for bird

wildlife tourism, offer magnificent landscape views include important paleontological sites. Bogoria isted as much for its hot springs, around the westernre of the lake, as for its flamingos; these springs areuted to be the most visually impressive and extensive inica. Both Bogoria and Elementeita have a spectacularnery of escarpments and extinct craters. Elementeitas formerly part of a much larger prehistoric lake basinose level was well above the present one, connected toh present day Nakuru to the North and Naivasha to theth. The lake shoreline was situated at the altitude of theionally most important stone tool site attributable to

Homo erectus, dated about 0.75 Ma, Kariandusi. LakeMagadi, in the South of the country, is in private ownershipand extensively exploited on an industrial scale for itsdeposits of soda ash (i.e., trona) left after evaporation.

3. Processes controlling the chemical composition oflake waters

Endorheic basins formed by tectonic processes generateaquatic ecosystems affected by strong evaporation underthe prevailing semi-arid climate and the intense equatorialradiation. The dominant lithology, consisting of recentvolcanic rocks and volcanoclastic sediments (e.g. MacDo-nald, 2003; Dawson, 2008; Abbate et al., 2015) is rapidlyweathered to produce highly soluble secondary minerals(e.g. nahcolite, trona, and thermonatrite). Soda lakeschemistry is associated with modern or past volcanicactivity (Pecoraino et al., 2015). High pH and Na-HCO3

dominance originate from the hydrolysis of the abundantsilicate minerals, such as sodium-rich plagioclase feldspar,whose weathering is very effective under the prevailinghigh temperatures. This process consumes hydrogen ionsfrom solution and release alkali cations, resulting in highpH and increase in dissolved Na+ concentrations. Oncereleased, dissolved silicate is transported to lakes. A strongreduction in dissolved reactive silicate has been noticed inthe last decades in freshwater lakes Victoria (Verschurenet al., 1998) and Naivasha (Pacini, unpublished data), alikely consequence of eutrophication and development ofdense communities of colonial diatoms.

In alkaline lakes, high evaporation may lead to theprecipitation of alkaline earth carbonates (e.g. calcite, Mg-calcite, smectite), which produces a decrease of Ca2+ andsecondarily, Mg2+ in solution, as shown in South Americanevaporitic alkaline lakes (Furquim et al., 2008; Barbieroet al., 2017). Mg precipitation in alkaline lakes is frequentlymediated by cyanobacteria (Shirokova et al., 2013). Theoccurrence of alkaline springs (e.g. Cioni et al., 1992) alsosignificantly contributes to the formation of sodic lakes.Their peculiar geochemical features are reflected in theratio between total dissolved inorganic carbon (TDIC)and Earth-alkaline elements reaching values much higherthan 1.

The caustic nature of carbonatic brines furtherenhances bedrock dissolution causing a release of nutri-ents limiting primary production. Phosphate concentra-tions that are naturally extremely low in tropicalfreshwaters due to sustained primary production, arecommonly found in alkaline lakes surrounded by rocks ofvolcanic origin, such as basalt, trachyte, phonolite, inwhich phosphorus tends to be moderately abundant. Afurther crucial limiting element is nitrogen; being primar-ily the product of bacterial fixation within surroundingsoils and wetlands, its presence is biologically regulatedand excess nitrate tends to inhibit the nitrogenase, i.e. theenzyme responsible for nitrogen fixation. Denitrificationtends to reduce dissolved nitrogen in tropical wetlands atalkaline lake shores.

Detailed descriptions and interpretations of the bio-geochemical properties of Kenyan soda lakes are poorlydeveloped. The closest to this topic is the research


0.1016/j.ecohyd.2017.09.003



Table 1

Physico-chemical characteristics of the analysed cluster of lakes within the Kenyan Rift Valley.

Latitude Altitude Tributaries Outflow Surface

(km2)

Max

Depth (m)

Alkalinity Salinity pH Dominant salt Hot springs Fish

Lake Natron 28250 S 675 Southern

Ewaso Ng’iro

None 930 9 – ca. 35% 11–12 Na carbonate Yes Alcolapia

latilabris (end.),

A. dalalani (end.),

A. alcalica (introd.)

Lake Magadi 18520 S 580 None None 108 5 380 meq L�1 ca. 35% 10.5 Na carbonate Yes Alcolapia grahami (end.)

Lake Nasikie

Engida

18420 S 613 None None 35 1.5 – ca. 30% 10.5 Na carbonate Yes Alcolapia grahami (end.)

Lake Oloidien 08480 S 1890 None (fed by

Lake Naivasha)

None 4.5 6 200 mg as

CaCO3 L�1

Low 10 Na carbonate No Tilapia

Lake Naivasha 08480 S 1888 Gilgil, Malewa Underground 150 17 190 mg as

CaCO3 L�1

<1% 8–8.5 Na carbonate No Tilapia, carp,

blackbass, catfish, barb

Lake Sonachi

(Crater Lake)

08470 S 1870 None None 0.8 7 – ca. 5% 10.5 Na carbonate Underground No

Lake

Elementeita

08270 S 1670 Mereroni

Kariandusi,

Mbaruk

None 18 2 130 meq L�1 ca. 5% 10.5 Na carbonate Yes No

Lake Nakuru 08220 S 1754 Njoro, Makalia,

Nderit,

Baharini Springs

None 50 2 110 meq L�1 ca. 5% 11 Na carbonate Yes Alcolapia grahami

(introd.)

Lake Bogoria 08150 N 1000 Waiseges, Emsos,

Fig Tree

None 100 10 25 g as

CaCO3 L�1

>30% 10–11 Na carbonate Yes No

Lake Baringo 975 Perkerra, Molo 160 9 9.15

Lake Turkana 38350 N 360 Omo, Kerio,

Turkwell

None 6405 106 0.2–1 meq L�1 ca. 2.4% 8–9.5 Na carbonate Yes >50 spp. (at least 11 end.)

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ducted by Maclntyre and Melack (1982) (Table 1).ention has been mainly given to inorganic carbon,ough dissolved organic matter (DOM) often represents

main carbon and energy source for aquatic heterotro-c communities as well as an important alternativerce of nitrogen and phosphorus. The quantitative andlitative characterisation of DOM including composi-, structure, molecular weight and bioavailability,ains an important missing gap in the understandingarbon cycling within the lakes of the Kenyan Rift.

quatic biodiversity, including microbiology

The East African Rift Valley is a cradle of mammalian avian biodiversity. Over millennia, its high mountains

ved as freshwater refuges at times of drought, while ther of the Rift Valley constituted a preferential corridorlatitudinal migration, as an adaptation to extremeditions dictated by periodical climate changes. Stillay, the Rift Valley shelters a high density of threatenedna (i.e., ungulates, primates, rodents and birds).aline lakes are part of a mosaic of diverse biotopest contribute to landscape diversity as well as to localdiversity. The aquatic organisms, which survive within

lakes themselves, are restricted to few species of tilapiaolapia grahami, A. alcalica, A. latilabris), and to a smallber of invertebrates (in alkaline lakes often a single

cies tends to dominate) belonging to Cladocera andepoda.

The water column of most soda lakes tends to beinated by the planktonic Arthrospira fusiformis, com-

nly known as ‘‘Spirulina’’, a colony forming rod-shapedegreen bacteria (cyanobacteria) that develops intocroscopic spirals of about 0.2–0.3 mm in length, visibleiny flakes by the naked eye. Over the years, due to itshly nutritious properties coupled to its high productiv- commercial cultures of A. fusiformis developed inical regions of the world. Early assessments from Lake

Sonachi indicated that A. fusiformis can achieve rates ofprimary productivity that place it among the fastestgrowing planktonic organisms in the world (Melack,1979a,b). Overall, saline–alkaline lakes dominated by A.

fusiformis colonies are characterised by high pH and stronglight inhibition through self-shading, but no lake remainsconsistently highly productive. The onset and the crash ofcyanobacterial blooms seem to be disconnected from theavailability of elements that commonly limit primaryproduction. One cause may be changes in hydrology thataffect lake alkalinity, causing a disruption of the monocul-ture of A. fusiformis in favour of more complex assemblagestypically dominated by colonial diatoms (Aulacoseira,Achnanthes) and other cyanobacteria (e.g. Microcystis).Another may be the wax and wane of cyanophages, knownto be abundant in these waters (Junaideen, 2010; Foster,2013; Peduzzi et al., 2014) (Fig. 2).

Few organisms have developed adaptations to feed onA. fusiformis, the most renown being the Lesser Flamingo,(Phoeniconaias minor). These large birds are entirelydependent on their A. fusiformis diet and have to feedduring most of their waking hours. The long-term survivalof their population depends upon the preservation of theregional network of lakes, enabling them to move awayfrom lakes whose food supply unexpectedly drops insearch of an alkaline lake with adequate A. fusiformis

blooms (Harper et al., 2016). Flamingo movements supportlake connectivity along the Rift Valley and contribute tothe dispersal of microorganisms and invertebrates thatremain attached to their feathers (Fig. 3).

Details about factors controlling the main A. fusiformis–

P. minor food chain have not improved significantly sinceearly studies carried out in Nakuru during the 1970s (e.g.Vareschi, 1978). Studies on A. fusiformis are frequent,addressing either a wide context (phytoplankton commu-nity) or focussing on the physiology and ecomorphology ofthe species (e.g. Schagerl, 2016 and references therein). A.

fusiformis can synthetise tryptophan, an amino acid withwell-known fluorescent properties in water. However, theavailability of DOM-associated tryptophane has beenlargely disregarded, as well as the potential impact oflarge-scale DOM-tryptophan leaching on the diversity andproduction of bacterial plankton. Monitoring the availabil-ity and the fate of DOM-tryptophan by detecting fluores-cence could reveal microbial loop interactions amongprimary and secondary producers in soda lakes (Suksomjitet al., 2009).

Recent work has quantified the high dynamics ofnatural populations (Tebbs, 2014) and provided supportfor the hypothesis that infection by cyanophages couldrepresent an important factor controlling their growthnext to nutrient and/or light limitation. Marine researchshowed that Cyanobacterial viruses tend to be tightlylinked to their hosts, to the extent that they are able toacquire from them a large number of genes (e.g., Clokieet al., 2006); these can be used to sustain host physiologyduring infection, in order to ensure that cells are ‘healthy’and can maintain an energy source to produce moreviruses. It is also known that the diversity of thecyanoviruses may drive bacterial diversity; this indicatesthat viruses are important for bacterial population

1. Location of the selected lakes within the Kenyan Rift Valley – World

gery.

rce: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus

USDA, USGS, AeroGRID, IGN, and the GIS User Community.


0.1016/j.ecohyd.2017.09.003



Table 2

Relevant published studies on the ecology of the lakes within the Kenyan Rift Valley.

Lakes Bacteria isolates Bacterial phylogeny

genomics

Phytoplankton community

physiology

Rotifers and ciliates Vertebrates Physico-chemical

characteristics

Palaeoecology

Natron Zaccara et al., 2014;

Kavembe et al., 2016b;

Krienitz et al., 2016b

Bettinetti et al.,

2011

Magadi van Zyl et al., 2016;

Zavarzina et al., 2013;

Ghauri et al., 2006;

Kevbrin et al., 1998;

Grant and Jones, 2016

Kambura et al., 2016;

Foti et al., 2006; Grant

et al., 1999

Mikhodiuk et al., 2008; Kotut

and Krienitz, 2011; Krienitz

et al., 2012; Krienitz and

Schagerl, 2016

Seegers et al., 1999;

Seegers and Tichy,

1999; Zaccara et al.,

2014; Kavembe et al.,

2016a,b; Krienitz et al.,

2016b

Jones et al., 1977;

Deocampo and

Renaut, 2016

Nasikie Engida Jones et al., 1977;

Renaut, 2011;

Deocampo and

Renaut, 2016

Oloidien Dadheech et al., 2009;

Luo et al., 2017

Krienitz et al., 2013a,c Yasindi and Taylor,

2016

Krienitz et al., 2016b Verschuren et al.,

2000

Naivasha Krienitz et al., 2013b,c Owino et al., 2001 Olago et al., 2009 Olago et al., 2009;

Trauth et al., 2010

Sonachi Grant and Jones, 2016 Melack, 1982; Melack et al.,

1982; Kotut and Krienitz, 2011;

Ballot et al., 2005; Krienitz and

Schagerl, 2016

Epp et al., 2010; Yasindi

and Taylor, 2016

Krienitz et al., 2016b Maclntyre and

Melack, 1982

Olago et al., 2009;

Verschuren et al.,

1999

Elmenteita Akhwale et al., 2015;

Marquez et al., 2011;

Mwirichia et al., 2010;


Foti et al., 2006;

Dadheech et al., 2009;

Mwirichia et al., 2011;

Melack, 1988; Melack &

Kilham, 1974; Ballot et al.,

2004; Krienitz et al., 2013a;

Kotut and Krienitz, 2011;

Krienitz and Schagerl, 2016

Yasindi and Taylor,

2016

Owino et al., 2001;



Olago et al., 2009 Olago et al., 2009;

De Cort et al., 2013

Nakuru Dadheech et al., 2012;


Foti et al., 2006;


Melack & Kilham, 1974;

Vareschi, 1982; Vareschi and

Jacobs, 1985; Ballot et al., 2004;

Kaggwa et al., 2013; Luo et al.,

2013; Krienitz et al., 2012;

Krienitz et al., 2013a; Kotut and

Krienitz, 2011; Krienitz and

Schagerl, 2016

Vareschi and Jacobs,

1984, 1985; Vareschi &

Vareschi, 1984; Burian

et al., 2016; Chemoiwa

et al., 2015; Burian

et al., 2013; Ong’ondo

et al., 2013; Yasindi and

Taylor.,2016

Vareschi, 1978, 1979;

Vareschi and Jacobs,

1984, 1985; Vareschi &

Vareschi, 1984; Owino

et al., 2001; Kavembe

et al., 2016b; Krienitz

et al., 2016b

Olago et al., 2009;

Jirsa et al., 2013

Olago et al., 2009;

De Cort et al., 2013

Bogoria Vargas et al., 2005;

Sorokin et al., 2001;


Foti et al., 2006;


Ballot et al., 2004; Kaggwa

et al., 2013; Krienitz et al.,

2013a; Dadheech et al., 2013;

Krienitz et al., 2012; Kotut and

Krienitz, 2011; Krienitz and

Schagerl, 2016

Ong’ondo et al., 2013;

Yasindi and Taylor,

2016

Harper et al., 2003;

Owino et al., 2001;

Wechuli et al., 2016;



Olago et al., 2009;

Jirsa et al., 2013;

Deocampo and

Renaut, 2016

Olago et al., 2009;

De Cort et al., 2013;

De Cort, 2016;

Renaut et al., 2017

Baringo Dadheech et al., 2009 Schagerl and Oduor, 2003. Britton et al., 2009 Olago et al., 2009;

Deocampo and

Renaut, 2016

Olago et al., 2009

Turkana Dadheech et al., 2009 Kallqvist et al., 1988; Krienitz

and Schagerl, 2016



Kallqvist et al.,

1988; Deocampo

and Renaut, 2016

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dynamics as well as their long-term horizontal evolution(Parsons et al., 2012). These relationships have been farless studied in lake systems than in the ocean but are likelyto be important here also and are likely to become a key toour understanding of lake microbiology. Virus–bacteriadynamics may change under climate change or otheranthropogenic factors, with implications for species relianton A. fusiformis. A serious limitation to our understandingof Arthrospira virus dynamics has been represented by thedifficulty involved in isolating them. This is due to the factthat Arthrospira does not grow well on a plate, and typicalvirus isolation assays cannot be applied. Recently Peduzziand co-workers (2014) provided strong evidence for therole of viruses in population crashes. They showed thatvirus-like particles accumulated inside Arthrospira, justbefore the population contracted and concomitantlyflamingos departed. Other organisms of the A. fusiformis

food chain have also received attention. Rotifers, who areable to consume A. fusiformis, have been the object of a fewpapers focusing on grazing, community diversity andgenetics (Table 2).

The East African saline–alkaline lakes are renowned asthe kingdom of prokaryotes, and in this respect, theyrepresent biodiversity foci of global relevance. Dense

2. Changes in hydrology affect lake alkalinity and disrupt A. fusiformis

ocultures in favour of more complex microbial assemblages. When

occurs, overall productivity decreases and flamingos are forced to

e in search of further ‘‘spirulina’’ lakes. Under different eco-

rological conditions, A. fusiformis blooms occur at different times in

rent lakes. The lake network is able to offer a permanent food supply

the East African lesser flamingo population. Flamingo movements

ort lake connectivity along the Rift Valley and contribute to the

ersal of microorganisms and invertebrates supporting regional

iversity.

3. Schematic conceptual model of the Rift Valley lake network focussing on interactions between hydrological and ecological features. Impacts on water

lity are represented in the lower part of the scheme. Lakes represented in green are dominated by A. fusiformis monocultures; in brown by complex

robial assemblages. East African lesser flamingo population only nest in Natron Lake.


0.1016/j.ecohyd.2017.09.003




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communities of cyanobacteria, archaea and microalgae,often forming mats and biofilms, grow upon bottom orlittoral substrata of each lake along natural alkalinity andtemperature gradients that develop as a result of inflowingfreshwater tributaries, presence of brackish riparianswamps, hot springs and geysers. Bacterial communitiesin alkaline lakes have fascinated biologists all over theworld as they host diverse microbial populations adaptedto chemolithotrophic modes of energy conversion. Thestudy of East African extremophiles, their metabolism,biology and ability to thrive in a range of extreme chemicaland physical conditions has promoted a deeper funda-mental understanding of bacterial physiology (Grant andJones, 2016). Relatively little work on strain isolation hasactually been carried out in this region, but data assembledso far suggest that the extant biological diversity providesoptions for huge biotechnological potential (as reviewed inGrant and Jones, 2016). Important applications can resultfrom the characterisation of novel genes encoded withinmicrobes, in particular those encoding proteins that areresistant to high temperatures, high alkalinity and salinity.Such proteins are used in pharmaceutical industries butalso in wood processing and in biotechnology. It should beexpected that bacterial and archaeal communities encodefor genes whose proteins could host precursors of novelantimicrobial and other therapeutic properties (Cragg andNewman, 2013).

5. Open issues and information gaps

The main topic of published researches addressedstructure and characterisation of microbial communities,especially cyanobacteria, including the genomic code of arestricted number of species. New species of bacteria havebeen isolated and described. Taking a food web perspec-tive, however, there are several key gaps in our under-standing of how the geochemistry may promote such alarge microbial biodiversity, and yet despite this, theenergy derived from microbial production enters veryshort low diversity food chains. It is probable that, giventhe moderate lake volume, hydrological processes have amuch stronger influence upon ecosystem structure andfunction in alkaline lakes than in larger freshwater lakesbecause of radical changes that may occur following lakelevel rise and dilution. As an example, the only planktonicinvertebrate consumers in Lake Bogoria up to 2010 wererotifers and protozoa (Burian et al., 2013; Ong’ondo et al.,2013). Since that time, lake levels have risen throughoutthe Rift Valley (2011–2016) and salinity became diluted byhalf (Amer, unpublished data). Since 2013 at least, theplankton has been invaded by Moina sp., a cladocerancrustacean never previously recorded from alkaline-sodalakes. Concomitantly, rotifera and protozoa have becomeirrelevant, probably being out-competed by the large-sizedfilter-feeder, while the population of A. fusiformis remainedat about half the density of the previous 20 years (Tebbs,2014).

A further gap in our understanding concerns the rangeof energy transfer mechanisms that sustain microbialcommunities. There is weak evidence that inorganicenergy-rich compounds can be reduced by unique

microbial assemblages, in a parallel situation to deep-sea vents. The composition of the microbial loop has beenapproached by recent studies (e.g., Burian et al., 2013;Ong’ondo et al., 2013), but nothing is known about thedetailed structure and dynamics of these communities. Wedo not understand, how much A. fusiformis is consumed byplanktonic invertebrates, as opposed to how much entersthe decomposer chain in different lakes. We do not knowhow much of the cyanobacterial turnover is caused by viralpredation, which has been shown to be a key driver inocean systems dominated by cyanobacteria (Sepulvedaet al., 2016). We do not know the extent to which themicrobial loop is able to regenerate inorganic phosphate,as opposed to its continuous regeneration from geochemi-cal sources.

6. Concluding remarks

Future climate changes could cause unpredictableecohydrological changes within lake basins throughoutEast Africa. At the same time, local impacts are pervasivewith rampant deforestation, land use intensification, waterabstraction for irrigation and inter-basin transfer. The highlake level phase that started in 2011 and continued untilpresent does not seem to match higher rainfall andprobably could be ascribed to higher runoff:rainfall ratiocaused by basin degradation (Odongo et al., 2015).Interpreting and predicting the factors that rule lakehydrology represent an increasingly urgent challenge.Dilution engendered by increased runoff is tied to changesin lake biogeochemistry with cascading effects ontobacterial communities and the food chains they support,up to flamingos. Greater research effort is needed toinvestigate the highly diverse bacterial communities thatdevelop in the Rift Valley lakes whose biodiversity is yet tobe revealed. This can be highly beneficial for ourunderstanding of bacterial ecology and dynamics ingeneral, as well as for the development of new biotechnol-ogies that can be supported by new enzymes isolated fromnatural bacterial communities.

Academic research should provide a coherent interdis-ciplinary perspective of the overall value of the ecosystemsservices offered by these lakes. These include culturalservices linked to tourism that need to be preservedthrough adequate conservation measures, as well asenhanced by tourism development strategies. The man-agement of these lakes will require a multi-disciplinaryecohydrological approach combined with a bio-geochem-ical understanding of the principles underlying theirfunctioning.

Conflict of interest

None declared.

Ethical statement

Authors state that the research was conducted accord-ing to ethical standards.




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nowledgements

This study was carried out in the framework ofESCO-IHP Ecohydrology Programme. The Authors wishhank G. Arduino and M. Zalewski for the coordination of Programme and for supporting the participation of N.P.the Addis Abeba Symposium. A.B. Petrangeli isnowledged for the preparation of the digital map.hors also thank two anonymous reviewers for theirful suggestions. D.H., N.P. and M.C. wish to thank A.er for her contribution.

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