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Small birds, big effects: the little auk transforms high Arctic ecosystems

February 15, 2017

Little Auk colony on the Cape York Peninsula, Greenland. Image: P Lyngs

The North Water Polynya is a large area of open sea in Baffin Bay between Greenland and Canada. The area is the largest polynya – an area of sea that remains ice free year-round, though surrounded by sea ice – in the world, and is one of the most biologically productive marine habitats in the Arctic Ocean.

Ecosystems on the Greenland coastline of the North Water Polynya are transformed – both positively and negatively – by nutrients brought back to land from the open sea by a tiny ‘ecosystem engineer’ bird, the little auk, according to a new study.

An estimated 30 million pairs of little auk travel to the North Water Polynya to breed each summer. At sea, they feed on nutrient-rich crustaceans called copepods. When they reach their breeding colonies on Greenland, the nutrients are largely excreted onto the land as guano.


The North Water Polynya. The study took place between Savissivik and Siorapaluk on the Greenland coast. Image: Wikipedia / NASA commons.

The impacts on the ‘fertilised’ Greenlandic landscape are significant. Areas of land outside bird colonies are largely barren with little vegetation, as is common in environments at 76º North. However, areas within bird colonies have lush vegetation and large numbers of grazing animals such as muskox and geese.

“Our study found that the little auk acts as an ecosystem engineer across a large area of North-West Greenland. The colonies stretch over a 400 km range and up to 10 km inland so a very large area is affected. This creates highly productive oases in an otherwise rather barren landscape” says researcher Thomas Davidson from Aarhus University, a co-author of the new study, published in Proceedings of the Royal Society B, which also involved MARS aquatic scientist Erik Jeppesen.

The research team undertook analyses of stable isotopes of carbon and nitrogen in the coastal Greenland environment to track the flow of the marine-derived nutrients from sea to land. The research involved limnology, aquatic ecology, isotope biochemistry and bird tracking methods, and is part of the interdisciplinary NOW-project with anthropologists, archaeologists and local Inuit hunters.


Musk ox and their young grazing on the lush green landscapes created by the little auk colonies. Image: P. Lyngs

Freshwater ecosystems, on the other hand, were negatively affected by the little auk’s ecosystem engineering. The bird’s guano is very high in nitrogen which, in addition to acting as a fertiliser, can cause the acidification of freshwater. One Greenlandic lake close to a colony had a water pH 3.4, which is more acidic than acid rain.

As a result, lakes and rivers affected by little auk colonies can support few invertebrates and no fish. As there are few grazing aquatic organisms able to survive in the acidic conditions, the nutrient-rich lakes are often green and eutrophic. The presence of little auk colonies is therefore a significant stressor on Greenlandic lakes and rivers.

This reduction in freshwater biodiversity caused by little auk colonies is opposite to the efffect of similar transfers of marine nutrients by migrating Pacific salmon. Numerous studies have shown that migrating salmon significantly increase biodiversity and ecosystem productivity in their spawning rivers in North America and Asia, both through their post-spawning decomposition and as prey to predators like bears.


A local hunter from Savvissik waits with his net for a flock of little auk to pass by. Image: K. Johansen

Thomas Davidson summarises the study, “On a broad scale we sampled over 30 locations, both with and without bird colonies along the 400km coastline of the North Water Polynya, from Savissivik in the south to Siorapaluk in the north and demonstrated that both aquatic and terrestrial productivity is much higher in bird colony areas. We found that at least 85% of off all terrestrial and aquatic biomass was fuelled by nutrients brought to land by the little auk.”

Climate change may alter the ecosystem dynamics of coastal Greenland in the future. During the breeding season, little auks depend on nutrient-rich copepod species which live in cold sea waters. It is predicted that little auk populations will decline in response to the ongoing warming of the Arctic. If the little auk population declines, a significant shift in the Greenlandic coastal landscape around the North Water Polynya is likely to result.


Little Auks gathering on the stones before descending into their nests or before setting out to sea to feed and collect food for their young. Image: S. Wetterich

Whilst this may mean less productive terrestrial ecosystems, it could be that lakes and rivers become less acidic, and become more habitable for aquatic life. However, a new stressor – climate change – will likely have significant effects on Greenlandic freshwater ecosystems as the effects of the little auks recede.

The new study sheds new light on interactions between marine, terrestrial and aquatic ecosystems in the Arctic, and reminds us that the impacts of future climate change are likely to be distributed in potentially unpredictable and surprising ways across inter-connected environments.

González-Bergonzoni, I et al (2017) Small birds, big effects: the little auk (Alle alle) transforms high Arctic ecosystems, Proceedings of the Royal Society B, 284: 20162572.

Largest freshwater Mediterranean lake may dry out in this century due to climate change and abstraction

February 10, 2017

The town of Beyşehir on the banks of Lake Beyşehir, Turkey. Image: Wikipedia Commons

Freshwater systems in the Mediterranean region are on the front line of climate change impacts in Europe. Future climate projections for the region indicate increasing air temperatures and decreasing precipitation rates through the 21st century.

Whilst fluctuations in water level and flow are a natural feature of freshwaters in the region, climate change is predicted to cause dramatic reductions in river flows and lake levels, causing severe water scarcity issues for the humans and non-humans that rely on them.

A new study suggests that if water abstraction rates from the region’s largest lake – Lake Beyşehir in Turkey – are not reduced, the lake will dry out in this century, potentially as early as the 2040s. The research, led by Tuba Bucak as part of the EU MARS and REFRESH projects, simulated the impact of future climate and land use changes on water levels in the lake.

Their models predict that increased temperatures and reduced rainfall coupled with ongoing water abstraction for agricultural irrigation place Lake Beyşehir at severe risk of drying out. If water abstraction rates are not reduced, the lake ecosystem and its rich biodiversity is likely to be significantly impacted (or even lost), and the human communities who rely on the lake for water and sustenance will lose the services and benefits the ecosystem provides.


A NASA satellite image of Lake Beyşehir. Image: Wikipedia Commons

All climate change scenarios (which used Representative Concentration Pathways) predicted a significant decreases in total water runoff into the lake (as a result of decreased rainfall), but the timescale of the decrease varied between the models. In comparison, simulated changes in land use had a minor impact on total runoff.

The decrease in water runoff common to each climate change scenario was projected to be more pronounced after the 2070s due to reduced precipitation and enhanced potential evapo-transpiration in the catchment. However, in one climate scenario modeled by the researchers, the lake was predicted to dry out completely by the 2040s.

The researchers write that despite the variance in their modelling results, that “a 9–60% reduction in outflow withdrawal was needed to prevent the lake from drying out by the end of this century.” In a water-scarce region, it would seem a challenging task for environmental managers and politicians to guide such a drastic change in water use.

However, there are precedents for similar large lakes to dry out. One Turkish lake, Lake Akşehir, has completely dried up in recent years, resulting in the extinction of the Central Anatolian Bleak.  Two other endemic fish species, the Eber Gudgeon and a local dace (Leuciscus anatolicus) are now critically endangered.

For Tuba Bucak, lead author of the study, water management in the region needs to undergo a significant shift if Lake Beyşehir is to be protected. She says,

“Mediterranean lakes may face a risk of drying out and losing their ecosystem service values in future if essential mitigating measures will not be taken into account. We need to implement adapting measures (eg. reducing water needs by promoting drought resistant crops and efficient irrigation technologies) for maintaining water sources in Mediterranean and ensure sustainable water usage in order to meet the future water demands.”

Seeking freshwater pandas: the ‘flagship umbrella species’ approach

February 3, 2017

European sturgeon (Acipenser sturio), a potential ‘flagship’ species which is threatened by pollution and habitat fragmentation. Image © A. Hartl

Freshwaters are amongst the most heavily modified global ecosystems, and the rich biodiversity they support is at a disproportionate risk of extinction. Conservation and restoration efforts aimed at protecting and improving freshwater habitats are being carried out across the world, but aquatic plants and animals remain amongst the most threatened components of global biodiversity.

One reason for this shortfall may be the lack of visibility – both literally and metaphorically – for freshwater life. Freshwaters may be murky, fast-flowing, deep, cold, ice-covered or turbulent, and the biodiversity they support can often be camouflaged, elusive and difficult to spot. The rich webs of animal and plant life below the surface of freshwaters are not as immediately perceptible as a wildflower meadow or a woodland, say. And, as the ‘shifting baseline’ concept illustrates, public and political perception of the health and diversity of ecosystems can significantly influence the support (or lack thereof) afforded to conservation and restoration schemes.

The identification of flagship species for aquatic ecosystems – so-called ‘freshwater pandas’ – may help bring threatened freshwater biodiversity ‘to life’ and increase awareness of, and support for, conservation measures, according to a new open-access study published in Conservation Biology. Flagship species were defined in 2000 by conservationists Nigel Leader-Williams and Holly Dublin as “popular charismatic species that serve as symbols and rallying points to stimulate conservation awareness and action.”

According to Dr Gregor Kalinkat from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin, the lead author of the new study, a suite of over 60 potentially suitable freshwater ‘umbrella flagship species’ may help strengthen and target existing – but often inadequate – conservation efforts.


The yellow-winged darter (Sympetrum flaveolum), a highly ‘charismatic’ aquatic insect. Image: © André Karwath (CC BY-SA 2.5)

Flagship and umbrella species

Flagship species are typically ‘charismatic’ species which enthuse, enchant and intrigue public and political audiences with the natural world. Environmental geographer Jamie Lorimer provides a helpful typology of such non-human charisma, which may be ecological (the environmental ‘detectability’ of an organism, e.g. through a call), aesthetic (its sensory impact: e.g. cuddly, fierce, curious) and/or corporeal (its emotive impact; or, how it makes us feel). For Lorimer, these aspects of non-human charisma are combined designating flagship species for conservation. For example the human empathy and care often sparked by a panda’s ‘teddy bear’ looks and precarious life habits (surviving on nutrient-poor bamboo) has long been mobilised by the World Wildlife Fund as a flagship logo to leverage funding and support, both for the conservation of the forests on which it survives, and for threatened ecosystems worldwide.

In other words, the charisma (and in the panda’s case, this might include the simple black and white replicability of its form as a logo in a pre-digital age) of flagship species may be mobilised to help strengthen conservation efforts for other less charismatic or visible species across wider ecosystems, whether locally or globally. In this way, the flagship concept has resonances with the ‘umbrella species’ approach to conservation which aims to protect ecosystems through conservation measures targeted at a small number of ‘keystone’ species which also have ecological benefits to the wider ecosystem. However, the flagship species approach has historically been used to mobilise public awareness of nature, rather than to specifically target ‘umbrella’ ecological interactions.


The arapaima (Arapaima gigas), a ‘flagship’ fish native to the rivers and seasonal pools of Amazonia. Image: © T. Voekler (CC BY-SA 3.0)

Identifying ‘freshwater pandas’

The research team behind the new Conservation Biology study call for the established ‘flagship’ and ‘umbrella’ species concepts to be combined to define a new set of ‘flagship umbrella species’. According to the authors, such species have the potential to both raise public and political awareness of imperiled species and ecosystems, and to provide a focus-point for conservation efforts which will ‘trickle down’ and benefit wider ecological communities.

They identify over 60 potentially suitable freshwater flagship umbrella species, based on their “potential to attract public attention and funding for conservation programs as well as [their] potential to protect co-occurring biodiversity in all types of freshwater habitats.” The species – which were selected on the basis of their ‘flagship’ potential as identified in existing conservation literature – are extremely diverse and distributed across the world.

They include algae, molluscs (such as the freshwater pearl mussel), spiders endemic to peat bogs, crustaceans (such as the fairy shrimp), insects (including dragonflies and damselflies), a wide array of fish species (including sturgeon, stingray, sharks, salmonids, catfish and cod), amphibians (various frogs, toads and newts), reptiles (including turtles, crocodiles and alligators), birds (particularly cranes, pelicans and storks), and mammals (including otters, dolphins, porpoises and beavers) (see the full list here).

Some notable examples include: the baiji, a functionally extinct species of freshwater dolphin formerly found only in the Yangtze River in China; the European sturgeon, a migratory fish impacted by the fragmentation and pollution of large river basins such as the Danube; the Siberian crane a critically endangered bird with migration routes across the wetlands of Central and East Asia; and the freshwater pearl mussel, a mollusc threatened by water pollution and over-harvesting.


A flock of Siberian crane (Leucogeranus leucogeranus). Image: © Crane Wu

How useful might ‘freshwater pandas’ be, and where?

It could be argued that the idea of promoting freshwater flagship species is not new: after all, the image of the Atlantic salmon is regularly used to promote river restoration efforts across Europe, and the Eurasian beaver is proving an effective (if controversial) flagship species for public debates over the forms and functions of ‘rewilded’ river catchments in the UK. Similarly, a recent study by Nishikant Gupta and colleagues describes the ‘charismatic’ ability of the golden mahseer, a river fish endemic to northern India, in bringing together river users to support conservation of its habitat. In this context, a key question is: can flagship and umbrella species be (more) useful in supporting freshwater conservation efforts, and if so, how?

A 2011 review of the conservation literature around flagship and umbrella species by environmental geographer Maan Barua yielded three important insights: first, that existing flagship and umbrella species are predominantly mammals; second, that everyday language plays a vital role in communicating environmental issues through flagships; and third, that metaphors are important in shaping public understandings and responses to conservation messages. Barua discusses how ‘mobilising metaphors’ is thus a key consideration in selecting flagship species: in other words, how might different ‘charismatic’ natures (e.g. curiosity, fragility, beauty or ugliness) be aligned to a range of environmental issues to be communicated to wider public audiences; what conservation ‘work’ might they do in the world when circulating as metaphors and abstractions?

Whilst the authors of the Conservation Biology study don’t explicitly address the same issues for flagship species selection, similar considerations circle their work. As ever, scale matters: at what scales (local, regional, global) are flagship species likely to find an audience, and what conservation messages will these audiences be receptive to? Through what channels will flagship representations ‘travel’ (e.g. social media, television), and at what scale is any resulting funding or political influence likely to feedback to influence conservation outcomes? These are big questions which require interdisciplinary research and practice if the use of freshwater flagship species is to have positive conservation outcomes.


Freshwater pearl mussels (Margaritifera margaritifera). Image: © Joel Berglund (CC BY-SA 3.0)

The promise of new data to support ‘flagship umbrella species’

In this context, the new Conservation Biology study outlines an approach to strengthen established ‘flagship’ and ‘umbrella’ species approaches by combining them, with the aid of new data gathering techniques. In other words, the authors envision the potential of ‘flagship umbrella species’ which can both leverage public support and awareness for conservation, and provide an ecological ‘umbrella’ for conservation measures which indirectly benefit wider ecological communities.

For example, molecular methods such as environmental DNA are improving swiftly, allowing researchers to determine the existence of fish or amphibian species from simple water samples, which in the past needed to be collected painstakingly by hand or using nets. Such methods offer the potential of developing our understanding of under-researched or ‘overlooked’ (as the authors put it) freshwater biodiversity across the world, and for targeted conservation measures to be developed, implemented and communicated.

The study’s lead author Gregor Kalinkat outlines the potential of new approaches, “To date, a disproportionately large amount of research and scientific data material has been collected on land and for marine species. In order to protect freshwater species, we are in urgent need of more comprehensive data, which can be collected both cost-effectively and extensively using innovative methods.”

The freshwater ‘flagship umbrella species’ approach is – like most conservation initiatives – inherently interdisciplinary: drawing together insights from the social sciences and humanities such as charisma and issue-framing, with cutting-edge scientific methods such as environmental DNA. Whether through ‘flagships’ or ‘umbrellas’, what is clear is that increasingly threatened freshwater ecosystems are in need of new beacons for conservation research, action and hope.

Read the open-access article ‘Flagship umbrella species needed for the conservation of overlooked aquatic biodiversity‘ in Conservation Biology here.

IGB Aquatic Biodiversity Research Group

Community habitat restoration on Burnley’s rivers

February 1, 2017

Urban rivers across Europe are subject to multiple stresses linked to the surrounding built environment, particularly pollution, fragmentation, barriers and habitat modification. However, increased focus on the many benefits of urban nature, coupled with the imperatives in the EU Water Framework Directive to improve such ‘heavily modified water bodies’ to ‘good ecological potential’ mean that urban river restoration projects are proliferating.

The rivers Brun and Calder meet in the town of Burnley, in North-West England, and are part of the wider Ribble catchment. Flowing through an urban landscape which has supported industrial activity for centuries, the Brun and Calder have both been heavily modified and impacted by humans. Long stretches of the rivers are enclosed by stone and concrete channels, and in some places the river beds are made up of the same cobblestones found paving old streets through the town.

A new video (which you can watch above) produced by The Ribble Rivers Trust documents the community-engaged habitat restoration of Burnley’s rivers undertaken through the Urban River Enhancement Scheme (URES).

The Ribble Rivers Trust is an environmental charity established in 1998 to protect and restore the rivers, streams and watercourses within the Ribble catchment and to raise public awareness of the value of local rivers and streams. The Trust was awarded over £600,000 by the Heritage Lottery Fund in 2013 to deliver the URES, which intends to improve the habitat quality and biodiversity of Burnley’s rivers, whilst engaging local communities through education and conservation programmes.

The video shows URES habitat improvement on Burnley’s rivers, removing litter and debris, uprooting invasive species such as Himalayan balsam, constructing fish passes on large weirs, and restructuring river beds to create semi-natural riffles and pools in place of the existing sewer-like channels. It shows the various ways in which local communities are consulted and engaged in this process, through school visits, environmental artworks and conservation action days.

Below is a podcast interview with MARS scientist Prof Steve Ormerod from Cardiff University, carried out on the banks of the River Brun. Steve – a Burnley native – gives us an insight into the ways in which urban nature, culture and heritage are entwined along the banks of Burnley’s rivers, and how such recent restoration projects have significantly improved their habitat quality and biodiversity.

Since the podcast was recorded, salmon parr have been found upstream of the town, an extremely encouraging sign that migratory salmon can now successfully navigate Burnley’s rivers to reach a wide area of upstream spawning grounds.

You can find out more about the Urban River Enhancement Scheme in Burnley here.

Caddisfly larvae tend remarkable underwater ‘gardens’

January 27, 2017
Caddisfly (Tinodes waeneri) larva. Image: Guam Insects | Creative Commons

Caddisfly (Tinodes waeneri) larva. Image: Guam Insects | Creative Commons

Caddisflies are found in freshwaters across Europe, with their larvae well-known for their remarkable ability to build cases from organic materials such as vegetation, sand and silt (which can take on beautiful creative forms). In Britain alone, there are around 200 different caddisfly species, making them one of the most diverse groups of pond animals.

New research by a team of ecologists from the UK, Germany and Malaysia has shown how caddisflies are not only resourceful ‘house builders’, but also productive ‘gardeners’ of their habitats. Writing in Freshwater Biology, the researchers, led by Nicola Ings, describe how caddisflies actively encourage food growth in their local environment, through ‘weeding’ and ‘fertilisation’.

The organic cases that caddisfly larvae build are known as galleries, held together with silk and fixed to a stream or lake bed. The team of researchers used samples of galleries built by a common caddisfly species, Tinodes waeneri, from five lakes in the Lake District. Their aim was to study whether gallery biofilms contained algae communities distinct from the biofilm on the surrounding lake bed (known as the epilithon), and if so, whether these algae ‘gardens’ were found across a range of lakes with different ecological productivity.

Caddisfly galleries. Image: SSC Harrison

Caddisfly galleries. Image: SSC Harrison

The researchers found that across all five studied lakes, caddisfly larva galleries had a greater content of diatom pigments, including fucoxanthin, as well as a distinct assemblage of diatoms. This abundance of diatoms – a rich food source for caddisfly larvae – on the galleries is the result of active ‘gardening’ by the larvae of their micro-habitat.

Caddisfly larvae live in their galleries (which can reach several centimetres in length), and graze algae around the gallery mouth. This ‘weeding’ helps prevent the gallery from becoming overgrown with filamentous green algae which can inhibit the growth of diatom-rich biofilm. The rear end of the gallery casing (where the biofilm fertilised by nutrient-rich excretions often grows) is gradually ingested by the larva, and the structure slowly extended forward with fresh silk and particles at the front.

This active modification of the caddisfly larva’s immediate environment has a number of benefits for the organism. The new silken material added to the front of the gallery casings creates new surfaces on which biofilm (on which they graze) can grow. At the same time, the older parts of the galleries are typically covered in biofilm rich in diatoms are harvested. In effect, the caddisfly larvae galleries undergo a slow migration across a lake or stream bed, creating new micro-habitats for algae growth at their head, which will be eventually harvested at the rear.

Adult caddisfly (Tinodes waeneri). Image: Janet Graham | Flickr Creative Commons

Adult caddisfly (Tinodes waeneri). Image: Janet Graham | Flickr Creative Commons

‘Gardening’ gives a key advantage to caddisfly larvae by widening the range of potential habitat conditions in which they can survive. The researchers speculate that nutrients will be more tightly retained in lake beds dominated by such sedentary, gardening insect larvae, compared with those dominated by more mobile collector grazers. As a result, the nutrients retained by ‘gardened’ larvae galleries may then be exported to the land when the adult caddisflies emerge.

The study gives a fascinating insight into the ability of microorganisms to actively modify their immediate environment to improve their life chances. It would be fair to say that caddisfly larvae may well be the smallest (and most resourceful) of all the water gardeners.

Ings, N, Grey, J, King, L, McGowan, S, Hildrew (2017) Modification of littoral algal assemblages by gardening caddisfly larvae, Freshwater Biology, doi:10.1111/fwb.12881

Antagonistic interactions between biological invasion and climate warming stressors in freshwaters

January 17, 2017

Gammarus pulex, a tiny crustacean native to the UK. Image: AJ Cann | Flickr Creative Commons

Freshwater ecosystems around the world are increasingly threatened by multiple stressors: the combined impacts of pollution, water abstraction, invasions, fragmentation, climate warming and so on. However, at present, scientific knowledge on the interactions and impacts of different stressor combinations across ecosystems remains incomplete.

A new study conducted at the University of Leeds, UK, gives new insights into how  simultaneous biological invasions and climate warming may affect freshwater ecosystem functioning. The team, led by Daniel Kenna, used laboratory experiments to study how changes in water temperature affected the rate at which two tiny freshwater crustaceans (one native to the UK, and the other an invasive) processed leaf-litter debris, which is an important source of nutrients commonly found on the bed of rivers and lakes.

Biological invasions are a common stressor in freshwater ecosystems across the world, as non-native species are either introduced by humans, or find their way into ecosystems made newly habitable by environmental change. Invasive species may out-compete native species for food and habitat, or carry harmful diseases (e.g. the signal crayfish in Europe). As a result, an influx of invasive species into a freshwater ecosystem may significantly alter its biodiversity, health and functioning.

Writing in Oecologia, the University of Leeds team describe their experiment involving two micro-crustaceans: Gammarus pulex, an amphipod native to the UK; and the so-called ‘killer shrimp’, Dikerogammarus villosus, a fast growing and comparatively large amphipod which is native to Eastern Europe, but increasingly invasive across the western continent.

Dikerogammarus villosus. Photo by S. Giesen (1998).

The invasive Dikerogammarus villosus, or ‘killer shrimp’. Image: NOAA Great Lakes | Flickr Creative Commons

When matched for size, the team found that the UK native Gammarus was more efficient than the ‘killer shrimp’ at leaf-litter processing. The invasive amphipod preferred warmer water temperatures, suggesting that invasions which displace the native Gammarus under climate warming, may lead to a reduction in leaf-litter processing, and so a decline in ecosystem functioning.

However, the ‘killer shrimp’ is a larger animal (around 30mm to Gammarus’s ~20mm), and large individuals can process leaf litter at a faster rate than smaller ones of comparable size to the native species. In addition, ‘killer shrimp’ processing rates increased at a faster rate in response to increasing water temperatures than those of Gammarus individuals of a similar size.

This means that any decreases in ecosystem functioning caused by the displacement of Gammarus populations by ‘killer shrimp’ invasions may be offset by increases in leaf-litter processing in the invasive species where water temperatures are increased.

As such, the study gives a novel insight into an antagonistic relationship between multiple stressors: where some of the potentially harmful effects of the invasive species (i.e. reduced ecosystem functioning) are largely mitigated by the effects of climate warming.

Kenna, D., Fincham, W.N.W., Dunn, A.M. et al. (2016) Antagonistic effects of biological invasion and environmental warming on detritus processing in freshwater ecosystems. Oecologia doi:10.1007/s00442-016-3796-x (Open access)

How groundwater influences Europe’s surface waters

January 13, 2017

Searching for groundwater on the Springendalse Beek, Netherlands. Image: Vince Kaandorp

This week we have a guest post by Vince Kaandorp of Deltares, a water research institute based in the Netherlands. Vince writes on the often-overlooked importance of groundwater in shaping and supporting life in rivers and lakes.


A large portion of the water on Earth is hidden from sight, stored below our feet as groundwater. About 30% of the freshwater globally is believed to be stored as groundwater: 25 times the amount of fresh surface water. This groundwater has an influence on the aquatic ecology in our surface waters. While a proportion of discharge in streams originates from overland flow or direct precipitation, another big part comes from groundwater: either through local springs, diffuse seepage (seepage over bigger areas), or drainage pipes in agricultural regions. Groundwater influences not only small streams, but also rivers and even lakes.

All streams are not created equal: some have a higher contribution of groundwater than others as a result of differences in geology and topography. Because precipitation needs time to travel through the soil, groundwater is a delayed form of discharge compared to overland flow and direct precipitation. As such groundwater is a relatively stable source of water throughout the year and can prevent streams from ceasing flow during dry periods.


Stream water is often heavily ‘topped up’ by groundwater inputs during dry weather. Image: Vince Kaandorp

This groundwater characteristic forms the basis of the Baseflow Index (BFI) which gives an indication of the size of the groundwater contribution and can be calculated from stream discharge measurements. This metric is often used in studies to get an idea of the importance of groundwater for streams. For instance, in the Regge and Dinkel catchment in the Netherlands, the tributaries of the Dinkel river have very different BFI values as some have more groundwater input than others. The streams with less groundwater are known to fall dry during summer, while the ones with more groundwater flow even in the driest periods of the year.


Golden saxifrage growing along the banks of a stream is a good indicator of groundwater inputs. Image: Vince Kaandorp

The influence of groundwater can be seen in the field, that is, if you know what you’re looking for. Springs are a clear direct indicator of groundwater but vegetation can also give a good idea about groundwater. Some species, such as the Golden saxifrage plant often grow on stream banks at locations with significant groundwater inputs.

Have you ever seen orange depositions or slime on a stream bank? Or an oily sheen floating on the water? You might have located a seepage zone too! Groundwater is often anoxic and contains dissolved iron. As a result, as soon as this water comes to the surface certain bacteria start oxidizing the iron, which results in these orange and oily phenomena.

Apart from providing a stable supply of water to streams, groundwater also influences water chemistry and temperature. Groundwater has a different chemical composition to surface water, can contain iron, and is often unpolluted. In addition, the temperature of groundwater is generally around the yearly average temperature (about 12°C in the Netherlands), and is thus a cold-water input during summer and a warm-water input during winter. In this way, groundwater can provide stable temperature habitats for aquatic ecology in streams, and help prevent the water from freezing during cold winters!


Groundwater and surface waters are jointly affected by multiple stressors. Image: Vince Kaandorp

Due to its stable discharge, stable temperature and often unpolluted chemistry, groundwater can mitigate the harmful effect of stressors. For example, a stream with a large groundwater input is likely to be less prone to the effects of climate change. On the other hand, groundwater also functions as a connecting flow path between the catchment and stream, and can thus connect agricultural fields with a stream. This means that chemicals used by farmers, such as nitrate from manure or herbicides and pesticides, flow through the ground and eventually appear in the stream.

There can be a large time lag in this process, because the travel time of the groundwater can be 10s or even 100s of years. This also means that the effect of management practices such as the removal of agricultural fields upstream can take multiple decades to manifest in the stream itself!


The River Elsbeek flowing through agricultural areas where it has been channelised. Image: Vince Kaandorp

In practice there are diverse linkages between groundwater and streams, because a complicated system of groundwater-surface water interactions exists in which groundwater input and output is variable both in time and space.

Because of its importance for many streams and its link with management practises, further research on the groundwater contribution to streams is done by Deltares within the MARS Regge and Dinkel Case Study. This study will help us gain better understanding how groundwater transports and influences stressors, how groundwater is linked with aquatic ecology and how groundwater can be conserved and protected through European management practices.

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