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