FRESHWATER ECOSYSTEMS (Chapter 13)

Lead Authors:  Frederick J. Wrona & James D. Reist 

Contributing Authors: Per-Arne Amundsen, Patricia A. Chambers, Kirsten Christoffersen, Joseph M. Culp, Peter D. di Cenzo, Laura Forsström, Johan Hammar, Jani Heino, Risto K. Heikkinen, Kimmo K. Kahilainen, Lance Lesack, Hannu Lehtonen, Jennifer Lento, Miska Luoto, Philip Marsh, David J. Marcogliese, Paul A. Moquin, Tero Mustonen, Terry D. Prowse, Michael Power, Mila Rautio, Heidi Swanson, Megan Thompson, Heikki Toivonen, Vladimir Vasiliev, Raimo Virkkala and Sergey Zavalko

SUMMARY

The Arctic contains an abundant and wide range of freshwater ecosystems, including lakes, ponds, rivers and streams and a complex array of wetlands and deltas. This broad range of freshwater ecosystem types contains a multitude of habitats of varying ecological complexity and supports a diversity of permanent and transitory organisms adapted to living in an often highly variable and extreme environment. Moreover, these habitats and species provide important ecological and economic services to northern peoples through the provision of subsistence foods (fish, aquatic birds and mammals), serve as seasonally important transportation corridors (e.g. ice roads), and are ecologically and culturally important habitat for resident and migratory aquatic species.

The Arctic region is currently undergoing significant and rapid environmental and socio-economic change, which in turn will have profound effects on the distribution, abundance and quality of freshwater ecosystems, their associated habitats and related biological and functional diversity. Climate change has been identified as the prominent environmental driver affecting Arctic freshwater ecosystems and their related biological and functional diversity, although other significant drivers and environmental stressors are increasing in relevance (e.g. point and non-point pollution, increased impoundment/diversion of freshwater, enhanced mining and
oil and gas activities and anthropogenic introduction of invasive species).

As a result, biodiversity within Arctic freshwater ecosystems is being rapidly altered by natural and anthropogenic drivers. Hence, a parallel understanding of functional diversity (food web structure and complexity, productivity, carbon and nutrient dynamics) is required to develop and implement appropriate conservation and management measures to ensure healthy and functioning ecosystems. Together these observations also contribute to understanding of the factors promoting services provided by freshwater ecosystems.

There have been changes to the permafrost: In the past ten years several lakes have disappeared both from the taiga and tundra area where we have our reindeer migration. Lakes have become rivers and drained out. You can see this in the tundra, but even more in forested areas. This impacts the fishing for sure. One of the lakes drained, and the fish got stuck on the bottom and died of course. Wetlands and marshes are deeper or are not so solid. Close to the rivers like Chukatsha, there are depression faults and holes in the ground. The marshlands cannot be used for reindeer travelling anymore. Dmitri Nikolayevich Begunov, a Chukchi reindeer herder from the Cherski town in Lower Kolyma in north-eastern Russia
(Mustonen 2009).

Currently, knowledge of Arctic freshwater ecosystems and related biodiversity is limited with large spatial gaps particularly in remote areas. The development of appropriate knowledge of reference states is critical to assess the variability and significance of change. Significant knowledge gaps remain in our understanding of how biodiversity contributes to, and how changes affect, freshwater ecosystem function and services. More systematic process-based studies are required to better understand the abiotic and biotic controls on ecosystem properties and to obtain a predictive understanding of how ecological communities are structured in response to changing anthropogenic and environmental drivers.

Future conservation and protection of Arctic freshwater ecosystems and their associated biodiversity requires appropriate long-term monitoring and associated process- based research across relevant spatial and temporal scales. Actions taken must be adaptive and responsive to new information in a rapidly changing Arctic.

INTRODUCTION

Freshwater ecosystems are abundant and diverse throughout the circumpolar region and include lakes, ponds, rivers, streams and a wide range of wetland complexes (Usher et al. 2005, Wrona et al. 2005, 2006a, Vincent & Laybourn-Parry 2008). The Arctic contains some of the world’s largest rivers and associated deltas (e.g. the Lena, Ob, Yenisei, Mackenzie), largest and deepest lakes (e.g. Great Bear Lake, Great Slave Lake and Lake Taymyr), numerous permanent and intermittent streams and rivers draining mountains, highlands and glaciated areas, and a myriad of smaller permanent and semi-permanent lakes, ponds and wetlands. In some regions of the Arctic, lake, pond and wetland complexes can cover > 80% of the total land area (Wrona et al. 2005, 2006a, Pienitz et al. 2008, Rautio et al. 2011).

This broad range of freshwater ecosystem types contains a multitude of habitats of varying complexity, which in turn support a diversity of permanent and transitory organisms adapted to living in an often highly variable and extreme environment (Rouse et al. 1997, Usher et al. 2005, Wrona et al. 2005, Prowse et al. 2006b, Rautio et al. 2008, Heino et al. 2009, Moss et al. 2009, Schindler & Lee 2010). In addition, high-latitude freshwater systems are of regional and global significance by serving as important tele-connections and providing feedbacks with climate and ocean systems, being critical habitat and/or refugia for unique species and communities, acting as significant sources and/or sinks of CO₂ and methane, and serving as transecosystem integrators and links of nutrient, organic matter and freshwater transport and f lux between the terrestrial and marine systems (Wrona et al. 2005, AMAP 2011b, Prowse et al. 2011c).

The Arctic region is currently in a period of major and rapid environmental and socio-economic change, which in turn will have profound effects on the distribution, abundance and quality of freshwater ecosystems and their associated habitats and biological and ecological diversity (Wrona et al. 2005, CAFF 2010, AMAP 2011b). While climate change is a key environmental driver affecting freshwater ecosystems and associated biota in the Arctic region and has received a significant amount of attention (ACIA 2005a, 2005b, IPCC 2007, Heino et al. 2009, AMAP 2011b, Rautio et al. 2011, Culp et al. 2012), a number of other significant drivers and environmental stressors are also increasing in relevance in their potential for affecting freshwater ecosystems and related biodiversity. These include, for example, point and non-point pollution (e.g. long-range aerial transport of contaminants; AMAP 2003, 2011a, Macdonald et al. 2005, Wrona et al. 2006b), altered hydrologic regimes related to increased impoundment/diversion of freshwater (Prowse et al. 2006a), water quality changes from landscape alterations (e.g. mining, oil and gas exploration) (AMAP 2008) and biological resource exploitation (e.g. subsistence and commercial fisheries). Furthermore, increased access to the north via land and sea transport including for example, the proliferation of roads in northern Canada and Russia, opens up efficient new dissemination pathways for invasive species (AMAP 2011b; see also Lassuy & Lewis, Chapter 16). Collectively, these drivers/stressors will often synergistically contribute to the alteration and/or degradation of biological diversity at the species, genetic and habitat- ecosystem levels (Pimm et al. 1995, ACIA 2005, Wrona et al. 2005, IPCC 2007, CAFF 2010).

In the following sections we summarize the current state of knowledge on the relative importance of the past, present and projected environmental and anthropogenic drivers in affecting the status, patterns and trends in ecosystem/habitat, structural and functional diversity of Arctic freshwater systems. In some circumstances it is difficult to fully adhere to the strict definition of the Arctic used in this assessment (see Section 2 in Meltofte et al., Introduction), as certain freshwater systems (notably the large rivers that discharge to the Arctic Ocean) cross several ecozones and related latitudinal and temperature gradients given the scale of their contributing drainage area. Such systems are used as key examples of how Arctic freshwater and habitat quality, quantity and related biodiversity can also be significantly affected through direct linkages to environmental and anthropogenic drivers and ecological processes that are extraneous to the Arctic per se.

Through the use of pertinent case studies and examples, we will provide an ecosystem-based, community or food web perspective on how key environmental and anthropogenic drivers in the Arctic, operating singly or in combination, affect the distribution and abundance of freshwater ecosystem types, their related habitats, and structural and functional ecological properties.

In the final section of the chapter we provide perspectives on current and proposed approaches for the conservation and protection of Arctic freshwater biodiversity, identify knowledge gaps and challenges, and forward recommendations on the future directions of monitoring and assessment of aquatic biodiversity in a rapidly changing Arctic.

CONCLUSIONS AND RECOMMENDATIONS

Arctic freshwater ecosystems are undergoing rapid eronmental change in response to the inf luence of both environmental and anthropogenic drivers. Primary drivers affecting the distribution, abundance, quality and hence diversity of freshwater lentic and lotic ecosystems and associated habitats include climate variability and change, landscape-level changes to the cryospheric components (i.e. permafrost degradation, alterations in snow and ice regimes), and changes to ultraviolet radiation (UVR). Key secondary environmental and anthropogenic drivers that are gaining circumpolar importance in affecting Arctic freshwater ecosystem quantity and quality include increasing acidification and pollution from deposition of industrial and other human activities (wastewater, release of stored contaminants, long-range transport and biomagnification of pollutants), landscape disturbance from human development (dams, diversions, mining, oil and gas activity, population increase) and exploitation of freshwater systems (fisheries, water withdrawals).

Changes in the magnitudes, duration and interactions among environmental and anthropogenic drivers will have profound effects on the distribution and abundance of Arctic freshwater ecosystem types, the quantity and quality of their habitats, and associated structural and functional biodiversity. In response to the observed and projected types and magnitudes of changes in environmental and anthropogenic drivers affecting the Arctic ecozone, freshwater ecosystem diversity (i.e. the range and types of freshwater systems), related changes to associated freshwater habitats, and corresponding faunal biodiversity will be affected at local, regional and circumpolar scales. Given the levels of ecological complexity and associated uncertainty with linking changes in physico-chemical factors to biological interactions, quantifying and monitoring changes in beta and gamma diversity in relation to changes in key drivers will be fundamental to the conservation and management of Arctic freshwater ecosystems and their biota.

Similarly, the biodiversity within freshwater ecosystems is being rapidly altered by natural and anthropogenic drivers, thus a parallel understanding of functional diversity (food web structure and complexity, productivity, carbon and nutrient dynamics) is required to develop and implement appropriate conservation and management measures to ensure continued ecosystem services. Together these observations also contribute understanding of factors promoting services provided by freshwater ecosystems.

Currently, knowledge of Arctic freshwater ecosystems and related biodiversity and stability is very limited due to a paucity of long-term monitoring sites resulting in large spatial and temporal time-series gaps particularly in remote areas. In the face of a rapidly changing Arctic, developing appropriate knowledge of reference states will be critical to assessing the variability and significance of change.

Significant gaps also remain in our understanding of how biodiversity contributes to, and how changes affect, freshwater ecosystem functions. The future conservation and protection of Arctic freshwater ecosystems and their associated biodiversity requires appropriate long-term monitoring across relevant spatial and temporal scales.  An important step to improving efforts in this area has been the approval for implementation of the circumpolar freshwater biodiversity monitoring plan developed by the Arctic Council Conservation of Flora and Fauna (CAFF) working group and its Circumpolar Biodiversity Monitoring Program (CBMP). The Arctic Freshwater Biodiversity Monitoring Plan (Culp et al. 2012) details the rationale and framework for improvements related to the monitoring of freshwaters of the circumpolar Arctic, including ponds, lakes, their tributaries and associated wetlands, as well as rivers, their tributaries and associated wetlands. The plan also provides Arctic countries with a structure and a set of guidelines for initiating and developing monitoring activities that employ common approaches and indicators.

Process-based studies are required to better understand the abiotic and biotic controls on ecosystem properties and to obtain a predictive understanding of how ecological communities are structured in response to changing anthropogenic and environmental drivers. Given the complex interactions between the abiotic and biotic drivers affecting rapid change in the Arctic, trans-disciplinary approaches will be instrumental in identifying and understanding key processes (Hodkinson et al. 1999).

Most analyses of status and trends of biodiversity and its change have been linked to the monitoring and assessment of species richness. Standard species-based approaches may misrepresent true structural and functional diversity and thus ecosystem stability and resilience in the face of change. Future assessments of biodiversity and its changes must also include consideration of ecosystem and functional attributes using both empirical and experimental approaches. There is also an identified need to develop integrated biological/hydro-ecological models (in particular regarding changes in cryospheric components) to predict freshwater biodiversity responses to a changing climate (Hodkinson et al. 1999, Prowse & Brown 2010b, 2010c, AMAP 2011b).

• The establishment of a long-term, circumpolar network of integrated freshwater research observatories and monitoring sites is required to achieve the above goals. The focus should be inclusive of biodiversity in ecosystems, biota and key physical and chemical drivers, as well as anthropogenic inf luences, across appropriate spatial scales.

Rapid Arctic change is outpacing present capacity for Arctic freshwater conservation and management. More over, spatial displacement of key habitats, rapid shifts in the nature of processes and colonization by southern biota all indicate that static approaches are insufficient to understand and manage these complex systems. Given the large spatial scale of potential changes in Arctic freshwater ecosystems (e.g. losses, shifts amongst types, productivity changes), systematic wide scale observations are required.

• Accordingly, management actions for conservation and protection of Arctic freshwater ecosystems must be adaptive in nature and the development of novel approaches is required.

Development of appropriate wide-scale and focal-point approaches to monitoring is required. These could include, for example, genomics-based diversity assessment, space-based remote sensing, networks of automated sensors systems operating at varying spatial and temporal scales, and inter-disciplinary transfer of key approaches. In addition, community-based monitoring can be an effective method to provide continuous data from remote inhabited areas. Such work could range from simple observation and documentation to the collection of samples including tissue samples taken from harvested species by subsistence hunters and fishers.

Freshwater ecosystems serve as trans-ecosystem integrators (e.g. linking terrestrial, freshwater and oceanic environments) of multiple environmental and anthropogenic drivers and stressors. In particular lakes act as sentinels and integrators of biological, geochemical and ecological events occurring in catchments and in lacustrine environments (Schlinder 2009). Ecological transtion zones within and between ecosystems concentrate key processes, drivers and diversity, thus are focal areas of rapid ecosystem change and thus represent ‘hot spots’ ideal for early warning.

• Consideration should be made of using basin or ‘catchment-based’ integrative approaches (e.g. Schinder 2009, Schindler & Lee 2010) for the development of appropriate monitoring and research programs that could link individual, population, community and ecosystem responses to changes in environmental and anthropogenic drivers. In addition, such an integrated approach will allow for the assessment of the current state of ecosystem health and cumulative impacts associated with biodiversity change.

There is a growing recognition and concern regarding the lack of understanding of the potential loss or gain of species and the consequent implications for associated ecosystem function (e.g. Hooper et al. 2005, Vaughn 2010). Given the functional importance of biota living in aquatic environments and the difficulties associated with cataloging their diversity and distribution, innovative approaches and studies must be taken along a range of spatial, temporal and organizational (e.g. system-based and species-based) scales to better understand the connections (e.g. the necessity of obtaining an improved mechanistic understanding of the individual effects and interactions among environmental stressors/drivers on all trophic levels and related ecosystem structure and function; see Bordersen et al. 2011). In addition, in a rapidly changing Arctic, there is a need to be aware of and to develop ways to detect and understand possible ecological ‘surprises’, which are unexpected findings or outcomes that are well outside what is expected to happen or not happen (Lindenmayer et al. 2010).

• Research involving a range of comparative short- and long-term field-based empirical studies, field experiments (including experimental manipulations) and laboratory experiments should be conducted to investigate and better understand the linkages and effects of biodiversity on ecosystem function and, consequently, on the ecological goods and services that Arctic freshwater ecosystems provide.