Introduction to freshwater ecosystems and fisheries in the Arctic

Published: February 9, 2010, 3:21 pm

Updated: May 7, 2012, 4:53 pm

Author: International Arctic Science Committee (Introduction to freshwater ecosystems and fisheries in the Arctic)

Topics:

Ecological Risk Assessment (main) Water (main) Biodiversity (main) Ecology (main) Natural Resource Management & Policy (main) Climate Change (main)

[1]

This is Section 8.1 of the Arctic Climate Impact Assessment
Lead Authors: Frederick J.Wrona,Terry D. Prowse, James D. Reist; Contributing Authors: Richard Beamish, John J. Gibson, John Hobbie, Erik Jeppesen, Jackie King, Guenter Koeck, Atte Korhola, Lucie Lévesque, Robie Macdonald, Michael Power,Vladimir Skvortsov,Warwick Vincent; Consulting Authors: Robert Clark, Brian Dempson, David Lean, Hannu Lehtonen, Sofia Perin, Richard Pienitz, Milla Rautio, John Smol, Ross Tallman, Alexander Zhulidov

The Arctic, which covers a significant area of the Northern Hemisphere, has a number of prominent and unique climatic, geological, and biophysical features. The region is typified by extreme variability in climate and weather, prolonged darkness in the winter and continuous daylight in the summer, the prevalence of vast areas of permafrost, and the dominance of seasonal ice and snow cover. The Arctic also has a diversity of terrains that contain a significant number and diversity of freshwater ecosystems.

The Arctic has some of the largest rivers in the world (e.g., the Lena, Mackenzie, Ob, and Yenisey); numerous permanent and semi-permanent streams and rivers draining mountains, highlands, and glaciated areas; large lakes such as Great Bear, Great Slave, and Taymir; a myriad of smaller permanent and semi-permanent lakes and ponds; vast areas of wetlands and peatlands; and coastal estuarine and river delta habitats. In turn, these freshwater systems contain a wide diversity of organisms that have developed adaptations to cope with the extreme environmental conditions they face. Examples include life-history strategies incorporating resting stages and diapause, unique physiological mechanisms to store energy and nutrients, an ability to grow and reproduce quickly during brief growing seasons, and extended life spans relative to more temperate species.

Thus, given the regional complexity of climate and landscape and the diversity of freshwater ecosystems and their associated biota, projecting the potential impacts of future climate (Climate change) change and ultraviolet (UV) radiation exposure presents significant challenges. What is certain is that the responses are likely to be quite variable and highly specific to particular freshwater ecosystems, their biota, and the ecological and biophysical circumstances in which they occur.

Challenges in projecting freshwater hydrologic and ecosystem responses (8.1.1)

Fig. 8.1. Climate–ecosystem interactions. The interactions among and within components tend to be sequential but complex. However, complex feedbacks also exist both within major classes of components (e.g., trophic structure linkages with biogeochemical cycling), as well as between components (e.g., ice duration and timing feedbacks to the regional climate system), but are not illustrated above for visual clarity.

The first and most significant challenge in projecting responses of freshwater systems to climate (Climate change) change relates to the limited understanding of how the climate system is coupled to, and influences, key physical and biophysical processes pertinent to aquatic ecosystems, and in turn how these affect ecological structure and function. Figure 8.1 summarizes the complex and often hierarchical interactions between climatic variables (e.g., radiation, precipitation, and temperature), their influence on the biophysical features of freshwater ecosystem habitat, subsequent effects on biological structure and function, and the interaction of feedbacks within and between components. Freshwater ecosystems are complex entities that consist of groups of species at various trophic levels, the hydrological and physical environment that makes up their habitat, the chemical properties of that environment, and the multiple physical, biogeochemical, and ecological processes that act on and within the system. Hence, any change in these attributes and processes as a result of changes in climate and UV radiation levels will ultimately contribute to variable and dynamic responses within freshwater systems. Even in ecosystems containing only simplified food webs (e.g., those having no predators such as fish or predatory macroinvertebrates), the interactions of environmental parameters such as temperature and precipitation with the system are still complex, and may be propagated in ways that are difficult to project (i.e., nonlinear or stepwise threshold responses in population/community dynamics and stability; see Section 8.4.1 (Introduction to freshwater ecosystems and fisheries in the Arctic). Because freshwater systems receive major inputs from terrestrial systems (Chapter 7 (Introduction to freshwater ecosystems and fisheries in the Arctic)) and provide major outputs to marine systems (Chapter 9 (Introduction to freshwater ecosystems and fisheries in the Arctic)), altered states and processes within freshwater systems are intimately linked to these arctic ecosystems through feedback and transfer mechanisms.

There are a number of levels within an ecosystem where changes in climate or UV radiation levels may interact with various ecosystem components, including:

• the individual, either within it (e.g., changes in physiological processes affecting thermoregulation, or effects on life processes such as growth and reproductive rates) and/or the whole individual (e.g., behavior);
• the population (e.g., life-history traits, rates of immigration and emigration, migrations, and intraspecific competition);
• the community (e.g., changes in trophic structure and in the levels and magnitudes of food-web interactions such as inter-specific competition, predation, and parasitism); and
• the ecosystem (e.g., changes that affect the nature of the environment that the organisms occupy, such as altered biogeochemical processes and hydrologic regimes).

Fig. 8.2. The four ACIA regions, the southern boundary of the Arctic used in this chapter, and the major river systems flowing through these regions to the Arctic Ocean.

Hence, there are a number of considerations in assessing the effects of a change in climate or UV radiation levels on freshwater ecosystems. First, changes in the environmental parameters may occur in a variety of ways. Second, these changes may be input to the various aquatic ecosystems in a variety of ways. Third, effects within the ecosystem may manifest at various levels and in various components within the system. Fourth, the effects may propagate through the ecosystem and affect different components or processes differently within the ecosystem. The inherent complexity of such interactions greatly hampers the ability to make accurate and reasonable projections regarding such effects within arctic freshwater ecosystems with high levels of certainty. Finally, the internal complexity of potential responses makes it difficult to project output effects on key linking ecosystems such as deltas and estuaries that form the interactive zones between terrestrial, marine, and freshwater systems.

General knowledge of how the hydrology, structure, and function of arctic aquatic ecosystems are responding to past (Section 8.3 (Introduction to freshwater ecosystems and fisheries in the Arctic)) and relatively recent changes in climate (Climate change) and UV radiation levels is gradually improving. However, much of the understanding of the processes and mechanics of potential impacts continues to be largely based on studies of aquatic systems outside of the Arctic. Hence, the development of detailed projections of climate (Climate change) change impacts on arctic freshwater ecosystems is limited by a lack of understanding of how these impacts will cascade through arctic ecosystems and create second- and higher-order changes.

With these limitations in mind, using the approach outlined in Quantifying impacts and likelihood (below), this chapter identifies and discusses projected changes in the hydrology and ecology of arctic freshwater ecosystems in response to scenarios of future climate and UV radiation levels for three time slices centered on 2020, 2050, and 2080 generated by the ACIA-designated models (Section 4.4 (Introduction to freshwater ecosystems and fisheries in the Arctic)). Where possible, similarities and/or differences in projected impacts between the four ACIA regions (Fig. 8.2; see also Section 18.3 (Introduction to freshwater ecosystems and fisheries in the Arctic)) are identified.

Quantifying impacts and likelihood (8.1.2)

The confidence level associated with projecting potential impacts of changes in climate and UV radiation levels is greatly hampered by the rudimentary level of understanding of arctic freshwater hydrology and ecology and their direct and indirect linkages, responses, and feedbacks to present and future climate. Moreover, the coarse spatial resolution of general circulation models (GCMs) and the uncertainty associated with complex, multilayered, and poorly understood interactions between climate variables greatly contribute to uncertainty in projections of future climate. This is exacerbated by other complexities such as inter- and intra-regional variation driven by, for example, latitude or proximity to marine ecosystems. When combined with uncertainties about how individual species and biological communities will respond to changes in climate and UV radiation levels, the ability to forecast hydro-ecological impacts and resulting cascading effects is significantly compromised. This makes precise quantification of climate change impacts difficult and often tenuous.

To address the issue of uncertainty and to recognize the substantial inter-[[region]al] and latitudinal differences in understanding and the broad spatial extent of arctic aquatic ecosystems, climate change and UV radiation impacts have been "quantified" using a "weight-of-evidence" approach. This approach uses a hierarchy of classes that represent the range of likelihood of the impact(s)/outcomes(s) occurring based on a compilation of information available from historical data, published literature, model projections, and the expert judgment of the authors. Using the ACIA lexicon (Section 1.3.3 (Introduction to freshwater ecosystems and fisheries in the Arctic)), projected likelihoods follow a progression from "very unlikely" (i.e., little chance of occurring) through "unlikely", "possible" (some chance), and "likely/ probable" to "very likely/very probable".

Although not strictly quantifiable in a numeric sense (e.g., exact probabilities), this approach provides a comparative and relative measure of the likelihood that the impact(s) will occur. Hence, a greater weight-of-evidence indicates a greater confidence in the findings (i.e., an increasing convergence of evidence from a number of independent, comprehensive empirical and/or experimental studies, model projections, etc.) that allows the classification of particular impact(s)/outcome(s) as either "very unlikely" or "very likely". The designation of particular impacts as "possible" or "likely" implies the presence of significant gaps in current knowledge. These gaps must be addressed to achieve a better understanding of impacts at the level of the ecosystem and its components. This "weight-of-evidence"-based lexicon is directly applied in the conclusions and key findings of the chapter (Section 8.8.1 (Introduction to freshwater ecosystems and fisheries in the Arctic) , thereby providing a relative "quantification" of the projected responses of freshwater ecosystems to changes in climate and UV radiation levels.

Chapter Structure (8.1.3) Section 8.2 (Introduction to freshwater ecosystems and fisheries in the Arctic)

(Introduction to freshwater ecosystems and fisheries in the Arctic) provides a broad overview of the general hydrological and ecological features of the various freshwater ecosystems in the Arctic, including descriptions for each ACIA region. [[Section 8.3 (Introduction to freshwater ecosystems and fisheries in the Arctic)]2] discusses how understanding past climate regimes using paleolimnological and paleoclimatic records helps to better understand present and future responses of freshwater ecosystems. Subsequent sections discuss the climate scenarios generated by the ACIA-designated models and project impacts on the hydrology and ecology of the major types of arctic freshwater ecosystems (Section 8.4 (Introduction to freshwater ecosystems and fisheries in the Arctic)), impacts on the major components of these ecosystems (Section 8.5 (Introduction to freshwater ecosystems and fisheries in the Arctic)), impacts of changes in UV radiation levels (Section 8.6 (Introduction to freshwater ecosystems and fisheries in the Arctic)), and the interactions of these impacts with contaminants (Section 8.7 (Introduction to freshwater ecosystems and fisheries in the Arctic)). A key feature of arctic freshwater ecosystems is the biota of direct relevance to humans, especially waterfowl, mammals, and fishes that provide the basis for harvests. Species within these groups are of special interest in that they also provide direct biotic linkages between major arctic ecosystems, thus either potentially input or output effects from, or to, terrestrial and marine systems. Fish are of particular relevance since two major ecological groups are present: those wholly associated with freshwaters and those which pass parts of their life history in both fresh and marine waters (i.e., diadromous fishes further divisible into catadromous species such as eels that rear in freshwater and breed in the sea, and anadromous species such as salmon that do the opposite). Anadromous fish provide major nutrient transfers from marine systems back into freshwater systems, thus are of particular significance. A logical extension is to also consider the effects of global change on fisheries for freshwater and diadromous forms; thus, Section 8.5.5 (Introduction to freshwater ecosystems and fisheries in the Arctic) parallels the treatment of marine fisheries in Chapter 13. Section 8.8 (Introduction to freshwater ecosystems and fisheries in the Arctic) summarizes key findings and identifies major knowledge gaps and future research needs.

Chapter 8: Freshwater Ecosystems and Fisheries
8.1. Introduction
8.2. Freshwater ecosystems in the Arctic
8.3. Historical changes in freshwater ecosystems
8.4. Climate change effects
8.4.1. Broad-scale effects on freshwater systems
8.4.2. Effects on hydro-ecology of contributing basins
8.4.3. Effects on general hydro-ecology
8.4.4. Changes in aquatic biota and ecosystem structure and function
8.5. Climate change effects on arctic fish, fisheries, and aquatic wildlife
8.5.1. Information required to project responses of arctic fish
8.5.2. Approaches to projecting climate change effects on arctic fish populations
8.5.3. Climate change effects on arctic freshwater fish populations
8.5.4. Effects of climate change on arctic anadromous fish
8.5.5. Impacts on arctic freshwater and anadromous fisheries
8.5.6. Impacts on aquatic birds and mammals
8.6. Ultraviolet radiation effects on freshwater ecosystems
8.7. Global change and contaminants
8.8. Key findings, science gaps, and recommendations

References

Citation

Committee, I. (2012). Introduction to freshwater ecosystems and fisheries in the Arctic. Retrieved from http://editors.eol.org/eoearth/wiki/Introduction_to_freshwater_ecosystems_and_fisheries_in_the_Arctic