Arctic Pollution: Confounding Climate Change

After considering the impacts of Arctic climate change, one of the issues I wanted to cover was the extent to which confounding factors play a role in inducing ecosystem responses. Although modern conditions are comparable to the Holocene Thermal Maximum (HTM), the unprecedented nature of ecological shifts recorded during the 20^th century, for example in Arctic lakes, question the involvement of additional factors (Holmgren et al., 2010).

Despite being regarded as pristine wilderness; the Arctic is as vulnerable to pollution as industrial regions of Europe and North America. The long-range transport of atmospheric pollutants (sulphur and nitrogen, black carbon, aerosols, heavy metals and organic compounds) from the industrialised mid-latitudes mean that remoteness from direct anthropogenic activity does not guarantee that Arctic ecosystems will be unaffected.

We have already seen how, in addition to increasing GHG concentrations, aerosols and black carbon have contributed to the recent warming in the Arctic. In this post, I want to investigate how pollution, alongside climate change, can synergistically force ecological change.

Arctic haze is a powerful reminder of the extent of anthropogenically-released atmospheric pollutants

Arctic acidification

Ice cores retrieved from the Arctic reveal enhanced concentrations of the major acidifying pollutants during the late 20^th century. Impacts resulting from acidification have mostly been recorded on the Kola Peninsula, Fennoscandia and in the Taymir region of Russia. Following legislation implemented to counteract acidification of surface waters, SO2 emissions declined by ~67% in Europe from 1980-2000. As a result, the recovery of lakes has been observed in the Barents region, in particular on the Kola Peninsula.

Acidification in the Arctic is at most a subregional issue, impacting poorly buffered areas where acid deposition levels exceed the neutralising capacity of the system (AMAP, 2006). Interaction between pollutants increases the complexity in system response and may mean that ecological changes are not simply due to acidification. Kashulina et al. (2003) showed that the widespread environmental damage from nickel industries on the Kola Peninsula was spatially variable and toxic elements, in addition to SO2, acted as a driving mechanism of vegetation damage. With SO2 the dominant component of emissions and exceeding critical levels, previous studies linked ecosystem degradation in the region to the acidifying impact of SO2. However, evidence of widespread acidification is unconvincing and ecogeochemical mapping indicates a complex interaction between pollutants, with elements of low volatility potentially resulting in greater damage despite being emitted in much lower concentrations. Furthermore, in the study areas the increase in base cations (Na⁺, Ca²⁺, Mg²⁺, K⁺) exceeded the deposition of acid anions (SO4^2-, Cl^-) counteracting acidification.

Acid rain has also led to changes in Arctic terrestrial ecosystems

Nutrient enrichment

Although sulphur has previously been of major concern with its role as a primary acidifying agent, major reductions in sulphur emissions over the last decades and less significant declines in nitrogen has brought further attention to the impact of nitrogen deposition. Terrestrial and aquatic studies have investigated both the acidifying role of nitrogen and more recently concerns have grown over its eutrophying potential in these typically nutrient-limited ecosystems. 

Holmgren et al. (2010) compared recent diatom and geochemical records against data from the early to mid-Holocene for four lakes in western Spitsbergen. Increases in diatom valve and chrysophyte cyst concentrations occurring during the past century, with the most pronouncing alterations in the last few decades, indicate enhanced primary production and taxonomic richness. The recent dramatic shifts in diatom assemblages and significant increase in taxonomic richness contrast the relatively sparse flora recorded during the HTM, pointing to additional explanatory variables. Progressive depletion in nitrogen isotopic composition by ~2% during the last part of the 20^th century coincides with community trends, suggesting both climate change and N deposition are synergistically driving shifts towards new ecological states that have not been recorded in the Holocene.

Relative abundance of diatoms in four lakes in western Spitsbergen, Svalbard, alongside concentrations of diatom valves and chrysophyte cysts (Holmgren et al., 2010)

With the possibility of future accelerations in soil mineralisation, increased nitrogen availability (despite declining atmospheric deposition rates) could further threaten Arctic ecosystems (Hobbie et al., 1999). Similarly to acidification, ecological responses to nitrogen deposition are highly variable because of high spatial heterogeneity in lake characteristics, nutrient limitation, community structure and N supply amongst arctic lakes (Hogan et al., 2014).

Heavy metals and persistent organic pollutants (POPs)

Deriving from mining and fossil fuel combustion, the accumulation of heavy metals in biota and transferal up food chains threatens Arctic ecosystems. Concentrations of heavy metals (Pb, Cd, Cu, Fe, Mn and Zn) exceeding levels in the Earth's upper crust and local rocks have been recorded in cryoconites (aggregates of mineral particles, organic substances and microorganisms on glacial surfaces). This has vital consequences for Arctic ecosystems as contaminants have already been reported in higher-trophic-level species including seals, polar bears and reindeer (Łokas et al., 2016).

Similarly to heavy metals, POPs (organic compounds found in pesticides, industrial chemicals and products of burning that do not break down naturally) bioaccumulate and can have major health implications for wildlife and people (Vorkamp and Rigét, 2014). In response, several global and regional conventions are responsible for the elimination and reduction of POPs and therefore much of the contamination occurring today is from 'legacy' POPs. Temporal trends of some legacy POPs in Arctic biota was examined by Rigét et al. (2010), discovering that many of the  compounds in biota show significant declining trends over the last few decades consistent with the decreasing trends recorded in Arctic air.

Ecological implications of nickel mining in the Russian Arctic town, Nikel