Anson W. Mackay

Looking forward through the past : identification of 50 priority research questions in palaeoecology

Summary 1. Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science. They are an effective way to identify research foci that advance the field and that also have high policy and conservation relevance. 2. To date there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct past ecological and environmental systems on timescales from decades to millions of years. 3. We adapted a well-established methodology to identify 50 priority research questions in palaeoecology. Using a set of criteria designed to identify realistic and achievable research goals, we selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners. This article is protected by copyright. All rights reserved. Accepted Article 4. The integration of online participation, both before and during the workshop, increased international engagement in question selection. 5. The questions selected are structured around six themes: human–environment interactions in the Anthropocene; biodiversity, conservation, and novel ecosystems; biodiversity over long timescales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesizing information from multiple records; and new developments in palaeoecology. 6. Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes, and the continued application of long-term data for better-informed landscape management. 7. Synthesis Palaeoecology is a vibrant and thriving discipline and these 50 priority questions highlight its potential for addressing both pure (e.g. ecological and evolutionary, methodological) and applied (e.g. environmental and conservation) issues related to ecological science and global change.

Detecting environmental change: science and society—perspectives on long-term research and monitoring in the 21st century

Widespread concern over the state of the environment and the impacts of anthropogenic activities on ecosystem services and functions has highlighted the need for high-quality, long-term datasets for detecting and understanding environmental change. In July 2001, an international conference reviewed progress in the field of long-term ecosystem research and monitoring (LTERM). Examples are given which demonstrate the need for long-term environmental monitoring and research, for palaeoecological reconstructions of past environments and for applied use of historical records that inform us of past environmental conditions. LTERM approaches are needed to provide measures of baseline conditions and for informing decisions on ecosystem management and environmental policy formulation. They are also valuable in aiding the understanding of the processes of environmental change, including the integrated effects of natural and anthropogenic drivers and pressures, recovery from stress and resilience of species, populations, communities and ecosystems. The authors argue that, in order to realise the full potential of LTERM approaches, progress must be made in four key areas: (i) increase the number, variety and scope of LTERM activities to help define the operational range of ecosystems; (ii) greater integration of research, monitoring, modelling, palaeoecological reconstruction and remote sensing to create a broad-scale early warning system of environmental change; (iii) development of inter-disciplinary approaches which draw upon social and environmental science expertise to understand the factors determining the vulnerability and resilience of the nature-society system to change; and (iv) more and better use of LTERM data and information to inform the public and policymakers and to provide guidance on sustainable development.

Does the terrestrial biosphere have planetary tipping points

Tipping points--where systems shift radically and potentially irreversibly into a different state--have received considerable attention in ecology. Although there is convincing evidence that human drivers can cause regime shifts at local and regional scales, the increasingly invoked concept of planetary scale tipping points in the terrestrial biosphere remains unconfirmed. By evaluating potential mechanisms and drivers, we conclude that spatial heterogeneity in drivers and responses, and lack of strong continental interconnectivity, probably induce relatively smooth changes at the global scale, without an expectation of marked tipping patterns. This implies that identifying critical points along global continua of drivers might be unfeasible and that characterizing global biotic change with single aggregates is inapt.

Sediment heavy metal record in Lake Baikal: natural and antrhopogenic sources

Geochemical analysis of six radiometrically dated short cores of recent sediment from Lake Baikal shows clear evidence of enhanced Pb supply. However, the sediment concentration increases are very small; the average Pb concentration rises from a baseline value of 10.9 μg g-1 to a peak value of only 14.8 μg g-1. In contrast to the more polluted lakes commonly studied in Europe and North America, variation in Pb concentration is far more strongly influenced by natural variation than by pollution. In sediment deposited over the last 150–200 years 73% of the variance in the sediment Pb concentration can be accounted for by variation in bulk composition of the sediment, and by atmospheric pollution. Factors influencing Pb concentrations over this time period are, in order of decreasing average importance (fraction of total variance explained), catchment supply (indicated by 226Ra activity variation) (43%), anthropogenic Pb emissions (24%), and dilution by ferromanganese hydroxides (6%). On longer (1000s of years) time scales dilution by biogenic silica is probably more important.The recent enhanced supply of catchment Pb correlates with accelerating accumulation rates, indicating a link with enhanced erosion. Anthropogenic sources dominate only in the southern basin, where local fossil-fuel burning industry is situated. The evidence for a local industrial source for the Pb pollution is strengthened by the high correlation between the inventories for Pb and for spheroidal carbonaceous particles. The absence of detectable anthropogenic Pb enrichment in the northern part of the lake suggests that long-distance Pb pollution is small compared with the local natural supply.

Sedimentary records of recent environmental change in Lake Baikal, Siberia:

Lake Baikal is the worlds largest freshwater lake and is internationally famous for its rich and largely endemic biota. Concern about this unique ecosystem has grown since the late 1970s but whether recent biological changes result from natural fluctuations or pollution is unclear. One way of discriminating between these processes is to examine records of recent change in radiometrically dated deep-water sediment cores. Here we use high-resolution diatom analysis of one core to show that abundances have not changed significantly over recent decades. By contrast, we demonstrate that the lake is contaminated by atmospheric pollutants and has experienced a small qualitative change in soil derived magnetic minerals. Sedimentary lead concentrations show an increasing trend in the c. 150-year core sequence and spheroidal carbonaceous particles (SCPs) contaminate post-1930 sediment. Although we provide no evidence that twentieth-century pollution has affected the endemic planktonic diatoms in the central western region of southern Lake Baikal, longer trends in species abundances could be related to naturally occurring climatic cycles or to global warming.

Paleolimnological assessment of recent environmental change in Lake Baikal: sediment chronology

Sediment cores collected from six sites in Lake Baikal as part of an extensive investigation of sediment records of recent environmental change were dated radiometrically by 210Pb. Although the results obtained were in some respects comparable to those obtained by previous 210Pb studies, there were some significant differences. Most notably, a core from abyssal depths in the centre of the middle basin appeared to record at least wo major episodes of rapid sedimentation, possibly caused by turbidity currents. All cores, including those from the North Basin, contained significant records of weapons test fallout 137Cs, though these were of little chronological value due to the long residence time of 137Cs in the water column. Models and budgets for sediment and radionuclide transport through Baikal are presented and used to help validate the 210Pb results.

The spatial and temporal distribution of fossil-fuel dervied pollutants in the sediment record of Lake Baikal, east Siberia

Spatial and temporal patterns of spheroidal carbonaceous particles (SCP) extracted from lake sediments provide an unambiguous record of the distributions of fossil-fuel derived pollutants. When applied to sediment cores taken from Lake Baikal spatial patterns show good agreement with the distribution of industry, with the highest concentrations found in the southern basin nearest to Irkutsk. SCP were found to occur in all cores from all areas of the lake in contrast to metal results where anthropogenically enhanced deposition was only demonstrable in the southern basin. SCP distribution within the sediments of Lake Baikal is seen to be distinctly regional and therefore long distance transport is not thought to be an important pathway for these pollutants. Temporal patterns of SCP show trends that reflect the development of industry in the area since the 1940s. Settling rates in the 1600 m water column suggest that the SCP sediment record may be approximately an order of magnitude more sensitive to depositional changes than that of trace metals.

Magnetic properties of recent sediments in Lake Baikal, Siberia

Mineral magnetic measurements of six 210Pb-dated surface cores from different basins of Lake Baikal, Siberia, show temporal records controlled by a range of internal and external processes. With the exception of sediments on the Academician Ridge, there is clear evidence for widespread reductive diagenesis effects on the ferrimagnetic component coupled with neo-formation of paramagnetic iron minerals. Greigite formation, bacterial magnetosome accumulation and turbidite layers may affect the properties of some sediment levels. Concentrations of canted antiferromagnetic minerals (eg. haematite) appear to increase from the 19th century onwards. These minerals are less affected by dissolution processes and probably represent detrital minerals delivered by catchment fluvial processes. The magnetic evidence for recent atmospheric pollution by fossil-fuel combustion processes is weak in all the cores, and supports the findings from studies of spherical carbonaceous particles (SCPs) and heavy metals that pollution is largely restricted to the southern basin. Correlations between recent sediments based on magnetic data may be insecure over long distances or between basins.

Is there an isotopic signature of the Anthropocene

We consider whether the Anthropocene is recorded in the isotope geochemistry of the atmosphere, sediments, plants and ice cores, and the time frame during which any changes are recorded, presenting examples from the literature. Carbon and nitrogen isotope ratios have become more depleted since the 19th century, with the rate of change accelerating after ~ad 1950, linked to increased emissions from fossil fuel consumption and increased production of fertiliser. Lead isotope ratios demonstrate human pollution histories several millennia into the past, while sulphur isotopes can be used to trace the sources of acid rain. Radioisotopes have been detectable across the planet since the 1950s because of atmospheric nuclear bomb tests and can be used as a stratigraphic marker. We find there is isotopic evidence of widespread human impact on the global environment, but different isotopes have registered changes at different times and at different rates.

Spatial and Seasonal Variability in Surface Water Chemistry in the Okavango Delta, Botswana: A Multivariate Approach

The annual flood pulse in the Okavango Delta (Botswana), has a major influence on water chemistry and habitat. We explore spatial and temporal patterns in a suite of chemical variables, analysed from 98 sample points, across four regions, taken at different stages of the flood cycle. The major pattern in water chemistry is characterised by an increasing gradient in ionic concentration from deep-water sites in the Panhandle to more shallow, distal regions to the south. Concentrations of cations, anions, dissolved organic carbon, and SiO2 are significantly higher in the seasonally inundated floodplains than in permanently flooded regions. Several variables (including Na and total nitrogen) significantly increase from low flood to high flood, while others (including HCO3, SiO2, and Cl) increase in concentration, initially between low flood and flood expansion, before declining at maximum flood extent. Redundancy analysis (RDA) revealed that hydrological variables (water depth, flow velocity, flood frequency, and hydroperiod class) significantly explain 17% variation in surface water chemistry. Predictions of increasing flood volume in the near future may result in a decline in alkalinity and dilution of DOC. Our study provides an important baseline from which to monitor future change in the Delta.