Bronwyn E. Keatley

Seabird-driven shifts in Arctic pond ecosystems.

Migratory animals such as seabirds, salmon and whales can transport large quantities of nutrients across ecosystem boundaries, greatly enriching recipient food webs. As many of these animals biomagnify contaminants, they can also focus pollutants at toxic levels. Seabirds arguably represent the most significant biovectors of nutrients and contaminants from the ocean to the land, given their sheer numbers and global distribution. However, long-term census data on seabirds are rare. Using palaeolimnological proxies, we show that a colony of Arctic seabirds has experienced climate-induced population increases in recent decades. We then document increasing concentrations of contaminants, including polychlorinated biphenyls and cadmium, in pond sediments that are linked to biotransport by seabirds. Our findings suggest that climate-related shifts in global seabird populations will have the unexpected consequence of restructuring coastal ecosystems.

Impacts of seabird-derived nutrients on water quality and diatom assemblages from Cape Vera, Devon Island, Canadian High Arctic

Allochthonous nutrient subsidies play an important role in shaping biotic communities, particularly in naturally oligotrophic ecosystems such as those commonly found in the Canadian High Arctic. Seabirds have been identified as an important vector capable of transporting significant quantities of nutrients from marine to terrestrial environments. However, the influence of seabird-derived nutrients on water quality and ecosystem functioning of Arctic freshwater systems has been largely unexplored. Here, we sampled 24 ponds on Cape Vera, Devon Island (Nunavut, Arctic Canada), an area that is home to over 10,000 nesting pairs of northern fulmars (Fulmarus glacialis), in order to explore the influence of seabirds on water quality and diatom ecology. Our data reveal distinctive water chemistry changes (e.g., high pH, nutrients) and diatom assemblages (e.g., very low diversity) related to varying degrees of bird influence. Using δ15N as a proxy of trophic level, we show that a small but significant portion of the variance in the diatom species data can be explained by seabird-derived nutrients. Although the generation of robust quantitative models predicting δ15N from fossil diatom data was limited by the overwhelming dominance of a few taxa, this study provides evidence that seabird-derived nutrients play a critical role in influencing the water quality of Arctic ponds. Interestingly, diatom assemblage composition does not respond in a simple fashion to seabird-derived nutrients, in contrast to diatom–nutrient relationships recorded in many temperate regions.

Prolonged Ice Cover Dampens Diatom Community Responses to Recent Climatic Change in High Arctic Lakes

ABSTRACT Numerous paleolimnological studies of Arctic lakes and ponds have shown marked shifts in both algal and invertebrate taxa within the past ∼150 years that are consistent with recent climatic warming. However, the magnitude and timing of changes are often non-uniform, with large, deep lakes frequently exhibiting muted assemblage shifts relative to smaller ponds. The hypothesis that duration and extent of ice cover exerts an overriding influence on habitat availability for biota has been commonly invoked to explain these differences, and many studies indicate that changes in ice cover are important drivers of recent biological changes. However, a detailed paleolimnological comparison of two lakes from the same region that have similar water chemistry but different ice cover regimes has not yet been attempted. Here we examine the influence of prolonged ice cover on the rate, magnitude, and direction of fossil diatom species shifts over time in two remarkably similar and adjacent Ellesmere Island lakes that mainly differ in their periods of ice cover. These two lakes exhibit strikingly different paleolimnological diatom profiles, despite their physical proximity, similar depths, and nearly identical water chemistry. In the lake characterized by prolonged ice cover, we find little evidence of diatom-inferred environmental change over its recent history, while diatom assemblages have undergone dramatic changes in the lake with the shorter duration of ice cover. This study supports the general hypothesis that changes in ice cover are a principle determinant of shifting diatom assemblages in High Arctic lakes.

Land-Use Legacies Are Important Determinants of Lake Eutrophication in the Anthropocene

Background A hallmark of the latter half of the 20th century is the widespread, rapid intensification of a variety of anthropogenically-driven environmental changes—a “Great Acceleration.” While there is evidence of a Great Acceleration in a variety of factors known to be linked to water quality degradation, such as conversion of land to agriculture and intensification of fertilizer use, it is not known whether there has been a similar acceleration of freshwater eutrophication. Methodology/Principal Findings Using quantitative reconstructions of diatom-inferred total phosphorus (DI-TP) as a proxy for lake trophic state, we synthesized results from 67 paleolimnological studies from across Europe and North America to evaluate whether most lakes showed a pattern of eutrophication with time and whether this trend was accelerated after 1945 CE, indicative of a Great Acceleration. We found that European lakes have experienced widespread increases in DI-TP over the 20th century and that 33% of these lakes show patterns consistent with a post-1945 CE Great Acceleration. In North America, the proportion of lakes that increased in DI-TP over time is much lower and only 9% exhibited a Great Acceleration of eutrophication. Conclusions/Significance The longer and more widespread history of anthropogenic influence in Europe, the leading cause for the relatively pervasive freshwater eutrophication, provides an important cautionary tale; our current path of intensive agriculture around the world may lead to an acceleration of eutrophication in downstream lakes that could take centuries from which to recover.

Accelerated delivery of polychlorinated biphenyls (PCBs) in recent sediments near a large seabird colony in Arctic Canada

Polychlorinated biphenyls (PCBs) were measured in sediment cores from ponds located near a large seabird colony at Cape Vera, Devon Island, Arctic Canada. Surface sediment PCB concentrations were approximately 5x greater in seabird-affected sites relative to a nearby control pond and were correlated with independent indicators of seabird activity including, sedimentary delta(15)N and lakewater chlorophyll a and cadmium concentrations. PCB fluxes were amongst the highest recorded from the High Arctic, ranging from 290 to 2400 ng m(-2) yr(-1). Despite a widespread ban of PCBs in the mid-1970s, PCB accumulation rates in our cores increased, with the highest values recorded in the most recent sediments. Possible mechanisms for the recent PCB increases include a vertical flux step driven by seabird-delivered nutrients and/or delayed loading of PCBs from the catchment into the ponds. The high PCB levels recorded in the seabird-affected sites suggest that seabird colonies are exposing coastal ecosystems to elevated levels of contaminants.

Historical seabird population dynamics and their effects on Arctic pond ecosystems: a multi-proxy paleolimnological study from Cape Vera, Devon Island, Arctic Canada

Rapid environmental changes occurring in polar regions may pose a signifi cant threat to the ~10 mil- lion seabirds currently inhabiting the Canadian Arctic. However, a paucity of long-term data on seabird population dynamics makes effective management diffi cult. As top predators in the oceanic pelagic foodweb, seabirds provide marine-derived nutrients to freshwater habitats via their guano, causing trophic cascades that may be tracked using paleolimnological techniques. Diatoms (Bacillariophyceae) are the most commonly used bioindicators in paleolim- nological studies and, because they are known to respond sensitively to changes in trophic status, may be effective proxies for tracking changes in seabird population dynamics. Here, we present diatom data obtained from sediment cores in seabird-affected ponds near Cape Vera, Devon Island, High Arctic Canada. We also report on additional sedimentary proxies that can be used to track seabird infl uence, namely stable isotopes of nitrogen (δ 15 N) and

Physical and chemical limnological characteristics of lakes and ponds across environmental gradients on Melville Island, Nunavut/N.W.T., High Arctic Canada

Physical and chemical limnological variables were measured from 40 ponds and 6 lakes across Melville Island, Nunavut/N.W.T., Canadian high Arctic, an environmentally sensitive region where very limited limnological data were available. Mean values of most variables were mid-range when compared to other high Arctic limnological surveys, yet the ranges of most measured variables were amongst the largest yet encountered in Canadian high Arctic regional surveys. The first two axes of a Principal Components Analysis explained 55.2 % of the variation in the environmental data. Variables most strongly associated with axis one were pH, dissolved organic carbon, total dissolved nitrogen, specific conductivity and related variables, while axis two represented gradients of other nutrients and trace metals. High elevation sites near permanent ice caps recorded the lowest specific conductivity and Ca 2+ values yet reported in high Arctic systems. High phosphorus values (>20 μg/L) in some of the Melville Island sites are likely indicative of re-suspended sediments, rather than eutrophic conditions. Total nitrogen to total phosphorus ratios suggest that ∼50 % of the sites are P limited, while 33 % are N limited, supporting previous research which suggests N limitation is more commonly encountered in Arctic than in temperate freshwater ecosystems. Finally, when freshwater sites on Melville Island were grouped according to predefined bioclimatic zones, only the most lushly vegetated zone appeared to affect limnological conditions. with these sites having higher mean total dissolved nitrogen, pH, and specific conductivity.

Evaluating the influence of environmental and spatial variables on diatom species distributions from Melville Island (Canadian High Arctic)

Diatom species assemblages were identified and enumerated from the surface sediments of 45 lakes and ponds across a wide spectrum of spatial and environmental gradients on Melville Island, Nunavut/N.W.T, Arctic Canada. Whereas the most common taxa were similar to those recorded elsewhere in the Canadian High Arctic, significant differences in assemblages existed between sites located in the different bioclimatic zones of Melville Island. For example, taxa recorded in the most lushly vegetated bioclimatic zone were similar to those found in lushly vegetated regions elsewhere in the Canadian Arctic Archipelago, and generally different from diatoms in the poorly vegetated regions on Melville Island. Of the measured environmental variables, pH, specific conductivity, surface area, elevation, and chlorophyll a explained significant portions of the variance in diatom assemblage composition at the scale of the entire island. However, only total dissolved nitrogen was an important explanatory variable within the ...