Marianne V. Moore

Sixty years of environmental change in the world's largest freshwater lake – Lake Baikal, Siberia

High-resolution data collected over the past 60 years by a single family of Siberian scientists on Lake Baikal reveal significant warming of surface waters and long-term changes in the basal food web of the worlds largest, most ancient lake. Attaining depths over 1.6 km, Lake Baikal is the deepest and most voluminous of the worlds great lakes. Increases in average water temperature (1.21 °C since 1946), chlorophyll a (300% since 1979), and an influential group of zooplankton grazers (335% increase in cladocerans since 1946) may have important implications for nutrient cycling and food web dynamics. Results from multivariate autoregressive (MAR) modeling suggest that cladocerans increased strongly in response to temperature but not to algal biomass, and cladocerans depressed some algal resources without observable fertilization effects. Changes in Lake Baikal are particularly significant as an integrated signal of long-term regional warming, because this lake is expected to be among those most resistant to climate change due to its tremendous volume. These findings highlight the importance of accessible, long-term monitoring data for understanding ecosystem response to large-scale stressors such as climate change.

POTENTIAL EFFECTS OF CLIMATE CHANGE ON FRESHWATER ECOSYSTEMS OF THE NEW ENGLAND/MID‐ATLANTIC REGION

Numerous freshwater ecosystems, dense concentrations of humans along the eastern seaboard, extensive forests and a history of intensive land use distinguish the New England/Mid-Atlantic Region. Human population densities are forecast to increase in portions of the region at the same time that climate is expected to be changing. Consequently, the effects of humans and climatic change are likely to affect freshwater ecosystems within the region interactively. The general climate, at present, is humid continental, and the region receives abundant precipitation. Climatic projections for a 2 x CO1 atmosphere, however, suggest warmer and drier conditions for much of this region. Annual temperature increases ranging from 3-5°C are projected, with the greatest increases occurring in autumn or winter. According to a water balance mode!, the projected increase in temperature will result in greater rates of evaporation and evapotranspiration. This could cause a 21 and 31% reduction in annual stream flow in the southern and northern sections of the region, respectively, with greatest reductions occurring in autumn and winter. The amount and duration of snow cover is also projected to decrease across the region, and summer convective thunderstorms are likely to decrease in frequency but increase in intensity. The dual effects of climate change and direct anthropogenic stress will most likely alter hydrological and biogeochemica! processes, and, hence, the flora! and fauna! communities of the region’s freshwater ecosystems. For example, the projected increase in evapotranspiration and evaporation could eliminate most bog ecosystems, and increases in water temperature may increase bioaccumulation, and possibly biomagnification, of organic and inorganic contaminants. Not a!! change may be adverse. For example, a decrease in runoff may reduce the intensity of ongoing estuarine eutrophication, and acidification of aquatic habitats during the spring snowmelt period may be ameliorated. Recommendations for future monitoring efforts include: (1) extending and improving data on the distribution, abundance and effect of anthropogenic stressors (non-point pollution) within the region; and (2) improving scientific knowledge regarding the contemporary distribution and abundance of aquatic species. Research recommendations include: (1) establishing a research centre(s) where field studies designed to understand interactions between freshwater ecosystems and climate change can be conducted; (2) projecting the future distribution, activities and direct effects of humans within the region; (3) developing mathematical analyses, experimental designs and aquatic indicators that distinguish between climatic and anthropogenic effects on aquatic systems; (4) developing and refining projections of climate variability such that the magnitude, frequency and seasonal timing of extreme events can be forecast; and (5) describing quantitatively the flux of materials (sediments, nutrients, metals) from watersheds characterized by a mosaic of land uses. 0 1997 by John Wiley & Sons, Ltd.

Zooplankton body size and community structure: Effects of thermal and toxicant stress

Episodic heat waves and an increase in pesticide use are widely cited as consequences of climatic warming. Recent studies show that these stressors often cause declines in the mean body size of zooplankton. Results from laboratory and field studies, as well as observations from both thermal- or toxicant-stressed natural systems, show (1) reductions in mean body size within stressed populations, or (2) changes in community composition that favor small-bodied over large-bodied species. During the past decade, it has become widely accepted that a shift in zooplankton body size can dramatically affect water clarity, rates of nutrient regeneration and fish abundances. Thus, climatic warming and associated change in pesticide use has the potential to cause striking change in the structure and functioning of temperate-zone lakes.

Climate Change and the World's “Sacred Sea”—Lake Baikal, Siberia

Lake Baikal—the worlds largest, oldest, and most biotically diverse lake—is responding strongly to climate change, according to recent analyses of water temperature and ice cover. By the end of this century, the climate of the Baikal region will be warmer and wetter, particularly in winter. As the climate changes, ice cover and transparency, water temperature, wind dynamics and mixing, and nutrient levels are the key abiotic variables that will shift, thus eliciting many biotic responses. Among the abiotic variables, changes in ice cover will quite likely alter food-web structure and function most because of the diverse ways in which ice affects the lakes dominant primary producers (endemic diatoms), the top predator (the worlds only freshwater seal), and other abiotic variables. Melting permafrost will probably exacerbate the effects of additional anthropogenic stressors (industrial pollution and cultural eutrophication) and could greatly affect ecosystem functioning.

The Rise and Fall of Plankton: Long-Term Changes in the Vertical Distribution of Algae and Grazers in Lake Baikal, Siberia

Both surface water temperatures and the intensity of thermal stratification have increased recently in large lakes throughout the world. Such physical changes can be accompanied by shifts in plankton community structure, including changes in relative abundances and depth distributions. Here we analyzed 45 years of data from Lake Baikal, the worlds oldest, deepest, and most voluminous lake, to assess long-term trends in the depth distribution of pelagic phytoplankton and zooplankton. Surface water temperatures in Lake Baikal increased steadily between 1955 and 2000, resulting in a stronger thermal gradient within the top 50 m of the water column. In conjunction with these physical changes our analyses reveal significant shifts in the daytime depth distribution of important phytoplankton and zooplankton groups. The relatively heavy diatoms, which often rely on mixing to remain suspended in the photic zone, shifted downward in the water column by 1.90 m y-1, while the depths of other phytoplankton groups did not change significantly. Over the same time span the density-weighted average depth of most major zooplankton groups, including cladocerans, rotifers, and immature copepods, exhibited rapid shifts toward shallower positions (0.57–0.75 m y−1). As a result of these depth changes the vertical overlap between herbivorous copepods (Epischura baikalensis) and their algal food appears to have increased through time while that for cladocerans decreased. We hypothesize that warming surface waters and reduced mixing caused these ecological changes. Future studies should examine how changes in the vertical distribution of plankton might impact energy flow in this lake and others.

Potential Effects of Canada Geese and Climate Change on Phosphorus Inputs to Suburban Lakes of the Northeastern U.S.A.

ABSTRACT Inputs of total phosphorus (TP) to a small lake (0.4 km2) located in western suburban Boston were compared during a drought (fall 1995) and a normal rainfall period (fall 1994) to explore potential effects of Canada geese (Branta canadensis maxima) and climate change on phosphorus loading to suburban lakes of the Northeastern U.S.A. In fall 1994, the watershed supplied 18 times more TP than Canada geese, but during the fall drought of 1995, TP from Canada geese exceeded that from the watershed by more than 7 times. Differences in the relative importance of TP loading from Canada geese and the watershed were caused by variation in streamflow between years. Under conditions of climatic warming, annual streamflow in the Northeast (U.S.A.) is projected to decline by ~30% with greatest reductions (~60%) occurring in the fall. At this time of year, Canada geese are most abundant and are likely to become the major contributor of TP to urban lakes. Furthermore, annual absolute inputs of TP from geese to ...

Influence of Long-Distance Climate Teleconnection on Seasonality of Water Temperature in the World's Largest Lake - Lake Baikal, Siberia

Large-scale climate change is superimposed on interacting patterns of climate variability that fluctuate on numerous temporal and spatial scales—elements of which, such as seasonal timing, may have important impacts on local and regional ecosystem forcing. Lake Baikal in Siberia is not only the worlds largest and most biologically diverse lake, but it has exceptionally strong seasonal structure in ecosystem dynamics that may be dramatically affected by fluctuations in seasonal timing. We applied time-frequency analysis to a near-continuous, 58-year record of water temperature from Lake Baikal to examine how seasonality in the lake has fluctuated over the past half century and to infer underlying mechanisms. On decadal scales, the timing of seasonal onset strongly corresponds with deviation in the zonal wind intensity as described by length of day (LOD); on shorter scales, these temperature patterns shift in concert with the El Nino-Southern Oscillation (ENSO). Importantly, the connection between ENSO and Lake Baikal is gated by the cool and warm periods of the Pacific Decadal Oscillation (PDO). Large-scale climatic phenomena affecting Siberia are apparent in Lake Baikal surface water temperature data, dynamics resulting from jet stream and storm track variability in central Asia and across the Northern Hemisphere.

Long-Term and Ontogenetic Patterns of Heavy Metal Contamination in Lake Baikal Seals (Pusa sibirica)

Little is known about the history of heavy metal pollution of Russias Lake Baikal, one of the worlds largest lakes and a home to numerous endemic species, including the Baikal Seal, Pusa sibirica. We investigated the history of heavy metal (V, Cu, Zn, Cd, Hg, Tl, Pb, U) pollution in Lake Baikal seals over the past 8 decades. C and N stable isotope analysis (SIA) and laser-ablation ICP-MS of seal teeth were used to examine changes in feeding ecology, heavy metal levels associated with life history events and long-term variation in metal exposure. SIA did not suggest large changes in the feeding ecology of Baikal seals over the past 80 years. LA-ICP-MS analyses revealed element-specific ontogenetic variability in metal concentrations, likely related to maternal transfer, changes in food sources and starvation. Hg and Cd levels in seals varied significantly across the time series, with concentrations peaking in the 1960s - 1970s but then declining to contemporary levels similar to those observed in the 1930s and 1940s. Trends in atmospheric emissions of Hg suggest that local sources as well as emissions from eastern Russia and Europe may be important contributors of Hg to Lake Baikal and that, despite the size of Lake Baikal, its food web appears to respond rapidly to changing inputs of contaminants.

Past and present mercury accumulation in the Lake Baikal seal: Temporal trends, effects of life history, and toxicological implications

Despite global efforts to reduce anthropogenic mercury (Hg) emissions, the timescale and degree to which Hg concentrations in the environment and biota respond to decreased emissions remain challenging to assess or predict. In the present study we characterize long-term trends and life-history patterns in Hg accumulation and toxicological implications of Hg contamination for a freshwater seal from one of the worlds largest lakes (Lake Baikal, Siberia, Russia) using contemporary tissues and archival teeth. Stable isotope analysis and Hg analyses of soft tissues (muscle, liver, kidney, blood, brain, heart) and teeth from 22 contemporary seals revealed rapid changes in diet and Hg accumulation in the first year of life with a stable diet and increase in tissue Hg throughout the rest of life. Although maternal transfer of Hg was an important source of Hg to seal pups, reproduction and lactation by female seals did not appear to result in sex-related differences in Hg concentrations or age-related accumulation in adult seals. Based on Hg analysis of archival teeth (n = 114) and reconstructed values for soft tissues, we also assessed temporal trends in seal Hg between the years 1960 and 2013. Seal Hg concentrations in hard (teeth) and soft (e.g., muscle, liver) tissues were highest in the 1960s and 1970s, followed by a decrease. The decline in seal Hg concentrations in recent decades was most likely driven by a reduction in Hg inputs to the lake, suggesting that global and regional efforts to reduce Hg emissions have been successful at reducing ecosystem and human health risks posed by Hg in Lake Baikal. Environ Toxicol Chem 2018;37:1476-1486.

Stable isotope signatures and distribution of deepwater sponges in Lake Baikal

To better understand the species composition and nutrition of deepwater sponges in Lake Baikal, we determined the depth, habitat, and stable isotopic signatures for deepwater sponges. All sponge specimens except one were collected at depths below the photic zone and in a variety of benthic habitats including methane seeps and hydrothermal vents. The freshwater sponge species of Lake Baikal generally occurred in aggregations (fields, carpets, and belts), and mainly on hard substrates (different types of bedrock and argillite, and bitumen). New maximum depth records were established for three species. The deepwater sponges clustered into two groups, based on their isotopic values, with members of one group assimilating organic carbon from photosynthetic sources and exhibiting δ13C values (−32 to −26.9‰) similar to those reported previously for littoral sponges. Members of the second group, distinguished by highly depleted δ13C values (−65 to −37.3‰), participate in a chemosynthetic food web. δ15N values of the deepwater sponges ranged widely (2.1–16.7‰) suggesting that they assimilate nitrogen from environmental sources and possibly from their microbial symbionts. Conservation of deepwater sponge diversity is therefore, likely dependent on the diversity of resources found in different habitats.