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Local climatic drivers of change in phenology at a boreal-temperate ecotone in eastern North America
Abstract
Ecosystems in biogeographical transition zones, or ecotones, tend to be highly sensitive to climate and can provide early indications of future change. To evaluate recent climatic changes and their impacts in a boreal-temperate ecotone in eastern North America, we analyzed ice phenology records (1975–2007) for five lakes in the Adirondack Mountains of northern New York State. We observed rapidly decreasing trends of up to 21 days less ice cover, mostly due to later freeze-up and partially due to earlier break-up. To evaluate the local drivers of these lake ice changes, we modeled ice phenology based on local climate data, derived climatic predictors from the models, and evaluated trends in those predictors to determine which were responsible for observed changes in lake ice. November and December temperature and snow depth consistently predicted ice-in, and recent trends of warming and decreasing snow during these months were consistent with later ice formation. March and April temperature and snow depth consistently predicted ice-out, but the absence of trends in snow depth during these months, despite concurrent warming, resulted in much weaker trends for ice-out. Recent rates of warming in the Adirondacks are among the highest regionally, although with a different seasonality of changes (early winter > late winter) that is consistent with other lake ice records in the surrounding area. Projected future declines in snow cover could create positive feedbacks and accelerate current rates of ice loss due to warming. Climate sensitivity was greatest for the larger lakes in our study, including Wolf Lake, considered one of the most ecologically intact ‘wilderness lakes’ in eastern North America. Our study provides further evidence of climate sensitivity of the boreal-temperate ecotone of eastern North America and points to emergent conservation challenges posed by climate change in legally protected yet vulnerable landscapes like the Adirondack Park.
... Specific to climate and lake ice, Beier et al. (2012) had success using statistical models to predict the date of lake freeze up for five lakes in northern New York State. They used an information theoretic approach based on Akaike's Information Criterion and their results offer encouragement for the present manuscript. ...
... They used an information theoretic approach based on Akaike's Information Criterion and their results offer encouragement for the present manuscript. Along with Beier et al. (2012) and others, we hope to demonstrate that relatively simple statistical and machine learning approaches offer utility for understanding the dynamics of ice on lakes world-wide. ...
... Accepted Article fall than in spring. This trend in recent decades is consistent with neighboring lakes (Beier et al., 2012). ...
Ice records at Lake George, an oligotrophic and dimictic freshwater lake in upstate New York, USA reveal that it has failed to freeze over completely 13 times since 1990. This transition from annual to intermittent ice cover is analogous to many other dimictic freshwater lakes globally. Over sixty years of meteorological observations from a nearby airport are analyzed and a complicated picture emerges when considering the specific characteristics of each year. For example, Lake George froze over in 1983 and 2007 despite the air temperature having a net warming effect on the lake in the month prior to ice‐in. Simple machine learning classifiers are trained using local weather data to predict the presence of complete ice coverage on Lake George and are found to perform adequately compared to observations, with one configuration having an accuracy of 91%.Using downscaled data from a coupled‐climate model through to 2100, projections with the trained classifiers suggest complete ice coverage will be a phenomenon of the past by the mid‐to‐late 21st Century. Furthermore, by 2080‐2100 the mean air temperature is projected to warm up to +8.0 C under Representative Concentration Pathway 8.5. These projections will be of concern to the communities and policy makers of Lake George responsible for the management of the ecological and socio‐economic systems. This article is protected by copyright. All rights reserved.
... We specifically evaluate annual trends because these are most likely to reflect broad-scale environmental change [Hanson et al., 2006]. Lakes in the Adirondack region are subject to changes due to recovery from acid precipitation and climate warming [Monteith et al., 2007;Waller et al., 2012;Beier et al., 2012]. Therefore, long-term monitoring of lake chemistry in this region gives a unique opportunity to evaluate lake pCO 2 response to these changes. ...
... μatm over the 18 year record) that corresponded with a significant (Mann-Kendall test p < 0.01) increase in April water temperatures (+4.9°C over the course of the record). While ice cover records for this lake are unavailable, April is the typical month for ice off in Adirondack Lakes, and we hypothesize that there has been a major shift in ice dynamics such that at the beginning of the record the lake was ice covered in April but that this ceased toward the end of the record [Beier et al., 2012]. This type of shift in ice cover would decrease under ice CO 2 accumulation and can be substantial to the extent that it is reflected in annual trends [e.g., Finlay et al., 2015]. ...
... Changes in Adirondack Lake ice cover are not widespread, in part, because local snow conditions and lake morphometry influence how well ice off tracks rising spring air temperatures. This mechanism could only be identified for Sunday Pond because of the dramatic nature of the change [Stager et al., 2009;Beier et al., 2012]. This emphasizes the difficulty in discerning drivers from monitoring data when there are no dramatic or consistent changes. ...
Lakes are globally significant sources of CO2 to the atmosphere. However, there are few temporally resolved records of lake CO2 concentrations and long-term patterns are poorly characterized. We evaluated annual trends in the partial pressure of CO2 (pCO2) based on chemical measurements from 31 Adirondack lakes taken monthly over an 18-year period. All lakes were supersaturated with CO2 and were sources of CO2 to the atmosphere. There were significant pCO2 trends in 29% of lakes. The median magnitude of significant positive trends was 32.1 µatm y-1. Overall, 52% of lakes had pCO2 trends greater than those reported for the atmosphere and ocean. Significant trends in lake pCO2 were attributable to regional recovery from acid deposition and changing patterns of ice-cover. These results illustrate that lake pCO2 can respond rapidly to environmental change, but the lack of significant trend in 71% of lakes indicates substantial lake-to-lake variation in magnitude of response.
... The Adirondack Park is part of a UNESCO Biosphere Reserve, the site of numerous major winter sport competitions, the largest park in the contiguous United States (2.4 million ha), and a unique mosaic of human communities on a largely undeveloped wild landscape. Apart from lake ice records [11][12][13] and paleoecological investigations [14][15][16][17] little information is currently available regarding the effects of climate change on species and ecosystems in the Adirondacks [12,18,19]. Evidence from elsewhere in North America indicates that future warming is likely to cause spring phenology dates to advance earlier [6][7][8] and that differing responses among species to such warming could lead to "ecological mismatches" between, for example, flowering plants and the pollinators upon whom they depend [8,[20][21][22]. ...
... In contrast, the short-term (1990-2020) ice records of Mirror Lake and Lower Saint Regis Lake were less consistent with those from the AEC where five lakes froze significantly earlier in autumn and thawed earlier between 1975 and 2007 [13]. The variability among these sites is not simply the result of analyzing different time intervals because thaw dates from Mirror and Lower Saint Regis Lakes displayed no significant trends over the 1975-2007 time frame either, and Mirror Lake freeze dates displayed no trends over the 1975-2004 interval. ...
Long-term monitoring of the spring and autumn phenology of five animal species, four plant species, phytoplankton communities, lake temperatures and ice cover on the Paul Smith’s College Phenology Trail in the uplands of the Adirondack State Park (NY, USA) has produced time series spanning 1990–2020 for the biological and water temperature records and 1909–2020 for lake ice. In conjunction with climate records from three nearby weather stations these observations demonstrate that the ice on Lower Saint Regis Lake now thaws one week earlier, on average, than it did in 1909 while the region as a whole warmed by 1.7°C and received 19 cm more precipitation annually. Statistically significant warming trends between 1990 and 2020 were restricted to July and September and therefore contributed to a scarcity of temporal shifts in the spring phenologies of species and lake ice during that shorter time frame, but the lake surface warmed by 1.9°C on average in October. Although most of the phenological records displayed no statistically significant directional change within the 1990–2020 time interval they revealed strong correlations between phenology and monthly air temperatures that are of predictive value. Together with projections from regionally down-scaled climate models these relationships suggest that the phenologies of the species and ice dynamics in question could shift by ca. 1–3 weeks by 2100 depending on the analytical approach used and the magnitude of fossil fuel emissions during this century. As Adirondack winters become shorter and milder before potentially losing snow and ice altogether over the longer term, the unique cultural ecology of the region’s human residents will face profound existential challenges along with the ecosystems and species around them.
... Peatlands and surrounding vegetation in this region have robust legal protections from land-use changes within the spatially extensive Adirondack Park (24,280 km 2 , with ca. half of this area considered a strict Forest Preserve of New York State), but they are exposed to both changing climate (Beier et al. 2012) and the highest atmospheric deposition rates of nitrogen in the northeastern United States (Driscoll et al. 2003). Our study had the following three objectives: (1) to develop a framework for using vascular plant community types for monitoring tree encroachment into large peatland complexes; (2) to quantify patterns in tree encroachment across one of the largest peatland complexes in New York State using tree demography; and (3) to discuss the applicability and potential of plant community classifications broadly used in the northeastern United States and eastern Canada for monitoring threats to biodiversity conservation by tree encroachment in BTE peatlands. ...
... While long-term monitoring is necessary to verify these 'early warning signs' of potential larger ecosystem changes due to tree encroachment into peatlands, tree demographic patterns (cf., age class distributions, seedling recruitment patterns) can be instrumental in prioritizing and planning future monitoring and potential conservation strategies. Such monitoring is urgently needed given the magnitude of the tree Fig. 7 Review of the distributions of peatland vegetation types at Shingle Shanty peatland complex and in the U.S. states and Canadian provinces in northeastern North America relative to substrate pH (New York-Edinger et al. 2014;Vermont-Thompson and Sorenson 2000;New Hampshire-NHDFL 2015, Sperduto and Kimball 2011, Maine-MNAP 2015, Labrador-Foster and Glaser 1986, Quebec-Andersen et al. 2011 (Lachance and Lavoie 2005;Pasquet et al. 2015) and given the significance of peatlands in biodiversity conservation within the BTE where changes in climate (e.g., Beier et al. 2012) and atmospheric deposition (Driscoll et al. 2003) are likely to exacerbate ongoing biodiversity losses (e.g., Kapfer et al. 2011;Evans and Brown 2017;Glennon et al. 2019). ...
Large peatland complexes at the boreal-temperate ecotone are essential habitats for boreal species at their southern range limits where they are threatened by tree encroachment accelerated by climate change and nitrogen deposition. To inform vascular plant and biodiversity conservation, we studied tree encroachment patterns in a large (> 400 ha) boreal peatland complex in the northeastern United States across vegetation types and environmental gradients. We characterized vascular plant composition, environmental drivers and tree demography on 50 plots (each 25 m2). We used non-metric multidimensional scaling (NMS) to identify two main drivers of vascular plant composition in the herbaceous layer—pH and tree canopy openness—that described three broad plant community types (open bog, forested bog, and fen). Tree demography suggested that woody encroachment (i.e., tree seedling recruitment) varied across these community types; open bog was colonized by Picea mariana seedlings, while forested bog and fen (dominated by evergreen conifers, Picea mariana and Thuja occidentalis, respectively) were colonized by deciduous tree species (Acer rubrum and Betula alleghaniensis). Our findings provide early warning signs of vegetation change in boreal peatlands near their southern range limits caused by the encroachment of temperate tree species into forested peatlands and expanding tree cover in open bogs.
... Mean annual temperatures in the Adirondack uplands since 1990 averaged 5.5 C and mean annual precipitation was approximately 1 m/yr (USHCN 2017). In addition to rising temperatures and decreasing ice cover (Beier et al. 2012), regional precipitation, lake levels, and river discharge have increased since the 1960s (Stager et al. 2009). As a result, a small island that was present in Bear Pond during the late 19 th century (Wallace 1880) and a large boulder near the northern shore ("swimming rock"), both observed by DFC and JCS during the 1970s and 1980s, have been submerged for the last decade or more. ...
... The increase of chrysophytes, in turn, could reflect greater bioavailability of carbon as DOC concentrations rose (Wolfe and Siver 2013). Higher epilimnetic temperatures associated with regional warming and enhanced light absorption by DOC or plankton (Fig. 7) (Beier et al. 2012, Solomon et al. 2015 would strengthen or prolong thermal stratification, which can further stimulate phytoplankton growth through internal loading of nutrients from bottom sediments under low-oxygen Figure 6. Percentages of A. ralfsii in core 17A plotted with total energy generation from wood, coal, petroleum, and natural gas in the United States (USEIA 2019) since the early 19 th century. ...
Stager JC, Wiltse B, Cumming BF, Holsen TM, Stetler J, Laxson C, Marcillo CE, Charles DF. 2019. A novel ecological state at Bear Pond (Adirondack Mountains, NY, USA) following acidification and partial recovery. Lake Reserv Manage. XX:XX–XX.
The pH of precipitation in the northeastern United States has risen as industrial sulfur and nitrogen oxide emissions have declined following amendment of the Clean Air Act in 1990, but the effects of this change on the region's lakes are not yet fully documented. Here we use the siliceous remains of diatoms and chrysophyte algae in a sediment core from Bear Pond (Adirondack State Park, NY), which acidified during the 20th century, to reconstruct pH variability during the last 2 centuries, evaluate the extent to which the lake has recovered from acidification, and determine the timing of that reversal to help identify its causes. Inferred pH declined erratically from a high of 6.4 during the 1860s to 5.7–5.9 during the 1930s, then decreased to the 4.9–5.4 range by 1995–2010. After 2010, inferred pH rose and remained within the 5.4–5.6 range following an abrupt rise in the pH of regional precipitation. Although the acidification trend at Bear Pond has now reversed, the lake ecosystem has not returned to its pre-impact condition. Distinctive members of the pre-acidification diatom community are still absent, chrysophytes have become unusually abundant, and water clarity (Secchi depth) has decreased by about half. Furthermore, the original fish community was lost due to stocking and piscicide treatment in 1958, and high concentrations of toxaphene residues from the piscicide are present in the sediments. Full ecological restoration of formerly acidic lakes such as Bear Pond may be unlikely due to complicating factors such as climate change and fisheries management practices.
... The key question however is how would subjecting soils to manipulated reduction and increase in ambient rainfall affect various properties? Experiments aimed at modeling soil eco-hydrological components across ecosystems have manipulated rainfall amount and tested its effect on soil properties (Knapp et al. 2008;Miranda et al. 2011;Beier et al. 2012). The African Savanna, particularly East and Central parts, have not been well represented, given that most experiments have focused South (February et al. 2013;Koerner and Collins 2014) and tested the effect of rainfall manipulation on plant community composition. ...
... Previous studies in various ecosystems (Emmett et al. 2004;English et al. 2005;Huxman et al. 2005;Miranda et al. 2011;Beier et al. 2012) on manipulated rainfall amount (35 to 152% of ambient) effect on soil moisture and other properties revealed much sensitivity towards drought compared to increased rainfall. Such responses could be attributed to variation in the sensible and latent heat fluxes (Bowen ratio) during drought and extremely wet season. ...
Purpose
The effect of uncontrolled grazing and unpredictable rainfall pattern on future changes in soil properties and processes of savanna ecosystems is poorly understood. This study investigated how rainfall amount at a gradient of 50%, 100%, and 150% would influence soil bulk density (ρ), volumetric water content (θv), carbon (C), and nitrogen (N) contents in grazed (G) and ungrazed (U) areas.
Materials and methods
Rainfall was manipulated by 50% reduction (simulating drought—50%) and 50% increase (simulating abundance—150%) from the ambient (100%) in both G and U areas. Plots were named by combining the first letter of the area followed by rainfall amount, i.e., G150%. Samples for soil ρ, C, and N analysis were extracted using soil corer (8 cm diameter and 10 cm height). Real-time θv was measured using 5TE soil probes (20 cm depth). The EA2400CHNS/O and EA2410 analyzers were used to estimate soil C and N contents respectively.
Results and discussion
The interaction between grazing and rainfall manipulation increased θv and C but decreased N with no effect on ρ and C:N ratio. Rainfall reduction (50%) strongly affected most soil properties compared to an increase (150%). The highest (1.241 ± 0.10 g cm⁻³) and lowest (1.099 ± 0.05 g cm⁻³) ρ were in the G50% and U150% plots respectively. Soil θv decreased by 34.0% (grazed) and 25.8% (ungrazed) due to drought after rainfall cessation. Soil ρ increased with grazing due to trampling effect, therefore reducing infiltration of rainwater and soil moisture availability. Consequently, soil C content (11.45%) and C:N ratio (24.68%) decreased, whereas N increased (7.8%) in the grazed plots due to reduced C input and decomposition rate.
Conclusions
The combined effect of grazing and rainfall variability will likely increase soil θv, thereby enhancing C and N input. Grazing during drought will induce water stress that will destabilize soil C and N contents therefore affecting other soil properties. Such changes are important in predicting the response of soil properties to extreme rainfall pattern and uncontrolled livestock grazing that currently characterize most savanna ecosystems.
... The forests in the Adirondacks Region of New York are a complex mixture of hardwood and softwood species that have a long and varied history of natural disturbance occurrences (Lorimer and White 2003) and human management (McMartin 1994). The region is considered an ecotone at the southernmost end of the eastern forest-boreal ecoregion with over 25 different tree species present and is particularly sensitive to variation in local climate (Beier et al. 2012). Due to variation in elevation and geology, a variety of forest communities occur in this region ranging from high alpine to northern hardwood (Leopold et al. 1988). ...
... Historically, research in the region was concentrated on spruce-fir (Picea -Abies) with increasing attention on northern hardwoods (Berven et al. 2013). The forest currently faces a number of issues including climate change (Beier et al. 2012), beech bark disease (McGee 2000), high fern cover (Engelman and Nyland 2006), and atmospheric deposition (Chen et al. 2004), which are all likely to affect future stand dynamics and management options. Consequently, there is a strong need to understand and project the potential influence of alternative forest management strategies. ...
Background
Growth and yield models are important tools for forest planning. Due to its geographic location, topology, and history of management, the forests of the Adirondacks Region of New York are unique and complex. However, only a relatively limited number of growth and yield models have been developed and/or can be reasonably extended to this region currently. Methods
In this analysis, 571 long–term continuous forest inventory plots with a total of 10 – 52 years of measurement data from four experimental forests maintained by the State University of New York College of Environmental Science and Forestry and one nonindustrial private forest were used to develop an individual tree growth model for the primary hardwood and softwood species in the region. Species–specific annualized static and dynamic equations were developed using the available data and the system was evaluated for long–term behavior. ResultsEquivalence tests indicated that the Northeast Variant of the Forest Vegetation Simulator (FVS–NE) was biased in its estimation of tree total and bole height, diameter and height increment, and mortality for most species examined. In contrast, the developed static and annualized dynamic, species–specific equations performed quite well given the underlying variability in the data. Long–term model projections were consistent with the data and suggest a relatively robust system for prediction. Conclusions
Overall, the developed growth model showed reasonable behavior and is a significant improvement over existing models for the region. The model also highlighted the complexities of forest dynamics in the region and should help improve forest planning efforts there.
... Phenology, #8: The objective is to document changes and trends in timing of natural events. The following variables have been recorded since at least 1939: Lake ice in -ice out dates with the earliest record from 1874 (Beier et al. 2012); ice thickness; high water date on Rich Lake; first leaf, lilac; blossoming of Trillium and other spring ephemeral species, witch hobble (Viburnum lantanoides), and serviceberry (Amelanchier spp.); full leaf-out of sugar maple (Acer saccharum) and American beech (Fagus grandifolia); first spring peepers (Pseudacris crucifer) and wood frogs (Lithobates sylvaticus) heard calling; first and last known date of presence of migratory bird species, especially American Robins (Turdus migratorius), Loons, Tree Swallows (Tachycineta bicolor) and Hooded Mergansers (Lophodytes cucullatus); sightings of rare or unusual animals such as accidentals from other parts of the globe; winter severity (number of days with >15 inches snow on ground; number days with minimum temp < 0 o F); notable weather events such as late spring snow, hail, damaging wind, ice, flooding etc.; frost occurrence between 15 May and 30 August, and estimated severity/plant damage; quantitative seed crop rating for masting and fruiting species (on a subjective scale of zero, poor, fair, good and excellent seed production; qualitative data are in ALTEMP #26); planted hybrid chestnut tree growth; and other variables as appropriate. Lake ice data are here: https://portal.edirepository.org/nis/mapbrowse?packageid=edi231.1 ...
The Adirondack Ecological Center (AEC) at ESF’s Newcomb Campus has one of the oldest and broadest records of scientific field research in North America. Located on the Anna and Archer Huntington Wildlife Forest, AEC is a biological field station and multi-disciplinary platform for research, education and outreach where the most pressing environmental challenges facing our society can be directly examined and understood. The Newcomb Campus (www.esf.edu/newcomb) includes the AEC, Northern Forest Institute, public Adirondack Interpretive Center and Forest Operations Adirondack Properties unit. The campus’ professional staff and scientists collectively maintain extensive data archives from a century of observation. This paper provides a “road map” for researchers, students, historians and others on what resources exist and how to access them
... However, local variation in the rate of long-term advancement of ice-out has been studied surprisingly little. For example, Beier et al. (2012) analyzed the timing of ice-out for five montane lakes in the Adirondack Mountains in the northeastern United States, at a local scale (maximum distance between any two lakes about 9 km) over a period of 33 years . These authors were primarily interested in common local climate drivers of the timing of ice-out, not in lake-specific characteristics per se; however, they reported that none of the five lakes showed a significant trend of earlier ice-out. ...
Timing of ice-out is important to fundamental hydrological and ecological processes in freshwater ecosystems at high northern latitudes. While earlier ice-out in lakes during the last century is a well-documented phenomenon across the Northern Hemisphere, local variation in the rate of advancement of ice-out has received little attention. Here, records of ice-out date in 1991–2020 from 37 small lakes in a boreal catchment area in southeastern Finland were used to study variation in the timing of ice-out and its advancement. In addition, data of settling phenology of migratory common goldeneyes (Bucephala clangula) at the study lakes were used to examine how between-year and within-season variation in the timing of ice-out affects lake settlement of the species. Overall, ice-out date (IOD, the timing of ice break-up in the spring) advanced 9.8 days during the 30-year study period, April temperature being more important than winter temperature (severity) in determining the IOD. Rate of the advancement of IOD in individual lakes varied from 1.5 to 16.1 days, having advanced more in relatively larger lakes. Lakes at higher elevations had later mean IOD than lakes at lower elevations. Within-season differences among the lakes in IOD increased from 1991 to 2020, this variation being mainly driven by temperature during the ice melting period. Lakes with late mean IOD were settled later in a season by breeding common goldeneyes than lakes with early IOD. The faster the ice melting progressed within a season, the faster common goldeneyes settled the breeding lakes. The results demonstrate how global warming differently affects IOD in boreal lakes even within the same catchment area. More research in the landscape context is needed to enhance our understanding of changes in IOD in boreal lakes and how differently advancing IOD affects local dynamics of species dependent on open water.
... Ecological change has been occurring in the mountains of northeastern North America since the glaciers receded more than 15,000 years ago (Martin and Germain 2016), yet the rate of change appears to be increasing in recent decades. Recent studies in the sensitive alpine and forested mountainous environments of the Northeast, for example, have documented changes in treeline (Beal 2009), phenology (Beier et al. 2012, McDonough MacKenzie 2017, plant species diversity (Maddalena-Lucey 2019), vegetation cover (Robinson et al. 2010), tree growth (Foster andD'Amato 2015, Wason et al. 2019), and breeding birds (DeLuca and King 2017). While difficult to assign a cause to these recent, more-rapid ecological changes, human-induced effects such as climate change, atmospheric deposition, and recreational activity are often at the top of the list (Malanson et al. 2019, Monz et al. 2010. ...
... The Adirondack ecoregion is composed of deciduous, coniferous, and mixed forests. The region is considered a transitional boreal-temperate ecotone (Beier et al. 2012). Our study area consisted of northern hardwoods (41%), mixed hardwood conifer (56%), and conifer stands (3%). ...
There has been limited research investigating summer habitat use of bats in managed forests in the northeastern United States. Consequently, there is limited knowledge to inform forest managers seeking to maintain or enhance bat habitat, particularly for several federally threatened, endangered, or candidate species. In summer 2017–2018, we conducted repeated acoustic surveys to determine what forest characteristics are associated with bat habitat use in managed forests in the Adirondack region of upstate New York. We modeled detection corrected probability of occupancy for bats in three phonic groups: high, mid, and low frequency. Across all phonic groups, probability of occupancy increased with decreasing canopy cover. High-, mid-, and low-frequency bats were more likely to use recently harvested sites (<10 years since harvest). High-frequency bats also used mature stands. Midfrequency bats demonstrated a preference for further distances from forest roads, whereas low-frequency bats preferred areas with a higher percentage of clutter. Our results suggest that tending and regenerating even-aged forest management practices can provide habitat for foraging bats in the Adirondacks.
... The permanently increasing concentration of carbon dioxide in the atmosphere, increase and contrasting oscillations of air temperature, variation of global atmospheric circulation and rainfall regimes (specific for different geographic zones), and increasing anthropogenic impact that also affect the ecological state of fresh-water objects. In our opinion, lake ecosystems, in which the natural purification is slow as compared to the atmosphere and rivers, are most afflicted (Beier et al., 2012;Kelly et al., 2001;Lapierre et al., 2013;Seekell et al., 2014). ...
We report long-term comprehensive measurements of CO2 in the atmosphere, surface water and the major nutrients obtained for the period 2004–2018. The research was conducted at the Baikal Atmospheric and Limnological Observatory (BALO), which is located in the coastal zone of South Baikal (coordinates 51° 54′ N, 105° 05′ E). The seasonal variation of these characteristics was analyzed. For our site, during the open water period (May-December) we assessed average flux of CO2, which amounted to −155 mmol m⁻² y⁻¹ (sink from the atmosphere to the water surface). Carbon dioxide content in the near-water air of Lake Baikal rises with a rate of 2.46 ppm per year, which is in good agreement with the global trend. The common effect of many factors (often multi-directional), such as variability of weather conditions, hydrological processes and productivity cycles of aquatic plankton in the Baikal waters, cause strong variations in the water characteristics, which we observed in different seasons and years. Under these conditions of strong inter-annual and seasonal variability of all characteristics, trend calculations using our long-term observations did not allow us to reveal reliable tendencies of changes in surface water CO2 concentrations.
... However, in spite of the known importance of landscape position in regulating GHG emissions from forest soils, capturing the variability of gas fluxes at the soil-atmosphere interface at the watershed scale still remains a challenge due to the known variability in biogeochemical activity occurring throughout the landscape [11]. Therefore, further characterizing the relationship(s) between GHG fluxes across time, space, and landscape characteristics in northern forested watersheds is important to provide a more comprehensive understanding of the dynamics of these gas fluxes at the watershed scale [21]. ...
... Ice-out timing also has stronger direct connection to climate change than ice-on because individual lake properties influence the freezing process more strongly than the thawing process (Spoka et al. 2006;Adrian et al. 2009). The timing of ice-out has advanced substantially, occurring up to 21 days earlier over the past 40 to 100 years at midlatitudes (Weyhenmeyer et al. 2005;Jensen et al. 2007;Beier et al. 2012;Benson et al. 2012) and up to 13 days earlier since 2000 in the Arctic (Smejkalova et al. 2016). ...
In boreal regions, increased precipitation events have been linked to increased concentrations of dissolved organic carbon (DOC), however less is known about the extent and implications of these events on lakes. We assessed the effects of precipitation events on six drinking water lakes in Maine, USA to better understand how DOC concentration and quality change in response to precipitation events. Our results revealed three types of responses: (1) an initial spike in DOC concentrations and quality metrics; (2) a sustained increase in DOC concentrations and quality metrics and; (3) no change during all sampling periods. Lake residence time was a key driver of changes in DOC concentration and quality. For the same set of drinking water lakes, we investigated a link between changes in DOC to a household’s willingness to pay (WTP). Our results revealed that percent change in DOC and SUVA254 correspond to initial Secchi depth values. This relationship was used to determine that WTP from improvement in water quality was highest in lakes with shallower Secchi depths and lowest in lakes with deeper Secchi depths. WTP estimates were also correlated with maximum depth, residence time, and percent of wetland coverage. A set of six lakes in Acadia National Park, Maine were evaluated to assess differences in seasonal storm response. Our results revealed differences in the response of DOC quality metrics to an early summer versus an autumn storm. The response of DOC quality metrics to storms was mediated by differing lake and watershed characteristics as well as seasonal changes in climate such as solar radiation and antecedent weather conditions in the early summer versus autumn. Investigation of the effects of ice-out timing on physical, biological, and biogeochemical lake characteristics in Arctic and boreal regions during an early and late ice-out regime revealed differences in mixing depths and strength and stability of stratification. Key drivers of observed responses included a combination of climate factors, including solar insolation, air temperature, precipitation, and, in the Arctic, permafrost thaw. This research provides important insights that will be useful for management of water resources as temperature and precipitation patterns continue to change.
... Ice-out timing also has stronger direct connection to climate change than ice-on because individual lake properties influence the freezing process more strongly than the thawing process [6,7]. The timing of ice-out has advanced substantially, occurring up to 21 days earlier over the past 40 to 100 years at mid-latitudes [8][9][10][11] and up to 13 days earlier since 2000 in the Arctic [12]. ...
The timing of lake ice-out has advanced substantially in many regions of the Northern Hemisphere, however the effects of ice-out timing on lake properties and how they vary regionally remain unclear. Using data from two inter-annual monitoring datasets for a set of three Arctic lakes and one boreal lake, we compared physical, chemical and phytoplankton metrics from two years in which ice-out timing differed by at least three weeks. Our results revealed regional differences in lake responses during early compared to late ice-out years. With earlier ice-out, Arctic lakes had deeper mixing depths and the boreal lake had a shallower mixing depth, suggesting differing patterns in the influence of the timing of ice-out on the length of spring turnover. Differences in nutrient concentrations and dissolved organic carbon between regions and ice-out years were likely driven by changes in precipitation and permafrost thaw. Algal biomass was similar across ice-out years, while cell densities of key Cyclotella sensu lato taxa were strongly linked to thermal structure changes in the Arctic lakes. Our research provides evidence that Arctic and boreal regions differ in lake response in early and late ice-out years, however ultimately a combination of important climate factors such as solar insolation, air temperature, precipitation, and, in the Arctic, permafrost thaw, are key drivers of the observed responses.
... Total annual precipitation averaged 1088.3 mm and winter precipitation typically occurred as snow (Daly et al., 2008). Recent decades have experienced seasonally variable warming, increased total precipitation, and extended growing season length (Hayhoe et al., 2007;DeGaetano, 2009;Beier et al., 2012;Seager et al., 2012;Pederson et al., 2013). These factors make the northeastern US (and central New York) well suited for evaluating changes in tree-growth patterns under variable and changing climate while providing an opportunity to examine the effects of hydrological setting on tree-growth for cooccurring boreal and temperate species. ...
We evaluated the effects of hydrologic setting on the growth sensitivity of two conifer species to recent atmospheric climatic variability and change in a region experiencing a warming (annual Tmin: 0.07 °C/ decade) and wetting trend (total annual PPT 9.8 mm/decade; 1911–2012). Tree-ring chronologies were constructed for the boreal disjunct balsam fir (Abies balsamea; n = 72; 1916–2012) and range-centered eastern white pine (Pinus strobus; n = 84; 1707–2012) at three forested, groundwater-fed wetlands (fens) and their neighboring uplands in New York State, USA. Soil temperature monitoring in 2010 confirmed that upland soils were significantly warmer than fen soils during the spring and summer months (11.5–13.9 °C; p < 0.05). Climate-growth relationships for Abies balsamea varied substantially based on hydrologic setting and season. Compared with a remnant upland population that showed an increasingly negative sensitivity to warm summer temperatures over time A. balsamea positioned in fens were less sensitive to recent warming. While atmospheric climate-growth relationships were more consistent across hydrologic settings for Pinus strobus, we still observed qualitatively different responses to atmospheric climate variables between fen and upland populations. Overall, the climate-growth relationships identified in this study suggest that relative to trees growing in mesic upland soils, growth sensitivity to warm ambient climate in summer is ameliorated by groundwater inputs. The climate modulating effects of groundwater on tree-growth observed in our study suggests that for temperate and boreal regions where fens are abundant further consideration of groundwater influences on climate-growth relationships is warranted.
... Colonial chrysophytes, represented primarily by the genus Synura, have become more common at Wolf Lake relative to solitary Mallomonas since the 1970s, while the duration of ice cover decreased by 3 weeks (Beier et al., 2012). This pattern resembles changes that have been reported in other north temperate lakes (Arseneau, 2014). ...
A high-resolution diatom record from Wolf Lake, a minimally disturbed ‘heritage’ lake, provides insights into the hydroclimatic history of the Adirondack Mountains of northern New York during the last c. 1600 years. Three pronounced dry periods occurred during c. AD 490–610, 780–870, and 1010–1080, and low precipitation generally prevailed during the warm Medieval Climate Anomaly (c. AD 950–1350), a finding that fills an important gap in knowledge of the spatial extent of droughts across North America during that period. During the cooler ‘Little Ice Age’ interval (c. AD 1350–1800), inferred water balance was generally more positive. Seven peaks in charcoal abundance represent fire events during both wet and dry periods. Unusually high charcoal and inorganic sediment deposition c. AD 1700 could reflect human activity in the watershed, as might an abrupt rise in the relative abundances of planktonic and tychoplanktonic diatoms in Wolf Lake during the AD 1860s. The diatom record displays periodicities of c. 256 and 512 years in addition to high-frequency fluctuations, suggesting that significant precipitation variability is likely to continue to disrupt climatic trends in this region.
... This brought major consequences for climate, ecosystems and human well-being. From an ecological perspective, the margins of the plateau in transitional areas often react more quickly and strongly to climate effects (Neilson 1993;Kupfer & Cairns 1996;Beckage et al. 2008;Beier et al. 2012). According to glacier observation data, the magnitude of glacier retreated on the Tibetan Plateau increased from the inland to the margins, reaching a maximum on the southeast plateau (Yao et al. 2004). ...
The Shangri-La County and its surrounding areas lie within the Hengduan Mountains system at the southwestern margin of the Tibetan Plateau, and belong to the core zone of Three Parallel Rivers of Yunnan Protected Areas. There are numerous snow mountains of special ecological and cultural significance. The investigation of snow cover dynamics is important for understanding how snow cover responds in the context of climate change. In this study, the spatial and temporal dynamics of snow cover in the entire area were analysed using 28-scene Landsat images from 1974–2012. Snow cover variability of different altitudinal zones and orientations was also discussed. Then, we explored the relationship between snow cover dynamics and both climate change and local tourism activities. The results show that snow cover area in the Shangri-La region continued a clear decreasing trend in the last 40 years, declining from 4188 km2 in 1974 to 901 km2 in 2012. The decrease of snow cover generally occurred from low to high altitude and was most pronounced at altitudes of 4000–5000 metres, with a reduction of 2800 km2 since 1974. Snow cover decreased more significantly in the northwest part of the area than in the southeast. The primary driving force for this decrease was attributed to the increase in air temperature (+0.22°C per decade in the area). Compared with a similar decreasing trend in the Meili Snow Mountains, a dramatic reduction of snow cover in the southeastern Yulong Snow Mountains is attributed partially to local tourism activities.
... Sediment heat flux during Winter 1 is important in small, shallow lakes (less than two meters; Kletetschka et al. 2013), but thought to be diminished in larger, deeper lakes (Farmer 1975;Kirillin et al. 2012). While previous studies have documented how weather conditions influence ice cover (Beier et al. 2012), less work has been conducted to determine how weather influences under-ice lake thermal stratification, especially the onset and length of Winter 1 and Winter 2 phases. ...
We measured under-ice thermal stratification from before ice-on through after ice-off in Lake Sunapee, New Hampshire, a large, deep, north temperate lake, using a high-frequency monitoring buoy in the winter season of 2007–2008 to quantify how lake thermal stratification varies throughout the under-ice season. We examined potential drivers of variation in under-ice stability, identified diel-scale patterns in under-ice stratification, and used this dataset to test the hypothesis that there are two distinct under-ice phases driven by heat flux from the sediment followed by increased solar radiation as winter progresses. High-frequency measurements demonstrated that only a small fraction of the under-ice period exhibited the traditional inverse stratification previously thought to prevail, based on temporally discrete under-ice temperature profiles. Local short-term weather conditions altered under-ice conditions throughout the ice season with brief periods of snow melt, resulting in several days of disrupted thermal stratification. Our data indicate that thermal structure under the ice in Lake Sunapee is dynamic, and in contrast to smaller, shallower lakes, may be categorized in three, not two, distinct phases. As the under-ice season continues to become shorter due to climate change, under-ice thermal stratification in lakes will likely decrease further.
... The same phenomenon has also been shown by Hodgins et al. [2002] in New England, USA, where the temperature increase of 1.5°C during the last 150 years has shifted the ice breakup to occur 16 days earlier in the south, whereas only 9 days earlier in the north. This is further supported by Beier et al. [2012], who have documented a rapidly decreasing trend of up to 21 days less ice cover between 1975 and 2007 in five lakes located in the Adirondack Mountains, northern New York state, USA, close to the southern New England lakes. As the length of ice cover determines the timing and nature of many physical, chemical, and biological processes, the shift in timing of the ice breakup of lakes located along a latitudinal temperature gradient may change the diversity of lake types in many areas in the future [Weyhenmeyer et al., 2004]. ...
A new quantitative diatom-based lake ice-cover inference model was developed to reconstruct past ice-cover histories and applied to four subarctic lakes. The used ice-cover model is based on a calculated melting degree-day value of +130 and a freezing degree-day value of -30 for each lake. The reconstructed Holocene ice-cover duration histories show similar trends to the independently reconstructed regional air temperature history. The ice-cover duration was around seven days shorter than the average ice-cover duration during the warmer Early-Holocene (ca. 10 to 6.5 cal kyr BP) and around 3-5 days longer during the cool Little Ice Age (ca. 500 to 100 cal yr BP). Although the recent climate warming is represented by only 2-3 samples in the sediment series, these show a rising trend in prolonged ice free periods of up to two days. Diatom-based ice-cover inference models can provide a powerful tool to reconstruct past ice-cover histories in remote and sensitive areas where no measured data are available.
... The Adirondacks could face a 3 to 6 C increase in temperature over the next 50-100 years, and possibly a 20% increase in overall annual precipitation (Frumhoff et al., 2007). Beier et al. (2012) observed decreasing periods of lake ice cover in the Adirondacks as evidence of climate change. Climate change is occurring over the entire northeast United States including the Adirondacks (Huntington et al., 2009) with important linkages to forest watershed hydrology and biogeochemistry (Campbell et al., 2009. ...
Atmospheric sulfur (S) emissions peaked in North America in the early 1970s followed by declines in S deposition and sulfate (SO42-) concentrations in surface waters. Changes in S biogeochemistry affect the mobilization of toxic (Al+3, H+) and nutrient (Ca2+, Mg2+, K+) cations, and the acid-base status of ecosystems. We focused on lake/watersheds in the Adirondack Mountains of New York, USA, one of the most acid-sensitive and acid-impacted regions in North America. We used 16 of the 17 original Adirondack Long-Term Monitoring Lakes from 1984 through 2010 and found significant declines (-2.14 μmolc l-1year-1) in SO42- concentrations. There were significant declines (-0.28kgS ha-1year-1) in total S deposition for all lake/watersheds. We constructed S mass balances for 14 lakes/watersheds from wet and dry S deposition and SO42- loss from drainage and found a comparable decline (-0.26kgS ha-1year-1) in lake SO42- export. There was a discrepancy (mean 2.34kgS ha-1year-1) between atmospheric S deposition and watershed S loss due to internal S sources. Using major solute chemistry including dissolved silica and watershed characteristics, it was evident that the watershed S budget discrepancy increased with thickness of surficial deposits. The annual discrepancies in S mass balances were strongly linked with annual watershed discharge. These results suggest that internal S sources are becoming increasingly important as atmospheric S inputs have declined. The internal SO42- supply of watersheds decreased concomitantly with lake acid neutralizing capacity (ANC). These findings suggest that the limited contributions from internal sources of SO42- will facilitate the recovery of ANC from those lake/watersheds with the lowest ANC. With long-term decreases in atmospheric S deposition, the effects of climate, especially increases in precipitation, will play an increasingly important role in regulating S budgets and the amount of SO42- mobilized from internal watershed sources.
Located in the Adirondack Mountains of northern New York State, Huntington Wildlife Forest (HWF) is a 6000‐ha research and education facility operated by SUNY ESF (State University of New York, College of Environmental Science and Forestry) with continuous long‐term monitoring programs spanning over six decades. One of the ‘cradles’ of acid rain research in North America, HWF was in the first cohort of National Atmospheric Deposition Program (NADP) sites beginning in 1978. HWF is currently the only location (NY‐20) in New York with the full suite of NADP programs in operation, including atmospheric mercury speciation (AMNet), along with EPA CASTNET. Nearby to NY‐20 at HWF, Arbutus Lake and its forested watershed have been the focus of intensive long‐term monitoring (LTM) since installation of v‐notch weirs at the lake outlet and inlet in 1991 and 1994, respectively. Discharge at these locations has been monitored continuously at 15‐minute intervals since 1999. Lake outlet water chemistry samples were collected starting in 1983. Weekly sampling of water chemistry at both weirs began in 1995 and was expanded to include two headwater streams and groundwater wells in 2007. More recently, LTM programs at HWF have been augmented by participation in the PhenoCam Network since 2008, collection of high‐resolution LiDAR in 2009, and installation of a precision NY Mesonet weather station in 2016. In 2018, we installed sensor networks that continuously monitor soil microclimate and snow depth. Lastly, we improved data access via a new website (www.adk‐ltm.org) where users can create custom queries and visualize outputs. This article is protected by copyright. All rights reserved.
Lake surveys conducted in 1987–88 and 2018–19 show changes in the chemical and optical properties of Adirondack lakes recovering from acidification. Among chronically acidified lakes (1980s pH < 5.5, ANC < 0 µeq L−1), increases in pH and reductions in monomeric Al were accompanied by significant increases in light attenuation, DOC, and CDOM. DOC-specific dissolved color (CDOM:DOC) doubled over the 30-year span, and is the likely factor accounting for loss of water clarity in Adirondack lakes during recovery from acidification. Monitoring data (1994–2002) from a subset of these lakes show that reductions in light attenuation were accompanied by stronger thermal stratification and greater hypolimnetic oxygen depletion. Lakes most affected by acidification experienced greater loss of water clarity during recovery relative to moderately acidified lakes. These findings are consistent with the hypothesis that lake acidification resulted in a reduction in light attenuation by CDOM resulting in greater water clarity in acidified lakes, and that this process has been reversed following regional declines in sulfate deposition.
Savanna ecosystems have undergone structural and functional transformations in the last two centuries, following a shift in the grazing communities from predominantly migratory wild mega-herbivores, to sedentary domestic herbivore populations (livestock). The dominance of livestock and their sedentary grazing patterns have increased pressure on the herbaceous layer communities. Changes in rainfall regimes, characterized by shorter but more intense rainy seasons (flooding) and prolonged dry seasons (drought) have also occurred during the same period. This transformation threatens the sustainability of the herbaceous layer, but has rarely been studied. Rapid increase in livestock populations in Lambwe Valley, a typical savanna in Western Kenya, has increased grazing pressure on the herbaceous vegetation during the last three decades. Extended dry periods and shorter, but more intense, rainy periods have also become common in the region. Phenotypic and structural alterations caused by the ongoing grazing pressure and increased rainfall variability are likely the visible ramification of the changing ecosystem processes, taking place at the background, and which have rarely been investigated. Lambwe valley is, therefore, a suitable study object for understanding how savanna ecosystems respond to the ongoing changes in grazing and rainfall variability. This study investigated how two levels of livestock grazing (grazed and ungrazed) and three levels of rainfall amounts (50%, 100%, and 150% of ambient) affected (i) soil properties; (ii) plant species diversity, and (iii) CO2 fluxes in the herbaceous layer community during dry and wet periods. Study plots were abbreviated using first letters of the grazing levels (grazed - G or ungrazed - U) followed by the amounts of rainfall (50%, 100% and 150%) i.e. G50%. Volumetric soil water content (VWC) increased along a rainfall gradient of 50–150% (RMSE = 3.55; r2 = 0.61; p < 0.05), from an average amount of 17.5 ± 4.9% to 26.9 ± 4.9% in the G50% and U150% plots, respectively. This shows that rainfall was the main source of water at the 20 cm soil depth during the measurement period. The grazed plots had higher soil bulk density of 3.2% and nitrogen (N) content of 7.8% compared to the ungrazed, however, VWC and soil carbon (C) content decreased by 19.64% and 11.45%, respectively in the grazed plots compared to the ungrazed. Reducing the ambient rainfall by 50% had a significant effect (p < 0.05) on the soil properties compared to a 50% increase (150%). VWC significantly correlated to soil bulk soil density (r2 > 0.62; p = 0.05). Livestock grazing increased species diversity (H), but decreased aboveground biomass (AGB). Hyparrhenia fillipendulla (Hochst) Stapf. and Brachiaria decumbens Stapf, dominated the ungrazed plots, making up > 70% of the relative abundance and a larger proportion of AGB. Mean H did not vary amongst G50%, G100%, and G150% plots. In the ungrazed plots, however, H was higher in the U100% than both U50% and U150% plots. The AGB and species abundance mediated (indirect-only mediation) the effect of VWC on H. The highest mean net ecosystem exchange (NEE) of –8.80 ± 2.26 µmol m–2 s–1, AGB of 1208.41 g m–2, and total biomass of 1589.06 g m–2 were reported in the U150% plot during the wet months. VWC significantly correlated (p < 0.05) to the changes in NEE (r2 ≥ 0.65), ecosystem respiration (Reco) (r2 ≥ 0.52), gross primary production (GPP) (r2 ≥ 0.71), and total biomass (r2 ≥ 0.61) across plots. CO2 fluxes and the total biomass of the herbaceous layer community decreased due to: grazing by livestock; 50% reduction of ambient rainfall; and during the dry months, when VWC was lower. During the dry months, NEE in the G50% plot declined to 3.68 ± 0.81 µmol m–2 s–1, from –3.06 ± 1.56 µmol m–2 s–1, observed when soil moisture was high. The interaction among grazing, rainfall manipulation, and seasonality in rainfall significantly regulated AGB, total biomass, and root to shoot biomass ratio (R:S). The total amount of rainfall received during the entire period of measurement directly affected soil moisture availability, however, variations in VWC among the plots resulted from the interaction of livestock grazing and rainfall manipulation. Grazing and reduction of ambient rainfall decreased the soil C content, species diversity, CO2 uptake, and biomass production, particularly, during the dry months when the negative effects were more pronounced. By reducing biomass of the most dominant species, grazing increased species diversity. This study demonstrated that the Lambwe Valley ecosystem has adjusted to the current grazing levels and rainfall amounts. Future decrease or increase in current ambient rainfall or grazing exclusion will lower herbaceous species diversity, due to adaptation of the current vegetation types to grazing under ambient rainfall amount. Interaction between livestock grazing and variation in rainfall amount will inform sustainable management strategies to regulate the herbaceous diversity and productivity.
Widespread changes in the relative abundances of Cyclotella sensu lato taxa have occurred in lakes of the Northern Hemisphere over the last ∼150 years, with these changes often attributed to climate-driven physical changes in lakes. While the links between Cyclotella ecology and lake thermal structure have been investigated extensively now, the role of the timing of ice-off in driving these diatom patterns remains unclear. We compared the seasonal distribution patterns of Cyclotella taxa in a boreal lake with high water transparency during two years with differing timing of ice-off. Vertical distributions of taxa in Jordan Pond (Maine, USA) were assessed every 5–24 days from early May to late October during an early ice-off year (19 March 2012) and a late ice-off year (29 April 2015). Seasonal succession patterns differed over the two years. During the early ice-off year, Lindavia bodanica cell densities were higher and peaked in the hypolimnion from July to October. The abundance of this taxon during the late ice-off year may have been negatively affected by fungal infection, which was visible with microscopic investigation. In contrast, Discostella stelligera cell densities were higher during the late ice-off year and peaked from May to August. This taxon was distributed uniformly in the water column throughout July, during phosphorus-limited conditions, and was then more abundant in the epilimnion during August, during nitrogen-limited conditions. Multiple linear regression models suggested that variation in D. stelligera cell densities was explained by year, number of days since ice-off and mixing depth (R² = 0.55), while variation in L. bodanica cell densities was explained by year, number of days since ice-off, total phosphorus, dissolved oxygen, and Secchi disk depth (R² = 0.16). Our results reveal variable seasonal distribution patterns of these two taxa over the two years and suggest that these patterns are the result of many drivers, some of which may be affected by ice-off timing.
Sequence data of 16S rRNA genes reveal that many bacterial taxa are found in all freshwater lakes. However, the global data set is highly weighted toward lakes in temperate regions of North America and northern Europe, and it is unclear whether bacterial communities in other northern latitude environments, such as boreal lakes in North America, differ from those in lower latitudes. This study used pyrosequences of the 16S rRNA gene to examine bacterial diversity in 37 temperate and boreal lakes in Québec, Canada, over the course of a year. Nearly all taxa in the global data set were also found in the Québec lakes, but relative abundances differed. Community structure varied geographically and seasonally for 97% similar operational taxonomic units (OTUs) but not at lower levels of similarity. Seasonal shifts in community structure were larger in temperate lakes than in boreal lakes, and community structure differed between boreal and temperate lakes in summer but not in winter. The differences in taxonomic composition between temperate and boreal lakes appear to be driven mostly by environmental processes influencing community structure of temperate lakes in summer. Our results provide a baseline for interpreting impacts of climate change in boreal biomes where community structure is driven by environmental factors.
Algal Turf Scrubbers (ATS) are water treatment devices that use light and
nutrients in the (waste)water to grow periphyton community; undesirable chemicals are
removed by physical, chemical and biological processes. So far, most ATS systems were
operated in water bodies with relatively high nutrient concentrations. Little is known
about the performance of ATS under low concentration of phosphorous (P), yet there are
potential applications where such conditions are met. The paper presents a series of
experiments that focus on the implementation of small-scale ATS systems to eliminate P
from natural swimming ponds (SP). SPs are typically subject to fluctuating P
concentrations and require the maintenance of very low levels of P (< 10 μg L-1) in order
to prevent undesirable algal growth. ATS systems proved to be capable of maintaining
such low levels, both in laboratory and field conditions.
Hydrologic processes mediate pronounced soil-microclimate variability that may significantly influence the distribution of organisms in rapidly changing climates. Conservationists are particularly interested in identifying and protecting areas that offer species with the best chances of survival under intensifying climate change impacts, but poor understanding of how hydrologic processes may contribute to and maintain refugia from climate change hinders the implementation of effective conservation strategies. To improve the quality of scientific recommendations available to conservationists I initiated a multi-faceted research program to characterize soil-microclimate variation across landscapes to better understand organismal responses to microclimatic factors. I developed landscape-scale and microsite-scale soil temperature models (daily min, max) from sensor networks distributed across a range of hydrologic conditions in priority conservation areas in New York State (NYS). Soil temperature models incorporated atmospheric and hydrologic conditions and accurately predicted observations from independent sensor networks not used for model building. I observed large differences in soil temperatures among monitoring locations and within sites over the monitoring periods (2010-2011). I also examined the distribution of plant species relative to microclimatic gradients in fens, and performed a dendroclimatic study examining climate-growth relationships for co-occurring balsam fir and eastern white pine trees in contrasting hydrologic settings. Differences in plant community composition were correlated with microclimatic gradients (soil temperature, snow cover), and climate-growth relationships for balsam fir and eastern white pine were strongly influenced by site hydrological factors. My studies demonstrate the significance of coupled hydrogeologic-atmospheric modeling approaches for improving the precision of soil temperature forecasting across complex terrain, particularly in wet environments. My studies also indicate that careful attention is needed to understand the sensitivity of biota in contrasting hydrologic environments to continued climate change. I suggest similar microclimate studies to those presented here may help conservationists to identify and mitigate threats in areas likely to serve as refugia from climate change.
We examined spatial patterns of trends in ice phenology and duration for 65 waterbodies across the Great Lakes region (Minnesota, Wisconsin, Michigan, Ontario, and New York) during a recent period of rapid climate warming (1975-2004). Average rates of change in freeze (3.3 d decade21) and breakup (22.1 d decade21) dates were 5.8 and 3.3 times more rapid, respectively, than historical rates (1846-1995) for Northern Hemisphere waterbodies. Average ice duration decreased by 5.3 d decade21. Over the same time period, average fall through spring temperatures in this region increased by 0.7uC decade21, while the average number of days with snow decreased by 5.0 d decade21, and the average snow depth on those days decreased by 1.7 cm decade21. Breakup date and ice duration trends varied over the study area, with faster changes occurring in the southwest. Trends for each site were compared to static waterbody characteristics and meteorological variables and their trends. The trend toward later freeze date was stronger in large, low-elevation waterbodies; however, freeze date trends had no geographic patterns or relationships to meteorological variables. Variability in the strength of trends toward earlier breakup was partially explained by spatial differences in the rate of change in the number of days with snow cover, mean snow depth, air temperature (warmer locations showed stronger trends), and rate of change in air temperature. Differences in ice duration trends were explained best by a combination of elevation and the local rate of change in either temperature or the number of days with snow cover.
Biogeochemical cycling of N and S was examined at two watersheds in the Adirondack Mountains, New York, to better understand the retention and loss of these elements during winter and spring snowmelt. We analyzed stable isotope compositions of NO3− (δ15N-NO3−, δ18O-NO3−) and SO42− (δ34S-SO42−, δ18O-SO42−), along with concentrations and fluxes of NO3− and SO42−, in precipitation, throughfall, snowpack, snowmelt, soil water, groundwater, and stream water. Isotopic results showed no evidence of NO3− and SO42− transformations in the forest canopy and snowpack; however, markedly decreased δ18O values of NO3− and SO42− in forest floor water suggest that microbial processing occurred in organic soil horizons. Similarly low δ18O values of NO3− and SO42− were observed in forest floor and mineral soil leachates, groundwater, and streams. Over the winter observation period, most of the NO3− and SO42− in stream water was from a watershed-derived source, whereas atmospheric contributions were relatively minor. Despite differences in soil water NO3− concentrations between watersheds, the isotopic composition of NO3− (δ15N-NO3−, δ18O-NO3−) was similar, and indicated that in both watersheds most of the NO3− was produced by nitrification in the forest soils. Although there was likely some contribution of SO42− from microbial oxidation of carbon-bonded sulfur, most of the stream water SO42− appeared to be derived from weathering of S-containing bedrock or parent material. The decreased δ18O values of NO3− and SO42− in upper soil horizons indicate that atmospheric deposition of N and S was not directly linked with stream water losses, even during winter and spring snowmelt.
We hypothesized that much of the variability in dissolved inorganic nitrogen (DIN) loss from forested catchments can be explained by land use history and interannual climatic variation, and that these factors determine the degree to which N deposition results in increased storage of C in forests. We used an existing model of C, N, and water balances in forest ecosystems in conjunction with long-term climate and N leaching loss data from several northern hardwood forest ecosystems to predict the effects of land use, climate variability and N deposition on C storage and N cycling and loss. Six sites from the White Mountains of New Hampshire with very different land use histories and annual stream DIN losses were used. The only model parameter that varied between sites was land use or disturbance history. Each site was simulated using both mean climate data for each year and actual time series climate data. Vegetation removal resulted in a period of increased DIN leaching, followed by losses below those in control stands for both measured and simulated data. One site with an extreme fire event over 170 years ago still showed reduced N losses in both modeled and measured data. Significant interannual variation in DIN loss is evident in the field data. Model predictions using actual climate time series data captured much of this variation. This high interannual variability along with the slow rate of change in DIN loss predicted by PnET-CN using mean climate throughout the simulations suggests that statistically significant increases in DIN leaching losses due to long-term increases in N deposition will not be detectable for several decades, given current rates of N deposition. N deposition increased C storage in all simulations, but the quantity stored was about 50% that predicted by another published model. This difference results from differences in the efficiency with which added N is retained in the ecosystem. The previous model used an 80% retention value, while retention was closer to 50% over most of the time period examined here.
Because of the difficulties involved with separating natural fluctuations in climatic variables from possible directional changes related to human activities (e.g., heightened atmospheric CO2 concentrations related to fossil fuel consumption), some researchers have focused on developing alternative indicators to detect hypothesized climate changes. It has, for example, been suggested that the locations of ecotones, transitions between adjacent ecosystems or biomes, should be monitored. It is assumed that changes in climate, especially increases in atmospheric temperature, will result in shifts in the location (altitude or latitude) of ecotones as plants respond to the newly imposed climatic conditions. In this article, we address the use of two montane ecotones, the alpine tree-line ecotone and the deciduous/Boreal forest ecotone, in monitoring global climatic change. In so doing, we 1) outline the factors that create and maintain each ecotone's position at a given location; 2) assess the projected response of the ecotones to various aspects of global warming; and 3) discuss the usefulness of both ecotones as indicators of global climate change. While it is likely that extended periods of directional climate change would bring about an altitudinal shift in the ranges of montane species and the associated ecotones, we question whether the response at either ecotone will be at a timescale useful for detecting climate change (a few decades) owing to disequilibrium related to upslope edaphic limitations and competitive interactions with established canopy and subcanopy individuals. Further, limitations related to the prediction of the complex and interacting effects of projected changes in temperature, precipitation and site water balance on photosynthetic processes of plant species raise uncertainties about the expected responses of both ecotones.
Paleoecological analysis of the sediment record of 12 Adirondack lakes reveals that the 8 clearwater lakes with current pH -1 have acidified recently. The onset of this acidification occurred between 1920 and 1970. Loss of alkalinity, based on quanitative analysis of diatom assemblages, ranged from 2 to 35 µeq l-1. The acidification trends are substantiated by several lines of evidence including stratigraphies of diatom, chrysophyte, chironomid, and cladoceran remains, Ca:Ti and Mn:Ti ratios, sequentially extracted forms of Al, and historical fish data. Acidification trends appear to be continuing in some lakes, despite reductions in atmospheric sulfur loading that began in the early 1970s. The primary cause of the acidification trend is clearly increased atmospheric deposition of strong acids derived from the combustion of fossil fuels. Natural processes and watershed disturbances cannot account for the changes in water chemistry that have occurred, but they may play a role. Sediment core profiles of Pb, Cu, V, Zn, S, polycyclic aromatic hydrocarbons, magnetic particles, and coal and oil soot provide a clear record of increased atmospheric input of materials associated with the combustion of fossil fuels beginning in the late 1800s and early 1900s. The primary evidence for acidification occurs after that period, and the pattern of water chemistry response to increased acid inputs is consistent with current understanding of lake-watershed acidification processes.
This investigation provides evidence of biological recovery from acidification in an acid-impacted Adirondack (New York, USA) lake. Water chemistry measurements collected monthly since 1982 show that Big Moose Lake is undergoing chemical recovery from acid deposition. To assess possible biological recovery, changes in chrysophyte, diatom, and cladoceran assemblages are analyzed in a sediment core. Three questions are addressed: (i) is there a significant shift in species composition after the 1995 implementation of the US Acid Rain Program? (ii) Are post-1995 changes in species composition consistent with chemical recovery from acidification or, rather, other changing chemical/climatic factors? (iii) Are the species assemblages returning to their pre-acidification state? Post-1995 declines in the relative abundance of diatom and chrysophyte taxa with low pH-optima and increases in taxa with higher pH-optima indicate biological recovery from acidification. In contrast, the cladocera remain unresponsive to post-1995 increases in pH. No species group has returned to its pre-disturbance state and post-ca. 1995 increases in certain taxa (e.g., Synura echinulata) may be related to recent climate warming in the Adirondacks.
Climate change is a reality. A warming climate will have large effects on lakes of the Boreal Shield. Our ability to forecast these effects, however, is hampered by a very incomplete understanding of the actual interactions between weather and many aspects of lake ecosystems. Climate change will affect lakes in very complex ways. Changing weather conditions will have direct effects on thermal habitats; however, there will also be very important indirect effects on lake ecosystems through influences on watershed processes that affect the thermal and chemical characteristics of lakes. Altered habitat conditions will affect the resident biota in both positive and negative ways and may favour range expansions of some native and non-native species. Our understanding of the altered biological interactions that will structure lake communities in a warmer climate is still limited, making the prediction of biological outcomes very difficult. Modelling efforts, experiments and empirical analyses of relationships between important attributes of lakes, lake communities, and weather conditions in the past are beginning to further our ability to predict likely future effects. Much more work is needed in all these research areas to further our understanding of the probable effects of climate change on Boreal Shield lakes. Because of the potential interactions of climate with other large-scale environmental stressors such as UV-B irradiance, exotic species invasions, base cation depletion, and acidification, future studies need to consider multiple stressor effects.
Freeze and breakup dates of ice on lakes and rivers provide consistent evidence of later freezing and earlier breakup around
the Northern Hemisphere from 1846 to 1995. Over these 150 years, changes in freeze dates averaged 5.8 days per 100 years later,
and changes in breakup dates averaged 6.5 days per 100 years earlier; these translate to increasing air temperatures of about
1.2°C per 100 years. Interannual variability in both freeze and breakup dates has increased since 1950. A few longer time
series reveal reduced ice cover (a warming trend) beginning as early as the 16th century, with increasing rates of change
after about 1850.
We examined long-term changes in phytoplankton composition from 1981 to 2003 in seven intensively studied lakes on the southern Canadian Shield in Ontario, Canada. Significant (P < 0.05), temporally coherent increases in the relative biovolume of colonial chrysophytes were observed in six of the seven lakes, with coincident declines in the relative biovolume of diatom algae. Variance partitioning analyses identified water chemistry variables, and the co-variation of water chemistry with physicoclimatic variables, as most important in structuring phytoplankton assemblages through time in the study lakes (variance explained: chemical variables (14%-47%, mean = 28.7%); chemistry and physicoclimatic variables (21%-30%, mean = 25.5%)). With the exception of Harp Lake, which was invaded by Bythotrephes in the early 1990s, grazing variables did not explain a significant portion of the phytoplankton variance. We hypothesize that the long-term changes in phytoplankton species composition is attributable to multiple anthropogenic stressors acting at a regional scale. Our results, coupled with paleoecological studies, indicate that increases in the relative importance of colonial chrysophytes are coincident with water chemistry changes associated with industrial activity since the mid-1900s and physical changes linked to climate indices such as the North Atlantic Oscillation.
—Fish habitat is strongly constrained,by water temperature,and the available dissolved oxygen,(DO). Fish habitat in small lakes of the contiguous,United States was therefore determined from simulated,daily water temperature,and dissolved oxygen,profiles. Twenty-seven,types of lakes were simulated,under past (1962‐1979) climate conditions and a projected doubling,of atmospheric carbon,dioxide,(23CO, climate scenario) at 209 locations in the contiguous,United States. The 23CO2 climate scenario,was,derived from,the output of the Canadian,Climate Centre’s General Circulation Model for a doubling of atmospheric CO2. A verified, process-oriented, dynamic, one- dimensional,(vertical) lake water quality model,(MINLAKE96) was used for the temperature,and DO simulations, which were run in a continuous mode over a 19-year simulation period. Water temperature and DO criteria for the survival and good growth of three fish guilds (cold-, cool-, and warmwater fish) were provided by the U.S. Environmental Protection Agency. Winterkill, which,occurs in the eutrophic,and mesotrophic,shallow,lakes of the northcentral and northeastern states under present climate conditions, is projected to disappear under the 2 3CO2 climate scenario due to a shortening,of the ice cover period. While coldwater,fish habitat is projected to persist in deep lakes near the northern border of the United States, it is likely to be eliminated from almost all shallow,lakes in the contiguous,states. Climate warming,is projected,to reduce the number,of locations in the contiguous,United States where,lakes have,suitable coldwater,and coolwater,fish habitat by up to 45% and 30%, respectively. Summerkill under the 23CO2 climate scenario is projected to have a significant negative influence on northern lakes and on coolwater,fish in southern lakes where,suitable habitat existed under,historical conditions. The largest negative,impact,of climate warming,on coldwater,fish habitat occurs in medium-depth,lakes (maximum,depth of 13 m); the largest negative impact,on coolwater,fish habitat occurs in shallow,lakes (maximum,depth
1] A uniquely comprehensive set of four decades of ice breakup data from 196 Swedish lakes covering 13° of latitude (55.7°N to 68.4°N) shows the relationship between the timing of lake ice breakup and air temperature to be an arc cosine function. The nonlinearity inherent in this relationship results in marked differences in the response of the timing of lake ice breakup to changes in air temperature between colder and warmer geographical regions, and between colder and warmer time periods. The spatial and temporal patterns are mutually consistent, suggesting that climate change impacts on the timing of lake ice breakup will vary along a temperature gradient. This has potentially important ramifications for the employment of lake ice phenologies as climate indicators and for the future behavior of lacustrine ecosystems.
1] Biogeochemical cycling of N and S was examined at two watersheds in the Adirondack Mountains, New York, to better understand the retention and loss of these elements during winter and spring snowmelt. We analyzed stable isotope compositions of NO 3 À (d 15 N-NO 3 À , d 18 O-NO 3 À) and SO 4 2À (d 34 S-SO 4 2À , d 18 O-SO 4 2À), along with concentrations and fluxes of NO 3 À and SO 4 2À , in precipitation, throughfall, snowpack, snowmelt, soil water, groundwater, and stream water. Isotopic results showed no evidence of NO 3 À and SO 4 2À transformations in the forest canopy and snowpack; however, markedly decreased d 18 O values of NO 3 À and SO 4 2À in forest floor water suggest that microbial processing occurred in organic soil horizons. Similarly low d 18 O values of NO 3 À and SO 4 2À were observed in forest floor and mineral soil leachates, groundwater, and streams. Over the winter observation period, most of the NO 3 À and SO 4 2À in stream water was from a watershed-derived source, whereas atmospheric contributions were relatively minor. Despite differences in soil water NO 3 À concentrations between watersheds, the isotopic composition of NO 3 À (d 15 N-NO 3 À , d 18 O-NO 3 À) was similar, and indicated that in both watersheds most of the NO 3 À was produced by nitrification in the forest soils. Although there was likely some contribution of SO 4 2À from microbial oxidation of carbon-bonded sulfur, most of the stream water SO 4 2À appeared to be derived from weathering of S-containing bedrock or parent material. The decreased d 18 O values of NO 3 À and SO 4 2À in upper soil horizons indicate that atmospheric deposition of N and S was not directly linked with stream water losses, even during winter and spring snowmelt.
Global climate change has already affected the abundances, range limits, and interactions of many species. The hemlock woolly
adelgid (Adelges tsugae), an invasive insect introduced to eastern North America from Japan, has decimated stands of eastern hemlock (Tsuga canadensis) and Carolina hemlock (T. caroliniana) from Georgia to Connecticut. However, its spread across central and northern New England has been slowed substantially by
its inability to tolerate cold winter temperatures. Using data from previous lab and field studies collected over the past
17years, including adelgid spread and overwintering mortality, we first characterize the temperature conditions that may
limit adelgid spread. We then show how, in the future, rising winter temperatures due to climate change are likely to remove
the conditions currently limiting adelgid spread, and facilitate the northward expansion as more suitable habitat becomes
available.
Climate projections at relevant temporal and spatial scales are essential to assess potential future climate change impacts
on climatologically diverse regions such as the northeast United States. Here, we show how both statistical and dynamical
downscaling methods applied to relatively coarse-scale atmosphere-ocean general circulation model output are able to improve
simulation of spatial and temporal variability in temperature and precipitation across the region. We then develop high-resolution
projections of future climate change across the northeast USA, using IPCC SRES emission scenarios combined with these downscaling
methods. The projections show increases in temperature that are larger at higher latitudes and inland, as well as the potential
for changing precipitation patterns, particularly along the coast. While the absolute magnitude of change expected over the
coming century depends on the sensitivity of the climate system to human forcing, significantly higher increases in temperature
and in winter precipitation are expected under a higher as compared to lower scenario of future emissions from human activities.
Forest ecosystems represent the dominant form of land cover in the northeastern United States and are heavily relied upon
by the region’s residents as a source of fuel, fiber, structural materials, clean water, economic vitality, and recreational
opportunities. Although predicted changes in climate have important implications for a number of ecosystem processes, our
present understanding of their long-term effects is poor. In this study, we used the PnET-CN model of forest carbon (C), nitrogen
(N) and water cycling to evaluate the effects of predicted changes in climate and atmospheric carbon dioxide (CO2) on forest growth, C exchange, water runoff, and nitrate (
\textNO - 3 {\text{NO}}^{ - }_{3} ) leaching at five forest research sites across the northeastern U.S. We used four sets of statistically downscaled climate
predictions from two general circulation models (the Hadley Centre Coupled Model, version 3 and the Parallel Climate Model)
and two scenarios of future CO2 concentrations. A series of model experiments was conducted to examine the effects of future temperature, precipitation,
CO2, and various assumptions regarding the physiological response of forests to these changes. Results indicate a wide range
of predicted future growth rates. Increased growth was predicted across deciduous sites under most future conditions, while
growth declines were predicted for spruce forests under the warmest scenarios and in some deciduous forests when CO2 fertilization effects were absent. Both climate and rising CO2 contributed to predicted changes, but their relative importance shifted from CO2-dominated to climate-dominated from the first to second half of the twenty-first century. Predicted runoff ranged from no
change to a slight decrease, depending on future precipitation and assumptions about stomatal response to CO2. Nitrate leaching exhibited variable responses, but was highest under conditions that imposed plant stress with no physiological
effects of CO2. Although there are considerable uncertainties surrounding predicted responses to climate change, these results provide a
range of possible outcomes and highlight interactions among processes that are likely to be important. Such information can
be useful to scientists and land managers as they plan on means of examining and responding to the effects of climate change.
Historical ice records, such as freeze and breakup dates and the total duration of ice cover, can be used as a quantitative indicator of climatic change if long homogeneous records exist and if the records can be calibrated in terms of climatic changes. Lake Mendota, Wisconsin, has the longest uninterrupted ice records available for any lake in North America dating back to 1855. These records extend back prior to any reliable air temperature data in the midwestern region of the U.S. and demonstrate significant warming of approximately 1.5 °C in fall and early winter temperatures and 2.5 °C in winter and spring temperatures during the past 135 years. These changes are not completely monotonie, but rather appear as two shorter periods of climatic change in the longer record. The first change was between 1875 and 1890, when fall, winter, and spring air temperatures increased by approximately 1.5 °C. The second change, earlier ice breakup dates since 1979, was caused by a significant increase in winter and early spring air temperatures of approximately 1.3 °C. This change may be indicative of shifts in regional climatic patterns associated with global warming, possibly associated with the ‘Greenhouse Effect’.
With the relationships between air temperature and freeze and break up dates, we can project how the ice cover of Lake Mendota should respond to future climatic changes. If warming occurs, the ice cover for Lake Mendota should decrease approximately 11 days per 1 °C increase. With a warming of 4 to 5 °C, years with no ice cover should occur in approximately 1 out of 15 to 30 years.
To assess the influence of global climate change at the regional scale, we examine past and future changes in key climate,
hydrological, and biophysical indicators across the US Northeast (NE). We first consider the extent to which simulations of
twentieth century climate from nine atmosphere-ocean general circulation models (AOGCMs) are able to reproduce observed changes
in these indicators. We then evaluate projected future trends in primary climate characteristics and indicators of change,
including seasonal temperatures, rainfall and drought, snow cover, soil moisture, streamflow, and changes in biometeorological
indicators that depend on threshold or accumulated temperatures such as growing season, frost days, and Spring Indices (SI).
Changes in indicators for which temperature-related signals have already been observed (seasonal warming patterns, advances
in high-spring streamflow, decreases in snow depth, extended growing seasons, earlier bloom dates) are generally reproduced
by past model simulations and are projected to continue in the future. Other indicators for which trends have not yet been
observed also show projected future changes consistent with a warmer climate (shrinking snow cover, more frequent droughts,
and extended low-flow periods in summer). The magnitude of temperature-driven trends in the future are generally projected
to be higher under the Special Report on Emission Scenarios (SRES) mid-high (A2) and higher (A1FI) emissions scenarios than
under the lower (B1) scenario. These results provide confidence regarding the direction of many regional climate trends, and
highlight the fundamental role of future emissions in determining the potential magnitude of changes we can expect over the
coming century.
Over the ages, human societies have altered local ecosystems and modified regional climates. Today, the human influence has attained a global scale. This reflects the recent rapid increase in population size, energy consumption, intensity of land use, international trade and travel, and other human activities. These global changes have heightened awareness that the long-term good health of populations depends on the continued stability and functioning of the biosphere's ecological, physical, and socioeconomic systems. The world's climate system is an integral part of the complex of life-supporting processes. Climate and weather have always had a powerful impact on human health and well-being. But like other large natural systems, the global climate system is coming under pressure from human activities. Global climate change is, therefore, a newer challenge to ongoing efforts to protect human health. This volume seeks to describe the context and process of global climate change, its actual or likely impacts on health, and how human societies and their governments should respond, with particular focus on the health sector.
Ecotones between biomes are sensitive areas of change that could be effectively modelled and monitored for future change. Ecotones are also important in influencing local and regional biodiversity patterns and ecological flows. The ecological processes that could affect change at ecotones and within biomes include internal ecosystem processes, such as competition, and external abiotic processes, most notably drought and related disturbances. Drought followed by infestations and fire appears to be the most likely process that could mediate ecological change under a rapidly changing climate. Predictions about the dynamics of ecotones can be made qualitatively, based on a theory of patch scaling and diversity in relation to abiotic stressors. Directional climatic change should promote a coalescence of patches on one side of the ecotone and increased fragmentation on the other side. -from Author
Despite emerging evidence that on‐going climate change is affecting species physiology, distribution, and phenology, there are few studies that examine changes in tree sapling establishment as a response. Changes in tree species composition can be expected due to increasing temperatures, with subsequent effects on future forest compositions. This study's objective was to examine changes in relative density of tree species assemblages within powerline corridors from 1975 to 2003 in New York State. Powerline corridors in New York are commonly surrounded by forests, which creates constant tree invasion pressure within a perpetual old‐field environment. This unique combination of factors allowed us to examine tree sapling establishment in a nearly constant environment over a 28‐year period, utilizing manova and PCA as primary statistical analyses. Tree species dynamics varied across the four ecological provinces within New York over time. Northern pioneer species (Betula populifolia, Fraxinus americana, Prunus serotina, and Tilia americana) declined across the state over the past 28 years, while the southern pioneer species (Betula lenta, Liriodendron tulipifera, and Sassafras albidum) increased in the hot continental division. In the warm continental division, the pine‐hemlock assemblage increased in the Northeastern Mixed Forest Province, while aspen‐birch increased in the Adirondack Highlands Forest Province, likely due to increases in precipitation. It appears that climate change may have had some influence on tree sapling composition that could affect future vegetation management decisions and expectations in powerline rights‐of‐way and forests.
The Paleoecological Investigation of Recent Lake Acidification'' (PIRLA) project, funded by the Electric Power Research Institute, is a broadly interdisciplinary paleoecological study of recent lake acidification. Approximately ten lakes are being studied in each of four low alkalinity regions in North America that are currently receiving acid deposition. The areas are the Adirondack Mountains (NY), northern New England, northern Great Lakes Region, and northern Florida. Sediment cores are being analyzed for diatom and chrysophyte remains to reconstruct acidification histories, including magnitude, rate, and timing of pH and alkalinity changes. Cores are dated using lead-210 and pollen and charcoal. Other sediment analyses include metals, sulfur, soot, and polycyclic aromatic hydrocarbons (PAH). These provide information on lake acidification histories, and the relative roles of natural acidification processes, watershed disturbance, and atmospheric deposition of strong acids. This interim report contains seven papers representing the status of project research as of March 1985. Results support the hypothesis that diatom and chrysophyte sediment stratigraphies can be used to determine the extent of past variations in the pH levels of lakes.
Information on lake ice characteristics is of interest to lake users, natural resource managers and researchers. Lake ice data for 143 North American freshwater lakes were assembled and analyzed. The principal data were observed ice-in dates, observed ice-out dates and observed ice thicknesses.Single variable linear regression and factor analysis were applied to find correlations with air temperature, lake morphometry (mean depth and surface area), latitude and topographic elevation. Strong correlations between lake ice parameters, latitude and mean air temperature were found and quantified. Lake morphometry exhibited consistent but less significant correlation to ice cover. Elevation showed varying degrees of correlation with the dependent variables.Multivariable regression analysis produced equations for ice-in date, ice-out date, ice-cover duration and maximum ice thickness. Despite low standard errors, the best regressions cannot account for the full range of annual variability in the historical records, implying the absence of influential factors from these regression models.Based on sensitivities gleaned from linear regression analysis, the effects of climate change on lake ice characteristics may also be estimated. The following are estimated shifts based on a 1 °C rise in average air temperature: ice-in date occurs ∼5 days later, ice-out date occurs ∼6 days earlier, ice cover duration (ICD) is reduced by ∼11 days, and maximum ice thickness is reduced by ∼7 cm. These values are on the order of those presented in prior studies using other methodologies and lakes.
Records of freezeup and breakup dates for Grand Traverse Bay, Michigan, and Lake Mendota, Wisconsin, are among the longest ice records available near the Great Lakes, beginning in 185 1 and 1855, respectively. The timing of freezeup and breakup results from an integration of meteorological conditions (primarily air temperature) that occur before these events. Changes in the average timing of these ice-events are translated into changes in air temperature by the use of empirical and process-driven models. The timing of freezeup and breakup at the two locations represents an integration of air temperatures over slightly different seasons (months). Records from both locations indicate that the early winter period before about 1890 was - 15°C cooler than the early winter period after that time; the mean temperature has, however, remained relatively constant since about 1890. Changes in breakup dates demonstrate a similar 1.0-l .5"C increase in late winter and early spring air temperatures about 1890. More recent average breakup dates at both locations have been earlier than during 1890-l 940, indicating an additional warming of 1.2"C in March since about 1940 and a warming of 1 . 1°C in January-March since about 1980. Ice records at these sites will continue to provide an early indication of the anticipated climatic warming, not only because of the large response of ice cover to small changes in air temperature but also because these records integrate climatic conditions during the seasons (winter-spring) when most warming is forecast to occur. Future reductions in ice cover may strongly affect the winter ecology of the Great Lakes by reducing the stable environment required by various levels of the food chain.
A physical lake model was employed to obtain a basis of discussing the impact of climate variability and climate change on the ecology of Lake Erken, Sweden. The validity of this approach was tested by running the PROBE-lake model for a 30-year period (STD) with observed meteorological data. The lake is adequately modelled, as seen in the comparison with actual lake ob- servations. The validated lake model was then forced with meteorological data obtained from a regional clim- ate model (RCM) with a horizontal resolution of 44 km for present (CLTR) and 2 ¥ CO2 (SCEN) climate condi- tions. The CLTR lake simulation compares reasonably with the STD. Applying the SCEN simulation leads to a climate change scenario for the lake. The physical changes include elevated temperatures, shorter periods of ice cover combined with two of ten years being totally ice-free, and changes in the mixing regime. The ecolog- ical consequences of the physical simulation results are derived from the historical dataset of Lake Erken. Con- sequences of a warmer climate could imply increased nutrient cycling and lake productivity. The results suggest that an application of RCMs with a suitable resolution for lakes in combination with physical lake models allows projection of the responses of lakes to a future climate.
A simulation model for ice and snow covers is applied to dimictic and polymictic lakes of the temperate zone to project the effects of possible climate warming on ice and snow covers. The winter cover model is associated with a deterministic, one-dimensional water temperature model. The lake parameters required as model input are surface area (AS), maximum depth (Hmax), summer and Secchi depth as a measure of radiation attenuation and trophic state. The model is driven by daily weather data. The model has been validated with extensive data. Standard errors between simulated and measured values are 0.12 m for ice thicknesses, 0.07 m for snow covers and less than 6 days for ice formation dates. The model is applied to simulate effects of projected climate change on winter ice and snow covers on different types of lakes in Minnesota. Lake depth and latitude are shown to have the strongest influence on freeze-over dates. Lake morphometry causes variations of up to 6 days in the mean value of ice-in dates. The trophic state and shape of a lake have little effect on ice-out date, but latitude is important.
The effect of ongoing climate change on lakes and reservoirs is one of the most serious issues facing human society. The projected changes in regional water balance will alter the capacity of lakes to provide ecosystem goods and services, such as inland fisheries and adequate supplies of safe drinking water. The ongoing warming trend will affect the physical, chemical, and biological properties of lake ecosystems, with implications for water quality (e.g., through the likely increased abundance of noxious cyanobacteria) and for wildlife habitats (e.g., through changes in littoral wetlands, stratification regimes, and primary production). At the most fundamental cellular and physiological level, changes in water temperature will affect the metabolic rates of aquatic organisms, and for some species there may be shifts beyond their critical threshold for survival. On the other hand, warmer temperatures will allow some newly invading species to survive and complete their life cycles, although this may come at the expense of any original species that are driven to extinction through predation or competition. At the broader ecosystem level, climate change will have pervasive effects on the physical structure and connectivity of lake ecosystems, their food webs and biodiversity, their biogeochemical characteristics, and their overall metabolic properties, including greenhouse gas production.
To simulate effects of projected climate change on ice covers of small lakes in the northern contiguous U.S., a process-based simulation model is applied. This winter ice/snow cover model is associated with a deterministic, one-dimensional year-round water temperature model. The lake parameters required as model input are surface area, maximum depth, and Secchi depth as a measure of radiation attenuation. The model is driven by daily weather data. Weather records from 209 stations in the contiguous U.S. for the period 1961–1979 were used to represent past climate conditions. The projected climate changes due to a doubling of atmospheric CO2 were obtained from the output of the Canadian Climate Center Global Circulation Model. To illustrate the effect of projected climate change we present herein winter ice cover characteristics simulated, respectively, with inputs of past climate conditions (1961–1979), with inputs of a projected 2×CO2 climate scenario as well as differences of those values. The dependence of ice cover characteristics on latitude and lake characteristics has been quantified by making simulations for 27 lake types at 209 locations across the contiguous U.S. It was found that the 2×CO2 climate scenario is projected to delay ice formation on lakes by as much as 40 days and melt ice by up to 67 days earlier. Maximum ice thicknesses are projected to be reduced by up to 0.44 m (Sault Ste. Marie, MI), and the ice cover periods will be shorter by up to 89 days (Rock Springs, WY). The largest changes are projected to occur east of Idaho from the Canadian border down to the states of Colorado, Nebraska, and Iowa and the northern parts of Illinois, Indiana, Ohio, and Pennsylvania. These changes would reduce fish winterkill in most shallow lakes of the northern states of the contiguous U.S. but may endanger snowmobiles and ice fishermen.
The relation between mean annual temperature (MAT), mean annual precipitation (MAP) and evapotranspiration (ET) for 38 forested watersheds was determined to evaluate the potential increase in ET and resulting decrease in stream runoff that could occur following climate change and lengthening of the growing season. The watersheds were all predominantly forested and were located in eastern North America, along a gradient in MAT from 3.5°C in New Brunswick, CA, to 19.8°C in northern Florida. Regression analysis for MAT versus ET indicated that along this gradient ET increased at a rate of 2.85cm°C−1 increase in MAT (±0.96cm°C−1, 95% confidence limits). General circulation models (GCM) using current mid-range emission scenarios project global MAT to increase by about 3°C during the 21st century. The inferred, potential, reduction in annual runoff associated with a 3°C increase in MAT for a representative small coastal basin and an inland mountainous basin in New England would be 11–13%. Percentage reductions in average daily runoff could be substantially larger during the months of lowest flows (July–September). The largest absolute reductions in runoff are likely to be during April and May with smaller reduction in the fall. This seasonal pattern of reduction in runoff is consistent with lengthening of the growing season and an increase in the ratio of rain to snow. Future increases in water use efficiency (WUE), precipitation, and cloudiness could mitigate part or all of this reduction in runoff but the full effects of changing climate on WUE remain quite uncertain as do future trends in precipitation and cloudiness.
The least squares estimator of a regression coefficient β is vulnerable to gross errors and the associated confidence interval is, in addition, sensitive to non-normality of the parent distribution. In this paper, a simple and robust (point as well as interval) estimator of β based on Kendall's [6] rank correlation tau is studied. The point estimator is the median of the set of slopes (Yj - Yi)/(tj-ti) joining pairs of points with ti ≠ ti, and is unbiased. The confidence interval is also determined by two order statistics of this set of slopes. Various properties of these estimators are studied and compared with those of the least squares and some other nonparametric estimators.
Increased losses of nitrate from watersheds may accelerate the depletion of nutrient cations and affect the acidification and trophic status of surface waters. Patterns of nitrate concentrations and losses were evaluated in four forested watersheds (East Bear Brook Watershed, Lead Mountain, ME; Watershed 6, Hubbard Brook Experimental Forest, White Mountains, NH; Arbutus Watershed, Huntington Forest, Adirondack Mountains, NY; Biscuit Brook, Catskill Mountains, NY) located across the northeastern United States. A synchronous pattern was observed in nitrate concentrations of drainage waters from these four sites from 1983 through 1993. Most notably, high concentrations and high drainage water losses followed an anomalous cold period (mean daily temperature −11.4 to −16 °C in December 1989) for all four sites. After high nitrate losses during the snowmelt of 1990, nitrate concentrations and fluxes decreased at all sites. These results suggest that climatic variation can have a major effect on nitrogen flux and cycling and may influence temporal patterns of nitrate loss in a region.
A prominent response of temperate aquatic ecosystems to climate warming is changes in phenology – advancements or delays in annually reoccurring events in an organism's life cycle. The exact seasonal timing of warming, in conjunction with species-specific life-history events such as emergence from resting stages, timing of spawning, generation times, or stage-specific prey requirements, may determine the nature of a species' response. We demonstrate that recent climate-induced shifts in the phenology of lake phytoplankton and zooplankton species in a temperate eutrophic lake (Müggelsee, Germany) differed according to differences in their characteristic life cycles. Fast-growing plankton in spring (diatoms, Daphnia) showed significant and synchronous forward movements by about 1 month, induced by concurrent earlier ice break-up dates (diatoms) and higher spring water temperature (Daphnia). No such synchrony was observed for slow-growing summer zooplankton species with longer and more complex life cycles (copepods, larvae of the mussel Dreissena polymorpha). Although coexisting, the summer plankton responded species specifically to seasonal warming trends, depending on whether the timing of warming matched their individual thermal requirements at decisive developmental stages such as emergence from diapause (copepods), or spawning (Dreissena). Others did not change their phenology significantly, but nevertheless, increased in abundances. We show that the detailed seasonal pattern of warming influences the response of phyto- and zooplankton species to climate change, and point to the diverse nature of responses for species exhibiting complex life-history traits.
Station metadata plays a critical role in the accurate assessment of climate data and eventually of climatic change, climate variability, and climate prediction. However, current procedures of metadata collection are insufficient for these purposes. This paper introduces the GeoProfile as a model for documenting and visualizing enhanced spatial metadata. In addition to traditional metadata archiving, GeoProfiles integrate meso-scale topography, slope, aspect, and land-use data from the vicinity of climate observing stations (http://kyclim.wku.edu/tmp/geoprofiles/geoprofiles_main.html). We describe how GeoProfiles are created using Geographical Information Systems (GIS) and demonstrate how they may be used to help identify measurement bias in climate observations due to undesired instrument exposures and the subsequent forcings of micro- and meso-environments. A study involving 12 COOP and US Historical Climate Network (USHCN) stations finds that undesirable instrument exposures associated with both anthropogenic and natural influences resulted in biased measurement of temperature. Differences in average monthly maximum and minimum temperatures between proximate stations are as large as 1.6 and 3.8 °C, respectively. In addition, it is found that the difference in average extreme monthly minimum temperatures can be as high as 3.6 °C between nearby stations, largely owing to the differences in instrument exposures. Likewise, the difference in monthly extreme maximum temperatures between neighboring stations are as large as 2.4 °C. This investigation finds similar differences in the diurnal temperature range (DTR). GeoProfiles helped us to identify meso-scale forcing, e.g. instruments on a south-facing slope and topography, in addition to forcing of micro-scale setting. Copyright © 2006 Royal Meteorological Society.
The largest uncertainty in forecasting the effects of climate change on eco-systems is in understanding how it will affect the nature of interactions among species. Climate change may have unexpected consequences because different species show unique responses to changes in environmental temperatures. Here we show that increasingly warmer springs since 1962 have disrupted the trophic linkages between phytoplankton and zoo-plankton in a large temperate lake because of differing sensitivity to vernal warming. The timing of thermal stratification and the spring diatom bloom have advanced by more than 20 days during this time period. A long-term decline in Daphnia populations, the keystone herbivore, is associated with an expanding temporal mismatch with the spring diatom bloom and may have severe consequences for resource flow to upper trophic levels.
1. Lake managers suspect that taste and odour-causing algal blooms are increasing in frequency and intensity, although long-term monitoring records are scarce, and a number of critical scientific and management questions remain unanswered. 2. In nutrient-poor lakes and reservoirs, these events are caused primarily by sporadic outbreaks of some chrysophyte algae, which leave identifiable markers in lake sediments. We examine the siliceous remains of these organisms in more than fifty boreal lakes at broad temporal and spatial scales. 3. Colonial scaled chrysophytes, including the taste and odour-causing Synura petersenii, have increased markedly in more that 90% of the lakes examined since pre-industrial times. 4. Detailed stratigraphic analyses of two lakes show a rise in the abundance of colonial taxa in the 1930s to 1950s, with a sharp increase over the past two decades. 5. An examination of biogenic silica and biological ratios in Crosson Lake, Ontario, Canada, indicate that these changes represent true increases in the absolute abundance of colonial chrysophytes. 6. Rapid increases over the past two decades indicate that these trends are the result of one or more anthropogenic stressors that are operating at a broad, regional scale.
A synthesis of over 200 diatom-based paleolimnological records from nonacidified/nonenriched lakes reveals remarkably similar taxon-specific shifts across the Northern Hemisphere since the 19th century. Our data indicate that these diatom shifts occurred in conjunction with changes in freshwater habitat structure and quality, which, in turn, we link to hemispheric warming trends. Significant increases in the relative abundances of planktonic Cyclotella taxa (P<0.01) were concurrent with sharp declines in both heavily silicified Aulacoseira taxa (P<0.01) and benthic Fragilaria taxa (P<0.01). We demonstrate that this trend is not limited to Arctic and alpine environments, but that lakes at temperate latitudes are now showing similar ecological changes. As expected, the onset of biological responses to warming occurred significantly earlier (P<0.05) in climatically sensitive Arctic regions (median age=ad 1870) compared with temperate regions (median age=ad 1970). In a detailed paleolimnological case study, we report strong relationships (P<0.005) between sedimentary diatom data from Whitefish Bay, Lake of the Woods (Ontario, Canada), and long-term changes in air temperature and ice-out records. Other potential environmental factors, such as atmospheric nitrogen deposition, could not explain our observations. These data provide clear evidence that unparalleled warming over the last few decades resulted in substantial increases in the length of the ice-free period that, similar to 19th century changes in high-latitude lakes, likely triggered a reorganization of diatom community composition. We show that many nonacidified, nutrient-poor, freshwater ecosystems throughout the Northern Hemisphere have crossed important climatically induced ecological thresholds. These findings are worrisome, as the ecological changes that we report at both mid- and high-latitude sites have occurred with increases in mean annual air temperature that are less than half of what is projected for these regions over the next half century.
Global climate change is frequently considered a major conservation threat. The Earth's climate has already warmed by 0.5 degrees C over the past century, and recent studies show that it is possible to detect the effects of a changing climate on ecological systems. This suggests that global change may be a current and future conservation threat. Changes in recent decades are apparent at all levels of ecological organizations: population and life-history changes, shifts in geographic range, changes in species composition of communities, and changes in the structure and functioning of ecosystems. These ecological effects can be linked to recent population declines adn to both local and global extinctions of species. Although it is impossible to prove that climate change is the cause of these ecological effects, these findings have important implications for conservation biology. It is no longer safe to assume that all of a species' historic range remains suitable. In drawing attention to the importance of climate change as a current threat to species, these studies emphasize the need for current conservation efforts to consider climate change in both in situ conservation and reintroduction efforts. Additional threats will emerge as climate continues to change, especially as climate interacts with other stressors such as habitat fragmentation. These studies can contribute to preparations for future challenges by providing valuable input to models and direct examples of how species respond to climate change.
Biogeochemical responses to changing climate and atmospheric deposition were investigated using nitrogen (N) and sulfur (S) mass balances, including dry deposition and organic solutes in the Arbutus Lake watershed in the Adirondack Mountains, New York State. Long-term monitoring of wet-only precipitation (NADP/NTN, 1983–2001) and dry deposition (AIRMoN, 1990–2001) at sites adjacent to the watershed showed that concentrations of SO42− in precipitation, SO42− in particles,and SO2 vapor all declined substantially (P<0.005) in contrast to no marked temporal changes observed for most N constituents (NH4+ in precipitation, HNO3 vapor, and particulate NO3−), except for NO3− in precipitation, which showed a small decrease in the late 1990s. From 1983 to 2001, concentrations of SO42− in the lake outlet significantly decreased (−2.1 μeq L−1 yr−1, P<0.0001), whereas NO3− and dissolved organic N (DON) concentrations showed no consistent temporal trends. With the inclusion of dry deposition and DON fluxes into the mass balance, the retained portion of atmospheric N inputs within the main subcatchment increased from 37% to 60%. Sulfur outputs greatly exceeded inputs even with the inclusion of dry S deposition, while organic S flux represented another source of S output, implying substantial internal S sources. A significant relationship between the annual mean concentrations of SO42− in lake discharge and wet deposition over the last two decades (r=0.64, P<0.01) suggested a considerable influence of declining S deposition on surface water SO42− concentrations, despite substantial internal S sources. By contrast, interannual variations in both NO3− concentrations and fluxes in lake discharge were significantly related to year-to-year changes in air temperature and runoff. Snowmelt responses to winter temperature fluctuations were crucial in explaining large portions of interannual variations in watershed NO3− export during the months preceding spring snowmelt (especially, January–March). Distinctive response patterns of monthly mean concentrations of NO3− and DON in the major lake inlet to seasonal changes in air temperature also suggested climatic regulation of seasonal patterns in watershed release of both N forms. The sensitive response of N drainage losses to climatic variability might explain the synchronous patterns of decadal variations in watershed NO3− export across the northeastern USA.
Various studies have shown that changes over time in spring ice-out dates can be used as indicators of climate change. Ice-out dates from 29 lakes in New England (USA) with 64 to 163 years of record were assembled and analysed for this study. Ice-out dates have become significantly earlier in New England since the 1800s. Changes in ice-out dates between 1850 and 2000 were 9 days and 16 days in the northern/mountainous and southern regions of New England respectively. The changes in the ice-out data over time were very consistent within each of the two regions of New England, and more consistent than four air-temperature records in each region. The ice-out dates of the two regions had a different response to changes in air temperature. The inferred late winter–early spring air-temperature warming in both regions of New England since 1850, based on linear regression analysis, was about 1.5°C. Published in 2002 by John Wiley & Sons, Ltd.
We evaluated long-term trends in average maximum and minimum temperatures, threshold temperatures, and growing season in eastern Colorado, USA, to explore the potential shortcomings of many climate-change studies that either: (1) generalize regional patterns from single stations, single seasons, or a few parameters over short duration from averaging dissimilar stations; or (2) generalize an average regional pattern from coarse-scale general circulation models. Based on 11 weather stations, some trends were weakly regionally consistent with previous studies of night-time temperature warming. Long-term (80 + years) mean minimum temperatures increased significantly (P < 0.2) in about half the stations in winter, spring, and autumn and six stations had significant decreases in the number of days per year with temperatures ≤ − 17.8 °C (≤0 °F). However, spatial and temporal variation in the direction of change was enormous for all the other weather parameters tested, and, in the majority of tests, few stations showed significant trends (even at P < 0.2). In summer, four stations had significant increases and three stations had significant decreases in minimum temperatures, producing a strongly mixed regional signal. Trends in maximum temperature varied seasonally and geographically, as did trends in threshold temperature days ≥32.2 °C (≥90 °F) or days ≥37.8 °C (≥100 °F). There was evidence of a sub-regional cooling in autumn's maximum temperatures, with five stations showing significant decreasing trends. There were many geographic anomalies where neighbouring weather stations differed greatly in the magnitude of change or where they had significant and opposite trends. We conclude that sub-regional spatial and seasonal variation cannot be ignored when evaluating the direction and magnitude of climate change. It is unlikely that one or a few weather stations are representative of regional climate trends, and equally unlikely that regionally projected climate change from coarse-scale general circulation models will accurately portray trends at sub-regional scales. However, the assessment of a group of stations for consistent more qualitative trends (such as the number of days less than −17.8 °C, such as we found) provides a reasonably robust procedure to evaluate climate trends and variability. Copyright © 2002 Royal Meteorological Society
Interactions between acidic deposition and watershed characteristics were evaluated for a group of lakes in the Adirondack Mountains, New York. Landscape characteristics were compiled and examined relative to paleolimnological inferences of historical acidification. Results of estimates of acidification using the Model of Acidification of Groundwater in Catchments (MAGIC) and paleolimnological analysis were compared to physical, biological, and landscape change data, including such factors as watershed disturbance, logging, fire, and windthrow, to evaluate if inclusion of additional processes could improve model estimates. Results of bivariate and multivariate analysis confirmed that lakes that have experienced historical acidification tend to be those that receive relatively high amounts of precipitation and have short hydraulic residence times. These variables explained 58% of the diatom-inferred acidification. A combined model of long-term precipitation amount, hydraulic residence time, and recent blowdown accounted for 71% of the historic acidification in the Adirondacks. Lakes that have increased in pH since pre-industrial times tend to be those subject to substantial human disturbance and those that burned during major fires recorded after 1900. The magnitude of the discrepancy between MAGIC model and diatom-inferred hindcasts of acidification was not significantly correlated with any of the landscape change variables, suggesting that additional modifications to the MAGIC model to take into account landscape change are not likely to appreciably improve model performance.
Chemical and biological sedimentary records of a high alpine lake were used to reconstruct palaeoecological conditions and compared with two centuries of instrumental temperature measurements. Air temperature determined the lake water pH throughout the past 200 yr almost regardless of the level of atmospheric deposition. Our data suggest a strong climate forcing of the acid-base balance in sensitive high-altitude lakes. Their physico-chemical conditions and biota strongly depend on the duration of ice and snow cover which is significantly different between warm and cold periods. Beside changes in weathering rates, in-lake alkalinity generation and water-retention time, delayed freezing in autumn and earlier ice-out dates with a shorter duration of CO2 over-saturation could be crucial for the tight temperature-pH coupling.
The calendar date of ice break-up on Lej da San Murezzan, a high-altitude (1768 m a.s.l.) lake in the Swiss Alps, has been recorded uninterruptedly since 1832. Based on this record and on shorter, interrupted records from two neighbouring lakes, the potential use of the timing of spring break-up as a proxy for local and regional surface air temperatures in the European Alpine region is investigated. Lej da San Murezzan exhibits an overall trend to earlier thawing (7.6 days per century) comparable to that of lakes in other parts of the Northern Hemisphere. Part of this trend may be due to shifts in mean break-up date around 1857 and 1932. The timing of break-up on all three lakes is strongly related to local and regional surface air temperatures centred on the middle of April and integrated over 4–8 weeks. Three empirical methods of relating break-up date to local air temperature yielded essentially the same proportion of shared variance (about 64%). Comparisons of break-up dates with surface air temperature data from Switzerland, the Netherlands and the United Kingdom suggest that the thawing of Alpine lakes is determined to a large extent by synoptic-scale meteorological processes. The timing of break-up on Lej da San Murezzan also tends to follow an index of global explosive volcanism with a time lag of about two years, volcanically quiescent periods being associated with early break-up, and volcanically active periods with late break-up. This suggests that modulation of incident radiation by stratospheric aerosols of volcanic origin may significantly affect the timing of break-up of high-altitude lakes.