Donald R. Whitehead

Late Quaternary Environmental History of Lake Valencia, Venezuela

Chemical, paleontological, and mineralogical analyses of a 7.5-meter core from the middle of Lake Valencia, Venezuela, have provided information on the paleoclimatic history of this low-elevation, low-latitude site for the last 13,000 years. The data show that dry climates existed in this region from 13,000 years before present (B.P.) until about 10,000 years B.P. The Lake Valencia Basin was occupied by intermittent saline marshes at that time. About 10,000 years B.P., a permanent lake of fluctuating salinity formed and arboreal plant communities replaced the earlier dominant xeric herbaceous vegetation and marsh plants. By 8500 years B.P., Lake Valencia reached moderate to low salinities and discharged water; the modern vegetation became established at that time. After 8500 years B.P., the lake twice ceased discharging as a result of reduced watershed moisture. The second of these drying episodes is still in progress and has been aggravated by human activities in the watershed.

Paleoecological investigation of recent lake acidification in the Adirondack Mountains, N.Y.

Paleoecological analysis of the sediment record of 12 Adirondack lakes reveals that the 8 clearwater lakes with current pH < 5.5 and alkalinity < 10 μeq l-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.

Late-Wisconsin vegetational changes in unglaciated Eastern North America

Abstract Recent pollen and macrofossil data from the Southeast is consistent with a displacement of boreal forest species by over 1000 km during full-glacial time. Data from west of the Appalachians suggests a displacement of some 600 km. Thus boreal forests were developed in a broad area south of the ice margin. Few deciduous forest elements persisted in that region. The displacement appears to have been azonal. There is good evidence to suggest a significant mid-Wisconsin interstadial (23,00036,000 BP) characterized by a more temperate biota.

Holocene Vegetation Patterns in the Adirondack Mountains

Pollen and plant macrofossil data from six sites along an elevational gradient (661-1320 m) in the east-central Adirondack Mountains (New York) reveal the history of six tree taxa (Picea, Abies, Pinus strobus, Tsuga, Betula papyrifera, B. lutea) in the region during the past 10 000 yr. Space-time plots of the data show how spatial patterns of vegetation along the elevational gradient changed during the Holocene in response to climatic, biotic, and other changes. The plots also illustrate the contrasting spatial scales at which pollen and plant macrofossil data sense forest composition. Vegetational patterns along the gradient changed substantially during the Holocene. Responses of the six tree taxa to temporal changes in environment were individualistic, resulting in continual changes in the spatial vegetation patterns. The modern elevational zonation developed only within the past 3000 yr. Each tree taxon had a unique abundance pattern along the spatial and temporal gra- dients. Pollen percentages of Picea, Pinus, Tsuga, and Betula did not vary systematically with elevation, but changed substantially with time, indicating changes in abundance of these taxa at a regional scale. Macrofossil percentages of all six taxa varied with both time and elevation, revealing temporal changes in abundance of these taxa along the elevational gradient. Abies populations were concentrated at higher elevations, while Pinus strobus, Tsuga, and Betula lutea trees were most abundant at lower elevations. The elevational distributions and low-elevation abundance of the latter three taxa changed substantially during the Holocene. Picea trees were rare at all elevations during the early and mid- Holocene, and increased in abundance at mid-elevation sites within the past 3000 yr.

Paleolimnological evidence for recent acidification of Big Moose Lake, Adirondack Mountains, N.Y. (USA)

Big Moose L. has become significantly more acidic since the 1950s, based on paleolimnological analyses of sediment cores. Reconstruction of past lakewater pH using diatom assemblage data indicates that from prior to 1800 to ca. 1950, lakewater pH was about 5.8. After the mid-1950s, the inferred pH decreased steadily and relatively quickly to about 4.6. Alkalinity reconstructions indicate a decrease of about 30 μeq · l-1 during the same period. There was a major shift in diatom assemblage composition, including a nearly total loss of euplanktonic taxa. Chrysophyte scale assemblages and chironomid (midge larvae remains also changed in a pattern indicating decreasing lakewater pH starting in the 1950s. Accumulation rates of total Ca, exchangeable and oxide Al, and other metals suggest recent lake-watershed acidification. Cores were dated using210Pb, pollen, and charcoal. Indicators of watershed change (deposition rates of Ti, Si, Al) do not suggest any major erosional events resulting from fires or logging. Accumulation rates of materials associated with combustion of fossil fuels (polycyclic aromatic hydrocarbons, coal and oil soot particles, some trace metals, and sulfur) are low until the late 1800s-early 1900s and increase relatively rapidly until the 1920s–1930s. Peak rates occurred between the late 1940s and about 1970, when rates declined.The recent decrease in pH of Big Moose L. cannot be accounted for by natural acidification or processes associated with watershed disturbance. The magnitude, rate and timing of the recent pH and alkalinity decreases, and their relationship to indicators of coal and oil combustion, indicate that the most reasonable explanation for the recent acidification is increased atmospheric deposition of strong acids derived from combustion of fossil fuels.

The PIRLA project: Paleoecological investigations of recent lake acidification

The PIRLA project is a broadly interdisciplinary paleolimnological investigation of five to fifteen comparable watershed/lake systems from each of four low-alkalinity regions in North America that are currently receiving acid deposition. The areas are the Adirondack Mountains (N.Y.), northern New England, northern Great Lakes states, and northern Florida. The primary objective of the study is to provide a detailed reconstruction of the recent acidification histories of a representative suite of lakes from each of the regions. The study will increase our understanding of the timing, rates, and magnitude of acidification (and other chemical changes), and the regional and inter-regional patterns of lake acidification.

Fossil Pine Pollen and Full-Glacial Vegetation in Southeastern North Carolina

A reassessment of the difficulties inherent in size—frequency identification of pollen indicates that the reliability of the method is of low order. Accurate identifications assume: (1) Adequate data on size variation for all relevant extant species; (2) a standardized method of preparation for all modern samples; (3) use of mounting medium in which size is stabilized (not glycerine or glycerine—jelly); (4) preparation of all samples from a given fossil profile by an identical technique (not necessarily the same as that employed for modern material); (5)cognizance of the fact that size of modern and fossil grains cannot be compared directly and that the size changes may occur as a function of sediment type within a profile; and (6) presentation of size—frequency curves for the fossil material. New Pollen size measurements for the 13 eastern pines indicate that no single species can be identified on a size—frequency basis. The mode for small pine grains described by Frey from the full—glacial portion (M Zone) of the Singletary Lake profile could have been contributed to by either jack pine or red pine (or both). These data and new pollen analyses from the M Zone sediments suggest that the dominant full—glacial forest type in the region consisted of widely spaced pines (jack and/or red pine) associated with heliophytic herbs and shrubs (Artemisia, Polygonella, Plantago, Ambrosia, caryophylls, and chenopods). Boreal elements (Picea, Abies, Schizeae pusilla, Sanguisorba canadensis, Lycopodium annotinum, L. lucidulum) may have occurred on more mesic sites surrounding the lakes or on the poorly drained inter—Bay regions.

Late-glacial and postglacial vegetational history of the Berkshires, western Massachusetts

Abstract A pollen analytical investigation of the sediments of Berry Pond, Berkshire County, Massachusetts, has demonstrated a sequence of pollen assemblage zones similar to those detected elsewhere in New England. From about 13,000 to 12,000 yr B.P. the vegetation of the region was treeless, probably tundra. By 11,500 yr tundra had been replaced by open boreal forest. Closed boreal forest became dominant by 10,500 yr. Boreal forests were replaced by mixed coniferous and deciduous forests with much white pine about 9600 yr ago. A “northern hardwoods” complex with much hemlock, beech, and sugar maple succeeded the mixed forests 8600 yr ago. Hemlock declined very rapidly approximately 4800 yr ago and was replaced by birch, oak, beech, ash, and red maple. This decline may have been biologically rather than climatically induced. There is a slight maximum of pine (much of it pitch pine) from 4100 to 2600 yr ago, perhaps indicative of warmer and/or drier conditions. There were slight changes in the forests about 1600 yr ago as chestnut immigrated and spruce and larch increased slightly. European land clearance and subsequent land abandonment are detectable in the uppermost levels.

The developmental history of Adirondack (N.Y.) Lakes

We utilized paleoecological techniques to reconstruct long-term changes in lake-water chemistry, lake trophic state, and watershed vegetation and soils for three lakes located on an elevational gradient (661–1150 m) in the High Peaks region of the Adirondack Mountains of New York State (U.S.A.). Diatoms were used to reconstruct pH and trophic state. Sedimentary chrysophytes, chlorophylls and carotenoids supplied corroborating evidence. Pollen, plant macrofossils, and metals provided information on watershed vegetation, soils, and biogeochemical processes. All three lakes were slightly alkaline pH 7–8) and more productive in the late-glacial. They acidified and became less productive at the end of the late-glacial and in the early Holocene. pH stabilized 8000–9000 yr B.P. at the two higher sites and by 6000 yr B.P. at the lowest. An elevational gradient in pH existed throughout the Holocene. The highest site had a mean Holocene pH close to or below 5; the lowest site fluctuated around a mean of 6. The higher pH and trophic state of the late-glacial was controlled by leaching of base cations from fresh unweathered till, a process accelerated by the development of histosols in the watersheds as spruce-dominated woodlands replaced tundra. An apparent pulse of lake productivity at the late-glacial-Holocene boundary is correlated with a transient, but significant, expansion of alder (Alnus crispa) populations. The alder phase had a significant impact on watershed (and hence lake) biogeochemistry. The limnological changes of the Holocene and the differences between lakes were a function of an elevational gradient in temperature, hydrology (higher precipitation and lower evapotranspiration at higher elevation), soil thickness (thinner tills at higher elevation), soil type (histosols at higher elevation), vegetation (northern hardwoods at lower elevation, spruce-fir at higher), and different Holocene vegetational sequences in the three watersheds.

Geolipid, pollen and diaton stratigraphy in postglacial lacustrine sediments

As part of our continuing investigation of specific compounds as organic matter indicators in lake bottoms, we have examined geolipids, pollen and diatoms in sediments from different periods in the postglacial history of Heart Lake, New York. Sediment core sections representing the major watershed vegetation periods were extracted for unbound and bound fatty acids, hydrocarbons and alcohols. Fatty acids constitute most of the extracted material. Minor decreases in unsaturated acids with depth indicate little degradation of organic matter in these sediments. The dominant unbound n-alkanoic acid in the core sections is either Cz2 or C24, but bound fractions contain few long chain acids and are dominated by n-Cry,. Nearly all the hydrocarbons are found in the unbound fraction. The ratio of C2,/C~7 n-alkanes increases from the bottom of the core to near the top as watershed forests have matured and lake productivity has diminished, but drops since European settlement of the region. Organic degradation in this lake bottom is mild, and input indicators appear to be well preserved.