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

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

Paleoecological investigations of recent lake acidification in northern Florida

Thirty-two northern Florida lakes were analyzed to construct a transfer function relating surface sediment diatom assemblages to lakewater pH (R ² =0.89, s.e.=0.34). A paleoecological analysis of sediment cores from six of these lakes indicated that two have become more acidic in the last 50 years. The diatom inferred (DI) pH of L. Barco has declined between 0.56–0.82 in the 1900's and DI ANC (acid neutralizing capacity) by 28–46 eq l^-1. The DI pH of nearby L. Suggs has declined 0.91 pH units and its DI ANC by 19 eq l^-1. The timing of the inferred acidification is synchronous with known increases in emissions of sulfates and nitrates that are associated with acidic precipitation. Also, the increasing accumulation of substances related to emissions from the burning of fossil fuels (e.g., Pb, PAH) co-occurs with the lowering of DI pH in the sedimentary record. However, other processes may have accounted for or contributed to recent lake acidification. For instance, the drawdown of local water tables by human consumption may decrease the inseepage of ANC to seepage lakes. Such an effect would be synchronous with increasing depositions of sulfate. There is also clear evidence that Florida lakes are naturally acidic. Thus, paleoecological results indicate acidic deposition to be at certain contributor, but not necessarily the sole cause, of the recent further acidification of some naturally acidic Florida lakes.This is the tenth of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series.     

A diatom-based inference model for autumn epilimnetic total phosphorus concentration and its application to a presently eutrophic boreal lake

A diatom transfer function to infer epilimnetic total phosphorus (TP) concentration was derived using surface sediment diatom data from 68 medium-sized (10–1000 ha) lakes in Southern Finland. Publicly available monitoring records were used in lake selection to avoid gradients caused by pH and humic substances. Constrained and partially constrained ordinations indicated that TP was an important variable influencing diatom assemblages. A long floristic gradient in relation to TP was also apparent and therefore an inference model was developed for TP using unimodal-based regression and calibration methods. The final model included 61 lakes with epilimnetic TP concentrations between 3 and 89 g P l^–1, measured during the autumnal circulation period. It has a jackknifed-estimated root mean squared error of prediction of 0.16 log g P l^–1, a maximum bias of 0.28 log g P l^–1, and an r² _jack of 0.76.The model was tested in the presently eutrophic Lake Valkjärvi (epilimnetic [TP] 60–85 g P l^–1), located in Southern Finland. It successfully predicted the measured autumnal epilimnetic TP concentration for the past twenty years and the changes in inferred [TP] reflected disturbances known to have occurred before that time. The diatom-based inferences show that Lake Valkjärvi was oligo-mesotrophic as late as the 1930's and has become eutrophic because of nutrient inputs from agriculture and, especially, municipalities. However, epilimnetic TP concentration has not increased further.     

Development of paleolimnological inference models for pH, total nitrogen and specific conductivity based on planktonic diatoms

Canonical correspondence analysis (CCA was used to explore and identify statistically significant relationships between the distributions of planktonic diatoms and the physical and chemical properties of 50 Connecticut lakes. Six variables (pH, total nitrogen, calcium, sulfate, potassium and chlorophyll- a concentrations) were found to be significantly correlated with either or both of the first two extracted axes. The pH and calcium concentration, and to a lesser extent total nitrogen concentrations, were the most important variables controlling the distributions of planktonic diatoms in this suite of lakes. Paleolimnological inference models were developed for pH, total nitrogen (TN) and specific conductivity. Weighted averaging with (WAtol) and without (WA) tolerance downweighting, with and without bootstrap resampling techniques, and using either classical or inverse deshrinking methods were used to develop inference models for each variable. The pH and TN yielded sufficiently high 1/2 ratios and a highly significant first (constrained) axis when entered as single variables in both constrained and partially constrained CCA analyses, supporting the idea that reliable inference models could be developed for these variables. The r2 and RMSE of prediction values ranged from 0.73 to 0.86 and 0.37 to 0.6, respectively for pH, and from 0.4 to 0.64 and 59 g/l to 95 g/l, respectively for TN. Inference models for specific conductivity also yielded significant goodness-of-fit statistics. However, because specific conductivity was removed from the CCA analysis due to its high variance inflation factor and did not yield a significant relationship when entered as the sole variable in a partial constrained CCA, inference models for this variable will probably not yield any additional environmental information. The use of only planktonic diatoms in construction of inference models is discussed.     

A microtome for sectioning lake sediment cores at a very high resolution

A microtome device for sectioning sediment cores at a very high resolution down to 100 m is described. It is suitable for a variety of applications, but it is described in this paper specifically for diatom analysis. The aim is to facilitate the study of annual or even seasonal variations. The instrument is of simple design and is easy to manipulate.     

Chrysophyte cysts as paleolimnological indicators of environmental change due to cottage development and acidic deposition in the Muskoka-Haliburton region, Ontario, Canada

Chrysophyte cysts preserved in recent and pre-industrial lake sediment samples from 54 Muskoka-Haliburton (Ontario) lakes were used in a paleolimnological study to determine the impact of acidic precipitation and cottage development on water quality. A total of 246 cyst morphotypes were identified. Ecological preferences of cyst morphotypes were determined using multivariate statistical analysis, cluster analysis, and species-environment correlations. Recent cyst assemblages were related to water chemistry and lake morphometric variables using Redundancy Analysis (RDA). The distribution of morphotypes was related to a gradient of acid neutralising capacity (ANC), expressed through the association of variables related to buffering (i.e. longitude, watershed area, and ionic concentration) with the first axis (₁ = 0.29). Cyst assemblages were also defined, to a lesser extent (₂ = 0.06), by a trophic status gradient, created through the combination of total nitrogen (TN), total phosphorus (TP), volume-weighted cottage density, and lake depth variables. The identification of lakewater pH and trophic status as important determinants of cyst assemblage structure allowed for the reconstruction of acidification and eutrophication related water chemistry changes using fossil cyst assemblages. The reconstruction of pre-industrial (pre-1850) water quality conditions with fossil cyst assemblages indicated that pH significantly decreased in 24.1% of the study lakes and increased in 16.7% of the lakes. Increases in pH in more alkaline drainage basins are attributed to alkalinity generation processes induced by acidic precipitation as has been shown in other studies. Total phosphorus (TP) concentrations significantly declined in 12.9% of the lakes and increased in 16.6% of lakes. Increases in [TP] were linked to cottage development. Decreases in trophic status may be due to landuse changes, the result of the acidification occurring in the area, or warmer and drier climates. A comparison of chrysophyte cyst and diatom water quality inferences show similar trends in pH changes. There is a good agreement between diatom and chrysophyte bioindicators with respect to [TP] changes in oligotrophic lakes (< 10 g/L); however, diatom inferences suggest that lakes with current [TP] values greater than 10 g/L have decreased in trophic status over time, while chrysophyte reconstructions suggest that these same lakes have become more productive systems.     

Retene and resin acid concentrations in sediment profiles of a lake recovering from exposure to pulp mill effluents

The stratigraphy of resin acids (pimaric, isopimaric, sandaracopimaric, dehydroabietic and abietic acids) and base neutral compounds (retene, tetrahydroretene, dehydroabietin and fichtelite) in sediments of a lake recovering after the mill closure from exposure to effluents from sulphite pulp mill was studied. The highest concentrations of these compounds were detected 1.5 km downstream from the effluent pipe in sediment depth of 7–11 cm. This sediment layer is approximately 30 yrs old. The highest concentration of resin acids was 1100 and of retene 3300 g/g d.w. The retene concentration observed is the highest reported in the literature so far. The results imply that high concentrations of retene may be common in sediments of Finnish lakes polluted by pulp mill effluents.     

The sedimentary record of environmental lead contamination at St. Louis,Missouri (USA) area smelters

Southeastern Missouri has been a major Pb mining region since 1720 AD. Missouri mines produce a Pb ore that has a distinctive elevated ²⁰⁶Pb/²⁰⁷Pb isotopic ratio (>1.30) that is easily recognized in Pb-contaminated sediments. Five ²¹⁰Pb dated sediment cores from Horseshoe Lake, Madison County, Illinois were examined to reconstruct Pb-contamination of the site from southeastern Missouri mines and from a local Pb smelter located adjacent to the lake. Pb concentrations increased in the cores from 5 ppm in the early 1800s to approximately 350 ppm in the late 1940s and 1950s. Pb concentrations in recently deposited sediment range from 100 to 300 ppm depending on the location within the lake. Throughout the 1800s and early 1900s the ²⁰⁶Pb/²⁰⁷Pb ratios in the sediment cores increased indicating contamination from southeastern Missouri (mean = 1.243). After the local smelter began recycling lead-acid storage batteries in the 1950s, the ²⁰⁶Pb/²⁰⁷Pb ratio declined (mean = 1.224) suggesting contamination of Horseshoe Lake with Pb from sources elsewhere around the world. The results of this study demonstrate how isotopic ratios of Pb can be used to reconstruct historical anthropogenic contamination.     

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 eq 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 eq 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 is the second of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.     

Sub-sampling unconsolidated sediments: A solution for the preparation of undistrubed thin-sections from clay‐rich sediments

Using the principles of electroosmosis, a subsampling technique for clay-rich sediments is introduced that produces undisturbed thinsections from sediment cores. The fragile sample remains in the same disposable box throughout the process, preventing collapse of its structure during subsampling, manipulation and impregnation, as well as other potential problems.     

Processes affecting deposition of sediment in a small, morphologically complex lake

Devil Lake is morphologically complex as a result of Pleistocene glacial erosion of the Frontenac Axis of the Canadian Shield. In order to assess the processes causing highly variable sedimentation in the lake, we monitored currents, suspended sediment and temperature in the lake before and during autumn overturn in 2002. Strong summer thermal stratification (stability number to 0.11 s^–1 declining with the approach of overturn) was insufficient to prevent a dynamic response in the hypolimnion to wind forcing. Superimposed on a gradual increase in suspended sediment concentration in the last weeks of stratification from less than 2 g/l to about 30 g/l were shorter-term rises lasting up to several days. Associated with these events was an increase in particle size of the sediment from a mode of 40–50 to 150–200 m ascribed to flocculation from primary particles. These events culminated in rapid (<1 h) clearing of the water associated with strong, sustained winds over the lake, especially from the southwest. After overturn, the events were more frequent, and flocculation was unable to develop as well in the more vigorous circulation. However, currents in the hypolimnion occurred throughout the period before, during and after overturn with speed related to wind speed, but direction largely independent of wind direction. The results represent an approach to understanding the nature of sedimentary processes and thus to strengthening the use of sedimentary records as proxy in environmental and paleoenvironmental assessment.     

The history and impact of air pollution at Čertovo Lake,southwestern Czech Republic

This multi-disciplinary investigation documents the longterm effects of atmospheric pollution of metals and acids on a geologically sensitive catchment in the umava Mountains, southwestern Czech Republic, a region with a long history of human disturbance. A 30 cm long sediment core (I) from ertovo Lake was analyzed for natural and artifical radionuclides, metals, diatoms, chrysophytes, and pollen in sediments accumulated during the last 200 years. A second core (II), extending to 95 cm, included sediment judged to be free of atmospheric deposition of pollutants associated with the Industrial Revolution. Chronostratigraphic markers include several changes in the pollen assemblages corresponding to well-documented changes in land-use, and distinct distributions of ¹³⁷Cs, ¹³⁴Cs and ²⁴¹Am from weapons testing and the 1986 nuclear accident at Chernobyl, Russia. These markers corroborate the ²¹⁰Pb dating and, together, produce a reliable chronology extending back nearly to 1800 A.D.Stratigraphic profiles of Cu, Pb, and Zn in Core I are unlike any previously reported in the literature. Concentrations of Cu, Pb, and Zn remain generally above 100, 400, and 200 g g^-1, respectively, for the 200 years represented by Core I. These values are unusually high for sediments from a watershed with no known heavy-metal ore bodies. Accumulation rates for Cu, Pb, and Zn, which include both atmospheric and watershed contributions, are also high (ca 1, > 1 and > 1 g cm^-2 yr^-1, respectively) for the same period, although the anthropogenic contribution of Zn rose from nearly zero at 1800 A.D. The Cu and Pb accumulation rates rose dramatically about 1640 A.D.Accumulation rates of anthropogenically-derived Be, a relatively abundant element in the soft coals of the region, are also elevated by about 0.01 g cm^-2 yr^-1 in sediments of this period. Vanadium accumulation rates increased only since 1980 A.D., presumably along with increased consumption of oil.Diatom assemblages illustrate that the lake was acidic (pH between 4.5 and 5) through at least the past 200 years. The pH declined significantly (from ca 5 to 4) between 1960 and 1985 with a slight increase to 4.5 in the last few years. Recent diatom and chrysophyte assemblages suggest high trace metal concentrations, consistent with the present lake-water chemistry.     

Hydrologic control on the oxygen-isotope relation between sediment cellulose and lake water, western Taimyr Peninsula, Russia: Implications for the use of surface-sediment calibrations in paleolimnology

Systematic variability occurs between the oxygen isotopic composition of lake water sampled in mid-summer 1993 and cellulose extracted from surficial sediments of a suite of lakes spanning the forest-tundra transition near Noril'sk, Russia. Some tundra and all forest-tundra lakes show greater deviation from expected cellulose-water isotopic separation than forest lakes, apparently because of greater sensitivity to ¹⁸O-depleted snowmelt contributions. Cellulose derived from aquatic plants naturally integrates fluctuations in lake water ¹⁸O, providing a signal that is inherently more representative of average thaw season lake water ¹⁸O than the measure of instantaneous ¹⁸O obtained from an individual sample of lake water. Thus, indiscriminate use of empirical cellulose-water relations derived from calibration samples could lead to erroneous assessment of paleohydrology from the oxygen-isotope stratigraphy of sediment cores from arctic lakes. However, deviation from the expected cellulose-water fractionation is a source of lake-specific hydrologic information useful for qualifying paleoenvironmental interpretations and possibly constraining non-isotopic methods that rely on surface-sediment calibrations.     

Paleoecological evidence for diatom response to metal pollution in Lake Orta (N. Italy)

Diatom remains were analysed in two short sediment cores from a subalpine Italian lake (Lake Orta), known for its major industrial pollution dating from the late 1920s, which has only recently been stopped. Copper was recognised as the main toxic agent for diatoms during the first 30 years of pollution (peak value: 100 g l-1 in the late 1950s). A diatom community similar to other deep subalpine lakes existed in the past, and was disrupted by the pollution events. Acute and long-term effects of Cu contamination were tracked by changes in three distinct groups of species around the sharp boundary corresponding to the onset of the pollution. These groups were respectively composed of: (1) Species quickly extirpated by the discharge, mostly belonging to Fragilaria and Cyclotella and never reappearing; (2) Species apparently not affected, or not immediately affected, by the pollution, showing no definite trends with time. Synedra species, with various deformities, were conspicuous among these; (3) Species with accumulation rates increasing with time irrespective of pollution, mostly belonging to Achnanthes. Properties and tolerances of these groups (e.g. Synedra and Achnanthes) are discussed in detail.     

Setting minimum head capsule abundance and taxa deletion criteria in chironomid-based inference models

Criteria for removing training set lakes and taxa in chironomidbased inference models, due to low abundances, have largely been ad hoc. We used an anoxia inference model and a hypolimnetic oxygen model from southcentral Ontario to determine what effect subfossil head capsule abundance and taxa deletion criteria have on fossil inference statistics. Results from six training set lakes suggest that a minimum abundance of 40–50 head capsules is sufficient for use in inference models, however more diverse samples likely require more than 50 head capsules. Taxa deletion criteria substantially improved the predictive ability of inference models (lowered the root mean squared error of prediction (RMSEP)). The common practice of including taxa with only 2% abundance in at least two lakes was one of the deletion criteria that much improved inference models. Similar deletion criteria, such as 2% in at least 3 lakes and 3% in at least 1 lake, produced comparable improvements (up to 18% reduction in RMSEP).     

Sequential indicator conditional simulation and indicator kriging applied to discrimination of dolomitization in GER 63-channel imaging spectrometer data

Laboratory reflectance spectra of synthetic mixtures of the carbonate minerals calcite and dolomite were measured in the visible and near-infrared wavelength region (0.4–2.5 m) using a high-spectral resolution laboratory spectrometer. The instrument measured reflectivity with an accuracy of 0.001 m, allowing detailed resolution of the carbonate spectrum. The spectra of calcite and dolomite could be characterized by the presence of a strong absorption band centered at 2.3465 m for pure calcite and at 2.3039 m for pure dolomite. Nine mixtures of intermediate composition were analyzed demonstrating that the position of the carbonate absorption band is semilinearly related to the calcite content of the sample. Theoretically, this model allows mapping of dolomitization from high-spectral resolution remotely sensed imagery, GER 63-channel imaging spectrometer data from southern Spain were used to attempt such a mapping. First, pixels of vegetation were removed. For the remaining pixels, the wavelength center of the carbonate absorption band was detected and converted to a category of calcite fraction. The percentage of calcite for the remaining pixels was estimated using direct indicator kriging (IK) and sequential conditional indicator simulation, assuming that the calcite content could be represented as a category variable (SCIS category variable) and as a continuous variable (SCIS continuous variable). Four realizations of an SCIS (category variable) showed that on the average, 60 percent of the data was simulated in the same class and over 90 percent of the data within one class difference. A comparison with field samples showed that IK estimates of calcite content were within 20 percent accurate. The SCIS (continuous variable) does not perform as well with differences between –45% and +26% calcite; however, simulation reproduces the spatial variability better.     

1400-year cold/warm fluctuations reflected by environmental magnetism of a lake sediment core from the Chen Co, southern Tibet, China

Lake Chen Co, situated at 90°33–39E, 28°53–59N with a lake level of 4420 m asl, is an enclosed lake with 148 km² of catchment area and 40 km² of lake surface. It is mainly supplied by glacier melt water either from surface inflow or groundwater. Atmospheric precipitation is mainly concentrated in June–September. A 216-cm long lake sediment core was obtained at a site with 8 m of water depth, 800 m from the lakeshore and 1.5% of the bottom slope in this lake. The sediment core was taken by a piston sampler and was sliced with an interval of 1 cm each. ²¹⁰Pb dating measurement suggested that the average sedimentary rate was 0.16 cm yr^–1, which also was confirmed by ¹³⁷Cs peak occurrence. Magnetic analyses included low-frequency dependent susceptibility (_LF), susceptibility of anhysteretic remanent magnetism (_ARM), the saturation isothermal remanent magnetism (SIRM), the isothermal remanent magnetism (IRM) reverse and Soft and Hard contents were performed for the sediment core. Results showed that _LF was an index for reflecting the environmental conditions, but was not sufficient to reveal details of magnetic features. This had been proved by measurements of IRM Reverse percentage and Soft and Hard magnetic minerals values. The log(SIRM/_LF) had much more information to reveal environmental changes. The _ARM/_LF might be more sensitive to the local environmental conditions because it was well able to indicate the grain-size variations of magnetic particles. In the past ca. 1400 years, the warm stages were ca. 620–740 AD, 1120–1370 AD and since ca. 1900 AD. After an intensively cold stage during ca. 1550–1690 AD, a cold-humid stage from ca. 1690–1900 AD and a warm-dry stage since ca. 1900 AD followed. Among these stages, the warmest one occurred in ca. 1120–1370 AD and the coldest stage was between ca. 1550 and 1690 AD. This result might be compared with many other research results from lake cores, ice cores and the Chinese historical documents.     

Lacustrine ostracodes as hydrochemical indicators in lakes of the north-central United States

The modern ostracode distribution in lakes of the north-central United States shows how ostracode abundances are related to concentrations of major ions such as calcium, sulfate, and bicarbonate. These relationships are quantified for species living in lakes that range from fresh water (200 S cm^-1) to saline water (17 000 S cm^-1). Lakes located in the Minnesota forests have different ostracode assemblages and different water chemistry than lakes located on the prairie of North Dakota and South Dakota. These differences are attributed to differences in precipitation and rock-water interactions. Multivariate analyses of the ostracode and water chemistry data set indicate that different ostracode species are associated with different water types. For example, Limnocythere sappaensis and Heterocypris glaucus are found in bicarbonate-enriched sulfate-dominated waters, whereas Limnocythere staplini is found in bicarbonate-depleted sulfate-dominated waters. Candona ohioensis and Limnocythere itasca are found in fresh water, and Candona rawsoni is eurytopic and found in both bicarbonate-enriched and bicarbonate-depleted sulfate-dominated waters. Ostracodes can be used to identify changes in both ionic composition (solutes) and ionic concentration.This publication is the second of a series of papers presented at the Conference on Sedimentary and Paleolimnological Records of Saline Lakes. This Conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr Evans is serving as Guest Editor for this series.     

Calibration of diatoms along a nutrient gradient in Florida Everglades Water Conservation Area-2A, USA

The relationship between diatom taxa preserved in surface soils and environmental variables at 31 sites in Water Conservation Area 2A (WCA-2A) of the Florida Everglades was explored using multivariate analyses. Surface soils were collected along a phosphorus (P) gradient and analyzed for diatoms, total P, % nitrogen (N), %carbon (C), calcium (Ca), and biogenic silica (BSi). Phosphorus varied from 315-1781 g g^-1, and was not found to be correlated with the other geochemical variables. Canonical correspondence analysis (CCA) was used to examine which environmental variables correlated most closely with the distributions in diatom taxa. Canonical correspondence analysis with forward selection, constrained and partial CCA, and Monte Carlo permutation tests of significance show the most significant changes in diatom assemblages along the P gradient (p < 0.01), with additional species differences correlated with soil C, N, Ca, and BSi.Weighted-averaging (WA) regression and calibration models of diatom assemblages to P and BSi were developed. The diatom-based inference model for soil [P] had a high apparent r² (0.86) with RMSE_boot = 218 g g^-1. Indicator diatom species identified by assessing species WA optima and WA tolerance to [P], such as Nitzschia amphibia and N. palea for high [P] (~1300-1400 g^-1) and Achnanthes minutissima var. scotica and Mastogloia smithii for low [P] (~400-600 g g^-1), may be useful as monitoring tools for eutrophication in WCA-2A as well as other areas of the Everglades. Diatom assemblages analyzed by cluster analysis were related to location within WCA-2A, and dominant taxa within clusters are discussed in relation to the geochemical variables measured as well as hydrology and pH. Diversity of diatom assemblages and a Disturbance Index based on diatom data are discussed in relation to the historically P-limited Everglades ecosystem. Diatom assemblages should be very useful for reconstructions of [P] through time in the Florida Everglades, provided diatoms are well preserved in soil cores.     

Estimating and simulating the degree of serpentinization of peridotites using hyperspectral remotely sensed imagery

The mineral products resulting from the process of serpentinization, by which primary magnesium silicate minerals in peridotites are replaced by hydrous serpentine-group minerals, are of economic importance since Alpine-type peridotites are the host rocks for virtually all large asbestos deposits, which may be attributed mainly to the serpentine-group mineral chrysotile. Conventional field mapping of the distribution of highly serpentinized areas is time consuming and requires detailed sampling and laboratory analysis. In 0.4- to 2.5-m reflectance spectra of serpentinized peridotites, serpentinization is responsible for a decrease in contrast of olivine-pyroxene iron absorption features and an appearance and increase in OH^– absorption features near 1.4 m and 2.3 m associated with serpentine minerals. The degree of serpentinization is positively correlated with the depth of the 1.4-m and 2.3-m absorption features for samples containing more than 55 weight percent serpentine minerals. Small amounts of magnetite in a sample obscure the spectral contrast and decrease the overall brightness of weakly serpentinized samples. A methodology is used for mapping serpentine minerals in ultrabasic rocks from imaging spectrometer data, which includes (1) vegetation masking, (2) calculating the absorption band depth of the 2.3-m absorption feature in unmasked pixels, (3) translating this value into percent serpentine minerals using an empirical linear model, and (4) estimating the degree of serpentinization at the remaining locations using conditional simulation techniques or ordinary block kriging. From the results of this study, it can be concluded that mapping the degree of serpentinization from high-spectral resolution imagery is possible within marginal statistical fluctuations. Conditional simulation reproduces the spatial and statistical variability of the data set; however, it sacrifices the local accuracy. Direct estimation using ordinary kriging provides a better local estimate but does not honor the statistics and spatial dispersion of the original data.The spectral analyses presented in this publication were carried out at the Jet Propulsion Laboratory in Pasadena, California. The author would like to thank Mrs. Cindy Grove for her help in processing the samples. Dr. Harold Lang is thanked for advice in interpreting the spectra. The article benefitted from critical comments by Dr. Roger Clark and Dr. John Mustard, and various discussions with Prof. Salemon Kroonenberg and Prof. Andrea Fabbri. The Spectral Image Processing System (SIPS) developed at the Center for the Study of Earth from Space (CSES) of the University of Colorado, Boulder, was used for the GERIS data calibration. This article benefitted from a critical review by Dr. Daniel H. Knepper, Jr.