Feasibility of using near-infrared reflectance spectroscopy for the analysis of C, N, P, and diatoms in lake sediments

The present study explored whether rapid, non-destructive near-infrared reflectance spectroscopy (NIRS) could complement conventional paleolimnological and chemical analyses of sediment cores for greater efficiency and cost-effectiveness. The study used a 47-cm long freeze-core from the deepest point in Lake Arendsee, Mecklenburg Plain in northern Germany taken in 1993 to elucidate eutrophication history and to identify the pre-impact algal communities in this system. The core had been analyzed for total C, CO32-, N, P, and diatoms. Thirty-four of the 47 1-cm thick core sections were scanned by NIRS and calibrations were developed for total C, CO32-, N, P, N:P, total diatoms, and three dominant diatom species with different sedimentary profiles (Stephanodiscus binatus, Cyclotella rossii, and Fragilaria crotonensis). Total C ranged from 167-194 mg g-1 dry weight (d.w.), CO32- from 31.3-66.4 mg g-1 d. w., N from 9.9-17.4 mg g-1 d. w., and P from 0.7-6.0 mg g-1 d. w. Calibrations developed using multiple linear regression between NIR-predicted values and chemically-measured values were excellent for P (r2 > 0.99), good for C, N, and N:P (r2 > 0.93), and satisfactory for CO32-(r2 > 0.8). Calibrations for total diatoms and for individual species were highly statistically significant (r2 between 0.54 and 0.69). Although the calibrations are not useful for reliable predictions of the content of diatoms in the samples, the results indicate that NIRS detects spectral properties associated with diatoms or lake conditions when they were present, and that further work is warranted to attempt to improve the results. The study demonstrated that rapid, non-destructive, simultaneous analysis of total C, CO32-, N, P, and N:P in sediment cores is feasible.     

Pulp and paper mill pollution and subsequent ecosystem recovery of a large boreal lake in Finland: a paleolimnological analysis

Sedimentary diatom frustules and chironomid remains, in addition to the chemical stratigraphy of 32 elements and resin acids, were studied from short-core samples taken from two basins and a sheltered bay of Lake Päijänne in southern Finland (about 61 °10–62 °15 N, 25 °30 E). The lake was formerly oligotrophic but has been subject to effluent loading from pulp and paper mills during the past century since the opening of the first pulp mill in the 1880s. Four developmental phases were distinguished and named mainly according to the effects found in the basin close to the pollution source: (1) the pre-industrial phase (from the 1800s to ca. 1920), including the early years of industrialization, with low impacts; (2) the phase of increasing pollution (ca. 1920–1969); (3) the phase of severe pollution (1970–1981); and (4) the water protection phase (1982 onwards).Distinct differences were observed between pelagic (diatoms) and benthic (chironomid) ecosystems in their response to pollution. Effluent loading from the pulp and paper mills had a pronounced impact on chironomid assemblages, but only a slight influence on diatoms in the basin close to the pollution source. In the southern basin, approximately 60 km downstream, an increase in acidophilous species was observed in the diatom assemblages during the early years of pollution, but changes in chironomids in this basin were negligible. The water protection work of the past 30 years, which has led to an improvement in water quality and a marked recovery of the profundal biota, has also resulted in a slight increase in primary production of the lake. The decrease in brown-coloured effluent water has led to an increase in thickness of the lake's photic productive layer, while the toxicity of the water has simultaneously diminished. Rapid changes in chironomid assemblages and sedimentation observed in the sheltered bay highlight the importance of local land-use activities as causes of environmental change in this area, and especially their effects on sedimentation and benthic life.     

Responses of diatoms to the Younger Dryas climatic reversal in a South Carpathian mountain lake (Romania)

A high-resolution paleolimnological study from Lake Brazi, a small mountain lake in the Southern Carpathian Mountains, Romania, shows distinct diatom responses to late glacial and early Holocene climate change between ca. 15,750 and 10,000?cal?year BP. Loss-on-ignition, titanium, sulphur, phosphorus, biogenic silica content, and diatom assemblage composition were used as proxies for past environmental changes. Total epilimnetic phosphorus (TP) concentrations and lakewater pH were reconstructed quantitatively using diatom-TP and pH transfer functions. The most remarkable changes in the aquatic ecosystem were found at ca. 12,870 and 10,400?cal?year BP. Whereas the onset of the Younger Dryas (YD) climatic reversal was conspicuous in our record, the beginning of the Holocene was not well marked. Two diatom assemblage zones characterize the YD in Lake Brazi, suggesting a bipartite division of this climatic oscillation. The diatom responses to the YD cooling were (1) a shift from Staurosira venter to Stauroforma exiguiformis dominance; (2) a decrease in overall diatom diversity; (3) a decrease in lake productivity, inferred from DI-TP, organic matter, and biogenic silica content; and (4) a lowering of the DI-pH. Compositional change of the diatom assemblages suggested a sudden shift towards more acidic lake conditions at 12,870?cal?year BP, which is interpreted as a response to prolonged ice cover and thus shorter growing seasons and/or enhanced outwash of humic acids from the catchment. Taking into account the chironomid-based inference of only moderate July mean temperature decrease (<1?°C), together with the pollen-inferred regional opening of the forest cover and expansion of steppe-tundra, our data suggest that ecosystem changes in the Southern Carpathians during the YD were likely determined by strong seasonal changes.     

Chironomidae (Diptera) remains in surficial lake sediments from the Canadian Cordillera: analysis of the fauna across an altitudinal gradient

The altitudinal distribution of Chironomidae (Diptera) in the southern Canadian Cordillera was analyzed by means of head capsules preserved in surficial sediments of 30 lakes. Taxa characteristic of late-glacial deposits of southern, coastal British Columbia are extant at high elevations, particularly in the Rocky Mountains, and in large, deep, low-elevation lakes. Many chironomid taxa common at low elevations in the southern Canadian Cordillera were not found in alpine and upper subalpine lakes. These faunal differences are probably climatically related. The differences in fauna between high and low-elevation lakes parallel differences between arctic and temperate lakes.     

Spatial variability of chironomid death assemblages in the surface sediments of a fluctuating tropical lake (Lake Naivasha,Kenya)

Studies addressing within-lake variability of fossil chironomid assemblages are very few, and all deal with hydrologically stable temperate lakes where the question of spatial integration mostly relates to the mixing of faunal assemblages associated with shallow, warm-water habitat and those associated with deeper, cold-water habitat. Here we study within-lake variability of surface-sediment chironomid assemblages in the fairly large (∼100–170 km² since 1983) and shallow (Z _max = 5–8 m) fluctuating tropical lake basin of Lake Naivasha, Kenya, and compare the patterns observed with those in two smaller adjacent basins, one similarly shallow (Lake Oloidien, 5.1–5.7 km2, 5–8 m), the other deep and stratified (Crescent Island Crater, 1.9 km², 14–17 m). Chironomid assemblages were analysed in core-top samples and surface sediments along inshore to offshore transects, and how well individual samples represented the total (basin-wide mean) subfossil assemblage was considered both in terms of taxon richness and taxon percent composition. Within-lake variability of subfossil chironomid concentrations (with generally higher absolute values in nearshore samples) could be explained by effects of sediment winnowing and focusing, whereas between-lake variability reflected their relative susceptibility to wind-driven sediment disturbance or bottom anoxia. In all study lakes, but most significantly in lakes Naivasha and Oloidien, species distribution in the subfossil chironomid assemblages showed a strong nearshore to offshore gradient, which in these shallow lakes, reflects the dominant control of substrate and food quality on species distribution in the living community. Particularly in the larger basins, nearshore samples better represented the total lake assemblage than offshore samples, because the former always contained a component of mud-dwelling species whereas the latter often lacked a component of macrophyte-dwelling species. Our results show that although sedimentation dynamics in the shallow, wind-stressed Lake Naivasha is dominated by frequent resuspension and random sediment redistribution, the near- to offshore gradient in chironomid habitat remains imprinted on subfossil assemblages. We conclude that also in shallow fluctuating lakes, given sufficient size, incomplete pre-burial spatial integration of habitat-specific chironomid assemblages can be exploited for within-lake calibration of environmental gradients.     

A comparison of the Si/Al and Si/time wet-alkaline digestion methods for measurement of biogenic silica in lake sediments

Existing techniques for measuring sediment Biogenic Silica (BSi) concentrations rely largely on conventional (Si-only) wet-alkaline digestion methods. Although results have provided detailed palaeoenvironmental information, potential errors can arise in accounting for sources of non-BSi. Here, I compare a conventional Si-only method to a Si/Al wet-alkaline digestion method, which in theory provides a more robust correction for concentrations of non-BSi. Late glacial/Holocene-aged sediment from Lake Baikal, Russia was used for the comparison. Results showed no significant difference between the two techniques, indicating that existing Si-only BSi methods are suitable for reconstructing environmental changes when levels of digested non-BSi are low to moderate.     

Lithological and geochemical record of anthropogenic changes in recent sediments of a small and shallow lake (Lake Pusty Staw,northern Poland)

The article presents the results of lithological and geochemical investigations of recent sediments of Lake Pusty Staw. The analysed sediments document about 300 years of the history of this lake. Historical materials indicate that significant changes in the catchment of the lake took place from the beginning of the 18th century (deforestation and afforestation) followed by 19th century tourist development, and 20th century industrialisation. The sediments were dated using the ²¹⁰Pb and ¹³⁷Cs method and core lithology. These made it possible to establish a reliable chronology to the year 1730. The calculated sedimentation rates ranged between 0.17 and 0.83 cm year^–1. There was a period of intensified erosion caused by land clearance between 1734 and 1810, which resulted in an acceleration in sedimentation rate (0.36 cm year^–1) and a change of lithological type of sediment from detritus gyttja to clayey gyttja. On the basis of Cu, Zn, Cd and Pb content in the sediments, it was determined that the beginning of pollution of the lake dates back to the 19th century and was caused probably by the existence of a health resort. A systematic increase in pollution occurred in the 20th century as a result of industrial plants. Normalised with respect to Al, the content of heavy metals in polluted sediments was from several to twenty times higher than in sediments of the preindustrial period, and a comparison of historical materials with changes of sediments in most cases made it possible to identify the direct causes of the increase in pollution.     

Reconstruction of the recent history of a large deep prealpine lake (Lake Bourget,France) using subfossil chironomids,diatoms, and organic matter analysis: towards the definition of a lake-specific reference state

This paper presents the recent history of a large prealpine lake (Lake Bourget) using chironomids, diatoms and organic matter analysis, and deals with the ability of paleolimnological approach to define an ecological reference state for the lake in the sense of the European Framework Directive. The study at low resolution of subfossil chironomids in a 4-m-long core shows the remarkable stability over the last 2.5 kyrs of the profundal community dominated by a Micropsectra-association until the beginning of the twentieth century, when oxyphilous taxa disappeared. Focusing on this key recent period, a high resolution and multiproxy study of two short cores reveals a progressive evolution of the lake’s ecological state. Until AD 1880, Lake Bourget showed low organic matter content in the deep sediments (TOC less than 1%) and a well-oxygenated hypolimnion that allowed the development of a profundal oxyphilous chironomid fauna (Micropsectra-association). Diatom communities were characteristic of oligotrophic conditions. Around AD 1880, a slight increase in the TOC was the first sign of changes in lake conditions. This was followed by a first limited decline in oligotrophic diatom taxa and the disappearance of two oxyphilous chironomid taxa at the beginning of the twentieth century. The 1940s were a major turning point in recent lake history. Diatom assemblages and accumulation of well preserved planktonic organic matter in the sediment provide evidence of strong eutrophication. The absence of profundal chironomid communities reveals permanent hypolimnetic anoxia. From AD 1995 to 2006, the diatom assemblages suggest a reduction in nutrients, and a return to mesotrophic conditions, a result of improved wastewater management. However, no change in hypolimnion benthic conditions has been shown by either the organic matter or the subfossil chironomid profundal community. Our results emphasize the relevance of the paleolimnological approach for the assessment of reference conditions for modern lakes. Before AD 1900, the profundal Micropsectra-association and the Cyclotella dominated diatom community can be considered as the Lake Bourget reference community, which reflects the reference ecological state of the lake.     

Climatic and environmental change in Yanchi Lake, Northwest China since the Late Glacial: A comprehensive analysis of lake sediments

Modern climate research has shown that the Asian summer monsoon water vapor transport is limited to the eastern part of the Qilian Mountains. On the Holocene millennial-scale, whether the northwest boundary of the summer monsoon varies according to climate change is a key scientific issue. Yanchi Lake is located in the northern Qilian Mountains and the middle of the Hexi Corridor, where the modern climate is less affected by the Asian summer monsoon. It is a key research area for examining the long-term variations of the Asian summer monsoon. Paleoclimatic data, including AMS ^14C dates of pollen concentrates and bulk organic carbon, lithology, grain-size, mineral composition and geochemical proxies were acquired from sediments of Yanchi Lake. The chronological results show that the lower part of the lacustrine section is formed mainly in the Late Glacial and early Holocene period, while the proxies＇ data indicate the lake expansion is associated with high content of mineral salts. The middle part of this section is formed during the transitional period of the early and middle Holocene. Affected by the reworking effect, the pollen concentrates AMS^14C dates from the middle part of the section are generally older than those from the lower part. Since the mid-Holocene, Yanchi Lake retreated significantly and the deposition rate dropped obvi- ously. The Yanchi Lake record is consistent with the Late Glacial and Holocene lake records in the Qinghai-Tibet Plateau and the climatic records in typical monsoon domain, which indicate the lake expansion and the strong Asian summer monsoon during the Late Glacial and early Holocene. The long-term monsoonal pattern is different from the lake evolution in Central Asia on the Holocene millennial-scale. This study proves the monsoon impacts on the northwestern margin of the summer monsoon, and also proves the fact that the northern boundary of the summer monsoon moves according to millennial-scale climate change.     

Catastrophic hurricane history revealed by organic geochemical proxies in coastal lake sediments: a case study of Lake Shelby,Alabama (USA)

We developed a new method for reconstructing millennia-long hurricane records from coastal environments that uses Organic Geochemical Proxies (OGPs) of organic carbon and nitrogen concentrations and their δ¹³C and δ¹⁵N compositions. The new method is independent of presence/absence of sand layers and improves significantly the severe-storm history resolution. The subject of this investigation is a 1.5 m long sediment core raised at 2.8 m water depth from the center of Lake Shelby, Alabama, a freshwater lake located approximately 250 m from the Gulf of Mexico, from which an overwash sand-layer based record was previously derived. The core contains two distinct sediment units; an upper 62 cm thick, fine-grained, organic-rich lacustrine sapropel (gyttja) that shows no visible structures except one sand lamina at 23.7 cm depth, and an underlying 90 cm thick, organic-poor lagoon/estuary clay unit. The sapropel unit was deposited over a 682 ± 30 cal year time interval (1320–2002 A.D.) with a mean sedimentation rate of 0.79 ± 0.04 mm/year. Lake Shelby’s water column exhibits two contrasting states based on water chemistry surveys (i) an “isolated”, stratified, mode under calm weather conditions with a relatively low trophic state, and (ii) a “flooded” mode occurring during storm surges when nutrient-rich seawater floods the lake. Statistically significant δ¹³C and δ¹⁵N positive excursions in organic matter, up to maximum values of −25 (‰ PDB) and 4 (‰ Air N₂), respectively, are interpreted as geochemical responses to the marine intrusions that fertilize the lake, increase light availability, and cause eutrophication spikes. Detailed OGPs analyses crossing a sand layer that offers visual evidence of a catastrophic hurricane overwash event at 1717 A.D. exhibit large δ¹³C and δ¹⁵N positive shifts bounded by rapid returns to base values, thus confirming the validity of the hurricane identification by the OGPs model. Our data indicate that 11 catastrophic hurricanes hit the Alabama coast over the past 682 years with a rough recurrence interval of one in 62 years.     

Detecting ancient wild rice (Zizania spp. L.) using phytoliths: a taphonomic study of modern wild rice in Minnesota (USA) lake sediments

Wild rice (Zizania spp. L.) is a North American native grain with spiritual and dietary significance to many native people. Wild rice is also an important aquatic plant that provides critical habitat to wetland and aquatic wildlife. Past distribution of wild rice in North America is poorly understood, largely because of the limited taxonomic resolution of Poaceae pollen. A novel technique for detecting diagnostic Zizania silica phytoliths allows unambiguous identification of this taxon in lake sediments. We need to better understand modern depositional patterns of phytoliths in lake sediments, however, before attempting detailed paleoreconstructions. We analyzed distributions of diagnostic Zizania and other Poaceae phytoliths in modern sediments from three lakes with variable percent cover of wild rice and a non-wild rice control lake in central Minnesota. Absolute counts of phytoliths per gram sediment were achieved using an exotic diatom marker. Non-Zizania short-cell phytoliths, i.e. phytoliths from wetland grasses Phragmites australis and Muhlenbergia glomerata, dominate the assemblages in all lakes. Most Poaceae short-cell phytoliths appear to be derived locally, with little evidence for regional inheritance from eolian or alluvial processes. Because of anatomical differences in decay of plant debris and other taphonomic issues, Zizania inflorescence rondel phytoliths were most abundant, with morphotypes from other parts rarely encountered. Even in sediments under the densest wild rice stands, Zizania phytoliths contributed a maximum of 9 % to total Poaceae phytolith abundance. Lake morphology also affects the depositional pattern of phytoliths in modern sediments, so coring locations should be considered carefully. At least 500 phytoliths should be counted to detect a sufficient number of wild rice phytolith morphotypes. Diagnostic Zizania phytoliths are a reliable tool for wild rice detection in paleolake sediments.     

Evaluation of conservative lithogenic elements (Ti,Zr, Al,and Rb) to study anthropogenic element enrichments in lake sediments

In lake sediment investigations of heavy metal pollution history, it has become a common approach to calculate enrichment factors (EFs) by normalizing elemental distributions to a reference lithogenic element. However, this approach requires that the reference element remains stable once it has been deposited to the sediment (it is not affected by diagenetic processes). This is rarely studied in well-controlled field experiments. Here, we test the commonly used reference elements titanium (Ti), zirconium (Zr), aluminum (Al), and rubidium (Rb). We use a unique series of freeze cores collected in different years since 1979 in Lake Nylandssjön in northern Sweden. This lake has sediment with distinct varves (annually laminated deposit). Element concentrations in individual varves were analyzed using X-ray fluorescence (XRF) spectroscopy. By tracking the newly formed surface varve from different cores across this core series, i.e., following the element concentration in a specific varve as it becomes progressively aged, it was possible to assess the potential impact of diagenetic processes on geochemical signatures. Results confirm the conservative character of the studied elements; there was neither an increasing nor a decreasing concentration trend with time during sediment ageing for any of these elements. Secondly, we addressed the question ‘which of them is the most appropriate for EFs estimates with the aim of distinguishing anthropogenic from geogenic inputs, for example in pollution studies’. To assess the reliability of the EFs we used lead (Pb) as an example, because anthropogenic Pb in the sediment could be independently calculated using stable Pb isotopes. When anthropogenic Pb concentrations calculated with Pb-EFs were compared to the anthropogenic Pb concentrations derived from stable Pb isotopes, the differences found were 20% for Ti, 10% for Zr, 11% for Al, and 27% for Rb when upper continental crust concentrations were used for the background ratio. Based on the results from Nylandssjön our suggestions are that (1) when using EFs on a single core, which is the normal case in paleolimnology, multiple reference elements should be used together and (2) the results from those should be critically evaluated.     

Charcoal morphotypes in lake sediments from British Columbia (Canada): an assessment of their utility for the reconstruction of past fire and precipitation

Quantitative analysis of variations in morphological types of charcoal were undertaken in sediment cores from three lakes on the Interior Plateau (BC, Canada) over the period AD 1919–2000. Seven distinct morphological types of charcoal were identified based on particle shape and structural features and were compared with seasonal precipitation and recorded area burned within 20 km-radius of study lakes. Fragile-type charcoal fragments, termed type M, displayed significant relationships to recorded area burned in sediment cores from Prosser (r ² = 0.5; p = 0.0001) and Opatcho (r ² = 0.2; p = 0.02) lakes. However, nonsignificant correlations (p > 0.05) were found between total charcoal and area burned. Robust and highly elongated morphotypes C and F were correlated to recorded spring precipitation (r ² = 0.5; p = 0.002) in Opatcho Lake. Charcoal from a sediment core from Big Lake, the lake with the largest watershed, was significantly but inversely related to past fires (r ² = 0.44; p = 0.0003), suggesting important contributions from secondary transportation and deposition. Models were developed to infer relative area burned and precipitation for the study lakes. Our results suggest that charcoal morphotypes are related to the biogeoclimatic and lake watershed characteristics. This study also suggest that charcoal morphotypes can provide insights on past fire and climate, which was not possible based on traditional analysis of total charcoal.     

Effects of climatic change on biomass and biomass allocation in Leymus chinensis (Poaceae) along the North-east China Transect (NECT)

A field experiment was conducted to examine the effects of large-scale climatic changes on biomass and biomass allocation in Leymus chinensis on an 11 longitude gradient along the North-east China Transect (NECT) in 2000. Ten sites, selected for plant sampling along the gradient, experienced approximately uniform theoretical radiation, but differed in precipitation and geographical elevation. The total biomasses, vegetative shoot biomass and reproductive shoot biomass of the species increased from the west to the east with the decrease of aridity or the increase of precipitation, but that of rhizome biomass decreased in the spatial ranging from 116° to 120° E. Vegetative shoot biomass allocation increased from the west to the east along the gradient; rhizome allocations, however, dropped significantly. Unlike those of rhizome and vegetative shoot, reproductive shoot biomass allocations at the two ends were remarkably lower than that in the middle of the gradient. In general, the total and component biomass and their allocations showed strong correlation with precipitation or aridity index along the gradient.     

The late Pleistocene ostracod record of the crater lake sediments from Lago di Albano (Central Italy): changes in trophic status, water level and climate

Four cores (ranging between ca. 9 and ca. 14 m in length) from Lago di Albano in Central Italy were studied for their ostracod content, as well as algal and bacterial pigments, CaCO3 and concentration of organic matter. Cores PALB 94 1E and PALB 94 1C from Site 1, located at the bottom of a steep slope at 70 m water depth, where oxygen concentration is below 6 mg l-1, spans the Holocene and the late Pleistocene until 28 kyr B.P. (calibrated age). The other cores, PALB 94 6A and PALB 94 6B taken at a depth of 30 m, where oxygen is 7--11 mg l-1, represent mainly Pleistocene deposits.Ostracod valves were found in the lowermost ca. 3 m of the sequence at Site 1, dated to ca. 28--24 kyr B.P., and throughout the sequence from Site 6 which represents the interval 23--17 kyr B.P.Candona neglecta is the dominant species in most of the levels at Site 1, whereas both C. neglecta and Cyclocypris sp. dominate during different biostratigraphic zones at Site 6. The influx of springs entering the lake at Site 1 was inferred on the basis of species of the genus Potamocypris and Ilyocypris bradyi present in the record. Wide fluctuations in species abundance and assemblages in both coring sites indicate lake-water level oscillations between 28 to 17 kyr B.P. In particular, a strong rise in water level of the order of 40 m occurred between 24 and 23 kyr B.P. Fluctuations in productivity, oxygen availability and water temperature at both sites were also reconstructed on the basis of the ostracod assemblages and the algal and bacterial pigment concentrations. The environmental reconstruction reached using ostracod remains and pigments was verified with other proxy records published elsewhere such as invertebrate remains, diatoms, magnetic properties, etc. A synthesis of climatic reconstructions for Central and Southern Italy for the late Full Glacial is attempted on the basis of previous studies on hydrology, lithostratigraphy and palynology. Sharp fluctuations in lake palaeoproductivity/palaeoclimate recorded by invertebrate and pigment remains at both sites from Lago di Albano might be related to similar events reported in North Atlantic Full-Glacial records from marine and ice cores.     

Adsorption-desorption of phosphate and its availability in the sediment of a saline lake (Fuente de Piedra,southern Spain)

Seasonal changes of soluble reactive phosphorus concentrations in sediments of Fuente de Piedra, a saline lake, have been observed and linked to salinity changes. Phosphate availability in sediments was studied in the laboratory under different salinities, from 10 to 70 g L⁻¹. Changes in adsorption of dissolved phosphate appear to be controlled by salinity variations. The adsorption coefficient increases with salinity and the amount of phosphorus adsorbed ranged between 10 and 30 per cent of the total. Salinity-modulated adsorption is proposed as the primary mechanism explaining the seasonal dynamics of phosphorus in this saline lake and its effects on progressive eutrophication.