Freeze Core Research Articles

Carbon and nitrogen loss rates during aging of lake sediment: Changes over 27 years studied in varved lake sediment

We used a collection of ten freeze cores of annually laminated (varved) lake sediment from Nylandssjön in northern Sweden collected from 1979 to 2007 to follow the long‐term loss of carbon (C) and nitrogen (N) due to processes that occur in the lake bottom as sediment ages. We compared specific years in the different cores. For example, the loss of C from the surface varve of the 1979 core (sediment deposited during 1978) was followed in the cores from 1980, 1985, 1989, and so on until 2006. The C concentration of the sediment decreased by 20% and N decreased by 30% within the first five years after deposition, and after 27 yr in the sediment, there was a 23% loss of C and 35% loss of N. Because the relative loss of C with time was smaller than loss of N, the C:N ratio increased with increasing age of the sediment; the surface varves start with a ratio of ~10, which then increases to ~12.

Mentally Ill Could Pay Price for Bush Budget Cuts

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High spatial resolution analysis of lake sediment cores by laser ablationinductively coupled plasma-mass spectrometry (LA-ICP-MS)

A procedure is presented for the high-resolution analysis of lake sediment cores. Sections of a sediment core collected by freeze coring in a dimictic lake were prepared by slow drying. Clear visual laminations in the prepared sections indicated that the layering of accumulated sediments was preserved during sampling and sample preparation. Concentration profiles for Al, Si, Fe, S, As, Cu, and Zn at a 0.25-mm resolution were obtained for 2 core sections corresponding to pre-industrial and industrial periods. Detection limits of 0.09% for Al, 0.006% for Fe, 0.07% for S, 0.75% for Si, 0.7 µg g–1 for As, 68 µg g–1 for Cu, and 32 µg g–1 for Zn enable the analysis of these elements in the sediment samples. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis enabled the resolution of subannual patterns in element concentrations. In the lake studied, a regular, alternating pattern of Al and S concentrations appears to provide markers of annual sediment accumulation in the relatively uncontaminated layers of the core. In the more highly contaminated layers, LA-ICP-MS provides a suitable tool for the detailed study of pollution events.

Flood effects on invertebrates, sediments and particulate organic matter in the hyporheic zone of a gravel‐bed stream

Summary1. We investigated the effects of a flood on the fauna and physical habitat of the hyporheic zone of the Kye Burn, a fourth order gravel‐bed stream in New Zealand.2. Freeze core hyporheic samples (to 50 cm depth) and benthic samples (to 10 cm) were taken, along with measurements of vertical hydrological gradient, before, 2 days after and 1 month after the flood (estimated return period: 1.5 years, estimated Qmax = 10.4 m3 s−1).3. The composition of the hyporheos differed over the three sampling occasions with fewer taxa collected immediately postflood than preflood. The equitability of the community was higher on both postflood occasions, consistent with the reduced densities of two abundant taxa (Leptophlebiidae and Copepoda).4. Total invertebrate abundance was lower on the postflood occasions than preflood in both benthic (0–10 cm) and hyporheic (10–50 cm) sediments. Several taxa, including asellotan isopods and amphipods, recovered within 1 month of the event. Hyporheic densities of larval Hydora and nematodes did not differ among the three sampling occasions, but the water mite Pseudotryssaturus was more abundant 1 month after the flood than preflood. There was no evidence of vertical movements (to 50 cm) by any taxa in response to the flood.5. The proportion of fine sediments (<1 mm) in the subsurface sediments (10–50 cm) increased over the three sampling occasions and median particle size declined, but sediment porosity did not change. More particulate organic matter was found in the sediments after the flood.6. Our study provides little evidence that the hyporheic zone (to 50 cm) acted as a significant refuge during the flood event, although movements to or recolonisation from sediments deeper than 50 cm could explain the recovery of many crustacean and mite taxa within 1 month.

Habitat quality of historic Snake River fall Chinook salmon spawning locations and implications for incubation survival. Part 1: substrate quality

We evaluated substrate quality at two historic fall Chinook salmon (Oncorhynchus tshawytscha) spawning sites in the Snake River, Idaho, USA. The primary objective of this evaluation was to measure sediment permeability within these areas to determine the potential quality of the habitat in the event that anadromous salmonids are reintroduced to the upper Snake River. Riverbed sediments within the two sites in the upper Snake River were sampled using freeze cores and hydraulic slug tests. Sediment grain size distributions at both sites were typical of gravel-bed rivers with the surface layer coarser than the underlying substrate, suggesting the riverbed surface was armoured. Despite the armoured nature of the bed, the size of the largest material present on the riverbed surface was well within the size limit of material capable of being excavated by spawning fall Chinook salmon. The percentage of fines was low, suggesting good quality substrate for incubating salmon embryos. Geometric mean particle sizes found in this study compared to a 55% to 80% survival to emergence based on literature values. Hydraulic slug tests showed moderate to high hydraulic conductivity and were comparable to values from current fall Chinook salmon spawning areas in the Hells Canyon Reach of the Snake River and the Hanford Reach of the Columbia River. Predicted estimates of mean egg survival at both sites (48% and 74%) equalled or exceeded estimates from fall Chinook salmon spawning areas in the Hells Canyon Reach and the Hanford Reach. Copyright © 2005 John Wiley & Sons, Ltd.

Biogeochemical processes and microbial characteristics across groundwater-surface water boundaries of the Hanford Reach of the Columbia River.

Biogeochemical processes within riverbed hyporheic zones (HZ) can potentially impact the fate and transport of contaminants. We evaluated a modified freeze core technique for the collection of intact cobble-bed samples from the Columbia River HZ along a stretch of the Hanford Reach in Washington State and investigated microbiological and geochemical parameters of corresponding frozen and unfrozen samples. During three sampling periods (March, May, and November 2000), relatively high numbers of viable aerobic heterotrophic bacteria were recovered from both unfrozen (10(6)-10(7) cfu/g) and frozen samples (10(5)-10(6) cfu/g). Relatively large populations of sulfate-, nitrate-, and iron-reducing bacteria were present, and significant concentrations of acid-volatile sulfide were measured in some samples, indicating that anoxic regions exist within this zone. Cr(VI), a priority groundwater pollutant on adjacent U.S. Department of Energy lands, was probably removed from solution in HZ samples by a combination of microbial activity and chemical reduction, presumably via products of anaerobic microbial metabolism. These results suggest that biogeochemical processes in the Columbia River HZ may contribute to the natural attenuation of Cr(VI). Although freezing modestly diminished recovery of viable bacteria, freeze core techniques proved reliable for the collection of intact hyporheic sediments.

Hyporheic community composition in a gravel‐bed stream: influence of vertical hydrological exchange, sediment structure and physicochemistry

Summary 1. We studied the relative contributions of the magnitude and direction of vertical hydrological exchange, subsurface sediment composition and interstitial physicochemistry in determining the distribution of hyporheic invertebrates in the Kye Burn, a fourth order gravel‐bed stream in New Zealand.2. In winter 2000 and summer 2001, we measured vertical hydrological gradient (VHG), dissolved oxygen, water temperature and water chemistry using mini‐piezometers, each installed in a different upwelling or downwelling zone. Next to every piezometer, a freeze core sample was taken to quantify the sediment, particulate organic matter and invertebrates.3. Dissolved oxygen concentration at 25 cm was high on both occasions (>9 mg L−1) but was higher in winter than summer. Interstitial water temperature was higher in down than upwellings and was substantially higher in summer than winter. Other features of the subsurface sediments and interstitial nitrate–nitrite concentrations were similar on both occasions and in up and downwellings. Interstitial ammonium and soluble reactive phosphorous concentrations were higher in winter than summer and ammonium was higher in up than downwelling areas.4. The proportion of fine sediment (63 μm–1 mm), sediment heterogeneity and VHG accounted for the greatest proportion of variance in invertebrate distributions in both summer and winter.5. The hyporheos was numerically dominated by early instar leptophlebiid mayfly nymphs and asellotan isopods. Water mites were a taxonomically diverse group with 13 genera. Taxonomic diversity (Shannon–Weaver), but not taxon richness, was higher in upwelling areas, reflecting lower numerical dominance by a few taxa in these locations.6. Sediment composition (particularly the amount of fine sediments) and vertical hydrological exchange determined the composition and distribution of the hyporheos. Patchiness in these factors is important in planning sampling regimes or field manipulations in the hyporheic zone.

Freeze coring of soft surface sediments at a water depth of several hundred meters

A freeze corer was developed specifically for the sampling of unconsolidated surface sediments by in-situ freezing. The new device which is presented here is designed to be used to a water depth of up to 1000 meters and was successfully tested at a depth of 200 m. The corer consists of a high pressure resistant housing with a vacuum insulated jacket for the ethanol which can be chilled by separate cooling agents, adjustable stabilizing legs, an electrical pump and a freezing wedge of 100 cm length. The freeze coring can be performed from a platform or a boat by using only a single cable to pull it up or to lower it. All other equipment is inside of the resistant housing. The core sample can easily be cut into two distinct slabs by use of the freeze-protectors on the small sides of the freeze wedge.

Detecting patterns in hyporheic community structure: Does sampling method alter the story?

Hyporheic invertebrates were sampled in six small headwater streams draining pine, pasture, and native forest catchments. Sites were sampled in autumn and spring using three different hyporheic sampling methods (colonisation pots, pump sampling, and freeze‐coring). Total invertebrate abundance and taxon richness differed significantly among sites on both sampling occasions for pump samples, whereas freeze‐coring did not discriminate among sites, and pot samples showed significant differences in autumn, but not in spring. Differences among sites with respect to community composition were not consistent between sampling methods. Community ordination indicated that samples from colonisation pots tended to group together, whereas pump and freeze core samples were widely separated. Differences across land uses were also apparent (native forest sites formed a distinct cluster separated from pine and pasture sites). Results suggest that colonisation pots may provide a pathway for the entry of epigean organisms into the hyporheic zone even when hydraulic connectivity between surface and hyporheic zones is low. Invertebrate abundance was very low in pump samples, and this method also captured the fewest taxa of the three methods. The size bias known to exist with pump sampling techniques may restrict the usefulness of the method when comparing streams of differing hydraulic conductivity.

Freeze core sampling of the hyporheos: implications of use of electropositioning and different settling periods

Invertebrate densities and taxon richness in freeze cores were compared between three different settling periods (zero, two and seven days) as well as between samples taken with two variations of electropositioning and samples taken without electropositioning with a settling period. Species composition differed significantly among the three settling periods, but few significant differences were found in density or richness. Eriopterini were more abundant in hyporheic sediments (10-50 cm below sediment surface) in samples settled for two days than in those settled for seven days. Benthic densities (0-10 cm) of nematodes were higher in samples taken without a settling period than with either of the two settling periods. Electropositioned samples did not differ from non-electropositioned samples, except that benthic densities of leptophlebiid mayflies were significantly higher in electropositioned samples taken with a settling period than those without a settling period. The results of this study indicate that the length of settling period is of minor consequence when sampling hyporheic invertebrates (10-50 cm) and also provide little evidence of a benefit from electropositioning before freeze coring.

Biodiversity of stream invertebrate faunas in a Waikato hill-country catchment in relation to land use

Stream invertebrates were collected from 24 sites surrounded by a mixture of native forest and pasture in the Mangaotama catchment near Hamilton, Waikato, between 1992 and 1999. Sampling methods used included Surber sampling for benthic invertebrates, pump sampling, freeze coring and colonisation baskets for hyporheic invertebrates, and light, sticky and Malaise trapping for winged adults.A total of 188 stream invertebrate taxa were identified during the course of this work, the greatest number reported for any catchment in New Zealand. Of these, 85% were insects comprising largely Trichoptera (68 taxa or 36%), followed by Diptera (40 taxa, 21%) and then Ephemeroptera (23 taxa, 12%). Light-trapping in summer on four occasions coupled with benthic sampling once in summer yielded 81% of total recorded taxa. Streams that drained catchments entirely in pasture or native forest had similar percentages of total invertebrate taxa, and of the Coleoptera, Diptera and Ephemeroptera faunas. However, native forest sites had lower percentages of Mollusca and “other” taxa, and more Trichoptera, Plecoptera and Crustacea taxa than pasture sites. Stream invertebrate distributional patterns in the Mangaotama catchment suggest changes in community composition and loss of some species adapted to forest cover in catchments converted entirely to pasture.

A century-scale record of the preservation of chlorophyll and its transformation products in anoxic sediments

We have determined the chlorophyll pigment composition by liquid chromatography (LC) and LC/MS/MS in a 1.45-m long freeze core, representing 157 years of annually varved sedimentation, from Saanich Inlet, B.C, Canada. We investigated the very early diagenetic processes of chlorophyll a alteration in these anoxic sediments and the possible implications for palaeoproductivity studies. Excellent preservation of pigments is indicated by high total pigment concentrations, and the presence of labile compounds such as chlorophyllide a. The lack of systematic down core changes in both the total pigment concentration and the chlorin composition indicates that no detectable alteration of the pigment composition has occurred during the past 157 years. The sedimentary pigment composition is the result of processes occurring in the water column, or within few months after deposition. Chlorophyll derivatives corresponding to different diagenetic processes have distinct down core profiles. Profiles of compounds related to grazing activity steryl pyrophaeophorbide esters (SPE) and pyrophaeophytin a, are very similar. In contrast, dephytylated compounds (chlorophyllide a and phaeophorbide a), which are related to chlorophyllase activity during the degradation of ungrazed diatom cells, show an independent pattern. Quantifying pigment composition in Saanich Inlet sediments can help constrain processes regarding the transport of algal pigments to the sediments.

Freeze coring soft sediments in tropical lakes

A new freeze corer is described that is specifically designed for operation in warm tropical lakes. It combines the standard wedge-shaped freeze-on container with a 20-liter thermos from which pellets of solid CO2 descend into the wedge to replace those that have sublimated. This extends the duration of effective freezing from ~20 to ~45 min, sufficient to form an adequate thickness of frozen crust in warm (> 22 °C) lakes and prevent its premature melting during retrieval through the water column. The instrument contains no electrical components, which simplifies construction, operation, and maintenance. The front and back surfaces of the freeze wedge are fitted length-wise with serrated ridges to facilitate removal of the crust as four rectangular sediment slabs. The feasibility of freeze coring studies in tropical regions is mainly determined by the local availability of a large-volume dry ice producer.

The influence of three methods of gravel cleaning on brown trout, Salmo trutta , egg survival

Siltation of spawning gravels in upland rivers appears to be an increasing hindrance to salmonids' spawning success. River managers seek an effective and non-labour intensive means of loosening gravel and reducing fine material, so improving spawning success; this study compared three practical gravel cleaning techniques, applied at realistic (rather than intensive) levels, by assessing survival to hatching of buried brown trout, Salmo trutta L., ova at five sites on four rivers with gravel substrate in southern England. Each site consisted of six reaches, of which three were cleaned by tractor rotovating, high pressure jet washing and pump washing; these were compared with adjacent, untreated reaches. Brown trout ova were buried in both fine mesh and coarse mesh boxes in each reach. Significant improvements (at P<0·05) in survival (number of live alevins) were found in three of the five pump washed reaches, two of the five tractor rotovated reaches and one pressure washed reach when the data were analysed by site. When data from all five sites were analysed together, all treated reaches showed a significant improvement (at P<0·05) in egg survival to hatching compared with control reaches for fine mesh egg boxes; for coarse mesh boxes only pump washed reaches showed such an improvement. We feel that pump-washing provides the most effective, inexpensive and suitably non labour-intensive means of improving gravel, although ultimately it may be better to reduce the silt load of rivers. Freeze core bed samples taken before and immediately after cleaning were analysed for silt content; pump washing and high pressure washing may have reduced the amount of fine material. Copyright © 1999 John Wiley & Sons, Ltd.

Vertical distribution and abundance of invertebrates in two New Zealand stream beds: a freeze coring study

Distribution of the invertebrate fauna within the stony beds of two upland streams was examined by freeze coring to a depth of 30 cm. Faunas of both streams were dominated by aquatic insects, and the only abundant group that might typically be described as hyporheic was the Ostracoda. Of 34 taxa recorded in each stream 13 and 19, respectively, were found at depths of 20–30 cm. About 50% of individuals occurred in the upper 10 cm of both stream beds, but the depth distributions of four common taxa differed from each other and within each stream bed. The greater relative abundance of invertebrates at 20–30 cm in one stream may indicate that more individuals move down into the bed to escape predation by fish (absent from the second stream), or that a higher quality hyporheic food resource occurred there. Comparisons of invertebrate densities in freeze cores and Surber samples showed that the latter substantially underestimated the abundances of some taxa even in the top 10 cm of stream bed. This has serious implications for the estimation of production using conventional surface sampling methods.

Individual flood events detected in the recent sediments of the Petit Lac d'Annecy, eastern France

A 90-cm long freeze core from the Petit Lac d'Annecy was sampled at 1-cm intervals and studied using magnetic measurements, chemical element and pollen analysis. The results reveal four distinctive horizons in each of which the different lines of evidence point to deposition during a single, major flood event. The magnetic evidence shows that the sediment deposited in each event included a high proportion of surface-soil derived material and this inference is consistent with the geochemical and pollen records from these layers. No firm dates can be ascribed to these inwash events at present, but a tentative chronology derived for the core from 210Pb measurements, varve counting where possible, and correlation with a nearby, previously dated core, suggest that these flood events date from the late seventeenth to early nineteenth centuries. A tentative correlation is suggested between the single-event deposits and the record of summer/autumn floods during the period.

A direct comparison between the historical record of lake level and the δ18 O signal in carbonate sediments from Lake Turkana, Kenya

We compared oxygen isotopic profiles from authigenic calcite in nine freeze cores from Lake Turkana, Kenya, with the historical record of lake levels for the past 105 years. 210Pb dating of the cores indicates that sediment in two of the cores spans the complete historical record. We observed spatial variability in 6180 and 617C values between cores and an offset from expected isotopic equilibrium values in several of the cores. Both of these characteristics can be explained by proximity to river input. In model calculations of lake level, we muted the spatial variability of the S1*O dataset by using a normalized and stacked record. There is good agreement between the lake level history modeled using the normalized and stacked record and the historical record of lake level. The lake level record derived from the S180 data indicates that lake level fluctuated by 15 m during the last century. Our model calculations indicate that S’*O records can be used to generate quantitative lake level curves even using datasets with significant spatial variability. The isotopic composition of carbonates has been used in numerous lacustrine studies to determine paleoclimatic information. Fluctuations in the isotopic record preserved in carbonates are created mainly by variations in the temperature and composition of the water in which the carbonate formed. In turn, these variations can be caused by climatic changes in the lake basin. Carbonates are therefore potentially an archive of the paleoenvironment of a lake basin. In tropical or closed-basin settings, shifts in the oxygenstable isotopic composition (S180) of carbonates are often attributed to shifts in the evaporation-to-input (E : Z) ratio of a lake. Previous workers have used the relationship between changes in the S180 value of carbonates and the E: Z ratio of a lake basin to discuss qualitative changes in paleo-lake levels. Although the relationship between the &*O composition of lake water and the various inputs and outputs to a basin has been described quantitatively (Gat 1984; Phillips et al. 1986; Benson and White 1994), only one quantitative comparison between a historical lake level record and lake level determined from the aI80 composition of carbonates has been attempted (Li 1995).

Eutrophication history of Lake Arendsee (Germany)

At the maximum depth of Lake Arendsee (49.5 m) only a thanatocenosis could be found in a freeze core with a length of 52 cm. According to varve-counting, the fauna changed between 1960 and 1972, characteristic of mesotrophic to eutrophic state. The cause for eutrophication could be correlated with the sewage loading of the town of Arendsee and the drainage of Lake Fauler See into Lake Arendsee. Lake Arendsee did not yet recover from the loading because of the long retention time of 114 years. The investigation of the living meio- and macrobenthos of Lake Arendsee shows that the lower profundal is not colonized.

A paleolimnological study of eutrophied Lake Arendsee (Germany)

To study the algal microfossil assemblages of eutrophic Lake Arendsee (Germany) prior to the beginning of a restoration project, a 47-cm long freeze core, dating back to ca 1800, was taken from the deepest area of the lake. Based on the CRS modeled 210Pb and 137Cs profiles from the core, 1948 is around 15 cm and the sedimentation rate has increased from ∼ 21.2 mg cm-2 yr-1 in 1900 to ∼ 56.6 mg cm-2 yr-1 in 1986. The sediments were dominated by three centric diatoms. Stephanodiscus binatus, a species associated with eutrophic environments, dominated the upper 19 cm of the core. Cyclotella rossii, a species commonly found in less productive freshwater systems, was found to dominate the lower portion of the core and was absent above 16 cm. S. agassizensis was found throughout the core. In addition to the centric diatoms, three penate diatoms were found to be abundant. Fragilaria crotonensis was found throughout the core, but was most abundant from 19 cm to 16 cm. Asterionella formosa was prevalent below 15 cm, while Diatoma elongatum was found to be common from 17 cm to the surface. The abundances of algal remains of cyanobacteria, chlorophytes, cryptophytes and dinoflagellates decrease dramatically below 25 cm. Zooplankton remains were most abundant around 20 cm, with copepod spermatophores, fecal pellets and protozoa remains most common in the lower portion of the core. The major species shifts observed in the core from Lake Arendsee occur in a transition zone between 20 cm and 15 cm (1920–1940), a time when agricultural production was being increase with the use of inorganic fertilizer.

Varve formation since 1885 and high-resolution varve analyses in hypertrophic Baldeggersee (Switzerland)

According to their microstratigraphical composition the laminated sediments of Baldeggersee are true varves. Two varve time-series from freeze cores taken in the deepest part (66 m) of Baldeggersee have been analysed for annual and seasonal layers. The varve time-series covers the period of 1885 to 1993. The two freeze-cores from Baldeggersee can be accurately correlated by means of distinct layers (e.g. marker varves, turbidites), lithological units, and varve measurements. The Baldeggersee varve chronology has been checked by independent high-resolution137Cs dating. Mobility of cesium has not been detected in Baldeggersee. A highly positive correlation between phosphorus concentration in the lake water and median grain size of calcite crystals has been observed and allows, together with the results of geochemical analyses, to hindcast the trophic state in Baldeggersee for periods where no limnological data are available. The main features of the Baldeggersee varve time-series can be summarized as follows: before 1885 there are packets of 5–10 varves interrupted by massive, homogeneous marl beds, indicating oscillating hypolimnetic oxygen levels until the lake ultimately became anoxic in 1885. Between 1885 and 1905 varves are thin, with a high carbonate content. Between 1905 and 1910 the thickness of varves increased steadily, and an increase in calcite grain size suggests a major step in eutrophication. Median grain size values increase again at the end of the 1940s, whereas the thickness of the seasonal layers decreased between the early 1940s and the early 1960s. At the onset of the 1960s, during the time of highest epilimnetic phosphorus concentrations in Baldeggersee, the total phosphorus concentrations in the sediments as well as the varve thickness and the total accumulation rates all increased. At the beginning of the 1980s the median grain size decreased substantially as a result of lower phosphorus concentrations in Baldeggersee.