Problems with the application of diatom-total phosphorus transfer functions: examples from a shallow English lake

1. A diatom‐total phosphorus transfer function has been applied to a sedimentary diatom sequence from Groby Pool, a small shallow lake in Leicestershire, U.K. 2. Extensive aquatic plant records exist for Groby Pool dating back over two centuries. These records, in conjunction with selected aquatic pollen and herbarium diatom data, provide independent, qualitative evidence for the progression of eutrophication and its effects on aquatic plant communities and habitat structure. 3. Before 1800, Groby Pool was probably mesotrophic with clear water and a diverse submerged macrophyte community, but subsequently it experienced considerable nutrient enrichment. Key evidence for this includes: (i) historical plant records indicating the loss of species associated with mesotrophic waters and their replacement by others typical of eutrophic conditions, (ii) a significant increase in the percentage of planktonic diatoms in the lake sediment record (particularly Cyclostephanos dubius) after 1890, and (iii) increases in percentages of Stephanodiscus parvus and Cocconeis placentula in the second half of the twentieth century. 4. Diatom‐inferred total phosphorus (DI‐TP) estimates were inconsistent with the qualitative evidence for eutrophication at Groby Pool. In particular the DI‐TP profile was thought to overestimate phosphorus during the period of dominance by small Fragilaria spp. before 1890, and to misjudge the timing and direction of subsequent changes in nutrient loading. 5. This study highlights some of the problems associated with the application of diatom‐TP transfer functions to sedimentary diatom sequences from shallow lakes. The major problem relates to the frequent dominance of non‐planktonic diatoms in the sediments of these systems, many species of which (particularly small Fragilaria spp.) appear to be more sensitive to changes in habitat availability than to phosphorus. Potential ways of improving diatom‐TP models via altered approaches to sampling are suggested.     

LIFE CYCLE OF A STEPHANODISCUS SP. (BACILLARIOPHYTA)1

Studies of the life cycle of a centric diatom, tentatively identified as Stephanodiscus neoastraea Håkansson & Hickel, showed that sexual reproduction occurred every year in a freshwater lake (Lough Neagh, Northern Ireland). Male and female gametes were produced in cells below 55% of the maximum diameter during a 3–4-week period in late summer, following the return of nitrate concentrations above 10 μM NO_3-N. The frequency of sexual reproduction was linked to the cycle of diameter size reduction and regeneration. The times of largest decreases in cell diameter were during nutrient stress in summer and low light conditions in late autumn, rather than during the main spring growth period. So, environmental conditions (combined with the limited life-spans of individual cells) affected the rate of diameter reduction and, therefore, the length of the life cycle (3–4 years).     

Diatom preservation: experiments and observations on dissolution and breakage in modern and fossil material

Selected aspects of diatom preservation in both laboratory and field environments are examined with a view to improving techniques and to help understand why only some lake sediments have good diatom preservation.Laboratory measurements of biogenic silica following diatom dissolution by alkali digestion are questioned because results are shown to be dependant on initial sample size. Diatom breakage experiments identified drying carbonate rich sediment as a major cause of fragmentation of the large robust diatom Campylodiscus clypeus Ehrenb. Diatom dissolution experiments in carbonate media indicated that carbonate rich lakes should preserve diatoms better in order of the particular alkali metal type (Ca > Mg > Na). A preliminary assessment of the role of depth in diatom preservation is made for Lake Baikal where partly dissolved Cyclotella are more common in deep water surface sediments. The effect of time on diatom dissolution is examined in a saline lake sediment core and by comparing dissolution rates of recent and geologically old diatom samples in the laboratory. A simple link between diatom dissolution and sample age was not established. Factors thought to be important in controlling diatom preservation in lake sediments are discussed.     

Climate drivers of diatom distribution in shallow subarctic lakes

相似文献   

Aulacoseira subarctica: taxonomy,physiology, ecology and palaeoecology

Knowledge of the morphology, taxonomy, physiology, ecology and palaeoecology of the filamentous freshwater diatom Aulacoseira subarctica (O. Müller) Haworth is reviewed from the literature. The species is widely distributed across Northern Europe, Scandinavia and North America, Japan, China, Australia and New Zealand, in the last usually as fo. subborealis. The species is rare in the Tropics and positive identifications are lacking for Africa. The importance of correct identification is stressed because literature reports of its occurrence often need revision. A comparison is made between two sites with detailed records of its seasonal cycle. Blelham Tarn, England, is a clear-water seasonally stratified lake; Lough Neagh, Northern Ireland, is a very large turbid and unstratified lake. In spite of their contrasting characters, Aulacoseira subarctica succeeds in both lakes. In Blelham Tarn, there is a strong seasonal cycle of growth, dormancy on the sediment and further growth on re-suspension. In Lough Neagh, there is a large deposition of cells at the end of the spring bloom but few of these cells survive grazing by benthic animals. Fossil occurrences are summarized from the species’ initial appearance in the Pliocene and its later occurrence during the last inter-glacial (Eemian) deposits in NW Europe, where it is an important ecological indicator. Palaeolimnological studies are reviewed to describe the contemporary distribution and ecological preference of this widespread diatom. Aulacoseira subarctica usually appears in response to moderate increases in nutrients but is disadvantaged by further enrichment. In Blelham Tarn the species only became abundant during the twentieth century, reaching a peak between 1930 and 1960. With nutrient enrichment, abundance has declined. In Lough Neagh, it has been present for much of the post-glacial period and still thrives today in spite of the highly enriched state of the lake. The species has disappeared from many eutrophic lakes and its sustained existence in Lough Neagh is anomalous. Lough Neagh may continue to offer a favourable habitat in spite of the poor light climate because the water depth, lack of stratification and long water retention time reduce losses to a sustainable level.     

The Nitrogen Cycle in Lough Neagh,N. Ireland 1975 to 1987

Results from thirteen years of weekly observations are presented on the nitrogen cycle in Lough Neagh. The data comprised catchment and atmospheric inputs, output via the outflow and calculated losses by sedimentation and denitrification. Nitrate-nitrogen in the rivers is the dominant input fraction and the nitrate loading has increased over the period observed. 52 % of the input N sediments to the lake bottom, but 65 % of this is lost by denitrification. In spite of increasing nitrogen inputs, the summer soluble nitrate concentrations have decreased due to uptake by a perpetual crop of the cyanobacterium Oscillatoria agardhii GOMONT .     

Interpretation of lake quality from contemporary diatom assemblages

Diatom assemblages from the topmost sediment of 49 lakes were ordinated by means of a program for detrended correspondence analysis and reciprocal averaging (Decorana). Five lake groups were separated, each having more or less characteristic diatom assemblages and water quality. Shifts from one group to another caused by factors such as acidification, artificial drainage, diffuse nutrient loading and sewage are discussed.     

Effects of increased salinity on the diatom assemblage in Fonda Lake,Michigan

A salt storage facility has been located adjacent to Fonda Lake since 1953. In February 1981 a core was taken from the profundal sediments of the lake and analyzed to determine the effects of salt perturbation on the diatom community over a 32-year period. Diatom assemblages from different levels were compared using multivariate techniques including cluster analysis and principal component analysis. Shifts in diatom composition related to salinification were revealed most clearly by subdominant taxa. Five distinct groups of diatom taxa were found to correspond with 5 depth intervals. The diatom component of the lake up to 1960 included two groups of taxa which were alkaliphilous and chloride indifferent. A reduction in species diversity beginning in 1960 may indicate a salt effect. By 1968, when diversity reached a minimum, a variety of halophilic taxa (including Diatoma tenue, Navicula gregaria and Synedra fasciculata) attained their highest relative abundances. At the top of the core, diversity increased slightly and some halophilic taxa decreased in relative abundance, which suggests a possible decrease in salt loading to the lake.     

Nutrients exert a stronger control than climate on recent diatom communities in Esthwaite Water: evidence from monitoring and palaeolimnological records

1. A long‐term monitoring programme on phytoplankton and physicochemical characteristics of Esthwaite Water (England) that started in 1945 provides a rare opportunity to understand the effects of climate and nutrients on a lake ecosystem. 2. Monitoring records show that the lake experienced nutrient enrichment from the early 1970s, particularly after 1975, associated with inputs from a local sewage treatment plant, resulting in marked increases in concentration of soluble reactive phosphorus (SRP). Climatic variables, such as air temperature (AirT) and rainfall, exhibit high variability with increasing trends after 1975. 3. Diatom analyses of an integrated ²¹⁰Pb‐dated lake sediment core from Esthwaite Water, covering the period from 1945 to 2004, showed that fossil diatoms exhibited distinct compositional change in response to nutrient enrichment. 4. Redundancy analysis (RDA) based on diatom and environmental data sets over the past 60 years showed that the most important variables explaining diatom species composition were winter concentrations of SRP, followed by AirT, independently explaining 22% and 8% of the diatom variance, respectively. 5. Additive models showed that winter SRP was the most important factor controlling the diatom assemblages for the whole monitoring period. AirT had little effect on the diatom assemblages when nutrient levels were low prior to 1975. With the increase in nutrient availability during the eutrophication phase after 1975, climate became more important in regulating the diatom community, although SRP was still the major controlling factor. 6. The relative effects of climate and nutrients on diatom communities vary depending on the timescale. RDA and additive model revealed that climate contributed little to diatom dynamics at an annual or decadal scale. 7. The combination of monitoring and palaeolimnological records employed here offers the opportunity to explore how nutrients and climate have affected a lake ecosystem over a range of timescales. This dual approach can potentially be extended to much longer timescales (e.g. centuries), where long‐term, reliable observational records exist.     

Sediment diatom assemblages and composition of pore-water dissolved organic matter reflect recent eutrophication history of Lake Peipsi (Estonia/Russia)

A paleolimnological approach was used for the assessment of the recent eutrophication history and identification of possible reference conditions in the large, shallow, eutrophic Lake Peipsi. Lake Peipsi is the fourth largest lake by area, and the largest transboundary lake in Europe, being shared between Estonia and Russia. Lake Peipsi has been anthropogenically impacted over a longer time-scale than that covered by instrumental limnological monitoring. The ²¹⁰Pb record and down-core distribution of fly-ash particles in the 40-cm core from the middle part of the lake suggest 130 years of sediment accumulation. Diatom assemblages indicate alkaline mesotrophic conditions and a well-illuminated water column, sediment pore-water fluorescence index values suggest low autochthonous productivity and a stable aquatic ecosystem similar to natural reference conditions during the second half of 19th and early 20th century. Near-synchronous stratigraphic changes including the expansion of the eutrophic planktonic diatom Stephanodiscus parvus, the appearance of new species associated with eutrophic lakes and the decrease in the relative abundance of littoral diatoms, together with changes in the fluorescence properties of sediment pore-water dissolved organic matter, imply increased nutrient availability, enlarged phytoplankton crops, reduced water-column transparency and the onset of human-induced disturbances in the lake since the mid-20th century. The most conspicuous expansion of eutrophic planktonic diatoms and maximum concentration of siliceous microfossils occur simultaneously with changes in the fluorescence indexes of pore-water dissolved organic matter, indicating a pronounced increase in the contribution of autochthonous organic matter to the lake sediment. This implies that nutrient loading and anthropogenic impact was at a maximum during the 1970s and 1980s. Sedimentary diatom flora may reflect a reduction of phosphorus loading since the 1990s. However, the absolute abundance of planktonic diatoms and sediment pore-water fluorescence index values vary greatly implying that the lake ecosystem is still rather unstable.     

A comparison of sedimentary and diatom-inferred phosphorus profiles: implications for defining pre-disturbance nutrient conditions

Interpreting sedimentary phosphorus profiles in terms of changes in the historical P load is difficult due to variable retention and post-depositional diagenesis. An alternative approach is to use diatom assemblages in surface sediments and derive a transfer function for epilimnetic SRP and total P concentrations using weighted average regression and calibration. The obtained relationship can then be applied to down-core changes in sedimentary diatom assemblages and diatom-inferred P (DI-P) used to assess historical changes in epilimnetic P-concentrations. A diatom-phosphorus calibration data set for 43 eutrophic lakes in Northern Ireland has been constructed and applied to two small eutrophic lakes (Lough Mann, White Lough). DI-total P (i.e. predicted) is highly correlated with observed TP (r ² = 0.75) for the surface-sediment training data-set. The resultant changes in DI-P derived from application of the transfer function to down-core changes in diatom assemblages are compared to sedimentary P concentrations. The latter are highly variable, presumably due to redox-derived effects, while DI-P profiles are more readily interpretable, and agree with other stratigraphic records of lake eutrophication. The method offers a good possibility of defining pre-disturbance (i.e. natural) phosphorus concentrations in lakes with associated implications for lake-restoration programmes.     

Diatom elemental and morphological changes in response to iron limitation: a brief review with potential paleoceanographic applications

Diatoms are a major group of phytoplankton that account for approximately 40% of the ocean carbon fixation and the vast majority of biogenic silica production through the construction of their cell walls (termed frustules). These frustules accumulate and are partially preserved in the ocean sediments. Diatom growth and nutrient utilization in high‐nitrate, low‐chlorophyll regions of the world’s oceans are mostly regulated by iron availability. Diatoms acclimate to iron limitation by decreasing cell size. The associated increase in surface area‐to‐volume ratio and decrease in diffusive boundary layer thickness may improve nutrient uptake kinetics. In parallel, cellular silicon (Si) contents are elevated in iron‐limited diatoms relative to nitrogen (N) and carbon (C). Variations in degree of silicification and nutritional requirements of iron‐limited diatoms have been hypothesized to account for higher cellular Si and/or lower cellular N and C, respectively. However, in some diatoms, frustule silicification does not significantly change when cells are iron‐limited. Instead, changes in the Si‐containing valve surface area relative to volume within these diatoms is hypothesized to be responsible for the variations in the cellular Si : N and Si : C ratios. In particular, some examined iron‐limited pennate diatoms have reduced widths relative to their lengths (i.e. lower length‐normalized widths, LNW) compared to iron‐replete cells. In the pennate diatom Fragilariopsis kerguelensis, the mean LNWs of valves preserved in sediments throughout the Southern Ocean (a well‐characterized iron‐limited region) is positively correlated with satellite‐derived, climatological net primary productivity in the overlying waters. Because of the specific morphological changes in pennate diatom frustules in response to iron availability, the valve morphometerics (e.g. LNWs) can potentially be used as a diagnostic tool for iron‐limited diatom growth and relative changes in the Si : N (and Si : C) ratios in extant diatom assemblages as well as those preserved in the sediments.     

A study of Lough Corrib,western Ireland and its phytoplankton

During 1980/1981, a twelve month study was carried out on the phytoplankton of Lough Corrib, a large freshwater lake in western Ireland. Cell counts indicated low phytoplankton productivity and this was reflected in low chlorophyll a values and high Secchi readings. Diatoms predominated in spring and were succeeded by blue-green algae in late summer. The spring diatom crop was apparently limited by either silicate or nitrogen. Mineral uptake by rooting macrophytes and benthic algae and phosphate recycling as a result of bottom sediment disturbance may be important elements in the nutrient cycling regime of the lake. Differences in morphology between the upper and lower basins of the lake are reflected, to some extent, in species composition and areal productivity.     

Salmon‐derived nutrients drive diatom beta‐diversity patterns

1. Pacific salmon are a textbook example of migratory animals that transfer nutrients between ecosystems, but little is known about how salmon‐derived nutrients (SDN) affect the biodiversity of recipient freshwater ecosystems. We examined paleolimnological records from six Alaskan lakes to define how changes in SDN from sockeye salmon (Oncorhynchus nerka) influenced sedimentary diatom community structure and beta‐diversity among lakes and through time. 2. Using an isotopic mixing model, we showed that SDN loading could account for >80% of the lake total nitrogen budgets and strongly regulated diatom community composition. Spatial dissimilarity in diatom communities was positively related to differences in SDN among lakes (r² = 0.69, P < 0.01, n = 10). Likewise, temporal dissimilarity in diatom communities was positively related to differences in SDN in a sediment core with substantial variation in salmon spawner dynamics between 1700 and 1950 AD (r² = 0.34, P < 0.01, n = 19). Finally, beta‐diversity metrics quantifying temporal turnover within each lake’s sediment record were also positively related to the variance in SDN loading among lakes (r² = 0.88, P < 0.05, n = 5). Mean SDN was only negatively correlated to temporal diatom beta‐diversity. 3. Spatially subsidised systems often receive temporally variable resource inputs, and thus, it is not surprising that, unlike previous studies, we found that resource variability was the key driver of community composition and beta‐diversity. In habitats that receive strongly fluctuating external nutrient loads, environment heterogeneity may overweigh stochastic community processes. In addition, freshwater diatoms are characterised by great dispersal capabilities and short life cycles and therefore may be a more sensitive indicator for evaluating the role of resource variability than previously used model organisms. These results suggest that productivity–diversity relationship vary with the nature of nutrient loading and the life history of the community studied. 4. Overall, our study highlights that the transport of nutrients by sockeye salmon across ecosystem boundaries is a significant driver of algal community and biodiversity in nursery lakes, mainly through changing the magnitude of nutrient variation. As such, freshwater species diversity in regions like the U.S. Pacific Northwest may become impoverished where there have been long‐term declines in salmon populations and decreases in nutrient variability among lakes.     

Spatial heterogeneity of diatom silicification and growth in a eutrophic reservoir

相似文献   

Monitoring lake recovery from point-source eutrophication: the use of diatom-inferred epilimnetic total phosphorus and sediment chemistry

1. Diatom and geochemical responses to reduced nutrient loading were followed in a small, monomictic eutrophic lake in Northern Ireland by use of short sediment cores taken c. 15 years after redirection of creamery waste away from the lake. 2. Epilimnetic total phosphorus (TP) concentrations (fig TP 1-^?1) were estimated for the period 1850–1990 using weighted averaging regression and calibration. Background TP levels, inferred using the diatom model, were c. 35μg TP 1-^?1 and increased to >140μg TP 1-^?1 in the late 1960s to early 1970s. Total P concentrations dropped to 80 μg TP 1-^?1 within 5 years of waste diversion (c. 1978–79), but varied between 1980 and 1990 (range 70–140 μg TP 1-^?1), perhaps due to internal loading, occasional continued disposal from the creamery and natural variations in stream P load. 3. Diatom-inferred TP concentrations were compared with monitored data where available, and the diatom model tended to overestimate TP concentrations by about 25 fig TP 1-^?1. Possible reasons for this are discussed (errors in the diatom model, stratigraphic variability, variability in the monitoring data). 4. Post-1980 geochemistry profiles (concentrations and accumulation rates) indicated some changes when compared with sediments deposited before 1980, perhaps reflecting the redirection of the creamery waste and reduced productivity of the lake (e.g. reduced calcium deposition). Phosphorus concentrations in the sediments changed very little over the last 150 years and, while sedimentary TP fluxes (g cm^?2 yr^?1) increase steadily up-core, they do not record the effluent redirection in the mid-1970s. There is, however, some indication of a slight lowering of P retention in the most recent sediments (1985–90). 5. The general implications of such an approach to monitoring (i.e. the use of short cores) are discussed and the value of diatom-inferred TP assessed. Diatom models offer the possibility of determining background TP concentrations and indicate that, despite the redirection of the creamery waste over 15 years ago, the pre-creamery epilimnetic TP concentrations have not yet been reached.     

Changing nutrient levels in Grasmere, English Lake District, during recent centuries

1. Historical nutrient changes in Grasmere were investigated using a 300‐year record derived from six sediment cores. One core was investigated at high resolution for diatoms, total sedimentary phosphorus, and loss‐on‐ignition (LOI), and was dated using ²¹⁰Pb and ¹³⁷Cs. Six other cores were scanned for magnetic susceptibility, diatoms and LOI to confirm the stratigraphic integrity of the primary record. 2. A rise in nutrient levels occurred after 1855 AD. This event was marked by a shift away from benthic diatom assemblages and a rise in Asterionella formosa. The onset of eutrophication from 1855 corresponds to the expansion of the local and tourist population in the area. 3. The replacement of A. formosa with Cyclotella spp. ca 1945–65 indicates reduced nutrient loads, possibly because of enhanced flushing brought about by the seasonal rainfall distribution. 4. After 1965 a step‐wise increase in both absolute and relative amounts of Asterionella was found. High sedimentary P and diatom inferred TP confirmed the high nutrient loading of the lake. Nutrient increase is attributable to problems with the Grasmere village sewage system and the installation of a wastewater treatment works (WwTW) on the River Rothay in 1971. Modifications to the WwTW in 1982 caused an initial improvement, but have not led to a full recovery to pre‐1965 ecological conditions. 5. The diatom record indicates a further improvement after 1990 by a return toward Achnanthes minutissima. 6. The sedimentary archive of sensitive sites provides important benchmarks against which to judge the attainment of water quality targets.     

Change of microplankton community structure in response to fertilization of an arctic lake

Microplankton in an oligotrophic arctic lake were assessed by direct counts for one summer prior to nutrient additions and three summers during which inorganic nitrogen and phosphorus were added to the lake at approximately ten times ambient loading rates. Protozoa increased significantly in both number and biomass following fertilization, and community structure changed from dominance by oligotrichs prior to fertilization to dominance by the bacterivorous peritrich Epistylis rotans in the second and third years of fertilization. Rotifer abundance and biomass was not significantly different among summers, although one species, Conochilus natans that had not been seen previously, was present during the second and third year of fertilization. By the third year of fertilization both protozoan and rotifer biomass had declined from peak levels, while crustacean zooplankton nauplius abundance had increased suggesting the emergence of top-down regulatory controls as the lake became eutrophic.     

Sensitivity and responses of diatoms to climate warming in lakes heavily influenced by humans

相似文献   

THE INFLUENCE OF SUBMERGED MACROPHYTES ON SEDIMENTARY DIATOM ASSEMBLAGES1

Submerged macrophytes are a central component of lake ecosystems; however, little is known regarding their long‐term response to environmental change. We have examined the potential of diatoms as indicators of past macrophyte biomass. We first sampled periphyton to determine whether habitat was a predictor of diatom assemblage. We then sampled 41 lakes in Quebec, Canada, to evaluate whether whole‐lake submerged macrophyte biomass (BiomEpiV) influenced surface sediment diatom assemblages. A multivariate regression tree (MRT) was used to construct a semiquantitative model to reconstruct past macrophyte biomass. We determined that periphytic diatom assemblages on macrophytes were significantly different from those on wood and rocks (ANOSIM R = 0.63, P < 0.01). A redundancy analysis (RDA) of the 41‐lake data set identified BiomEpiV as a significant (P < 0.05) variable in structuring sedimentary diatom assemblages. The MRT analysis classified the lakes into three groups. These groups were (A) high‐macrophyte, nutrient‐limited lakes (BiomEpiV ≥525 μg · L^?1; total phosphorus [TP] <35 μg · L^?1; 23 lakes); (B) low‐macrophyte, nutrient‐limited lakes (BiomEpiV <525 μg · L^?1; TP <35 μg · L^?1; 12 lakes); and (C) eutrophic lakes (TP ≥35 μg · L^?1; six lakes). A semiquantitative model correctly predicted the MRT group of the lake 71% of the time (P < 0.001). These results suggest that submerged macrophytes have a significant influence on diatom community structure and that sedimentary diatom assemblages can be used to infer past macrophyte abundance.