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1.
The Ramsar-listed Coorong lagoon lies at the terminus of the Murray-Darling River system in South Australia. Diatom and foraminifera relationships with water quality were characterised in order to develop diatom- and foraminifera-based models with the potential to infer water column salinity. Seventy-four samples were collected during 2007, a year of continuing drought in the catchment, and of no discharges at the Murray Mouth. The sample sites had a salinity gradient of 1.8–190 g l−1 total dissolved solids. The diatom data set comprised 215 taxa, while there were only eight taxa in the foraminiferal data set. Canonical correspondence analysis of diatom species-environment relationships showed that salinity explained the largest proportion of diatom variance. Hence, a diatom-based salinity transfer function with reasonable predictive power (measured vs. diatom-inferred salinity r jack2 = 0.82; Root Mean Squared Error of Prediction = 16 g l−1) was developed. Application of the transfer function to fossil diatom assemblages from The Coorong suggested that pre-European salinity values were generally >50 g l−1 and that salinity declined following settlement. These results, however, contradict the recent history of The Coorong where there have been substantial lagoon-wide salinity increases. The pre-impact diatom flora has no analogue in the modern data set, highlighting the degree of departure from past conditions. CCA of the foraminiferal data set identified salinity and total nitrogen as the variables with the greatest explanatory power. However, accurate predictive models could not be developed using either variable due to low foraminiferal abundance and species richness. These factors may have been a consequence of diminished foraminiferal recruitment rates over successive years, an artefact of reduced marine water input to The Coorong. Future attempts to generate predictive models from this region would benefit from the inclusion of data from distant locations, since suitable analogue sites do not exist in close proximity. The study has generated useful insights to the apparently broad salinity tolerances for several cosmopolitan diatom and foraminifera species, and has identified a number of diatom and foraminifera taxa that may prove useful in the qualitative interpretation of down-core trends in The Coorong and the lower Murray River region.  相似文献   

2.
To quantify the relationship between diatom species assemblages and the water chemistry of southeast Australian estuaries and coastal lakes, a new dataset of 81 modern diatom samples and water chemistry data was created. Three hundred and ninety-nine species from 53 genera were identified in 36 samples from 32 coastal water bodies in eastern Tasmania and 45 samples from 13 coastal water bodies in southern Victoria. Multivariate statistical analyses revealed that the sampling sites were primarily distributed along salinity and nutrient gradients, and that salinity, nitrate + nitrite, phosphate and turbidity explained independent portions of variance in the diatom data. Species salinity optima and tolerances were determined and a diatom-salinity inference model (WAinv r 2 = 0.72, r 2jack = 0.58, RMSEP = 0.09 log ppt) was developed. This new information on diatom species’ salinity preferences provides a useful tool for quantitatively reconstructing salinity changes over time from diatom microfossils preserved in the sediments of a range of estuaries and coastal lakes in southeast Australia. This is valuable for studies investigating long-term human impacts and climate change in the region.  相似文献   

3.
Nutrient over-enrichment of estuarine environments is increasing globally. However, it is difficult to determine the eutrophication trend in estuaries over long periods of time because long-term monitoring records are scarce and do not permit the identification of baseline environmental conditions. In this study, preliminary diatom based transfer functions for the inference of total phosphorus (TP) and total nitrogen (TN) in east-Australian sub-tropical estuaries were developed to address the deficiency in knowledge relating to historical estuary water quality trends. The transfer functions were created from a calibration set consisting of water quality and associated surface sediment diatom assemblage data from fifty-two sub-tropical estuaries in New South Wales and Queensland, Australia. Following data screening processes, Canonical Correspondence Analysis confirmed that TP and TN both explained significant, independent variation in the diatom assemblages. Variance partitioning, however, indicated that the TP was confounded with and may receive some strength from TN. WA and WA-PLS 2 component models for TP that included all calibration set sites yielded statistically weak results based on the jack-knifed r 2 scores $ \left( {r_{\text{jack}}^{{^{ 2} }} \, = 0.22\;{\text{and}}\;0. 2 2 {\text{ respectively}}} \right) $ . Removal from the calibration set of 12 sites that had all PO4, NH4, NO2, and NOx concentrations below detection limit resulted in a substantial improvement in WA-PLS 2 component TP model scores $ \left( {r_{\text{jack}}^{{^{ 2} }} \; = \;\,0.69} \right) $ , indicating that this model is statistically robust, and thus suitable for down core nutrient reconstructions. Caution, however, is required when developing diatom based inference models in Australian estuaries as nutrient cycling processes may have the potential to influence diatom based transfer functions. The model reported on here provides a foundation for reconstructing nutrient histories in eastern Australian sub-tropical estuaries in the absence of monitoring data.  相似文献   

4.
Physical, chemical, and biological data were collected from a suite of 57 lakes that span an elevational gradient of 1360 m (2115 to 3475 m a.s.l.) in the eastern Sierra Nevada, California, USA as part of a multiproxy study aimed at developing transfer functions from which to infer past drought events. Multivariate statistical techniques, including canonical correspondence analysis (CCA), were used to determine the main environmental variables influencing diatom distributions in the study lakes. Lakewater depth, surface-water temperature, salinity, total Kjeldahl nitrogen, and total phosphorus were important variables in explaining variance in the diatom distributions. Weighted-averaging (WA) and weighted-averaging partial least squares (WA-PLS) were used to develop diatom-based surface-water temperature and salinity inference models. The two best diatom-inference models for surface-water temperature were developed using simple WA and inverse deshrinking. One model covered a larger surface-water temperature gradient (13.7 °C) and performed slightly poorer (r2 = 0.72, RMSE = 1.4 °C, RMSEPjack = 2.1 °C) than a second model, which covered a smaller gradient (9.5 °C) and performed slightly better (r2 = 0.89, RMSE = 0.7 °C, RMSEPjack = 1.5 °C). The best diatom-inference model for salinity was developed using WA-PLS with three components (r2 = 0.96, RMSE = 4.06 mg L–1, RMSEPjack = 11.13 mg L–1). These are presently the only diatom-based inference models for surface-water temperature and salinity developed for the southwestern United States. Application of these models to fossil-diatom assemblages preserved in Sierra Nevada lake sediments offers great potential for reconstructing a high-resolution time-series of Holocene and late Pleistocene climate and drought for California.  相似文献   

5.
Quantitative and qualitative diatom analyses from the north Nile Delta lakes sediments of Egypt were used to evaluate the paleoenvironmental development of the lakes and climatic changes during the late Holocene. We analyzed 565 samples taken from 19 cores from Manzala, Burullus and Edku lakes. A total of 263 diatom species and varieties were identified. Multivariate statistical analyses distinguished 17 ecological groups that reflect changes in water salinity, lake-level and trophic state of the lakes, which in turn are mainly related to climatic changes and anthropogenic impacts. Manzala and Burullus lakes experienced a series of alternation between fresh, brackish and marine episodes, which were associated with wet and dry climates. Edku Lake cores, however, contained only three ecological groups that are characteristic of brackish water conditions. The general depositional regime in the lakes indicated five environmental phases: (a) a deep freshwater phase when the Nile flood water reach the lakes during humid warm climate; (b) a shallow freshwater phase with some macrophytes during a dry climate; (c) a shallow brackish water phase when Nile floodwater ceased during a dry climate and the lakes shifted to brackish conditions; (d) a mixed environmental phase when the seawater mixed with freshwater from drains and canals (water salinity fluctuated widely from freshwater to estuarine and full marine conditions); (e) a fully marine phase when seawater entered the lakes at all stages of the tide.  相似文献   

6.
Shifts in diatom species composition may be used to infer past changes in environmental conditions in fresh, estuarine and marine systems. Establishing the primary drivers of present day diatom community composition is a vital step in their use as a proxy for past conditions. Moreton Bay, Australia, has experienced extensive modification of its catchments and western and southern shorelines. Regional weather patterns and terrestrial runoff have created a gradient in water quality from relatively degraded western and southern areas to relatively pristine northern and eastern areas. The aim of this study was to examine the relative impact of short term changes to light and/or nutrient availability and long term changes in sediment type, light and nutrient availability to subtidal benthic community composition. Short term changes were imposed using a manipulative field experiment whilst long term changes were obtained from a field survey of sites across the gradient of water quality. Diatoms were found to be the dominant microalgal group at all studied sites. The diatom communities were comprised primarily of small benthic epipsammic species and community composition was primarily driven by changes in sediment silt content. Short term changes in light and/or nutrient availability had little impact on community composition. In this open estuarine system the use of diatom indices to infer past water quality must take into account the sediment silt content in their interpretations.  相似文献   

7.
Diatom assemblages of surface sediments in 46 billabongs from four river floodplains in the southeast Murray-Darling Basin, Australia were sampled to investigate drivers of species distribution. The principal purpose of the study was to derive information to aid interpretation of diatom-based palaeoecological studies of these systems and of floodplain lakes more generally. Patterns in billabong diatom assemblages in relation to river reach, hydrology and farming intensity on surrounding land were examined, as were correlations with water quality variables. Seasonal variation in billabong water quality was high relative to spatial variation, and spatial patterns in billabong water quality were weak. In contrast, strong patterns were evident in diatom assemblages. Three main patterns were observed: (1) a distinction between billabongs dominated by planktonic diatoms from those dominated by benthic and attached forms; (2) differences in diatom assemblages in billabongs on different river reaches; and (3) differences in assemblages in billabongs with different hydrology. Of all water quality variables tested, total phosphorus (TP), total nitrogen (TN) and pH exerted the strongest independent influence on diatom distribution; however, only TP remained an important variable when species variation due to river reach, hydrology, and aquatic plant cover was taken into account. The weak influence of water quality on diatom distribution is interpreted as reflecting the dichotomy between plankton and non-plankton-dominated billabongs, the influence of hydrology and biogeography, the lack of strong spatial water quality gradients and the high degree of temporal variability in water quality. The findings show that diatom records from billabong sediments can provide evidence of long-term changes in the abundance of aquatic macrophytes and hydrology. They also suggest that merging calibration data sets across regions for the purpose of improving diatom transfer functions for water quality reconstruction is of limited value for floodplain lakes, and that performance is more likely to be gained by boosting site numbers within regions.  相似文献   

8.
Previous studies have shown chironomids to be excellent indicators of environmental change and training sets have been developed in order to allow these changes to be reconstructed quantitatively from subfossil sequences. Here we present the results of an investigation into the relationships between surface sediment subfossil chironomid distribution and lake environmental variables from 42 lakes on the Tibetan Plateau. Canonical correspondence analysis (CCA) revealed that of the 11 measured environmental variables, salinity (measured as total dissolved solids TDS) was most important, accounting for 10.5% of the variance in the chironomid data. This variable was significant enough to allow the development of quantitative inference models. A range of TDS inference models were developed using Weighted Averaging (WA), Partial Least Squares (PLS), Weighted Averaging–Partial Least Squares (WA–PLS), Maximum Likelihood (ML), Modern Analogues Technique (MAT) and Modern Analogues Techniques weighted by similarity (WMAT). Evaluation of the site data indicated that four lakes were major outliers, and after omitting these from the training set the models produced jack-knifed coefficients of determination (r 2) between 0.60 and 0.80, and root-mean-squared errors of prediction (RMSEP) between 0.29 and 0.44 log10 TDS. The best performing model was the two-component WA–PLS model with r 2 jack = 0.80 and RMSEPjack = 0.29 log10 TDS. The model results were similar to other chironomid-salinity models developed in different regions, and they also showed similar ecological groupings along the salinity gradient with respect to freshwater/salinity thresholds and community diversity. These results therefore indicate that similar processes may be controlling chironomid distribution across salinity gradients irrespective of biogeographical constraints. The performance of the transfer functions illustrates that chironomid assemblages from the Tibetan Plateau lakes are clearly sensitive indicators of salinity. The models will therefore allow the quantification of long-term records of past water salinity for lacustrine sites across the Tibetan Plateau, which has important implications for future hydrological research in the region.  相似文献   

9.
In order to assess the recent anthropogenic environmental changes in Lake Kitaura, central Japan, changes during the past few centuries were reconstructed from results of radiometric and tephrochlonological age determination, magnetic susceptibility measurements, total organic carbon analyses, total nitrogen analyses and fossil diatom analyses on a sediment core from the lake. A total of six major and sub-zones are recognized according to the diatom fossil assemblages, and we discuss aquatic environmental change in Lake Kitaura mainly based on these diatom assemblage change. Zone Ia and Zone Ib (older than AD 1707) are marine to brackish. In Zone IIa (AD␣1707–AD 1836), most of the brackish diatoms disappeared, and were replaced by freshwater species indicating a decrease in salinity. We interpret the salinity decrease in Zone I–IIa as a sea-level fall during the Little Ice Age. The salinity of the lake decreased to near freshwater conditions in Zone IIb (AD 1836–AD 1970), which could arise from alteration in River Tone or development of a sandspit in the mouth of River Tone in addition to sea-level change. In Zone IIIa (AD 1970–AD 1987), the diatom assemblage indicates a freshwater environment, and sedimentation rates increase rapidly. These changes reflect sedimentary environment change and an ecosystem transition due to the construction of the tide gate. In Zone IIIb (AD 1987–AD 2002), the diatom flux (valves cm−2 y−1) increased and species composition changed. The changes in Zone IIIb show a good agreement with limnological monitoring data gathered from the lake. These paleolimnological data suggest that the recent human-induced changes of the aquatic environment of the lake after the 1970s exceed rates during the period concerned in this study.  相似文献   

10.
Paleoecological reconstructions of Holocene sea-level changes in Argentinean coastal regions were based mainly on ecological data gathered from other regions, as there was a lack of information on modern estuarine diatom distributions. The aim of the present work was to assess the spatial variation of diatom assemblages in two representative estuaries of Argentina in order to gather ecological information for paleoecological reconstructions in the region. The two selected estuaries have different geomorphologic features and salinity regimes: Mar Chiquita Lagoon is shallow, which prevents the development of a stable salinity gradient as it occurs in the Quequén Grande River. Surface sediment samples were taken from selected stations representative of the environmental gradient from the inlet to the inner reaches of both estuaries. Cluster analysis defined three diatom zones at Mar Chiquita: marine/brackish assemblages dominate the inlet (zone I), where salinity, tidal range and current speed are higher. The brackish/freshwater tychoplankton Staurosira construens var. venter and Staurosirella pinnata dominate the inner lagoon (zone II), where environmental conditions are very variable and concentrations of suspended sediments are higher. Brackish/freshwater euryhaline diatoms dominate the headwaters (zone III). On the other hand, the Quequén Grande River was divided into three diatom zones: coastal taxa are distributed at the inlet (zone I), while the middle estuary (zone II) is dominated by brackish/freshwater euryhaline taxa. At the upper estuary region (zone III), freshwater diatoms dominate, and the halophobous Nitzschia denticula increased in abundance values. Diatom distributions were most closely related to the salinity gradient at Quequén Grande River than at Mar Chiquita Lagoon. Fossil data of a sequence from Mar Chiquita Lagoon (Las Gallinas Creek) were compared to the modern data set in order to search for analogies between fossil and modern diatom assemblages. DCA results showed that fossil diatom assemblages have modern counterparts. Most diatom assemblages of Las Gallinas Creek fall within Mar Chiquita zone III, representing a shallow brackish/freshwater environment, with low salinity fluctuations (~1–9‰) and no tidal influence. Therefore, our modern diatom data provide useful analogs to interpret paleoenvironments in the region.  相似文献   

11.
Surficial sediments of three northern Egyptian lakes (Manzala, Burullus and Edku) show differences in diatom assemblages deposited in different sites of these lakes. A total of 172 species and varieties belonging to 58 genera were identified and counted from 62 samples. Of these, 163 diatom taxa were recorded from Manzala Lake sediments, 147 taxa were found in Burullus Lake sediments, and 117 taxa were identified in Edku Lake sediments. The considerable variation in the composition and distribution of the diatom assemblages among these lakes was mainly related to differences in the water quality, salinity, the concentration of nutrients and climatic changes. The planktonic diatom Cyclotella meneghiniana was dominant in the majority of the samples from Manzala Lake, but dominant in only a few samples from the middle parts of Burullus and Edku lakes. The non-planktonic epiphytic taxa Cocconeis placentula and Epithemia sorex were the subdominant species in the surface sediments, especially in shallow and marginal parts of the lakes. Multivariate statistical techniques (hierarchical ascending clustering and canonical correspondence analysis) were used to identify ecological groups of diatoms and to investigate which environmental variables were important in explaining the variation between these groups. Eight ecological groups containing distinctive diatom assemblages reflect current environmental conditions; especially saltwater intrusion in the north and nutrient-rich freshwater in the south.  相似文献   

12.
Diatom analysis of a varved sediment core from Elk Lake, Minnesotadocuments important natural and human-caused shifts in primary productivity atdecadal scales for the past 1500 years. Interpretations from a perspective ofplanktic diatom seasonal dynamics and from total phosphorus inferences based ona 111-lake training set of freshwater Canadian lakes reveal a major change tomore productive environments after 1000 years ago probably caused by earlierice-out and stronger, longer periods of lake circulation during the spring.European impacts in the region, principally logging in the Elk Lake drainage,during the past 100 years increased nutrient fluxes and turbulence during theopen water season to promote blooms of Aulacoseiraambigua. High resolution (semi-decadal) diatom analyses suggestsunspot cycle periodicities that may reflect short-term changes in thecharacter of irradiance and (or) sun-climate interactions. Total epilimneticphosphorus inferences from the Canadian training set applied to the Elk Lakediatom record document both long-term and short-term variations inproductivity and reconstruct past phosphorus values consistent with somepresent-day measured values at Elk Lake. The Elk Lake study underscores theneed for neolimnological monitoring of both training set and target lakes aswell as for the application of a multiple proxy protocol to documentpaleo-productivity that approaches neolimnological resolution.  相似文献   

13.
A diatom-conductivity transfer function for Spanish salt lakes   总被引：3，自引：0，他引：3  
Diatom-salinity transfer functions for interpretation of palaeosalinity and palaeoclimate change have been developed successfully for parts of North America and North and East Africa, but there is a need for data-sets in other saline lake regions of the world. A data-set of 74 modern diatom samples and associated water chemistry data is described from Spain. The influence of conductivity and other environmental variables on diatom distribution is explored using canonical correspondence analysis (CCA) and partial CCAs. A transfer function is derived for conductivity (70 samples) whose apparent predictive ability is high (apparent r2 = 0.91). Performance under jackknifing is poor due to the heterogeneous nature of the data-set and poor coverage of the freshwater end of the salinity gradient. There is a lack of suitable low-salinity sites in Spain, and the accuracy of estimated salinity optima and tolerance ranges may be improved by merging this data-set with those of other regions. The Spanish transfer function has strong affinities with the African data-set and contributes important ecological data for diatom taxa which are absent or poorly represented in the modern flora of African lakes, and for which, in fossil material, there were previously no good modern analogues.  相似文献   

14.
A 72-lake diatom training set was developed for the Irish Ecoregion to examine the response of surface sediment diatom assemblages to measured environmental variables. A variety of multivariate data analyses was used to investigate environmental and biological data structure and their inter-relationships. Of the variables used in determining a typology for lakes in the Irish Ecoregion, alkalinity was the only one found to have a significant effect on diatom assemblages. A total of 602 diatom taxa were identified, with 233 recorded at three or more sites with abundances ≥1%. Generally diatom data displayed a high degree of heterogeneity at the species level and non-linear ecological responses. Both pH and total phosphorus (TP) (in the ranges of 5.1–8.5 and 4.0–142.3 μg l−1 respectively) were shown to be the most significant variables in determining the surface sediment diatom assemblages. The calibration models for pH and TP were developed using the weighted averaging (WA) method; data manipulation showed strong influences on model performances. The optima WA models based on 70 lakes produced a jack-knifed coefficient of determination (r 2 jack) of 0.89 with a root mean squared error (RMSEP) of 0.32 for pH and r 2 jack of 0.74 and RMSEP of 0.21 (log10 μg l−1) for TP. Both models showed strong performances in comparison with existing models for Ireland and elsewhere. Application of the pH and TP transfer functions developed here will enable the generation of quantitative water quality data from the expanding number of palaeolimnological records available for the Irish Ecoregion, and thus facilitate the use of palaeolimnological approaches in the reconstruction of past lake water quality, ecological assessment and restoration.  相似文献   

15.
The Nebraska Sand Hills are a distinctive eco-region in the semi-arid Great Plains of the western United States. The water table underlying the Sand Hills is part of the High Plains/Ogallala aquifer, an important water resource for the central Great Plains. Lake levels are affected directly by fluctuations in the water table, which is recharged primarily by local precipitation and responds quickly to climatically induced changes in regional water balance. Instrumental records are available for only 50–100 years, and paleolimnological data provide important insights into the extremes and variability in moisture balance over longer time scales. A set of 69 lakes from across Nebraska was used to establish a statistical relationship between diatom community composition and water depth. This relationship was then used to develop a diatom-based inference model for water depth using weighted averaging regression and calibration techniques. Development of the inference model was complicated by strong intra-seasonal variability in water depth and the linkages between depth and other limnologic characteristics, including alkalinity, water clarity and nutrient concentrations. Analysis of historical diatom communities from eight lakes allowed for the reconstruction of lake-level fluctuations over the past several thousand years. Comparisons of the more recent portion of these reconstructions with the instrumental Palmer Drought Severity Index (PDSI) showed that sediment records may not faithfully reflect short-term fluctuations in water level, except where sedimentation rates are very high. However, large and persistent changes in moisture availability were discernible even in longer, low-resolution records. Thus, diatoms are a useful addition to the tools available for understanding past drought in the central Great Plains, especially when trajectories of change are constrained by data from multiple sites or other proxies.  相似文献   

16.
The water chemistry of lake systems on the edge of the Antarctic continent responds quickly to changes in the moisture balance. This is expressed as increasing salinity and decreasing lake water level during dry periods, and the opposite during wet periods. The diatom composition of the lakes also changes with these fluctuations in salinity and lake water depth. This is important, as their siliceous remains become incorporated into lake sediments and can provide long-term records of past salinity using transfer functions. In order to develop transfer functions, diatoms and water chemistry data were inter-calibrated from five different East Antarctic oases, namely the Larsemann Hills, the Bølingen Islands, the Vestfold Hills, the Rauer Islands and the Windmill Islands. Results indicate that salinity is the most important environmental variable explaining the variance in the diatom flora in East Antarctic lakes. In oligo- saline lakes the variance is mainly explained by lake water depth. This dataset was used to construct a weighted averaging transfer function for salinity in order to infer historical changes in the moisture balance. This model has a jack-knifed r2 of 0.83 and a RMSEP of 0.31. The disadvantage of this transfer function is that salinity changes in oligo-saline lakes are reconstructed inaccurately due to the edge effect and due to the low species turnover along the salinity gradient at its lower end. In order to infer changes in the moisture balance in these lakes, a second transfer function using weighted averaging partial least squares (with two components) for depth was constructed. This model has a jack-knifed r2 of 0.76 and a RMSEP of 0.22. Both transfer functions can be used to infer climate driven changes in the moisture balance in lake sediment cores from oligo-, hypo-, meso- and hyper-saline lakes in East Antarctic oases between 102–75°E. The transfer function for lake water depth is promising to track trends in the moisture balance of small freshwater lakes, where changes in shallow and deep-water sediments are readily reflected in changing diatom composition.  相似文献   

17.
The contemporary distribution of benthic diatoms and their use as ecological indicators were examined in a coastal wetland, the Ebro Delta, as a representative of environmental conditions in Mediterranean coastal wetlands. A total of 424 diatom taxa were identified across 24 sites encompassing a wide range of wetland habitat types (coastal lagoons, salt and brackish marshes, shallow bays, microbial mats and nearshore marine waters) and conductivities. Canonical correspondence analysis showed that water conductivity and water depth were the main factors structuring the diatom assemblages. Cluster analysis identified five habitat types according to the similarity in diatom species composition: salt marshes, brackish marshes, brackish coastal lagoons and bays, coastal lagoons with fresher conditions, and nearshore open sea. For each wetland habitat, diatom indicator species were identified. Partial canonical correspondence analysis showed that water conductivity, a proxy for salinity, was the most statistically significant and independent variable for explaining the distribution of benthic diatoms in the study area. A transfer function, using a weighted average regression model, was developed for conductivity and displayed reasonable performance (r 2 = 0.64; RMSEP = 0.302 log10 mS/cm). Our study in the Ebro Delta provides a basis for using diatom assemblages to make quantitative conductivity inferences, and for using diatom indicator species to identify wetland habitats. These approaches are complementary and may be valuable for paleoenvironmental studies of (1) effects of large-scale, natural changes in the Delta (e.g. sea-level fluctuations), and (2) impacts of short-term anthropogenic changes, such as the introduction and development of rice agriculture.  相似文献   

18.
Surface sediments from 68 small lakes in the Alps and 9 well-dated sediment core samples that cover a gradient of total phosphorus (TP) concentrations of 6 to 520 g TP l-1 were studied for diatom, chrysophyte cyst, cladocera, and chironomid assemblages. Inference models for mean circulation log10 TP were developed for diatoms, chironomids, and benthic cladocera using weighted-averaging partial least squares. After screening for outliers, the final transfer functions have coefficients of determination (r2, as assessed by cross-validation, of 0.79 (diatoms), 0.68 (chironomids), and 0.49 (benthic cladocera). Planktonic cladocera and chrysophytes show very weak relationships to TP and no TP inference models were developed for these biota. Diatoms showed the best relationship with TP, whereas the other biota all have large secondary gradients, suggesting that variables other than TP have a strong influence on their composition and abundance. Comparison with other diatom – TP inference models shows that our model has high predictive power and a low root mean squared error of prediction, as assessed by cross-validation.  相似文献   

19.
Climate in central Asia is dominated by the Asian monsoon. The varying impact of the summer monsoon across the Tibetan (Qinghai-Xizang) Plateau provides a strong gradient in precipitation, resulting in lakes of different salinity. Diatoms have been shown to indicate changes in salinity. Thus, transfer functions for diatoms and salinity or related environmental variables represent an excellent tool for paleoclimatic reconstructions in the Tibetan Plateau. Forty freshwater to hypersaline lakes (salinity: 0.1 to 91.7 g l–1) were investigated in the eastern Tibetan Plateau. The relationship between 120 diatom taxa and conductivity, maximum water depth and major ions were analyzed using an indicator value approach, ordination and taxon response models. Canonical correspondence analysis indicated that conductivity was the most important variable, accounting for 10.8% of the variance in the diatom assemblages. In addition water depth and weathering were influential. Weighted Averaging (WA) and Weighted Averaging Partial Least Square (WA-PLS) regression and calibration models were used to establish diatom-conductivity and water depth transfer functions. An optimal two-component WA-PLS model provided a high jack-knifed coefficient of prediction for conductivity (r2 jack = 0.92), with a moderate root mean squared error of prediction (RMSEPjack = 0.22), a very low mean bias (0.0003), and a moderate maximum bias (0.26). A WA model with tolerance downweighting resulted in a slightly lower r2 jack (0.89) for water depth, with RMSEPjack= 0.26, mean bias = –0.0103 and maximum bias = 0.26.  相似文献   

20.
Twenty high Arctic lakes and ponds were sampled for water chemistry and modern diatom assemblages in two distinct physiographic sectors of Sirmilik National Park, Nunavut, Canada. Sites on southwestern Bylot Island were warmer, more alkaline, less dilute, and had higher concentrations of nutrients, DOC and Chl-a (mesotrophic to oligo-mesotrophic), whereas sites on Qorbignaluk Headland on northern Baffin Island were deeper, very dilute, mostly oligotrophic and had lower pH. Diatom assemblages differed markedly between these two regions as a consequence of limnological differences between them. Paleolimnological records, spanning > 200 years and dated by 210Pb activity, were produced from each region to compare biological responses to recent warming inferred from glaciological studies on Bylot Island and regional syntheses for the Arctic. Diatom assemblages began to change around AD 1900 at both sites. At Qorbignaluk Headland, marked shifts in diatom community composition occurred during the twentieth century, with large increases in the abundance of planktonic diatoms. At Bylot Island, diatom community changes began around the same time, and involved modest decreases in planktonic diatoms and increases in inferred specific conductance, likely because of a decrease in the areal extent of the small lake as a response to warming. The study confirms that responses of freshwater ecosystems to climate warming vary depending on local physiographic factors.  相似文献   

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