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1.
Erin M. Barley Ian R. Walker Joshua Kurek Les C. Cwynar Rolf W. Mathewes Konrad Gajewski Bruce P. Finney 《Journal of Paleolimnology》2006,36(3):295-314
Freshwater midges, consisting of Chironomidae, Chaoboridae and Ceratopogonidae, were assessed as a biological proxy for palaeoclimate in eastern Beringia. The northwest North American training set consists of midge assemblages and data for 17 environmental variables collected from 145 lakes in Alaska, British Columbia, Yukon, Northwest Territories, and the Canadian Arctic Islands. Canonical correspondence analyses (CCA) revealed that mean July air temperature, lake depth, arctic tundra vegetation, alpine tundra vegetation, pH, dissolved organic carbon, lichen woodland vegetation and surface area contributed significantly to explaining midge distribution. Weighted averaging partial least squares (WA-PLS) was used to develop midge inference models for mean July air temperature (r
boot2 = 0.818, RMSEP = 1.46°C), and transformed depth (ln (x+1); r
boot2 = 0.38, and RMSEP = 0.58). 相似文献
2.
Peter Roseacute;n Roland Hall Tom Korsman Ingemar Renberg 《Journal of Paleolimnology》2000,24(2):109-123
The relationships between diatoms (Bacillariophyceae) in surface sediments of lakes and summer air temperature, pH and total organic carbon concentration (TOC) were explored along a steep climatic gradient in northern Sweden to provide a tool to infer past climate conditions from sediment cores. The study sites are in an area with low human impact and range from boreal forest to alpine tundra. Canonical correspondence analysis (CCA) constrained to mean July air temperature and pH clearly showed that diatom community composition was different between lakes situated in conifer-, mountain birch- and alpine-vegetation zones. As a consequence, diatoms and multivariate ordination methods can be used to infer past changes in treeline position and dominant forest type. Quantitative inference models were developed to estimate mean July air temperature, pH and TOC from sedimentary diatom assemblages using weighted averaging (WA) and weighted averaging partial least squares (WA-PLS) regression. Relationships between diatoms and mean July air temperature were independent of lake-water pH, TOC, alkalinity and maximum depth. The results demonstrated that diatoms in lake sediments can provide useful and independent quantitative information for estimating past changes in mean July air temperature (R2
jack = 0.62, RMSEP = 0.86 °C; R2 and root mean squared error of prediction (RMSEP) based on jack-knifing), pH (R2
jack = 0.61, RMSEP = 0.30) and TOC (R2
jack = 0.49, RMSEP = 1.33 mg l-1). The paper focuses mainly on the relationship between diatom community composition and mean July air temperature, but the relationships to pH and TOC are also discussed. 相似文献
3.
Diatom-based models for reconstructing past water quality and productivity in New Zealand lakes 总被引：17，自引：12，他引：5
The trophic status of lakes in New Zealand is, on average, low compared to more densely populated areas of the globe. Despite this, trends of eutrophication are currently widespread due to recent intensification in agriculture. In order to better identify baseline productivity and establish long-term trends in lake trophic status, diatom-based transfer functions for productivity-related parameters were developed. Water quality data and surface sediment diatom assemblages from 53 lakes across the North and South Islands of New Zealand were analysed to determine species responses to the principal environmental gradients in the data set. Repeat sampling of water chemistry over a 12-month period enabled examination of species responses to annual means as well as means calculated for stratified and mixed periods. Variables found to be most strongly correlated with diatom species distributions were chlorophyll a (Chl a), total phosphorus (TP), dissolved reactive phosphorus (DRP), ionic concentration (measured as electrical conductivity (EC)) and pH. These variables were used to develop diatom-based transfer functions using weighted averaging regression and calibration (simple, tolerance down-weighted and with partial least squares algorithm applied). Overall, models derived for stratified means were weaker than those using annual or isothermal means. For specific variables, the models derived for the isothermal mean of EC (WA-tol r2jack = 0.79; RMSEP = 0.15 log10 S cm–1),the annual mean of pH (WA r2jack = 0.72; RMSEP = 0.25 pH units) and the isothermal mean of Chl a (WA r2jack = 0.71; RMSEP = 0.18 log10 mg m–3 Chl a) performed best. The models derived for TP were weak in comparison (for the annual mean of TP: WA r2jack = 0.50; RMSEP = 0.24 log10 mg m–3 TP) and residuals on estimates for this model were correlated with several other water quality variables, suggesting confounding of species responses to TP concentrations. The model derived for the isothermal mean of DRP was relatively strong (WA-tol r2jack = 0.78; RMSEP = 0.17 log10 mg m–3 DRP); however, residual values for this model were also found to be strongly correlated with several other water quality variables. It is concluded that the poor performance of the TP and DRP transfer functions relative to that of the Chl a model reflects the coexistence of nitrogen and phosphorus limitation within the lakes in the data set. In spite of this, the suite of transfer functions developed from the training set is regarded as a valuable addition to palaeolimnological studies in NewZealand. 相似文献
4.
Development of a diatom-based model for inferring total phosphorus in southeastern Australian water storages 总被引：1，自引：0，他引：1
John Tibby 《Journal of Paleolimnology》2004,31(1):23-36
Diatom-based transfer functions for inferring epilimnetic total phosphorus (TP) have been developed from a data set of 33 southeastern Australian water storages. Regular institutional monitoring of these sites has allowed comparison of models developed from TP data covering different time periods. A model based on mean annual TP performs better than models derived from winter maximum TP, spring minimum TP or TP nearest the time of diatom sampling. A mean annual TP model (WA-PLS 2 component) has a jack-knifed diatom-inferred versus measured TP correlation coefficient (r
2
jack) of 0.69 and a root-mean-square-error of prediction (RMSEP) of 0.246 log10g TP l–1, while alternative models have RMSEP > 0.27. Deletion of two samples with uncharacteristic species composition and environmental conditions improved performance of the mean annual TP model (r
2
jack= 0.74; RMSEP = 0.233 log10g TP l–1). Comparison with other published diatom-TP calibration models indicates that this model performs relatively well, with possible contributing factors including the extensive characterisation of TP (with an average 15 determinations making up the annual mean) and the dominance of planktonic diatoms in most sites. Downcore application of the model will allow the reconstruction of reservoir nutrient histories since commissioning, and thus provide a basis for understanding and management of reservoirs. 相似文献
5.
撞击坑是月表最主要的地貌形态,相关研究多采用撞击坑深度和坑口直径比值作为月球形貌研究依据。事实上撞击坑的形状不是典型的圆锥,而是上大下小的截锥形。依据"嫦娥一号"影像图和全月球数字高程模型数据,获取了1000个撞击坑坑唇等效半径r1、坑底等效半径r2,撞击坑的深度h,进而对r1、r2、h三个参数进行了统计分析和聚类分析。结果表明:(1)撞击坑数目与r1和r2的分形维数分别为D1=1.88、D2=1.51,都大于地球撞击坑的分维数1.16,表明月表撞击坑复杂度受到外界的影响较地球低,且坑唇的复杂度比坑底高;(2)r1-r2之间具有很好的线性正相关关系,聚类结果将其分为三类,决定系数分别为R12=0.685、R22=0.886、R32=0.974;(3)对r1-r2-h三者进行线性拟合,决定系数R2=0.968,表明三者之间同样具有显著线性关系,且月表撞击坑的形成过程以及形成之后都处于相似的动力环境下。 相似文献
6.
Chrysophycean stomatocysts were identified and enumerated from the surface sediments of 60 lakes located on the Interior Plateau of British Columbia. The lakes span a salinity gradient from freshwater to hypersaline (0.0–92.4 g L–1), with the majority being fresh to hyposaline. One hundred and ten stomatocyst morphotypes, almost all of which were previously described, were identified from the lake sediments. The first axis of direct gradient analysis, which was highly significant, was essentially a salinity axis (i.e. [Ca], [Mg], [K], [Na], [SO4], [DIC], and [Cl]). Most cysts were found to have fairly broad tolerances, with the narrowest tolerances occurring among morphotypes with the lowest salinity optima. Weighted-averaging regression and calibration techniques were used to develop an inference model to measure the relationship between measured average lakewater salinity and stomatocyst inferred salinity (apparent r2=0.80). Simple weighted-averaging produced a model with a lower bootstrapped RMSE of prediction than weighted-averaging with tolerance downweighting. These data indicate that chrysophyte stomatocysts are useful quantitative indicators of past lakewater salinity (in the freshwater to hyposaline range) in B.C. lakes, and can be used to strengthen the interpretations from diatom-inference models already developed from the same region. 相似文献
7.
采用动态密闭气室法测定分析了科尔沁沙地典型玉米(Zea mays)农田垄上和垄间土壤呼吸速率的差异及自养和异养呼吸特征,并估算了生态系统碳平衡。结果表明:(1)垄上和垄间土壤呼吸速率存在极显著差异(p0.001),且存在线性关系(p0.05);季节水平上垄上土壤呼吸可解释垄间土壤呼吸98.4%的变异。(2)季节水平上土壤总呼吸(RS)、异养呼吸(RH)和自养呼吸(RA)的温度敏感性指数Q10大小顺序为:RA(4.35)RS(3.10)RH(2.08)。(3)RS和RH之间存在显著差异,RA与RS和RH之间不存在显著差异;RA占RS比例的季节变化范围为28.1%~71.1%,生长季RH和RA占RS的比例均值分别为44.4%和55.6%。(4)科尔沁沙地典型农田生态系统在生长季为碳汇,可净固存大气CO2-C的量为659.1g·m-2。 相似文献
8.
Diatom-based total phosphorus (TP) and pH transfer functions for the Irish Ecoregion 总被引：2，自引：0，他引：2
Guangjie Chen Catherine Dalton Manel Leira David Taylor 《Journal of Paleolimnology》2008,40(1):143-163
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
9.
10.
We present a simple method to derive spatial precipitation (P) and evapotranspiration (ET) for the typical steppe of the Xilin river catchment at 1 km and 8-day resolution during the main vegetation period (23 April to 28 August) of 2006. The hydrological model BROOK90 was parameterised from eddy covariance measurements. The daily model input data, precipitation, minimum (Tamin) and maximum air temperature (Tamax), were derived by manipulating MODIS leaf area index (LAI) and surface temperature data. P was estimated based on a linear regression of P measured at several sites against the mean gain of the MODIS LAI of surrounding 3 × 3 pixels areas (R2 = 0.76). Tamin and Tamax were derived using a relationship between measured Tamin and Tamax and MODIS surface temperatures (R2 = 0.92 and R2 = 0.88, respectively). The mean precipitation was 145 mm; it varied between 52 mm in the north-western region and 239 mm in the eastern region. In spring, the modelled ET was low (<0.8 mm d−1); evaporation dominated over transpiration and spatial differences were small. At the end of June, the mean ET reached its maximum (2 mm d−1) and spatial differences were pronounced. From July on, transpiration dominated over declining evaporation, and spatial differences decreased in August. 相似文献
11.
Luc Denys 《Journal of Paleolimnology》2007,38(1):97-116
Quantitative inference models for water-chemistry variables are derived from epiphytic diatom assemblages in 186 lentic and
mostly shallow freshwaters in lower Belgium (Flanders). When the complete pH range is considered (pH 3.4–9.3), robust transfer
functions are obtained for median pH (jack-knifed r
2 = 0.88, RMSEP = 0.38 pH units or 6.4% of the observed range) and dissolved inorganic carbon concentration (jack-knifed r
2 = 0.86, RMSEP = 0.194 log10 mg DIC l−1 or 10.2% of the observed range) by means of weighted-averaging partial least squares regression (WA-PLS). For these variables,
the calibration models are as reliable as those based on sedimentary diatom assemblages. Inferences of pH may be improved
by combining estimates from epiphytic and sediment assemblages. In circumneutral and alkaline conditions, WA-PLS calibration
of maximum or median total phosphorus is possible (log-transformed; jack-knifed r
2 = 0.64 or 0.66 and RMSEP = 14% or 12.3% of the observed range, respectively). It makes little difference if taxa showing
no response to TP are taken into consideration or not. These models considerably expand the prospects of using historical
herbarium materials to hindcast environmental conditions and also allow more accurate interpretation of current compositional
changes in epiphytic communities. Compared to littoral sediment assemblages, fewer water-column variables can be inferred
reliably from epiphyton. This probably results from differences between the effective gradients in both habitats, together
with lower in situ species diversity and less effective spatial integration (i.e. lower recruitment of phytoplankton) in the
epiphyton. A comparison of the HOF response-model types and WA-optima of diatom taxa for epiphytic and sediment assemblages
shows that the relationship to individual variables, and in particular to those related to trophic status, may differ with
habitat. Thus, the combination of samples from both habitat types in the same calibration model is not recommended.
Electronic Supplementary Material Supplementary material is available and is accessible for authorised users in the online version of this article at 相似文献
12.
Julien M.J. Racca Aline Philibert Robert Racca Yves T. Prairie 《Journal of Paleolimnology》2001,26(4):411-422
We explored the possibility of using artificial neural networks (ANN) to develop quantitative inference models in paleolimnology. ANNs are dynamic computer systems able to learn the relations between input and output data. We developed ANN models to infer pH from fossil diatom assemblages using a calibration data set of 76 lakes in Quebec. We evaluated the predictive power of these models in comparison with the two most commonly methods used in paleolimnology: Weighted Averaging (WA) and Weighted Averaging Partial Least Squares (WA-PLS). Results show that the relationship between species assemblages and environmental variables of interest can be modelled by a 3-layer back-propagation network, with apparent R2 and RMSE of 0.9 and 0.24 pH units, respectively. Leave-one-out cross-validation was used to access the reliabilities of the WA, WA-PLS and ANN models. Validation results show that the ANN model (R2
jackknife = 0.63, RMSEjackknife = 0.45, mean bias = 0.14, maximum bias = 1.13) gives a better predictive power than the WA model (R2
jackknife = 0.56, RMSEjackknife = 0.5, mean bias = –0.09, maximum bias = –1.07) or WA-PLS model (R2
jackknife = 0.58, RMSEjackknife = 0.48, mean bias = –0.15, maximum bias = –1.08). We also evaluated whether the removal of certain taxa according to their tolerance changed the performance of the models. Overall, we found that the removal of taxa with high tolerances for pH improved the predictive power of WA-PLS models whereas the removal of low tolerance taxa lowered its performance. However, ANN models were generally much less affected by the removal of taxa of either low or high pH tolerance. Moreover, the best model was obtained by averaging the predictions of WA-PLS and ANN models. This implies that the two modelling approaches capture and extract complementary information from diatom assemblages. We suggest that future modelling efforts might achieve better results using analogous multi-model strategies. 相似文献
13.
Luc Denys 《Journal of Paleolimnology》2006,35(4):763-787
Relationships between littoral surface-sediment diatom assemblages and ambient limnological conditions were examined in 186
lentic fresh waters throughout lower Belgium (Flanders). Most of these waters were small, unstratified, alkaline and rich
in nutrients. Using weighted-averaging techniques, robust and accurate transfer functions were developed for median pH-values
ranging from 3.4 to 9.3 and dissolved inorganic carbon concentrations from <1.6 to 63 mg l−1 (jackknifed r
2≈ 0.87, RMSEP <10% of the observed range), while a less precise model was obtained for sodium (2–571 mg l−1; jackknifed r
2 0.69, RMSEP 9.9% of the range). Restricting the data set to circumneutral and alkaline sites (pH≥6.5) revealed the importance
of additional variables, including calcium, silica, chemical oxygen demand and potential gross oxygen production (a proxy
for metabolic activity and phytoplankton abundance). Calibration models for these variables were strong enough to be useful
(jackknifed r
2 0.57–0.59, RMSEP 13.1–16.4% of the observed range), although estimations should not always be considered entirely independent.
Except for the predominant pH gradient, removal of all taxa with a distribution unrelated to the variable of interest improved
model performance. In general, such taxa were proportionally represented among taxa classified according to their principal
habitat. Application of the present models to diatom assemblages of shallow-water sediments obtained from historical samples
and, most importantly, herbarium-macrophyte specimens, will improve hindsight into regional freshwater conditions and add
to base-line setting of ecological quality standards in a highly impacted region.
Electronic supplementary material Electronic supplementary material is available for this article at
and accessible for authorised users. 相似文献
14.
华北平原典型农田水、热与CO2通量的测定 总被引：42，自引：1，他引：42
在中国科学院栾城农业生态试验站用波文比-能量平衡法与涡度相关技术对净辐射通量（Rn)，潜热通量（λE），感热通量（H），土壤热通量（G）与冠层CO2通量（Fco2)进行了长期定位研究，结果显示Rn大部分用于作物潜热的消耗，连续2年4个生长季λE/Rn都在70%以上，在作物生育盛期，夏玉米λE/Rn略高于冬小麦，H/Rn都在15%左右，G/Rn在5%-13%之间，且冬小麦G/Rn明显高于夏玉米。蒸发比值（EF）在不同的理想环境条件下，随着可供能量（Rn-G)的增加表现出先迅速下降，后缓慢下降，最后趋于稳定的趋势，并在冬小麦环境条件下得到了验证，直角双曲线模型可以模拟Fco2随光通量密度（PPFD）的响应过程。晴天冠层水分利用效率（WUE）不是在正午出现最高值，当PPFD达到1500μmolm^-2s^-1左右时，WUE却略有下降。 相似文献
15.
We examined the relationship between three key environmental variables (water depth, loss-on-ignition, and bottom-water temperature)
and fossil chironomid distributions sampled from within-lake gradients in three small, moderately deep (18–35 m), maar lakes
on St Michael Island, western Alaska. Site-specific (one lake, 29 samples) and local (three lakes, 87 samples) inference models
for reconstructing water depth were developed using partial least squares regression and calibration. These models and a previously
published regional model (136 lakes, one central-lake sample from each) are used to infer water depths from 78 fossil samples
spanning the last ~30,000 14C years B.P. at Zagoskin Lake. Although the site-specific [r
2
boot = 0.90, root mean square error of prediction (RMSEP) = 1.76] and local (r
boot2 = 0.68, RMSEP = 4.36) inference models have better performance statistics than the regional model, few clear trends among
all three models exist in the lake-level reconstruction. We propose that multiple, within-lake sampling of gradients can be
used to improve the performance statistics of water-depth transfer functions and ultimately reconstruct paleohydrology in
regions known to exhibit large fluctuations in moisture balance through time given that: (1) adequate analogs are established
and (2) taphonomic processes important to benthic invertebrate remains are more fully understood. 相似文献
16.
We set up an automatic weather station over a playa (the flat floor of an undrained desert basin that becomes at times a shallow lake), approximately 65 km east–west by 130 km north–south, located at the U.S. Army Dugway Proving Ground (40°08′N, 113°27′W, 1124 m above mean sea level) in north-western Utah, U.S.A., in 1999. This station measured the incoming (Rsi) and outgoing (Rso) solar or shortwave radiation using two CM21 Kipp & Zonen pyranometers (one inverted), the incoming (Rli or atmospheric) and outgoing (Rlo or terrestrial) longwave radiation, using two CG1 KippZonen pyrgeometers (one inverted), and the net (Rn) radiation using a Q*7 net radiometer (Radiation Energy Balance System, REBS). We also measured the 10-m wind speed (U10) and direction (R.M. Young wind monitor) and precipitation (Campbell Sci., Inc.). The measurements were taken every 2 s, averaged into 20-min, continuously, throughout the year. The annual (August 1999 – August 2000) comparisons of global or solar radiation and windiness with two other stations in central (Hunter) and northern (Logan) Utah, indicate higher solar radiation (Rsi,Dugway=7797 MJ m−2 period−1vs. Rsi, Hunter=7021 MJ m−2 period−1 and Rsi, Logan=6865 MJ m−2 period−1) and much higher annual mean windiness (UDugway=387 km day−1vs. UHunter=275 km day−1 and ULogan=174 km day−1) throughout the period over the playa. These data reveal the possibility of simultaneously harvesting these two sources of clean energies at this vast and uniform playa. 相似文献
17.
James O. Sickman Danuta M. Bennett Delores M. Lucero Thomas J. Whitmore William F. Kenney 《Journal of Paleolimnology》2013,50(2):159-174
We investigated relationships among modern diatom species composition and physical and chemical characteristics of high-elevation lakes of the Sierra Nevada (California), to develop transfer functions that can be used to infer historic lake conditions. Data were collected from 50 lakes in National Parks and Forests of the central and southern Sierra Nevada. Multivariate statistical methods revealed that acid neutralizing capacity (ANC) and nitrate accounted for significant variation in diatom taxa. A training set with 242 modern diatom taxa from a subset of 41 lakes was used to develop transfer functions for ANC and nitrate using weighted averaging techniques. ANC and nitrate calibration ranges were 23.0–137 μEq/L and 0.18–9.5 μM, respectively. Coefficients of determination for the models were: ANC: R2 = 0.76, and R jackknife 2 = 0.44; NO3: R2 = 0.67, and R jackknife 2 = 0.27. The ANC model was applied to the top 50 cm of sediments in Moat Lake to reconstruct ANC from ca. AD 350 to 2005. The reconstruction suggests that ANC declined by about 40 % (101–60 μEq/L) between the 1920s and the 1960s and then recovered to pre-1920s levels during 1980–2000. The magnitude of this ANC excursion was the largest observed during the past 1,600 years. We hypothesize that temporal variations in ANC were influenced by: (1) changes in rates of acid deposition, especially nitric acid and (2) variations in the timing and magnitude of snowmelt runoff. 相似文献
18.
Song Yanchen Wang Enze Peng Yuting Xing Haoting Wu Kunyu Zheng Yongxian Zhang Jing Zhang Na 《Natural Resources Research》2021,30(6):4355-4377
The Paleogene upper Xiaganchaigou Formation (E32) is the most important source rock and reservoir in the Qaidam Basin. However, there are few studies on the processes of hydrocarbon accumulation in this formation; therefore, its hydrocarbon resource potential has not been estimated reasonably. This paper evaluates the hydrocarbon generation properties in light of an improved hydrocarbon generation and expulsion potential model. According to the geochemical characteristics of source rocks and the petrological features of reservoirs, the potentials of different resource types, including conventional oil, tight oil and shale oil, are quantified by combining the buoyancy-driven hydrocarbon accumulation depth (BHAD) and the lower limit for movable resource abundance. The results show that the source rocks are characterized by a large thickness (more than 1000 m), moderate organic matter content, high marginal maturity and a high conversion rate (50% hydrocarbons have been discharged before Ro?=?1%), which provide sufficient oil sources for reservoir formation. Moreover, the reservoirs in the Qaidam Basin consist mainly of low-porosity and low-permeability tight carbonates (porosity of 4.7% and permeability less than 1 mD). The maximum hydrocarbon generation, expulsion, retention and movable retention intensities at present are 350?×?104 t/km2, 250?×?104 t/km2, 130?×?104 t/km2 and 125?×?104 t/km2, respectively. The thresholds of hydrocarbon generation, expulsion and BHAD were 0.46% Ro, 0.67% Ro and 0.7% Ro, respectively. Moreover, the dynamic evolution process of hydrocarbon accumulation was divided into three evolution stages, namely, (a) initial hydrocarbon accumulation, (b) conventional hydrocarbon reservoir and shale oil accumulation and (c) unconventional tight oil accumulation. The conventional oil, tight oil and movable shale oil resource potentials were 10.44?×?108 t, 51.9?×?108 t and 390?×?108 t, respectively. This study demonstrates the good resource prospects of E32 in the Qaidam Basin. A comprehensive workflow for unconventional petroleum resource potential evaluation is provided, and it has certain reference significance for other petroliferous basins, especially those in the early unconventional hydrocarbon exploration stage.
相似文献19.
The resolution achievable for chironomid identifications has increased in recent years because of significant improvements
in taxonomic literature. However, high taxonomic resolution requires more training for analysts. Furthermore, with greater
taxonomic resolution, misidentifications and the number of rare, poorly represented taxa in chironomid calibration datasets
may increase. We assessed the effects of various levels of taxonomic resolution on the performance of chironomid-based temperature
inference models (transfer functions) and temperature reconstruction. A calibration dataset consisting of chironomid assemblage
and temperature data from 100 lakes was examined at four levels of taxonomic detail. The coarsest taxonomic resolution primarily
represented identifications to genus or suprageneric level. At the highest level of taxonomic resolution, identification to
genus level was possible for 37% of taxa, and identification below genus was possible for 60% of taxa. Transfer functions
were obtained using Weighted Averaging (WA) and Weighted Averaging-Partial Least Squares (WA-PLS) regression. Cross-validated
performance statistics, such as the root mean square error of prediction (RMSEP) and the coefficient of determination (r
2) between inferred and observed values improved considerably from the lowest taxonomic resolution level (WA: RMSEP 1.91°C,
r
2 0.78; WA-PLS: RMSEP 1.59°C, r
2 0.86) to the highest taxonomic resolution level (WA: RMSEP 1.66°C, r
2 0.84; WA-PLS: RMSEP 1.41°C, r
2 0.89). Reconstructed July air temperatures during the Lateglacial period based on fossil chironomid assemblages from Hijkermeer
(The Netherlands) were similar for all levels of taxonomic resolution, except the coarsest level. At the coarsest taxonomic
level, reconstruction failed to infer one of the known Lateglacial cold episodes in the record. Also, the difference in reconstructed
values based on lowest and highest taxonomic resolutions exceeded sample-specific estimated standard errors of prediction
in several instances. Our results suggest that chironomid-based transfer functions at the highest taxonomic resolution outperform
models based on lower-resolution calibration data. However, transfer functions of intermediate taxonomic resolution produced
results very similar to models based on high-resolution taxonomic data. In studies that include analysts with different levels
of expertise, inference models based on intermediate taxonomic resolution, therefore, might provide an alternative to transfer
functions of maximum taxonomic detail in order to ensure taxonomic consistency between calibration datasets and down-core
records produced by different analysts. 相似文献
20.
Enlou Zhang Richard Jones Alan Bedford Peter Langdon Hongqu Tang 《Journal of Paleolimnology》2007,38(4):477-491
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