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1.
The nitrogen stable isotopic signature (δ15N) of sediment is a powerful tool to understand eutrophication history, but its interpretation remains a challenge. In a large-scale comparative approach, we identified the most important drivers influencing surface sediments δ15N of 65 lakes from two regions of Canada using proxies that reflect watershed nitrogen (N) sources, internal lake microbial cycling and productivity. Across regions, we found that water column total nitrogen (TN), %N in the sediments and lake morphometric variables were the best predictors of sedimentary δ15N, explaining 66 % of its variation. Significant relationships were also found between sediment δ15N and human-derived N load ( \( R_{{{\text{adj}} .}}^{2} \) = 0.23, p < 0.001), the latter being a strong predictor of TN ( \( R_{{{\text{adj}} .}}^{2} \) = 0.68, p < 0.001). Despite a relatively strong overall relationship, variation partitioning revealed an interesting difference in the dominant variable that influenced regional δ15N. Alberta lake sedimentary δ15N signature was dominated by human derived N load. In contrast, internal processing appeared to be more important in Quebec lakes, where sediment δ15N was best explained by %N in the sediments and lake volume. Overall, our findings support the use of δ15N in paleolimnological investigations to reconstruct changing N sources to lakes but also highlight that regions may have distinctive drivers. Interpretations of sediment δ15N are likely to be strongest when multiple lines of evidence are employed and when placed in a regional context. 相似文献
2.
Sidney Kuerten Mauro Parolin Mario L. Assine Michael M. McGlue 《Journal of Paleolimnology》2013,49(2):171-183
Sponge spicules are siliceous microfossils that are especially useful for analysis of sandy fluvio-lacustrine sediments. Sponge spicules in a long sediment core (~550 cm below surface), consisting of fine sand, sandy silt, and organic-rich mud, recovered from the floodplain of the Nabileque River, southern Pantanal, Brazil (S20°16′38.3″/W57°33′00.0″), form the basis of a novel paleoenvironmental interpretation for this region. Optically stimulated luminescence dates constrain the timing of deposition to the middle-late Holocene and all spicules identified are typical of the Brazilian cerrado biome. The base of the section is dominated by Oncosclera navicella Carter 1881, Metania spinata Carter 1881, and Corvospongilla seckti Bonetto and Ezcurra de Drago 1966, which indicate a lotic to semi-lotic environment strongly influenced by an actively meandering river channel at ~6.7–5.7 ka BP. The appearance of Heterorotula fistula Volkmer-Ribeiro and Motta 1995, Dosilia pydanieli Volkmer-Ribeiro 1992 and Radiospongilla amazonensis Volkmer-Ribeiro and Maciel 1983 at ~340 cm downcore suggests a reduction in flowing water and a more stable lentic environment, consistent with deposition in an oxbow lake. This oxbow lake environment existed during an interval of regional aridity between ~4.5 and 3.9 ka BP. Spicules, as well as phytoliths and diatoms, are highly variable moving up-section, with species from both lotic and lentic ecosystems present. Above ~193 cm, the total abundance of spicules declines, consistent with wetter climate conditions and development of an underfit river similar to the modern floodplain. Results support hypotheses related to migration of the Paraguay River inferred from geomorphological studies and add a key southern-region dataset to the emerging Holocene database of paleoenvironmental records from the Pantanal wetlands. 相似文献
3.
Carsten Meyer-Jacob Hendrik Vogel Florian Boxberg Peter Rosén Michael E. Weber Richard Bindler 《Journal of Paleolimnology》2014,52(3):245-255
We present an independent calibration model for the determination of biogenic silica (BSi) in sediments, developed from analysis of synthetic sediment mixtures and application of Fourier transform infrared spectroscopy (FTIRS) and partial least squares regression (PLSR) modeling. In contrast to current FTIRS applications for quantifying BSi, this new calibration is independent from conventional wet-chemical techniques and their associated measurement uncertainties. This approach also removes the need for developing internal calibrations between the two methods for individual sediments records. For the independent calibration, we produced six series of different synthetic sediment mixtures using two purified diatom extracts, with one extract mixed with quartz sand, calcite, 60/40 quartz/calcite and two different natural sediments, and a second extract mixed with one of the natural sediments. A total of 306 samples—51 samples per series—yielded BSi contents ranging from 0 to 100 %. The resulting PLSR calibration model between the FTIR spectral information and the defined BSi concentration of the synthetic sediment mixtures exhibits a strong cross-validated correlation ( \( {\text{R}}^{ 2}_{\text{cv}} \) = 0.97) and a low root-mean square error of cross-validation (RMSECV = 4.7 %). Application of the independent calibration to natural lacustrine and marine sediments yields robust BSi reconstructions. At present, the synthetic mixtures do not include the variation in organic matter that occurs in natural samples, which may explain the somewhat lower prediction accuracy of the calibration model for organic-rich samples. 相似文献
4.
Rivers and streams originating in the surrounding mountainous area are the major sources of salt in the Salinas Grandes basin (Córdoba, Argentina). These rivers infiltrate when they reach the sandflat or in the fringes of the mudflat, feeding springs which often form shallow lakes. Presently, the lakes are distant from the playa edge, thus allowing inflow waters to dissolve ancient (Pleistocene?) evaporite beds. In the sandflat environment, two dominant types of water have been recognized (SO 4 2? -Cl?-HCO 3 ? -Na+, and Cl?-SO 4 2? -HCO 3 2? -Na+), both considered as original members of the brine in the saline complex. Two main sources of solutes were distinguished, one related to the waters supplied by the southern sector and another to waters of the eastern sector. As a result of the chemical evolution in the playa environment, all brines belong to the neutral type (Cl?-SO 4 2? -Na+). Following Hardie and Eugster's (1970) model, waters from the southern sector should evolve towards an alkaline brine (Cl?-SO 4 2? -HCO 3 ? -Na+), whereas those from to the eastern sector should evolve towards a neutral one (Cl?-SO 4 2? -Na+). A computer simulation was carried out to model the chemical evolution of source waters. The results obtained by this methodology showed the same dichotomy (alkaline vs. neutral) established by Hardie and Eugster's (1970) model. The deficit in alkalinity could not be explained by any of the mechanisms published until now. Gypsum dissolution is the most likely mechanism which accounts for the chemical evolution of the waters investigated. When such a process is included in the computations, the Ca2+ supplied by gypsum beds generates an increase in the ion activity product (aCa+2·aCO 3 2? ) and produces a significant change in the 2Ca+2/(2CO 3 2? +HCO 3 ? ) ratio, switching from values less than 1 to values greater than 1. This process determines the precipitation of calcite, and leads to a decrease in alkalinity, which in turn would explain the existence of a neutral brine in the saline complex. An intermediate salinity brine was detected in the mudflat, which, according to the model (Hardie and Eugster, 1970), should evolve towards a SO 4 2? -free neutral brine (Cl?-Na+-Ca2+). The absence of this type of brine may be explained through mixing processes. 相似文献
5.
Patrick Rioual Yanbin Lu Handong Yang Louis Scuderi Guoqiang Chu Jonathan Holmes Bingqi Zhu Xiaoping Yang 《Journal of Paleolimnology》2013,50(2):207-229
We describe a dataset of 26 modern diatom samples and associated environmental variables from the Badain Jaran Desert, northwest China. The influence of electrical conductivity (EC) and other variables on diatom distribution was explored using multivariate analyses and generalized additive modeling of species response curves. A transfer function was derived for EC, the variable with the largest unique effect on diatom variance, as shown by partial canonical correspondence analysis. Weighted-averaging partial least squares regression and calibration provided the best model, with a high coefficient of determination ( $ {\text{r}}_{\text{boot}}^{2} $ = 0.91) and low prediction error (RMSEPboot = 0.136 log10 μS cm?1). To assess its potential for palaeosalinity and palaeoclimate reconstructions, the EC transfer function was applied to fossil diatom assemblages from 210Pb-dated short sediment cores collected from two subsaline lakes of the Badain Jaran Desert. The diatom-inferred (DI) EC reconstructions were compared with meteorological data for the past 50 years and with remote sensing data for the period AD 1990–2012. Changes in DI–EC were small and their relationship with climate was weak. Moreover, remote sensing data indicate that the surface areas and water depths of these lakes did not change, which suggests that water loss by evaporation is compensated by groundwater inflow. These results suggest that the response of these lakes to climate change is mediated by non-climatic factors such as the hydrogeological setting, which control recharge from groundwater, and may be non-linear and non-stationary. 相似文献
6.
Grass seed farmers have burned their fields in Idaho and Washington State for decades. Field burning, however, creates small particulate matter air pollution, thus engendering a growing public backlash by the 1990s that manifested itself in new clean air advocacy groups. The new groups’ push for policy change eventually met with significant success in both cases. How did each set of advocates approach the challenge of policy change? More specifically, what kinds of policy venues did each group choose and why? This research uses the cases to explore and explain each clean air group's choices vis-à-vis hypotheses of venue choice. Three hypotheses are tested—Schattschneider's (1960) “expanded scope of conflict” thesis, ACF's (Sabatier and Jenkins-Smith 1999) contention that groups strategically apply their resources in order to increase the likelihood of achieving their primary goal(s), and Pralle's (2003, 2010) thesis that internal group constraints deter groups from moving into new venues. 相似文献
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8.
Guofeng Cao Phaedon C. Kyriakidis Michael F. Goodchild 《International journal of geographical information science》2013,27(10):1741-1750
Li and Zhang (2012b, Comments on ‘Combining spatial transition probabilities for stochastic simulation of categorical fields’ with communications on some issues related to Markov chain geostatics) raised a series of comments on our recent paper (Cao, G., Kyriakidis, P.C., and Goodchild, M.F., 2011. Combining spatial transition probabilities for stochastic simulation of categorical fields. International Journal of Geographical Information Science, 25 (11), 1773–1791), which include a notation error in the model equation provided for the Markov chain random field (MCRF) or spatial Markov chain model (SMC), originally proposed by Li (2007b, Markov chain random fields for estimation of categorical variables. Mathematical Geology, 39 (3), 321–335), and followed by Allard et al. (2011, An efficient maximum entropy approach for categorical variable prediction. European Journal of Soil Science, 62, 381–393) about the misinterpretation of MCRF (or SMC) as a simplified form of the Bayesian maximum entropy (BME)-based approach, the so-called Markovian-type categorical prediction (MCP) (Allard, D., D'Or, D., and Froideveaux, R., 2009. Estimating and simulating spatial categorical data using an efficient maximum entropy approach. Avignon: Unite Biostatisque et Processus Spatiaux Institute National de la Recherche Agronomique. Technical Report No. 37; Allard, D., D'Or, D., and Froideveaux, R., 2011. An efficient maximum entropy approach for categorical variable prediction. European Journal of Soil Science, 62, 381–393). Li and Zhang (2012b, Comments on ‘Combining spatial transition probabilities for stochastic simulation of categorial fields’ with communication on some issues related to Markov chain geostatistics. International Journal of Geographical Information Science) also raised concerns regarding several statements Cao et al. (2011, Combining spatial transition probabilities for stochastic simulation of categorical fields. International Journal of Geographical Information Science, 25 (11), 1773–1791) had made, which mainly include connections between permanence of ratios and conditional independence, connections between MCRF and Bayesian networks and transiograms as spatial continuity measures. In this response, all of the comments and concerns will be addressed, while also communicating with Li and other colleagues on general topics in Markov chain geostatistics. 相似文献
9.
1 Introduction Ecological environment such as water, soil, etc. are very fragile in the karst area because of the special geological background. With the fast increase of the population and rapid social and economic development in karst area, contradictio… 相似文献
10.
Alexander A. Prokopenko Christopher St. G. C. Kendall 《Journal of Paleolimnology》2008,40(4):1185-1192
This paper seeks to arrive at a consistent interpretation of (1) the age model, (2) the grain size record, and (3) seismic reflection data from Lake Hovsgol (a.k.a Khubsugul or Hövsgöl), Mongolia, reported by Fedotov et al. (2007, earlier by Fedotov et al. 2002, 2004). In their most recent contribution, the grain size record of the KDP-01 drill core is interpreted as a climatic signal while little consideration is given to lake-level changes and hence to basin-wide changes in depositional setting evident from seismic profiles; also, a nearly linear age model is at odds with the seismic evidence for a major angular unconformity in the sediment strata. The lack of regional seismic stratigraphic analysis has thus led to an improbable interpretation of the Lake Hovsgol sediment grain size record and ultimately to an improbable scenario of Mongolian glaciation history. Using the available seismic profiles, here we show that the drill core penetrated several transgressive/regressive sedimentary sequences and a major angular unconformity. Therefore, the drilled sediment section cannot represent continuous sediment accumulation and the Brunhes age model across the unconformity cannot be nearly linear; the time interval representing a hiatus remains to be determined. The assumed nearly linear age/depth relationship in the upper 23 m above the angular unconformity is also an unlikely relationship, given the evidence of repeated changes in lake level, and hence in the depositional setting and sedimentation rates. We further propose a qualitative reference model for changes in the Lake Hovsgol depositional setting (presented as a step-by-step animation – see supplementary material) based on manually ‘backstripping and rebuilding’ the seismic pattern. We argue that this model provides a useful template of the likely sediment facies changes in the deep axial part of the Hovsgol basin: our crude model in fact captures the major depositional trends in the KDP-01 drill core section located some 10 km NW along the seismic line. We contend that changes in the depositional setting provide the first-order control on sediment grain size in the Hovsgol record. Our study provides important new constraints on the nature of sedimentary proxy records in Lake Hovsgol and on their interpretation as a record of Mongolian glaciation history. 相似文献
11.
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
12.
Mary D. Curtis 《The Journal of geography》2019,118(3):130-142
Preparing learners for the future requires twenty-first-century teaching that integrates professional tools in the classroom. Geospatial technologies (GST), which represent geographical professional technologies, lack robust integration in high school geography. Researchers continue to ask why educators teach about rather than with GST. Understanding teacher decisions is paramount. This mixed methods study examined commonalities among teachers who use GST using Mishra and Koehler’s (2006) Technological, Pedagogical, Content Knowledge (TPCK) framework as a theoretical lens. This investigation examined whether geography teachers who exhibit stronger geospatial TPCK used GST more frequently than other teachers who exhibited a less developed knowledge base. 相似文献
13.
Bruce Thom 《The Australian geographer》2004,35(1):3-16
This paper examines how legal structures interact with land‐use decisions in the coastal zone. The emphasis is on NSW where there has been a steady evolution of legislative and other measures to regulate how the coast is to be planned and managed. These measures arise from a long history of individual, corporate, local government and State agency actions directed more at private benefit than at protecting and conserving environmental values for the public good. Alienation of foreshores, restrictions on access, buildings located in hazardous areas, canals exposing soils rich in acids, and pollution of waterways are examples of degradation on this coast. Yet much remains to be protected. Expansion of coastal national parks over the past decade has helped. But new planning controls have been introduced to support the NSW Coastal Policy (1997). In essence, there is evidence that the State government seeks to implement environmentally sustainable development principles to ensure that as the population continues to grow, decisions on future land uses will reflect the functioning of ecosystems and the dynamics of coastal and catchment geomorphology and hydrology. Pressures from individuals and corporations exercising traditional property rights need to be managed within a statutory framework that facilitates sustainability of coastal environmental values cherished by so many. 相似文献
14.
Gail Christine Potgieter Florian Johannes Weise Bettina Wachter Jörg Melzheimer Ingrid Wiesel Ken Stratford 《社会与自然资源》2017,30(10):1299-1303
Carnivore conservationists agree that addressing the socioeconomic needs of people is critical to human-carnivore conflict mitigation. We therefore welcome studies that encompass complex social and cultural factors that affect the severity of human-carnivore conflict on Namibian farmlands. However, we contend that the recent study by Rust et al. (2016) was poorly designed, used inappropriate sampling methods, lacked quantitative information on their qualitative results, and ultimately produced unsupported conclusions about the role of historic apartheid and current racism in exacerbating human-carnivore conflict in Namibia. We outline our concerns regarding the methods used, and demonstrate that the conclusions drawn by Rust et al. were not supported by their data. 相似文献
15.
Jeffrey J. Cook 《社会与自然资源》2014,27(12):1257-1270
The preproposal stage of the rulemaking process is notoriously understudied, but enormously important in determining regulatory outputs. Recently, Rinfret (2011c) analyzed the U.S. Fish and Wildlife Service (USFWS) rulemaking process and developed a frame analysis model to interpret stakeholder influence during the preproposal stage. Rinfret argues that stakeholders use three frames to influence agency rulemaking, including an expertise, a fiscal feasibility, and an information frame. This article tests this model to determine whether it is applicable to other federal agencies such as the National Park Service (NPS). Through an analysis of stakeholder framing within the 2012 NPS Yellowstone Winter Use Rule, this research confirms that Rinfret's model is indeed applicable to the NPS process. Therefore, this research suggests that this theoretical model examining stakeholder influence is applicable to other public land agencies, and arguably can be applied across the bureaucracy. 相似文献
16.
Between 2000 and 2014, more than thirty geography departments adopted revised or new names, with some entirely dropping geography. Although renaming and rebranding efforts are not new to higher education, the rapid pace at which geography department names have changed raises questions about the discipline's identity and health. We examine the renaming trend within geography programs together with intended and unexpected factors as perceived by faculty. Specifically, we look at the renaming and rebranding trend within the context of four pillars offered by Pattison (1964) to define geography's principal academic domains—earth-science, man–land, area/regional studies, and spatial traditions. 相似文献
17.
Daniel Sui Michael Goodchild 《International journal of geographical information science》2013,27(11):1737-1748
It is hard to believe that 10 years have passed since we wrote our guest editorial for IJGIS (Sui and Goodchild 2001). Using the nascent evidence that emerged in the late 1990s, we speculated back in 2001 that geographic information systems (GIS) were rapidly becoming part of the mass media. On the basis of the proposition of GIS as media, we were able to link GIScience with theories in media studies such as Marshall McLuhan's law of the media, which considers modern media as modifiable perceptive extensions of human thought (Sui and Goodchild 2003). Remarkable conceptual and technological advances in GIS have been made during the past 10 years. The goal of this review is to provide an update on the ‘GIS as media’ argument we made 10 years ago and to discuss the new challenges for GIScience posed by the growing convergence of GIS and social media. 相似文献
18.
Y. Nakaguro S.S. Makhanov M.N. Dailey 《International journal of geographical information science》2013,27(5):765-783
Higher-order active contours or snakes show much promise for the extraction of complex objects from noisy imagery. These models provide an elegant mathematical framework for specifying the desired properties of target objects through energy functionals that can be minimized with standard optimization techniques. However, techniques to allow quadratic snakes to change topology during segmentation have not been fully exploited. Additionally, external forces for improving convergence of quadratic snakes have similarly yet to be explored. In this article, we propose a model that allows multiple quadratic snakes to split, merge, and disappear. Although the separate components of our approach have been introduced elsewhere by Cohen (1991), Xu and Prince (1997), and Rochery et al. (2006), this article is the first comprehensive empirical study of their performance on real-world complex network extraction tasks. We analyze the applicability of the model to road extraction from satellite images that vary in complexity from simple networks to large networks with multiple loops. We also analyze the effects of external forces enhanced by oriented filtering, gradient vector flow fields, and Canny edge detection. In a series of experiments, we found that the multiple cooperating quadratic snake model performs well on complex, noisy images. Our experiments also establish a performance improvement when the proposed quadratic model is coupled with the Canny-based gradient vector flow technique. 相似文献
19.
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
20.
Barbara P. Buttenfield 《International journal of geographical information science》2013,27(5):661-665
In this article, we present a geographically explicit agent-based model (ABM), loosely coupled with vector geographical information systems (GISs), which explicitly captures and uses geometric data and socioeconomic attributes in the simulation process. The ability to represent the urban environment as a series of points, lines, and polygons not only allows one to represent a range of different-sized features such as buildings or larger areas portrayed as the urban environment but is a move away from many ABMs utilizing GIS that are rooted in grid-based structures. We apply this model to the study of residential segregation, specifically creating a Schelling (1971) type of model within a hypothetical cityscape, thus demonstrating how this approach can be used for linking vector-based GIS and agent-based modeling. A selection of simulation experiments are presented, highlighting the inner workings of the model and how aggregate patterns of segregation can emerge from the mild tastes and preferences of individual agents interacting locally over time. Furthermore, the article suggests how this model could be extended and demonstrates the importance of explicit geographical space in the modeling process. 相似文献