Seasonal-dependence in the responses of biological communities to flood pulses in warm temperate floodplain lakes: implications for the “alternative stable states” model     

Griselda Chaparro  María Soledad Fontanarrosa  María Romina Schiaffino  Paula de Tezanos Pinto  Inés O’Farrell 《Aquatic Sciences - Research Across Boundaries》2014,76(4):579-594

In floodplains located in temperate regions, seasonal variations in temperature affect biological communities and these effects may overlap with those of the flood regime. In this study we explored if and how timing (with regard to temperature seasonality) influences the responses of planktonic and free-floating plants communities to floods in a warm temperate floodplain lake and assessed its relevance for determining state shifts. We took samples of zooplankton, phytoplankton, picoplankton, heterotrophic nanoflagellates and free-floating macrophytes at four sites of the lake characterized by the presence-absence of emergent or free-floating macrophytes along a 2-year period with marked hydrological fluctuations associated to river flood dynamics. We performed ANOVA tests to compare the responses of these communities to floods in cold and warm seasons and among sites. Planktonic communities developed high abundances in response to floods that occurred in the cold season, while the growth of free-floating macrophytes was impaired by low winter temperatures. Spring and summer floods favored profuse colonization by free-floating plants and limited the development of planktonic communities. The prolonged absence of floods during warm periods caused environmental conditions that favored Cyanobacteria growth, leading to a “low turbid waters” regime. The occurrence of floods early in the warm season caused phytoplankton dilution and promoted free-floating plant colonization and a shift towards a “high clear waters” state. Zooplankton:phytoplankton biomass ratio was very low during floods in warm seasons, thus zooplankton grazing on phytoplankton seemed to play a minor role in the maintenance of the clear regime.  相似文献   

GPS L1-Frequency Observations of Equatorial Scintillations and Irregularity Zonal Velocities     

Marcio T. A. H. Muella  Eurico R. de Paula  Olusegun F. Jonah 《Surveys in Geophysics》2014,35(2):335-357

In this work, the climatology of ionospheric scintillations at global positioning system (GPS) L-band frequency and the zonal drift velocities of scintillation-producing irregularities were depicted for the equatorial observatory of São Luis (2.33°S; 44.21°W; dip latitude 1.3°S), Brazil. This is the first time that the hourly, monthly, and seasonal variations of scintillations and irregularity zonal drifts at São Luis were characterized during periods of different solar activity levels (from December 1998 to February 2007). The percentage occurrence of scintillations at different sectors of the sky was also investigated, and the results revealed that the scintillations are more probable to be observed in the west sector of the sky above São Luis, whereas the north–south asymmetries are possibly related to asymmetries in the plasma density distribution at off-equatorial latitudes. The scintillations on GPS signals occurred more frequently around solar maximum years, but it is also clear from the results of a strong variability in the scintillation activity in the years with moderate solar flux during the descending phase of the solar cycle. The equatorial scintillations occur predominantly during pre-midnight hours with a broad maximum near the December solstice months. In general, weak level of scintillations (S ₄ index between 0.2 and 0.4) dominated at all seasons; however, during the winter months around solar maximum years (although the scintillation occurrence is extremely low), stronger levels of scintillations (S ₄ > 0.6) may occur at comparable rate with the weak scintillations. The irregularity zonal velocities, as estimated from the GPS spaced-receiver technique, presented a different scenario for the two seasons analyzed; during the equinoxes, the magnitude of the zonal velocities appeared not to change with the solar activity, whereas during the December solstice months, the larger magnitudes were observed around solar maximum years. Other relevant aspects of the observations are highlighted and discussed.  相似文献   

Perception of change in freshwater in remote resource-dependent Arctic communities   总被引：1，自引：0，他引：1  

Lilian Alessa  Andrew Kliskey  Paula Williams  Michael Barton 《Global Environmental Change》2008,18(1):153-164

This paper provides empirical evidence to support existing anecdotal studies regarding the mechanisms by which human communities become vulnerable to rapid changes in freshwater resources on the Seward Peninsula, Alaska. We interviewed adults, stratified by age, sex, and extended family, in Inupiat communities on the Seward Peninsula. Using categorical indices as part of a semi-structured interview we elicited a respondent's perception of the availability and quality of freshwater resources in their community as well as their perception of change in the availability and quality of freshwater during the period of their lifetime in that community. Significant relationships were observed between age groups for the perception of change in the availability of the local water source and the perception of change in its quality—older generations perceiving more change than younger age groups. These perceptions of change were examined with respect to recent historic changes in precipitation and temperature on the Seward Peninsula. These findings suggest that individual perceptions are instrumental in determining whether or not change merits response. The findings also provide evidence that oral traditional knowledge systems have shifted from continuous to discontinuous transmission, distancing the users from traditional resources. We discuss the role of collective knowledge, through the transmission of knowledge from elders to subsequent generations, in aiding the development of a community's ability to note and respond to changes in critical natural resources.  相似文献   

Community resilience to tsunamis along the Southeastern Pacific: a multivariate approach incorporating physical,environmental, and social indicators     

Villagra  Paula  Herrmann  Marie Geraldine  Quintana  Carolina  Sepúlveda  Roger D. 《Natural Hazards》2017,88(2):1087-1111

Tsunamic events are a frequent hazard to coastal towns. Despite this, the extent to which resilience models can be applied to coastal towns as well as the aspects that should be considered when doing so have not been fully evaluated. There is little information regarding the specific indicators that allow cities to better cope and adapt to the impacts of tsunamis, and this information is especially scarce for developing countries such as Chile. The main objective of this study is to develop a resilience model to explore the extent to which local characteristics influence the resilience of Chilean coastal communities to tsunami hazards. Accordingly, this study presents the Coastal Community Resilience model (The CORE model) for exploring the adaptive capacity of coastal areas affected by tsunamis. This model was then applied to fourteen coastal villages, distributed within four towns, three communes, and two regions of Chile. Data comprising 21 indicators that address the physical, environmental, and social resilience aspects of the villages were obtained on-site and from governmental and municipality databases; these data were then subjected to multivariate analysis in order to determine which indicators most and least affect resilience and whether indicators affect resilience positively or negatively. Variation in resilience among the villages was explained by similarities and differences in the administrative-political, urban, rural, and indigenous characteristics of the study areas. In addition to these results, we discuss land use planning considerations to build community resilience, and we provide insight into the utility of the resilience model proposed here. Overall, our findings shed light on gaps in planning policies and opportunities for planning coastal resilient communities, particularly for those where data of explicit indicators are scarce like in Chile and other developing countries.

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An inter-regional assessment of concentrations and δ13C values of methane and dissolved inorganic carbon in small European lakes     

Päivi Rinta  David Bastviken  Maarten van Hardenbroek  Paula Kankaala  Markus Leuenberger  Jos Schilder  Tabea Stötter  Oliver Heiri 《Aquatic Sciences - Research Across Boundaries》2015,77(4):667-680

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Dynamic issues in the SE South America storm surge modeling     

Paula Etala 《Natural Hazards》2009,51(1):79-95

The ability of the SMARA storm surge numerical prediction system to reproduce local effects in estuarine and coastal winds was recently improved by considering one-way coupling of the air–sea momentum exchange through the wave stress, and best forecasting practices for downscaling. The inclusion of long period atmospheric pressure forcing in tide and tide/surge calculations corrected a systematic error in the surge, produced by the South Atlantic Ocean quasi-stationary pressure patterns. The maximum forecast range for the storm surge at Buenos Aires provided by the real-time use of water level observations is approximately 12 h. The best available water level prediction is the 6-h forecast (nowcast) based on the closest water level observations. The 24-h forecast from the numerical models slightly improves this nowcast. Although the numerical forecast accuracy degrades after the first 48 h, the improvement to the full range observation-based prediction is maintained at the inner Río de la Plata area and extends to the first 3 days at the intermediate navigation channels.  相似文献   

Near-future changes in storm surges along the Atlantic Iberian coast     

Fortunato  André B.  Meredith  Edmund P.  Rodrigues  Marta  Freire  Paula  Feldmann  Hendrik 《Natural Hazards》2019,98(3):1003-1020

Natural Hazards - Decadal predictions bridge the gap between the short-term weather/seasonal forecasts and the long-term climate projections. They target the reproduction of large-scale weather...  相似文献   

Predicting the activity of Cd and Zn in soil pore water from the radio-labile metal fraction     

A.M Tye  N.M.J Crout  S Preston  W Davison  G.I Paton  L Resende 《Geochimica et cosmochimica acta》2003,67(3):375-385

Cadmium and zinc were added at 3 and 300 mg kg⁻¹, respectively, to 23 soils and incubated at 16°C and 80% field capacity for 818 d. Following addition of metal, changes in the radio-labile concentrations of both elements were examined on seven separate sampling occasions over 818 d. At each sample time, soil pore water was extracted using Rhizon soil solution samplers, and concentrations of Cd, Zn, dissolved organic carbon, and major cations and anions were determined. The chemical speciation program WHAM 6 was used to determine free metal ion activity, (M²⁺). Similar measurements were made on a set of historically contaminated soils from old mining areas, sewage sludge disposal facilities, and industrial sources. The two data sets were combined to give a range of values for p(Cd²⁺) and p(Zn²⁺) that covered 5 and 4 log₁₀ units, respectively. A pH-dependent Freundlich model was used to predict Zn²⁺ and Cd²⁺ ion activity in soil pore water. Total and radio-labile metal ion concentration in the solid phase was assumed to be adsorbed on the “whole soil,” humus, or free iron oxides to provide alternative model formats. The most successful models assumed that solubility was controlled by adsorption on soil humus. Inclusion of ionic strength as a model variable provided small improvements in model fit. Considering competition with Ca²⁺ and between Zn²⁺ and Cd²⁺ produced no apparent improvement in model fit. Surprisingly, there was little difference between the use of total and labile adsorbed metal as a model determinant. However, this may have been due to a strong correlation between metal lability and pH in the data set used. Values of residual standard deviation for the parameterized models using labile metal adsorbed on humus were 0.26 and 0.28 for prediction of p(Cd²⁺) and p(Zn²⁺), respectively. Solubility control by pure Zn and Cd minerals was not indicated from saturation indices. However there may have been fixation of metals to non-radio-labile forms in CaCO₃ and Ca-phosphate compounds in the soils in the higher pH range. Independent validation of the Cd model was carried out using an unpublished data set that included measurements of isotopically exchangeable Cd. There was good agreement with the parameterized model.  相似文献   

(Ca,Mg)2Si2O6 clinopyroxenes: A solution model based on nonconvergent site-disorder     

Paula M. Davidson  John Grover  Donald H. Lindsley 《Contributions to Mineralogy and Petrology》1982,80(1):88-102

Experiments at high pressure and temperature indicate that excess Ca may be dissolved in diopside. If the (Ca, Mg)₂Si₂O₆ clinopyroxene solution extends to more Ca-rich compositions than CaMgSi₂O₆, macroscopic regular solution models cannot strictly be applied to this system. A nonconvergent site-disorder model, such as that proposed by Thompson (1969, 1970), may be more appropriate. We have modified Thompson's model to include asymmetric excess parameters and have used a linear least-squares technique to fit the available experimental data for Ca-Mg orthopyroxene-clinopyroxene equilibria and Fe-free pigeonite stability to this model. The model expressions for equilibrium conditions \(\mu _{{\text{Mg}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{opx}}} = \mu _{{\text{Mg}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{cpx}}} \) (reaction A) and \(\mu _{{\text{Ca}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{opx}}} = \mu _{{\text{Ca}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{cpx}}} \) (reaction B) are given by: 1 $$\begin{gathered} \Delta \mu _{\text{A}}^{\text{O}} = {\text{RT 1n}}\left[ {\frac{{(X_{{\text{Mg}}}^{{\text{opx}}} )^2 }}{{X_{{\text{Mg}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} }}} \right] - \frac{1}{2}\{ W_{21} [2(X_{{\text{Ca}}}^{{\text{M2}}} )^3 - (X_{{\text{Ca}}}^{{\text{M2}}} ] \hfill \\ {\text{ + 2W}}_{{\text{22}}} [X_{{\text{Ca}}}^{{\text{M2}}} )^2 - (X_{{\text{Ca}}}^{{\text{M2}}} )^3 + \Delta {\text{G}}_{\text{*}}^{\text{0}} (X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Ca}}}^{{\text{M2}}} )\} \hfill \\ {\text{ + W}}^{{\text{opx}}} (X_{{\text{Wo}}}^{{\text{opx}}} )^2 \hfill \\ \Delta \mu _{\text{B}}^{\text{O}} = {\text{RT 1n}}\left[ {\frac{{(X_{{\text{Ca}}}^{{\text{opx}}} )^2 }}{{X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Ca}}}^{{\text{M2}}} }}} \right] - \frac{1}{2}\{ 2W_{21} [2(X_{{\text{Mg}}}^{{\text{M2}}} )^2 - (X_{{\text{Mg}}}^{{\text{M2}}} )^3 ] \hfill \\ {\text{ + W}}_{{\text{22}}} [2(X_{{\text{Mg}}}^{{\text{M2}}} )^3 - (X_{{\text{Mg}}}^{{\text{M2}}} )^2 + \Delta {\text{G}}_{\text{*}}^{\text{0}} (X_{{\text{Mg}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} )\} \hfill \\ {\text{ + W}}^{{\text{opx}}} (X_{{\text{En}}}^{{\text{opx}}} )^2 \hfill \\ \hfill \\ \end{gathered} $$ where 1 $$\begin{gathered} \Delta \mu _{\text{A}}^{\text{O}} = 2.953 + 0.0602{\text{P}} - 0.00179{\text{T}} \hfill \\ \Delta \mu _{\text{B}}^{\text{O}} = 24.64 + 0.958{\text{P}} - (0.0286){\text{T}} \hfill \\ {\text{W}}_{{\text{21}}} = 47.12 + 0.273{\text{P}} \hfill \\ {\text{W}}_{{\text{22}}} = 66.11 + ( - 0.249){\text{P}} \hfill \\ {\text{W}}^{{\text{opx}}} = 40 \hfill \\ \Delta {\text{G}}_*^0 = 155{\text{ (all values are in kJ/gfw)}}{\text{.}} \hfill \\ \end{gathered} $$ . Site occupancies in clinopyroxene were determined from the internal equilibrium condition 1 $$\begin{gathered} \Delta G_{\text{E}}^{\text{O}} = - {\text{RT 1n}}\left[ {\frac{{X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} }}{{X_{{\text{Ca}}}^{{\text{M2}}} \cdot X_{{\text{Mg}}}^{{\text{M1}}} }}} \right] + \tfrac{1}{2}[(2{\text{W}}_{{\text{21}}} - {\text{W}}_{{\text{22}}} )(2{\text{X}}_{{\text{Ca}}}^{{\text{M2}}} - 1) \hfill \\ {\text{ + }}\Delta G_*^0 (X_{{\text{Ca}}}^{{\text{M1}}} - X_{{\text{Ca}}}^{{\text{M2}}} ) + \tfrac{3}{2}(2{\text{W}}_{{\text{21}}} - {\text{W}}_{{\text{22}}} ) \hfill \\ {\text{ (1}} - 2X_{{\text{Ca}}}^{{\text{M1}}} )(X_{{\text{Ca}}}^{{\text{M1}}} + \tfrac{1}{2})] \hfill \\ \end{gathered} $$ where δG _E ⁰ =153+0.023T+1.2P. The predicted concentrations of Ca on the clinopyroxene Ml site are low enough to be compatible with crystallographic studies. Temperatures calculated from the model for coexisting ortho- and clinopyroxene pairs fit the experimental data to within 10° in most cases; the worst discrepancy is 30°. Phase relations for clinopyroxene, orthopyroxene and pigeonite are successfully described by this model at temperatures up to 1,600° C and pressures from 0.001 to 40 kbar. Predicted enthalpies of solution agree well with the calorimetric measurements of Newton et al. (1979). The nonconvergent site disorder model affords good approximations to both the free energy and enthalpy of clinopyroxenes, and, therefore, the configurational entropy as well. This approach may provide an example for Febearing pyroxenes in which cation site exchange has an even more profound effect on the thermodynamic properties.  相似文献   

Geochemistry of Mesozoic plutons, southern Death Valley region, California: Insights into the origin of Cordilleran interior magmatism     

Tapani O. Rämö  James P. Calzia  Paula J. Kosunen 《Contributions to Mineralogy and Petrology》2002,143(4):416-437

Mesozoic granitoid plutons in the southern Death Valley region of southeastern California reveal substantial compositional and isotopic diversity for Mesozoic magmatism in the southwestern US Cordillera. Jurassic plutons of the region are mainly calc-alkaline mafic granodiorites with )_Ndi of -5 to -16, ⁸⁷Sr/⁸⁶Sr_i of 0.707-0.726, and ²⁰⁶Pb/²⁰⁴Pb_i of 17.5-20.0. Cretaceous granitoids of the region are mainly monzogranites with )_Ndi of -6 to -19, ⁸⁷Sr/⁸⁶Sr_i of 0.707-0.723, and ²⁰⁶Pb/²⁰⁴Pb_i of 17.4-18.6. The granitoids were generated by mixing of mantle-derived mafic melts and pre-existing crust - some of the Cretaceous plutons represent melting of Paleoproterozoic crust that, in the southern Death Valley region, is exceptionally heterogeneous. A Cretaceous gabbro on the southern flank of the region has an unusually juvenile composition ()_Ndi -3.2, ⁸⁷Sr/⁸⁶Sr_i 0.7060). Geographic position of the Mesozoic plutons and comparison with Cordilleran plutonism in the Mojave Desert show that the Precambrian lithosphere (craton margin) in the eastern Mojave Desert region may consists of two crustal blocks separated by a more juvenile terrane.  相似文献