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Paleolimnological evidence of limnetic nutrient concentration equilibrium in a shallow, macrophyte-dominated lake 总被引:5,自引:0,他引:5
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Brent B. Wolfe Tammy L. Karst‐Riddoch Roland I. Hall Thomas W. D. Edwards Michael C. English Roger Palmini Suzanne McGowan Peter R. Leavitt Sheila R. Vardy 《水文研究》2007,21(2):151-168
We used stable isotopes (δ18O and δ2H) and water chemistry to characterize the water balance and hydrolimnological relationships of 57 shallow aquatic basins in the Peace‐Athabasca Delta (PAD), northern Alberta, Canada, based on sampling at the end of the 2000 thaw season. Evaporation‐to‐inflow ratios (E/I) were estimated using an isotope mass‐balance model tailored to accommodate basin‐specific input water compositions, which provided an effective, first‐order, quantitative framework for identifying water balances and associated limnological characteristics spanning three main, previously identified drainage types. Open‐drainage basins (E/I < 0·4; n = 5), characterized by low alkalinity, low concentrations of nitrogen, dissolved organic carbon (DOC) and ions, and high minerogenic turbidity, include large, shallow basins that dominate the interior of the PAD and experience frequent or continuous river channel connection. Closed‐drainage basins (E/I ≥ 1·0; n = 16), in contrast, possess high alkalinity and high concentrations of nitrogen, DOC, and ions, and low minerogenic turbidity, and are located primarily in the relict and infrequently flooded landscape of the northern Peace sector of the delta. Several basins fall into the restricted‐drainage category (0·4 # E/I < 1·0; n = 26) with intermediate water chemistries and are predominant in the southern Athabasca sector, which is subject to active fluviodeltaic processes, including intermittent flooding from riverbank overflow. Integration of isotopic and limnological data also revealed evidence for a new fourth drainage type, mainly located near the large open‐drainage lakes that occupy the central portion of the delta but within the Athabasca sector (n = 10). These basins were very shallow (<50 cm deep) at the time of sampling and isotopically depleted, corresponding to E/I characteristic of restricted‐ and open‐drainage conditions. However, they are limnologically similar to closed‐drainage basins except for higher conductivity and higher concentrations of Ca2+ and Na+, and lower concentrations of SiO2 and chlorophyll c. These distinct features are due to the overriding influence of recent summer rainfall on the basin water balance and chemistry. The close relationships evident between water balances and limnological conditions suggest that past and future changes in hydrology are likely to be coupled with marked alterations in water chemistry and, hence, the ecology of aquatic environments in the PAD. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Food insecurity is a major concern in the United States, particularly in high-poverty areas and among households with children. Urban agriculture helps address food insecurity and promote recreation, aesthetics, biodiversity, and other benefits. This article reports a socioeconomic evaluation of ten different variables, including in situ analysis of healthy, nutritious food options, of a small, intensely urbanized city to identify neighborhoods that would benefit from urban agriculture. We produced a hierarchy of locations (using census block groups), from least to greatest socioeconomic need, for new urban agriculture sites. Our results found that one block group qualified in all ten variables and two-thirds demonstrated a need in at least half of the variables. The majority of these block groups were distributed within the middle of the city. 相似文献
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This paper explores the potential adaptation of harvest tags to the Gulf of Mexico recreational reef fish fishery. The discussion addresses conceptual, theoretical, and practical issues surrounding the application of harvest tags, as well as challenges and opportunities related to the design of tag programs. A review of hunting and fishing tag programs around the world and analysis of Gulf recreational fisheries suggests that tags have the potential to improve control over total catches, increase economic benefits and provide better information for fishery management. Results also provide insight into potential use of fish tags in large-scale recreational fisheries nationwide. 相似文献
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A model for the economics of marine conservation is developed and tested using data from a global sample of Marine Protected Areas (MPAs). Results from logistic regressions indicate that significant determinants of positive MPA effects vary among MPA subgroups. These significant regressors include enforcement in later time periods and certain “goodwill building activities” carried out by MPA management, as well as a number of institutional and socioeconomic characteristics of the communities. Policy implications and recommendations for additional research are discussed. 相似文献
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Matt D. Anders Joel L. Pederson Tammy M. Rittenour Warren D. Sharp John C. Gosse Karl E. Karlstrom Laura J. Crossey Ronald J. Goble Lisa Stockli Guang Yang 《Quaternary Science Reviews》2005,24(23-24):2428-2448
We report new mapping, soils, survey, and geochronologic (luminescence, U-series, and cosmogenic-nuclide) data from Pleistocene deposits in the arid setting of eastern Grand Canyon. The result is a stratigraphic framework of inset fill gravels and associated terraces that provide a record of the responses of hillslopes, tributary streams, and the Colorado River to the last 400 kyr of glacial–interglacial climate change. The best-preserved last 80 kyr of this record indicates a stratigraphic–chronologic disconnect between both deposition and incision along the Colorado River versus along the trunks of local tributaries. For example, the Colorado River finished aggrading and had already begun incising before the main pulse of aggradation in the trunks of local catchments during Marine Isotope Stage 3, and then tributary incision followed during the millennial-scale fluctuations of the last glacial epoch, potentially concurrent with mainstem aggradation. The mainstem record appears to broadly correlate with regional paleoclimate and upstream geomorphic records and thus may be responding to climatic–hydrologic changes in its mountain headwaters, with aggradation beginning during full-glacial times and continuing into subsequent interglacials. The contrasting lag time in responses of the dryland catchments within Grand Canyon may be largely a function of the weathering-limited nature of hillslope sediment supply. 相似文献
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Brent B. Wolfe Tammy L. Karst-Riddoch Matthew D. Falcone Thomas W.D. Edwards 《Quaternary Research》2005,64(2):147-162
Multi-proxy paleolimnological analyses on lake sediment cores from “Spruce Island Lake” (58° 50.82′ N, 111° 28.84′ W), a perched basin in the northern Peace sector of the Peace-Athabasca Delta (PAD), Canada, give insights into the relative roles of flow regulation of the Peace River and climatic variability on the basin hydro-ecology. Results indicate substantial variability in basin hydro-ecology over the past 300 years ranging from seasonal to periodic desiccation in the 1700s to markedly wetter conditions during the early 1800s to early 1900s. The reconstruction is consistent with (1) dry climatic conditions that defined the peak of the Little Ice Age and subsequent amelioration evident in conventional ring-width and isotopic analyses of tree-ring records located hydrologically and climatically upstream of the PAD, and (2) Peace River flood history inferred from sub-annual magnetic susceptibility measurements from another lake sediment record in the Peace sector of the PAD. Although regulation of the Peace River for hydroelectric power generation since 1968 has long been considered a major stressor of the PAD ecosystem leading to reduced frequency of ice-jam and open-water flooding and an extended period of drying, our results show that current hydro-ecological status is not unprecedented as both wetter and drier conditions have persisted for decades in the recent past under natural climatic variability. Furthermore, paleolimnological evidence from Spruce Island Lake indicates that recently observed dryness is part of a longer trend which began some 20-40 years prior to Peace River regulation. 相似文献