A multicatchment analysis of headwater and downstream temperature effects from contemporary forest harvesting          下载免费PDF全文

Kevin D. Bladon  Catalina Segura  Nicholas A. Cook  Sharon Bywater‐Reyes  Maryanne Reiter 《水文研究》2018,32(2):293-304

Stream temperature is a key physical water‐quality parameter, controlling many biological, chemical, and physical processes in aquatic ecosystems. Maintenance of cool stream temperatures during summer is critical for high‐quality aquatic habitat. As such, transmission of warm water from small, nonfish‐bearing headwater streams after forest harvesting could cause warming in downstream fish‐bearing stream reaches with negative consequences. In this study, we evaluate (a) the effects of contemporary forest management practices on stream temperature in small, headwater streams, (b) the transmission of thermal signals from headwater reaches after harvesting to downstream fish‐bearing reaches, and (c) the relative role of lithology and forest management practices in influencing differential thermal responses in both the headwater and downstream reaches. We measured summer stream temperatures both preharvest and postharvest at 29 sites—12 upstream sites (4 reference, 8 harvested) and 17 downstream sites (5 reference, 12 harvested)—across 3 paired watershed studies in western Oregon. The 7‐day moving average of daily maximum stream temperature (T_7DAYMAX) was greater during the postharvest period relative to the preharvest period at 7 of the 8 harvested upstream sites. Although the T_7DAYMAX was generally warmer in the downstream direction at most of the stream reaches during both the preharvest and postharvest period, there was no evidence for additional downstream warming related to the harvesting activity. Rather, the T_7DAYMAX cooled rapidly as stream water flowed into forested reaches ~370–1,420 m downstream of harvested areas. Finally, the magnitude of effects of contemporary forest management practices on stream temperature increased with the proportion of catchment underlain by more resistant lithology at both the headwater and downstream sites, reducing the potential for the cooling influence of groundwater.  相似文献   

Conventional Oil—The Forgotten Part of the Water-Energy Nexus     

Jennifer C. McIntosh  Grant Ferguson 《Ground water》2019,57(5):669-677

The impacts of unconventional oil and gas production via high-volume hydraulic fracturing (HVHF) on water resources, such as water use, groundwater and surface water contamination, and disposal of produced waters, have received a great deal of attention over the past decade. Conventional oil and gas production (e.g., enhanced oil recovery [EOR]), which has been occurring for more than a century in some areas of North America, shares the same environmental concerns, but has received comparatively little attention. Here, we compare the amount of produced water versus saltwater disposal (SWD) and injection for EOR in several prolific hydrocarbon producing regions in the United States and Canada. The total volume of saline and fresh to brackish water injected into depleted oil fields and nonproductive formations is greater than the total volume of produced waters in most regions. The addition of fresh to brackish “makeup” water for EOR may account for the net gain of subsurface water. The total amount of water injected and produced for conventional oil and gas production is greater than that associated with HVHF and unconventional oil and gas production by well over a factor of 10. Reservoir pressure increases from EOR and SWD wells are low compared to injection of fluids for HVHF, however, the longer duration of injections could allow for greater solute transport distances and potential for contamination. Attention should be refocused from the subsurface environmental impacts of HVHF to the oil and gas industry as a whole.  相似文献   

Population structure of the sicklefin lemon shark Negaprion acutidens within the Curieuse Marine National Park,Seychelles     

RD Hodgkiss  A Grant  JHR McClelland  R Quatre  B Rademakers  C Sanchez 《African Journal of Marine Science》2017,39(2):225-232

This study produced the first data on population parameters for sicklefin lemon shark Negaprion acutidens at the granitic Seychelles Islands, adding to a limited catalogue of species information. Juveniles at a site in the Curieuse Marine National Park were tagged over two periods, in 2014–2015 and 2015–2016, with measurements of length (precaudal, fork and total) and weight, sex, and state of the umbilical opening recorded. Recapture data were used to calculate growth rates and population size. Mean annual growth rate was 5.40 cm y^–1. A mean size at birth of 62.5 cm TL is in line with previous assessments of the species. Population-size estimates were similar for the two sampling periods (comprising 311 and 255 individuals) and higher than anticipated. Movements to outside the lagoon were recorded for early ages, and this, combined with weight loss and a reduction in condition factor as displayed in several individuals, suggests that the study area alone could not support the large number of sharks pupped yearly.  相似文献   

Improved performance‐based seismic assessment of buildings by utilizing Bayesian statistics          下载免费PDF全文

Omid Esmaili  Lisa Grant Ludwig  Farzin Zareian 《地震工程与结构动力学》2016,45(4):581-597

This paper addresses two important issues of concern to practicing engineers and researchers alike in application of performance‐based seismic assessment (PBSA) methodology on buildings: (i) the number of ground motion records required to exercise PBSA—current practice (FEMA P‐58‐1) requires eleven or more pairs of motions for this purpose, and (ii) the time and effort associated with performing the number of nonlinear response history analyses required to exercise PBSA. We present a method for exercising of PBSA that employs classical linear modal analysis to develop a first estimate (i.e., a priori) of probability distribution of loss, followed by utilizing Bayesian statistics to update this estimate using estimates of loss obtained by utilizing a small number of nonlinear response history analyses of a detailed model of the building (i.e., posterior). The proposed technique is used to assess the distribution of monetary loss of two case studies, a 4‐story reinforced concrete moment‐resisting frame building and a 20‐story steel moment‐resisting frame building, both located in Los Angeles, for a ground motion hazard with 10% probability of exceedance in 50 years. The efficiency of the proposed PBSA method is demonstrated by showing the similarity between the distribution of monetary loss at each story of case study buildings obtained from the traditional/sophisticated PBSA methodology and the proposed PBSA method in this study. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Using meteorological observer data to compare wind erosion during two great droughts in eastern Australia; the World War II Drought (1937–1946) and the Millennium Drought (2001–2010)          下载免费PDF全文

Tadhg O'Loingsigh  Grant H. McTainsh  Katherine Parsons  Craig L. Strong  Phil Shinkfield  Nigel J. Tapper 《地球表面变化过程与地形》2015,40(1):123-130

Australian meteorological observers started using the World Meteorological Organization (WMO) weather coding system in the 1950s. This system is still in use around the world today. However, observing and recording the weather in an organized and systematic manner had been ongoing for over 100 years prior to the adoption of this coding system, and much like Australia, most countries will have historical meteorological records. In this paper we compare the wind erosion of two of the greatest droughts in Australian recorded history; the World War II (WWII) Drought (1937–1945) and the Millennium Drought (2001–2009). To do this we analysed previously unavailable meteorological observer records from the Australian Bureau of Meteorology (ABM). Wind erosion records, mostly in long‐hand written form, were translated to the modern WMO coding system for the WWII Drought and compared with the wind erosion of Australia's recently‐ended Millennium Drought, one of the longest and harshest on record. We quantify wind erosion using Dust Event Days (DED) and a modified version of a published Dust Storm Index (DSI) to show that wind erosion during the WWII Drought was up to 4.6 times higher than during the Millennium Drought. This study has international significance because it demonstrates a methodology for tracking changes in wind erosion over the past 75 years based on observer records available in every country with a history of organized weather observation. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Drivers of Australian dust: a case study of frontal winds and dust dynamics in the lower lake Eyre basin          下载免费PDF全文

Matthew Baddock  Katherine Parsons  Craiq Strong  John Leys  Grant McTainsh 《地球表面变化过程与地形》2015,40(14):1982-1988

The roles of pre‐frontal, frontal and post‐frontal winds as the primary wind systems for dust entrainment and transport in Australia are well established. While the relevance of each system has been observed across different wind erosion events in central Australia, the entrainment of dust by all three winds during the passage of an individual front has not been demonstrated until now. Synoptic information, satellite aerosol and imagery, meteorological and dust concentration data are presented for a single case study erosion event in the lower Lake Eyre Basin. This event demonstrates variable dust transport in three different directions from one of the southern Hemisphere's most significant source regions, and the changing nature of the active dust pathways during the passage of a frontal system. While only a single dust event is considered, the findings show the complexity of mineral aerosol emission and transport patterns even within an individual dust outbreak. For the lower Lake Eyre Basin, this appreciation of pathway behaviour is significant for better understanding the role of aeolian inputs from the dominant Australian source to surrounding marine systems. In a wider context, the findings exhibit the detailed insights into major dust source dynamics that can be obtained from high resolution spatial and particularly temporal data, as used in combination. This work highlights the importance of adequately resolved data for the accurate determination of dust entrainment and transport patterns of major dust sources. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Water quality in a polluted lowland stream with chronically depressed dissolved oxygen: Causes and effects     

Robert J. Wilcock  Graham B. McBride  John W. Nagels  Grant L. Northcott 《新西兰海洋与淡水研究杂志》2013,47(2):277-288

Abstract

The Whangamaire Stream (North Island, New Zealand) has high concentrations of nitrate nitrogen (NO^? ₃‐N), biochemical oxygen demand (BOD₅), and Kjeldahl nitrogen (TKN) as a result of catchment land use practices. The lower reaches of the stream drain intensively farmed land and have dissolved oxygen (DO) levels of 10–50% saturation. The dominant riparian vegetation, Apium nodiflorum, provides a large organic loading by intercepting nutrients in run‐off and then decaying in the stream channel. Water quality and reaeration aspects of the stream were studied in order to explain the observed low DO levels. Measurements of the reaeration coefficient at 20°C, K₂ ²⁰, using methyl chloride (CH₃Cl) as a gas tracer, yielded values of 1.1–3.0 d^?1 for the upper part of the study reach and 15.5–16.2 d^?1 for the lower reach (overall average 12.5 ± 2.5 d^?1). These were in agreement with values inferred from single‐station diurnal curve analysis, which also showed that respiration was dominant in the lower reach where photo‐synthetic activity was inhibited by shade. The relatively large reaeration coefficients ensure that parts of the stream do not become anoxic at night time. Better riparian management and reduced nutrient inputs are likely to improve stream water quality.  相似文献   

Reproductive characteristics and steroid levels in the scleractinian coral Oculina patagonica inhabiting contaminated sites along the Israeli Mediterranean coast     

Armoza-Zvuloni R  Kramarsky-Winter E  Rosenfeld H  Shore LS  Segal R  Sharon D  Loya Y 《Marine pollution bulletin》2012,64(8):1556-1563

In this study we compared reproductive characteristics and steroid hormone levels in the non-indigenous scleractinian coral, Oculina patagonica, inhabiting contaminated vs. uncontaminated reference sites along the Israeli Mediterranean coast. Our results indicate significantly higher steroid levels in both seawater and coral tissue samples from contaminated sites as compared to reference sites, suggesting that corals tend to accumulate steroids from the surrounding waters. Despite their higher steroid levels, corals from the contaminated sites showed reproductive potential comparable to those of the reference sites. Interestingly, a clear distinction could be seen between corals exposed to pollution for long vs. short durations, with the latter showing a failure to complete gametogenesis. This suggests that reproduction in O. patagonica is susceptible to acute rather than chronic stress. The involvement of adjustment/adaptation processes may explain this species tolerance, and may reflect the ability of O. patagonica to successfully invade new areas in the Mediterranean Sea.  相似文献   

Challenges associated with pre-border management of biofouling on oil rigs     

Grant A. Hopkins  Barrie M. Forrest 《Marine pollution bulletin》2010,60(11):1924-1929

The potential for oil rigs to transport diverse, reef-like communities around the globe makes them high risk vectors for the inadvertent spread of non-indigenous species (NIS). This paper describes two case studies where a suite of pre-border management approaches was applied to semi-submersible drilling rigs. In the first case study, a drilling rig was defouled in-water prior to departure from New Zealand to Australia. Risk mitigation measures were successful in reducing biosecurity risks to the recipient region, but they resulted in the unintentional introduction of the non-indigenous brown mussel (Perna perna) to New Zealand when the rig was defouled in-water by divers. In the second case study, lessons learned from this high-profile incursion resulted in a more structured approach to pre-border management, and this serves as a useful template for future rig transfers.  相似文献   

Gendered Spaces of Informal Entrepreneurship in Soweto,South Africa   总被引：1，自引：1，他引：0  

Richard Grant 《Urban geography》2013,34(1):86-108

Abstract

The full diversity of economic activities in the informal economy is not well understood. The apartheid legacy of limiting informal entrepreneurship explains the most obvious geographical patterns in South Africa. After a decade and a half since the end of apartheid, however, knowledge about the places from which informal entrepreneurs operate is incomplete. Retailing is overemphasized and production firm entrepreneurs, both male and female, remain a neglected spatiality. This study reports on a survey of 100 firms in Soweto and in-depth interviews with 30 firm owners. The findings challenge the representations of isolated urban entrepreneurs dependent on inherited social capital and of women's exclusive engagement in retail. Entrepreneurs create their own social capital in work-related realms, but there are important gender differences. More finely tuned conceptualizations of entrepreneurs and of gendered working spaces need to be developed so that policy does not perpetuate unitary myths and incomplete spatial representations. [Key words: entrepreneurship, Soweto, informal economy, gender.]  相似文献