Sedimentary Environment Influences Ecosystem Response to Nutrient Enrichment     

Emily J. Douglas  Conrad A. Pilditch  Andrew M. Lohrer  Candida Savage  Louis A. Schipper  Simon F. Thrush 《Estuaries and Coasts》2018,41(7):1994-2008

As coastal catchment land use intensifies, estuaries receive increased nutrient and sediment loads, resulting in habitats that are dominated by muddy organic-rich sediments. Increased mud (i.e. silt-clay (particles <?63 μm)) content has been associated with negative effects on soft sediment biodiversity and ecosystem functioning, but the simultaneous impact of nutrient enrichment on ecosystem response is unclear. Nutrient recycling and denitrification in estuarine soft sediments represent important ecosystem functions regenerating nutrients for primary producers and regulating the ability to remove excess terrestrially derived nitrogen. To test the effect of sedimentary environment on ecosystem resilience to nutrient perturbation, we experimentally enriched sediments with slow release fertiliser across an intertidal sedimentary gradient (0–24% mud content). The enrichment successfully elevated pore water ammonium concentrations (median 36?×?control) to levels representative of enriched estuaries. Findings show that the sedimentary environment can influence ecosystem function response to nutrient stress. In particular, denitrification enzyme activity was suppressed by nutrient enrichment, but the effect was greater as sediment mud content increased. Furthermore, compared with sandy sediments, sediments with high mud content may restrict nutrient processing (release, uptake or transformation of organic nutrients by the benthos) facilitating ecosystem shifts toward eutrophication. These results show the value of investigating the impacts of stressors in different environmental settings and demonstrate that land use practices that increase the proportion of muddy habitats in estuaries may reduce denitrification which in turn may reduce ecosystem resilience to eutrophication.  相似文献   

How the Distribution of Anthropogenic Nitrogen Has Changed in Narragansett Bay (RI,USA) Following Major Reductions in Nutrient Loads     

Autumn Oczkowski  Courtney Schmidt  Emily Santos  Kenneth Miller  Alana Hanson  Donald Cobb  Jason Krumholz  Adam Pimenta  Leanna Heffner  Sandra Robinson  Joaquín Chaves  Rick McKinney 《Estuaries and Coasts》2018,41(8):2260-2276

Over the past decade, nitrogen (N) loads to Narragansett Bay have decreased by more than 50%. These reductions were, in large part, the direct result of multiple wastewater treatment facility upgrades to tertiary treatment, a process which employs N removal. Here, we document ecosystem response to the N reductions and assess how the distribution of sewage N in Narragansett Bay has changed from before, during, and shortly after the upgrades. While others have observed clear responses when data were considered annually, our seasonal and regional comparisons of pre- and post-tertiary treatment dissolved inorganic nitrogen (DIN) concentrations and Secchi depth data, from bay-wide surveys conducted periodically from the early 1970s through 2016, resulted in only a few subtle differences. Thus, we sought to use stable isotope data to assess how sewage N is incorporated into the ecology of the Bay and how its distribution may have changed after the upgrades. The nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotope measurements of particulate matter served as a proxy for phytoplankton, while macroalgae served as short-term integrators of water column bio-available N, and hard clams (Mercenaria mercenaria) as integrators of water column production. In contrast to other estuarine stable isotope studies that have observed an increased influence of isotopically lower marine N when sewage N is reduced, the opposite has occurred in Narragansett Bay. The tertiary treatment upgrades have increased the effluent δ¹⁵N values by at least 2‰. The plants and animals throughout Narragansett Bay have similarly increased by 1–2‰, on average. In contrast, the δ¹³C values measured in particulate matter and hard clams have declined by about the same amount. The δ¹⁵N results indicated that, even after the N reductions, sewage N still plays an important role in supporting primary and secondary production throughout the bay. However, the δ¹³C suggests that overall net production in Narragansett Bay has decreased. In the 5 years after the major wastewater treatment facilities came on-line for nutrient removal, oligotrophication has begun but sewage remains the dominant source of N to Narragansett Bay.  相似文献   

Farmer Identity in Multifunctional Landscapes: using a collective identity construct to explore the nature and impact of occupational identity     

Theresa M. Groth  Emily Mendham  Eric Toman 《The Australian geographer》2014,45(1):71-86

The use of multifunctionalism to conceptualise contemporary rural landscapes has focused attention on the increased extent and impact of non-farmers in traditionally agriculture-based rural communities. Typologies of rural landholders have been developed as part of that research effort. However, those typologies are not grounded in established theory, including collective identity theory that could provide an important foundation for the study of occupational identity. Indeed, most quantitative studies may be flawed in drawing on only one of the seven elements contributing to collective identity. This paper examines the efficacy of relying on self-declared occupational identity through the analysis of rural landholder survey data in an Australian region. Tests for expected relationships between self-declared identity of farmer/non-farmer and social and farming variables expected to be correlated with occupation, such as property size, profitability, hours worked on- and off-property, enterprise type and membership of farming-related local organisations found that the expected relationships existed. It seems that self-declared occupational identity is a valid and cost-effective way to explore occupational identity amongst rural landholders. Collective identity, however, is complex and it is unlikely that important research questions can be adequately explored without a more holistic approach to the study of farmer identity in multifunctional landscapes. The paper concludes with a discussion of the potential benefits of moving beyond self-declared occupation to include other elements in the collective identity construct.  相似文献   

A comparative study of melt-rock reactions in the mantle: laboratory dissolution experiments and geological field observations   总被引：2，自引：2，他引：0  

Emily Tursack  Yan Liang 《Contributions to Mineralogy and Petrology》2012,163(5):861-876

Systematic variations in mineralogy and chemical composition across dunite-harzburgite (DH) and dunite-harzburgite-lherzolite (DHL) sequences in the mantle sections of ophiolites have been widely observed. The compositional variations are due to melt-rock reactions as basaltic melts travel through mantle peridotite, and may be key attributes to understanding melting and melt transport processes in the mantle. In order to better understand melt-rock reactions in the mantle, we conducted laboratory dissolution experiments by juxtaposing a spinel lherzolite against an alkali basalt or a mid-ocean ridge basalt. The charges were run at 1 GPa and either 1,300°C or 1,320°C for 8–28 h. Afterward, the charges were slowly cooled to 1,200°C and 1 GPa, which was maintained for at least 24 h to promote in situ crystallization of interstitial melts. Cooling allowed for better characterization of the mineralogy and mineral compositional trends produced and observed from melt-rock reactions. Dissolution of lherzolite in basaltic melts with cooling results in a clinopyroxene-bearing DHL sequence, in contrast to sequences observed in previously reported isothermal-isobaric dissolution experiments, but similar to those observed in the mantle sections of ophiolites. Compositional variations in minerals in the experimental charges follow similar melt-rock trends suggested by the field observations, including traverses across DH and DHL sequences from mantle sections of ophiolites as well as clinopyroxene and olivine from clinopyroxenite, dunite, and wehrlite dikes and xenoliths. These chemical variations are controlled by the composition of reacting melt, mineralogy and composition of host peridotite, and grain-scale processes that occur at various stages of melt-peridotite reaction. We suggest that laboratory dissolution experiments are a robust model to natural melt-rock reaction processes and that clinopyroxene in replacive dunites in the mantle sections of ophiolites is genetically linked to clinopyroxene in cumulate dunite and pyroxenites through melt transport and melt-rock reaction processes in the mantle.  相似文献   

Two new eucrite breccias from Northwest Africa     

Sheryl A. SINGERLING  Aubrey L. MODI  Blake MCFERRIN  Emily A. WORSHAM  Harry Y. MCSWEEN JR.  Douglas RUMBLE III  Ryoji TANAKA  Lawrence A. TAYLOR 《Meteoritics & planetary science》2013,48(2):E1-E9

Abstract– This work describes two newly discovered eucrite breccias: three presumably paired meteorites, all named Northwest Africa (NWA) 6105, and NWA 6106. For each meteorite, major‐ and minor‐element compositions of minerals were determined using the electron microprobe. Pyroxene Fe‐Mn co‐variations and bulk‐rock oxygen isotope compositions confirm their classification as eucrites. Variations in mineral compositions and textures are attributed to differences in clast types present (i.e., basaltic or cumulate eucrite). The pyroxene compositions support the hypothesis that samples NWA 6105,1; 6105,2; and 6105,3 are paired polymict eucritic breccias, whereas sample NWA 6106 is a monomict basaltic eucritic breccia. Two‐pyroxene geothermometry yields temperatures too low for igneous crystallization. The variation in temperatures among samples suggests that metamorphism occurred prior to brecciation.  相似文献   

Thermal Monitoring of Natural Source Zone Depletion          下载免费PDF全文

Kayvan Karimi Askarani  Emily B. Stockwell  Keith R. Piontek  Tom C. Sale 《Ground Water Monitoring & Remediation》2018,38(3):43-52

Natural depletion of subsurface petroleum liquids releases energy in the form of heat. The rate of natural source zone depletion (NSZD) can be derived from subsurface temperature data. An energy balance is performed to resolve NSZD‐generated energy in terms of W/m². Biodegradation rates are resolved by dividing the NSZD energy by the heat of reaction in joules/mol. Required temperature data are collected using data loggers, wireless connections, and automated data storage and analysis. Continuous thermal resolution of monthly NSZD rates at a field site indicates that apparent monthly NSZD rates vary through time, ranging from 10,000 to 77,000 L/ha/year. Temporal variations in observed apparent NSZD rates are attributed to processes governing the conversion of CH₄ to CO₂, as opposed to the actual rates of NSZD. Given a year or more of continuous NSZD rate data, it is anticipated that positive and negative biases in apparent NSZD rates will average out, and averaged apparent NSZD rates will converge to true NSZD rates. An 8.4% difference between average apparent NSZD rates over a 31‐month period using the thermal monitoring method and seven rounds of CO₂ efflux measurements using CO₂ traps supports the validity of both CO₂ trap and thermal monitoring methods. A promising aspect of thermal monitoring methods is that continuous data provide a rigorous approach to resolving the true mean NSZD rates as compared to temporally sparse CO₂ trap NSZD rate measurements. Overall, a vision is advanced of real‐time sensor‐based groundwater monitoring that can provide better data at lower costs and with greater safety, security, and sustainability.  相似文献   

Middle Pleistocene environments,landscapes and tephrostratigraphy of the Armenian Highlands: evidence from Bird Farm 1, Hrazdan Valley     

Jenni E. Sherriff  Keith N. Wilkinson  Poppy Harding  Hayley Hawkins  Rhys G. O. Timms  Daniel S. Adler  Emily J. Beverly  Simon P. E. Blockley  Boris Gasparyan  Christina J. Manning  Darren Mark  Samvel Nahapetyan  Katie J. Preece 《第四纪科学杂志》2022,37(1):6-27

The significance of the southern Caucasus in understanding Pleistocene hominin expansions is well established. However, the palaeoenvironments in which Palaeolithic occupation of the region took place are presently poorly defined. The Hrazdan river valley, Armenian Highlands, contains a rich Palaeolithic record alongside Middle Pleistocene volcanic, fluvial and lacustrine strata, and thus offer exciting potential for palaeoenvironmental reconstruction. We present the first results of sedimentological, geochemical, tephrostratigraphical and biological (diatoms) study of the sequence of Bird Farm 1, located in the central part of the valley. These data show six phases of landscape development during the interval 440–200 ka. The sequence represents the first quantitative Pleistocene diatom record from the Armenian Highlands and the southern Caucasus, and indicates the persistence of a deep, stratified lacustrine system, with evidence for changing lake productivity that is tentatively linked to climate. Furthermore, major element chemical characterization of visible and crypto-tephra horizons in the sequence enables the first stages of the development of a regional tephrostratigraphy. Together, the evidence from Bird Farm 1 demonstrates the importance of lacustrine archives in the region for palaeoenvironmental reconstruction and highlights the potential for linkages between archives on both a local and regional scale.  相似文献   

Chemical and genetic characterization of the ungrouped pallasite Lieksa     

Emily M. Chiappe  Richard D. Ash  Arto Luttinen  Sari Lukkari  Jukka Kuva  Connor D. Hilton  Richard J. Walker 《Meteoritics & planetary science》2023,58(12):1747-1759

The meteorite Lieksa was found in 2017 in Löpönvaara, Finland, and later donated to the Finnish Museum of Natural History. Here, we report siderophile element concentrations, genetic isotopic data, and a metal–silicate segregation age for the meteorite. The ~280 g Lieksa is ~80% metal and ~20% silicate and oxide inclusions by volume, with the inclusions consisting primarily of Fe-rich olivine. Due to Lieksa's silicate content, coupled with a texture characterized by metal enclosing the silicates, it has been classified as a pallasite. Lieksa's olivine and bulk chemical characteristics are distinct from those of the known pallasite and iron meteorite groups, consistent with its classification as ungrouped. The meteorite exhibits a flat, chondrite-normalized highly siderophile element pattern, consistent with an origin as an early crystallization product from a metallic melt with chondritic relative abundances. Molybdenum, Ru, and ¹⁸³W isotopic data indicate that Lieksa formed in the non-carbonaceous (NC) domain of the solar nebula. Radiogenic ¹⁸²W abundances for Lieksa yield a model metal–silicate segregation age of 1.5 ± 0.8 Myr after calcium-aluminum-rich inclusion formation, which is within the range established for other NC-type pallasite and iron meteorite parent bodies.  相似文献