Sediment remobilisation from decomposing cordgrass (Spartina anglica) patches on a wave‐exposed intertidal flat     

Andrew Swales  Ron Ovenden  Iain T. MacDonald  Andrew M. Lohrer  Karen L. Burt 《新西兰海洋与淡水研究杂志》2013,47(6):1305-1319

Abstract

Concerns about the potential adverse effects of Spartina invasion on New Zealand estuaries, such as habitat loss and degradation, have led to herbicide use to control its spread. An experiment was conducted in the Manukau Harbour (New Zealand) to determine sediment remobilisation rates (?E) from herbicide‐treated S. anglica patches. Paired treatment and control patches (≤25 m diam.) were monitored at two sites 500 m apart with different wave exposures. Above‐ (AGB) and below‐ground (BGB) biomass decomposition and AE were determined from repeat surveys over c. 2.5 years. Work done by waves (W), which integrates wave‐energy dissipation at the bed over time, was used as a surrogate measure of sediment transport potential. Complete AGB loss occurred in both treated patches within 3 months of initial herbicide application, whereas BGB (a matrix of roots and rhizomes) persisted much longer. An exponential decay model (r ² = 0.6) fitted to the site‐two treatment data predicted an c. 85% reduction in BGB after 5 years, whereas the BGB changes for the larger and more heterogeneous site‐one treatment were more complex. BGB was a better predictor of average bed elevation than AGB in multiple regression models and, although bed elevation decreased through time and with waves, BGB was positively related to bed elevation at both sites. AE was similar for both treatment patches (c. 0.05 and c. 0.06 m yr^‐1, P < 0.001, r² ≥ 0.97) and complete sediment loss was predicted to occur within 6–10 years. The site‐one control patch accumulated sediment (0.01 m yr^‐1 , P < 0.001, r ² = 0.81) whereas the more wave‐exposed site‐two control eroded (0.01 m yr^‐1, P = 0.0017, r ² = 0.61). The potential for adverse sediment effects resulting from Spartina control at wave‐exposed sites will be minimal if the treated areas are small relative to the size of the estuary.  相似文献   

Resistance to oxidative stress is not associated with the exceptional longevity of the freshwater pearl mussel,Margaritifera margaritifera nor three unionid species     

Iain Ridgway  T. J. Bowden  A. Roman-Gonzalez  C. A. Richardson 《Aquatic Sciences - Research Across Boundaries》2014,76(2):259-267

Bivalve molluscs are newly discovered models of successful ageing. Here, we test the hypothesis that extreme longevity of freshwater mussels is associated with an enhanced resistance to oxidative stress. We assess whether resistance to oxidative stress might be causally involved in the exceptional longevity exhibited by the freshwater pearl mussel Margaritifera margaritifera. We compared resistance to oxidative stress and total haemocyte counts, a health status biomarker in M. margaritifera (maximum lifespan potential 190 years) with three other freshwater bivalve species spanning a range of longevities. Previous studies of the comparative stress resistance and longevity of marine bivalves provide evidence for the hypothesis that an association exists between longevity and not only an enhanced resistance to oxidative stress but also a general resistance to multiplex stressors. We compared baseline total haemocyte counts, age-related changes, and responses to exposure to the oxidative stressor tert-butyl hydroperoxide (TBHP). Surprisingly our data does not support the premise that extreme longevity in M. margaritifera is associated with enhanced resistance to oxidative stress. In comparison with its shorter-lived counter parts M. margaritifera was the least resistance to oxidative stress. Following TBHP exposure, no association between longevity and resistance to oxidative stress-induced mortality nor a marked resistance to oxidative stress-induced declines in total haemocyte counts were observed. The results suggest longevity evolved separately in freshwater mussels and this group warrants further attention from biogerontologists because such study may provide novel insights not detected through the study of the marine members of the class, where most attention is currently focused.  相似文献   

Evidence for seiches and short‐period internal waves in lake Tekapo,South Island,New Zealand     

N. M. Ridgway 《新西兰海洋与淡水研究杂志》2013,47(3):541-550

Vertical temperature profiles obtained in April 1971 along the length of Lake Tekapo suggest the presence of an internal seiche. A simple model gives a theoretical period of 48 h. Successive vertical temperature profiles made at 5‐min intervals over 70 min showed in‐phase fluctuations in the isotherms both above and below the thermocline. The fluctuations had an average period of 12.7 min and could have been generated by a surface sieche operating between the southern end of the lake and Motuariki Island, situated about 7.6 km from the southern end.  相似文献   

Correction of tree ring stable carbon isotope chronologies for changes in the carbon dioxide content of the atmosphere   总被引：2，自引：0，他引：2  

Danny McCarroll  Mary H. Gagen  Iain Robertson  Sietse Los  Risto Jalkanen  John S. Waterhouse 《Geochimica et cosmochimica acta》2009,73(6):1539-114

Tree-ring stable carbon isotope ratios (δ¹³C) often display a decline over the industrial period (post-AD1850) that is only partly explained by changes in the isotopic ratio of carbon dioxide (CO₂) and may represent a response to increased atmospheric concentrations of CO₂ (ca). If this is not addressed, reconstructions using long tree-ring stable isotope chronologies calibrated using the modern period, for which meteorological records are available, may be compromised. We propose a correction procedure that attempts to calculate the δ¹³C values that would have been obtained under pre-industrial conditions. The correction procedure uses nonlinear (loess) regression but the magnitude of the adjustment made is restricted by two logical constraints based on the physiological response of trees: first, that a unit increase in ca cannot result in more than the same unit increase in the internal concentration of CO₂ (ci), and second, that increases in water-use efficiency as a result of an increase in ca are limited to maintaining a constant ci/ca ratio. The first constraint allows retention of a falling trend in δ¹³C, which exceeds that which could logically be attributed to a passive response to rising ca. The second constraint ensures that any increase in δ¹³C, reflecting a change in water-use efficiency beyond maintenance of a constant ci/ca, is not removed. The procedure is tested using ‘pseudoproxies’, to demonstrate the effect of the correction on time-series with different shapes, and data from three sites in Finland and Norway. Two of the time-series retain a significant trend after correction, and in all three cases the correction improves the correlation with local meteorological measurements.  相似文献   

Late Quaternary neotectonics and mass movement in South East Raasay,Inner Hebrides,Scotland     

David E. Smith  Iain S. Stewart  Stephan Harrison  Callum R. Firth 《Proceedings of the Geologists' Association. Geologists' Association》2009,120(2-3):145-154

Features associated with the Hallaig Fault, SE Raasay, are examined. The fault, which runs along the NW slope of the hill mass of Beinn na Leac, is marked by a narrow trench, running for over 3 km NE–SW. About 600 m from its N end, the trench becomes almost obscured for 500 m by a bench composed of talus. SW of this a ridge of talus up to 5 m high occupies the downslope side of the trench for 1.2 km. The total volume of talus is estimated at around 90,000 m³. In the SW, the trench splits into two, separating discrete bedrock areas from the hillside. Possible mechanisms forming the trench and associated features are considered. It is maintained that the features were primarily the result of the reactivation of a listric fault, triggered by isostatic processes during and following deglaciation and that they reached their present form during the Younger Dryas. Maximum vertical movement is estimated at at least 5 m. The unconsolidated sediment comprising the ridge and bench is believed to have been primarily the product of periglacial processes and paraglacial activity.  相似文献   

Postglacial fault movement and palaeoseismicity in western Scotland: A reappraisal of the Kinloch Hourn fault, Kintail     

Iain S. Stewart  Callum R. Firth  Derek J. Rust  Philip E.F. Collins  Judith A. Firth 《Journal of Seismology》2001,5(3):307-328

The Kinloch Hourn fault is the most prominent of a number of suspectedpostglacial faults in the western Scottish Highlands. These faults areinterpreted to have been reactivated by repeated large (M > 6)palaeoseismic events following deglaciation 10,000–13,000 years ago.Based on inferred deflections of drainage courses, previous studies of thefault have estimated 160 ± 40 m cumulative left-lateral displacementalong a 14 km long active segment during postglacial times. Reportedsoft-sediment deformation phenomena imply that activity on the KinlochHourn fault has persisted into the late Holocene, with the most recentmovement having been associated with a magnitude 5.5–6.0 surface-faultingevent between 3500 and 2400 years ago. The marked contrast betweensuch palaeoseismic activity and the present-day seismic quiescence ofwestern Scotland has stimulated this critical reappraisal of the KinlochHourn fault.This paper reassesses the key lines of evidence for postglacial fault activityand palaeoseismicty on the Kinloch Hourn fault, combining the analysis of1:15,000-scale air photos, field-based geomorphic mapping andpalaeoenvironmental investigations. Our reappraisal of inferred drainagedeflections across the fault contends that previous reports of significant(10² m) left-lateral slip on the fault during the Holocene arespurious. Instead, incidences of Holocene channel abandonment along thefault line are non-synchronous and probably reflect non-tectonic drainagechanges. The timing of soft-sediment deformation in the vicinity of the faultis revised to an early Holocene date (8990–8580 calendar years BP), whichis in accord with both the palaeoenvironmental history of the site andconsistent with published ages of earthquake-induced liquefactionphenomena documented elsewhere in western Scotland. An alleged recent(post-2400 radiocarbon years BP) ground rupture on the fault isquestioned in the light of uncertainty about both the nature of the faultedsoil deposit and the late Holocene age attributed to it.The study concludes that there is no convincing evidence for postglacialsurface rupture on the Kinloch Hourn fault and speculates that the casefor significant (10¹–10² m) postglacial movement on otherfaults in western Scotland may be similarly `unproven'.  相似文献   

Temporal variations in the trace-element content of stream sediments: an example from the seasonally wet-dry tropics     

J. Ridgway  P.N. Dunkley 《Journal of Geochemical Exploration》1989,32(1-3)

Zimbabwe has a markedly seasonal climate with a dry period from May to November in which virtually no rain falls. Two streams draining known bedrock and soil geochemical anomalies from unexploited mineralization were sampled at times spanning both wet and dry seasons.  相似文献   

Don’t Blame It on the Moonlight: Abiotic Drivers of Reproductive Development in an Estuarine-Dependent Prawn     

Caitlin L. Young  Iain M. Suthers  Daniel D. Johnson  Charles A. Gray  Faith A. Ochwada-Doyle 《Estuaries and Coasts》2018,41(2):444-452

Lunar phase is regarded as a key driver of reproductive development and spawning activity in prawns, but across smaller-temporal scales, other processes may have a significant influence. Here, we examined the effects of lunar phase and other abiotic variables on the reproductive development of an estuarine-dependent prawn, Metapenaeus bennettae Racek & Dall. We found that turbidity, salinity, water temperature and lunar phase each had a significant independent influence on the likelihood of female prawns being ripe throughout the spawning period. The likelihood of catching a ripe female increased on the new moon and first quarter of the moon and also during conditions of low turbidity, high salinity and high water temperature. For male prawns, however, significant interactions between salinity and lunar phase and also between turbidity and lunar phase were detected. These interactions indicated that salinity and turbidity have variable effects among the different lunar phases. Such complex relationships of reproductive timing and spawning success of M. bennettae, and potentially other aquatic species, are most likely adaptive responses to the highly variable conditions of estuarine environments.  相似文献   

Visualisation techniques to support public interpretation of future climate change and land-use choices: a case study from N-E Scotland     

Chen Wang  David Miller  Iain Brown  Yang Jiang  Marie Castellazzi 《International Journal of Digital Earth》2016,9(6):586-605

Mitigating and adapting to climate change includes a requirement to evaluate the role of future land uses in delivering robust integrated responses that are sensitive to local landscape contexts. In practice, this emphasises the need for community engagement, planning and inclusive decision-making. Community engagement may be potentially facilitated by the use of spatially explicit quantitative scenarios of land-use change in combination with interactive visualisation. This requires a coherent framework to integrate spatial data modelling, analytical capabilities and visualisation tools in a format that will also engage diverse public audiences. These challenges were explored with a case study of virtual landscapes from N-E Scotland that was used to test preferences for scenarios of future land use. Visualisations employed texture-based rendering rather than full photo-realistic rendering to facilitate interactivity and this provided additional scope for audiences to explore multiple future scenarios compared to the present landscape. Interactive voting in a virtual landscape theatre suggested preferences for visual diversity, good stewardship and perceived naturalness that should be considered in developing planned responses to change. Further investigation of preferences was conducted using interactive 3D features located within the landscape. Study findings are reviewed against objectives for inclusive engagement in the Digital Earth agenda and used to make further recommendations on the use of scenarios and visualisation tools. In particular, technical advances in user engagement need to be developed in conjunction with emerging good practice that addresses ethical, behavioural and inclusion issues so that the content is presented in as transparent and unbiased format as possible.  相似文献   

Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits     

Clifford G. C. Patten  Iain K. Pitcairn  Damon A. H. Teagle  Michelle Harris 《Mineralium Deposita》2016,51(2):179-200

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