Evaluating practical macrophyte control tools on small agricultural waterways in Canterbury,New Zealand     

Kathryn E. Collins  Catherine M. Febria  Helen J. Warburton  Hayley S. Devlin  Kristy L. Hogsden  Brandon C. Goeller 《新西兰海洋与淡水研究杂志》2019,53(2):182-200

Excessive macrophytes can cause significant problems in agricultural waterways requiring active management. Conventional control techniques can have a range of adverse effects. We investigated several control tools in two experiments: firstly, we tested eight treatments at a small-scale (2?m?×?2?m). We found intensive hand weeding, weed mat and herbicide spraying to be effective treatments, reducing macrophyte cover to <5%. Hand weeding and weed mat immediately reduced cover, while dieback from herbicide took two months. Weed mat was a novel and effective control mechanism along stream banks. Secondly, we tested the impact of shading on macrophyte growth. Macrophyte growth was enhanced under partially shaded conditions, but with 80% effective shading over the entire channel, cover was reduced to 17%. Once treatments ceased, macrophytes grew back within 3–5 months. Long-term, control methods will require combinations of tools but will need to include optimal shading for the target species.  相似文献   

A Triple‐Stack Column Procedure for Rapid Separation of Cu and Zn from Geological Samples     

Heye Freymuth  Callum D. J. Reekie  Helen M. Williams 《Geostandards and Geoanalytical Research》2020,44(3):407-420

We present a new procedure for the separation and purification of Cu and Zn from geological samples. Our procedure employed a single pass, triple‐stack column set‐up. The first column, filled with TRU resin (TrisKem International), quantitatively removed Fe and Ti from sample matrices. A second column, filled with pre‐filter resin (TrisKem International), removed organic compounds. Finally, a third column, filled with anion exchange resin (AG1‐X8, 200–400 mesh, Bio‐Rad), was used to separate Cu and Zn from the remaining matrix. Our procedure required about 50% less acid volume than previously reported methods for Cu and Zn separation, thereby minimising analytical blanks and column running times. Copper and Zn stable isotope ratios were determined by a Thermo Neptune Plus MC‐ICP‐MS using Zn and Cu external normalisation, respectively, in addition to sample‐standard bracketing to correct for instrumental mass bias. We explore the inter‐calibration of Cu and Zn isotope fractionation coefficients during analysis by measuring mixed Cu–Zn solutions with enhanced mass bias variation generated by varying sample gas flow rates. Our results demonstrate that this procedure is useful when variation in instrumental mass bias throughout analytical sequences is insufficient to inter‐calibrate Cu and Zn fractionation coefficients.  相似文献   

Mapping spatial variation in demersal fish species diversity and composition in the North Sea: accounting for species- and size-related catchability in survey trawls     

Fraser  Helen M.; Greenstreet  Simon P. R.; Fryer  Rob J.; Piet  Gerjan J. 《ICES Journal of Marine Science》2008,65(4):531-538

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The age of the meteorite recovery surfaces of Roosevelt County,New Mexico,USA     

Michael E. Zolensky  Helen M. Rendell  Ivan Wilson  Gordon L. Wells 《Meteoritics & planetary science》1992,27(4):460-462

Abstract— We have obtained minimum age estimates for the sand units underlying the two largest meteorite deflation surfaces in Roosevelt County, New Mexico, USA, using thermoluminescence dating techniques. The dates obtained ranged from 53.5 (±5.4) to 95.2 (±9.5) ka, and must be considered lower limits for the terrestrial ages of the meteorites found within these specific deflation surfaces. These ages greatly exceed previous measurements from adjacent meteorite-producing deflation basins. We find that Roosevelt County meteorites are probably terrestrial contemporaries of the meteorites found at most accumulation zones in Antarctica. The apparent high meteorite accumulation rate reported for Roosevelt County by Zolensky et al. (1990) is incorrect, as it used an age of 16 ka for all Roosevelt County recovery surfaces. We conclude that the extreme variability of terrestrial ages of the Roosevelt County deflation surfaces effectively precludes their use for calculations of the meteorite accumulation rate at the Earth's surface.  相似文献   

Using an inverse modelling approach with equifinality control to investigate the dominant controls on snowmelt nutrient export     

Diogo Costa  John Pomeroy  Helen Baulch  Jane Elliott  Howard Wheater 《水文研究》2019,33(23):2958-2977

There is great interest in modelling the export of nitrogen (N) and phosphorus (P) from agricultural fields because of ongoing challenges of eutrophication. However, the use of existing hydrochemistry models can be problematic in cold regions because models frequently employ incomplete or conceptually incorrect representations of the dominant cold regions hydrological processes and are overparameterized, often with insufficient data for validation. Here, a process‐based N model, WINTRA, which is coupled to a physically based cold regions hydrological model, was expanded to simulate P and account for overwinter soil nutrient biochemical cycling. An inverse modelling approach, using this model with consideration of parameter equifinality, was applied to an intensively monitored agricultural basin in Manitoba, Canada, to help identify the main climate, soil, and anthropogenic controls on nutrient export. Consistent with observations, the model results suggest that snow water equivalent, melt rate, snow cover depletion rate, and contributing area for run‐off generation determine the opportunity time and surface area for run‐off–soil interaction. These physical controls have not been addressed in existing models. Results also show that the time lag between the start of snowmelt and the arrival of peak nutrient concentration in run‐off increased with decreasing antecedent soil moisture content, highlighting potential implications of frozen soils on run‐off processes and hydrochemistry. The simulations showed TDP concentration peaks generally arriving earlier than NO₃ but also decreasing faster afterwards, which suggests a significant contribution of plant residue Total dissolved Phosphorus (TDP) to early snowmelt run‐off. Antecedent fall tillage and fertilizer application increased TDP concentrations in spring snowmelt run‐off but did not consistently affect NO₃ run‐off. In this case, the antecedent soil moisture content seemed to have had a dominant effect on overwinter soil N biogeochemical processes such as mineralization, which are often ignored in models. This work demonstrates both the need for better representation of cold regions processes in hydrochemical models and the model improvements that are possible if these are included.  相似文献   

Multi-proxy evidence of postglacial climate and environmental change at Two Frog Lake,central mainland coast of British Columbia,Canada     

Jennifer M. Galloway  R. Timothy Patterson  Christine T. Doherty  Helen M. Roe 《Journal of Paleolimnology》2007,38(4):569-588

Pollen and diatoms preserved in the radiocarbon dated sediments of Two Frog Lake in the Seymour-Belize Inlet Complex of the central mainland coast of British Columbia document postglacial climate change. Two Frog Lake was isolated from the sea prior to 11,040 ± 50 yr BP (13,030 cal. yr BP) when the climate was cool and dry, and open Pinus contorta woodlands covered the landscape. These woodlands were replaced by a mixed conifer forest ca. 10,200 yr BP (ca. 12,300 cal. yr BP) when the climate became moister. A relatively dry and warm early Holocene climate allowed Pseudotsuga menziesii to migrate northward to this site where it grew with Picea, Tsuga heterophylla and Alnus. The climate became cooler and moister at ca. 8,000 yr BP (ca. 9,200 cal. yr BP), approximately 500–1,000 years prior to sites located south of Two Frog Lake and on the Queen Charlotte Islands, but contemporary with sites on the northern mainland coast of British Columbia and south coastal Alaska. Climate heterogeneity in central coastal British Columbia appears to have occurred on a synoptic scale, suggesting that atmospheric dynamics linked to a variable Aleutian Low pressure system may have had an important influence on early Holocene climate change in the Seymour-Belize Inlet Complex. The transition to cooler and moister conditions facilitated the expansion of Cupressaceae and the establishment of a modern-type coastal temperate rainforest dominated by Cupressaceae and T. heterophylla. This was associated with progressive lake acidification. Diatom changes independent of vegetation change during the late Holocene are correlative with the mid-Neoglacial period, when cooler temperatures altered diatom communities.  相似文献   

Kinematic analysis of aeromagnetic data: Looking at geophysical data in a structural context     

Peter Betts  Helen Williams  John Stewart  Laurent Ailleres 《Gondwana Research》2007,11(4):582-583

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Late Holocene Mediterranean coastal change along the Tiber Delta and Roman occupation of the Laurentine shore, central Italy     

Helen M. Rendell  Amanda J. Claridge  Michle L. Clarke 《Quaternary Geochronology》2007,2(1-4):83-88

A line of Roman villas once dominated the Mediterranean coastline to the south of the Tiber river mouth near Ostia in central Italy. The Roman remains, which were constructed within a series of dune ridges, now lie up to 900 m from the current shoreline as a result of the continued evolution of the Tiber delta in response to postglacial sea level rise, sediment inputs from the Tiber river catchment and tectonic uplift. Infrared stimulated luminescence (IRSL) ages of potassium-rich feldspars extracted from dune sands are in good agreement with the independent age control provided by the Roman structures and allow us to hypothesise an increase in aggradation rates of five times since the end of the period of Roman occupation compared with the earlier Holocene.  相似文献   

Factors influencing the release of dissolved organic carbon and dissolved forms of nitrogen from a small upland headwater during autumn runoff events   总被引：1，自引：0，他引：1  

Richard Cooper  Vera Thoss  Helen Watson 《水文研究》2007,21(5):622-633

We identify and assess the relative importance of the principal factors influencing the release of dissolved organic carbon (DOC) and dissolved forms of nitrogen (N) from a small upland headwater dominated by podzolic soils during a sequence of autumn runoff events. We achieve this by subjecting high‐resolution hydrometeorological and hydrochemical data to an R‐mode principal component factor analysis and a stepwise multivariate regression analysis. We find that the release of DOC and N is influenced by four principal factors, namely event magnitude, soil water flow through the Bs horizon, the length of time since the soil profile was last flushed, and rewetting of the H horizon. The release of DOC and dissolved organic nitrogen (DON) is most strongly influenced by the combination of event magnitude and soil water flow through the Bs horizon, and to a lesser extent by the length of time since the soil profile was last flushed. Rewetting of the H horizon also influences the release of DOC, but this is not the case for DON. The release of nitrate (NO₃‐N) is most strongly influenced by the combination of the length of time since the soil profile was last flushed and rewetting of the H horizon, and to a lesser extent by event magnitude. Soil water flow through the Bs horizon does not influence the release of NO₃‐N. We argue that the mechanisms by which the above factors influence the release of DOC and N are probably strongly associated with moisture‐dependent biological activity, which governs the turnover of organic matter in the soil and limits the availability of NO₃‐N in the soil for leaching. We conclude that the release of DOC and N from upland headwaters dominated by podzolic soils is largely controlled by the variable interaction of hydrometeorological factors and moisture‐dependent biological processes, and that a shift in climate towards drier summers and wetter winters may result in the release of DOC and N becoming increasingly variable and more episodic in the future. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Bringing it all back home: The extensification and ‘overflowing’ of work: The case of San Francisco’s new media households     

Helen Jarvis  Andy C. Pratt 《Geoforum》2006,37(3):331-339

This paper explores the extensification of work—that is the distribution or exporting of work across different spaces/scales and times—and its impact on individual workers and households. We argue that contracting out and the work life balance debates might be developed more usefully within the holistic framework of extensification. The key process that we follow can be described as overflowing. We contrast the universally positive representations of spillovers and embedding that we are familiar with in economic geographies with the more negatively characterised overflowing of work into and out of the household. The paper is built around a case study of those involved in the new media industry in San Francisco: households, workers and companies.  相似文献