Spread and status of seven submerged pest plants in New Zealand lakes     

Mary D. deWinton  Paul D. Champion  John S. Clayton  Rohan D.S. Wells 《新西兰海洋与淡水研究杂志》2013,47(2):547-561

The distribution of seven submerged aquatic pest plants is reported. Lake vegetation surveys recorded pest plants in 27.9% of 344 lakes, with two species co‐occurring in 5.8%, and three species in 2.6% of lakes. Egeria densa was most frequent (15.4% of lakes), followed by Ceratophyllum demersum (9.0%), Lagarosiphon major (7.3%), and Utricularia gibba (5.5%). Spread since 2000 has continued for five pest plants, with 34 lakes invaded by U. gibba over 2004–08 alone. Early regional sites in proximity to human population centres were likely plant liberations and numerous potential founder colonies remain in garden ponds. Human activities were important for inter‐lake dispersal, with the exception of bird‐dispersed U. gibba. Significant lake associations between pest plants, and with presence of six exotic fish species, suggest common dispersal pathways and similar introduction risks. Therefore, predictions of future spread should be possible based on sources, dispersal pathways, and identifying key risk factors for lakes.  相似文献   

Submerged vegetation of Lakes Sumner,Marion, Katrine,Taylor, and Sheppard in Canterbury,New Zealand     

Maryd De Wemton  John S. Clayton  Rohan D. S. Wells  Chris C. Tanner  Suzanne T. Miller 《新西兰海洋与淡水研究杂志》2013,47(2):145-151

The submerged vegetation of Lakes Sumner, Marion, Katrine, Taylor, and Sheppard was surveyed in May 1987. These high‐altitude lakes lie at c. 600 m a.s.l., within the largely unmodified upper Hurunui catchment. Submerged vegetation was diverse and included numerous short shallow‐water species, dense swards of Isoetes alpinus, low covers of taller native vascular plants, and charophyte meadows beyond the depth limit of vascular plants to a maximum of 15 m. A sparse deepwater bryophyte community was observed from 11 to 32 m depth in Lake Sumner. Displacement of native vegetation by dense growths of the adventive oxygen weed Elodea canadensis over mid‐depths of 3–6 m was noted in all lakes, except Lake Marion.  相似文献   

Thermal constraints on glycolytic metabolism in the New Zealand abalone,Haliotis iris: the role of tauropine dehydrogenase     

Anthony J. R. Hickey  Rufus M. G. Wells 《新西兰海洋与淡水研究杂志》2013,47(4):723-731

Black‐foot abalone, Haliotis iris, were sampled from two populations in warm northern waters, and from two in colder southern waters. Abalone muscle is characterised by high activity of the glycolytic pyruvate reductase enzyme, tauropine dehydrogenase (TDH). Adductor muscle TDH was profiled for thermostability and activity to test the hypothesis that the enzyme may show adaptation in titre or kinetic characteristics reflecting thermal habitat. Temperature dependency of the apparent Michaelis‐Menten constant of TDH for pyruvate (_appKm_pyr) suggested eurythermal enzyme behaviour below 20°C, and compromised function at the higher temperatures of northern populations occurring in the summer months. Thermostability profiles and enzyme activities suggest TDH expression does not differ significantly among populations (P > 0.05), indicating that this locus shows no compensation for temperature. The optimal temperature for efficient TDH function, estimated from V_max./_appKm_pyr, is close to 20°C. The possible thermal constraints on glycolytic metabolism in H. iris are discussed.  相似文献   

Hillslope and point based soil erosion – an evaluation of a Landscape Evolution Model     

G.R. Hancock  T. Wells  C. Dever  M. Braggins 《地球表面变化过程与地形》2019,44(5):1163-1177

Excessive soil erosion and deposition is recognised as a significant land degradation issue. Quantifying soil erosion and deposition is a non-trivial task. One of these methods has been the mathematical modelling of soil erosion and deposition patterns and the processes that drive them. Here we examine the capability of a landscape evolution model to predict both soil erosion rate and pattern of erosion and deposition. This numerical model (SIBERIA) uses a Digital Elevation Model (DEM) to represent the landscape and calculates erosion and deposition at each grid point in the DEM. To assess field soil redistribution rates (SRR) and patterns the distribution of the environmental tracer ¹³⁷Cs has been analysed. Net hill slope SRR predicted by SIBERIA (a soil loss rate of 1.7 to 4.3 t ha^-1 yr^-1) were found to be in good agreement with ¹³⁷Cs based estimates (2.1 – 3.4 t ha^-1 yr^-1) providing confidence in the predictive ability of the model at the hillslope scale. However some differences in predicted erosion/deposition patterns were noted due to historical changes in landscape form (i.e. the addition of a contour bank) and possible causes discussed, as is the finding that soil erosion rates are an order of magnitude higher than likely soil production rates. The finding that SIBERIA can approximate independently quantified erosion and deposition patterns and rates is encouraging, providing confidence in the employment of DEM based models to quantify hillslope erosion rates and demonstrating the potential to upscale for the prediction of whole catchment erosion and deposition. The findings of this study suggest that LEMs can be a reliable alternative to complex and time consuming methods such as that using environmental tracers for the determination of erosion rates. The model and approach demonstrates a new approach to assessing soil erosion that can be employed elsewhere. © 2018 John Wiley & Sons, Ltd.  相似文献   

Automated watershed subdivision for simulations using multi-objective optimization   总被引：1，自引：1，他引：0  

Henrique G. Momm  Ronald L. Bingner  Randall Emilaire  Jurgen Garbrecht  Robert R. Wells  Roger A. Kuhnle 《水文科学杂志》2017,62(10):1564-1582

A qualitative trial-and-error approach is commonly used to define watershed subdivisions through varying a single topographic threshold value. A methodology has been developed to quantitatively determine spatially variable threshold values using topography and a user-defined landscape reference layer. Optimization and topographic parameterization algorithms were integrated to create solutions that minimize the number of sub-watersheds and maximize the agreement between the discretized watershed and the reference layer. The system was evaluated using different reference datasets such as soil type, land management, and landscape form. Comparison of simulated results indicated that the scenario using land management as the reference layer yielded results closer to the scenario subdivided using a constant topographic threshold but with approximately 10 times more sub-catchments and therefore indicating customization of the watershed subdivision to the user-defined reference layer. The proposed optimization technology could be used in adequately applying watershed modeling technology in developing conservation practice implementation plans.  相似文献   

Mid‐Holocene environmental changes in the Bay of Skaill,Mainland Orkney,Scotland: an integrated geomorphological,sedimentological and stratigraphical study     

Anne C. de la Vega Leinert  David H. Keen  Robert L. Jones  James M. Wells  David E. Smith 《第四纪科学杂志》2000,15(5):509-528

A detailed multidisciplinary investigation of intertidal freshwater sediments exposed in the north of the Bay of Skaill, Mainland Orkney, Scotland, have revealed a complex sedimentary sequence. This provided evidence for dynamic coastal environmental changes in the area since the mid‐Holocene. Freshwater ponds developed on glacial sediments ca. 6550 ± 80 yr BP (cal. bc 5590–5305). From ca. 6120 ± 70 yr BP (cal. bc 5040–4855), these were infilled by blown sand from the distal edge of a dune ridge located to the west. Thereafter, a series of sand‐blow events alternating with periods of quiescence occurred until ca. 4410 ± 60 yr BP (cal. bc 3325–2900). Between ca. 5240 ± 160 and 4660 ± 80 yr BP (cal. bc 4370–3115), pollen and charcoal records show evidence of anthropogenic activities, associated with the nearby Neolithic settlement of Skara Brae. Agriculture was probably affected by recurrent sand movement and widespread deposition of calcium carbonate in the hinterland of the bay. Machair development between ca. 6100 and 5000 yr BP (cal. bc 5235–3540) corresponds to a mid‐Holocene phase of dune formation recorded elsewhere in northwest Europe. The more recent and progressive formation of the bay has probably been related to increasing external forcing via storminess, long‐term relative sea‐level change and sediment starvation within this exposed environment. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Dynamics of settling-driven convection beneath a sediment-laden buoyant overflow: Implications for the length-scale of deposition in lakes and the coastal ocean     

Shahrzad Davarpanah Jazi  Mathew G. Wells 《Sedimentology》2020,67(1):699-720

A series of laboratory experiments was conducted in order to determine how settling-driven convection influences the length-scale over which the majority of particles settle beneath a buoyant sediment-laden plume spreading over a denser saline layer. This system is analogous to sediment-laden river water spreading into a lake or the coastal ocean. The key dimensionless parameter that controls the settling dynamics of such flows is the density ratio, defined as the ratio of density differences due to the added salt and sediment. For a buoyant plume, this ratio has to be greater than unity, so that the experiments in the current study were performed for density ratios between one and five. When density ratio was close to one, settling-driven convection was vigorous and the length-scale over which sedimentation occurred was very small. A strong secondary turbidity current was generated in this case. On the other hand, for larger values of density ratio, the predicted length-scale over which a secondary plume was generated increased in proportion to the density ratio. A complete mathematical expression for this length-scale was developed using recent theory that described the timescale over which settling-driven convection evolved. The theoretically predicted propagation length-scale showed very good quantitative agreement with laboratory experiments. The use of the dimensionless density ratio allows the expression to predict which sediment-laden river plumes in lakes and the coastal ocean could quickly form secondary turbidity currents.  相似文献   

Salado archaeology of the Upper Gila,New Mexico     

E. Christian Wells 《Geoarchaeology》2004,19(2):181-183

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Biomonitoring the Health of Coastal Marine Ecosystems – The Roles and Challenges of Microscale Toxicity Tests     

Peter G. Wells 《Marine pollution bulletin》1999,39(1-12):39-47

Coastal marine ecosystems in many parts of the world are under unrelenting stress caused by urban development, hazardous or toxic substances, overfishing, habitat destruction, the introduction of exotic species and natural toxins. Biomonitoring plays a vital role in governmental and industrial strategies to identify, assess, control and reduce these problems. Sensitive and practical techniques in biomonitoring are needed in all of the strategic approaches – from toxic chemical rating and classification, to pollution source control, status and trends monitoring, and assessments of “marine ecosystem health”. Due to the shear magnitude and scope of the challenge, biomonitoring coastal ecosystems demands new and innovative approaches that are relatively easy and cheap to deploy and that provide timely and accessible information to environmental managers and policy makers.

This paper explores recent developments in microscale toxicity testing – a branch of aquatic toxicology involving the discovery and application of small-scale, innovative, sensitive, practical, inexpensive and frequently automated biological techniques. Highlights of a recent unique synthesis ([Reference to Wells et al., 1998]) are given, describing microscale tests at various biological and phylogenetic levels. Many of these tests are marine and focus on gametes, embryos and other young life stages. They can be utilized in the field (in vivo), with field collected samples, and in the laboratory. Their low cost, sensitivity, practicality and speed are their strengths, and commercial test kits have been developed as a result. But being largely “single-species” and sub-individual-level biomonitors, do such microscale tests provide information directly useful to protecting vital ecosystem processes? Indeed, how can this question be addressed? The needs and challenges of matching the most promising of the microscale tests with higher level (population, community, ecosystem) measurements to protect habitats and biodiversity are discussed. Improving marine biomonitoring and protecting coastal ecosystem health demands such new techniques within the context of new paradigms and rigorous approaches for their application.  相似文献   

Do galaxy mergers form elliptical galaxies? A comparison of kinematic and photometric properties     

Phil James  Cheryl Bate  Martyn Wells  Gillian Wright  René Doyon 《Monthly notices of the Royal Astronomical Society》1999,309(3):585-592

We present near-infrared K -band imaging and spectroscopy of a sample of galaxy mergers, which we use to derive light profile indices, absolute magnitudes and central velocity dispersions. We find that the light distributions of mergers more nearly resemble those of ellipticals than those of bulges, but that the mergers lie well away from the Fundamental Plane defined by the ellipticals. We interpret this as being due to enhancement of the K -band surface brightness of the mergers by a significant population of supergiant stars, and independent evidence for such a population is inferred from measurements of the depth of the 2.3-μm CO absorption feature.  相似文献