Temporal variability in suspended sediment delivery processes was studied during three seasons in a 7·9 km 2 catchment at Cape Bounty, Melville Island, Nunavut in the Canadian High Arctic. Discharge was controlled primarily by the magnitude of snowmelt, with limited inputs from ground ice melt and precipitation. Years with greater snowpack non-linearly increased sediment yield and resulted in seasonal counter-clockwise hysteresis, while a year with low snowpack resulted in reduced sediment yield and clockwise hysteresis, and indicates that sediment was increasingly available after the onset of streamflow. In addition to the event-scale hysteresis observed during the nival discharge peak, diurnal clockwise hysteresis was observed during all three seasons and suggests daily exhaustion of sediment supplies. These results indicate that the channel snowpack plays a primary role over sediment accessibility during the nival discharge peak. Similarly, grain size analysis of suspended material in the river showed that the coarsest mean grain size was transported during the early phase of peak nival discharge and indicates that isolated sources of coarse material were being accessed by high velocity flow. Snowpack is present through the peak nival period and conditions sediment availability by isolating channel sediments from high-energy flow. These results indicate sediment delivery characteristics in small High Arctic catchments reflect complex interactions with channel snowpack and disproportionate responses to flow conditions that differ from glacial and temperate settings. Results HydrometeorologyThe three seasons studied exhibited substantially different hydrological and meteorological conditions. Both 2004 and 2006 were characterized as cool and wet melt periods, while 2005 was relatively warm and had substantially lower SWE prior to melt (Table I and Figure 3).During the winters prior to the 2004 and 2005 seasons, wind extensively redistributed snow and filled the channel with dense snowpack (depth σ = 27·4 and 29·1 cm, respectively).In 2006, snowpack was spread relatively evenly over the landscape (depth σ = 22·3 cm), and showed little evidence of Figure 2. An example of clockwise diurnal discharge-suspended-sediment-yield hysteresis on 27-28 July 2004 with k = 0·5. Q min , Q mid and Q max represent the discharge at the onset of the hysteresis event, the mid-event discharge and the maximum discharge, respectively. Q min , Q mid and Q max are used to calculate the hysteresis index detailed by Lawler et al. (2006).Figure 3. Daily mean air temperature and total precipitation from 2004 to 2006.Figure 5. Hourly (A) discharge, (B) suspended sediment concentration (SSC), (C) velocity and (D) peak mean daily grain size collected from the West River station in 2005. The dashed line represents the division between nival event and the recession-baseflow period. Error bars associated with the peak mean daily grain size represent one standard deviation from the mean. Gaps in the flow velocity resulted from stage falling below ...
2010: Assessment of a time-integrated fluvial suspended sediment sampler in a High Arctic Setting. Geogr. Ann., 92 (2): 225-235.ABSTRACT. Two versions of a fluvial sediment trap designed to collect integrated samples of ambient suspended sediment load were deployed in a small river at Cape Bounty, Melville Island, Nunavut in the Canadian High Arctic. Daily and bi-daily sediment capture in the traps was broadly proportionate with suspended loads estimated directly from daily sediment flux measurements but showed highly variable trap capture rates. Grain size analysis showed that the median grain size (D 50 ) of the captured material was significantly coarser than the ambient material, although the D 50 of the two trap versions deployed was not significantly different. These results suggest that the traps did not consistently collect a representative mass or particle size sample in a river environment with highly variable conditions. This is explained by consideration of the hydraulic design of the traps and a highly dynamic stream environment. Hence, deployment of fluvial traps in small ephemeral Arctic rivers will require further testing and refinement of the hydraulic design.
ABSTRACT. During June 2005, we identified the presence of sediment buried within multi-year channel snowpack of a small river located near Cape Bounty, Melville Island, Nunavut (74˚55' N, 109˚35' W). Photographic evidence indicates that the sediment was deposited during the 2003 season by the initial meltwater flowing on the snowpack, which was dammed by snow upstream of a channel constriction. The resulting pond covered a minimum area of 180 m 2 and contained an estimated minimum 27 Mg of sediment. Suspended sediment measurements during the 2003 season indicate that deposition on the snowpack at this location represented 49% -65% of the sediment transport prior to the ponding and emplacement of the sediment on the snow, and approximately 20% of the measured sediment flux for the entire season. Multi-year snow accumulations immediately downstream exhibited similar sediment deposition on snow, but no evidence of multi-year sediment storage was present. By contrast, a similar stream in an adjacent watershed channelized rapidly, with minimal sediment deposition on the snow, and delivered a large pulse of sediment to the downstream lake. These results provide quantitative evidence for the magnitude of sediment storage on snowpack and point to the unique role that snow plays in the fluvial geomorphology of High Arctic watersheds. Les accumulations de neige de plusieurs années immédiatement en aval comptaient des dépôts de sédiment semblables sur la neige, quoi qu'aucun emmagasinage de sédiment sur plusieurs années n'était présent. Par contraste, un cours d'eau similaire d'un bassin hydrographique adjacent s'est canalisé rapidement, avec peu de dépôts de sédiment sur la neige, puis a laissé une grande quantité de sédiment au lac en aval. Ces résultats fournissent des preuves quantitatives quant à l'ampleur de l'emmagasinage de sédiment sur la plaque de neige et laissent envisager le rôle unique que joue la neige sur la géomorphologie fluviale des bassins hydrographiques de l'Extrême-Arctique.Mots clés : hydrologie, transport de sédiment, géomorphologie fluviale, neige, accumulation d'eau, emmagasinage de sédiment, île Melville, érosion Traduit pour la revue Arctic par Nicole Giguère.
Tamoxifen is the most widely prescribed anti-neoplastic drug for the treatment of both localized and metastatic breast cancer. It is also the prototype for a class of drugs that are referred to as selective estrogen receptor modifiers (SERMs), most of which have both estrogenic and anti-estrogenic activity in estrogen target tissues including the breast and endometrium. The underlying mechanisms of action of SERMs in the breast and endometrium that lead to profound differences in the tissue-specific effects of tamoxifen have not yet been elucidated.We have compared the effects of tamoxifen and the pure anti-estrogen ICI 182,780 (Faslodex) in the RUCA-I hormone-responsive rat endometrial cell line in vitro and in vivo. In cell culture, RUCA-I cells responded to both estrogens and anti-estrogens, and the expression of clusterin and complement C3 mRNAs required the presence of estradiol and was repressed in the absence of estradiol or in the presence of the pure anti-estrogen ICI 182,780. Tamoxifen, on the other hand, induced both complement C3 and clusterin mRNA in the absence of estradiol and failed to repress their expression in the presence of estradiol. When grown as subcutaneous xenografts in syngeneic Da/Han rats for 5 weeks, the RUCA-I cells retained their sensitivity to estradiol, as demonstrated by significantly enhanced tumor growth in intact female rats compared with the growth in ovariectomized rats. But neither ICI 182,780 nor tamoxifen had a significant impact on tumor growth in cycling or ovariectomized animals. On the other hand, tamoxifen was potently estrogenic in metastatic lymph nodes, increasing the size of the lymph node tumors almost 6-fold over that seen in the intact cycling animals. In primary tumors, the expression of complement C3 mirrored that seen in vitro, although tamoxifen showed some agonist activity in ovariectomized animals. Tamoxifen also displayed marked agonist activity with respect to clusterin expression and enhanced clusterin mRNA levels and protein in both the primary tumors and lymph metastases in intact and ovariectomized animals.Given the recent demonstration that over-expression of clusterin increases the metastatic potential of breast cancer cells, these data may provide a mechanistic explanation for the increased incidence of endometrial cancer in postmenopausal patients treated with tamoxifen.
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