The spring freshet is the dominant annual hydrologic event occurring on largely nival Arctic river systems. It provides the greatest proportion of freshwater influx to the Arctic Ocean, amongst all other atmospheric input sources. To assess whether any shift in the seasonality of spring freshets has occurred, and how climatic drivers and flow regulation govern trends in sub-basin freshets and their contribution to outlet flow, a temporal and spatial analysis of 106 hydrometric stations located across four major Arctic-draining river systems is performed to extract information regarding the timing, magnitude and volume of the spring freshet of the four largest Arctic-draining rivers; namely, the Mackenzie River in Canada, and the Ob, Yenisei and Lena rivers in Eurasia. Total annual freshwater influx to the Arctic Ocean from these basins increased by 14% during 1980-2009. Despite freshet volume displaying a net increase, its proportional contribution to annual flow has decreased. In fact, rising winter, spring and fall discharge proportions, combined with lower peak freshet magnitudes, potentially increased freshet durations, and lower summer proportions indicate a shift towards flatter, more gradual annual hydrographs with earlier pulse onsets. Discharge assessed on a sub-basin level during 1962-2000 and 1980-2000 reveals regional differences in trends, with higher-relief drainage areas displaying the strongest trends. Sub-basin trends generally agree with those at the outlets, particularly in sub-basins without upstream flow regulation. Flow regulation has had a greater impact on observed trends in freshet volume compared to peak freshet magnitude. Timing measures are found to be strongly linked to spring temperatures. Volume relationships are also apparent with winter precipitation, however, these are less distinct. Moreover, flow regulation appears to suppress climatic drivers of freshet volume but has a lesser effect on timing measures. Significant relationships are found with several major atmospheric and oceanic teleconnections indices. This study provides valuable information regarding the dominant controls of freshet generation, whilst highlighting potential impacts of freshet variability on the freshwater balance of the Arctic Ocean. / Graduate / 0388 / 0368 / roxannea@uvic.ca

<p>A priori limit operator&gt;. maps sequence of a set X into a subset of X.<br />There exists maximal topology on X such that for each sequence x there holds<br />&gt;.(x) C limx. The space obtained in such way is always sequential.<br />If a priori limit operator each sequence x which satisfy lim sup x = lim inf x<br />maps into {lim sup x}, then we obtain the sequential topology Ts.&nbsp; If a priori &#39;limit<br />operator maps each sequence x into {lim sup x}, we obtain topology denoted by<br />aT. Properties of these topologies, in general, on class of Boolean algebras with<br />condition (Ii) and on class of weakly-distributive b-cc algebras are investigated.<br />Also, the relations between these classes and other classes of Boolean algebras are<br />considered.</p> / <p>A priori limit operator A svakom nizu elemenata skupa X dodeljuje neki<br />podskup skupa X. Tada na skupu X postoji maksimalna topologija takva da za<br />svaki niz x vazi A(X) c lim x. Tako dobijen prostor je uvek sekvencijalan.<br />Ako a priori limit operator svakom nizu x koji zadovoljava uslov lim sup x =<br />liminfx dodeljuje skup {limsupx} onda se, na gore opisan nacin, dobija tzv.<br />sekvencijalna topologija Ts. Ako a priori limit operator svakom nizu x dodeljuje<br />{lim sup x}, dobija se topologija oznacena sa OT.&nbsp; Ispitivane su osobine ovih<br />topologija, generalno, na klasi Bulovih algebri koje zadovoljavaju uslov (Ii) ina<br />klasi slabo-distributivnih i b-cc algebri, kao i odnosi ovih klasa prema drugim<br />klasama Bulovih algebri.</p>

Tropical Storm Irene’s most extreme rainfall resulted in record-breaking sediment loads from upland tributaries to the Connecticut River. However, was the event exceptional with respect to resultant deposition downstream? Off-river waterbodies to the Lower Connecticut River, such as cut-off meanders and blocked valley lakes, are a particularly important floodplain environment, which have been shown to serve as a focal point for the trapping of sediment and associated contaminants. This study evaluates the relative role of extreme events like Tropical Storm Irene in infilling these off-river environments. To meet this objective we compare the magnitude and composition of resultant sedimentation from Irene to that observed following the 2011 and 2013 spring freshets. Tropical Storm Irene deposits were identified as compositionally distinct, grey layers that were relatively inorganic compared to sediments deposited by the annual spring freshet. Sediment within the Irene deposit was enriched in elemental potassium and depleted in zircon, a finding consistent with being enriched by glacigenic lacustrine and till sediments. Decreased mercury levels in the Irene deposits suggest that this event served to cap highly contaminated, industrial era sediment with a layer of relatively clean, fine-grained silt and clay. Resampling of these waterbodies in Fall 2012 revealed preservation of the 2-3 cm thick Irene deposit as well as 3-4 cm of more recent sediments deposited on top of this event. Sediment contributions from rare events, like Tropical Storm Irene, were found to be less influential than the annual spring freshet in the long-term infilling of waterbodies along the Lower Connecticut River. However, sediments from Irene are compositionally unique and serve to highlight the importance of this event in removing glacially derived fines from the river’s upland catchments.