A critical area of uncertainty in arctic environmental change research is the influence of increasing temperatures on the hydrosphere and aquatic ecosystems. The Arctic hydrological cycle is characterized by an intense period of spring runoff due to the melting of winter snowpack. In summer, low precipitation and reduced hydrologic connectivity due to greater soil storage mean that the bulk of runoff to streams and lakes occurs during the brief spring freshet. Because arctic freshwaters are characteristically oligotrophic due to low productivity and limited nutrient cycling, high latitude lake ecosystems may be particularly sensitive to changes in catchment hydrology that affect the delivery of nutrients and other important constituents to the basin. This research characterizes the seasonal hydrochemistry of two adjacent High Arctic lakes (Cape Bounty, Melville Island; 74°55' N, 109°35' W) and their respective inflow streams, in order to better understand the influence of hydrologic variability on downstream aquatic ecosystems. Comparison of two similarly sized systems in close proximity (1 km apart) affords a unique opportunity to recognize factors influencing the character and timing of runoff and the range of limnological responses generated by the same hydroclimatic conditions.

Water samples were systematically collected from the river gauging stations and lake moats approximately every 5-6 days from snowmelt to early August in 2003 and 2004. Analyses included alkalinity, dissolved oxygen, pH, conductivity, nutrients (including organic and inorganic nitrogen, phosphorus and carbon species), dissolved silica, chlorophyll, major and minor ions and trace metals. Water column profiles of temperature, dissolved oxygen, and alkalinity were also conducted. In addition, continuous streamflow measurements (discharge, temperature, specific conductivity, transmissivity) and weather conditions were recorded in both catchments.

Chemical analyses of East and West Lake indicate similar limnological conditions. Both lakes are relatively dilute (mean pH=7.4, mean EC=37 us/s), with low nutrient concentrations and low productivity (mean Chl-a=1.16 ug/l), even by arctic standards. DOC levels were low (mean 1.6 mg/l), and suggest a vulnerability to increased UV-B penetration (Pienitz and Vincent, 2000). Similar to most arctic sites, TN:TP ratios and soluble reactive phosphorus (SRP) concentrations suggest that phosphorus is likely the limiting nutrient, although it appears that both P and N are effectively limiting in some instances, particularly in 2003. However, linear regressions of Chl-a and TN and Chl-a and TP revealed weak positive correlations, suggesting factors other than nutrients, such as water temperature, may be restricting productivity. For instance, productivity is highest late in the season when water temperature is also at a maximum.

Although outwardly similar, some important differences exist between the two lakes and may lead to a differential response to changing hydroclimatic conditions. Chlorophyll levels in East Lake and River are almost double those of West Lake in both years. In addition, potassium concentrations, which are associated with leaching from higher plants, are also higher in the East catchment. A large residual snowbank that drains through a lush slope on the north shore of East Lake, and schools of fish along this shoreline point to higher productivity.

River nutrient concentrations and flux rates suggest that spring discharge is a major mechanism for the delivery of major nutrients including N, P and C, to the lake. However, this trend is not reflected in lake nutrient concentrations, suggesting that the influence of early season high discharge on lake nutrient status is relatively minor or altered by inflow conditons. Despite this, lake nutrient concentrations remain highly dependent on external sources, as is the case for most arctic lakes. For example, POC:Chl-a ratios, which are an indication of whether organic carbon is predominantly terrestrial or aquatic in origin, indicate that terrestrial carbon formed the dominant contribution in all lake samples except at the very end of 2004, when autochthonous carbon sources predominated in both lakes.

Although long term monitoring of arctic freshwaters are generally lacking, recent efforts to document baseline physical and chemical limnology across the Canadian Arctic have been significant (see Keatley et al., 2007). However, our understanding of seasonal changes in limnology and hydrochemistry remains very limited (Forsström et al., 2007). Moreover, uncertainties surrounding the hydroclimatic controls on arctic aquatic ecosystems make it difficult to anticipate the response of these systems to projected climate change. Seasonal data from Cape Bounty shed light on the relationship between hydroclimatic variability and physical and chemical limnology in High Arctic catchments. In addition, comparison of two adjacent watersheds provided an opportunity to separate site specific influences from local hydroclimatic conditions.