Average rates of atmospheric deposition of total phosphorus (TP) and total nitrogen (TN) to Narrow Lake, located on sedimentary bedrock in the boreal forest of central Alberta, were 20 and 424 mg m z yr-l, respectively, between 1983-1986. There were no significant differences (P > 0.05) in deposition rates between sites on Narrow Lake, on the lake shore, and on land 18 km away. Deposition of TP, but not TN, followed a distinct pattern during the open-water season; TP was highest just after ice-off (May) and decreased throughout the remainder of the open-water season. Deposition during the winter accounted for only 4 and 12% of the annual TP and TN loads, respectively. Dry fallout contributed 50 and 33% of atmospheric deposition of TP and TN, respectively. In both dry and wet fallout, dissolved P (< 0.45 lam) and organic N were the predominant fractions of TP and TN, respectively. During July 1986, unusually heavy rainfalls caused an increase in TP, but not TN, concentrations in the epilimnion of Narrow Lake. Wet fallout accounted for only 9% of the observed increase of epilimnetic TP; the rest was from surface runoff from the drainage basin. The design of sampling programs to measure atmospheric deposition of nutrients to lakes is discussed.

An integrated approach was used to quantify groundwater phosphorus flux to Narrow Lake, a smallglacial-terrain lake in central Alberta. Data from a drilling program, major ion concentrations, environmental isotopes, and computer simulations indicated that the lake gains water through the nearshore region from a small, shallow groundwater flow system; at deep offshore regions, water moves from the lake to the groundwater flow system. Seepage flux was quantified by water budget, Darcy's equation with data from wells near the lake, Darcy's equation with data from minipiezometers in the lake, and seepage meters. Whole-lake seepage flux determined from minipiezometer data (30 mm yr-I) was only lO-25% of the other estimates (mean, 221 mm yr-I; range, 133-332 mm yr-l from seepage meter and water budget data, respectively). Groundwater contributed -30% of the annual water load to the lake. The P concentration, [PI, in pore water from lake sediments (mean, 175 mg m-') was 8 times higher than groundwater from wells near the lake (mean, 2 1 mg m-3). Thus, if well water was used to estimate the [P] of the seepage water, the rate of groundwater P loading to the lake would be underestimated. The rate of groundwater P loading to the lake computed from average seepage flux and average pore-water [P] was 39 mg m-2 yr-I, and groundwater may be the largest single source of P to epilimnetic water in the lake.

Primary productivity provides most of the energy to support aquatic food chains. The rate is not only influenced by available solar radiation but also by temperature, availability of phosphorus, and the influence of physical mixing processes. The special features of Lake Ontario such as changes in phosphorus concentration, calcium carbonate precipitation, and silica deficiency on primary productivity, concentration of particulate carbon, and chlorophyll are discussed. Our lack of understanding of food chain and nutrient regeneration processes is illustrated through our failure to balance carbon production with losses through zooplankton grazing and sedimentation. It was demonstrated, however, that bacteria are not responsible for nutrient regeneration through "mineralization" but nutrients are effectively recycled in the water column at the second and third trophic levels.

The seasonal pattern of zooplankton succession in Lake Ontario was similar at three stations along a north–south transect, with differences attributable to physical factors. Because of warming within the thermal bar zone, the spring succession at the northshore station was early relative to the midlake station, but after stratification the northshore station lagged behind due to frequent upwelling events. Thermal bar formation along the south shore was followed by downwelling throughout the summer, giving a deeper epilimnion. These events may have contributed to not only the greater biomass at this location, but also succession which preceded that at the other stations during summer and fall. The species composition and the timing of the summer succession were very similar to those reported for 1970. Lake Ontario zooplankton did not change markedly in response to changes in nutrient loading and salmonid predators during the 1970's.

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