Effects of acidity and doc on phytoplankton community structure and production in three acid lakes (Nova Scotia)

Phytoplankton community structure varied between the three lakes and between years within lakes. The Beaverskin Lake phytoplankton community was dominated by cyanophytes and chlorophytes in the summer and chrysophytes in the winter. Kejimkujik Lake was dominated by bacillariophytes in the summer of 1979 but no single group dominated in 1980 or 1981. Pebbleloggitch Lake phytoplankton consisted mainly of chlorophytes in 1979 but low biomass and no dominant groups characterized this lake during the growing season of 1980. Daily integral planktonic primary production measured simultaneously in the three lakes showed that in both years annual planktonic primary production was highest in the clear water lake, Beaverskin Lake, which also had lower dissolved organic carbon (DOC) concentration compared to the two dystrophic lakes. In the clear water lake annual production was similar between years but in the two colored lakes annual production was 40% higher in the second year. The observed increases in annual production between years in the colored lakes were largely due to changes in euphotic depth resulting from variations in hydrology and DOC export from the lake catchments. Lower discharges in the colored lakes in 1980 were accompanied by significantly lower in lake DOC concentrations, water color, light extinction coefficients and increased euphotic depth. Similar changes in discharge accompanied by lower DOC concentration in the clear water lake did not produce significant changes in water color, light extinction coefficient nor annual production between years. Rates of primary production at light optimum (P-max) were consistently higher in the most colored, acidic lake indicating that relatively high rates of autotrophic production will occur under acidic conditions if nutrient supply is maintained.     

Sources of sulphate and acidity in wetlands and lakes in Nova Scotia

There is a declining gradient of wet SO₄ deposition from south to north in Nova Scotia with the highest values being in the south, along with a localized increase around the Halifax metropolitan area, due to local SO₄ emission. Edaphic conditions such as drainage from soils containing gypsum or drainage on disturbed rocks containing pyrite, provide additional SO₄ to surface waters.Acidity is usually absent in the former (pH > 7.0) and very high in the latter (as low as pH 3.6). By contrast peaty, organic drainages release water low in SO₄ during the growing season but they release high amounts of organic anions (A?), consequently, these waters maintain decreased pH values, usually < 4.5. A study of over 80 wetlands and lakes during the ice free period in Nova Scotia showed that sea salt corrected SO₄ concentrations range from 45 ueq L^?1 in the south end of the province, ～30 ueq L^?1 in the Kejimkujik area and < 17 ueq L^?1 in the northern areas with values > 85 ueq L^?1 in the Halifax area, reflecting the atmospheric deposition pattern of SO₄ The SO₄ concentrations may be > 2000 ueq L^?1 in drainages containing gypsum, > 700 ueq L^?1 in drainages over pyrite bearing socks but < 20 ueq/L^?1 in streams draining bogs. The SO₄ concentrations change considerably during the non-growing season when the ground is saturated with water or frozen, and the runoff is high (snow and rain often alternate in winter). Under such conditions SO₄ concentration drops in the two former cases and increases in bog drainages, accompanied with a considerable drop in (A?) concentrations. Care should be taken when interpreting SO₄ concentrations in surface waters in Nova Scotia with respect to atmospheric SO₄ deposition.     

Denitrification and fermentation in plant-residue-amended soil

Summary Nitrous oxide production (denitrification) during anaerobic incubation of ground-alfalfa-, red-clover-, wheat-straw-, and cornstover-amended soil was positively related to the initial water-soluble C content of the residue- amended soil. The water-soluble C concentration decreased in all treatments during the first 2 days, then increased in the alfalfa-, red-clover-, and wheat-straw-amended soil until the end of the experiment at 15 days. An accumulation of acetate, propionate, and butyrate was partly responsible for the increased water-soluble C concentration. Denitrification rates were much higher in the alfalfa-and red-clover-amended soil, but NO ₃ ^– was not fully recovered as N₂O in these treatments. Supported by earlier experiments in our laboratory, we conclude that some of the NO ₃ ^– was reduced to NH ₄ ⁺ through fermentative NO ₃ ^– reduction, otherwise known as dissimilatory NO ₃ ^– reduction to NH ₄ ⁺ . Acetate, the primary product of anaerobic fermentation, accumulated in the alfalfa- and red-clover-amended soil in the presence of NO ₃ ^– , supporting previous observations that the processes of denitrification and fermentation occur simultaneously in C-amended soil. The partitioning of NO ₃ ^– between denitrification and fermentative NO ₃ ^– reduction to NH ₄ ⁺ depends on the activity of the denitrifying and fermentative bacterial populations. NO₂ concentration may be a key in the partitioning of NO ₃ ^– between these two processes.