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  • 1
    Electronic Resource
    Electronic Resource
    Impact of global change on the biogeochemistry and ecology of an Arctic freshwater system (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Polar research 18 (1999), S. 0 
    Details
    ISSN: 1751-8369
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography , Geosciences
    Notes: Lakes and streams in the foothills near Tookik Lake, Alaska, at 68°N have been studied since 1975 to predict physical, chemical and biological impacts of future global change. Experimental manipulations include whole lake and continuous stream fertilization as well as removal and addition of predators (copepods, lake trout, grayling, sculpin). Based on our evidence the following scenario is likely. Warming thaws the upper layers of permafrost and streams and lakes become enriched with phosphorus. Streams respond quickly with higher production of diatoms but animal grazers keep biomass changes to a minimum. Fish productivity also increases. If phosphorus levels are too high, mosses become the dominant primary producer and sequester all of the nutrients. Growth of Arctic grayling under the present conditions only occurs in summers with higher than average stream flow. The present population would be stressed by warmer temperatures. When higher phosphorus levels reach lakes and cause slight europhication, the number of trophic levels will increase, especially within the microbial food web. Warmer lake temperatures increase stratification and, combined with eutrophication, could decrease oxygen in the hypolimnion. Oxygen levels will also decrease in winter under the ice cover. Eventually this habitat change will eliminate the lake trout, a top predator. Removal of lake trout results in a striking increase in abundance and productivity of smaller fish, including small lake trout, and the emergence of burbot as an alternate top predator. Large species of zooplankton will become virtually extinct.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1751-8369.1999.tb00295.x
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  • 2
    Electronic Resource
    Electronic Resource
    Long-term response and recovery to nutrient addition of a partitioned arctic lake (2005)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 50 (2005), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. To study the bottom-up linkages in arctic lakes, we treated one side of a partitioned lake with inorganic nitrogen and phosphorus for a 6-week period each summer for 6 years starting in the summer of 1985. We took a variety of weekly measurements to determine the impact of the nutrient loading on the lake and continued weekly measurements for 2–6 years after the cessation of nutrient loading to observe the recovery of the treated side. The loading rates (2.91 mmol N m−2 day−1 and 0.23 mmol P m−2 day−1) were five times the calculated loading rates for Toolik Lake, located nearby.2. In all 6 years of nutrient addition, phytoplankton biomass and productivity were greater in the treated sector than the reference sector. In the first 4 years of nutrient addition there was no flux of phosphorus from the mineral-rich sediments. This changed in the last 2 years of nutrient addition as phosphorus was released to the lake.3. The response of the animal community to increased plant production was mixed. One of the four macro-zooplankton species (Daphnia longiremis) increased in number by about twofold in the first 5 years. However, the copepod Cyclops scutifer showed no response during the treatment phase of the study. The benthic invertebrate response was also mixed. After a 2-year lag time the snail Lymnaea elodes increased in the treated lake sector but chironomids did not.4. Ecosystem response to fertilisation was not controlled solely by nutrient addition because phosphorus was not recycled from the sediments until the last 2 years of nutrient addition. Phytoplankton still showed the effects of nutrient addition in the recovery period and the hypolimnion of the treated sector was still anaerobic starting at 6 m in 1996.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2005.01354.x
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  • 3
    Electronic Resource
    Electronic Resource
    Snail populations in arctic lakes: competition mediated by predation? (1990)
    Springer
    Oecologia 82 (1990), S. 26-32 
    Details
    ISSN: 1432-1939
    Keywords: Competition ; Facilitation ; Lake trout ; Predation ; Snails
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary For 2 species of snails in arctic Alaskan lakes, I studied the patterns of snail distribution with respect to habitat, distribution of predatory fish, and the potential for interspecific competition. The snails Lymnaea elodes and Valvata lewisi co-exist in these arctic lakes, either in the presence of lake trout, Salvelinus namaycush, or in the absence of predation. Intensive sediment core sampling of Toolik Lake and Lake N-2, with trout and lacking trout, respectively, showed that the smaller snail, Valvata, was abundant in Toolik but ocurred at very low densities in Lake N-2. On the open sediments of lakes containing trout, diver surveys revealed very low densities of adult Lymnaea (0.12±0.12/m2), but similar surveys in lakes without trout revealed much higher densities of adult Lymnaea (7.1±1.8/m2). A survey of 14 lakes indicated that adult Lymnaea grew to a smaller mean size in lakes with trout than in lakes which lacked trout. In laboratory and field experiments, the presence of Lymnaea lowered the fecundity of Valvata. Laboratory experiments also showed that Lymnaea fecundity was enhanced by the presence of Valvata. Enhancement was not due to predation by Lymnaea on Valvata eggs or young. The observed patterns of distribution and abundance in the absence of trout, combined with results from laboratory experiments, are consistent with the hypothesis that competitive and facilitative interactions control the population dynamics of the two snails. The distribution and abundance patterns of snails where trout are present suggest that trout predation rather than competition controls snail population dynamics in lakes containing trout.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318529
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of methoprene and Bti (Bacillus thuringiensis var. israelenis) on non-target insects (1995)
    Springer
    Hydrobiologia 308 (1995), S. 219-227 
    Details
    ISSN: 1573-5117
    Keywords: Bti ; chironomids ; drought ; methoprene ; mosquito control ; non-target insects ; temporary ponds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of mosquito larvicides Bacillus thuringiensis israelensis (Bti) and methoprene, on non-target benthic invertebrates were studied in a divided pond experiment in south-central Minnesota, USA, during the spring and summer of 1989. Density and biomass of insects and other benthic macroinvertebrates were quite low in all sections of the three ponds studied, which may have been due to three consecutive years of drought, but richness appeared to be high and we observed no evidence of dominance by a particular group. We also saw no evidence of negative effects of larvicide treatment on density or biomass of any invertebrate group, nor was there a treatment-related decrease in richness of benthic invertebrate taxa under these drought conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00006873
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  • 5
    Electronic Resource
    Electronic Resource
    A comparison of slimy sculpin (Cottus cognatus) populations in arctic lakes with and without piscivorous predators (1992)
    Springer
    Hydrobiologia 240 (1992), S. 189-201 
    Details
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Arctic slimy sculpin were sampled by passive trapping in lakes containing the predators lake trout and burbot (LT lakes), and lakes lacking sculpin predators (NoLT lakes). Sculpin food abundance (chironomid biomass) from the rocky littoral zone was compared with that from the deep water sediment zone. Distribution, size, growth, age, condition and relative abundance of sculpin were examined. Spatial distribution of sculpin was different between lake types, with more and larger sculpin found over the sediment zone in NoLT lakes. There were no seasonal patterns evident in this distribution and catch per unit effort was not significantly different between LT and NoLT lakes. Biomass of chironomids, the major food of the sculpin, was higher in the sediments than on the rocks, suggesting that sediments should be the preferred environment in the absence of piscivores. Longevity of sculpins varied between IV and VIII years and was not correlated with lake type. Sculpin size frequency distributions were shifted toward slightly larger fish in NoLT lakes. Sculpin growth curves and condition estimates did not reveal a difference between lake types, but comparison of mean ototlith interannular distances between lake types showed a trend, significant in year 4, toward more growth in no lake trout lakes. These results suggest that the presence of piscivores is an important factor limiting arctic slimy sculpin distribution and may act in concert with food supply to impact sculpin growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00013460
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  • 6
    Electronic Resource
    Electronic Resource
    Salmonid diet and the size, distribution, and density of benthic invertebrates in an arctic lake (1992)
    Springer
    Hydrobiologia 240 (1992), S. 225-233 
    Details
    ISSN: 1573-5117
    Keywords: arctic ; benthic ; lake trout ; predation ; snails
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Size selective predation on molluscs was apparent for lake trout (Salvelinus namaycush) and round whitefish (Prosopium cylindraceum), but not for arctic grayling (Thymallus arcticus), in the Toolik Lake region of arctic Alaska during the summer of 1986. Lake trout consumed significantly larger molluscs of all taxa than did round whitefish, and selected larger molluscs than were available on either rocky or soft-sediment habitats. Round whitefish were not size-selective on the snail Lymnaea, but were size-selective on the snail Valvata and on clams from the soft sediments. Round whitefish consumed fewer and smaller Lymnaea compared to lake trout. Because lake trout ate more Lymnaea and also tended to select larger, reproductive-sized individuals, this fish could potentially have a more detrimental impact on the Lymnaea population. Finally, differences in Lymnaea densities and size distributions between lakes with and without lake trout suggest that these fish may be responsible for the pattern of distribution, size, and density observed for Lymnaea in Toolik Lake and other area lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00013464
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of fish predation on larval chironomid (Diptera: Chironomidae) communities in an arctic ecosystem (1992)
    Springer
    Hydrobiologia 240 (1992), S. 203-211 
    Details
    ISSN: 1573-5117
    Keywords: arctic ; chironomidae ; diversity ; predation ; slimy sculpin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chironomid communities were analyzed in systems with three types of predator regimes to determine hierarchical effects of predation; ponds without fish present, lakes with slimy sculpin (Cottus cognatus) present, and lakes with slimy sculpin present along with burbot (Lota Iota) and lake trout (Salvelinus namaycush). Samples were collected by coring bare sediment habitats in 4 systems of each type near the Toolik Lake field station in northern Alaska. Lakes with burbot and lake trout present in addition to slimy sculpin displayed significantly higher (P〈0.05) biomass, density, richness, and diversity. This is likely due to the increased complexity of the predator regime. Ponds without fish had a significantly greater percentage of predacious chironomids present.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00013461
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  • 8
    Electronic Resource
    Electronic Resource
    Black fly (Diptera: Simuliidae) response to phosphorus enrichment of an arctic tundra stream (1992)
    Springer
    Hydrobiologia 240 (1992), S. 259-265 
    Details
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This study reports on the density, growth, and production response of the dominant black fly, Prosimulium martini, to whole river fertilization of the Kuparuk River in arctic Alaska during the summer of 1984. Beginning in 1983, a long term study of fertilization effects was initiated in the Kuparuk River. Increased nutrient supply stimulated algal and microbial biomass and microbial activity, which in turn affected the larval growth and abundance of Prosimulium. This experiment allowed us to isolate the effects of nutrient supply from other factors in determining black fly growth and abundance. Phosphorus addition had the following indirect effects on Prosimulium: growth was higher, but abundance decreased in the enriched section, leading to a net decrease in secondary production from 2.62 g m−2 yr−1 to 0.77 g m−2 yr−1. Prosimulium emergence rates were not measureably affected. The decrease in abundance and production appears to be a result of competitive displacement by the caddisfly Brachycentrus americanus which increased in abundance in the fertilized section of the river.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00013467
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  • 9
    Electronic Resource
    Electronic Resource
    The biogeochemistry and zoogeography of lakes and rivers in arctic Alaska (1992)
    Springer
    Hydrobiologia 240 (1992), S. 1-14 
    Details
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Water samples from 45 lakes and 8 rivers in arctic Alaska were analyzed for major anions, cations, nutrients, chlorophyll, zooplankton, and benthos. The waters were dilute (conductivities of 30 to 843 µS cm−1), and their composition varied from Na-Ca-Cl waters near the Arctic Ocean to Ca-Mg-HCO3 waters further inland. Sea salt input in precipitation was important in determining the chemistry of coastal lakes, partly because of low groundwater flow and less time for water to react with shallow unfrozen soils. Further inland, variations in water chemistry among sites were related mainly to differences in bedrock, the age of associated glacial drift, and the input of wind blown sediment. Variations in zooplankton species composition among the lakes were related more to latitude, lake morphometery, and biotic interactions than to water chemistry. The presence of fish as predators mostly determined the overall size structure of the zooplankton community. The chironomid taxa identified have been previously reported from the Neararctic, except for Corynocera oliveri which is a new record. The abundance of the widely distributed chironomid Procladius appears to be controlled by sculpin predation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00013447
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  • 10
    Electronic Resource
    Electronic Resource
    Shifts in abundance and growth of slimy sculpin in response to changes in the predator population in an arctic Alaskan lake (1992)
    Springer
    Hydrobiologia 240 (1992), S. 219-223 
    Details
    ISSN: 1573-5117
    Keywords: slimy sculpin ; lake trout ; predation ; benthos ; habitat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lake trout (Salvelinus namaycush) in Toolik Lake are tightly coupled to the benthos, since they have no pelagic forage fishes. Slimy sculpins (Cottus cognatus) are a prey of lake trout and the soft sediment chironomids are an important prey for the sculpin. Our previous work showed that the median size of lake trout in Toolik Lake had decreased significantly between 1977 and 1986, and smaller lake trout are likely to be less effective as sculpin predators. Using our historic data on the slimy sculpin population from 1978, we took advantage of the recent change in the predator community to examine for subsequent changes in the sculpin community. Between 1978 and 1987, the percentage of slimy sculpin caught in the soft sediments has increased (25% to 39.5%). In 1987 there was a significant difference in the mean weight of sculpin caught on different substrates. The mean individual weight of sculpins increased from the nearshore rock area to the rock/soft-sediment interface to the soft sediments. There was no difference in mean individual weight with habitat in 1978. The mean total length at age for slimy sculpins during this time has also increased significantly. We suggest that the risk of predation while foraging in the soft sediments has declined. The increased use of the soft sediment area appears to have contributed to their increased growth, likely due to greater food abundance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00013463
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