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Lake N1

Bathymetric Map

Manipulation

As one of several experiments investigating bottom up controls in arctic lakes, lake N1 was fertilized at 4 times the annual loading of Toolik lake for 5 summers (1990 - 94) with inorganic nitrogen as NH4NO3, and inorganic phosphorus as H3PO4. The recovery of N1 has been monitored since 1994 and will continue in the future.

Lake Description

Description is from: Bettez, N. D. 1996. Changes in Abundance, species composition, and controls within the microbial loop of a fertilized arctic lake. Masters Thesis University of North Carolina Greensboro , Greensbor o , NC .

Lake N1 is one of several lakes at the Arctic LTER research site that is undergoing long term manipulation and measurement.

Lake N1 is typical of many lakes in the region in both size and species components. It is a dimictic kettle hole lake, although for several years during the study it was monomictic. Lake N1 is 4.8 x 103 m2 in size, with a volume of 1.72 x 105 m3; it has a maximum depth of 14 m and a mean depth of 3.9 m. The lake is ice free from mid June until late September after which ice forms up to 2 m thick. The average summer temperature is 12 0C in the epilimnion, and 5.1 0C in the hypolimnion. Lake N1 is a highly oligotrophic lake (Miller et al., 1986) with pre- treatment concentrations of 0.13 umol NH4+ L -1, 0.23 umol NO3- L -1, and 0.23 umol PO4 L -1 (Kling et al., 1992). The pre- treatment summer average primary productivity of the epilimnion is 11.28 mg C m-2 day-1; and the chlorophyll a concentration is 0.56 ug chlorophyll a L-1.

In 1989, prior to fertilization, lake N1 was typical of other lakes at the Arctic LTER site with respect to species composition and nutrient pools (Kling et al., 1992). Although algal composite samples from N1 prior to fertilization have not been quantified, small autotrophs generally constitute a significant portion (36-63 %) of the algal communities in oligotrophic arctic lakes (Hobbie, 1973). Average primary production of the epilimnion for the summer prior to fertilization was 11.28 mg C m-2 day-1 and chlorophyll a values were 0.56 ug chlorophyll a L-1. The protozoan population was comprised mainly of the oligotrich protozoans Strombidium, Strobilidium, and Halteria spp. The average biomass of the protozoans was 0.48 ug C L-1 with values never exceeding 1.44 ug C L-1 during the summer. The rotifer population was primarily composed of small-particle feeders, with Conochilus unicornis and Keratella cochlearis being the predominant species. Kellicottia longispina, Keratella quadrata, Filinia terminalis, Conochilus natans, Gastropus stylifer, and Ascomorpha (Chromogaster) ecaudis were also present in low abundance. The predatory rotifers Polyarthra vulgaris and Synchaeta spp., which eat flagellated algae, would occasionally appear in low numbers as well. The rotifers comprised an average of 35 % of the microplankton biomass, about 2.1 ug C L-1. The average biomass of the zooplankton nauplii in 1989 was 3.6 ug C L-1. Prior to fertilization, the zooplankton community was dominated by the large zooplanktivous copepod Heterocope septentrionalis with densities of 0.048 individual L-1 in early July which increased to 0.13 individual L-1 by early August.

Elevation (m): 731

Surface Area (ha): 4.4

Volume (cubic meters): 172,000

Mean Depth (m): 3.9

Max Depth (m): 14

Catchment Area (ha): NA

Water Retention Time (years): NA

Fish

Arctic Grayling (Thymallus arcticus)

Slimy sculpin (Cottus cognatus)

Lake Trout (Salvelinus namaycush)

Burbot (Lota lota)

Microplankton

Keratella cochlearis

Keratella quadrata

Kellicottia longispina

Polyarthra vulgaris

Chromogaster ecaudis

Synchaeta sp.

Conochilus unicornis

Conochilus natans

Filinia terminalis

Gastropus stylifer

Zooplankton

Daphnia middendorffiana

Heterocope septentrionalis

Holopedium gibberum

Daphnia longiremis

Bosmina longirostris

Diaptomus pribilofensis

Cyclops scutifer

Polyphemus pediculus

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