zooplankton and phytoplankton interactions. Northeast Greenland 2013

Study Extent

Field sampling of zooplankton, phytoplankton and catchment vegetation coverage where conducted in the Zackenberg area, North East Greenland during the period July to August 2013.

Sampling

Zooplankton was sampled by filtering 20 l of water through a 90 µm plankton net. The water samples were from the deepest point of the lake, or as far out as accessible with waders (ca. <1.5 m depth). Three replicated samples per lake where collected at each sampling day. Water samples for chlorophyll a and chemical analysis were taken as surface samples over the deepest point in the lake, or as far out as accessible with waders (ca. <1.5 m). Water samples for chemical parameters where frozen at -18 °C at the day of sampling and later analyzed for total organic carbon (TOC), total nitrogen (totN) and total phosphorous (totP) according to standard procedures in an accredited (NS EN ISO 17025) water laboratory (Analysesenteret, https://www.trondheim.kommune.no/analysesenteret/). Vegetation coverage of lake catchment areas where determined by walking transects in four directions (north, east, south and west) to the end of the catchment or 200 meters (whatever came first). A minimum of four plots per transect (2 square meters) where set at regular intervals and percentage coverage of 11 classes (rock or gravel, bare soil, mosses, graminoids, Dryas, lichens, Salix, Cassiope, Saxifraga, bogs or wetland, and other) where determined by visual inspection. Mean coverage of vegetation classes throughout all sampling plots belonging to a particular lake where then used as proxy for catchment vegetation cover of that lake.

Quality Control

Data where entered on paper forms in field or lab, and transferred manually to spreadsheets (Microsoft xl). Spreadsheets where subsequently manually checked against the original field forms.

Method steps

1. Zooplankton was stored in 70% ethanol. All organisms in a sample were counted, with exception of some samples where naupli larvae where counted using subsamples. In this case, a known fraction were examined until at least 200 organisms were counted. Cyclops spp. where identified to genus level, whereas the other main zooplankton taxa (Macrothrix hirsuticornis, Daphnia pulex, Chydorus sphaericus) where determined to species level. Biomass of zooplankton where determined by measuring a subsample of individuals from one of the replicates at each lake at each sampling occasion (25 or as many as in sample if less) under a dissection microscope. Dry mass (µg) where determined using length-weight regression following Botrell et al. (Nor J Zool. 24, 419–456, 1976), and in case of naupli larva Dumont et al. (Oecologia 19, 75–97, 1975). Information on presence or absence of fish (Arctic char, Salvelinus alpinus L.) was based on previous gillnet test fishing in the lakes.
2. Chlorophyll a where extracted from filtered water samples according to standard methods (ISO 10 260) at the Department of Biology, Norwegian University of Science and Technology. Water samples used for chlorophyll a measures (1 – 2 liters) where kept dark and cool and filtered (Whatmann GF/C) using a suction pump, on the day of collection. Filters where then dried and packed in aluminium foil, wrapped in plastic and immediately frozen at -18 °C at the field lab. The samples where kept frozen until returning to Norway and there stored at -70°C until analysed. Chlorophyll a concentrations where measured by photometrical absorbance at 665 and 750 nm after solving filters in ethanol.

Two main study areas: Zackenberg valley (close to the Zackenberg research station) and Lille Sødal (close to the Daneborg research station).