Lake Vechten (52°04’N, 5°05’E) is located in the center of The Netherlands, a few kilometers southeast of Utrecht, which is a large city with >350 000 people. The lake is located next to a golf court, squeezed between two highways and two major railways. The lake was formed by sand excavation to build the highway A12 in 1941 (Steenbergen and Verdouw 1982 ). There are no waste dumpsites and no ditches or streams connecting the lake with the city or the agricultural area east of the city. The lake is largely fed by groundwater and rainwater, including surface runoff from the golf court and the adjacent highway. The lake consists of two basins with a total surface area of 4.7 ha, and has a maximum depth of 11.9 m.
Vertical profiles of temperature, dissolved oxygen (DO), chlorophyll
a, photosynthetically active radiation (PAR), specific conductivity, and pH of the lake water were measured
in situ using a multiprobe Hydrolab DataSonde 4a (Hydrolab Corporation, Austin, TX, USA). From every meter depth in the Western Basin, water samples were collected monthly or biweekly from March 2013 to September 2014. Water was pumped via a hose connected to the Hydrolab Datasonde to make sure the water samples matched the conditions measured by the Hydrolab Datasonde at each particular depth. Water samples were filtered through 0.20 µm nylon membrane filters (Millipore, GNWP) to collect microorganisms. The filters were immediately frozen and stored at −20°C until further analysis. Sediment samples (0–10 cm) were collected monthly with a box-corer from the same location, transported to the laboratory in a dry shipper and stored at −20°C until further analysis. Dry weight of the sediment was determined after drying for 2 days at 60°C.
Subsequent to filtration, ammonium (NH
4+), nitrite (NO
2−), nitrate (NO
3−), dissolved inorganic nitrogen (DIN), sulfate (SO
42−), phosphate (PO
43−), and chloride (Cl
−) were measured with an auto-analyzer (SAN
++, Skalar, The Netherlands), while dissolved organic carbon (DOC) was measured with a total organic carbon analyzer (TOC-V
CPH, Shimadzu, Japan). For sulfide (S
2−) measurements, lake water was filtered through 0.20 µm polyethersulfone membrane filter and fixed with zinc acetate (10% w/v) immediately in the field. Afterward, sulfide was measured in the laboratory according to the methylene blue spectroscopic method (Trüper and Schlegel 1964 (
link)). The data were visualized with Ocean Data View version 4.7.8 (Schlitzer 2002 ).
Diao M., Balkema C., Suárez-Muñoz M., Huisman J, & Muyzer G. (2023). Succession of bacteria and archaea involved in the nitrogen cycle of a seasonally stratified lake. FEMS Microbiology Letters, 370, fnad013.