Seasonal changes in the contents of nutrients in five macrophyte species from the lake Velenjsko jezero (Slovenia) | Sezonske spremembe vsebnosti hranil v petih vrstah makrofitov iz Velenjskega jezera (Slovenija)

anglais. The study was designed to depict the seasonal dynamic in relative abundance of macrophyte species, nutrient availability and their content in macrophytes to assess the capability of different species to store nutrients in nutrient rich lake Velenjsko jezero. The concentrations of total nitrogen and total phosphorus in the lake sediment, water and aboveground biomass of macrophytes (Nuphar luteum, Najas marina, Najas minor, Potamogeton lucens andPotamogeton pectinatus) were measured at three locations monthly from June to September 2004. Seasonal variability in the contents of total phosphorus in macrophyte tissues was high, but all examined species reached similar maximal concentration in the beginning of their growth. Later in the season, concentrations declined to a high degree. Seasonal variability in the contents of total nitrogen was smaller. Floating-leaved species Nuphar luteum was present in a low amounts and contained much more total nitrogen in its above-ground tissues than the submersed species. Because of different species lifespans, differences in the content of nutrients among species were very high in particular month. Nuphar luteum, Najas minor and Potamogeton lucens were rarely present in the lake and they contributed less to storing nutrients in their biomass. Potamogeton pectinatus was commonly present in the early summer, but in August Najas marina prevailed by far and its growth had high effect on the concentration of nutrients in sediment and water. Thereforenremoving of 1 t dry weight of Najas marina biomass from the lake would contribute to removal of 2.7 kg of phosphorus and 28.2 kg of nitrogen from the lake.

slovène. V pričujoči raziskavi smo spremljali sezonske spremembe v abundanci makrofitskih vrst ter vsebnosti celotnega dušika in celotnega fosforja v sedimentu, vodi in v makrofitih (Nuphar luteum, Najas marina, Najas minor, Potamogeton lucens in Potamogeton pectinatus) Velenjskega jezera. Sezonska nihanja v vsebnosti TP v rastlinah so bila zelo velika, vendar so vse vrste v začetku svoje rasti dosegale podobne maksimalne vsebnosti TP, nato pa so koncentracije s časom večinoma pri vseh vrstah hitro upadale. Sezonska nihanja v vsebnosti TN v rastlinah so bila manjša. Največja maksimalnakoncentracija celotnega dušika je bila izmerjena v nadzemnih tkivih v jezeru redko prisotne submerzne vrste s plavajočimi listi – Nuphar luteum. Maksimalne koncentracije v popolnoma potopljenih makrofitih (Najas marina, Najas minor, Potamogeton pectinatus in Potamogeton lucens) pa so bile zelo podobne. Zaradi različnega življenjskega cikla makrofitskih vrst, so bile sicer razlike med vrstami v določenem mesecu zelo velike. Prisotnost vrst Nuphar luteum, Najas minor in Potamogeton lucens je bila v jezeru redka, zato je bil njihov prispevek k zmanjšanju hranil v sedimentu in vodi jezera majhen. Potamogeton pectinatus je bila s svojo relativno zmerno prisotnostjo prevladujoča vrsta v jezeru spomladi, poleti pa je nad njo močno prevladala vrsta Najas marina. Njena razrast je imela večji učinek na zmanjšano koncentracijo hranil v sedimentu in v vodi. Odstranitev 1 tone suhe biomase makrofita Najas marina v mesecu avgustu, bi prispevala k odstranitvi 2,7 kg fosforja in 28,2 kg dušika iz jezera.