The transformation of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorous (SRP), and the release of dissolved organic and particulate N and P, were analyzed in two lake complexes (Uzlina-Isac and Puiu-Rosu-Rosulet) of the Danube Delta wetland during flood conditions in May and at low water level in September 2006. The Uzlina-Isac complex was hydrologically tightly-connected with the Danube River and was flushed with river-borne nutrients and organic matter. These lakes acted as effective transformers for nutrients and produced large amounts of fresh biomass, that promoted the excretion of dissolved organic N and P during active growth. Biomass breakdown created particulate matter (<0.45μm), which was widely liberated during low flow in the fall. The Puiu-Rosu-Rosulet complex was characterized by a more distant position to the Danube and proximity to the Black Sea, and received dominantly transformed organic compounds from the flow-through water and vast vegetation cover. Due to reduced nutrient input, the internal production of organic biomass also was reduced in these more remote lakes. Total N and P export from the lake nearest to the shelf was governed by dominantly dissolved organic and particulate compounds (mean 58 and 82%, respectively). Overall, this survey found that these highly productive wetlands efficiently transform nutrients into a large pool of dissolved organic and particulate N and P. Hence, wetland lakes may behave widely as net sources of organic N and P to downstream waters and coastal marine system
