Abstract
Compared to external loads from tributaries and sediment recycling, the role of waterbirds as phosphorus (P) sources in estuaries is overlooked. We performed monthly ship-based surveys of waterbird abundance in the Lithuanian part of the Curonian Lagoon, calculated their potential P excretion, and compared its relevance to the riverine inputs. Phosphorus excretion rates for the censused species were assessed accounting for variations of body weights, daily feces production and their P content, and assigning species to different feeding and nutrient cycling guilds. During the study period (March–November 2018), 32 waterbird species were censused, varying in abundance from ~18,000–32,000 (October–November) to ~30,000–48,000 individuals (June–September). The estimated avian P loads during the whole study period varied between 3.6 and 25 tons, corresponding to an area load between 8.7 and 60.7 mg P m−2. Waterbird release of reactive P to the system represented a variable but not negligible fraction (1%–12%) of total external P loads, peaking in June–September and coinciding with cyanobacterial blooms. This study is the first in the Baltic Sea region suggesting that waterbirds are potentially important P sources to phytoplankton in large estuaries, in particular, during low discharge periods.
Highlights
Phosphorus (P) total and relative availability can regulate both primary productivity and algal community composition in aquatic environments [1,2,3]
The highest total bird number was registered in June–September (30,000–48,000 ind.), and the lowest number was registered in October–November (18,377–31,905 ind.) (Table 1)
P to largequantitative ecosystems evidence such as estuaries. Such evidence was derived from amounts monthly of reactive to large ecosystems such as estuaries. Such evidence was derived from monthly monitoring of bird numbers in the Lithuanian part of the Curonian Lagoon, the largest in Europe, and monitoring of bird numbersPininputs the Lithuanian partafter of the Lagoon, the largest inexcretion
Summary
Phosphorus (P) total and relative availability can regulate both primary productivity and algal community composition in aquatic environments [1,2,3]. Past and recent research analyzed in detail two main aspects of P biogeochemistry: the inventory of point inputs from tributaries or sewage treatment plants of dissolved and particulate P forms and the reactivity of sedimentary P pools [7,8,9]. The latter aspect lead to the development of sequential extraction techniques and to the analysis of the redox dependence of P mobility [10]. The role of other biotic components of aquatic ecosystems as regulators of P cycling has been overlooked
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