title: Critical nutrient thresholds needed to control eutrophication and synergistic interactions between phosphorus and different nitrogen sources.
abstract: Eutrophication is one of the greatest threats to global freshwater ecosystems. The phytoplankton responses to nutrient inputs vary in different water bodies, so it is particularly important to determine the nutrient thresholds and synergistic interactions between nutrients in different freshwater ecosystems. Field sampling and bioassay experiments were conducted to determine the thresholds of soluble reactive phosphorus (SRP), nitrate-nitrogen (NO3-N), and ammonium-nitrogen (NH4-N) in Miyun Reservoir. A separate nutrient addition bioassay was designed to assess the synergistic interactions between these nutrients. Chlorophyll a (Chl a) concentrations were used to estimate phytoplankton biomass. The results showed the following: (1) nutrient threshold bioassay indicated that eutrophication thresholds of SRP, NO3-N, and NH4-N should be targeted at below 0.04 mg P L-1, 0.5 mg N L-1, and 0.3 mg N L-1, respectively, to limit the growth of phytoplankton. (2) The stimulatory effect of "NH4-N plus P" on phytoplankton biomass was greater than "NO3-N plus P" at the same N concentration, and "NH4-N plus NO3-N" did not show such associated stimulatory effect as "NH4-N plus P" or "NO3-N plus P". (3) The average concentrations of total phosphorus (TP), NO3-N, and NH4-N in Miyun Reservior were 0.017 mg P L-1, 0.620 mg N L-1, and 0.143 mg N L-1, respectively. The reservoir-wide average Chl a is below 20 μg L-1on an annual basis. (4) Ammonium was an important factor for the growth of phytoplankton and inputs of both NH4-N and NO3-N should be reduced to control bloom formation. Our findings imply that although P load reduction is important, appropriate reductions of all forms of N in watershed is recommended in the nutrient management strategy for Miyun Reservoir.
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Shuangqing Road 18, Beijing, 100085, People's Republic of China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Qinghui
authors.initials: Q
authors.lastname: Zeng
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Shuangqing Road 18, Beijing, 100085, People's Republic of China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Lihuan
authors.initials: L
authors.lastname: Qin
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Shuangqing Road 18, Beijing, 100085, People's Republic of China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Linlin
authors.initials: L
authors.lastname: Bao
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Shuangqing Road 18, Beijing, 100085, People's Republic of China.|College of Environment and Planning, Henan University, Henan, 475004, People's Republic of China.
authors.forename: Yayong
authors.initials: Y
authors.lastname: Li
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Shuangqing Road 18, Beijing, 100085, People's Republic of China. xyli@rcees.ac.cn.
authors.forename: Xuyong
authors.initials: X
authors.lastname: Li
mesh_terms: D064751:Ammonium Compounds / Q000032:analysis; D018533:Biomass; D002734:Chlorophyll / Q000032:analysis; D000077194:Chlorophyll A; D017753:Ecosystem; D005068:Eutrophication; D005618:Fresh Water; D009566:Nitrates / Q000032:analysis; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D010839:Phytoplankton / Q000254:growth & development; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D014874:Water Pollutants, Chemical; D002734:Chlorophyll; D010758:Phosphorus; D009584:Nitrogen; D000077194:Chlorophyll A
keywords: Ammonium; Bioassays; Eutrophication; Multiple nutrient limitations; Nutrient threshold; Synergistic interaction