Assessing responses of the Hiroshima Bay ecosystem to increasing or decreasing phosphorus and nitrogen inputs.
The Japanese Government is seeking an appropriate level of nutrient load from the land to maintain the highest possible estuarine fishery production and water transparency simultaneously. To provide a scientific basis for the governmental inquiry, we conducted sensitivity analyses using an ecosystem model of Hiroshima Bay in order to assess the ecosystem's responses to phosphorus and nitrogen inputs. Load levels of phosphorus (Case P), nitrogen (Case N) and both phosphorus and nitrogen (Case NP) that were different from the average loading recorded during 1991-2000 (±25%, ±50%, and ±75%) were applied. The results showed that phosphorus had a significantly greater impact on the primary production of the bay than nitrogen. Case P+25 increased the primary production but led to N-limitation. However, it was found that Case NP at the levels over +25% could bring the Hiroshima Bay ecosystem back to its eutrophic state of 30 years ago.
Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan. Electronic address: jutaratk@fisheries.go.th.
Jutarat
J
Kittiwanich
Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan. Electronic address: tamyama@hiroshima-u.ac.jp.
Tamiji
T
Yamamoto
Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan. Electronic address: o-kawaguchi88559@pref.hiroshima.lg.jp.
Osamu
O
Kawaguchi
Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan.
Ione
I
Madinabeitia
D000818:Animals; D017756:Aquaculture; D061006:Bays; D017753:Ecosystem; D005068:Eutrophication; D007564:Japan; D009584:Nitrogen / Q000032:analysis*; D010125:Ostreidae / Q000254:growth & development; D010758:Phosphorus / Q000032:analysis*; D010839:Phytoplankton / Q000254:growth & development; D014874:Water Pollutants, Chemical / Q000032:analysis*
D014874:Water Pollutants, Chemical; D010758:Phosphorus; D009584:Nitrogen
Ecosystem; Eutrophication; Hiroshima Bay; Modeling; Nitrogen; Phosphorus