Secchi depth calculations in BALTSEM

• Secchi depth measurements have been carried out for over 100 years in the Baltic Sea and the changes in Secchi depth give indications of the development of phytoplankton biomass in response to eutrophication. In the implementation of the ecosystem approach to Baltic Sea management, indicators based on Secchi depth are unique in that targets representing a good environmental status can be obtained from actual observations, whereas most other indicators lack observational evidence of a reference state representing conditions before substantial eutrophication. In the on‐going revision of the HELCOM Baltic Sea Action Plan, new targets on e.g., Secchi depth have been developed (HELCOM2012). The following step is to use modeling to find nutrient inputs to the Baltic Sea, so called Maximum Allowable Inputs, that result in ecosystem changes so that eventually the good environmental status indicated by the targets is reached. This modeling effort is carried out using the coupled physical‐biogeochemical model BALTSEM developed at BNI. The BALTSEM model resolves the Baltic Sea horizontally with 13 sub‐basins, but each of these with high vertical resolution. The biogeochemical model includes inorganic and bioavailable organic nitrogen, phosphorus and silica, three phytoplankton groups, zooplankton and oxygen. Benthic nutrient regeneration and retention are modeled in addition. This report describes a statistical post‐processing algorithm to calculate Secchi depth from BALTSEM results to provide additional accuracy and confidence of Secchi depth estimates compared to the simplistic intrinsic transparency calculations within the BALTSEM model. The additional quality in the Secchi depth calculation results isof major importance for the results of the calculation of the Maximum Allowable Inputs.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geokemi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geochemistry (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Oceanografi, hydrologi och vattenresurser (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Oceanography, Hydrology and Water Resources (hsv//eng)

Publication and Content Type

vet (subject category)

rap (subject category)