| Water category: | Coastal |
| Pressure categories |
Nutrients
|
| Pressure detail |
Concentration of total nitrogen and total phosphorus |
| Specific Index |
Bloom are defined as observations that exceed the 99th percentile of the prediction interval using a simple seasonal model. The frequency of these observations and their mean value provide metrices |
| Brief text description |
A new indicator has been developed to characterise the frequency and intensity of summer algae blooms |
| Long text description |
We propose a definition for identification of blooms and use this definition to investigate the underlying
mechanisms of summer blooms and their link to nutrient enrichment. Blooms were defined as chlorophyll
a observations deviating significantly from a normal seasonal cycle; the frequency and magnitude of these
deviating observations characterized bloom frequency and intensity. The definition was applied to a large
monitoring data set from five estuaries in Denmark with at least biweekly sampling. Four mechanisms with links
to nutrient enrichment were identified as sources of summer blooms: (1) advection from biomass-rich inner
estuary, (2) resuspension of nutrients and algae from sediments, (3) nutrient releases from sediments during
hypoxic conditions, and (4) decoupling of benthic grazers. Summer blooms were mostly dominated by diatoms,
and in 33% of the bloom samples the dominating species was also dominant prior to the bloom. Only four species
(Cerataulina pelagica, Chaetoceros socialis/radians, Prorocentrum micans, and Prorocentrum minimum) typically
(.50% of blooms) increased their biomass proportion during bloom initiations. Bloom frequency and intensity
decreased from 1989 to 2004, corresponding to decreases in nutrient inputs and concentrations, but only bloom
frequency could be directly linked to the actual total nitrogen concentrations, whereas bloom intensities depended
on site-specific features, particularly a threshold response for stations exposed to hypoxia. Bloom frequency has
increased over longer timescales in response to nutrient enrichment. |
| History of development |
Work initiated in 2005 as a joint effort between NERI and JRC. Manuscript submitted November 2005, accepted August 2006 and published February 2007 |
| References |
http://aslo.org/lo/toc/vol_52/issue_1/0370.pdf |
| Geographical region (GIG) - CT |
CBA - Baltic
|
| Country |
DK Denmark
|
| Geographical location of source data |
National |
| Reference conditions |
Not considered |
| Development |
Rebecca |
| Uncertainty |
Considered |
| Link to document store |
Not given |
| BMW Toolbox |
No |
| Entry status |
Validated |