SPI and benthic fauna – Comparison and evaluation of classifications and applications

Summary

We have compared classification by Benthic Habitat Quality-index (BHQ-index) for Sediment Profile Imagery (SPI) and normalized Ecological Quality Ratio (nEQR) for benthic fauna. The SPI-data were collected from NIVAs SPI-database. Data on benthic fauna were collected from databases at NIVA, Akvaplan NIVA and Uni Research. 121 stations were defined as comparable based on a maximum deviation of 290 meters in distance, 6 months in time and 10 m in depth between SPI samples and benthic fauna samples. Based on the five quality classes in the Water Framework Directive (“High”, “Good”, “Moderate”, “Bad”, and “Poor”) there was a 50% conformity between the BHQ and nEQR classifications. When grouping “High” and “Good” together and “Moderate”, “Bad”, and “Poor” together the conformity was 72%. Whether the BHQ classification can be used under the Water Framework Directive is outside the scope of this report. Based on logistic regression, we think there is a potential to increase the compliance between SPI and benthic fauna classification by adding new parameters or changing the influence of the existing parameters in the index when assessing the classification. This requires further data analysis including testing of different models for classifications and potentially gathering more comparable data from the two methods. The BHQ-index can be used for the classification of environmental conditions in marine sediment, however the classification often deviates from classification based on benthic fauna. It is our opinion that SPI cannot replace benthic fauna for classification on a general basis. However, it can be a more reasonable alternative in some situations. Mapping of gradients in oxygen conditions or effects of known sources of contamination are some examples where SPI may be a useful tool. Especially when the source of contamination is visual in nature, or produces effects which are visually detectable. When used as complimentary tools, SPI can be used to map which areas are affected, which can be used as a guide for a better sampling strategy for the benthic fauna. Both by reducing the number of samples required, and improving the placement of sampling stations. In addition, SPI-data can be used to obtain better spatial or temporal resolution of data.