The importance of long-term environmental monitoring and research for detecting and understanding changes in ecosystems and human impacts on natural systems is widely acknowledged. Over the last decades a number of critical components for successful long-term monitoring have been identified. One basic component is quality assurance/quality control protocols to ensure consistency and comparability of data. In Norway, the authorities require environmental monitoring of the impacts of the offshore petroleum industry on the Norwegian continental shelf, and in 1996 a large-scale regional environmental monitoring program was established. As a case study, we used a sub-set of data from this monitoring to explore concepts regarding best practices for long-term environmental monitoring. Specifically, we examined data from physical and chemical sediment samples and benthic macro-invertebrate assemblages from 11 stations from six sampling occasions during the period 1996-2011. Despite the established quality assessment and quality control protocols for this monitoring program, we identified several data challenges, such as, missing values and outliers, discrepancies in variable and station names, changes in procedures without calibration, and different taxonomic resolution. Furthermore, we show that the use of different laboratories over time makes it difficult to draw conclusions with regard to some of the observed changes. We offer recommendations to facilitate comparison of data over time. We also present a new procedure to handle different taxonomic resolution so valuable historical data is not discarded. These topics have a broader relevance and application than for our case study.

Faunal data: Long-term environmental monitoring for assessment of change: measurement inconsistencies over time and potential solutionsData on soft-sediment macrobenthos from 11 regional stations collected at the southern part of the Norwegian continental shelf (Region I, i.e. the Ekofisk-region) from six sampling occasions during the period 1996-2011. The data were extracted from the Environmental Monitoring Database (the MOD-database), owned by the Norwegian Oil and Gas Association. We used a version of the MOD-database from March 2013.R1Bio_22.09.14.txtR script: Long-term environmental monitoring for assessment of change: measurement inconsistencies over time and potential solutionsData analyses, including the procedure of lumping/splitting taxa in the species list prior to data analyses. All analyses were done using R. Data on soft-sediment macrobenthos from 11 regional stations collected at the southern part of the Norwegian continental shelf (Region I, i.e. the Ekofisk-region) from six sampling occasions during the period 1996-2011 are given in the file “Faunal data”.MOD-DRYAD.R