Berthelsen, A., Clark, D., Pavanto, H. (2022). The sediments and biota within Te Ihutai/Avon Heathcote Estuary 2007-2021. Cawthron Institute.

Prepared by the Cawthron Institute for Environment Canterbury (ECan) in 2022, the purpose of this report was to review current sediment and biota ecological monitoring data from the Ihutai estuary and make comparisons to historical data. This type of report is produced every five years, and draws on data collected annually to assess the ecological health of the estuary and environmental drivers.

Overall, results indicated that nutrient enrichment was greatest at the Ōtākaro Avon River Mouth, and that enrichment had increased over time at the Pleasant Point and Plover Street sites. Enrichment appeared to have decreased around Discharge Point and Humphreys Drive since wastewater discharge was diverted from the estuary, however, these sites were still considered enriched as their sediment organic carbon reflected poor health. Regarding sedimentation, Ihutai estuary was considered muddy overall, especially at the river sites. Sedimentation impacts appeared to be getting noticibly worse at Plover Street, however, seagrass cover and cockle/tuaki abundance also increased at the site, suggesting that sedimentation to date had not limited those species. Sedimentation effects were lowest at the causeway site, indicated by moderate abundances of mud-sensitive taxa. Metal contamination within Ihutai sediments was generally low in relation to guidelines, with the exception of 2016 sampling results at the Avon River Mouth site.

Following these results, the report made several recommendations for future monitoring, including using the National Estuary Monitoring Protocol (NEMP), considering guidance for the design of long-term monitoring programmes, and adding additional parameters to account for covariables that may drive natural cycles. It also recommended that annual sediment quality data should be taken at all sites, that significant habitats like salt marsh should be mapped frequently, and that the National BHMs should continue to be used.

Estuary Sediments & Biota - 2022

Estuary Sediments & Biota - Berthelsen et al., 2022