Report identifies sources of Te Hoiere/Pelorus sedimentation

Marlborough District Council recently commissioned NIWA to study sediment sources in Te Hoiere/Pelorus Sound using the latest scientific techniques.

Coastal Scientist Oliver Wade says the new study improves our understanding of the area’s human-induced and natural erosion sources that impact the marine environment.

“The report identifies the sources of sediment deposited in Te Hoiere/Pelorus River catchment and Mahau Sound.”

“Seventy percent of material deposited in the Sound over the last century is ‘legacy sediment’. Goldmining, native forest clearance, pastoral farming and more recent agricultural and forestry activities have all left their legacy. Thirty percent of the deposited sediment comes from contemporary land uses.”

“Subsoils and streambank erosion are the largest contemporary sources of sediment, with smaller proportions attributed to erosion from land associated with primary industry and native forest. These proportions vary according to location,” Mr Wade said.

The effects of increased soil erosion and sedimentation have ranged in scale, from localised impacts on cockle beds in Mahau Sound to extensive catchment-wide soil erosion and sedimentation since European settlement.

The NIWA report is called ‘Sources of fine sediment and contribution to sedimentation in the inner Pelorus Sound Te Hoiere’ and is accompanied by a short summary document called ‘Tracing the sediment in Pelorus Sound’.