Sed­i­ment study re­sults were ‘sober­ing’

Rodney Times - - FUN & FLAVOUR - DANIELLE CLENT

Sheep, beef and dairy farms are blamed for the ma­jor­ity of sed­i­ment end­ing up in the Kaipara Har­bour and it could cost up to $331 mil­lion a year to fix it.

North­ern Re­gional Coun­cil (NRC) and Auck­land Coun­cil com­mis­sioned ex­perts to re­search a range of so­lu­tions to re­duce the loss of sed­i­ment into the har­bour.

NRC water pol­icy spe­cial­ist Ben Tait said there were con­cerns about the large amount of sed­i­ment getting into the har­bour and the ef­fects it had.

This in­cluded smoth­er­ing shell­fish beds and re­duc­ing water clar­ity.

The study showed the cur­rent an­nual-av­er­age sed­i­ment load into the har­bour was about 700,000 tonnes per year.

It found the best op­tion to re­duce sed­i­ment in the Kaipara Har­bour was to plant trees along the coast­line.

This could re­duce sed­i­ment by up to 88 per cent at a cost of be­tween $255 and $331 mil­lion per year.

‘‘The re­sults were sober­ing,’’ Tait said.

One of the study’s re­searchers Mal­colm Green said sed­i­ment had nu­mer­ous ad­verse ef­fects on the har­bour’s ecol­ogy.

‘‘Sed­i­men­ta­tion can smother habi­tats and shell­fish beds,’’ he said.

‘‘You get re­duced light pen­e­tra­tion and water clar­ity with high sed­i­ment loads that af­fects sea­grass and the abil­ity of fish and birds to feed.’’

Green said meet­ings had been held with key par­ties to de­cide on sce­nar­ios to re­search.

In nearly all sce­nar­ios looked at, sheep and beef farms faced the largest costs.

This was be­cause about half of the sed­i­ment loss came from sheep and beef farms, the study showed. About a quar­ter came from dairy farms.

Ex­clud­ing stock and sta­bil­is­ing large tracts of highly erodi­ble land could re­duce sed­i­ment in the har­bour by 41 per cent at a cost of $13m a year, the study said.

Fed­er­ated Farm­ers se­nior pol­icy ad­vi­sor Richard Gard­ner said it would be look­ing to get the study ‘‘ground truthed’’ to make sure the re­sults were ac­cu­rate.

How­ever, Gard­ner said the or­gan­i­sa­tion recog­nised that there was an issue with sed­i­men­ta­tion getting into the Kaipara Har­bour.

‘‘Even now, farm­ers are doing an aw­ful lot about it by way of ri­par­ian plant­ing [and] re­strict­ing live­stock ac­cess to wa­ter­ways,’’ he said.

GEMMA WOOD/ STUFF

A new study shows about 700,000 tonnes of sed­i­ment goes into the Kaipara Har­bour each year.

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