Motupipi Estuary is a moderate-sized (169 ha), shallow, well-flushed, seawater-dominated, tidal lagoon type estuary with one tidal opening and two main basins. The western arm, dominated by the Motupipi River, responds more like a tidal river system. The upper estuary experiences salinity stratification during stable baseflows (i.e. salt wedge effect). The resulting high salinity bottom layer is generally more stable (less well-flushed) and therefore experiences nuisance algae blooms when nutrient inputs are elevated. The eastern basin is seawater-dominated, elevated, which dries rapidly and remains exposed for much of the tidal cycle. Much of the immediate estuary margin is directly bordered by developed pasture/rural land, roads, and seawalls. Causeways separate small sections of saltmarsh from the main estuary.
Historically, the Tākaka landfill was sited on the estuary margin, but heavy metals, used as an indicator of potential toxicants, were very low at sites around the estuarine perimeter of the landfill and at fine scale monitoring sites.
The catchment (41 km2) is dominated by high producing pasture (45%), native forest and scrub (37%) and exotic forestry (8%).
More information and monitoring data is also available on the LAWA website.(external link)
Ecologically, habitat diversity is moderate to high with much of the intertidal vegetation intact, extensive shellfish beds, large areas of saltmarsh (38% of estuary), and some seagrass (1.6% of estuary). However, the estuary is excessively muddy (36% soft and very soft mud in 2015), and much of the natural vegetated margin has been lost and developed for grazing. Since 1943 there has been a loss of 28ha of saltmarsh through drainage and reclamation, although significant saltmarsh modification is likely to have also occurred prior to this.
The major current estuary stressors are considered to be: excessive muddiness for ecological condition, disease risk for contact recreation and shellfish gathering, habitat loss and changes in biota as a result of climate change. Localised eutrophication is present in poorly flushed upper estuary arms at times.
Broad-scale mapping using the National Estuary Monitoring protocol was conducted in 2007 and 2015 and fine-scale surveys in 2008 and 2017-19.
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