Impact on Exmouth Gulf nutrient inputs little to none.
Key points
Impacts to nutrient pathways, as a result of the proposed Ashburton Salt project, will not be great enough to impact the Exmouth Gulf, new research has found.
The research into nutrient pathways was conducted by Water Technology and peer-reviewed by DHI Water & Environment, an EPA-approved third-party expert, as part of the Ashburton Salt project.
It is excellent news according to K+S Salt Australia Managing Director Gerrit Gödecke.
“While nutrient flows may not be as exciting as whales or dugongs, it is possibly the area most important to research properly and get right,” Mr Gödecke said.
“Even though salt flats may seem dry and lifeless, they form part of a wider wetland ecosystem, which supports algal mats and mangroves and underpins productivity of nearby waters.
“Put simply, nutrients are ‘food for the ecosystem’ so we needed to get the science right to address potential environmental impacts.
“By doing this, we have planned the project in a way that reduces impacts of changed nutrient flow to next to nothing – which is exactly the way it should be.”
The solar salt project, which comprises predominantly a series of large saltwater lakes is proposed to be located on existing salt flats south of Onslow.
This region is known to play a critical role in the marine ecosystem of nearby waters, and also the Exmouth Gulf, by providing nutrients that “feed” nearby marine life when flushed into the ocean.
In essence, nutrients – in particular Nitrogen – are the beginning of the food chain for the Exmouth Gulf and feed it through two sources:
Ocean upwelling is the process by which deep, cold, nutrient-rich water rises toward the surface (known as “Ekman transport”). Ebb and flood of tides, providing water from offshore sources and removing water from nearshore sources, has a “mixing effect” combining nutrients from offshore sources into nearshore water.
Tidal creeks, mangrove habitats in the intertidal zone, algal mats and salt flats beyond the tidal limit of the mangrove zone all provide a nutrient source for creek and nearshore waters during regular tidal inundation.
The Project terrestrial rainfall catchment area also provides a source of nutrients to nearshore waters after overland flows and rainfall run-off, particularly after extreme rainfall events. After major rainfall events, nutrient rich overland flows reach coastal waters, including the Exmouth Gulf.
To evaluate the impact of the proposed Ashburton Salt project on nutrient flow, and therefore marine life in nearby waters and the Exmouth Gulf, a robust model of water flow and nutrient was modelled after several years and multiple site vists.
Site visits were conducted to not only collect samples of nutrients but also to log water catchment and water flow direction on salt flats, creeks and nearby regions, a process that took two years.
The finding of samples were then modelled by Water Technology and peer-reviewed by an independent, EPA approved third party expert (DHI Water & Environment) to verify the findings were scientifically robust.
A series of modelling scenarios were then completed to assess changes to tidal inundation and overland flows from rainfall events and, importantly, assess potential changes in local nutrient pathways and contributors to Exmouth Gulf.
When this modelling was complete the K+S team was able to alter the location, size and shape of potential salt ponds and model the impacts of the proposed salt lakes and other project areas.
In addition, culverts and drainage diversions were also designed to minimise impacts to tidal and surface water flows and nutrient pathways, therefore minimising related impacts to intertidal habitats.
The findings of the study show that while the proposed project would have an impact on estimated nutrient flows into the project catchment and Exmouth Gulf, they were very small – less than one percent.
The research found that the Ashburton Salt project is located predominantly within areas which are not major nutrient sources for local or regional ecosystems.
In addition the studies predicted that, if developed, the Ashburton Salt project would reduce nutrient flow from land and ocean sources by:
The study confirmed the proposed Ashburton Salt project would not significantly alter nutrient exports or pathways and as a result compared to the overall nitrogen ‘budget’ of the Exmouth Gulf, the potential impact of the project would be “little to none”.
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