13. Use of the Coastal Environment Volume One Sea water is pumped into the lake through an intake structure and a series of concentrating ponds where its concentration increases. Salt is finally deposited on the bottom of the crystallising ponds in summer and harvesting usually begins by early March. Between 60 and 70 thousand tonnes of salt are harvested each year. A variety of storage and processing facilities on the edge of the lake have been established in connection with the harvest of solar produced salt from the crystallising ponds. From the stockpiled mounds, salt is processed into a cleaned, bagged product or refined and processed to specific end products. Issue 13L – The production of solar salt at Lake Grassmere is important to Marlborough but there is potential for adverse effects on the environment to arise through production and harvesting processes. It is important to recognise that although there are economic benefits to Marlborough and New Zealand from the salt works, its operations need to be carefully managed to ensure adverse effects do not arise. The production of solar salt at Lake Grassmere contributes to the Marlborough economy through the provision of employment at the salt works and during harvest when contract equipment is needed, (for example, trucks to transport salt). The salt works operation also contributes to the national economy through the export of high grade specialist salt (refined at Mt Maunganui from salt harvested at Lake Grassmere). While the salt works operations have continued for over 60 years, there is the potential that the salt production process will have adverse effects on the surrounding environment. Despite the modifications made to the lake in the development of salt works activities, the lake and its environs still hold a number of important values: • Lake Grassmere is highly valued for its bird life. It has national importance as a stopover for domestic and overseas migrating birds, including species such as the rarely-seen New Zealand dotterel; • areas of remnant estuarine habitat, including saltmarsh; and • the area around the southern and south-eastern side of the lake has considerable historical significance for some of Marlborough’s tangata whenua iwi. It is important that these values continue to be unaffected by salt works activities. Lake Grassmere was chosen for the solar production of salt partly because of the hot, drying winds in summer that aid in the crystallisation process. However, these same winds can also carry dust, which may be salt laden. If salt-laden dust falls on properties surrounding the lake, farmland could potentially be contaminated. Salt-laden foam generated by waves on the lake can also potentially be a problem for adjoining properties if winds are strong enough to carry foam. Salt-laden water can also be pushed by strong winds up Cattle Creek, which runs through a diversion channel around the south end of the crystallising ponds before exiting into Lake Grassmere under the rail bridge. This could affect the ability of Cattle Creek to be used for stock drinking water. The Lake Grassmere area has low annual rainfall ideal for salt production, but management of freshwater becomes important during storm events or periods of prolonged rain. Rainwater lying on top of the crystallising ponds is decanted off as it can dissolve the salt crust as it forms. The decanted seawater is salt-laden and is used to help control dust in the areas surrounding the crystallising ponds or can be recycled through the concentration ponds. 13 – 56