Rob Guyton has good information on the threat to Waituna Wetland in Southland, including reproducing some letters to the editor.
Environment Southland might try to halt further dairy farm development in the Waituna catchment in a bid to prevent the area's internationally significant lagoon from suffering irreversible damage. Monitoring of the lagoon, southeast of Invercargill, revealed high levels of nitrogen and phosphorous in sediments were threatening to "flip" the lagoon from an ecosystem with clear water featuring aquatic plants and fish species to one with murky, turbid water dominated by algae. When The Southland Times visited the lagoon this month with Environment Southland water quality scientist Kirsten Meijer, she showed us black mud on the edges of a tributary to the lagoon. "There's a lot of sediment going into the lagoon and the mud goes black (instead of being brown). It smells like sulphur, no oxygen, nothing can live in it," she said.And further north in the Waikato
Hundreds of thousands of fish were found dead in the Whangamarino Wetland, near Te Kauwhata, last week. The fish were killed by low levels of dissolved oxygen in the water, according to the Conservation Department. "The drought at the end of 2010 exposed large areas of the wetland and rapid plant growth occurred in areas usually under water," Mr Hutchinson said. "High rainfall in January, compounded by the baked dry ground in the catchment, meant water rapidly ran off into the wetland and water levels remained consistently high for about three consecutive weeks." Mr Hutchinson said resulting decomposing plant matter started a bacterial process which depleted oxygen in the water. "This was shown further by the layer of oily scum present on the surface of the water, which was natural oils released by decomposing plants, the dark black colour of the water and the soft, wilting emergent vegetation starting to break down," he said. "The decomposition is also identifiable by an unpleasant smell, very similar to that from a compost bin." But a wetland resident, who did not want to be named, said the decomposition smelled more like sewage. "I have lived here since the 50s and I have never seen anything this bad before," he said. "It's an environmental disaster. This wetland is dying."So down south dairying is identified as a major if not THE major factor in the degradation of the Waituna Wetland and black mud is an identifier, but in the Waikato, one of the most intensive dairying areas, the black mud is supposedly because of the drought and then big rains - I'll let you draw your own conclusions...
I have posted about wetlands here.