Levels of the nitrogen-dependent phytoplankton in Lake Taupo are currently very low, so the clarity of the lakewater is exceptionally good. This is because loads of nitrogen to the lake from the catchment are currently low (averaging 3–4 kg N/ha/yr). Changing to more intensive land-uses is likely to increase the nitrogen input. Converting 100–250 km2 of sheep/ beef pasture to intensive dairying yielding 30 kg N/ha/yr would increase the overall nitrogen load to the lake by 20–60%. This could cause phytoplankton levels to increase by a similar proportion, so that water clarity would fall by 20–40%.

B, Vant, and B Huser

Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 261-264, 2000
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