The chemistry of the surface and bottom waters of seven Rotorua lakes (Okataina, Rotoma, Tikitapu, Okareka, Rotokakahi, Ngapouri, and Okaro) was examined monthly between April 1970 and April 1971 in relation to the biology of the lakes. Twenty-four parameters were measured, including dissolved 0 2 , major ions, silica, phosphorus, nitrogen, algal pigments, and some trace elements. All lakes were warm monomictic, second-class lakes. All lakes contained "bicarbonate waters" except Rotoma which had "chloride waters". The waters were soft and variations between lakes in composition of major cations and anions appeared to be related to catchment differences. The major cations and CT varied little with season. Sulphate varied seasonally in the hypolimnia of the most productive lakes (Okaro, Ngapouri, and Rotokakahi). Silica was abundant in all lakes, except Tikitapu where diatoms were poorly represented. Depletion of silica by diatom populations was only observed in the two most productive lakes (Okaro and Ngapouri). All lakes except Ngapouri showed anomalous silica distribution, with lower concentrations in the bottom waters at all times.

Uptake of stream nutrients by organisms or sediments of the stream bed is affected by the nutrient loading to which the stream is accustomed. In a stream with nutrient-poor waters, added phosphate and ammonia were removed rapidly and efficiently at water temperatures within the range 4.5-15.0°c on passing over a mat of filamentous algae and trapped sediment. Nitrate was removed less efficiently or not at all. In another stream where nutrients were abundant, phosphate and nitrate from a sewage outfall were not significantly removed by the stream bed flora up to 100 m downstream at summer temperatures. Sodium was used as an inert marker to measure the dilution of added nutrients or sewage effluent by the stream waters; electrical conductivity was rejected as a measure because it is influenced by photosynthesis. Studies of nutrient runoff should take account of stream-bed removal when the effects of runoff on eutrophication of lakes are being considered.

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Chemical parameters (pH, Eh, carbon, Kjeldahl nitrogen, total phosphorus, 0.5M H 2 SO 4 -extractable phosphorus, organic phosphorus, and water-soluble phosphorus) were measured in the surface layers of sediments collected from various depths in Lakes Rotowhero, Okaro, Ngapouri, Rotokakahi, Okareka, Tikitapu, Okataina, and. Rotoma during October 1972. The sediments of the productive geothermal lake, Rotowhero, were markedly different from those of the cold-water lakes: they had relatively low pH values, high carbon (mean 8.5%) and organic phosphorus (mean 4160 µg.g -1 ) concentrations, and very high total phosphorus concentrations (mean 4770 µg.g -1 ), probably as a result of enrichment by hot springs.The mean concentrations in the sediments of the cold-water lakes were carbon 3.2-7.9%, Kjeldahl nitrogen 3380-8310 µg.g -1 and phosphorus 690-1780 µg.g -1 . These concentrations are within the ranges for New Zealand terrestrial topsoils, but the lake sediments appear enriched in phosphorus relative to local topsoils. Total carbon, nitrogen, and phosphorus concentrations of sediments tended to be highest in the eutrophic lakes (Okaro, Ngapouri) although the deep oligotrophic lakes (Okataina, Rotoma) had relatively high total phosphorus concentrations (means 1400, 1510 µg.g -1 ). Overall, the carbon, nitrogen, and phosphorus concentrations of the sediments showed little relationship to the trophic state of the lake.Organic phosphorus concentrations of the surface layers of sediments were similar in all the cold-water lakes (mean 319 µg.g -1 ). The proportion of the total phosphorus apparently 'fixed' in mineral material was minimal (0-1%) in sediments from the eutrophic and mesotrophic lakes, but in the oligotrophic lakes was similar to that in New Zealand topsoils (9-14%). Reducing conditions may cause solution of a high proportion of the 'fixed' phosphorus in the eutrophic lakes.The water-soluble phosphorus concentrations in the sediments of the five shallow cold-water lakes (Okaro, Ngapouri, Rotokakahi, Okareka, Tikitapu) correlated positively with trophic state and with concentrations of dissolved phosphorus in the lake waters.Carbon, nitrogen, and phosphorus concentrations in the sediments tended to vary with overlying water depth. This should be considered when comparisons are made between lakes.

Phosphorus and nitrogen were measured in stream run-off from the four catchments of the Taita Experimental Basin (41° 11´ S, 174° 58´ E). The land is used as exotic conifer forest, native forest, and hill pasture. Multiple regression analysis was used to estimate chemical losses per unit area in floods and at low flows.At low flows, the hill pasture (fertilised with lime at 630 kg·ba -1 ·y -1 , and superphosphate at 380 kg·ha -1 ·y -1 ) tended to lose more phosphorus and nitrate than the forested land, but differences were small, and not always significant. During large floods, the hill pasture (No. 5 Catchment) lost about 3 times as much reactive phosphate and 2-5 times as much total phosphorus as the forested land, and 130-190 times as much nitrate as land in the Exotic Forest and Native Forest 2 Catchments. Nitrate losses from land in the No. 4 Catchment (mainly native forest) were as high as those from the hill pasture, so high nitrate loss is not associated solely with agriculture.Losses of total phosphorus via the catchment streams were estimated as: No. 5 Catchment (hill pasture), 293 g·ha -1 ·y -1 ; Native Forest 2 Catchment, 201 g·ha -1 ·y -1 ; No. 4 Catchment, 124 g·ha -1 ·y -1 ; Exotic Forest Catchment, 71 g·ha -1 .y -1 . Nitrate-N losses were estimated to have been 1356 g·ha -1 ·y -1 , 11.5 g·ha -1 ·y -1 , 1436 g·ha -1 ·y -1 , and 44 g·ha -1 ·y -1 respectively. Phosphorus and nitrate concentrations were similar in the Exotic Forest and Native Forest 2 streams, but the Exotic Forest tended to lose smaller amounts because it yielded about 50% less water per unit area.Over the 2-y study, an estimated 47-70% of phosphorus losses and up to 83% nitrate losses occurred in large floods; 31% and 48% respectively were apparently lost from the hill pasture catchment in a single flood. Less than 20% of estimated phosphorus losses and as little as 1% of nitrate losses occurred at low flows.Run-off of phosphorus and nitrate was spasmodic, and this should be considered in assessing the impact of surface run-off on the biology and chemistry of receiving waters.