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New Zealand Journal of Marine and Freshwater Research abstractsCHEMISTRY OF SEDIMENTS IN RELATION TO TROPHIC CONDITION OF EIGHT ROTORUA LAKESR. H. S. McCoix*Soil Bureau, DSIR, Private Bag, Lower Hutt, New ZealandAbstract Chemical parameters (pH, Eh, carbon, Kjeldahl nitrogen, total phosphorus, 0.5M H2SO4-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 /*g.g ;l) concentrations, and very high total phosphorus concentrations (mean 4770 ^g.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 pg.g""* and phosphorus 690-1780 /tg.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/ig.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/ig.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.
N.Z. Journal of Marine and Freshwater Research 11 (5) : 509-23 Received 25 May 1976; revision received 3 December 1976 PDF file of entire paper: medium quality (1054K); (scanned from paper original: notes about this process) This year's abstracts | Journal home page | All abstracts | Publishing home page |