Silvester, Warwick B.Clayton, JohnMiller, Suzanne Thelma2026-07-132026-07-131990https://hdl.handle.net/10289/18445The discharge of treated sewage from the Taupo Borough-Pollution Control Plant was associated with a dramatic change in downstream phytobenthos associations found in the Upper Waikato River. Displacement of epilthic moss assemblages by Cladophora, and domination of epiphyte habitats by Enteromorpha were observed downstream of this discharge. In essence, this situation is a species replacement series in response to a changing water quality gradient attributable to the inflow of treated sewage. Aerial photographs, transect surveys and drift diving showed that the extent of phytobenthos development through the entire length of the Upper Waikato River was primarily limited by substrate availability. Areas of gravel/pebble/sand were not immobile long enough in current flow to allow for the development of macroscopic vegetation either up- or downstream of the sewage discharge. However, there were similar stable habitats for phytobenthos development both up- and downstream of the sewage discharge. The greatest change in water quality attributable to the TBPCP discharge was increase in both NH₄-N (relative significance to all loads 61.5%) and DRP (relative significance to all loads 55.6%). However, even below the TB-PCP discharge average concentrations of NH₄-N (ca.10 mg m-³) and DRP (ca. 4 mg m-³) were still low and water may still be classified as oligotrophic. The ratio of TN-DON: TP-DOP is low in water leaving Lake Taupo (10.4), the inflow from the TBB-PCP sewage discharge further decreases this ratio to 6.2, measured at Reid’s Farm. A prediction of nitrogen limitation of algal growth was made from these low ratios. Nutritional studies of Oedogonium upstream of the TB-PCP sewage discharge supported the hypothesis of N limitation derived from N:P ratios. Oedogonium consistently exhibited tissue nitrogen levels below critical values. The same nutritional studies applied to Enteromorpha and Cladophora growths downstream of the TB-PCP sewage discharge showed that neither species was consistently limited by available N or P nutrients, and both species showed a greater susceptibility to N limitation. This was not expected from the predictions based on N:P ratios. Enteromorpha and Cladophora may be able to sustain adequate tissue N levels by maintaining high uptake rates. Both A A R and PUR rates were high for these species in the NATS monitoring programme. However, due to the high pulse concentration and the static nature of these techniques, results are not likely to be indicative of in-situ conditions. These results merely indicate that the algae have the capacity for high uptake rates. A greater relative importance of N compared to P inputs from the TB-PCP discharge for Enteromorpha and Cladophora growth was concluded from the pilot algae transplant experiment. Phosphorus tissue NATS did not show P limitation of upstream transplants after one and two weeks, compared to decreases in N tissue tests below critical levels. Results from this transplant experiment support the hypothesis that N concentrations in the Upper Waikato River above the TB-PCP discharge may be too low to support significant Enteromorpha and Cladophora growths. The increase in ammoniacal nitrogen from the TB-PCP discharge may represent a critical change for periphytic algal growth, given the physical environs of this river. Three new techniques have been trialled in this study: # use of a chain transect to survey phytobenthos of a deep, swift flowing river, # use of s15N signatures of plants growing up- and downstream of a point-source discharge in order to ascertain the extent of effluent N nutrient utilisation by plants growing downstream of the sewage discharge, # algae transplant experiment as a method for examining the relative importance of increased nutrient loads to changes in phytobenthos correlated to the inflow form point-source discharges. Preliminary application of these techniques has been useful in the Upper Waikato River to describe the biological impact of the TB-PCP discharge on benthic vegetation. In the Upper Waikato River phytobenthos associations found below the TB-PCP sewage discharge during 1989-1990 are not consistent with the ‘oligotrophic plant assemblage’ described by Coffey (1979). A major habitat degradation in the Upper Waikato River has occurred and is associated with the inflow from the Taupo Borough-Pollution Control Plant. No change in Coffey’s (1979) classification of ‘oligotrophic plant assemblage’ of the Waikato River from the Lake Taupo Control Gates to the upstream end of the point of inflow of the TB-PCP sewage discharge was concluded from this study.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.Thesis