An assessment was made of the water quality and the magnitude of growth of rooted aquatic plants in a nutrient-enriched, shallow stream system in order to provide a basis for evaluating the recovery of the ecosystem following the implementation of a program of phosphorus removal, which utilizes spray irrigation of treated domestic waste water. Field investigations defined the temporal and spatial changes of plant biomass in selected study sections. A model to predict changes in macrophyte biomass as a result of varying environmental factors including nutrient flux was evaluated, refined and calibrated. The potential of the biomass model as a management tool to assess the impact of nutrient reductions on stream oxygen budgets was investigated. The plant biomass model defined the rate of biomass production as a function of specific photosynthetic and respiration rates, advective loss and plant mortality. Specific photosynthetic rates were calculated from estimates of gross photosynthetic production made from diurnal oxygen measurements, and from biomass measurements. An empirical equation defining these rates as a function of irradiance, nutrient availability, temperature and plant maturity was formulated. Using Michaelis-Menton Kinetics, half-saturation constants of 313 kcal/sq.m/day and 4.7 (mu)g/l P were estimated for the light intensity and phosphorus functions respectively. A maximum specific photosynthetic rate of 0.572 day('-1) was empirically determined for the study stream. Specific plant respiration rates, estimated on a monthly basis were deduced from biomass simulations, employing literature derived plant mortality rates. A statistically significant relationship defining in-stream advective transport of aquatic macrophytes as a function of plant biomass was developed.
