Donald B. Porcella

The effect of carbon on algal growth—Its relationship to eutrophication

Abstract The literature has been reviewed to obtain a proper perspective on the role of carbon in natural aquatic ecosystems and to provide a comprehensive picture of carbon interactions (physical, chemical, and biological)in aquatic systems. Discussion of the carbon cycle comprises the processes of synthesis, degradation, and excretion of organic carbon compounds and the role of various microorganisms in these processes. Inorganic carbon chemistry is developed with specific emphasis on alkalinity components, buffering, chemical and biological reaction rates, and carbonic anhydrase activity. Organic and inorganic carbon utilization by algae and comparison of natural aquatic systems with laboratory and wastewater treatment systems are considered in relation to the question of algal growth. The final sections consider nutrient utilization by algae and the role of carbon in eutrophication processes. The overall conclusion of this review is that carbon will rarely if ever be limiting in natural environments.

Chemical and biostimulatory properties of cattle feedlot runoff

Abstract Standard bottle test bioassays and chemical analyses were used to assess the biostimulatory and chemical properties of snowmelt runoff from two small cattle feedlots. Nutrient supplements (spikes) were employed to determine the levels at which nitrogen and phosphorus became limiting to algal growth. An abundance of both elements existed in the heavily enriched feedlot runoff. However, further growth was eventually limited by rapid algal uptake of phosphorus or nitrogen. Balanced algal growth occurred when the nitrogen: phosphorus ratio was about 15:1. When the ratio was initially below this number, nitrogen was first to become limiting; when the ratio was above 15:1 phosphorus limited growth. Chemical analyses predicted qualitatively and quantitatively limiting nutrients, and algal bioassays substantiated the predictions. Bioassays revealed the possible effects of such nutrient enrichment on an aquatic system and also indicated that while feedlot runoff is usually biostimulatory it may also be quite toxic to algae. Geological and physical differences between the feedlots resulted in variations of limiting nutrients.