Nutrient addition bioassays

Holmboe, N., Jensen, H. S., and Andersen, P.0. (1999). Nutrient addition bioassays as indicators of nutrient hmitation of phytoplankton in an eutrophic estuary. Mar. Ecol. Prog. Ser. 186, 95-104. 

Nutrient Addition Bioassay Experiment, Ti Neuse River, Juiy 2003... 

Figure ll.ll Results from a set of in situ nutrient addition bioassays conducted at three locations along the axis of the Neuse River Estuary that was routinely monitored for ambient nutrient (ammonium, nitrate, phosphate) concentrations and chlorophyll a as an indicator phytoplankton biomass. All nitrogen forms were added at 20 jlM-N, while phosphate was added at 5 pM-P. The locations of bioassays are shown (symbols) on the map (A) just upstream of the chlorophyll a maximum (Cniax)l ( ) the Cmax i d (C) downstream of the Cmax- Strong N limitation was encoun-... 

Fisher, T. R., and Gustafson, A. B. (2004). Nutrient-Addition Bioassays in Chesapeake Bay to Assess Resources Limiting Phytoplankton Growth, Progress Report Aug. 1990—Dec. 2003. Rep. Maryland Dept. Natural Resources, Annapolis, MD. p. 50. 

Figure Effect of nutrient additions on N2 fixation rates at three stations during bioassay...

A more direct indication of nutrient limitation than is available from nutrient ratios can be gained from bioassay experiments. In this procedure a small volume of natural lake water is enclosed and various known concentrations of potentially limiting nutrients are added (145-147). A growth response (usually measured as an increase in biomass) in treatments containing an added nutrient constitutes evidence of limitation by that nutrient. The results of such experiments are available for only a few selected nutrient-poor lakes, however. They indicate a variety of responses, including strong P limitation (148), limitation by P and iron (147), simultaneous N and P limitation in which the two nutrients are so closely balanced that addition of one alone simply leads to limitation by the other (147), and limitation primarily by N (142, 149). No clear pattern of N or P limitation develops from an examination of these few studies. 

In addition, the testing laboratory for both nutrients and unintentional contaminants, including carcinogens, may perform periodic analysis of the basal diet. The results of such analysis should be retained and included in the final report on each chemical. When the test chemical is administered in water or food, stability tests are essential. Properly conducted stability and homogeneity tests, prior to the chronic study, should be used to establish the frequency of diet preparation and monitoring required. When diets are sterilized, the effects of such procedures on the test chemical and dietary constituents should be known. Appropriate adjustments to nutrient levels should be performed. The effect of chemical sterilants, (e.g., ethylene oxide) on the bioassay should be ascertained. 

The measurement of alkaline phosphatase activity (APA) of target phytoplankton is a recently developed bioassay that has been used to determine the algicidal effects of polyphenols from Eurasian watermilfoil (Myriophyllum spicatum) [80]. Phytoplankton produce extracellular enzymes, such as alkaline phosphatase, to provide additional sources of nutrients. Fluorescence spectrometry is used to measure APA, with methylumbeliferyl-phosphate used as substrate and mixed with the algal or cyanobacterial suspension and the suspected inhibitor. 

What follows this introduction to plant-plant interactions (Chapter 1) are three additional chapters. The first chapter (Chapter 2) describes the behavior of allelopathic agents in nutrient culture and soil-microbe-seedling systems under laboratory conditions. Simple phenolic acids were chosen as the allelopathic agents for study in these model systems (see justifications in Section 2.2.6). The next chapter (Chapter 3) describes the relationships or lack of relationships between weed seedling behavior and the physicochemical environment in cover crop no-till fields and in laboratory bioassays. Here as well the emphasis is on the potential role of phenolic acids. The final chapter (Chapter 4) restates the central objectives of Chapters 2 and 3 in the form of testable hypotheses, addresses several central questions raised in these chapters, outlines why a holistic approach is required when studying allelopathic plant-plant interactions, and suggests some ways by which this may be achieved. 

With each series of samples being bioassayed prepare 7 flasks containing 20 ml of vitamin-free sea water enriched with the nutrient solutions as described in F.2. To one flask make no addition and to the other six flasks add 0.1 ml of solution B-G, respectively. The concentrations of added biotin in the sea water of the external series will be 5, 4, 3, 2, 1, and 0.5 m/ng biotin/liter, respectively. Inoculate and incubate these standards as described in Section F.3-6 along with the samples being bioassayed. Prepare a calibration curve by plotting the counts/min against the concentration of biotin in that standard. The biotin concentrations in the samples and the internals are read from the calibration curve. 

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