Physiological tests and bioassays: aids or superfluities to the diagnosis of phytoplankton nutrient limitation? A comparative study in the Broads and the Meres of England

Abstract

Relationships between phytoplankton growth and supplies of phosphorus and nitrogen have been variously investigated in three lakes in two contrasted English lake areas using physiological nutrient indices (alkaline phosphatase activity, phosphorus debt, surplus phosphorus, phosphorus uptake kinetics, dark ammonium uptake, ammonium uptake kinetics, stimulation of "%C uptake, and batch bioassay) and by inspection of water chemistry. None of the lakes was significantly affected by wastewater effluent but all lay in agricultural catchments. Physiological indices and water chemistry suggested limitation of phytoplankton biomass mostly by phosphorus, and to some extent by nitrogen in summer in North Ormesby Broad, by nitrogen in summer and to some extent by phosphorus in Lily Broad and by nitrogen in White Mere. Indices did not always accord with one another, though were not severely misleading. They added little to conclusions that could be drawn from water chemistry alone. Reasons for the differential relative importance of nitrogen and phosphorus in the two lake areas are discussed. The paradigm of phosphorus limitation, though unchallenged in upland waters and those on poorly weathered rocks, may be less relevant in lowland lakes.

Responses of elemental and biochemical composition of Chaetoceros muelleri to growth under varying light and nitrate : phosphate supply ratios and their influence on critical N: P

“…Measurement of low levels of nutrients in the environment is not sufficient to infer nutrient limitation of growth rate, although it might be sufficient to indicate that there is limited potential to increase cell yield. However, nutrient limitation of growth rate can produce variations in elemental composition (Goldman et al 1979), macromolecular composition (Lynn et al 2000), enzyme activity (e.g., increase in alkaline phosphatase activity in P-limiting conditions, Hammed et al 1999; single cell immunoassay, Dyhrman and Palenik 2001), and cell physiology (e.g., maximum nutrient assimilation and photosynthetic rates, Rhee 1978;Zevenboom et al 1980). The utility of measurements of elemental or macromolecular composition to diagnose nutrient limitation of growth rate could be compromised by the physiological plasticity of phytoplankton.…”

Water pollution by agriculture

“…More surprising was the high failure rate on nitrate concentrations, even using a criterion of 10.5 mg NO 3 -N l K1 , appropriate to risks of methaemoglobinaemia in bottle-fed babies but about an order of magnitude too high where ecological standards are concerned (James et al 2005). Though phosphorus has been traditionally regarded as the most important nutrient influencing ecological quality in freshwaters, this view is changing as evidence accumulates for nitrogen limitation, especially in summer, in warmer, shallower and more lowland water bodies (Hameed et al 1999), and the strong inverse link between plant diversity and nitrogen availability, evident from any fertilized meadow, has been revealed in the aquatic plant communities of freshwaters (James et al 2005). The most diverse plant communities in shallow lakes in the UK are only half as diverse as those in the much less intensively farmed landscapes of Poland and achievement of just half the maximum UK diversity will require reduction of winter nitrate maxima in British waters to approximately 1-2 mg NO 3 -N l K1 .…”

Active fluorometry improves nutrient-diffusing substrata bioassay

“…Effective (p , 0.001) and maximum (p , 0.001) PSII efficiencies were significantly stimulated by nutrients. These results indicate that the responses of these variables to nutrient addition can be used as a bioassay for algal nutrient limitation, as has been done with traditional 14 C-based photosynthesis measurements (Hameed et al 1999, Francoeur et al 2003. One would expect that elevated photosynthesis would be an important mechanism driving nutrientinduced increases in microalgal biomass.…”

“…14 C-based measurement of photosynthetic activity under nutrient-enriched conditions has been used as a bioassay for planktonic and benthic microalgal nutrient limitation (Hameed et al 1999, Francoeur et al 2003. Thus, perhaps TABLE 1.…”