Role of nutrients and zooplankton grazing on phytoplankton growth in a temperate reservoir in New South Wales, Australia

Abstract

The role of nitrogen (N) and phosphorus (P) and zooplankton grazing on the growth of a phytoplankton community was investigated at different times in the Ben Chifley reservoir. In situ nutrient enrichment bioassays (n�= 12) indicated that phytoplankton growth was limited by P in 33% of experiments, by both N and P in 25% of experiments and no limitation was found in 42%. The hypothesis that N or P limitation occurred when ambient N : P ratios were different from the Redfield ratio was supported in 33% of bioassay experiments, suggesting that ambient N : P ratios do not always correctly indicate if N or P is limiting. Grazing rates of the reservoir zooplankton (>150�μm in size) ranged from 0.023–0.199 day–1 (mean: 0.078 day–1, n = 8). The grazing efficiency, as measured by a weight-specific clearance rate, ranged from 0.049–0.743 mL μg dry wt–1 day–1, and was positively correlated with the relative biomass of Daphnia in the community. The nutrient-stimulated growth of phytoplankton ranged from 0.085–1.031 day–1 (mean: 0.461 day–1, n = 10). The effect of nutrient enrichment exceeded that of zooplankton grazing in 62% of experiments. Further study is necessary to understand a qualitative effect of nutrients and zooplankton grazing on the phytoplankton community structure in the Ben Chifley reservoir.

Changes in N and P limitation induced by water level fluctuations in Nature Park Kopački Rit (Croatia): nutrient enrichment bioassay

“…For example, ambient N:P ratios in Australian reservoirs correctly indicated if N or P is limiting in 33% of bioassay experiments (Kobayashi and Church 2003). Similarly, in the Great Salt Lake, USA, TN:TP ratios normally suggest P limitation, but bioassay experiments routinely demonstrate N limitation of phytoplankton (Wurtsbaugh 1988).…”

Limitation of lowland riverine bacterioplankton by dissolved organic carbon and inorganic nutrients

“…Each microcosm experiment was performed using 1.25-l transparent polyethylene terephthalate (PET) bottles and 15-l transparent PET carbuoys to determine the effect of microbial community responses to additions of DOC to both container types, and N and P to the bottles only. The use of bioassays can provide direct evidence of nutrient limitation in natural plankton communities in which the planktonic growth response is measured by the addition of one or more nutrients (Kobayashi & Church, 2003). Another advantage of in situ microcosms (bioassays) in determining dissolved organic matter (DOM) limitation as opposed to open water experiments is that it is a relatively simple protocol that is easily repeatable and allows a direct comparison between treatment types and is deemed to give a reasonable estimate of potential water-column activity (Buffam et al, 2001).…”

“…The importance of the inorganic nutrients, phosphorus (P) and nitrogen (N), in freshwater aquatic ecosystems is well documented (e.g. Rier & Stevenson, 2002;Baldwin et al, 2010), particularly as a key factor in controlling phytoplankton growth, with P often regarded as the most common limiting nutrient (Kobayashi & Church, 2003). However, when P and N are abundant in aquatic systems, heterotrophic bacterial growth is often increased by the addition of DOC (Buffam et al, 2001), often out-competing phytoplankton (Findlay, 2003).…”

Zooplankton diversity and assemblages in arid zone rivers of the Lake Eyre Basin, Australia

“…The role of microfauna as an important link in the food chain of arid zone rivers has been identified using stable isotope analysis (Bunn et al 2003). They are an obvious food source for larger invertebrate predators and planktivorous fish (Meredith et al 2003;Wallace et al 2005) and some waterbirds (Crome 1985), as well as being an important grazer of phytoplankton (Kobayashi and Church 2003).…”