Experimental evaluation of nutrient limitation of phytoplankton communities in the Gulf of Riga

Abstract

. PO -P l and two levels of combined additions were followed for 3 days using 6 l experimental units. To evaluate the 4 nutrient limitation patterns, time series of chlorophyll a were analysed using polynomial regression models and ranking method, taking advantage of the relatively constant experimental error. Apparent nutrient depletion rates and ratios were estimated, and compared with the changes in particulate nutrient ratios. During the spring diatom bloom in 1995, ambient inorganic nutrient concentrations were still high, and thus phytoplankton biomass did not respond to additions of nutrients. Ž Ž . y1 y1 Ž Chlorophyll a specific nutrient depletion rates were low 0.01-0.12 mg N mg chl a h and 0.002-0.016 mg P mg chl . y1 y1 . a h and linear over time, thus also revealing that phytoplankton was not limited by these nutrients in that time. In June 1994, there was an areal shift from N limitation in the outer Irbe Strait towards co-limitation in the southern Gulf. Later in July 1994, during the bloom of N-fixing Aphanizomenon flos-aquae, the N limitation was obvious for the whole study Ž Ž . y1 y1 area. For this period chlorophyll a specific nutrient depletion rates were high 0.36-0.67 mg N mg chl a h and Ž . y1 y1 . 0.089-0.135 mg P mg chl a h , and added nutrients were almost totally depleted during the first light period. After the collapse of cyanobacterial bloom in August 1993, the experiment carried out in the southern Gulf indicated P limitation of phytoplankton. The central Gulf was obviously co-limited, while the area between northern Gulf and outer Irbe Strait was N-limited. Our results indicate that phytoplankton in the Gulf of Riga, earlier considered strictly as P-limited, is at least until late-summer period N-or co-limited. It seems also obvious that there exists a spatial tendency in the phytoplankton limitation patterns, generally from more P-or co-limited southern Gulf towards more N-limited northern basin. q

Stream Health Evaluation Using a Combined Approach of Multi-Metric Chemical Pollution and Biological Integrity Models

“…TN:TP ambient ratios showed oligotrophic states at all sites showing higher values. Previous studies have shown that TN:TP ratio in ambient water was an indirect indicator of nutrient limitation for primary productivity [71,72], and if lower, showed higher nutrient pollutants leading to eutrophication [21]. Mean concentration of sestonic CHL-a confirmed the assessment of S1 and S2 as oligotrophic, having CHL-a levels lower than 3 µg/L.…”

Picophytoplankton responses to changing nutrient and light regimes during a bloom

“…These interpretations are based on the assumption that phytoplankton communities assimilate macronutrients at a constant ratio, and therefore deviations from such ratios indicate limitation by one nutrient over another. However, nutrient co-limitation can occur in oligotrophic waters (Seppala et al 1999;Mills et al 2004) where addition of one nutrient may rapidly induce limitation for another nutrient as soon as limitation by the former is relieved. In these cases phytoplankton communities are eVectively colimited because addition of both nutrients is required to elicit substantial increases in biomass.…”

Fate of increased production in late-summer plankton communities due to nutrient enrichment of the Baltic Proper

“…It has been studied by a variety of methods such as nutrient contents of cells, nutrient uptake rates and physiological indicators (e.g. Granéli 1984, Sakshaug & Olsen 1986, Zevenboom 1986, Hecky & Kilham 1988and references therein, Graziano et al 1996, Hameed et al 1999, Holmboe et al 1999, Mallin et al 1999, Seppälä et al 1999. Bioassays, in which the response of phytoplankton primary production (PP) and biomass accumulation is followed after nutrient enrichment, have been used in several studies (Granéli et al 1990, Kivi et al 1993, Downing et al 1999 and references therein).…”

“…Bioassays, in which the response of phytoplankton primary production (PP) and biomass accumulation is followed after nutrient enrichment, have been used in several studies (Granéli et al 1990, Kivi et al 1993, Downing et al 1999 and references therein). The overall conclusion of the bioassays carried out in coastal areas of the Baltic Sea is that the limiting nutrient varies not only areally but also seasonally between phosphorus and nitrogen, while the open sea areas are largely nitrogen limited (Granéli et al 1988, Kivi et al 1993, HELCOM 1996, Seppälä et al 1999. Besides N and P, Fe has also been suggested as limiting the growth of filamentous cyanobacteria in the open areas of the Baltic Sea (Stal et al 1999).…”