Relative importance of iron and molybdenum in restricting phytoplankton biomass in high phosphorus saline lakes

Abstract

Eleven prairie saline (conductivity 1.8-58.8 mS cm-') lakes were examined over the 1994 growing season to determine what salinity-related factor or factors were responsible for controlling phytoplankton standing crops. The study lakes were characterized by high total P (0.15-24.2 mg liter-'), total N (3.75-12.35 mg liter-'), total Fe (55-2,800 p,g liter-'), dissolved organic C (40-195 mg liter-l), pH and alkalinity, but comparatively low (usually cl00 kg liter-') dissolved inorganic N. Chlorophyll a (Chl a) concentrations in all but the two least saline lakes were relatively low (20 pg liter-'), up to three orders of magnitude below those predicted by freshwater P-based models. High alkaline phosphatase activities (APA) and rapid '2P0, (orthophosphate) uptake indicated that the two least saline lakes were P limited; these lakes had seston deficient in P, N, and protein. APA and "2P0, uptake were below detection in the more saline lakes (conductivity >3 mS cm-'), indicating P sufficiency; seston from these lakes was deficient in N but not protein. Nitrogen-fixing cyanophytes were important only in one of the lakes examined. Nutrient addition bioassays indicated that phytoplankton biomass was not limited exclusively by inorganic N availability, nor by a combination of MO and N. For water from all but one of the P-sufficient lakes, addition of Fe to bioassays resulted in a remarkable increase in Chl a concentrations. Addition of Fe and MO had the same effect as that of Fe alone, while the most saline lake appeared to be limited by one or more additional trace elements (but not MO). Reducing the alkalinity of the bioassay water stimulated growth in the same manner as the Fe additions, suggesting that the bioavailability of the (largely particulate) Fe already present was severely restricted by lakewater alkalinity. Some component of lake-water alkalinity (which increased with conductivity in these lakes) appears to be the key factor limiting Fe bioavailability and restricting phytoplankton standing crops in the higher salinity lakes.

Phosphorus dynamics during the transition from nitrogen to phosphate limitation in the central Baltic Sea

“…The absence of ambient levels of phosphate, the C:P ratio in particulate organic material, APA, and turnover times of phosphate were used for characterization of the phosphate limitation of plankton in various ecosystems (Graneli et al 1990, Fisher et al 1992, Thingstad et al 1993, Cotner et al 1997, Evans & Prepas 1997, Robarts et al 1998. Our investigations showed that the estimated time of phosphate limitation varied with the parameter used.…”

Light‐induced redox cycling of iron in circumneutral lakes

“…Tahoe (Chang et al 1992), and iron has been shown to restrict phytoplankton growth in high phosphorous saline lakes (Evans and Prepas 1997) and in hard-water calcareous lakes (Schelske 1962;Schelske et al 1962;Wetzel 1965).…”

Effects of the substances secreted from Closterium aciculare (Charophyceae, Chlorophyta) on the growth of freshwater phytoplankton under iron-deficient conditions

“…Iron has the potential to control the growth and composition of phytoplankton communities (Murphy et al 1983;Chang et al 1992;Pollingher et al 1995;Evans & Prepas 1997;Sunda & Huntsman 1997;Hyenstrand et al 1999;Schmidt & Hutchins 1999;Twiss et al 2000;Shaked et al 2004;Noiri et al 2005). This study demonstrated that the secretion from C. aciculare showed some patterns of selectivity in its effect on phytoplankton growth.…”

“…Iron limitation in freshwater is suggested to occur mainly via complexation of iron by organic matter (Imai 1999) and sulfide clusters (Rozan et al 2000). Phytoplankton has been shown to be limited by low availability of iron in hard-water lakes and saline lakes (Schelske 1962;Schelske et al 1962;Wetzel 1966;Evans & Prepas 1997). To survive under low iron availability conditions, many eukaryotic phytoplankton appear to acquire iron in a manner similar to 'strategy I' (Römheld 1987) for higher plants, in which iron limitation leads to an increase in plasma membrane ferric chelate reductase activity (Weger et al 2002).…”