Aerosol‐nutrient‐induced picoplankton growth in Lake Tahoe

Abstract

Lake Tahoe is an oligotrophic lake appreciated for its transparent waters, yet the Lake's clarity has been declining for several decades due in part to eutrophication. At the same time, a shift from nitrogen (N) toward phosphorus (P) limitation of phytoplankton has occurred that could be due to atmospheric deposition of nutrients with high N:P ratios. Atmospheric particle samples collected during 2005–2006 had a mean soluble N:P ratio of 192:1, well above the Redfield ratio of 16:1 typically required by phytoplankton. Samples collected during the Angora Fire that occurred in 2007 were particularly enriched in N relative to P, with a mean ratio >2800:1. A bioassay incubation experiment was conducted using locally collected atmospheric total suspended particulate (TSP) matter. TSP samples with high ammonium (NH4+) and low P content favored the growth of picoplankton (cells <3 µm) and opportunistic filamentous cyanobacteria, whereas larger nanophytoplankton (cells 3–20 µm) were better competitors when more P was available. Picoplankton growth can increase primary productivity without causing a large increase in chlorophyll (chl a) or biomass. Aerosol‐nutrient‐induced picoplankton growth (together with shifts in grazing dynamics and stratification trends) may contribute to the uncoupling between primary productivity, chl a, and biomass that has been observed in Lake Tahoe in the last several decades and, in particular, following the Wheeler and Angora Fires. The chemical composition of aerosols has a marked impact on ecosystem dynamics in Lake Tahoe with potential consequences to lake productivity and microbial community dynamics.

Size Class Dependent Relationships between Temperature and Phytoplankton Photosynthesis-Irradiance Parameters in the Atlantic Ocean

“…This relationship contrasts that observed in other studies where picophytoplankton and temperature are positively correlated (e.g. Mackey et al, 2013).…”

Effects of African dust deposition on phytoplankton in the western tropical Atlantic Ocean off Barbados

“…These ratios are consistent with the high ratios previously reported for aerosols collected in this region over the past two decades [ Baker et al ., ; Zamora et al ., ] and with the relatively low phosphate solubility of African dust over this region (~8%) [ Zamora et al ., ]. This high N:P ratio in the soluble fraction of atmospheric deposition throughout the world's ocean is simulated in the atmospheric deposition models we used (Figure b) and fits other model predictions [ Okin et al ., ] and many observations of aerosol chemistry throughout the world [ Baker et al ., ; Baker et al ., ; Chen et al ., ; Mackey et al ., ; Markaki et al ., ; Paytan et al ., ; Srinivas and Sarin , ]. Although we used only dry deposition in our incubation experiment, similarly high N:P values have been reported for wet deposition in this region [ Zamora et al ., ] and elsewhere [ Altieri et al ., ; Markaki et al ., ; Özsoy , ; Williams et al ., ; Zhang et al ., ].…”

Refractory dissolved organic nitrogen accumulation in high-elevation lakes

“…These data may have captured a phenomenon restricted to similar lacustrine environments where ultraviolet transparency 51 facilitates photochemical alteration of proteins 61 . Alternatively, retarded degradation of N-rich compounds in this environment may be linked to the limited bioavailability of P 14 , a condition that is prevalent in lake systems and limits LT autotrophy 16,62,63 and, potentially, heterotrophy 64 . Such limitation on heterotrophic bacteria could make N remineralization less efficient.…”

“…In this study, the contribution of autochthonous and allochthonous processes to C and N storage within DOM was examined in the Lake Tahoe Basin, which is a high-elevation watershed in the California Sierra Nevada. Lake Tahoe (LT) is the largest lake within this watershed, and climate change and atmospheric N deposition have already begun to alter its phytoplankton species composition and nutrient stoichiometry [12][13][14][15][16] . There are several lakes in this basin that share similar external C and N inputs, but they vary widely in size and water residence time.…”