Light attenuation characteristics of glacially-fed lakes

Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially-fed lakes may be a particularly sensitive sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially-fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400–700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity-specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity-specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non-glacially-fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially-fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems

Global lake responses to climate change

Climate change is one of the most severe threats to global lake ecosystems. Lake surface conditions, such as ice cover, surface temperature, evaporation and water level, respond dramatically to this threat, as observed in recent decades. In this Review, we discuss physical lake variables and their responses to climate change. Decreases in winter ice cover and increases in lake surface temperature modify lake mixing regimes and accelerate lake evaporation. Where not balanced by increased mean precipitation or inflow, higher evaporation rates will favour a decrease in lake level and surface water extent. Together with increases in extreme-precipitation events, these lake responses will impact lake ecosystems, changing water quantity and quality, food provisioning, recreational opportunities and transportation. Future research opportunities, including enhanced observation of lake variables from space (particularly for small water bodies), improved in situ lake monitoring and the development of advanced modelling techniques to predict lake processes, will improve our global understanding of lake responses to a changing climate

Response of Cyclotella species to nutrients and incubation depth in Arctic lakes

This article is closed access.The relative abundances of small centric diatoms have increased in many Arctic lakes over the past century, with these changes commonly attributed to warming. However, the specific mechanisms by which diatom community structure is changing in response to warming remain unclear. We investigated the responses of two common centric diatoms to nutrient enrichment and incubation depth, the latter used to manipulate light availability which is a key factor that changes with altered mixing depths in lakes. We conducted 2 × 2 factorial experiments, manipulating nutrients (none added or N + P addition) and incubation depth (shallow or deep), and measured changes in growth rates and cell densities of Discostella stelligera and Puncticulata radiosa. A second set of experiments was conducted on D. stelligera in a growth chamber to separate temperature and light effects associated with incubation depth. Puncticulata radiosa was always more abundant in the shallow depth incubations, regardless of nutrient conditions. In contrast, D. stelligera responded most strongly to nutrient additions, and cell densities of this species were affected by interactions between nutrients and incubation depth or light. Our research suggests that processes that alter light availability (such as water clarity and water column stability) and nutrient concentrations are likely to play a major role in controlling the growth of small centric diatoms in Arctic lakes