Hydrodynamic control of the underwater light climate in fluvial Lac Saint‐Pierre

Abstract

We measured characteristics of the underwater light spectra (e.g., attenuation of ultraviolet [UV] radiation, photosynthetically active radiation) and select dissolved and particulate physicochemical properties (e.g., chromophoric dissolved organic carbon [CDOM], dissolved and particulate organic carbon, inorganic dry weights, beam attenuation coefficients, particulate absorption coefficients, and nutrients) in different water masses of fluvial Lac Saint-Pierre (Canada). We used these variables as tracers to reveal the extent and magnitude of spatial and temporal heterogeneity in this large, shallow, fluvial lake of the St. Lawrence River. We superimposed these tracer variables over radiance data obtained from satellite images to identify spatial and temporal changes in the distribution of different water masses and their bio-optical components. The underwater light environment showed strong horizontal (longitudinal and lateral) variability because of the strong connectivity between the terrestrial and aquatic environments in the lake's tributaries and adjoining wetlands. Analyzing the downstream distribution of optical and chemical variables as a function of transport time rather than distance from source tributaries allowed us to demonstrate large differences in the age of the different water masses depending on the characteristics of the source tributary, in-stream processes, and distance from its source. CDOM explained most of the UV attenuation and allowed the greatest discrimination between water masses.

The effects of UVR irradiance and spectral composition on yellow perch (Perca flavescens) larvae survival

“…Our study avoids this problem: although treatments without non-selective screens were probably too harsh for larvae, conditions in the other treatments were close to what is potentially found in the field. The irradiance received under the low and medium quantity treatments were close to the light conditions that could be found in the first 30 cm of the water column of some sections of the St. Lawrence River (Frenette et al 2006), where yellow perch larvae are commonly found (Magnan and Bertolo, personal observations). The use of natural solar radiation allowed us to get a more realistic interpretation of the impact of UVR in a natural Our results are in accordance with those of Williamson et al (1997) who showed that yellow perch egg survival was strongly affected when exposed in clear water to UV-B ?…”

Terrestrial support of zebra mussels and the Hudson River food web: A multi‐isotope, Bayesian analysis

“…Large, deep rivers can be extreme in this regard. In turbid, well-mixed waters, phytoplankton can be severely light limited, and macrophytes and benthic algae are restricted to the shallowest, light-exposed portions (Frenette et al 2006). At the same time, the flow of water from the watershed brings with it a great deal of dissolved and particulate organic matter of terrestrial origin that can dwarf autochthonous primary production (Vannote et al 1980).…”

Relationship between water color, water levels, and climate indices in large rivers: Case of the St. Lawrence River (Canada)

“…Franc ?ois river and the l'Assomption river located, respectively, on the south and north shores, which strongly drain agricultural watersheds. CDOM input in the river from these two tributaries, in particular, and from other tributaries, in general, has already been documented by several authors [e.g., Frenette et al, 2003Frenette et al, , 2006Frenette et al, , 2012Vis et al, 2007;Massicotte and Frenette, 2011].…”

“…The SLR forms a complex system composed of a mosaic of heterogeneous zones such as fluvial lakes, connecting reaches and wetlands interacting with inflowing tributaries. In SLR, 21 principal tributaries drain a watershed of 1,600,000 km 2 , where land use is dominated by a high degree of urbanization near Montreal and areas of agriculture, pastures, forests, and wetlands in the mid and lower reaches of the stream system [Frenette et al, 2006, Vis et al, 2007. For instance, water intrusions from tributaries become distinct water masses flowing down the river and contributing to spatial and temporal heterogeneity in optical characteristics [Frenette et al, 2003[Frenette et al, , 2006Rice et al, 2006].…”

“…To answer the above question, the main goal of the study is to correlate the color of St. Lawrence River (SLR, a typical large river system) waters with water levels over the period from 1984 to 2009. All studies looking at water color in rivers to date have focused on measurement methods, processes, and factors that affect this color [e.g., Kirk, 1988Kirk, , 1994DaviesColley and Nagels, 2008;Thorp et al, 2006;Frenette et al, 2003Frenette et al, , 2006Frenette et al, , 2012Stomp et al, 2007;Julian et al, 2008a;Bukata, 1995;. Although the existence of a link between climate indices and flow (or water levels) in rivers has been demonstrated by many authors (e.g., Assani et al [2010aAssani et al [ , 2010bAssani et al [ , 2011 for Quebec), to our knowledge, no study has examined the relationship between water color in rivers and water levels, so the present study aims to fill this gap.…”