Effects of Fish and Plankton on Lake Temperature and Mixing Depth

Abstract

A comparative study of small temperate lakes (<20 square kilometers) indicates that the mixing depth or epilimnion is directly related to light penetration measured as Secchi depth. Clearer lakes have deeper mixing depths. This relation is the result of greater penetration of incident solar radiation in lakes and enclosures with high water clarity. Data show that light penetration is largely a function of size distribution and biomass of algae as indicated by a relation between the index of plankton size distribution (slope) and Secchi depth. Larger or steeper slopes (indicative of communities dominated by small plankton) are associated with shallower Secchi depth. In lakes with high abundances of planktivorous fish, water clarity or light penetration is reduced because large zooplankton, which feed on small algae, are reduced by fish predation. The net effect is a shallower mixing depth, lower metalimnetic temperature and lower heat content in the water column. Consequently, the biomass and size distribution of plankton can change the thermal structure and heat content of small lakes by modifying light penetration.

Mesozooplankton influences on the microbial food web: Direct and indirect trophic interactions in the oligotrophic open ocean

“…The strong coupling of nonadjacent trophic levels via indirect cascade effects is a well-established phenomenon in freshwater systems, where the presence or absence of piscivorous fish can profoundly influence zooplankton community composition, phytoplankton abundance, water clarity, heat budgets, and mixing depth (Carpenter et al 1985;McQueen et al 1986;Kerfoot 1987;Mazumder et al 1990;Pace et al 1998). In contrast, this area has received little attention in marine systems, despite recent evidence that the harvesting of the oceans is systematically diminishing the average trophic level of top consumers and concerns about long-term shifts in community structure (Dayton et al 1995;Myers et al 1997;Pauly et al 1998).…”

Interaction of Nutrients and Turbidity in the Control of Phytoplankton in a Large Western Canadian Lake Prior to Major Watershed Impoundments

“…Thermal stratification was more sharply defined in the South Arm, with higher late summer near-surface water temperatures. Light penetration alone can have a significant effect on the depth of the epilimnion in lakes (Mazumder et al 1990), and this is likely the reason for the observed differences in thermal stratification. The ratio of the euphotic zone to the mixed-layer depth was as low as 0.1 in the South Arm and usually above 0.6 in the North Arm.…”

Les réseaux trophiques lacustres: structure, fonctionnement, interactions et variations spatio-temporelles

“…Si plusieurs expé-riences en enceintes indiquent que le broutage par les daphnies favorise les algues peu consommables (LAMPERT et ai, 1986;KERFOOT étal., 1988), d'autres expériences aboutissent au résultat inverse (SHAPIRO et WRIGHT, 1984 ;CHRISTOFFERSEN étal., 1993;SARNELLE, 1993). Ces contradictions indiquent clairement que l'issue des interactions entre producteurs primaires, herbivores et poissons ne repose pas uniquement sur le caractère consommable ou non des algues, mais aussi sur d'autres facteurs, tels que les modifications du recyclage et de l'équilibre des nutriments (ELSER étal., 1988;VANNI et FINDLAY, 1990;LYCHE étal., 1996a) et de l'atténuation de la lumière par l'action des herbivores (MAZUMDER et al, 1990a ;MAZUMDER et TAYLOR, 1994) ou l'existence de seuils de densité à partir desquels les algues peu consommables ne peuvent plus être régulées par le zooplancton (GLiwicz, 1990).…”