Search

Phytobenthos are often underrepresented in both limnological and paleolimnological studies but may play key roles in whole‐lake production and ecosystem processes including eutrophication, food‐web dynamics, and ecosystem state changes.Photosynthetic pigments, stables isotopes, and diatoms were quantified from surface sediments (0–1 cm) collected across a depth transect of a small, DOC‐rich, mesotrophic lake in boreal northwestern Ontario to assess spatial variation in phytobenthos abundance and production.Maximal concentrations of siliceous algae and cyanobacteria pigments occurred at ~2–6 m depth, with abundant tychoplanktonic diatoms, depleted sedimentary δ13C values, and elevated ratios of precursor chlorophyll a to product pheophytin a, all aligning well with the depths of the thermocline, epilimnetic mixing, and maximum light penetration.These patterns demonstrated the presence of three discrete community assemblages, with greatest mass accumulation occurring at intermediate depths where warm illuminated sediments provide habitat for tychoplanktonic diatoms and cyanobacteria between turbulent shallows and cold and dark depths.If widespread among boreal lakes, this tychoplanktonic zone may exert important effects on whole‐lake production, carbon sequestration, benthic‐pelagic food‐web coupling, eutrophication, and ecosystem state change. [ABSTRACT FROM AUTHOR]

1. Spatial and temporal variations in algal concentrations are controlled in many aquatic ecosystems by the availability of solar irradiance, rather that nutrients or grazing. In such light limiting conditions, changes in the optical or hydrological characteristics of the water column will directly impact biomass concentrations. Here we develop and test an approach based on the relationship between available solar irradiance within the mixed layer and algal biomass concentrations. 2. As with most nutrient/biomass relationships, an increase in available solar energy favours an increase in biomass when light limitation prevails. The ratio between light/biomass is then used to determine a critical light requirement that can be used to estimate critical depth and compensation irradiance and open the way to exploring how changes in mixing depth and vertical attenuation may influence algal biomass concentrations. 3. This approach is used to describe real conditions in two disparate algal communities; the phytoplankton community in Lake Victoria, East Africa and the microphytobenthos community in the lacustrine system of Esteros del Iberá (South America). 4. Differences in the critical light requirement were used to examine the relative efficiency of the algal communities in their use of available solar energy. The tropical phytoplankton community showed similar energetic requirements to theoretical estimates and were found to be less efficient when compared with the phytobenthos community. [ABSTRACT FROM AUTHOR]