Determination of phytoplankton crops by top‐down and bottom‐up mechanisms in a group of English lakes, the West Midland meres

Abstract

Twenty-four lake basins formed in glacial drift ranged in maximum depth from 1.5 to 3 1 m and were characterized by generally low inorganic N concentrations and very high total P concentrations. The high P values were in some cases related to farm effluent pollution but in many others, despite annual mean values up to 1.46 mg liter-I, appear natural and due to the local mineralogy.For the entire group, there were no significant relationships between mean growth season chlorophyll a concentration and any measured chemical, morphometric, or zooplankton variable. When the group was divided on the basis of maximum depth and presence or absence of thermal stratification in summer into a shallow group (~3 m) and a deep group (>3 m), strong inverse correlation was obtained between chlorophyll a and cladoceran abundance in the shallow group and strong direct correlation with inorganic N in the deep group. Grazer control in the shallow group is probably linked with the dominance of submerged macrophytes and the refuges they provide for grazers. Some of the controversy presently surrounding the relative importance of top-down vs. bottom-up control of phytoplankton populations may thus be removed if consideration is given to the morphometry of the lakes.

Avoidance by Daphnia magna of fish and macrophytes: Chemical cues and predator‐mediated use of macrophyte habitat

“…Nevertheless, the Daphnia behaviors we documented are consistent with the suggestion by Moss et al (1994) that macrophytes are important refuges for large zooplankton in shallow lakes and allow zooplankton to suppress phytoplankton abundance even in the presence of zooplanktivorous fish. Abstract-The feeding-deterrent properties of a suite of common holoplankton (nine species representing five phyla) collected from oceanic waters near Bermuda were investigated.…”

Evaluation of Spatial-Temporal Variations of Water Quality and Plankton Assemblages and Its Relationship to Water Use in Kulekhani Multipurpose Reservoir, Nepal

“…In addition to the reservoir temperature, transparency, pH and alkalinity also showed positive correlation with the planktons' diversity and abundance in the reservoir water. While P is considered as the prime nutrient that limits primary productivity in lakes and reservoirs [45] [46], numerous studies have shown that the biomass of phytoplanktons can be nitrogen-limited [39] [47]. The relatively higher concentrations of phosphate than nitrate, observed in the present study, indicates that the plankton's density in the reservoir was mainly the function of N. In general, inorganic forms of N and P were usually depleted in spring very rapidly and their concentrations remain at the low level till late autumn.…”

Ancient blue‐green blooms

“…Conductivity is high (300-350 s cm Ϫ1 ), alkalinity is moderate (1.7 Ϯ 0.1 meq liter Ϫ1 , and pH ranges from 6.7 to 9.8. Soluble reactive and total phosphorus concentrations span 0.5 to Ͼ1.0 mg liter Ϫ1 , which is not atypical of stratified meres in the region (Reynolds 1971; Moss et al 1994Moss et al , 1997. There are no point sources of eutrophication and no surface inflows.…”