Combining a regional climate model with a phytoplankton community model to predict future changes in phytoplankton in lakes

1. Linking a regional climate model (RCM) configured for contemporary atmospheric greenhouse gas concentrations, with a phytoplankton community model (PROTECH) produced realistic simulations of 20 years of recent phytoplankton data from Bassenthwaite Lake, in the North‐West of England. 2. Meteorological drivers were derived from the RCM to represent a future climate scenario involving a 1% per annum compound increase in atmospheric CO₂ concentrations until 2100. Using these drivers, PROTECH was run for another 20 year period representing the last two decades of the 21st century. 3. Comparison of these present and future simulations revealed likely impacts on the current seasonal phytoplankton development. Under future climate conditions, the simulated spring bloom showed an increase in cyanobacteria dominance caused by greater success of Planktothrix. Also, the summer cyanobacteria bloom declined earlier because of nutrient limitation caused by the increased spring growth. Overall productivity in the lake did not change. 4. Analysis showed that these predicted changes were driven by changes in water temperature, which were in turn triggered by the higher air temperatures predicted by the RCM.     

The incidence and spatial pattern of Nothofagus cunninghamii (Hook.) Oerst. attacked by Platypus subgranosus Schedl in Tasmania's cool temperate rainforest

Data from transect surveys of 20 cool temperate rainforest sites in Tasmania were used to quantify the incidence and spatial distribution of myrtle, Nothofagus cunninghamii, attacked by the mountain pinhole borer, Platypus subgranosus. Attack by this insect is indicative of the disease ‘myrtle wilt’ caused by the pathogenic hyphomycete, Chalara australis. The proportion of myrtle trees attacked by the disease ranged from 9.4 to 53.4%, with an average incidence of 24.6%. Regression analysis indicated that attack decreased with increasing altitude and, after adjusting for altitude, callidendrous forests had a higher incidence of attack than thamnic-implicate forests. In mixed eucalypt-rainforest stands, the incidence of attack increased as both relative and absolute measures of myrtle density increased. However, a significant amount of variation in the incidence of attack remained unexplained by the site and stand variables measured. The incidence of attack differed significantly between diameter classes with the larger diameter trees having the highest incidence of attack. Trees with stem and crown damage had a significantly higher incidence of attack than undamaged trees. Attacked trees tended to be clumped, with the degree of clumping reasonably constant across sites, but dependent on nearest neighbour distance within sites. Dying trees occurred at an average rate of 2.4 trees ha^-1 per year or 1.6% of live trees per year across the sites.     

The seasonal sensitivity of Cyanobacteria and other phytoplankton to changes in flushing rate and water temperature

The phytoplankton lake community model PROTECH (Phytoplankton RespOnses To Environmental CHange) was applied to the eutrophic lake, Esthwaite Water (United Kingdom). It was validated against monitoring data from 2003 and simulated well the seasonal pattern of total chlorophyll, diatom chlorophyll and Cyanobacteria chlorophyll with respective R²‐values calculated between observed and simulated of 0.68, 0.72 and 0.77 (all P<0.01). This simulation was then rerun through various combinations of factorized changes covering a range of half to double the flushing rate and from ?1 to +4 °C changes in water temperature. Their effect on the phytoplankton was measured as annual, spring, summer and autumn means of the total and species chlorophyll concentrations. In addition, Cyanobacteria mean percentage abundance (%Cb) and maximum percentage abundance (Max %Cb) was recorded, as were the number of days that Cyanobacteria chlorophyll concentration exceed two World Health Organization (WHO) derived risk thresholds (10 and 50 mg m^?3). The phytoplankton community was dominated in the year by three of the eight phytoplankton simulated. The vernal bloom of the diatom Asterionella showed little annual or seasonal response to the changing drivers but this was not the case for the two Cyanobacteria that also dominated, Anabaena and Aphanizomenon . These Cyanobacteria showed enhanced abundance, community dominance and increased duration above the highest WHO risk threshold with increasing water temperature and decreasing flushing rate: this effect was greatest in the summer period. However, the response was ultimately controlled by the availability of nutrients, particularly phosphorus and nitrogen, with occasional declines in the latter's concentration helping the dominance of these nitrogen‐fixing phytoplankton.     

Critical periods in the life cycle and the effects of a severe spate vary markedly between four species of elmid beetles in a small stream

1. The chief objectives were: (i) to describe quantitatively the life cycles of four species of Elmidae, Elmis aenea, Esolus parallelepipedus, Oulimnius tuberculatus and Limnius volkmari; (ii) to use life tables to identify critical periods for survival in the life cycle of each species; (iii) to evaluate the immediate and longer‐term effects of a severe spate on densities of the four species. Monthly samples were taken over 63 months at two contrasting sites in a small stream: one in a deep section with macrophytes abundant, and the other in a shallow stony section. 2. There were five larval instars for O. tuberculatus, seven for L. volkmari and six for the other two species. The life cycle of each species took 1 year from egg hatching (chiefly in June for E. aenea and O. tuberculatus, and July for the other species) to pupation in the stream bank and a further year before the adults in the stream matured and laid their eggs. Mature adults were present in most months, but were rare or absent in January and February and attained maximum densities in April for O. tuberculatus and May for the other species. 3. Laboratory experiments provided data on egg hatching and pupation periods and the number of eggs laid per female. Life tables compared maximum numbers per square metre for key life‐stages. Within each species, mortality rates between adjacent life‐stages were fairly constant among six cohorts and between sites, in spite of large differences in numbers. The only exception for all species was the high adult, but not larval, mortality during a severe spate. 4. Standardised life tables, starting with 1000 eggs, identified key life‐stages with the highest mortality, namely the early life‐stages for E. aenea (36% mortality), start of the overwintering period to pupation for O. tuberculatus (41%) and L. volkmari (51%), start of pupation to the maximum number of immature adults for E. parallelepipedus (41%) and between the maximum numbers of immature and mature adults for O. tuberculatus (41%). Therefore, critical periods for survival in the life cycle differed between species, presumably because of their different ecological requirements. Similarly, the effects of the spate on adult mortality, and hence egg production, varied between species, being most severe and long‐term for E. aenea and O. tuberculatus, less severe for E. parallelepipedus and least severe with a rapid recovery for L. volkmari. Possible reasons for these discrepancies are discussed, but more data are required on the food and microhabitat requirements of the elmids before satisfactory explanations can be found.