Primary and bacterial production in lakes: are they coupled over depth

Abstract. The coupling of prlmary and bacterial production over depth was examined in three lakes which differed greatly in vertical patterns of primary productivity. We measured bacterial production, chlorophyll and light, and estimated primary production in Paul Lake (Gogebic County, Michigan) and Crystal and Trout lakes (Vilas County, Wisconsin) during the summer strat~fication period (May-September 1991). Bacterial productivity was measured using the ['Hlleucine incorporation method and primary productivity estimated from measured photosynthesis-irradiance relationships. Three distinct vertical patterns were observed. In Paul Lake, bacterial production was highest at the interface between the aerobic and anaerobic layers, well below the depth of maximum primary production. In Crystal Lake, bacterial production was uniform with depth, although primary b 4-' gaductivity was highest in the hypolimnion. In the largest lake, Trout Lake, primary and bacterial production tended to co-vary with maximum rates of both processes occurring in the metalimnion. Overall, bacterial productivity was poorly related to contemporaneous primary production in the three lakes, suggesting that other factors, such as nutrient recycling, phytoplankton loss rates and allocthonous loading, determine patterns in the depth distribution of bacterial productivity

Junior Recital: Stacey L. Novik, trumpet

This recital is presented in partial fulfillment of requirements for the degree Bachelor of Music in Performance. Ms. Novik studies trumpet with Lester Walker.https://digitalcommons.kennesaw.edu/musicprograms/1041/thumbnail.jp

Seagrass ecosystem recovery: Experimental removal and synthesis of disturbance studies

Net global losses of seagrasses have accelerated efforts to understand recovery from disturbances. Stressors causing disturbances (e.g., storms, heatwaves, boating) vary temporally and spatially within meadows potentially affecting recovery. To test differential recovery, we conducted a removal experiment at sites that differed in thermal stress for a temperate seagrass (Zostera marina). We also synthesized prior studies of seagrass recovery to assess general patterns. Seagrass shoots were removed from 28.3 m2 plots at edge and central sites of a meadow in South Bay, Virginia, USA. We hypothesized faster recovery for edge plots where greater oceanic exchange reduces thermal stress. Contrary to our hypothesis recovery was most rapid in the central meadow matching control site shoot density in 24 months. Recovery was incomplete at the meadow edge and estimated to require 158 months. Differences in recovery were likely due to storm-driven sediment erosion at the edge sites. Based on data from prior recovery studies, which were primarily on monospecific meadows of Zostera, seagrasses recover across a broad range of conditions with a positive, nonlinear relationship between disturbance area and recovery time. Our experiment indicates position within a seagrass meadow affects disturbance susceptibility and length of recovery. Linking this finding to our literature synthesis suggests increased attention to spatial context will contribute to better understanding variation in recovery rates

Prevelance of Tinea Pedis and Onychomycosis in Malta : the Achilles project

The Achilles project was set up because of the general poor awareness of foot disease, espe- cially of fungal foot infections. Foot diseases are often not viewed as a real problem, and the general public has limited knowledge of them. Most previous studies have involved small and specific population groups, such as school children, subjects visiting swimming baths, populations with specific occupations, or patients with underlying diseases like diabetes. Moreo- ver, patients often had to diagnose the condition themselves. The results of these self-assess- ments, was an underestimation of the prevalence of foot infections. (1, 2) The Achilles project was the largest epidemiological study ever to be carried out on foot health in Europe and other countries, related to the part of the body below the Achilles heel (e.g. foot, toes, toenails). Started in 1998, the aim of the project was to gain a better understanding of diseases affecting the feet and their prevalence among different patient groups with a view to improve the timely diagnosis and optimal treatment of this significant medical problem. The project also allowed an insight to be gained into the predisposing factors and quality of life in a large population, and to generate clinical data from a sample of the population. The data also served as the basis for epidemiological studies, allowing both medical professionals and pa- tients to benefit from this knowledge. The ultimate goal is therefore to increase the chance for timely diagnosis and treatment of foot disorders. Several European countries, including Austria, Belgium, the Czech Republic, Germany, Greece, Hungary, Italy, Luxembourg, the Netherlands, Portugal, Poland, Russia, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom (UK), have thus far participated in this foot-screening project, which was endorsed by the European Academy of Dermatology and Venerology (EADV) and the European Nail Society. Following the example of these countries, in 1999 Malta, Jordan and Cyprus implemented the Achilles project.peer-reviewe

Trophic Cascades, Nutrients, and Lake Productivity: Whole-Lake Experiments

Responses of zooplankton, pelagic primary producers, planktonic bacteria, and CO2 exchange with the atmosphere were measured in four lakes with contrasting food webs under a range of nutrient enrichments during a seven-year period. Prior to enrichment, food webs were manipulated to create contrasts between piscivore dominance and planktivore dominance. Nutrient enrichments of inorganic nitrogen and phosphorus exhibited ratios of N:P \u3e 17:1, by atoms, to maintain P limitation. An unmanipulated reference lake, Paul Lake, revealed baseline variability but showed no trends that could confound the interpretation of changes in the nearby manipulated lakes. Herbivorous zooplankton of West Long Lake (piscivorous fishes) were large-bodied Daphnia spp., in contrast to the small-bodied grazers that predominated in Peter Lake (planktivorous fishes). At comparable levels of nutrient enrichment, Peter Lake\u27s areal chlorophyll and areal primary production rates exceeded those of West Long Lake by factors of approximately three and six, respectively. Grazers suppressed pelagic primary producers in West Long Lake, relative to Peter Lake, even when nutrient input rates were so high that soluble reactive phosphorus accumulated in the epilimnions of both lakes during summer. Peter Lake also had higher bacterial production (but not biomass) than West Long Lake. Hydrologic changes that accompanied manipulation of East Long Lake caused concentrations of colored dissolved organic carbon to increase, leading to considerable variability in fish and zooplankton populations. Both trophic cascades and water color appeared to inhibit the response of primary producers to nutrients in East Long Lake. Carbon dioxide was discharged to the atmosphere by Paul Lake in all years and by the other lakes prior to nutrient addition. During nutrient addition, only Peter Lake consistently absorbed CO2 from the atmosphere, due to high rates of carbon fixation by primary producers. In contrast, CO2 concentrations of West Long Lake shifted to near-atmospheric levels, and net fluxes were near zero, while East Long Lake continued to discharge CO2 to the atmosphere

Individual-based modelling of adaptive physiological traits of cyanobacteria: Responses to light history

Adaptive physiological traits of cyanobacteria allow plasticity of responses to environmental change at multiple time scales. Most conventional phytoplankton models only simulate responses to current conditions without incorporating antecedent environmental history and adaptive physiological traits, thereby potentially missing mechanisms that influence dynamics. We developed an individual-based model (IBM) that incorporates information on light exposure history and cell physiology coupled with a hydrodynamic model that simulates mixing and transport. The combined model successfully simulated cyanobacterial growth and respiration in a whole-lake nutrient enrichment experiment in a temperate lake (Peter Lake, Michigan, USA). The model also incorporates non-photochemical quenching (NPQ) to improve simulations of cyanobacteria biomass based on validation against cyanobacteria cell counts and chlorophyll concentration. The IBM demonstrated that physical processes (stratification and mixing) significantly affect the dynamics of NPQ in cyanobacteria. Cyanobacteria had high fluorescence quenching and long photo-physiological relaxation periods during stratification, and low quenching and rapid relaxation in response to low light exposure history as the mixing layer deepened. This work demonstrates that coupling adaptive physiological trait with physical mixing into models can improve our understanding and enhance predictions of bloom occurrences in response to environmental changes