Effects of physical disturbance on phosphorus uptake in temperate stream biofilms

Microbial biofilm nutrient uptake kinetics can provide insight into assimilative mechanisms that regulate stream primary productivity. While kinetic experiments are often performed, little work has estimated uptake in connection with disturbance (removal) or detailed the effects that common scour events may have on benthic microbes; therefore, the goal of this study was to evaluate physical disturbances on benthic stream biofilms to determine effects on phosphorus (P) uptake rate, physiological capability, and abiotic sorption. Artificial substrata were collected from 2 reaches along a temperate stream; resident biofilms were either removed via abrasion (disturbed) or left intact. A series of short-term radiotracer (H333PO4) experiments were then conducted to measure P uptake. In vivo autofluorescence was measured as a proxy of algal physiological condition. The experiments showed no difference in P-uptake rates (μgP/μgChl/d) between disturbed (x̄ = 0.77 ± 0.11 [SE] μgP/μgChl/d) and intact (x̄ = 0.91 ± 0.17 μgP/μgChl/d) biofilms (t = 0.69, p = 0.492, df = 33). Further, microbial physiology was not depressed by physical disturbance. While killed samples yielded significantly lower uptake compared to live biota (F = 17.51, p = 0.001), abiotic sorption still accounted for a moderate fraction (range = 0.021–0.038 μgP/μgChl/d) of total uptake and thus warrants estimation in metabolic studies. Overall, these findings lend credence to numerous experiments that investigate benthic microbial physiologic responses post-disturbance and highlight the importance of uptake following common physical disturbances that occur in turbulent environments. In addition, our work measured several kinetic constants across both disturbance and temporal gradients, and we discuss their significance within a physiological framework

The importance of zooplankton‐protozoan trophic couplings in Lake Michigan

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109824/1/lno19913671335.pd

Ratios of Community Respiration to Photosynthesis and Rates of Primary Production in Lake Erie Via Oxygen Isotope Techniques

ABSTRACT. To evaluate levels of primary production and community metabolism in Lake Eri

Physical-Biological Coupling in Southern Lake Michigan: Influence of Episodic Sediment Resuspension on Phytoplankton

The influence of episodic, sediment resuspension on phytoplankton abundance/volume and composition, the photosynthetic maximum rate (P B max ) and efficiency (α B ), and chlorophyll-specific growth (μ Chl ) was evaluated during the spring isothermal period in southern Lake Michigan (Laurentian Great Lakes, USA). Resuspension altered the nutrient and light climate of nearshore waters; light attenuation (K d ) and phosphorus concentrations corresponded (p ≤ 0.0001 and p ≤ 0.001, respectively) with concentrations of suspended particulate matter (SPM). Phytoplankton cell volume and diatom cell abundance and volume were not associated with SPM concentrations (p > 0.05). Diatom composition displayed spatial dissimilarities corresponding with resuspension (p ≤ 0.001); small centric diatoms exhibiting meroplanktonic life histories and pennate diatoms considered benthic in origin were most abundant within SPM-impacted, nearshore waters whereas taxa typically comprising assemblages in optically-clear, offshore waters and the basin-wide, spring bloom were not. Values of P B max and α B corresponded (p ≤ 0.0001) with both K d coefficients and SPM concentrations, potentially reflecting increased light harvesting/utilization within impacted assemblages. However, integral production was inversely associated with K d coefficients and SPM concentrations (p < 0.0001) and photosynthesis was light-limited (or nearly so) for most assemblages. Although μ Chl values corresponded with K d coefficients (p ≤ 0.05), values were quite low (x ± S.E., 0.10 ± 0.004 d -1 ) throughout the study. Most likely, distinct rate processes between SPM- and non-impacted assemblages reflected short-term compositional (and corresponding physiological) variations due to infusion of meroplankton and/or tributary-derived phytoplankton. Overall, resuspension appears to have little, if any, long-term impact upon the structure and function of the lake’s phytoplankton.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41735/1/10452_2004_Article_5149255.pd

Understanding the meaning of medications for patients: The medication experience

Objective: To understand and describe the meaning of medications for patients. Methods: A metasynthesis of three different, yet complementary qualitative research studies, was conducted by two researchers. The first study was a phenomenological study of patients’ medication experiences that used unstructured interviews. The second study was an ethnographic study of pharmaceutical care practice, which included participant observation, in-depth interviews and focus groups with patients of pharmaceutical care. The third was a phenomenological study of the chronic illness experience of medically uninsured individuals in the United States and included an explicit aim to understand the medication experience within that context. The two researchers who conducted these three qualitative studies that examined the medication experience performed the meta-synthesis. The process began with the researchers reviewing the themes of the medication experience for each study. The researchers then aggregated the themes to identify the overlapping and similar themes of the medication experience and which themes are sub-themes within another theme versus a unique theme of the medication experience. The researchers then used the analytic technique, “free imaginative variation” to determine the essential, structural themes of the medication experience. Results: The meaning of medications for patients was captured as four themes of the medication experience: a meaningful encounter; bodily effects; unremitting nature; and exerting control. The medication experience is an individual’s subjective experience of taking a medication in his daily life. It begins as an encounter with a medication. It is an encounter that is given meaning before it occurs. The experience may include positive or negative bodily effects. The unremitting nature of a chronic medication often causes an individual to question the need for the medication. Subsequently, the individual may exert control by altering the way he takes the medication and often in part because of the gained expertise with the medication in his own body. Conclusion: The medication experience is a practice concept that serves to understand patients’ experiences and to understand an individual patient’s medication experience and medication-taking behaviors in order to meet his or her medication-related needs

The Changing Face of Winter: Lessons and Questions From the Laurentian Great Lakes

Among its many impacts, climate warming is leading to increasing winter air temperatures, decreasing ice cover extent, and changing winter precipitation patterns over the Laurentian Great Lakes and their watershed. Understanding and predicting the consequences of these changes is impeded by a shortage of winter-period studies on most aspects of Great Lake limnology. In this review, we summarize what is known about the Great Lakes during their 3–6 months of winter and identify key open questions about the physics, chemistry, and biology of the Laurentian Great Lakes and other large, seasonally frozen lakes. Existing studies show that winter conditions have important effects on physical, biogeochemical, and biological processes, not only during winter but in subsequent seasons as well. Ice cover, the extent of which fluctuates dramatically among years and the five lakes, emerges as a key variable that controls many aspects of the functioning of the Great Lakes ecosystem. Studies on the properties and formation of Great Lakes ice, its effect on vertical and horizontal mixing, light conditions, and biota, along with winter measurements of fundamental state and rate parameters in the lakes and their watersheds are needed to close the winter knowledge gap. Overcoming the formidable logistical challenges of winter research on these large and dynamic ecosystems may require investment in new, specialized research infrastructure. Perhaps more importantly, it will demand broader recognition of the value of such work and collaboration between physicists, geochemists, and biologists working on the world\u27s seasonally freezing lakes and seas

Benthic algal response to N and P enrichment along a pH gradient

Nutrient enrichment and its effect on benthic algal growth, community composition, and average cell size was assessed across two sites of differing pH within a single habitat. Nutrients were added using in situ substrata, which released either N, P, or no additional nutrients (controls) at each site for 21 days. Upon collection, chlorophyll and biovolume standing stocks of the attached algal microflora were measured. Chlorophyll concentration was different among all treatments, accumulating greatest on P, followed by N, and the least on C substrata (P < 0.001) and was highest at site-2 (P < 0.001), while total algal biovolume was highest on P compared to both N and C substrata (P < 0.05) and did not vary between sites. Increased growth on P substrata was due to the enhanced biovolume of filamentous green algae, although the affected taxa varied between sites. Biovolume to cell density ratios (as a measure of average cell size) were highest on P substrata over both N-enriched and control substrata (P < 0.05) and this pattern was similar between sites. Progression towards a community composed of larger cells following P enrichment observed along this pH gradient, seems to be related to the dominance of larger celled filamentous green algae. Thus, nutrients exhibited greater control on benthic algal growth than did changes in hydrogen ion concentration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42877/1/10750_2004_Article_BF00007599.pd

The colonization of Smith's Fen and Bryant's Bog by diatom communities.

http://deepblue.lib.umich.edu/bitstream/2027.42/53493/1/1928.pdfDescription of 1928.pdf : Access restricted to on-site users at the U-M Biological Station

The effects of phosphate and nitrate stimulation on periphyton communities occurring in areas of varying pH in Inverness Mud Lake Bog, Michigan.

http://deepblue.lib.umich.edu/bitstream/2027.42/53590/1/2026.pdfDescription of 2026.pdf : Access restricted to on-site users at the U-M Biological Station