Phosphorus Limitation, Uptake, and Turnover in Benthic Stream Algae

In this chapter, three different aspects of P utilization by benthic algae will be covered: (1) assessment of P limitation, (2) measurement of P uptake rates, and (3) determination of the release rate of P (expressed as the turnover rate). We note two caveats regarding this chapter. First, we focus exclusively on inorganic P; it is likely that dissolved organic phosphorus plays an important, albeit relatively undefined role, in the nutrient dynamics of freshwater algae (cf. Hwang et al., 1998; Pant et al., 2002), especially in P-limited environments (Karl and Björkman, 2015). However, treatment of this topic is beyond the scope of this chapter (but see Chapter 24). Second, although we use the term benthic algae throughout the chapter, it should be noted that the benthic algae attached to submerged substrata in streams usually exist as part of a complex assemblage variously referred to as periphyton, aufwuchs, or biofilm. This assemblage usually consists of algae, bacteria, fungi, and meiofauna (see Chapters 9e11, 14) that exist within a mucilaginous, poly- saccharide matrix (Lock et al., 1984), and each biotic group has different affinities for P. Indeed, even within a group, P uptake and cycling may be influenced by the abundance of different species and growth forms (cf. Steinman et al., 1992; Davies and Bothwell, 2012)

Effects of water level fluctuation and sediment–water nutrient exchange on phosphorus biogeochemistry in two coastal wetlands

Freshwater coastal wetlands are sensitive to drying and wetting events (DWE), associated with water level fluctuations. Prior studies have shown that DWE influence sediment–water nutrient exchange, but the fate of these nutrients has received much less attention. To address this information gap, we investigated how microbial (i.e., bacteria and phytoplankton) structure and function respond to DWE-induced release of nutrients from the sediment of mesotrophic and eutrophic coastal wetlands. Our approach was three-fold: (1) sediment from each wetland was subjected to a desiccation (2 month) and re-wetting (2 days) period in the laboratory; (2) the overlying water column from the DWE was measured for nutrient concentration; and (3) we conducted a microbial response experiment using the water from either DWE experiment (containing the nutrients released during the DWE) or with added nutrients obtained from commercially available sources (but at similar concentrations to those released from the sediments), to test the effect of nutrient concentration and source on microbes inhabiting the water column and their role in the fate of the released nutrients, in particular phosphate (Pi). In both coastal wetlands, the microbial community structure in the water column (absolute and relative abundance of different microbial groups) was modified by bacteria resuspended from the sediment after re-wetting. However, results from the microbial response experiments showed that the microbial communities did not grow following inputs of commercially available nutrients or release of sediment nutrients. In Pi amended treatments, Pi uptake rates increased but not enough to reduce Pi turnover time to values measured in the control. As a result, Pi concentration and turnover remained high. In coastal wetlands with limited hydrologic exchange, these elevated nutrients will accumulate and lead to further eutrophication. However, in open coastal wetlands, with substantial hydrologic exchange, advected nutrients may influence biological activity in the nearshore zone

Effects of current velocity, irradiance, and herbivory on algal assemblages in laboratory streams

Effects of current velocity, irradiance, and grazing on the biomass, taxonomic structure, physiognomy, and chemical composition of lotic algal assemblages were investigated. Four experiments, lasting 32 to 75 days, were conducted in laboratory streams to determine how these factors affect algal assemblages singly, and in concert with each other. Regardless of light level, low current velocities (5 cm.s⁻¹) enhanced initial rates of colonization, presumably because of high settling rates. However, in streams exposed to equal irradiances, greater biomass levels eventually developed in streams with high current velocities (15 cm.s⁻¹). Few taxonomic differences could be attributed solely to current velocity regimes. Algal assemblages exposed to high (400 and 150) as opposed to low (50 and 15 μE.m⁻²s⁻¹) irradiances were characterized by higher biomass, a greater amount of filamentous chlorophytes, and lower concentrations of total lipid and the 18:1 and 20:5 fatty acids. The physiognomy of the assemblage was also more complex at high irradiances. Effects of grazing on taxonomic structure were primarily a function of algal growth form and herbivore feeding behavior. Large, overstory cells were vulnerable to grazing and decreased in relative abundance as grazing pressure increased, while small, adnate cells increased in relative abundance. The snail Juga silicula had little effect on algal dynamics at low densities (125/stream = 62/m²), although at higher snail densities (500 and 1000/stream) and at all densities of the caddisfly Dicosmoecus gilvipes, grazing resulted in low algal biomasses and a dominance of adnate cells. Fatty acids were more robust indicators of algal taxonomic structure than amino acids. A separate experiment showed that at densities of 500 snails/stream (250/m²), algal biomass levels were similar in grazed and ungrazed streams by day 43 in channels exposed to 100 and 400 μE.m⁻².s⁻¹. At 15 μE.m⁻².s⁻¹, algal biomass levels were similar (and low) throughout the experiment. Grazing reduced amounts of taxa with large growth forms, regardless of irradiance level. A detailed process model of herbivory was developed, which allows both quantitative (i.e. biomass) and qualitative (i.e. taxonomic and chemical composition) components to be assessed. The proposed model can be used to generate hypotheses about how algal assemblages respond to current velocity, irradiance, and grazing in natural streams

Joint analysis of stressors and ecosystem services to enhance restoration effectiveness

With increasing pressure placed on natural systems by growing human populations, both scientists and resource managers need a better understanding of the relationships between cumulative stress from human activities and valued ecosystem services. Societies often seek to mitigate threats to these services through large-scale, costly restoration projects, such as the over one billion dollar Great Lakes Restoration Initiative currently underway. To help inform these efforts, we merged high-resolution spatial analyses of environmental stressors with mapping of ecosystem services for all five Great Lakes. Cumulative ecosystem stress is highest in near-shore habitats, but also extends offshore in Lakes Erie, Ontario, and Michigan. Variation in cumulative stress is driven largely by spatial concordance among multiple stressors, indicating the importance of considering all stressors when planning restoration activities. In addition, highly stressed areas reflect numerous different combinations of stressors rather than a single suite of problems, suggesting that a detailed understanding of the stressors needing alleviation could improve restoration planning. We also find that many important areas for fisheries and recreation are subject to high stress, indicating that ecosystem degradation could be threatening key services. Current restoration efforts have targeted high-stress sites almost exclusively, but generally without knowledge of the full range of stressors affecting these locations or differences among sites in service provisioning. Our results demonstrate that joint spatial analysis of stressors and ecosystem services can provide a critical foundation for maximizing social and ecological benefits from restoration investments. www.pnas.org/lookup/suppl/doi:10.1073/pnas.1213841110/-/DCSupplementa

Rating impacts in a multi‐stressor world: a quantitative assessment of 50 stressors affecting the Great Lakes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/116318/1/eap2015253717.pd

Epidemiological Interactions between Urogenital and Intestinal Human Schistosomiasis in the Context of Praziquantel Treatment across Three West African Countries

© 2015 Knowles et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article

Hurricane Effects on a Shallow Lake Ecosystem and Its Response to a Controlled Manipulation of Water Level

In order to reverse the damage to aquatic plant communities caused by multiple years of high water levels in Lake Okeechobee, Florida (U.S.), the Governing Board of the South Florida Water Management District (SFWMD) authorized a "managed recession" to substantially lower the surface elevation of the lake in spring 2000. The operation was intended to achieve lower water levels for at least 8 weeks during the summer growing season, and was predicted to result in a large-scale recovery of submerged vascular plants. We treated this operation as a whole ecosystem experiment, and assessed ecological responses using data from an existing network of water quality and submerged plant monitoring sites. As a result of large-scale discharges of water from the lake, coupled with losses to evaporation and to water supply deliveries to agriculture and other regional users, the lake surface elevation receded by approximately 1 m between April and June. Water depths in shoreline areas that historically supported submerged plant communities declined from near 1.5 m to below 0.5 m. Low water levels persisted for the entire summer. Despite shallow depths, the initial response (in June 2000) of submerged plants was very limited and water remained highly turbid (due at first to abiotic seston and later to phytoplankton blooms). Turbidity decreased in July and the biomass of plants increased. However, submerged plant biomass did not exceed levels observed during summer 1999 (when water depths were greater) until August. Furthermore, a vascular plant-dominated assemblage (Vallisnera, Potamogeton, and Hydrilla) that occurred in 1999 was replaced with a community of nearly 98% Chara spp. (a macro-alga) in 2000. Hence, the lake’s submerged plant community appeared to revert to an earlier successional stage despite what appeared to be better conditions for growth. To explain this unexpected response, we evaluated the impacts that Hurricane Irene may have had on the lake in the previous autumn. In mid-October 1999, this category 1 hurricane passed just to the south of the lake, with wind velocities over the lake surface reaching 90 km h-1 at their peak. Output from a three-dimensional hydrodynamic / sediment transport model indicates that during the storm, current velocities in surface waters of the lake increased from near 5 cm s-1 to as high as 100 cm s-1. These strong velocities were associated with large-scale uplifting and horizontal transport of fine-grained sediments from the lake bottom. Water quality data collected after the storm confirmed that the hurricane resulted in lake-wide nutrient and suspended solids concentrations far in excess of those previously documented for a 10-year data set. These conditions persisted through the winter months and may have negatively impacted plants that remained in the lake at the end of the 1999 growing season. The results demonstrate that in shallow lakes, unpredictable external forces, such as hurricanes, can play a major role in ecosystem dynamics. In regions where these events are common (e.g., the tropics and subtropics), consideration should be given to how they might affect long-term lake management programs

Part II, Provider perspectives: should patients be activated to request evidence-based medicine? a qualitative study of the VA project to implement diuretics (VAPID)

<p>Abstract</p> <p>Background</p> <p>Hypertension guidelines recommend the use of thiazide diuretics as first-line therapy for uncomplicated hypertension, yet diuretics are under-prescribed, and hypertension is frequently inadequately treated. This qualitative evaluation of provider attitudes follows a randomized controlled trial of a patient activation strategy in which hypertensive patients received letters and incentives to discuss thiazides with their provider. The strategy prompted high discussion rates and enhanced thiazide-prescribing rates. Our objective was to interview providers to understand the effectiveness and acceptability of the intervention from their perspective, as well as the suitability of patient activation for more widespread guideline implementation.</p> <p>Methods</p> <p>Semi-structured phone interviews were conducted with 21 primary care providers. Interviews were transcribed verbatim and reviewed by the interviewer before being analyzed for content. Interviews were coded, and relevant themes and specific responses were identified, grouped, and compared.</p> <p>Results</p> <p>Of the 21 providers interviewed, 20 (95%) had a positive opinion of the intervention, and 18 of 20 (90%) thought the strategy was suitable for wider use. In explaining their opinions of the intervention, many providers discussed a positive effect on treatment, but they more often focused on the process of patient activation itself, describing how the intervention facilitated discussions by informing patients and making them more pro-active. Regarding effectiveness, providers suggested the intervention worked like a reminder, highlighted oversights, or changed their approach to hypertension management. Many providers also explained that the intervention 'aligned' patients' objectives with theirs, or made patients more likely to accept a change in medications. Negative aspects were mentioned infrequently, but concerns about the use of financial incentives were most common. Relevant barriers to initiating thiazide treatment included a hesitancy to switch medications if the patient was at or near goal blood pressure on a different anti-hypertensive.</p> <p>Conclusions</p> <p>Patient activation was acceptable to providers as a guideline implementation strategy, with considerable value placed on the activation process itself. By 'aligning' patients' objectives with those of their providers, this process also facilitated part of the effectiveness of the intervention. Patient activation shows promise for wider use as an implementation strategy, and should be tested in other areas of evidence-based medicine.</p> <p>Trial registration</p> <p>National Clinical Trial Registry number NCT00265538</p

Nurse-Led Medicines' Monitoring for Patients with Dementia in Care Homes: A Pragmatic Cohort Stepped Wedge Cluster Randomised Trial

People with dementia are susceptible to adverse drug reactions (ADRs). However, they are not always closely monitored for potential problems relating to their medicines: structured nurse-led ADR Profiles have the potential to address this care gap. We aimed to assess the number and nature of clinical problems identified and addressed and changes in prescribing following introduction of nurse-led medicines' monitoring.Pragmatic cohort stepped-wedge cluster Randomised Controlled Trial (RCT) of structured nurse-led medicines' monitoring versus usual care.Five UK private sector care homes.41 service users, taking at least one antipsychotic, antidepressant or anti-epileptic medicine.Nurses completed the West Wales ADR (WWADR) Profile for Mental Health Medicines with each participant according to trial step.Problems addressed and changes in medicines prescribed.Information was collected from participants' notes before randomisation and after each of five monthly trial steps. The impact of the Profile on problems found, actions taken and reduction in mental health medicines was explored in multivariate analyses, accounting for data collection step and site.Five of 10 sites and 43 of 49 service users approached participated. Profile administration increased the number of problems addressed from a mean of 6.02 [SD 2.92] to 9.86 [4.48], effect size 3.84, 95% CI 2.57-4.11, P <0.001. For example, pain was more likely to be treated (adjusted Odds Ratio [aOR] 3.84, 1.78-8.30), and more patients attended dentists and opticians (aOR 52.76 [11.80-235.90] and 5.12 [1.45-18.03] respectively). Profile use was associated with reduction in mental health medicines (aOR 4.45, 1.15-17.22).The WWADR Profile for Mental Health Medicines can improve the quality and safety of care, and warrants further investigation as a strategy to mitigate the known adverse effects of prescribed medicines.ISRCTN 48133332