Management of the phosphorus-cladophora dynamic at a site on lake Ontario using a multi-module bioavailable P model

The filamentous green alga Cladophora grows to nuisance proportions in Lake Ontario. Stimulated by high phosphorus concentrations, nuisance growth results in the degradation of beaches and clogging of industrial water intakes with attendant loss of beneficial uses. We develop a multi-module bioavailable phosphorus model to examine the efficacy of phosphorus management strategies in mitigating nuisance algal growth. The model platform includes modules simulating hydrodynamics (FVCOM), phosphorus-phytoplankton dynamics (GEM) and Cladophora growth (GLCMv3). The model is applied along a 25 km stretch of the Lake Ontario nearshore, extending east from Toronto, ON and receiving effluent from three wastewater treatment plants. Simulation results identify the Duffin Creek wastewater treatment plant effluent as a driving force for nuisance conditions of Cladophora growth, as reflected in effluent bioavailable phosphorus concentrations and the dimensions of the plant’s phosphorus footprint. Simulation results demonstrate that phosphorus removal by chemically enhanced secondary treatment is insufficient to provide relief from nuisance conditions. Tertiary treatment (chemically enhanced secondary treatment with ballasted flocculation) is shown to eliminate phosphorus-saturated conditions associated with the Duffin Creek wastewater treatment plant effluent, providing local relief from nuisance conditions. Management guidance presented here has wider application at sites along the highly urbanized Canadian nearshore of Lake Ontario

Iodinated NanoClusters as an inhaled CT contrast agent for lung visualization

Author's Pre-print: grey tick subject to Restrictions below, author can archive pre-print (ie pre-refereeing) Restrictions: Must obtain written permission from Editor Must not violate ACS ethical Guidelines Author's Post-print: grey tick subject to Restrictions below, author can archive post-print (ie final draft post-refereeing) Restrictions: If mandated by funding agency or employer/ institution If mandated to deposit before 12 months, must obtain waiver from Institution/Funding agency or use AuthorChoice 12 months embargo Publisher's Version/PDF: cross author cannot archive publisher's version/PDF General Conditions: On author's personal website, pre-print servers, institutional website, institutional repositories or subject repositories Non-Commercial Must be accompanied by set statement (see policy) Must link to publisher version Publisher's version/PDF cannot be use

Comment on Bachmann et al. (2013): A nonrepresentative sample cannot describe the extent of cultural eutrophication of natural lakes in the United States

In their recent paper, Bachmann et al. (2013) evaluate the extent to which natural lakes in the contiguous United States have been affected by cultural eutrophication since Europe-an settlement, using paleolimnological data collected during the 2007 National Lakes Assessment (NLA; U.S. Environ-mental Protection Agency [USEPA] 2009). The NLA sites were selected using a statistically valid sampling design that allows for the overall ecological condition of the nation’s lakes to be accurately characterized (USEPA 2009). Given the current consensus among limnologists regarding the prevalence of culturally eutrophic lakes (Finlayson and D’Cruz 2005; Carpenter et al. 2011), the conclusion of Bachmann et al. that ‘‘in the United States of America, the extent that natural lakes have been changed by cultural eutrophication does not seem to be large’’ (Bachmann et al. 2013, p. 950) is surprising. The findings of Bachmann et al. supporting this statement are not based on the entire NLA sample of natural lakes but rather on a subset of them. We demonstrate below that not only is this subset not representative of the entire population of natural lakes in the United States, but that it is biased toward lakes in regions with less anthropogenic activity and substantially lower nutrient concentrations. Consequently, we argue that the conclusions drawn by Bachmann et al. (2013) at the national scale are based upon a statistically flawed analysis

Foraging Behavior and Success of a Mesopelagic Predator in the Northeast Pacific Ocean: Insights from a Data-Rich Species, the Northern Elephant Seal

The mesopelagic zone of the northeast Pacific Ocean is an important foraging habitat for many predators, yet few studies have addressed the factors driving basin-scale predator distributions or inter-annual variability in foraging and breeding success. Understanding these processes is critical to reveal how conditions at sea cascade to population-level effects. To begin addressing these challenging questions, we collected diving, tracking, foraging success, and natality data for 297 adult female northern elephant seal migrations from 2004 to 2010. During the longer post-molting migration, individual energy gain rates were significant predictors of pregnancy. At sea, seals focused their foraging effort along a narrow band corresponding to the boundary between the sub-arctic and sub-tropical gyres. In contrast to shallow-diving predators, elephant seals target the gyre-gyre boundary throughout the year rather than follow the southward winter migration of surface features, such as the Transition Zone Chlorophyll Front. We also assessed the impact of added transit costs by studying seals at a colony near the southern extent of the species’ range, 1,150 km to the south. A much larger proportion of seals foraged locally, implying plasticity in foraging strategies and possibly prey type. While these findings are derived from a single species, the results may provide insight to the foraging patterns of many other meso-pelagic predators in the northeast Pacific Ocean

Using a model selection criterion to identify appropriate complexity in aquatic biogeochemical models

Aquatic biogeochemical models are widely used as tools for understanding aquatic ecosystems and predicting their response to various stimuli (e.g., nutrient loading, toxic substances, climate change). Due to the complexity of these systems, such models are often elaborate and include a large number of estimated parameters. However, correspondingly large data sets are rarely available for calibration purposes, leading to models that may be overfit and possess reduced predictive capabilities. We apply, for the first time, information-theoretic model-selection techniques to a set of spatially explicit (1D) algal dynamics models of varying parameter dimension. We demonstrate that increases in complexity tend to produce a better model fit to calibration data, but beyond a certain degree of complexity the benefits of adding parameters are diminished (the risk of overfitting becomes greater). The particular approach taken here is computationally expensive, but several suggestions are made as to how multimodel methods may practically be extended to more sophisticated models. © 2009 Elsevier B.V. All rights reserved

Modeling historical trends in Lake Superior total nitrogen concentrations

Nitrate concentrations in Lake Superior increased fivefold between 1900 and 1980, and have remained nearly constant since that time. Such rapid changes in concentration in a lake with a long hydraulic residence time (~190years) are surprising. We developed a model to better understand the causes of the historical changes and to predict future changes in nitrate concentrations. Historical loadings were reconstructed based on average national NOx emissions estimates, recent (past ~30years) atmospheric N deposition data, recent tributary concentration data, and basin-wide runoff estimates. Increases in atmospheric N deposition alone were insufficient to have resulted in the observed trends. However, model runs combining increased atmospheric deposition with increased tributary N loading and/or decreased burial+denitrification mid-century reproduced the observed accumulation of N. Because internal N fluxes are an order of magnitude greater than external fluxes, relatively small changes in the lake\u27s internal N cycle may produce relatively large changes in total N concentrations. Land-use changes in the watershed, particularly increases in logging activity, may have altered riverine N inputs. Regardless of the historical mechanisms leading to the rise in nitrate concentrations, it appears as though the system is currently at or is approaching peak N content. © 2010 International Association for Great Lakes Research

Can spatial heterogeneity explain the perceived imbalance in Lake Superior\u27s carbon budget? A model study

Lake Superior is the largest lake in the world by surface area, containing 10% of the world\u27s surface freshwater. Yet, little is known about its role within the regional carbon budget. Observational studies on Lake Superior have been limited by harsh winters and the challenges of covering such a vast expanse. To date, carbon budgets extrapolated from observational studies are largely out of balance and suggest a large efflux of carbon dioxide to the atmosphere (∼3 TgC/yr) that cannot be supported by the estimated net inputs into the lake ( \u3c 1 TgC/yr). We couple a hydrodynamic model of Lake Superior to an ecosystem model to understand the seasonal cycle of the partial pressure of carbon dioxide (pCO \u3c inf\u3e 2 ) in the lake surface waters, the resulting air-lake carbon dioxide (CO \u3c inf\u3e 2 ) fluxes, and whether spatial heterogeneity can explain the previously imbalanced carbon budget. The model sufficiently simulates lake productivity, circulation, respiration, pCO \u3c inf\u3e 2 , and chlorophyll. We find that the seasonal cycle of pCO \u3c inf\u3e 2 is generally a double sinusoidal curve during the simulated period of 1996-2001. The lake acts as a sink of carbon dioxide in summer and during late winter of cold years and as a source to the atmosphere during winter and spring. We find significant spatial heterogeneity of respiration in Lake Superior, with near-shore to offshore rates of respiration varying by two orders of magnitude. Thus, Lake Superior need not act as a significant source of carbon dioxide (∼0.5 TgC/yr) to the atmosphere in order to be consistent with in situ observations of respiration. © 2012. American Geophysical Union. All Rights Reserved

Temperature explains the formation of a metalimnetic oxygen minimum in a deep mesotrophic lake

Green Lake, a deep mesotrophic lake located in a primarily agricultural watershed in central Wisconsin, USA, has experienced annual metalimnetic oxygen minima since the early 20th century. However, the severity of the phenomenon has increased over time, and late-summer dissolved oxygen (DO) concentrations have typically been L−1 in recent years. In situ, high-frequency observations of oxygen depletion at multiple depths reveal that while DO consumption during stratification occurs most rapidly in the metalimnion, there is synchrony between DO time series extending into the hypolimnion. A biochemical oxygen demand-based modeling approach suggests that much of the relationship between water depth and respiration rates can be explained by differences in water temperature. The amount of labile organic matter present throughout the water column at the onset of stratification seems to be a primary determinant of the severity of the annual metalimnetic DO minimum in late summer. Productivity has increased in the lake as a result of increased nutrient loading and is the likely driver of the decrease in minimum DO concentrations. In addition, the onset and duration of stratification is an important factor in determining the severity of the DO minimum