Pathways to enhanced lake integrity: A Framework to assess the effectiveness of local lake associations

The promise of collaborative governance is to implement policies that address uncertain and multi‐scale environmental problems while also allowing local social systems to successfully adapt. The success of such efforts is contingent on the capacity of community‐based institutions such as lake associations to effect change. These organizations encapsulate the values communities hold for lakes and their catchments and can play a central role in managing the integrity of lakes’ freshwater resources. To this end, we develop a framework to delineate the pathways lake associations can take to contribute to the management of lakes and their catchments. We suggest the cornerstones of effective engagement in collaborative governance are the goals the organization sets for itself (mission), the capital that can be mobilized by the organization (capacity) and the activities the organization undertakes (actions). We propose measurable indicators for each component and suggest how the framework can be used to assess contributions of lake associations to multi‐scale governance. Finally, we suggest how this framework can be integrated with ecological monitoring frameworks as part of a long term social‐ecological research and monitoring program.     

Escherichia coli toxin and attachment genes in sand at Great Lakes recreational beaches

The United States Environmental Protection Agency recommends density thresholds for the fecal indicator organism Escherichia coli in order to ensure the safety of recreational waters. A number of studies published over the past ten years indicate that E. coli is encountered frequently in sand at recreational beaches. While a majority of the sand-associated E. coli may be commensal or environmental strains, the potential for pathogenic strains of E. coli to be present exists. Therefore, the aim of this study was to assess the presence of attachment and virulence genes associated with enteropathogenic and enterohemorrhagic strains of E. coli (EPEC and EHEC) in populations of E. coli recovered from swash zone sand from seven recreational beaches along Lake Huron and Lake St. Clair in eastern Michigan, USA. Genes coding for attachment proteins in EPEC and EHEC were very prevalent in sand E. coli, but genes coding for toxin genes were uncommon. The paucity of genes associated with E. coli toxins suggests that the EPEC and EHEC pathotypes are not common in sand; however, the high prevalence of genes associated with attachment in E. coli pathotypes suggests that these genes are being retained within the beach sand E. coli population.     

Approximation Schemes for Packing Splittable Items with Cardinality Constraints

We continue the study of bin packing with splittable items and cardinality constraints. In this problem, a set of n items must be packed into as few bins as possible. Items may be split, but each bin may contain at most?k (parts of) items, where k is some given parameter. Complicating the problem further is the fact that items may be larger than?1, which is the size of a bin. The problem is known to be strongly NP-hard for any fixed value of?k. We essentially close this problem by providing an efficient polynomial-time approximation scheme (EPTAS) for most of its versions. Namely, we present an efficient polynomial time approximation scheme for k=o(n). A?PTAS for k=Θ(n) does not exist unless P = NP. Additionally, we present dual approximation schemes for k=2 and for constant values of?k. Thus we show that for any ε>0, it is possible to pack the items into the optimal number of bins in polynomial time, if the algorithm may use bins of size 1+ε.     

Comparing online algorithms for bin packing problems

The relative worst-order ratio is a measure of the quality of online algorithms. In contrast to the competitive ratio, this measure compares two online algorithms directly instead of using an intermediate comparison with an optimal offline algorithm.     

The importance of benthos in weight of evidence sediment assessments--a case study

Sediment quality in a Texas reservoir subject to point and non-point sources of contaminants was assessed using the Sediment Quality Triad weight of evidence approach. Fifteen stations were sampled plus a reference station which, unfortunately, comprised a different habitat type than the other 15 stations. Accordingly, standard comparisons between reference and exposed stations were inappropriate. Interpretation of potential relationships between benthic community structure and sediment-associated contaminants was also confounded by differences in habitat-related characteristics (e.g., water depth and total organic carbon) within the reservoir. Multivariate analyses of the benthic community identified two station groupings separated primarily by habitat-related differences rather than contaminant-related toxicity. Laboratory toxicity tests and chemical analyses, including measures of bioavailability, did not differ consistently between the two community-based station groupings, indicating that toxicity resulting from chemical contamination was not the primary factor in observed community structure in the reservoir, although alterations to the benthos due to chemical contamination could not be ruled out in the absence of an appropriate reference comparison. Appropriately giving highest weight to resident benthic community structure, followed by the results of laboratory toxicity tests, then chemical analyses, provided the best possible assessment of chemical pollution in the absence of a suitable reference comparison. The alternative approach of relying on only sediment toxicity and chemistry data, without considering the full weight of evidence, would have provided misleading information.     

Probing protein structure by amino acid‐specific covalent labeling and mass spectrometry

For many years, amino acid‐specific covalent labeling has been a valuable tool to study protein structure and protein interactions, especially for systems that are difficult to study by other means. These covalent labeling methods typically map protein structure and interactions by measuring the differential reactivity of amino acid side chains. The reactivity of amino acids in proteins generally depends on the accessibility of the side chain to the reagent, the inherent reactivity of the label and the reactivity of the amino acid side chain. Peptide mass mapping with ESI‐ or MALDI‐MS and peptide sequencing with tandem MS are typically employed to identify modification sites to provide site‐specific structural information. In this review, we describe the reagents that are most commonly used in these residue‐specific modification reactions, details about the proper use of these covalent labeling reagents, and information about the specific biochemical problems that have been addressed with covalent labeling strategies. © 2008 Wiley Periodicals, Inc., Mass Spec Rev 28:785–815, 2009     

Gadolinium-containing copolymeric chelates—a new potential MR contrast agent

Rationale and objectives: To develop and partially characterize a new class of potential blood pool magnetic resonance (MR) contrast agents.Methods: Various copolymeric chelates of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) were prepared with differing molecular weights of polyethylene glycol (PEG) or polypropylene glycol (PPG) as linkers between the monomeric chelate units. Gadolinium content of the polymeric chelates was determined by atomic absorption spectra. Relaxivity of the polymeric chelates was measured at 1.5 Tesla and compared with Gadolinium-DTPA. MR angiography (MRA) was performed in rabbits comparing Gd-DTPA with Gd-copolymers.Results: The gadolinium content of the copolymeric chelates ranged from 2.95 to 22.2% on weight basis. The molecular weight of the PEG linkers in the copolymers ranged from about 150 to about 3400. Ther ₁ (1/T1, mM⁻¹ s⁻¹) for Gd-DTPA=4.1. Ther ₁ values for the different Gd-containing polymers ranged from 3.8 to 5.8, with the lowestr ₁ for the polymer prepared with the lowest-molecular-weight complex. The higher-molecular-weight complexes resulted in moderately higher relaxivity. MRA with Gd-copolymers, in rabbits, showed markedly greater vascular enhancement relative to an equivalent dose of Gd-DTPA. Vascular enhancement was much more sustained with the copolymeric agent and confined to vascular space; i.e. no appreciable background tissue enhancement—a reflection of distribution into extravascular fluid space—was observed.Conclusions: Relative to Gd-DTPA monomers, PEG-containing Gd-DTPA polymeric complexes provided moderate increases in relaxivity but markedly greater efficacy during in vivo MRA. In vitro relaxivity studies of Gd-copolymers showed only an approximately 50% increase inr ₁ relaxivity compared with Gd-DTPA. The PEG-containing complex's lack of rigidity may have diminished the effect of spin diffusion on relaxation, thereby accounting for this modest increase. The greater efficacy of Gd-copolymers during in vivo MRA may reflect compartmentalization within the vascular space and possibly enhanced relaxation of the macromolecular copolymers in the blood. Gd-copolymers are promising agents that merit additional study.