Cyanobacterial influence on diatom community lifeform dynamics in shallow subtropical lakes of Florida USA

Fragilarioid diatom taxa are often deemed ubiquitous in shallow lake systems. Their presence has been described as contributing to statistical noise in paleolimnological studies of cold-temperate lakes. In shallow, warm-temperate lakes of Florida, long-term transitions from assemblages dominated by Aulacoseira spp. to fragilarioid taxa, particularly Pseudostaurosira brevistriata, Staurosira construens var. venter, and Staurosirella pinnata, often occur. Distinctly higher limnetic nutrient optima are demonstrated by these fragilarioid taxa than by planktonic Aulacoseira spp. Community successions occur during eutrophication, and progressive replacement of Aulacoseira spp. and other planktonic taxa by fragilarioid taxa is concurrent with and apparently related to the onset of cyanobacterial dominance. We examine successions from Aulacoseira-dominated to fragilarioid-dominated assemblages in sediment cores from subtropical Florida lakes that have undergone eutrophication. Diatom profiles are compared with sedimented pigments, nitrogen stable isotopes of organic matter, and with silica accumulation rates. These study lakes have little if any macrophyte presence. Their light-extinction depths are extremely shallow, yet diatom communities are dominated by bottom-dwelling rather than planktonic taxa. Frequent wind-generated mixing, sometimes to lake bottoms, is sufficient to sustain the light needs of benthic and tychoplanktonic taxa. We conclude that assemblage changes generally are not caused by reduced water depths, silica limitation, nor increased incipient stratification, but that cyanobacteria are responsible for reducing planktonic Aulacoseira in favor of fragilarioid taxa. Cyanobacteria blooms persist over a wide seasonal range because of warm climate and high limnetic nutrient concentrations in Florida lakes. Cyanobacteria progressively displace and outcompete Aulacoseira and other planktonic taxa as eutrophication proceeds. Reduced light availability, changes in mineral/nutrient availability, and other aspects of competitive exclusion, such as cyanobacterial allelotoxins, might contribute to observed changes. Climate warming is not likely to account for Aulacoseira reduction as in colder regions because it is less pronounced in this subtropical district. Lakes with low nutrient levels and less cyanobacteria still sustain large Aulacoseira populations, and decreases in limnetic nutrients sometimes lead to the return of planktonic Aulacoseira. Rather than simply representing statistical noise for paleolimnological reconstructions, shifts to certain fragilarioid taxa indicate when subtropical Florida lakes progressed to hypereutrophic conditions that were marked by cyanobacterial proliferation.     

“A Mirror and a Lamp”: The Role of Power in the Rural Landscape Trajectory of the Ovens Region of Australia

Power relationships structure discourse and its influence on policy and rural land use planning, but little research has examined how this might be observed in the dynamics of rural landscape transition. In a qualitative case study of the Ovens catchment, Victoria, Australia, discursive power is observed through sites of tension between informant interpretations of past, present, and future landscapes and contemporary local decision making. Three main tensions and an observation emerged that suggest discourse and power can be observed through the transfer and support of social memory narratives. We conclude that the identification of tensions between stakeholder perceptions of the past, present, and future of their landscape; awareness of the influence of those interpretations on current decision making; and attention to social memory narratives can provide invaluable insights for those seeking to understand local relationships of power.     

Can Distrust Enhance Public Engagement? Insights From a National Survey on Energy Issues in Canada

Research examining the relationship between trust, public engagement, and natural resource management asserts that trust fosters positive behavior and enhanced cooperation. Yet some scholars are finding that certain kinds of distrust are helpful in achieving democratic outcomes by providing would-be participants with the motivation to engage in issues of public concern. This article seeks to clarify this apparent disjuncture in the trust literature by examining the multidimensional nature of trust as it relates to public engagement on energy-related issues in Canada. Based on a national online survey (n?=?3000) we use a binary probit model to explore the connections between trust, knowledge, and public engagement. About 70% of respondents had participated in at least one form of public engagement over the last 3 years. Drawing on a two-dimensional conception of trust, we find that general trust on its own is not positively linked to public engagement. A combination of general trust and skepticism, however, is positively associated with public engagement and confirms our hypothesis that at least some concern regarding credibility, bias, and vested interest can motivate public engagement. In this sense, trust is not uniformly good for public engagement. These results signal a need to further refine our assumptions about the relationship between public trust, public engagement and environmental governance.     

Mapping Farmer Identity: why,how, and what does it tell us?

Rural areas in developed economies are becoming increasingly multi-functional in that their character is being shaped by a mix of production, consumption and conservation values. Agriculture may remain the dominant land use, but many landholders do not see themselves as farmers by occupation. Researchers have demonstrated that occupational identity influences land use and management. However, efforts to explore the influence of occupational identity often rely on surrogate measures and have largely ignored identity theory. We build on research demonstrating that collective identity theory can be used to develop a valid and reliable measure of farmer identity and to then classify rural landholders across a natural resource management (NRM) region. The contribution of this paper is to explain how that measure of farmer identity can be mapped and then demonstrate the relevance of doing so for regional NRM in Australia. As expected, farmer identity varied across the case study region with distance from urban centres, and across different environmental assets. Those findings should lead to a more targeted approach to landholder engagement in NRM. We suggest that farmer identity (i.e. farmer-collective occupational identity construct; F-COIC) might provide a next step for responding to the challenges of interpreting and mapping multi-functionality.     

Linked and Independent African American Migration from Los Angeles

This paper examines African American migration from Los Angeles County, 1985–1990, utilizing Census Public Use Microdata Samples (PUMS) data to identify linkages between Los Angeles migrants and others in destination households. Increased migration to suburban counties and to regions outside of the South, since 1975–1980, suggests an overall diversification of African American migration. The majority of outmigrants were “independent” because they moved into 1990 destination households that contained only migrants from the same origin, Los Angeles County. Others were linked either to nonmovers or to migrants from other places in destination households. A discriminant analysis suggests that many migrants linked to nonmigrants were moving for assistance, depending on others at the destination for housing and financial resources. In contrast, independent migrants have the personal resources to set up their own destination households.     

Human Dimensions of Climate Change: Cultural Theory and Collective Action

Mobilizing collective action to cope with climate change is difficult at any level, but the larger the community the more difficult the task. How to achieve cooperation in the common interest without imposing excessive governmental coercion is a fundamental political conundrum. Using the cultural typology suggested by Cultural Theory (CT), this paper explores diverse worldviews that inform individual and collective attitudes relevant to climate change. Responses from a sample of 441 individuals to statements drawn from the public discourse on environmental issues are used to classify respondents according to the cultural types posited by CT. Analysis indicates that most respondents mix elements of CT's egalitarianism, hierarchy, and individualism, though many individuals clearly lean toward one or another of the cultural types. There seems to be a melding of individualistic and hierarchic elements in opposition to egalitarian elements. Definitions of what is natural, fair and right – of equity – are fundamental issues between cultures, and non-coercive resolution of issues may be promoted by exploring cultural interstices, where cosmological boundaries are weakest. The cultural typology used in Cultural Theory, less spatially or temporally bound than some other typologies, promises to be a useful analytic tool in exploring cultural differences and overlaps.     

Critical loads of acidity for Irish lakes

Critical loads of acidity have been estimated for Irish lakes (277) using survey data from the Republic of Ireland and Northern Ireland, and compatible inputs and methods across both regions. This is the first trans-region application of the Steady-State Water Chemistry model for the island of Ireland. Results indicate that a small percentage of lakes (10.8%, 30 lakes) have low critical loads of acidity (<50.0 mmol_c m^-2 yr^-1). Based on bulk sulphate deposition, exceedance of critical load was observed in 6.9% of the sampled lakes (19 lakes). Inferences relating to the whole lake population cannot be made, as statistical lake surveys were not carried out. However, as the surveys were weighted towards acid-sensitive lakes, the current study suggests that Irish lakes are not under a significant threat from anthropogenic acidification. The acidifying impact of nitrogen was incorporated into the exceedance calcula tion by superimposing the present leaching of nitrogen onto sulphate deposition. This increased exceedance by ഌ% (i.e., from 11 to 19 lakes). Despite the potential uncertainties associated with using default values and relationships in the Steady-State Water Chemistry model, uncertainty analysis indicated that the critical loads were relatively stable. The critical acid neutralising capacity limit (specified water quality criterion) had the greatest effect on the critical load. In the current study, a catchment dependent limit was employed (ranged: 0-50 7mol_c L^-1; mean: 35 7mol_c L^-1) rather than a single fixed value.     

Contributions of coastal and watershed energy sources to secondary production in a Northeastern Pacific Estuary

We examined the relationship between variation in origin of organic matter and benthic secondary production in a shallow, macrotidal estuary on the United States Pacific Northwest coast, Willapa Bay, Washington. Spatial variation in energy sources and benthic productivity were investigated at both local (vertical height and cross-bank components) and regional (sites within the bay) scales. We determined the stable carbon isotope ratios of oysters (Crassostrea gigas) to evaluate marine versus terrestrial energy sources, compared growth rates of oysters, and made time series measurements of physical variablest at estuarine channel and intertidal stations. The stable carbon isotope ratios of oysters ranged from ?22‰ in inner portions of the estuary to ?18‰ near the mouth and oysters grown on the substrate surface were enriched in δ¹³C relative to those grown in the water column. These patterns are consistent with terrigenous inputs away from the estuary mouth and benthic microalgae in the diets of on-bottom oysters. The highest oyster growth was found at an inner estuary site where riverine inputs are relatively high and coincided, with high ammonium in the water column. However, for most sites in Willapa Bay, oyster growth actually declined away from the estuary mouth. Reducing the time available for feeding by transplanting oysters higher in the intertidal zone had significant negative effects on growth(e.g., a reduction of 27–35% over 0.5 m). Despite the fact that oysters grown on-bottom had access to different resources than those in the water column, their growth was slower at amy given tidal elevation, which may be due to on-bottom competition with other suspension feeders, boundary layer effects, or interference from turbidity. In a practical sense, oyster growers have been adjusting to allochthonous energetic support of food webs in Willapa Bay for more than a century, because they have traditionally moved oysters from southern parts of the bay where recruitment is relatively high to beds where market-size oysters can be grown closer to the mouth. This study provides mechanistic support for these practices and suggests that climatic events on a variety of temporal scales (Pacific Decadal Oscillation, upwelling events) could have economic consequences for aquaculture.     

Assessing the Efficacy of Transition Theory to Identify Industry Transformation: a case study examining the deregulation of Australia's dairy industry

Transformation is a key concept in social-ecological systems research, and transition theory in particular; however, the essential elements of a transformation are yet to be clearly articulated. This article explores the changes that took place when Australian governments deliberately set out to restructure the Australian dairy industry. Using the subtropical dairy industry as a case study, we conducted semi-structured interviews with industry stakeholders. Our analysis was structured around transition concepts thus testing the framework's efficacy. We found that deregulation substantially altered the culture of the industry and the structure and working practices of the production system, supply chain, industry organisations and government agencies. Transition theory and its concepts provided a useful framework to explain how systemic change transformed the industry. Transition theory identified the multi-scalar nature of the interactions between structure and practice and the social and power relationships that reinforced change.