Biomass and productivity of seagrasses in Africa

There is growing interest in carbon stocks and flows in seagrass ecosystems, but recent global reviews suggest a paucity of studies from Africa. This paper reviews work on seagrass productivity, biomass and sediment carbon in Africa. Most work was conducted in East Africa with a major geographical gap in West Africa. The mean above-ground, below-ground and total biomasses from all studies were 174.4, 474.6 and 514 g DW m-2, respectively with a global range of 461-738 g DW m-2. Mean annual production rate was 913 g DW m-2 yr-1 (global range 816 - 1012 g DW m-2 yr-1). No studies were found giving sediment organic carbon, demonstrating a major gap in seagrass blue carbon work. Given the small numbers of relevant papers and the large geographical areas left undescribed in Africa, any conclusions remain tentative and much remains to be done on seagrass studies in Africa

Carbon storage in the seagrass meadows of Gazi Bay, Kenya

Vegetated marine habitats are globally important carbon sinks, making a significant contribution towards mitigating climate change, and they provide a wide range of other ecosystem services. However, large gaps in knowledge remain, particularly for seagrass meadows in Africa. The present study estimated biomass and sediment organic carbon (Corg) stocks of four dominant seagrass species in Gazi Bay, Kenya. It compared sediment Corg between seagrass areas in vegetated and un-vegetated ‘controls’, using the naturally patchy occurence of seagrass at this site to test the impacts of seagrass growth on sediment Corg. It also explored relationships between the sediment and above-ground Corg, as well as between the total biomass and above-ground parameters. Sediment Corg was significantly different between species, range: 160.7–233.8 Mg C ha-1 (compared to the global range of 115.3 to 829.2 Mg C ha-1). Vegetated areas in all species had significantly higher sediment Corg compared with un-vegetated controls; the presence of seagrass increased Corg by 4–6 times. Biomass carbon differed significantly between species with means ranging between 4.8–7.1 Mg C ha-1 compared to the global range of 2.5–7.3 Mg C ha-1. To our knowledge, these are among the first results on seagrass sediment Corg to be reported from African seagrass beds; and contribute towards our understanding of the role of seagrass in global carbon dynamics

Does Proximity to Retailers Influence Alcohol and Tobacco Use Among Latino Adolescents?

Despite decades of research surrounding determinants of alcohol and tobacco (A&T) use among adolescents, built environment influences have only recently been explored. This study used ordinal regression on 205 Latino adolescents to explore the influence of the built environment (proximity to A&T retailers) on A&T use, while controlling for recognized social predictors. The sample was 45% foreign-born. A&T use was associated with distance from respondents’ home to the nearest A&T retailer (−), acculturation (+), parents’ consistent use of contingency management (−), peer use of A&T (+), skipping school (+), attending school in immediate proximity to the US/Mexico border (+), and the interaction between the distance to the nearest retailer and parents’ consistent use of contingency management (+). The association between decreasing distance to the nearest A&T retailer and increased A&T use in Latino adolescents reveals an additional risk behavior determinant in the US–Mexico border region

NYS HIGH SCHOOL GRADUATION RATE DISPROPORTIONALITY

This quantitative study examines the impact that social contextual factors, such as racial composition, segregation, socioeconomic status, and school factors, such as per-pupil expenditure, student-to-teacher ratio, and school size have on the White-Black and White-Hispanic high school graduation rates within New York State school districts. Theoretically, I frame my study using Nasir and Hand’s (2006) Sociocultural Theory Framework, which addresses the intersectionality of race, culture, and inherent learning biases that impact minoritized students educated in incompatible historical school structures. The dissertation addresses several research questions, such as (1) What determines the variation of cohort graduation rates in NYS school districts; (2) The characteristics of districts that explain the variability in graduation rates; (3) The variation of race-specific cohort graduation rates in NYS school districts; (4) The factors that explain the variability in NYS graduation rates. SPSS and HLM software are used to analyze EDFacts’ adjusted cohort graduation rates by subgroup for all public high schools in New York State from 2010-17. The significance of this dissertation is to identify key school and social contextual factors within NYS schools that enable Black and Hispanic students to thrive academically. The findings of this dissertation determine that social contextual factors, particularly SES, are highly predictive of student achievement

The relationship between carbon and biovolume in marine microbial mesocosms under different nutrient regimes

Nutrient manipulation experiments were conducted on a natural planktonic community in outdoor mesocosms. Inorganicnitrogen (N) and silicon (Si) were added to achieve N: Si ratios of 1:1 and 4: 1. Total particulate carbon (PC) biomass ofthe microbial assemblage was determined by elemental analysis. Cell volume measurements by microscope on individualcomponents of the community (bacteria, diatoms, photosynthetic nano¯agellates, heterotrophic nano¯agellates,dino¯agellates and ciliates) were also made. We applied published C:volume relationships to determine the volumeestimated C content (CBV) of these microbial groups and hence of the total assemblage. The total CBV and total PC werecompared to test the applicability of C:volume relationships under different nutrient regimes both before and after nutrientexhaustion. For initial N: Si ratios of 1: 1, prior to nutrient exhaustion, the relationship between CBV and PC was linearwith a gradient of approximately 1, (0±99³0±06), indicating that the published C:volume relationships accurately predictedthe C content of the microbial assemblage. For N: Si ratios of 4: 1, a linear relationship was again evident between CBVand PC (slope : 1±36³0±08). However, statistical comparison using a general linear model indicated that the gradient of thisrelationship differed signi®cantly from that when the N: Si ratio was 1: 1, and hence CBV overestimated elemental C. Forboth N: Si ratios, subsequent to nutrient exhaustion (N or Si), and hence when the diatom fraction of the microbialassemblage was in yield-limited post-exponential phase, the two measures of biomass were not well correlated. Thisindicated that measured cytoplasmic cell volume was a poor indicator of C biomass within the microbial assemblage innutrient-deplete conditions

Microalgae, macrofauna and sedimentary stability: an experimental test of a reciprocal relationship.

A manipulative field experiment was conducted at Blackness in the Firth of Forth, Scotland, to study the effects of differences in microphytobenthos abundance on sediment stability and macrofauna. Opaque and transparent Perspex was used to construct shaded and controlled treatments, respectively. Shading resulted in significantly lower levels of chlorophyll a recorded from the sediment. Shaded treatments showed significant reductions in populations of Macoma balthica, Hydrobia ulvae and Corophium volutator, 3 of the dominant species at this site. Largely as a result of changes in the abundance of these species, multivariate analyses showed significant differences between shaded and control communities. The impacts of shading on individual species depended on the sediment characteristics. There were no significant differences between treatments in recorded sediment accretion/erosion rates. These results demonstrate the importance of microphytobenthos for the deposit feeders M. balthica, H. ulvae and C. volutator. The absence of any effect on sediment stability might result from the reciprocal, opposite effects of macrofauna and microphytobenthos on sediment stability cancelling each other out in this experiment

A dynamic CSTT model for the effects of added nutrients in Loch Creran, a shallow fjord

Despite a tendency for the complexity of physical–biological models to increase, simple coupled models remain useful for some applications and can provide insights into crucial links between physical and biological processes. This argument is illustrated with an account of a simple 3-box model intended to help assess the capacity of fjords to assimilate nutrients from fish farms. The model, a dynamic version of the UK " Comprehensive Studies Task Team " (CSTT) steady-state model for eutrophication, was applied to Loch Creran (Scottish Western Highlands) and was implemented using Stella 8 and tested using historical data from 1975 (before the installation of a salmon farm) and field data collected in 2003, during the period of operation of the farm. The model's biological state variables are chlorophyll, dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP), and it includes a simple runoff model to convert rainfall into river discharge. The physical processes involved in exchange between the loch and the adjacent waters of the Firth of Lorne were parameterised as a constant daily exchange rate. Between 1975 and 2003, local inputs of nutrient increased but, despite this, there was little apparent increase in nutrient concentrations in the loch, and observed chlorophyll concentrations decreased substantially. Model simulations of chlorophyll and DIN agreed well with observations in 1975, as did DIN simulations in 2003. However, simulated chlorophyll was overestimated in 2003. Some of the agreement between observations and simulations come from the use of observed boundary conditions to force the model. However, even when boundary conditions are subtracted from simulations and observations, the simulations in most cases retain a significant correlation with observations, demonstrating that the model's 'interior' processes do add to its ability to replicate conditions in the loch

Coupled dynamics of dimethylsulfoniopropionate and dimethylsulfide cycling and the microbial food web in surface waters of the North Atlantic.

Oceanic dimethylsulfide (DMS), the main natural source of sulfur to the global atmosphere, is suggested to play a key role in the interaction between marine biota and climate. Its biochemical precursor is dimethylsulfoniopropionate (DMSP), a globally distributed, intracellular constituent in marine phytoplankton. During a multidisciplinary Lagrangian experiment in the subpolar North Atlantic, we determined the fluxes of DMSP and DMS through phytoplankton, microzooplankton, and bacterioplankton and compared them with concurrent carbon and sulfur fluxes through primary and secondary productions, grazing, and release and use of dissolved organic matter. We found that DMSP and derivatives contributed most (48-100%) of the sulfur fluxes and 5-15% of the carbon fluxes. Our findings highlight DMSP as a prominent player in pelagic biogeochemical pumps, especially as a major carrier in organic sulfur cycling. Also, our results illustrate the key role played by microzooplankton and heterotrophic bacteria (hence the microbial food web) in controlling the amount of phytoplanktonic DMSP that ultimately vents to the atmosphere in the form of DMS