Integrated assessment of oyster reef ecosystem services: Quantifying Denitrification Rates and Nutrient Fluxes

Measurements of nutrient exchange were made in restored oyster reefs and creek sediments in 2014 and 2015 in Harris Creek, Maryland, USA. Rates of ammonium, nitrate and di-nitrogen fluxes were much higher in reef environments than in sediments, and rates of oxygen uptake reflected high inputs of biodeposits. The rate of denitrification was related to oyster biomass and oyster numbers. The shallow nature of the restoration allows light to reach the bottom and benthic microalgal photosynthesis affects the net nutrient exchange with the bottom. After several years, oyster restoration has increased denitrification in Harris Creek, though observations in mature upper Choptank restored reefs are higher. The trajectory of increase of the nutrient ecosystem services is positive and will be followed over time

Integrated assessment of oyster reef ecosystem services: Quantifying denitrification rates and nutrient fluxes

Fluxes of N2-N (denitrification), dissolved ammonium, nitrate plus nitrite, and dissolved oxygen were determined at teh 350 acre oyster restoration project at Harris Creek, Maryland. The ex situ incubation approach involved adding oyster communities to embedded trays for ~1 mo incubating the trays under dark and light conditions for 1-2 hour time courses for gas and solute sampling, adn determination of the rates of gas and solute exchange for 136 individual reef tray incubations. Reef exchange rates were compared to rates of sediment water exchange in core incubations throughout Harris Creek and in reef-adjacent environments

Comparison of methods for determining biogeochemical fluxes from a restored oyster reef

Oyster reef restoration can significantly increase benthic denitrification rates. Methods applied to measure nutrient fluxes and denitrification from oyster reefs in previous studies include incubations of sediment cores collected adjacent to oyster clumps, benthic chambers filled with intact reef segments that have undergone in situ equilibration and ex situ incubation, and cores with single oysters. However, fluxes of nutrients vary by orders of magnitude among oyster reefs and methods. This study compares two methods of measuring nutrient and metabolic fluxes on restored oyster reefs: incubations including intact segments of oyster reef and incubations containing oyster clumps without underlying sediments. Fluxes of oxygen (O-2), dissolved inorganic carbon (DIC), ammonium (NH4+), combined nitrate and nitrite (NO2/3-), di-nitrogen (N-2), and soluble reactive phosphorus (SRP) were determined in June and August in Harris Creek, a tributary of the Chesapeake Bay, Maryland, USA. Regression of fluxes measured from clumps alone against those measured from intact reef segments showed significant positive relationships for O-2, DIC, NH4+, and SRP (R-2 = 0.920, 0.61, 0.26, and 0.52, respectively). Regression of clump fluxes against the oyster tissue biomass indicates significant positive relationships for O-2 and NH4+, marginally significant and positive relationships for DIC and N-2, and no significant relationship for NO2/3- or SRP. Although these results demonstrate that the incubation of oyster clumps without underlying sediments does not accurately represent biogeochemical fluxes measured from the whole oyster and sediment community, this work supports the need to understand the balance between the metabolism of oysters and local sediments to correctly estimate biogeochemical rates

Linking structural and functional characteristics of restored oyster reefs : A Restoration Project in the Virginia Coast Reserve

Eighteen native oyster reefs (16-m2 each) were restored using six oyster densities (0, 10, 25, 50, 100 and 250 adult oysters m-2) with three replicates of each density at an intertidal site in The Nature Conservancy’s Virginia Coast Reserve. Reef construction was successful and continues to provide a range of oyster biomass densities useful for exploring relationships between oyster reef structural and functional parameters. Between April 2012 and July 2013, a science-based monitoring program explored quantitative relationships between structural and functional characteristics of these restored reefs. Structural parameters examined included oyster abundance, oyster size/biomass, surface shell volume, reef topographic complexity and sediment characteristics. Functional parameters included denitrification rates and macrofaunal abundance and biomass. Relationships between reef structural parameters and functional parameters were complex and variable. As of July 2014, these reefs continue to serves as a platform for continued studies of the relationships between reef structural and functional characteristics

Modeling the impact of floating oyster (Crassostrea virginica) aquaculture on sediment−water nutrient and oxygen fluxes

Bivalve aquaculture relies on naturally occurring phytoplankton, zooplankton, and detritus as food sources, thereby avoiding external nutrient inputs that are commonly associated with finfish aquaculture. High filtration rates and concentrated bivalve biomass within aquacul- ture operations, however, result in intense biodeposition of particulate organic matter (POM) on surrounding sediments, with potential adverse environmental impacts. Estimating the net deposi- tional flux is difficult in shallow waters due to methodological constraints and dynamic processes such as resuspension and advection. In this study, we combined sediment trap deployments with simulations from a mechanistic sediment flux model to estimate seasonal POM deposition, resus- pension, and processing within sediments in the vicinity of an eastern oyster Crassostrea virginica farm in the Choptank River, Maryland, USA. The model is the stand-alone version of a 2-layer sediment flux model currently implemented within larger models for understanding ecosystem responses to nutrient management. Modeled sediment−water fluxes were compared to observed denitrification rates and nitrite + nitrate (NO2 −+NO3 −), phosphate (PO4 3−) and dissolved O2 fluxes. Model-derived estimates of POM deposition, which represent POM incorporated and processed within the sediment, comprised a small fraction of the material collected in sediment traps. These results highlight the roles of biodeposit resuspension and transport in effectively removing oyster biodeposits away from this particular farm, resulting in a highly diminished local environmental impact. This study highlights the value of sediment models as a practical tool for computing inte- grated measures of nitrogen cycling as a function of seasonal dynamics in the vicinity of aquaculture operations

Scaling Ecosystem Services to Reef Development : Effects of oyster density on nitrogen removal and reef community structure

Eighteen native oyster experimental reefs (16-m2 each) were restored using six oyster densities (0, 10, 25, 50, 100 and 250 adult oysters m-2) with three replicates of each density at each of two sites: one subtidal site in Onancock Creek, Virginia and one intertidal site in Hillcrest Oyster Sanctuary within The Nature Conservancy’s Virginia Coast Reserve. A science-based monitoring program explored quantitative relationships between structural and functional characteristics of these restored reefs. Structural parameters examined included oyster abundance, oyster size/biomass, surface shell volume, reef topographic complexity and sediment characteristics. Functional parameters included denitrification rates and macrofaunal abundance and biomass. Data were collected from the intertidal site during six sampling periods between April 2012 and July 2013 and from the subtidal site in April and June 2012. Relationships between reef structural parameters and functional parameters were complex and variable. As of July 2014, the intertidal reefs continue to serve as a platform for continued studies of the relationships between reef structural and functional characteristics

Who Believes in Me? The Effect of Student-Teacher Demographic Match on Teacher Expectations

Teachers are an important source of information for traditionally disadvantaged students. However, little is known about how teachers form expectations and whether they are systematically biased. We investigate whether student-teacher demographic mismatch affects high school teachers’ expectations for students’ educational attainment. Using a student fixed effects strategy that exploits expectations data from two teachers per student, we find that non-black teachers of black students have significantly lower expectations than do black teachers. These effects are larger for black male students and math teachers. Our findings add to a growing literature on the role of limited information in perpetuating educational attainment gaps

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives