The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

Physical ecosystem engineers are organisms that directly or indirectly control the availability of resources to other organisms by causing physical state changes in biotic or abiotic materials. Physical ecosystem engineering by organisms is the physical modification, maintenance, or creation of habitats. Ecological effects of engineers on many other species occur in virtually all ecosystems because the physical state changes directly create nonfood resources such as living space, directly control abiotic resources, and indirectly modulate abiotic forces that, in turn, affect resource use by other organisms. Trophic interactions and resource competition do not constitute engineering. Engineering can have significant or trivial effects on other species, may involve the physical structure of an organism (like a tree) or structures made by an organism (like a beaver dam), and can, but does not invariably, have feedback effects on the engineer. We argue that engineering has both negative and positive effects on species richness and abundances at small scales, but the net effects are probably positive at larger scales encompassing engineered and nonengineered environments in ecological and evolutionary space and time. Models of the population dynamics of engineers suggest that the engineer/habitat equilibrium is often, but not always, locally stable and may show long-term cycles, with potential ramifications for community and ecosystem stability. As yet, data adequate to parameterize such a model do not exist for any engineer species. Because engineers control flows of energy and materials but do not have to participate in these flows, energy, mass, and stoichiometry do not appear to be useful in predicting which engineers will have big effects. Empirical observations suggest some potential generalizations about which species will be important engineers in which ecosystems. We point out some of the obvious, and not so obvious, ways in which engineering and trophic relations interact, and we call for greater research on physical ecosystem engineers, their impacts, and their interface with trophic relations.

Positive and negative effects of organisms as physical ecosystem engineers

Acquisition, optimization and interpretation of X-ray computed tomographic imagery: applications to the geosciences

Ocean forecasting in terrain-following coordinates: Formulation and skill assessment of the Regional Ocean Modeling System

Mollusk shells are abundant, persistent, ubiquitous physical structures in aquatic habitats. Using an ecosystem engineering perspective, we identify general roles of mollusk shell production in aquatic ecosystems. Shells are substrata for attachment of epibionts, provide refuges from predation, physical or physiological stress, and control transport of solutes and particles in the benthic environment. Changes in availability of these resources caused by shell production have important consequences for other organisms. Colonization of shelled habitat depends on individual shell traits and spatial arrangement of shells, which determine access of organisms to resources and the degree to which biotic or abiotic forces are modulated. Shell production will increase species richness at the landscape level if shells create resources that are not otherwise available and species are present that use these resources. Changes in the availability of resources caused by shells and the resulting effects on other organisms have both positive and negative feedbacks to these engineers. Positive feedbacks appear to be most frequently mediated by changes in resource availability, whereas negative feedbacks appear to be most frequently mediated by organisms. Given the diversity of species that depend upon resources controlled by shells and rapid changes in global shell production that are occurring due to human activities, we suggest that shell producers should not be neglected as a targets of conservation, restoration and habitat management.

Mollusks as ecosystem engineers: the role of shell production in aquatic habitats

/pdf/depositional-sedimentary-environments-106r28he2c.pdf

Depositional Sedimentary Environments

The stability of tidal flats in Venice Lagoon—the results of in-situ measurements using two benthic, annular flumes

In situ erosion measurements on fine-grained sediments from the Bay of Fundy

The effect of growth and carbohydrate production by the diatom Nitzschia cuwilineata on sediment erodibility was explored in laboratory flume experiments. Diatom cultures, incubated on sediment, were monitored daily for chlorophyll and carbohydrate concentrations and eroded in a recirculating flume at successive stages of growth. Because variations in erosion rate were far greater than variations in erosion threshold during the diatom growth period, erosion rate may be a more sensitive index of sediment stability. Erosion rate was negatively correlated with sediment chlorophyll (r2 = 0.759; P = 0.024) and bulk carbohydrate (r2 = 0.958; P = 0.001) concentrations. A strong negative correlation was found between the sediment bulk carbohydrate-to-chlorophyll ratio and erosion rate (r2 = 0.996; P < O.OOl), suggesting that this ratio would serve as a good indicator of sediment erodibility. The size of eroding particles or aggregates increased with the age of the biofilm, probably due to the pervasion of sediment with mucilage and changes in “stickiness” of the resulting sediment microfabric. Sediment stability increased throughout the stationary phase of growth regardless of lift forces produced by trapped bubbles within the biofilm and progressively smaller increases in sediment carbohydrate concentrations during this period. Knowledge of the physiological status of diatom biofilms is essential for the quantitative prediction of sediment transport, since diatom growth phase alters the behavior of sediment erosion.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1998.43.1.0065

The effect of carbohydrate production by the diatom Nitzschia curvilineata on the erodibility of sediment

A benthic annular flume (Sea Carousel) has been developed and tested to measure in situ the erodibility of cohesive sediments. The flume is equipped with three optical backscatter sensors, a lid rotation switch, and an electromagnetic (EM) flow meter capable of detecting azimuthal and vertical components of flow. Data are logged at rates up to 10·66 Hz. Erodibility is inferred from the rate of change in suspended sediment concentration detected in the annulus. The energy-density/wave number spectrum of azimuthal flow showed peaks in the energy spectrum at paddle rotation wave numbers (k) of 14 and 7 m −1 (macroturbulent time scales) but were not significant. Friction velocity ( U *), measured (1) at 1 Hz using a flush-mounted hot-film sensor, and (2) derived from measured velocity profiles in the inner part of the logarithmic layer gave comparable results for Ū * −1 . At higher values of U*, method (2) underpredicted by up to 20%. Method (1) showed radial increases in Ū * in the annulus for Ū y > 0·32 m s −1 . Radial velocity gradients were proportional to ( Ū y − 0·32 m s −1 ). Maximum radial differences in U * were 10% for Ū y = 0·5 ms −1 . Suspended sediment mass concentration ( S ) in the annulus resulted in a significant decrease (10·5%) in Ū * derived by method (1) over the range 0 S −1 . These decreases were not evident in method (2). Method (1) may, therefore, be subject to changes in stress sensor calibration with changes in S . Subaerial deployments of Sea Carousel caused severe substrate disturbance, water losses, and aeration of the annulus. Submarine deployments produced stable results, though dispersion of turbid flume water took place. Results clearly demonstrated the existence of ‘Type I’ and ‘Type II’ erosion documented from laboratory studies.

Carl L. Amos

Papers

Depositional Sedimentary Environments

The stability of tidal flats in Venice Lagoon—the results of in-situ measurements using two benthic, annular flumes

In situ erosion measurements on fine-grained sediments from the Bay of Fundy

The effect of carbohydrate production by the diatom Nitzschia curvilineata on the erodibility of sediment

Sea Carousel--A Benthic, Annular Flume