William R. Herb

Integral growth of submersed macrophytes in varying light regimes

The coverage, density, and species diversity of macrophytes in the shallow portion of lakes have important effects on water quality, ecosystem health, and sediment deposition, and are important factors in lake use for fishing, boating, swimming, and as waterfowl habitat. This significance and the complex requirements for macrophyte growth have stimulated the development of growth models to predict macrophyte biomass, oxygen production, nutrient cycling, etc. However, there is a lack of relationships that characterize the response of macrophyte growth to varying physical conditions. The growth model developed in this study relates the rate of production of rooted aquatic macrophytes to basic physiological parameters (growth and respiration rates) and controlling physical parameters (incident irradiance, water temperature, light attenuation by water and phytoplankton). The model is developed to be general, rather than specific to a particular plant species, with the intention of broadly characterizing macrophyte growth behavior as a function of a few key parameters. The growth equations are solved analytically using the assumption of uniform temperature and biomass over depth. Expressions for instantaneous rate of growth, daily production, and equilibrium biomass are found. A set of dimensionless parameters are defined and used to characterize four growth regimes. Model results are given in terms of the governing dimensionless parameters and then related to real world, dimensional parameters.

Temperature Stratification and Mixing Dynamics in a Shallow Lake With Submersed Macrophytes

ABSTRACT This paper describes an investigation of temperature stratification and vertical mixing in lacustrine macrophyte beds. Field measurements in a shallow lake show pronounced diel temperature dynamics, driven by surface heat transfer. The temperature stratification data also indicate a significant dependence of vertical mixing characteristics on macrophyte stand height. While natural convective mixing during night-time cooling was rather uniform between measurement sites, wind-driven mixing during the day was significantly attenuated in dense, full-depth macrophyte beds, resulting in increased stratification and higher maximum surface temperatures. An unsteady, one-dimensional heat transfer model has been formulated to simulate temperature dynamics in shallow lakes with submersed macrophytes. Surface mixed layer dynamics are successfully modeled at time scales down to 1 hour, using an integral energy model formulated to include the effect of light attenuation and turbulent kineuc energy dissipation by submersed macrophytes. The results of this study have implications for the management of water quality and ecology of shallow lakes, as variation of thermal stratification and mixing likely has corresponding effects on the transport of dissolved oxygen and nutrients.

Simulation and Characterization of Asphalt Pavement Temperatures

ABSTRACT Characterization of pavement temperature, including, substantial analysis of measured asphalt temperature data from the MnROAD facility and simulations of pavement temperature using a one-dimensional finite difference heat transfer model are presented. The measured pavement temperatures are characterized at diurnal and seasonal time scales, including daily extreme temperatures, temperature gradients, diurnal cycling, and seasonal variations. The temperature simulations provide more detailed information on temperature gradients in the pavement and on the surface heat transfer components than the measurements, and also help to evaluate the quality of the pavement temperature and climate measurements. This information is critical in quantifying aging effects at the surface of asphalt pavements and in modeling the asphalt pavement system response to environmental and traffic loading.

Runoff Temperature Model for Paved Surfaces

Interest in thermal pollution due to storm-water runoff has risen significantly since it was recognized that fish habitat in coldwater streams may deteriorate or even disappear following urban development or logging. The need to project changes in both runoff temperature and volume in response to land use changes has been recognized. Surface runoff hydrographs can be predicted or simulated using a variety of existing models. Few tools exist to predict or simulate the thermograph of that runoff, i.e., the water flow rate and temperature as a function of time. To simulate runoff temperature for small parcels of land of uniform cover such as parking lots, a new hydrothermal runoff model was developed. The runoff portion of the model is semianalytical and spatially integrated. The runoff model is discrete in time, so that it may be used to analyze events with observed rainfall intensity variations at a resolution of 15 min or less. The runoff model closely approximates the simulation results of a one-dimensio...

Case study of simulation of heat export by rainfall runoff from a small urban watershed using MINUHET

AbstractThe influence of urban development on the volume of storm water runoff and on water temperature, and the associated impact on streams in urban watersheds, has generated a need for tools to predict the temperature of urban storm water runoff, particularly for the assessment of future urban development. To address this need, the Minnesota Urban Heat Export Tool (MINUHET) model was developed to simulate the flow of heat and storm water through a small urban watershed for a rainfall-runoff event. The tool includes process-based hydrological and thermal models for runoff from developed, undeveloped, or vegetated land uses, for various components of drainage networks, and for some best management practices such as detention and infiltration ponds, storm water vaults, and rock cribs. The primary output of MINUHET is a time series of the flow rate and temperature of runoff, which can be used to determine the heat content of the runoff at the outlet of the modeled watershed and aid in the assessment of the...