Midhat Hondzo

Regional water temperature characteristics of lakes subjected to climate change

A deterministic, validated, one-dimensional, unsteady-state lake water quality model was linked to a daily weather data base to simulate daily water temperature profiles in lakes over a period of twenty-five (1955–79) years. Twenty seven classes of lakes which are characteristic for the north-central U.S. were investigated. Output from a global climate model (GISS) was used to modify the weather data base to account for a doubling of atmospheric CO2. The simulations predict that, after climate change, epilimnetic temperatures will be higher but increase less than air temperature, hypolimnetic temperatures in seasonally stratified dimictic lakes will be largely unchanged or even lower than at present, evaporative water loss will be increased by as much as 300 mm for the season, onset of stratification will occur earlier and overturn later in the season, and overall lake stability will become greater in spring and summer.

Riverbed heat conduction prediction

Heat flux between river water and riverbed contributes significantly to river water heat content and river temperature, especially in shallow rivers. A numerical model of heat conduction in a riverbed was verified with detailed temperatures measurements in a riverbed. Three different methods, the heat budget method, the gradient method, and an inverse method, were used alternatively for the estimation of the riverbed heat flux. Propagation of uncertainty in the riverbed temperature model was studied using a vector state space perturbation method. Output uncertainty was estimated by random perturbations of the effective thermal conductivity from the main value. The coefficient of variation of effective thermal conductivity was 0.1. Temperatures and heat fluxes in the riverbed were affected by the uncertain thermal conductivity.

Three Case Studies of Lake Temperature and Stratification Response to Warmer Climate

The impact of climatic warming on lakes will most likely have serious implications for water resources and water quality. Rather than using model predictions of greenhouse warming, this paper looks at the changes in heat balance and temperature profiles in a particularly warm year (1988) compared to a more normal one (1971). The comparisons are made for three different morphometrically different lakes located 45°N latitude and 93°W longitude (north central United States) and for the summer period (April 1 to October 31). Water temperatures are daily values simulated with a model driven by daily weather parameters and verified against several sets of measurements. The results show that in the warmer year epilimnetic water temperatures were higher, evaporative water loss increased, and summer stratification occurred earlier in the season.

Dissolved oxygen dynamics of streams draining an urbanized and an agricultural catchment

The extreme value method (EVM), based on the maximum and minimum dissolved oxygen (DO) deficits, was derived to estimate metabolism rates (photosynthesis and respiration) in streams. The proposed method was applied to DO concentrations that were measured in two creeks located in urbanized and agricultural watersheds, respectively. The results obtained by the EVM agree with the delta method used for the estimation of metabolism rates in streams. Diurnal DO variations were explained using a DO mass balance equation with the estimated daily metabolism rates. A comparison between the metabolism rates obtained in two creeks indicates that the creek located in a non-urban watershed has higher metabolism rates than the creek located in an urban watershed. The non-urban creek was periodically autotrophic, and the urban creek was heterotrophic during the measurement period. Simulations conducted by using 1-day metabolism rates and augmenting the basic DO mass balance equation with the dimensionless relationships between the metabolism rate and discharge in creeks followed actual diurnal DO concentrations measured in the streams.

Dissolved oxygen transfer at the sediment‐water interface in a turbulent flow

Laboratory experiments have been conducted in an effort to elucidate the details of the dissolved oxygen transfer mechanism at the sediment-water interface. Near-bed liquid turbulence and dissolved oxygen concentrations were measured for a range of Reynolds numbers from 2700 to 10,600 over a smooth bed. The results show that the shear stress velocity controls the dissolved oxygen diffusive layer thickness and therefore the local mass transfer coefficient at the sediment-water interface. From a dynamic point of view the results suggest the possibility that streamwise vortices control the interfacial dissolved oxygen transfer process. The research results will provide an opportunity to validate the existing conceptual models as well as enhance the development of new models that can improve our ability to predict dissolved oxygen and transport related parameters in lakes, reservoirs, coastal waters, and rivers.

Extreme Value Analysis of a Fish/Temperature Field Database

Abstract Extremes of water temperatures limit the presence of various fishes in streams and lakes. Upper extreme water temperatures and their uncertainties are determined by several statistical methods from a large field database. There are over 140 000 weekly mean fish/stream temperature matched pairs in the database. Three different techniques are employed to estimate upper extremes of habitat temperatures for 12 fish species. To quantify the uncertainty of the estimated extremes the bootstrap method, the method of moments and the residual method are applied. The data above the maximum growth temperature are matched well by a type III extremal or a three-parameter lognormal distribution. Standard error of the estimated extreme habitat temperatures depends on species and varies from 0.1°C to 0.6°C at the 95% cumulative probability of occurrence.

Validation of a fish habitat model for lakes

Water temperatures and dissolved oxygen concentrations in 27 classes of lakes have been hindcast by simulation models and related to presence of coldwater, coolwater, and warmwater fishes in 3002 Minnesota lakes. A one-dimensional, dynamic water quality model driven by 25 years of daily weather data was used to model water temperature and dissolved oxygen profiles of these lakes. Fish presence data were available for these lakes from the Minnesota Lake Fisheries Data Base. Water temperature and dissolved oxygen criteria derived from a very large United States Environmental Protection Agency fish-temperature database and dissolved oxygen observations were used to define and link simulated water temperatures and dissolved oxygen conditions to suitability of habitats for coldwater, coolwater, and warmwater fish assemblages. Good agreement was found between fish presence and numerical simulations of fish habitat defined by water temperatures and dissolved oxygen concentrations. Generally water temperature and DO are good indicators of suitable fish habitat.

Propagation of uncertainty due to variable meteorological forcing in lake temperature models

Propagation of uncertainty in lake temperature models is studied using a vector state space method. The output uncertainty is defined as the result of deviations of the meteorological variables from their mean values. The analysis is applied to systems with correlated and uncorrelated meteorological variables. Surface water temperatures are strongly affected by uncertain meteorological forcing. Air temperatures and dew point temperature fluctuations have significant effect on lake temperature uncertainty. Ignoring correlation in meteorological variables underestimates uncertainties in lake temperature estimates. Long-term average water temperature structure in lakes can be estimated by computer model simulation for just 1 year when results from a statistical analysis of meteorological variables are used as input. The analysis presents a useful alternative for the study of long-term averages and variability of water temperature structures in lakes due to variable meteorological forcing.