Effects of Chronic Waterborne Nickle Exposure on Two Successive Generations of \u3cem\u3eDaphnia Magna\u3c/em\u3e

In a 21-d chronic toxicity test in which an F0 generation of Daphnia magna were exposed to waterborne Ni, the noobservable-effect concentration (for survival, reproduction, and growth) was 42 μg Ni L-1, or 58% of the measured 21-d median lethal concentration (LC50) of 71.9 μg Ni L-1 (95% confidence interval, 56.5–95.0). Chronic exposure to 85 μg Ni L-1 caused marked decreases in survival, reproduction, and growth in F0 animals. In the F1 generation (daphnids born of mothers from the chronically exposed F0 generation), animals chronically exposed to 42 μg Ni L-1 for 11 d weighed significantly less (20%) than controls, indicating increased sensitivity of F1 animals. Additionally, in this successive generation, significant decreases in whole-body levels of metabolites occurred following exposure to both 42 μg Ni L-1 (decreased glycogen and adenosine triphosphate [ATP]) and 21 μg Ni L-1 (decreased ATP). No significant changes were observed in whole-body total lipid, total protein, and lactate levels at any concentration. Whereas F1 neonates with mothers that were exposed to 21 μg Ni L-1 showed increased resistance to acute Ni challenge, as measured by a significant (83%) increase in the acute (48-h) LC50, F1 neonates with mothers that were exposed to 42 μg Ni L-1 were no more tolerant of acute Ni challenge than control animals were. Nickel accumulations in F1 animals chronically exposed to 21 and 42 μg Ni L-1 were 11- and 18-fold, respectively, above control counterparts. The data presented suggest that chronic Ni exposure to two successive generations of D. magna lowered the overall energy state in the second generation. Whereas the quantity of neonates produced was not affected, the quality was; thus, environmentally meaningful criteria for regulating waterborne Ni concentrations in freshwater require consideration of possible multigenerational effects

Research into the influence of spatial variability and scale on the parameterization of hydrological processes

The objectives of the research were as follows: (1) Extend the Representative Elementary Area (RE) concept, first proposed and developed in Wood et al, (1988), to the water balance fluxes of the interstorm period (redistribution, evapotranspiration and baseflow) necessary for the analysis of long-term water balance processes. (2) Derive spatially averaged water balance model equations for spatially variable soil, topography and vegetation, over A RANGE OF CLIMATES. This is a necessary step in our goal to derive consistent hydrologic results up to GCM grid scales necessary for global climate modeling. (3) Apply the above macroscale water balance equations with remotely sensed data and begin to explore the feasibility of parameterizing the water balance constitutive equations at GCM grid scale

Heterogeneity and scaling land-atmospheric water and energy fluxes in climate systems

The effects of small-scale heterogeneity in land surface characteristics on the large-scale fluxes of water and energy in land-atmosphere system has become a central focus of many of the climatology research experiments. The acquisition of high resolution land surface data through remote sensing and intensive land-climatology field experiments (like HAPEX and FIFE) has provided data to investigate the interactions between microscale land-atmosphere interactions and macroscale models. One essential research question is how to account for the small scale heterogeneities and whether 'effective' parameters can be used in the macroscale models. To address this question of scaling, three modeling experiments were performed and are reviewed in the paper. The first is concerned with the aggregation of parameters and inputs for a terrestrial water and energy balance model. The second experiment analyzed the scaling behavior of hydrologic responses during rain events and between rain events. The third experiment compared the hydrologic responses from distributed models with a lumped model that uses spatially constant inputs and parameters. The results show that the patterns of small scale variations can be represented statistically if the scale is larger than a representative elementary area scale, which appears to be about 2 - 3 times the correlation length of the process. For natural catchments this appears to be about 1 - 2 sq km. The results concerning distributed versus lumped representations are more complicated. For conditions when the processes are nonlinear, then lumping results in biases; otherwise a one-dimensional model based on 'equivalent' parameters provides quite good results. Further research is needed to fully understand these conditions

Simulation of Boreal Ecosystem Carbon and Water Budgets: Scaling from Local to Regional Extents

A coupled water and energy balance model is developed. This model can predict the partitioning of water and energy between major source, sink and storage elements within the Boreal-Ecosystem-Atmospheric Study (BOREAS) areas. The results of testing the model against data collected at BOREAS tower sites during Intensive Field Campaigns and remotely sensed data collected across the BOREAS region are presented

Scaling Water and Energy Fluxes in Climate Systems: Three Land-Atmospheric Modeling Experiments

The effects of small-scale heterogeneity in land-surface characteristics on the large-scale fluxes of water and energy in the land-atmosphere system have become a central focus of many of the climatology research experiments. The acquisition of high-resolution land-surface data through remote sensing and intensive land-climatology field experiments(like HAPEX and EIFE) has provided data to investigate the interactions between microscale land-atmosphere interactions and macroscale models. One essential research question is how to account for the small-scale heterogeneities and whether `effective\u27 parameters can be used in the macroscale models. To address this question ofscaling, three modeling experiments were performed and are reviewed in the paper. The first is concerned with the land-surface hydrology during rain events and between rain events. The second experiment applies the Simple Biosphere Model (SiB) to a heterogeneous domain and the spatial and temporal latent beat flux is analyzed. The third experiment uses thermatic mapper (TM) data to look at the scaling of the normalized vegetation index (NDVI), latent heat flux, and sensible heat flux through either scaling of the TM-derived fields using the TM data or the fields derived from aggregated TM data.In all three experiments it was found that the surface fluxes and land characteristics can be sealed, and that macroscale models based on elective parameters are sufficient to account for the small-scale heterogeneities investigated. The paper also suggests that the scale at which a macroscale model becomes valid, the representative elementary scale (REA), is on the order 1.5-3 correlation lengths, which for land processes investigated appears to be about 1000-1500 m. At scales less than the REA scale, exact patterns of subgrid heterogeneities are needed for accurate small-scale modeling

A detailed model for simulation of catchment scale subsurface hydrologic processes

A catchment scale numerical model is developed based on the three-dimensional transient Richards equation describing fluid flow in variably saturated porous media. The model is designed to take advantage of digital elevation data bases and of information extracted from these data bases by topographic analysis. The practical application of the model is demonstrated in simulations of a small subcatchment of the Konza Prairie reserve near Manhattan, Kansas. In a preliminary investigation of computational issues related to model resolution, we obtain satisfactory numerical results using large aspect ratios, suggesting that horizontal grid dimensions may not be unreasonably constrained by the typically much smaller vertical length scale of a catchment and by vertical discretization requirements. Additional tests are needed to examine the effects of numerical constraints and parameter heterogeneity in determining acceptable grid aspect ratios. In other simulations we attempt to match the observed streamflow response of the catchment, and we point out the small contribution of the streamflow component to the overall water balance of the catchment

Evapotranspiration and runoff from large land areas: Land surface hydrology for atmospheric general circulation models

A land surface hydrology parameterization for use in atmospheric GCM's is presented. The parameterization incorporates subgrid scale variability in topography, soils, soil moisture and precipitation. The framework of the model is the statistical distribution of a topography-soils index, which controls the local water balance fluxes, and is therefore taken to represent the large land area. Spatially variable water balance fluxes are integrated with respect to the topography-soils index to yield our large topography-soils distribution, and interval responses are weighted by the probability of occurrence of the interval. Grid square averaged land surface fluxes result. The model functions independently as a macroscale water balance model. Runoff ratio and evapotranspiration efficiency parameterizations are derived and are shown to depend on the spatial variability of the above mentioned properties and processes, as well as the dynamics of land surface-atmosphere interactions

Effects of spatial variability and scale on areal -average evapotranspiration

This paper explores the effect of spatial variability and scale on areally-averaged evapotranspiration. A spatially-distributed water and energy balance model is employed to determine the effect of explicit patterns of model parameters and atmospheric forcing on modeled areally-averaged evapotranspiration over a range of increasing spatial scales. The analysis is performed from the local scale to the catchment scale. The study area is King's Creek catchment, an 11.7 sq km watershed located on the native tallgrass prairie of Kansas. The dominant controls on the scaling behavior of catchment-average evapotranspiration are investigated by simulation, as is the existence of a threshold scale for evapotranspiration modeling, with implications for explicit versus statistical representation of important process controls. It appears that some of our findings are fairly general, and will therefore provide a framework for understanding the scaling behavior of areally-averaged evapotranspiration at the catchment and larger scales

Evaluation of Special Sensor Microwave/Imager Satellite Data for Regional Soil Moisture Estimation over the Red River Basin

Regional-scale estimation of soil moisture using in situ field observations is not possible due to problemswith the representativeness of the sampling and costs. Remotely sensed satellite data are helpful in this regard.Here, the simulations of 19- and 37-GHz vertical and horizontal polarization brightness temperatures and estimationof soil moistures using data from the Special Sensor Microwave/Imager (SSM/I) for 798 0.258 3 0.258boxes in the southwestern plains region of the United States for the time period between 1 August 1987 and31 July 1988 are presented. A coupled land-canopy–atmosphere model is used for simulating the brightnesstemperatures. The land-surface hydrology is modeled using a thin-layer hydrologic model. The canopy scatteringis modeled using a radiative transfer model, and the atmospheric attenuation is characterized using an empiricalmodel. The simulated brightness temperatures are compared with those observed by the SSM/I sensor aboardthe Defense Metereological Satellite Program satellite. The observed brightness temperatures are used to derivethe soil moistures using the canopy radiative transfer and atmospheric attenuation model. The discrepanciesbetween the SSM/I-based estimates and the simulated soil moisture are discussed. The mean monthly soilmoistures estimated using the 19-GHz SSM/I brightness temperature data are interpreted along with the meanmonthly leaf area index and accumulated rainfall. The soil moistures estimated using the 19-GHz SSM/I dataare used in conjunction with the hydrologic model to estimate cumulative monthly evaporation. The results ofthe simulations hold promise for the utilization of microwave brightness temperatures in hydrologic modelingfor soil moisture estimation

A Soil-Canopy-Atmosphere Model for Use in Satellite Microwave Remote Sensing

Regional and global scale studies of land-surface-atmosphere interactions require the use of observations for calibration and validation. In situ field observations are not representative of the distributed nature of land surface characteristics, and large-scale field experiments are expensive undertakings. In light of these requirements and shortcomings, satellite observations serve our purposes adequately. The use of satellite data in land surface modeling requires developing a hydrological model with a thin upper layer to be compatible with the nature of the satellite observations and that would evaluate the soil moisture and soil temperature of a thin layer close to the surface. This paper outlines the formulation of a thin layer hydrological model for use in simulating the soil moistures and soil temperatures. This thin layer hydrological model is the first step in our attempt to use microwave brightness temperature data for regional soil moisture estimation. The hydrological model presented here has been calibrated using five years (1980–1984) of daily streamflow data for the Kings Creek catchment. The calibrated parameters are used to validate the daily streamflows for the next 5 year period (1985–1989). The comparison of surface soil moistures and surface temperatures for the period of the Intensive Field Campaigns (IFCs) during the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE) in 1987 is carried out and yields good results. The thin layer hydrological model is coupled with a canopy radiative transfer model and an atmospheric attenuation model to create a coupled soil-canopy-atmosphere model in order to study the effect of the vegetation and the soil characteristics on the Special Sensor Microwave Imager (SSM/I) brightness temperatures. The sensitivities of the brightness temperatures to the soil and vegetation is examined in detail. The studies show that increasing leaf area index masks the polarization difference signal originating at the soil surface