R. Dawson

Lake Ecosystem Health Assessment: Indicators and Methods

A set of ecological indicators including structural, functional, and system-level aspects were proposed for a lake ecosystem health assessment, according to the structural, functional, and system-level responses of lake ecosystems to chemical stresses including acidification, eutrophication and copper, oil and pesticide contamination. The structural indicators included phytoplankton cell size and biomass, zooplankton body size and biomass, species diversity, macro- and micro-zooplankton biomass, the zooplankton phytoplankton ratio, and the macrozooplankton microzooplankton ratio. The functional indicators encompassed the algal C assimilation ratio, resource use efficiency, community production, gross production/respiration (i.e. P/R) ratio, gross production standing crop biomass (i.e. P/B) ratio, and standing crop biomass unit energy flow (i.e. B/E) ratio. The ecosystem-level indicators conisisted of ecological buffer capacities, energy, and structural energy. Based on these indicators, a direct measurement method (DMM) and an ecological modeling method (EMM) for lake ecosystem health assessment were developed. The DMM procedures were designed to: (1) identify key indicators; (2) measure directly or calculate indirectly the selected indicators; and, (3) assess ecosystem health on the basis of the indicator values. The EMM procedures were designed to: (1) determine the structure and complexity of the ecological model according to the lakes ecosystem structure; (2) establish an ecological model by designing a conceptual diagram, establishing model equations, and estimating model pararmeters; (3) compare the simulated values of important state variables and process rates with actual observations; (4) calculate ecosystem health indicators using the ecological model; and, (5) assess lake ecosystem health according to the values of the ecological indicators. The results of a case study demonstrated that both methods provided similar results which corresponded with the lakes actual trophic state.

EVALUATION AND ANALYSIS OF TRAFFIC NOISE FROM THE MAIN URBAN ROADS IN BEIJING

Abstract Traffic noise surveying and analysis was performed along three main roads in the Beijing urban area—the 2nd and 3rd ring roads circling the central downtown area and Chang-An Avenue, a major east—west corridor road through the heart of the city. The results indicate that these main roads are overloaded by traffic flow during daytime and noise levels due to road traffic along these roads are above relevant environmental standards by 5 dBA. The spatial variance of traffic noise was also analyzed, with the results indicating that the spatial differences result primarily from the unbalanced development of Beijings urban districts.

Relations between AVHRR NDVI and ecoclimatic parameters in China

Based on monthly AVHRR NDVI data and weather records collected from 160 stations throughout China for 10 years, the relationships between NDVI and two ecoclimatic parameters (growing degree-days (GDD) and rainfall) were analysed. The results indicate that a significant correlation exists between NDVI and the two ecoclimatic parameters; the NDVI/GDD correlation was stronger than the NDVI/rainfall correlation. The NDVI/rainfall correlation coefficient exhibits a clear structure in terms of spatial distribution. Further, the results indicate that for natural vegetation, the NDVI/rainfall correlation coefficient increases in order from evergreen forest, to deciduous forest, to shrubs and desert vegetation, to steppe and savanna. The correlation coefficients associated with cultural vegetation type depend on a number of factors including annual rainfall, seasonal variation in precipitation, type and intensity of irrigation practice and other environmental factors.

A GIS based road traffic noise prediction model

Abstract A road traffic noise prediction model has been developed suitable for use in China. This model is based on local environmental standards, vehicle types and traffic conditions. The model was accurate to 0.8 dBA at locations near the road carriage way and 2.1 dBA within the housing estate, which is comparable to the FHWA model. An integrated noise-GIS system was developed to provide general functions for noise modeling and an additional tool for noise design, where a new interaction mode in “WHAT IF Question/Explanation” format was used. Application of this system offered improvements in the efficiency and accuracy of traffic noise assessment and noise design.

Characterizing and comparing risks of polycyclic aromatic hydrocarbons in a Tianjin wastewater-irrigated area.

A probability risk assessment was conducted to characterize the ecotoxicity of three polycyclic aromatic hydrocarbons (PAHs), including benzo[a]pyrene, fluoranthene, and phenanthrene, to various species in a wastewater-irrigated area of Tianjin, China. The relative risk of these chemicals was investigated using joint risk probability distribution curves, which were generated based on the distributions of exposure and acute toxicity data. Risk at various exposure levels was discussed. The results indicated that among the three PAHs studied, the overall risk of phenanthrene was the highest, with that of benzo[a]pyrene the lowest, due mainly to their exposure concentrations. For lower exposure levels at which the percentage of species affected was less than 20%, the risk associated with benzo[a]pyrene was clearly higher than that of the other two chemicals.

A GIS-based method of lake eutrophication assessment

Abstract A geographical information system (GIS)-based method of lake eutrophication assessment was undertaken to study the spatial distribution of eutrophication conditions in lake environments. A trophic state index (TSI) consisting of six physical, chemical and biological indicators including total phosphorus (TP), total nitrogen (TN), chemical oxygen demand (COD), Secchi disk depth (SD), chlorophyll-a concentration (Chl-a) and phytoplankton biomass (CA) was constructed to describe the eutrophication state of the lake environment. A 0–100 eutrophication scale was also developed to indicate seven different trophic levels within the lake environment: oligotrophic, lower-mesotrophic, mesotrophic, upper-mesotrophic, eutrophic, hypereutrophic and extremely hypereutrophic. A representation of the spatial distribution of TSI TP , TSI TN , TSI COD , TSI SD , TSI Chl-a and TSI CA was developed using the inverse distance weighted (IDW) interpolation method. By categorizing the interpolated values, a clear illustration of the different trophic levels was developed on six thematic maps. A GIS overlay technique was applied to synthesize the information from the six thematic maps into a final map illustrating the spatial distribution of eutrophication conditions within the study area. The different periods or levels associated with lake eutrophication assessment using GIS were then discussed.

Estimation of bioconcentration factors of nonionic organic compounds in fish by molecular connectivity indices and polarity correction factors

A bioconcentration factor (BCF) estimation model for a wide range of nonionic organic compounds was developed on the basis of molecular connectivity indices and polarity correction factors. The nonlinear topological modeling using polarity correction factors resulted in the best BCF estimation quality for all of the 239 compounds studied, with a mean absolute estimation error of 0.478 log units. Residual analysis indicated that the estimation errors came from many sources including BCF measurement, test species, and selection of descriptors. Statistical robustness of the developed model was validated by modified jackknifed tests where random deletion of a set of compounds and specific deletion of a class of compounds were both performed. Comparison between the MCI-based (molecular connectivity indices) model and a Kow-based (octanol/water partition coefficient) model revealed that the BCF estimation based on topological parameters was as good as that achieved by Kow.

A method for lake ecosystem health assessment: an Ecological Modeling Method (EMM) and its application

Ecosystem health is a newly proposed concept that sets new goals for environmental management. Its definition, indexing and assessment methods are still being perfected. An Ecological Modeling Method (EMM) for lake ecosystem health assessment is proposed in this paper. The EMMs procedures are: (1) to analyze the ecosystem structure of a lake in order to determine the structure and complexity of the lakes ecological model; (2) to develop a model having ecological health indicators, by designing a conceptual diagram, establishing model equations, estimating model parameters and being integrated with ecological indicators; (3) to compare the simulated and observed values of important state variables and process rates (i.e. model calibration) in order to evaluate the applicability of the model to lake ecosystem health assessment; (4) to calculate ecosystem health indicators based on the developed model; and (5) to assess lake ecosystem health according to the values of the ecosystem health indicators. The EMM was applied, as a case study, to the ecosystem health assessment of a eutrophic Chinese lake (Lake Chao) between April 1987 and March 1988. A relative order of health states from poor to good was determined as follows: August–October 1987 > April–May 1987 > June–July 1987 > November–December 1987 > January–March 1988. These results compared quite favourably with the actual current conditions at Lake Chao. The EMM method, therefore, was suitable in assessing lake ecosystem health at Lake Chao.

Simulation of acid–base condition and copper speciation in the fish gill microenvironment

pH, alkalinity, and mucus content in the fish gill microenvironment of carp (Cyprinus carpio) were measured by exposing fish to copper at various water pH levels using an apparatus which separates inspired and expired water. The relationship between pH levels inside and outside of the gill microenvironment, between pH and alkalinity, and between mucus secretion, pH, and copper exposure concentration were modeled. Copper speciation in the surrounding water and in the fish gill microenvironment was simulated using MINTEQA2 chemical equilibrium calculation software. The results of the modeling for pH, alkalinity, and mucus calculation were then adopted as inputs for purposes of parameter identification in the speciation modeling. The differences observed in the copper species distribution between that of the fish gill microenvironment and the surrounding water were based on the speciation modeling. The change in copper bioavailability for fish uptake was also examined. The results indicate the presence of an experimental pH balance point at 6.9, where the pH in the fish gill microenvironment is identical to that of the surrounding water. The observed deviation range in pH levels between that found at the gills and that of the surrounding water varied from -0.4 to 0.8 units. A sinusoidal model was developed for calculation of gill pH based on the pH of the surrounding water. Models calculating alkalinity either in the gill microenvironment or in the surrounding water and for estimating mucus secretion were also developed. The results of the chemical equilibrium calculations demonstrate that, within a pH range of 6-9, the dominant species of copper in bulk solution shifted from free ions to that of the hydroxo complex. With respect to the fish gill microenvironment, the dominant species found under acidic conditions were the mucus copper complex and free ions. Because of the influence of mucus complexation and pH change, bioavailable copper species in the fish gill microenvironment were significantly lower than that in the bulk solution, especially under acidic conditions.

Prediction of fish bioconcentration factors of nonpolar organic pollutants based on molecular connectivity indices.

The relationship between bioconcentration factors and molecular connectivity indices was investigated. A regression model was developed using 80 measured BCFs of nonpolar organic pollutants. The five topological parameters used were 1 chi, 2 chi, 3 chi c, 0 chi v and 2 chi v. Modified jackknife tests were applied to examine the robustness of the model by repeatedly removing a set of or a class of compounds from the database. The model was compared with one using Kow as an independent parameter. The mean absolute errors for the 80 compounds studied were 0.288 and 0.302 log-unit for the two models, respectively.