排序方式: 共有7条查询结果,搜索用时 15 毫秒
1
1.
2.
Knut Lehre Seip Gulbrand Lunde Sigurd Melsom Even Mehlum Angelika Melhuus Hans Martin Seip 《Ecological modelling》1979,6(2):133-166
A mathematical model has been developed to study the distribution and abundance of benthic algae species in a Norwegian fjord. The main forcing functions are the physical factors which have well defined gradients in this area, but biotic interactions are also accounted for in the model.The distribution of algae along vertical transects in the intermediate fjord area has been simulated, and the observed distribution is reproduced fairly well. This indicates that the major factors determining the equilibrium elevation between intertidal and subtidal vegetations in this area are adequately represented in the model.Based on observations in a fjord branch with a high level of freshwater influx and polluted by heavy metals, assumptions are made of the combined influence of these contaminants on growth characteristics of the species considered. The resulting effects on community development and community patterns are simulated. For a certain level of contamination, the decrease in abundance, community development rate and species separation have been determined. It is also shown that the fluctuations in biomass during a year are more pronounced than under unaffected conditions.The relative importance of external growth regulating factors and self-shading is demonstrated for different degrees of community development, and we have indicated that this may be an important factor in the assessment of transient and long-term responses to “natural” and man-made influences on the shore-line vegetation.One of the main problems during model development was the formulation of the interaction function for factors influencing growth parameters. Several alternatives were examined.The differences between the most frequently used forms were small with respect to abundance and not very large with respect to possible changes in distribution. It was noted that even by including only the most limiting factor at each instant, (Liebig's form) a high percentage of the potentially limiting factors did actually limit growth during periods of the year.The model is intended as a working tool for the studies of changes in the shore-line vegetation caused by man-made interferences like heavy metal and oil pollution, and we believe that the results presented demonstrate that it can successfully be used for this purpose. 相似文献
3.
4.
Kevin B. Lunde Matthew R. Cover Raphael D. Mazor Christopher A. Sommers Vincent H. Resh 《Environmental management》2013,51(6):1262-1273
Identification of minimally disturbed reference sites is a critical step in developing precise and informative ecological indicators. We tested procedures to select reference sites, and quantified natural variation (inter-site and -annual variability) among reference conditions using a macroinvertebrate data set collected from 429 mediterranean-climate stream reaches in the San Francisco Bay Area, California (USA). We determined that a landscape GIS-based stressor screen followed by a local field-based stressor screen effectively identified least-disturbed reference sites that, based on NMS ordination results, supported different biological communities than sites identified with only landscape (GIS) or local (field) stressors. An examination of least-disturbed reference sites indicated that inter-site variability was strongly associated with stream hydrology (i.e., perennial vs. non-perennial flow) and annual precipitation, which highlights the need to control for such variation when developing biological indicators through natural gradient modeling or using unique biological indicators for both non-perennial and perennial streams. Metrics were more variable among non-perennial streams, indicating that additional modeling may be needed to develop precise biological indicators for non-perennial streams. Among 192 sites sampled two to six times over the 8-year study period, the biological community showed moderate inter-annual variability, with the 100 point index of biotic integrity scores varying from 0 to 51 points (mean = 11.5). Variance components analysis indicated that inter-annual variability explained only a fraction (5–18 %) of the total variation when compared against site-level variation; thus efforts to understand causes of natural variation between sites will produce more precise and accurate biological indicators. 相似文献
5.
6.
Despite California policies requiring assessment of ambient wetland condition and compensatory wetland mitigations, no intensive
monitoring tools have been developed to evaluate freshwater wetlands within the state. Therefore, we developed standardized,
wadeable field methods to sample macroinvertebrate communities and evaluated 40 wetlands across Northern California to develop
a macroinvertebrate index of biotic integrity (IBI). A priori reference sites were selected with minimal urban impacts, representing
a best-attainable condition. We screened 56 macroinvertebrate metrics for inclusion in the IBI based on responsiveness to
percent urbanization. Eight final metrics were selected for inclusion in the IBI: percent three dominant taxa; scraper richness;
percent Ephemeroptera, Odonata, and Trichoptera (EOT); EOT richness; percent Tanypodinae/Chironomidae; Oligochaeta richness;
percent Coleoptera; and predator richness. The IBI (potential range 0–100) demonstrated significant discriminatory power between
the reference (mean = 69) and impacted wetlands (mean = 28). It also declined with increasing percent urbanization (R
2 = 0.53, p < 0.005) among wetlands in an independent validation dataset (n = 14). The IBI was robust in showing no significant bias with environmental gradients. This IBI is a functional tool to determine
the ecological condition at urban (stormwater and flood control ponds), as well as rural freshwater wetlands (stockponds,
seasonal wetlands, and natural ponds). Biological differences between perennial and non-perennial wetlands suggest that developing
separate indicators for these wetland types may improve applicability, although the existing data set was not sufficient for
exploring this option. 相似文献
7.
Pilot-scale experiments were carried out to study the formation of chlorinated hydrocarbons through combustion of PVC. Vinyl chloride, dichloro-, trichloro-, tetrachloro-, pentachloro-, and hexachlorobenzenes were determined by GC/ECD. Furthermore, some peaks in the chromatogram were tentatively assigned to octachlorostyrene and PCB. The total amount of lipophilic organochlorinated compounds was determined by neutron activation analysis. The results indicate that incineration of PVC is not a major source of chlorinated hydrocarbons in the environment. 相似文献
1