Düsseldorf, Universiẗat, Diss., 2001.

Mainz, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Mainz, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Mainz, Universiẗat, Diss., 2001.

No description available.

The effect of pH upon the aquatic toxicity of cyfluthrin was determined in 48 h static acute toxicity tests using 2nd instar Chironomus tentans larvae. Tests were conducted in both dechlorinated tap water and lake water of pH 8.0, 7.2, and 6.6. After 48 h, immobilized and dead larvae were removed and replaced with 2nd instar larvae to assess the persistence of toxicity. Midges were cultured in water adjusted to the pH values used in testing. Toxicity if cyfluthrin varied inversely with pH. An increase in the pH of tap water by 2 units resulted in a 2-decrease in toxicity. Toxicity of cyfluthrin also varied between tap and lake water of the same pH. EC50 values in lake water were approximately 2-3 times lower than those in tap water. Toxicity in the lake water and tap water at every pH tested was also significantly different when regression line elevations were compared. Natural waters amended with cyfluthrin were consistently more toxi to the chironomids than tap water of the same pH. Persistence of cyfluthrin at low pH also influenced chironomid behavior. Recovery of normal behavior generally began within 24 h at pH 8.0 At pH 6.0, recovery did not begin until one week after dosing. The persistence of cyfluthrin also varied with pH. Averaged across all concentrations, 30% of the initial dose remained in tap water (pH 8.0) after 48 h, compared with 45% (pH 7.2), and 75 % (pH 6.6).

Tübingen, Univ., Diss., 1978.

Seston is the complex of organic and inorganic particles suspended in the water column in stream ecosystems. This detrital pool is a significant vector of energy and nutrients from headwaters to the ocean. Many of the processes involved in seston generation in streams involve the terrestrial ecosystems they drain. My objective was to determine how land use influences seston quality. Seston was collected from 9 streams along a gradient of catchment forest cover, draining 3 land-use categories: forested, agricultural, and residential. Quality variations were determined through the physical composition (size classes and concentration), chemical composition (carbon, nitrogen, and phosphorous) and organic content of seston, as well as microbial respiration of associated assemblages and growth rates of Chironomus tentans fed seston. There was more seston in streams draining less forested catchments but proportionally that material was less organic. Ultrafine particles dominated seston size classes at all sites and was higher in streams with less catchment forest cover. Phosphorous content of seston, as a % of ash free dry mass, and dissolved P in the water were higher in more disturbed streams, and C:N and N:P ratios of seston were higher in forested streams. Microbial respiration and instantaneous growth rates of C. tentans were highest on residential seston, indicating seston from those streams was more bioavailable. These results indicate that the quality of seston in stream ecosystems is linked to terrestrial processes and influenced by land use. / Master of Science