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Recent studies of lakes suggest that the relative availability of light and phosphorus in the mixed layer helps determine the quality of phytoplankton consumed by herbivorous zooplankton. In turn, increases in algal quality positively affect zooplankton growth and reproductive rates. However, these studies have concentrated on explaining variation among lakes over relatively short time periods and have not evaluated the temporal dynamics in the physical-chemical forcing on zooplankton production. We investigated whether there were seasonal changes in the relationship between Daphnia fecundity and the physical-chemical environment, algal community characteristics, and Daphnia length using dynamic linear models (DLM) to analyze a high-resolution, 16-yr time series from Lake Washington. We used two metrics to describe algal quality: the percentage of blue-green algae and the light to total phosphorus (TP) ratio as an indirect metric for algal C : P. Chlorophyll a (Chl a) concentration and algal biovolume served as measures of algal quantity. As expected, both the light : TP ratio and the percentage of blue-green algae had negative effects on Daphnia fecundity, and Chl a concentration and biovolume had positive effects on fecundity. However, we found a comparatively stronger effect of Daphnia length on fecundity, although it was negative and therefore opposite to expectation. In all cases, we observed strong seasonal differences in environmental effects, but no temporal change in the fundamental relationships between our indices of algal quantity and quality, allometry, and Daphnia reproduction. Our results support a hypothesis of physical-chemical coupling to algal quality and zooplankton production but highlight the importance of temporal variation in this forcing.

\" W. T. Edmondson has spent his career answering questions about the ecological impacts of human experiments on lakes in Washington State. In this volume, he recounts these studies and captures from his experiences a larger view of the nature of our environmental problems. . . . While the commentary is wide ranging, the foundation is a personal account of one ecologist's lifetime experience on the dual points of research and public application of that research.\"-Research and Exploration\"W. T. Edmondson, a zoologist, extracts enduring lessons from his more than 50 years of experience in persuading political powers to make use of scientific knowledge when they set about drawing up laws for managing human interventions in the environment. Any scientist who follows in Edmondson's footsteps should benefit from reading this sensitive recounting of political battles.\"-Garrett Hardin, Pacific Northwest Quarterly

Variations with depth in properties of the sediment of Lake Washington are compared with known conditions in the lake. Annual changes of deposition form pairs of cryptic layers, dominated respectively by diatoms and mineral particles, that are revealed by X-radiography. A period of eutrophication is recorded by sediment rich in phosphorus. Two later peaks of P can be attributed to deposition of eroded material during floods. The relative importance of diatom species changed in coordination with changes in nutrition and the presence of Oscillatoria which can supress some species of centric diatoms by antibiosis. Experiments confirm that selective feeding by oligochetes can result in nonrandom transport of different components of sediment. Sporadic, brief outbursts of rare species of diatoms give precise dating and opportunity for measuring bioturbation under fully natural conditions by repeated sampling. Precise data on vertical distribution of diatoms are given by overlapping scanning electron micrographs of dried cores.

In 1976 Daphnia, a genus that had been incospicuous in the zooplankton of Lake Washington, suddenly became dominant. The mean summer transparency of the lake doubled. The major change affecting the success of Daphnia evidently was a decrease in the abundance of the predatory Neomysis mercedis in the mid-1960s. Daphnia propably did not increase at that time because of the continued persistence of significant quantities of Oscillatoria until 1975. Eight species of Daphnia have been seen in the lake, but only three have become abundant. Daphnia publicaria has been continuously present since its appearance in May 1976, although it becomes very scarce in winter. Daphnia galeata mendotae and Daphnia thorata have had much more limited occurrence. In each year from 1976 to 1980, two species formed separate population maxima, except in fall 1979 when D. thorata, although present, failed to increase. Instead, the plankton became dominated by the rotifer Conochilus hippocrepis which had been increasing for several years. In 1980 D. thorata and D. pulicaria made maxima, but in reverse order from earlier years. Several other species of zooplankton have been less abundant since the resurgence of Daphnia than during the period of eutrophication and recovery.

Lake Washington received increasing amounts of secondary sewage effluent from 1941 to 1963 and responded by changes in the amount of nutrients in the water and in the kind and quantity of phytoplankton. From 1963 to 1968 the amount of effluent entering the lake was progressively decreased to zero, and the lake promptly responded with decreases in the amount of nutrients, the quantity of phytoplankton, and the proportion of blue-green algae. The lake could be regarded as having recovered from eutrophication by 1975. Phosphorus and nitrogen income from sewage, inlets, and atmosphere were calculated from direct measurements or approximated from other data and from regressions with hydrological income. Total phosphorus input varied from a maximum of 204.2 × 103 kg· yr-1 in 1964 to a low of 42.9 in 1973 and 1976. The maximum fraction from sewage was 72.4% in 1962. Total nitrogen varied from 1,419 × 103 kg· yr-1 in 1964 to 734 in 1976. The total P content of the lake varied in close correlation with input from a maximum of about 200 × 103 kg (equivalent to a mean concentration of about 69 μ g · liter-1) to a mean of about 50 × 103 kg durign the postrecovery era. The sewage episode affected the phosphorus regime much more than that of nitrogen. There were seasonal differences in the deposition of phosphorus to and release from the sediments, the average net long term retention being about 57% of the income; slight changes in retention during and after diversion resulted in a greater fraction of the influent P being lost to the sediments after diversion. The amount of phosphorus lost permanently to the sediments during a year is more closely related to the annual income than to the mean concentration in the water.

After diversion of sewage effluent from Lake Washington, winter concentrations of phosphate and nitrate decreased at different rates. From 1963 to 1969, phosphate decreased to 28 percent of the 1963 concentration, but nitrate remained at more than 80 percent of the 1963 value. Free carbon dioxide and alkalinity remained relatively high. The amount of phytoplanktonic chlorophyll in the summer was very closely related to the mean winter concentration of phosphate, but not to that of nitrate or carbon dioxide.

Phytoplankton and environmental conditions in Lake Washington, Seattle, Washington, are discussed from the perspective of dynamic relationships between taxon-specific growth rates and environmental variables. More than four decades of measurements permit inspection of conditions associated with net increase and decrease for 40 phytoplankton species or species groups. Reproducible patterns exist for growth responses to over 25 environmental factors including nutrient chemistry, physical variables, and herbivorous zooplankton species. There appear to be no more than six main modalities of response to environmental factors, and responses to chemical and physical variables show coherence across taxa. Diatoms show a near uniform positive growth response to abundant inorganic nutrients, cold and transparent water, deep mixing, and intolerance for virtually all zooplankton grazers. Many chlorophytes and cyanobacteria show equally uniform growth responses to chemical and physical variables, although their preferences are virtually opposite from the diatoms. They benefit from the presence of copepods but show highly specific growth rate responses to different cladocerans and rotifers. Growth rate variations among the diatoms sort out along gradients of resource and physical factors, but there is coherence to the rise and fall of multiple species. Among the other algal divisions, despite a common set of physical and chemical conditions that promote growth rates, the species do not increase and decrease together. Instead, the prevailing grazer community appears to shape the phytoplankton community by admitting only certain species from the large pool of contenders.

Heightened scientific and public interest in biodiversity has been driven by the accelerated rates of species extinctions at local and global scales. The question of which species are expendable derives from the humble realization that society is not able to prevent the extinctions of all species with which humans interact. The benefits of preventing extinctions are often in direct conflict with economic development in human societies. Asking scientists to estimate the expendability of specific species is a seductive solution to asking which species are worth “saving” versus which species will not be missed if they go extinct. The problem of

“ W. T. Edmondson has spent his career answering questions about the ecological impacts of human experiments on lakes in Washington State. In this volume, he recounts these studies and captures from his experiences a larger view of the nature of our environmental problems. . . . While the commentary is wide ranging, the foundation is a personal account of one ecologist’s lifetime experience on the dual points of research and public application of that research.”—Research and Exploration“W. T. Edmondson, a zoologist, extracts enduring lessons from his more than 50 years of experience in persuading political powers to make use of scientific knowledge when they set about drawing up laws for managing human interventions in the environment. Any scientist who follows in Edmondson’s footsteps should benefit from reading this sensitive recounting of political battles.”—Garrett Hardin, Pacific Northwest Quarterly