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Lake Rotorua has become increasingly eutrophic over the past 2 to 3 decades. The sediments of the lake have been shown to exert an important influence on this eutrophication process. Chemistry of the sediments has been studied to determine the nature, composition and distribution of elements, through a 1.5 year coring programme. A geophysical survey together with sub-bottom profiling has provided stratigraphic information related to the bathymetry of the lake. Lake Rotorua has two types of sediments: coarse, dense (density c. 0.5 g/cm3) sediments comprised of clastic erosion products and coarse rhyolitic airfall components covering approximately 60% of the lake area; and fine, low-density (approximatly 0.02 g/cm3) diatomaceous ooze that covers the remaining 40% of the lake, accumulated from deposition of biota, predominantly diatom frustules of Aulacoseira granulata. The sediment contains a record of volcanic eruptions, with the Tarawera Tephra typically found 0.5 m below the sediment water interface and Kaharoa Tephra typically between 2 to 3 m depth, in water depths of 10-15 m. Phosphorus concentration in Lake Rotorua sediments decreases with sediment depth. In the centre of the lake phosphorus concentrations in the top 2 cm can exceed 2500 g/tonne and decline to 800 g/tonne at 20 cm depth. Accumulation rate of phosphorus in the sediment based on the nutrient budget is approximatly 29.6 t/yr. Iron and manganese concentrations in the sediment depend on the availability of the element and the sedimentation rate of diatom frustules, and are controlled by the redox conditions in the sediment. The average concentration of iron and manganese in the sediment is approximately 8000 g/tonne and between 300 and 400 g/tonne, respectively. Iron accumulates in the sediment at a rate of 385 t/yr and manganese at 17.9 t/yr. Maximum concentrations of arsenic in the sediment are 250 g/tonne but are generally between 50-100 g/tonne, depending on the water depth. Lead concentrations are typically below 15 g/tonne. Sediment concentrations of both arsenic and lead are highly correlated with iron and manganese concentrations in the sediment and mimic the respective concentration profiles. Arsenic and lead accumulate in the sediment at a rate of 3.71 and 0.49 t/yr, respectively. All elements show a peak in concentration in the tephra layers. The bathymetry of Lake Rotorua is dominated by a curved depression extending from Sulphur Point and almost reaching the Ohau Channel. This depression is probably a structural feature likely associated with the collapse of the caldera, but could be an ancient drainage channel. A series of conical depressions clustered to the north of Sulphur Point and to the east of Mokoia Island are likely to be hydrothermal explosion creators. In the north in the lake at water depths less than 10 m, a series of near-shore terraces are preserved in the sediment. Sub-bottom echo-sounding shows no return of sonic and seismic signals from most of the lake floor, indicating total absorption by the methane gas-filled sediment. In the shallow lake margin environments, generally less than 10 m water depth, gas is absent and a detailed stratigraphy of multiple reflectors from tephra layers was observed with sub-bottom profiles. The basin sediments of Lake Rotorua are significantly pockmarked, with deep, circular flat-bottomed depressions c. 20-60 m diameter and 0.5-6 m depth. The pockmarks are located on the lake floor in areas where the sediment is saturated with gas.

The physiological responses involved in mediating adaptive change due to varying environmental conditions or social interactions are complex and involve integration of numerous signaling pathways. With Drosophila melanogaster, I can investigate the responses to varied environmental and social stimuli through quantification of signaling activity, stress resistance, and changes in gene expression and behavior. My work focuses on investigating signaling pathways that adult insects use to regulate homeostasis. The steroid hormone 20- hydroxyecdysone (ecdysone) and its receptor (EcR/USP) are vital during arthropod development for coordinating molting and metamorphosis. However, recent adult studies in Drosophila melanogaster indicate that the hormone and receptor influence many processes. I characterized the wild-type expression patterns and activity of ecdysone receptors in individual tissues during early adult life. I found that receptor components EcR and usp were expressed in numerous adult tissues, but receptor activation varied depending on tissue type and adult age. EcR/USP activity did not detectably change in response to environmental stimuli but is reduced when a constitutively inactive ecdysone receptor is present. The current state of our understanding of this signaling system is reviewed with reference to my findings. I discuss future directions focusing on identifying locations of hormone synthesis, metabolism, and storage, isoform-specific roles of EcR, and functional roles of gene repression and activation to link hormone receptor activity with physiological responses. Adult physiology is also regulated by interactions between adipose tissue and the central nervous system. Genes expressed in the insect fat body are involved in regulating nutrient homeostasis, stress resistance, immunity, reproduction, and behavior. Of particular interest is female-specific independent of transformer (fit). Several studies indicate that fat body expression of fit may influence responses to environmental change by altering adult behavior or physiology. Our lab created fit mutants that I used to assess the effects of these mutations on adult Drosophila physiology and behavior. I found that fit mutant adults survive longer without food, have increased nutrient levels, are more active, and feed extensively. My findings indicate that the fat-biased gene fit influences multiple aspects of adult physiology that affect appetite modulation, metabolism, and behavior.