A set of near-stream flowpaths in pasture, native forest and exotic pine plantations in New Zealand was sampled to describe differences in dissolved organic carbon (DOC). The quantity and bioavailability of DOC varied among flowpaths in different land uses, with higher concentrations of DOC in near-stream flow paths than the parent groundwater emerging from the hillslope. Tiles incubated in these waters did not consistently yield higher bacterial growth rates than tiles incubated in groundwaters. DOC composition, measured as fluorescence and absorbance properties and extracellular enzyme fingerprints, differed significantly among land uses and position along flowpath.Differences in riparian vegetation can indirectly affect DOC by altering exposure to ultraviolet radiation. A 2-h exposure of water from subsurface flowpaths to full sunlight caused marked changes in fluorescence characteristics of water from the pasture catchment but only small changes in water from the native forest catchment. There were up to fivefold differences in extracellular enzyme activities on tiles incubated in light-exposed water for the native forest site, but not for the pasture site. Bacterial growth and respiration were higher on tiles incubated in native forest water exposed to sunlight, but there was no light effect on growth for tiles incubated in water from the pasture flowpath. These results indicate that riparian flowpaths will affect the quantity and character of DOC delivered to streams and ultraviolet exposure may, at least in some cases, alter DOC bioavailability.

Although the importance of the subsurface saturated interstitial zone (hyporheic zone) to the ecological functioning and maintenance of water quality of stream ecosystems is well known, there is little information on the impacts of different forms of land use upon this zone. Hyporheic physico-chemistry and invertebrates were compared among small streams draining hillcountry catchments under pasture, exotic pine forest, and native forest near Hamilton, New Zealand. In streams draining native forest, the hyporheic zone harboured a relatively diverse invertebrate fauna comprising mostly taxa common in the surface benthos, although a few apparently obligate hyporheic taxa (ostracods, blind amphipods) were collected. Few individuals and taxa occupied the hyporheic zones of streams draining pasture with some groups such as water mites conspicuously absent. The hyporheos of the stream in exotic pine forest was similar in richness and abundance to that of the pasture streams. Hyporheic water temperatures were significantly higher in the pasture streams than those in pine or M96091

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Climate warming is rapid in the Arctic, yet impacts to biological systems are unclear because few long-term studies linking biophysiological processes with environmental conditions exist for this data-poor region. In our study spanning 25 years in the Alaskan Arctic, we demonstrate that climate change is affecting the timing of freeze-thaw cycles in the active layer of permafrost soils and altering the physiology of arctic ground squirrels ( Urocitellus parryii ). Soil freeze has been delayed and, in response, arctic ground squirrels have delayed when they up-regulate heat production during torpor to prevent freezing. Further, the termination of hibernation in spring has advanced 4 days per decade in females but not males. Continued warming and phenological shifts will alter hibernation energetics, change the seasonal availability of this important prey species, and potentially disrupt intraspecific interactions.

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