Preliminary estimates of mass-loss rates, changes in stable isotope composition, and invertebrate colonisation of evergreen and deciduous leaves in a Waikato, New Zealand, stream.

Rates of mass loss are important in the choice of tree species used in riparian rehabilitation because leaves that break down fast should contribute to stream food-webs more rapidly than leaves that break down more slowly. To examine comparative mass-loss rates of some native evergreen and introduced deciduous trees in a New Zealand stream, fallen leaves were incubated in bags with 2 x 3 mm mesh openings. The native trees were mahoe (Melicytus ramiflorus), kahikatea (Dacrycarpus dacrydioides), silver beech (Nothofagus menziesii), rewarewa (Knightia excelsa), tawa (Beilschmiedia tawa), and the introduced trees were silver birch (Betula pendula) and alder (Alnus glutinosa). The leaf bags were left in the Mangaotama Stream for 28 days from mid April to mid May 1995 when mean water temperature was 14.5deg.C, giving a total of 406 degree days. Rates of mass loss followed the sequence: mahoe > silver birch > alder > kahikatea > silver beech > rewarewa > tawa. Mean mass-loss rate for mahoe, assuming a negative exponential model, was 0.0507 k day-1 (0.00350 k (degree day)-1), and for tawa was 0.0036 k day-1 (0.00025 k (degree day)-1). C:N ratio decreased on average from 45:1 to 35:1, and d15N increased between 0.7 and 3.0[[perthousand]] (1.8 +/- 0.41[[perthousand]], mean +/-1 standard error), excluding kahikatea. Changes in d13C were smaller and not consistent in direction. Biomass of invertebrates was greatest in bags that had lost 25-45% of their initial leaf biomass

Ecological and physical characteristics of the Te Awa O Katapaki Stream, Flagstaff, Waikato

1. The fish, macroinvertebrates, aquatic vegetation, and water quality indicate that the Te Awa O Katapaki Stream is an unpolluted, pastureland stream that is typical of the Waikato region. 2. The stream has very high nutrient concentrations that probably result from the dairy farming upstream. 3. The fish fauna is dominated by the native shortfinned eels. The presence of the migratory common smelt indicates that swimming fish species also have free access to the stream from the Waikato River. 4. Fish of high conservation value, such as giant or banded kokopu (Galaxias argenteus or G. fasciatus) were absent, which is predictable given the warm, unshaded nature of the stream. 5. Fish and invertebrates would soon recolonise the restored stream following any work in the streambed

Fish populations of Lake Ngaroto, Waikato, and fish passage at the outlet weir.

1.Lake Ngaroto has a diverse fauna of native and introduced fish. It is largest of the Waipa lakes, is hypertrophic (i.e., has very high concentrations of plant nutrients), and is highly productive for this reason. 2.In an exhaustive fish survey that used gill nets, fyke netx, and beach seining, 4,317 fish of nine species were caught. The catch included five species of introduced fish. Over 70% of the catch was brown bullhead catfish; rudd, goldfish, a single mosquitofish, and a single koi carp were also caught. In summer, mosquitofish numbers a likely to be very high. 3.Four species of native fish were caught, and of these, shortfinned eels wer the most numerous. Common bullies, a few longfinned eels, and a single common smelt were caught, thought common smelt and common bullies are expected to be much more numerous in summer. 4.The migratory species in the lake are the eels and common smelt. Eels are always migratory, as they spawn in the tropical ocean. Common smelt may be wither migratory or lake-resident, and the single individual caught in this survey had vertebral and gill raker counts diagnostic of a migratory fish. As smelt migrate upstream from the ocean in spring and summer, but are generally absent from freshwaters in winter, the low abundance in August and October 2001 is not surprising. 5.Eels are string migrators, and can climb rock faces and wriggle through small cracks and crevices during their migration. Common smelt migrate by swimming, and high velocities and free-falling water barriers can prevent their upstream passage. 6.We recommend that to all upstream passage of swimming species such as common smelt the rebuilt weir has zones with mean water column velocities no greater than 0.5 m s⁻¹, and preferably 0.3-0.4 m s⁻¹. The length of the downstream slop of the weir should be no more than 4 m, and the water depth over the weir should be at least 5 cm during the time of principal upstream migration (August to December)