[1] Subsurface flow within a single riffle of a low-gradient gravel bed stream was modeled in three dimensions using MODFLOW, a finite difference groundwater flow model. Model simulations showed that exchange flows can only occur in this low-gradient, gaining stream because of a zone of alluvial sediment around the stream that has much higher permeability than the surrounding catchment (K = 10 À4 m s À1 , compared with K = 10 À6 to 10 À8 m s À1 ). The key factors controlling exchange flow within the alluvial zone were identified as the hydraulic conductivity of the alluvium, the hydraulic gradient between upstream and downstream ends of the riffle, and the flux of groundwater entering the alluvium from the sides and beneath. In the study riffle each of these factors changes with season, causing a reversal of flow paths in the alluvium and a reduction in exchange flows from about 0.2-0.5 m 3 d À1 per meter stream length in summer to about 0.008-0.04 m 3 d À1 per meter stream length during fall to spring. The model also revealed that exchange flows are up to twice as strong, but more variable, at the sides of the stream than near the center, and that vertical flow paths beneath the channel are more persistent under the range of conditions modeled than lateral flow paths into the banks.

Perennial rivers and streams make a disproportionate contribution to global carbon (C)cycling. However, the contribution of intermittent rivers and ephemeral streams, which

1. Studies of hyporheic microbial ecology have suggested an important role for hyporheic microbial processes in stream ecosystem functioning. Using evidence from microbial communities in other aquatic habitats, some predictions are made concerning the diversity of microbial types and microbial processes likely to occur in the hyporheic zone, and the relative importance of these various types to the hyporheic ecosystem. 2. It is predicted that the biofilm growth form of interstitial micro‐organisms will create a variety of microniches, allowing coexistence of a great diversity of microbial types, and promoting the activity of some otherwise poor competitors. It is further predicted that the confluence of reduced groundwaters and aerobic surface waters will favour chemolithotrophic processes in the hyporheic zone, but that these will contribute significantly to hyporheic production only if surface water is very low in dissolved organic carbon, or the groundwater is extremely reduced, such as by the influence of riparian wetlands. A variety of anaerobic respiratory pathways, such as nitrate, ferric ion, sulphate and even methanogenic respiration will be employed in the hyporheic zone, with biofilm dynamics permitting these to occur even in aerobic sediments. Anaerobic pathways may account for a significant proportion of total hyporheic organic matter mineralization. 3. The role of fungi in hyporheic dynamics is, as yet, almost completely unstudied. However, it is expected that they will be important in breaking down buried particulate organic matter (POM), which may account for a large proportion of total stream POM. 4. Physicochemical conditions in hyporheic sediments appear to be highly heterogeneous, and this heterogeneity may be very important in the cycling of certain nutrients, especially nitrogen, which involves a series of steps requiring different conditions. 5. Various new techniques are now available by which biofilm dynamics and in situ microbial processes may be measured. Studies are recommended of intact microbial communities both at the microscale of the biofilm and at the scale of the heterogeneities occurring in hyporheic sediments. Studies are needed that measure actual rates of microbial processes under in situ conditions.

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ABSTRACT. Recent freshwater policy reforms in New Zealand promote increased community involvement in freshwater decision making and management. Involving community members in scientific monitoring increases both their knowledge and their ability to discuss this knowledge with professionals, potentially increasing their influence in decision-making processes. However, these interactions rarely occur because, in particular, of perceptions that volunteer-collected data are unreliable. We assessed the agreement between volunteer (community group) and local government (regional council) data at nine stream sites across New Zealand. Over 18 months, community groups and regional council staff monitored, in parallel, a common set of water quality variables, physical habitat, periphyton and benthic macroinvertebrates that are routinely used by regional councils for statutory state of environment reporting. Community groups achieved close agreement (correlations ≥ 0.89, bias < 1%) with regional councils for temperature, electrical conductivity, visual water clarity, and Escherichia coli. For dissolved oxygen, nitrate, and pH, correlations were weaker (0.2, 0.53, and 0.4, respectively). Volunteer assessments of physical habitat were as consistent over time as those of councils. For visual assessments of thick periphyton growths (% streambed cover), volunteers achieved a correlation of 0.93 and bias of 0.1% relative to councils. And for a macroinvertebrate biotic index that indicates water and habitat quality, correlation was 0.88, bias was < 5%, and the average difference was 12% of the index score. Volunteers showed increased awareness of local freshwaters, understanding of stream ecosystems, and attentiveness to local and national freshwater issues. Most volunteers had shared their knowledge and interest with others in their community. Most groups had developed relationships with their regional council, and some volunteers became more interested in engaging in freshwater decision making. Given adequate professional support, community-based water monitoring can provide data reliable enough to augment professionally collected data, and increase the opportunities, confidence, and skills of community members to engage in freshwater decision making.

1. The rainforest canopy has been called 'the last biological frontier', and if this is true, there should be more undescribed species in this stratum than the ground stratum.2. Here, we test this and other hypotheses regarding traits of described and undescribed species by a sub-sample of 156 species into 96 described and 60 undescribed species from a beetle assemblage of 1473 species collected from the canopy and ground in an Australian lowland rainforest.3. We show that described species are significantly more likely to be in the canopy, are more likely to be larger and, if they are large, are more likely to have been described earlier.4. Undescribed species are just as likely to be found near the ground as in the canopy and are more likely to be smaller. 5. After the first year of sampling, 'new' described and undescribed species not previously encountered continued to appear in each of three further years of trapping.6. These data show that the canopy fauna is in fact relatively 'well known', and that the undescribed species to be found in both strata are likely to be smaller than described species and are less likely to be plant feeders. ResultsOf the 156 species examined, 96 (61.5%) were assessed to be described species and 60 (38.5%) to be undescribed (Table 1).116 Nigel E. Stork et al.

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Macroinvertebrate communities in three stony-bottomed intermittent headwater streams in central Hawke's Bay, New Zealand, were sampled once per month (on average) for 11 months from autumn 2005 to summer 2006, and compared with communities in three perennial streams and three intermittent streams with perennial headwaters. Among the intermittent headwater sites, 95 taxa were found, with Oligochaeta, Copepoda, Chironomidae, and Ostracoda occurring in greatest abundance. Eight mayfly, 6 stonefly and 16 caddisfly species were found. Macroinvertebrate abundance at intermittent headwater sites was equal to nearby perennial sites, but taxon richness per sample was lower. Community composition changed progressively during the autumn-to-spring flow period (MarchNovember 2005) at one intermittent headwater site, but at the other two sites a directional change was not evident, probably because stream flow stopped briefly several times during the flow period. Most of the taxa collected in riffles during the flow period were also in disconnected pools after flow stopped in summer (January 2006), but some taxa were absent and the disconnected pools contained several additional species. The disconnected pools in January had higher macroinvertebrate density and richness than connected pools during the flow period. At intermittent sites with perennial headwaters, taxon richness and EFT (Ephemeroptera, Plecoptera, and Trichoptera) richness were intermediate between intermittent headwater sites and perennial streams. Two weeks after flow began, the intermittent sites with perennial headwaters showed much higher EPT abundance and richness than the intermittent headwater sites, but after 8 weeks the proportional difference was less.