1. Recovery of acidified aquatic systems may be affected by both abiotic and biotic processes. However, the relative roles of these factors in regulating recovery may be difficult to determine. Lakes around the smelting complexes near Sudbury, Ontario, Canada, formerly affected by acidification and metal exploration, provide an excellent opportunity to examine the factors regulating the recovery of aquatic communities. 2. Substantial recovery of zooplankton communities has occurred in these lakes following declines in acidity and metal concentrations, although toxicity by residual metals still appears to limit survival for many species. Metal bioavailability, not simply total metal concentrations, was very important in determining effects on zooplankton and was associated with a decrease in the relative abundance of cyclopoids and Daphnia spp., resulting in communities dominated by Holopedium gibberum. 3. As chemical habitat quality has improved and fish, initially yellow perch and later piscivores (e.g. smallmouth bass, walleye), have invaded, biotic effects on the zooplankton are also becoming apparent. Simple fish assemblages dominated by perch appear to limit the survival of some zooplankton species, particularly Daphnia mendotae. 4. Both abiotic (residual metal contamination) and biotic (predation from planktivorous fish) processes have very important effects on zooplankton recovery. The re-establishment of the zooplankton in lakes recovering from stress will require both improvements in habitat quality and the restoration of aquatic food webs.

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Swimming is a popular activity in Aotearoa-New Zealand (NZ). Two variables that strongly influence swimming suitability of waters are faecal contamination, as indicated by the bacterium Escherichia coli, and visual clarity as it affects aesthetics and safety with respect to submerged hazards. We show that E. coli and visual clarity are inversely related overall in NZ rivers (R = -0.54), and more strongly related in many individual rivers, while similar (but positive) correlations apply also to turbidity. This finding, apparently reflecting co-mobilisation of faecal contamination and fine sediment, suggests that visual clarity, measured or estimated from appearance of submerged features, should be a valuable indicator of faecal contamination status and (more generally) swimming suitability. If swimmers were to avoid river waters <1.6 m black disc visibility (a long-established NZ guideline for swimming) they would also avoid microbial hazards (E. coli <550 cfu/100 mL about 99% of the time in NZ rivers). However, urban-affected rivers might sometimes be microbially contaminated when still clear. Water management agencies should measure visual clarity together with E. coli in river surveillance. Real-time information on swimming suitability could then be based on continuous monitoring of turbidity locally calibrated to both visual clarity and E. coli.

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Zooplankton and phytoplankton communities play host to a wide diversity of parasites, which have been found to play a significant role in a number of ecosystem processes, such as facilitating energy transfer and promoting species succession through altering interspecific competition. Yet we know little about the mechanisms that drive parasite dynamics in aquatic ecosystems. Recent mathematical models have shown how habitat can shape parasite dynamics through influencing the efficacy of parasite transmission; however, these predictions have yet to be tested at larger ecological scales. Here, we present a comparative analysis of parasitism in planktonic communities, assembling data from a range of host and parasite taxa, habitat types, and geographic regions. Our results suggest that the prominent depth-prevalence relationship observed in studies on Daphnia in temperate lakes of North America is applicable to a wide range of aquatic habitats, hosts, and parasites; however, differences in transmission strategies between parasites can lead to considerable variation in parasite dynamics. Observational studies which incorporate a diversity of habitat types will be important in uncovering the mechanisms which underlie this relationship. In particular, more experimental work on transmission stage survivability and infectivity in aquatic environments will be necessary before we can make accurate predictive models of parasite spread in these ecosystems. Additional Supporting Information may be found in the online version of this article *Correspondence: amanda.valois@otago.ac.nz 1707 LIMNOLOGY and OCEANOGRAPHY

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This article overviews community-based water monitoring (CBWM) in Aotearoa-New Zealand (NZ). CBWM was strongly boosted in NZ around 2000 by the development of the Stream Health Monitoring and Assessment Kit (SHMAK) and the Wai Care community initiative. Reform of freshwater management in NZ may be one driver for renewed interest recently in CBWM. Because professionals perceive volunteer-monitoring data as unreliable, they currently give little support to volunteer monitoring. To address their concern, we compared CBWM with measurements by regional authorities (RAs) – the main water management agencies in NZ. Agreement was encouragingly close for a comprehensive range of variables, including the important state-of-environment (SoE) indicators: visual clarity, Escherichia coli and macroinvertebrates. Community volunteers need and want ongoing professional support and encouragement, and, fortunately, there are important benefits for water management agencies, including engagement of citizens in water management and use of volunteer data. Professional support for CBWM in NZ could include: advice and encouragement, training, database development and quality assurance. Current research and development is focused on improving resources and systems for volunteer monitoring, notably with upgrading of the SHMAK. We are enlisting volunteers, equipped with improved tools and support systems, to assess the benefits of riparian rehabilitation and the suitability of water for swimming.