Dense macrophyte beds are known to produce extreme diurnal oxygen and temperature conditions in shallow lakes. However their influences in managed hydropeaking reservoirs has received limited attention. We measured dissolved oxygen, pH and water temperature in the Lake Kar apiro hydroreservoir, northern New Zealand, across a gradient of proportional water-column height occupied by the invasive macrophytes Egeria densa and Ceratophyllum demersum, which dominated in the upperriverine (variable water inflow) and lower-lacustrine (variable water level) sections, respectively. Hypoxia and anoxia events that occurred inside invasive macrophyte beds during their summer peak biomass accumulation period were more pronounced for C. demersum than for E. densa, and within the bottom 20% of the water column. In contrast, pH and temperature changed little in relation to proportional macrophyte height. Macrophyte species differences in the production of hypoxia and anoxia events increased when site-specific hydropeaking management covariates (depth, inflows, water level) were accounted for. This association with hydropeaking likely resulted from contrasting hydrodynamics in the lower-lacustrine and upper-riverine lake sections, where oxygen can decrease with higher water levels and lower water inflow rates, respectively. During the course of our study, some macrophyte beds were treated with herbicide, enabling us to document prolonged and sustained hypoxic/anoxic conditions near the bottom following spraying. These results underscore the adverse effects of invasive macrophytes on water physicochemical attributes that sustain aquatic biota, and highlight the context-dependent nature of these effects moderated by reservoir management for hydropeaking and macrophyte control.

1. Understanding the multiple agents of decline is important for the conservation of globally threatened Unionida (Class Bivalvia), but threats from non-native species have received limited attention. To address this gap, a global meta-analysis was conducted aimed at identifying known interactions and mechanisms of impact and informing potential effect pathways for the New Zealand unionid fauna.2. The main non-native groups identified as interacting with unionids were fish (38% of published studies), macrophytes (33%), and vertebrate predators (30%), with 70% of interactions leading to adverse impacts on mussels. Most studies used field surveys (~50%) and were conducted in rivers (~50%).3. Impacts occurred across the unionid life cycle (adult, glochidia, host, and juvenile), and primarily affected processes that determine the transitions between life-cycle stages (fertilization, infestation, settlement, and maturation). The impacts of nonnative macrophytes and fish were predicted to be greater for transitional stages than the impact of vertebrate predators, which mostly affected adult mussels. New ZealandUnionida are most likely to be affected by interactions with nonnative species in lowland lakes and waterways, where connectivity for diadromous native fish hosts and high bioinvasion potential intersect.

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Making high quality but affordable Pinot noir (PN) wine is challenging in most terroirs and New Zealand (NZ)’s situation is no exception. To increase the probability of making highly typical PN wines, producers choose to grow grapes in cool climates on lower fertility soils while adopting labour intensive practices. Stringent yield targets and higher input costs necessarily mean that PN wine cost is high, and profitability lower, in affordable varietal wine ranges.To understand if higher-yielding vines produce wines of lower quality we have undertaken an extensive study of PN in NZ. Since 2018, we established a network of twelve trial sites in three NZ regions to find individual vines that produced acceptable commercial yields (above 2.0 kg per metre of row) and wines of composition comparable to “Icon” labels. Approximately 20 % of 660 grape lots (N = 135) were selected within a narrow juice Total Soluble Solids (TSS) range of 22.0 ± 1.0 °Brix and made into single-vine wines under controlled conditions.Multiple Factor Analysis of the vine, berry, juice and wine parameters from three vintages found grape Berry Weight to be the most effective clustering variable. As the Berry Weight category decreased, there was a systematic increase in the probability of higher berry red colour and total phenolics with a parallel increase in wine phenolics and decreased juice amino acids. The influence of berry weight on wine composition would appear stronger than the individual effects of Vintage, Region, Vineyard or vine Yield. Our observations support the hypothesis that it is possible to produce PN wines that fall within an “Icon” benchmark composition range at yields above 2.5 kg per vine, provided that the Leaf Area:Fruit Weight ratio is above 11 cm2 per g, mean berry weight is below 1.2 g and juice TSS is above 22 °Brix.