New Zealand chironomids as proxies for human-induced and natural environmental change: Transfer functionsfor temperature and lake production (chlorophyll a)

The analysis of chironomid taxa and environmental datasets from 46 New Zealand lakes identified temperature (February mean air temperature) and lake production (chlorophyll a (Chl a)) as the main drivers of chironomid distribution. Temperature was the strongest driver of chironomid distribution and consequently produced the most robust inference models. We present two possible temperature transfer functions from this dataset. The most robust model (weighted averaging-partial least squares (WA-PLS), n = 36) was based on a dataset with the most productive (Chl a > 10 lg l)1) lakes removed. This model produced a coefficient of determination (r2 jack) of 0.77, and a root mean squared error of prediction (RMSEPjack) of 1.31C. The Chl a transfer function (partial least squares (PLS), n = 37) was far less reliable, with an r2 jack of 0.49 and an RMSEPjack of 0.46 Log10lg l)1. Both of these transfer functions could be improved by a revision of the taxonomy for the New Zealand chironomid taxa, particularly the genus Chironomus. The Chironomus morphotype was common in high altitude, cool, oligotrophic lakes and lowland, warm, eutrophic lakes. This could reflect the widespread distribution of one eurythermic species, or the collective distribution of a number of different Chironomus species with more limited tolerances. The Chl a transfer function could also be improved by inputting mean Chl a values into the inference model rather than the spot measurements that were available for this study.

Chlorophyll-a concentrations and macroinvertebrate declines coincide with the collapse of overwintering diving duck populations in a large eutrophic lake

1. Lough Neagh is one of the most important non-estuarine sites in the British Isles for overwinteringwildfowl. A change in the waterbird assemblage following the winter of 2000/2001 was drivenmainly by a rapid decline in the population of overwintering diving ducks. Sudden and discretechanges in resident as well as migratory waterbirds may suggest an intrinsic cause.
2. We compared the density and biomass of benthic macroinvertebrates, the food of overwinteringdiving ducks, in 2010 (following the diving duck population decline) with values from a baselinesurvey conducted in 1997/1998 (before the decline in diving ducks).
3. The mean total density of macroinvertebrates declined significantly by c. 65% from 15 300 m2in1997/1998 to 5136 m2in 2010. There was a concomitant c. 70% decline in mean macroinvertebratebiomass from 15 667 mg m2to 5112 mg m2. In terms of taxonomic composition, the relativecontribution of Tanypodinae, Glyptotendipes spp . and Tanytarsini declined, while the relativecontribution of Chironomus spp. increased.
4. We describe a shift in chlorophyll-a concentration, a proxy of phytoplankton biomass, in thelargest freshwater lake in the British Isles coincident with a significant reduction in macroinverte-brate density and biomass, with potential implications for ecosystem processes and ecologically andeconomically important consumer populations, including waterbirds and fishes