Marc Schallenberg

An analysis of phytolith assemblages for the quantitative reconstruction of late Quaternary environments of the Lower Taieri Plain, Otago, South Island, New Zealand I. Modern assemblages and transfer functions

An analysis of modern phytolith assemblages is presented.Phytolith assemblages were studied in modern surface soils and sediments of 28sites from east Otago, New Zealand, within a range of vegetation types andmicroclimates. No simple distinction could be made between vegetation types onthe basis of phytolith assemblage composition. A Principal Components Analysis(PCA) of the phytolith data set revealed that festucoid, chloridoid andspherical phytolith morphotypes formed strong associations with sites fromwetland, grassland, and forest vegetation types, respectively. Moreimportantly, a comparison of sample replicates from each field site using Squared ChordDistance (SCD) assemblage analysis showed that wetland and grassland sitestended to produce more internally consistent phytolith assemblages than forestsites. Environmental variables including pH, conductivity, altitude,precipitation and temperature were also gathered for each site. The ability ofeach environmental variable to reflect variance in the entire phytolithdata set was estimated by a series of Redundancy Analyses (RDA) with MonteCarlo permutation tests of statistical significance. After a forward selectionprocess, transfer functions were generated using Partial Least Squares (PLS)regression and calibration with jack-knife validation. The final transferfunctions have root mean squared errors of prediction for pH (0.47), logconductivity (0.38 μS cm), average annual precipitation (63mm), and average annual (0.28 °C), spring (0.38 °C) andautumn temperature (0.41 °C); the smallest group of environmental variablesexplaining the most variance in the modern phytolith data set. The most usefultransfer functions for application to fossil phytolith data andpaleoenvironmental interpretation are pH, log conductivity and annualprecipitation. The relationship between changes in pH and annual precipitationand phytolith assemblage composition found in this study presents aprima facie relationship with the potential to providedirect proxies for soil weathering and indirectly for paleoenvironmentalreconstruction.

Regime shifts between clear and turbid water in New Zealand lakes: Environmental correlates and implications for management and restoration

Abstract We reviewed lakes in New Zealand reported to have undergone regime shifts between macrophyte‐dominated clear water states and de‐vegetated, turbid states. Regime‐shifting lakes (RSLs) occurred along a wide latitudinal gradient. We obtained catchment land‐use data as well as data on the occurrences of introduced (non‐indigenous) macrophytes and herbivorous and benthivorous fish for the 37 RSLs and for 58 lakes with similar maximum depths and climates, but which had not been reported to have undergone regime shifts. All RSLs had a maximum depth <20 m and mean annual surface air temperature between 9 and 16°G Regime shifts were positively related to the percentage of the catchment in pasture and negatively related to the percentage of the catchment in forest. The occurrences of the introduced macrophyte Egeria densa and the introduced fish, Ameiurus nebulosus (catfish), Carassius auratus (goldfish), Scardinius erythrophthalmus (rudd), Cyprinus carpio (koi carp), and Tinca tinca (tench), were significantly correlated to regime shifts in lakes. Although the presence of other introduced aquatic macrophytes was not significantly correlated with RSLs, the number of exotic fish taxa present in lakes was strongly positively correlated with increasing prevalence of regime shifts. The strength of the correlations between land use and introduced species versus regime shifts illustrates a number of factors which could be managed to reduce the susceptibility of lakes to regime shifts and to restore lakes that have become de‐vegetated. Our findings also suggests that regime shifts in lakes were unlikely to have been common in New Zealand lakes before anthropogenic deforestation and introductions of introduced aquatic taxa.

Responses of lake phytoplankton to micronutrient enrichment: a study in two New Zealand lakes and an analysis of published data

Abstract.Natural and anthropogenic changes in nutrient concentrations can affect phytoplankton in marine and freshwater environments. However, potential micronutrient limitation of phytoplankton productivity in fresh waters is often overlooked. To investigate the responses of lake phytoplankton to micronutrient enrichment, we conducted a study in two contrasting New Zealand lakes, and analysed data from the published international literature.We undertook nutrient enrichment bioassays of phytoplankton communities sampled from a mesotrophic reservoir and an eutrophic coastal lake to determine the relative occurrence of micronutrient (iron, boron, cobalt, copper, molybdenum) and macronutrient (nitrogen, phosphorus) limitation. In the mesotrophic reservoir, phytoplankton productivity was phosphorus limited. No evidence of micronutrient limitation was found in six bioassays in summer. In the eutrophic lake, tenfold enrichment of ambient micronutrient concentrations increased the primary productivity in four of 11 bioassays. During a cyanobacterial bloom in the eutrophic lake, experimental enrichment with boron, cobalt, copper or molybdenum increased primary productivity by 40%. These four micronutrients are commonly applied as agricultural fertiliser in the lake’s catchment. Nitrogen or phosphorus enrichment had no effect on phytoplankton productivity at this time. Micronutrient limitation has been reported in more than 40 lakes internationally, and our analysis of published data suggests that the prevalence of micronutrient limitation is unrelated to lake size or trophic state. As micronutrient enrichment can significantly increase phytoplankton productivity in a range of lakes types, the potential contribution of micronutrient enrichment to eutrophication should not be overlooked.

A temperate, tidal lake‐wetland complex 2. Water quality and implications for zooplankton community structure

Abstract Lakes Waihola and Waipori are shallow, coastal, tidal lakes that experience wind‐induced sediment resuspension, saline intrusions, and high inputs of nutrients. To determine the influence of externally‐driven, physical factors on spatial and temporal patterns of water quality in the two lakes, meteorological, hydrological, and water quality data were collected over 1 year. Multivariate analyses indicated that wind energy was driving the main water quality gradient in the lakes, which was primarily related to wind‐induced resuspension of lake sediments. The major, seasonally regulated, non‐tidal freshwater inflow was important in determining nutrient and salinity gradients in the lakes. The main nutrient inputs to the system were identified as the regulated, non‐tidal inflow (the upper Waipori River) and the tidal inflow (lower Waipori River). The impact of water quality gradients on zooplankton community structure in the lakes was assessed by canonical multivariate methods. Salinity gradients, caused by seasonal saltwater intrusions, were strongly related to zooplankton community structure in the lakes. Nutrient gradients (indicative of trophic state) were also related to zooplankton community structure. Although wind‐induced sediment resuspension had the largest impact on water quality in the lakes, it had little impact on the zooplankton community structure in either lake. The relationships between water quality and zooplankton community structure were confounded in Lake Waipori because of its very short hydraulic residence time (annual mean =1.9 days). Zooplankton community structure was resilient to short‐term changes in suspended particulate matter concentrations but not to seasonal changes in salinity. The results of this study support others which have shown impacts of even relatively small variations in salinity on the structure of zooplankton communities. This highlights the vulnerability of zooplankton communities in coastal lakes and wetlands to increasing salinity resulting from sea level rise and global climate change.

Short‐term impacts of nutrients, Daphnia, and copepods on microbial food‐webs of an oligotrophic and eutrophic lake

Abstract Metazooplankton are potentially important links between classical food chains and pelagic microbial food‐webs of lakes. We determined the short‐term effects of nutrient enrichment and predation on the microbial food‐webs of oligotrophic Lake Manapouri and eutrophic Lake Hayes, New Zealand, in summer, by adding calanoid copepods (Boeckella hamata Brehm) and cladocerans (Daphnia carinata King) to in situ enclosures in the presence and absence of added nutrients (nitrogen, phosphorus). In Lake Manapouri, bacteria and phytoplankton, but not picocyanobacteria, increased in response to nutrients; Daphnia reduced the densities of phytoplankton, bacteria, heterotrophic nanoflagellates (HNF), and ciliates; and Boeckella lowered the densities of HNF and ciliates. In Lake Hayes, the growth of bacteria, HNF, and phytoplankton, including eukaryotic picoautotrophs, was enhanced by enrichment; Daphnia depressed the concentrations of picoautotrophs and HNF, whereas Boeckella decreased the density of ciliates. In both lakes, Boeckella removed ciliates at higher rates per unit biomass than Daphnia. Our study provides clear evidence of stimulation and inhibition of pico‐plankton by nutrients, and of potential consumer‐mediated control of microbial food‐webs by crustacean zooplankton.

Phytoplankton biomass and productivity in two oligotrophic lakes of short hydraulic residence time

Abstract Phytoplankton biomass and productivity at two sites in the newly impounded Lake Dunstan and, upriver, in Lake Wakatipu (Frankton Arm) showed ranges throughout 1 year of 0.2–2.0 mg chlorophyll a m−3 and 0.9–6.0 mg C m−3 h−1 (maximum rate of carbon fixation). Peaks in phytoplankton abundance occurred in spring and summer in both lakes, but relationships of biomass and productivity vs light and nutrients differed between the lakes. In Lake Dunstan, P‐vs‐I parameters indicated that phytoplankton were photo‐acclimated to prevailing light conditions. In the Frankton Arm, P‐vs‐I parameters indicated that phytoplankton were poorly adapted to light conditions. Phytoplankton biomass and productivity were only depressed at the shortest observed hydraulic residence times (< 3 days). Phytoplankton biomass and productivity in Lake Dunstan were predicted from dissolved and particulate nitrogen concentrations and mean mixed‐layer light intensity. Annual mean chlorophyll a level was predicted satisfactorily using...

Shallow coastal lakes in New Zealand: current conditions, catchment-scale human disturbance, and determination of ecological integrity

We present the results of an effort to develop a national-scale predictive model to describe the current condition of shallow, coastal New Zealand lakes. Comprehensive biological, physical and chemical data from 45 shallow, coastal lakes are compared to catchment-level disturbance indices (indigenous vegetation loss, nutrient loading, invasive species) derived by New Zealand’s Waters of National Importance (WoNI) Programme. Few strong relationships were identified, but some general patterns were evident: lakes in disturbed catchments tended to have a higher trophic state, higher pH, reduced light penetration, lower submerged macrophyte cover, smaller food webs, lower rotifer diversity, and a larger proportion of introduced fish species. We discuss these patterns in the context of “ecological integrity” (EI), a subjective descriptor used in WoNI and other management programmes. A lack of historical data and difficulties in quantifying “integrity” remain persistent challenges for linking science with management for EI. Relationships between the WoNI indices and measured limnological conditions were not strong enough to build a predictive, nationally relevant model for estimating the EI. However, we present an alternative method for estimating EI based on expert assessment; expert assessment EI was significantly correlated to both WoNI pressure indices and many of the limnological variables measured here.

A temperate, tidal lake‐wetland complex 1. Water balance and ecological implications

Abstract A water‐balance model was developed for a tidal lake‐wetland complex to: (1) determine the relative contribution of hydrological flows through the lake‐wetland complex; (2) determine the tidal and non‐tidal hydraulic residence times of two lakes in the lake‐wetland complex; and (3) estimate the potential importance of groundwater inputs to the lake‐wetland complex. All surface hydrological inputs to the system were either measured or estimated over 1 year. Daily evaporation from the water bodies was also estimated. Discharge at the outflow of the lake‐wetland complex was monitored to calculate the net daily outflow. A correction procedure was used to remove the error resulting from aliasing of the daily calculation period and the tidal period. The difference between the measured net outflow and that calculated by the water‐balance model indicated that a large amount of net discharge from the lake‐wetland complex may have been a result of previously unrecognised groundwater inputs to the system. The non‐tidal hydraulic residence times of the two lakes differed markedly as did the relative importance of tidal inflows. The influence of variation in tidal and non‐tidal hydraulic residence time on limnological processes is discussed, particularly with respect to impacts of global climate change on tidal lake ecosystems.

Assessment of antibiotic activity in surface water of the lower Taieri Plain and impacts on aquatic bacteria in Lake Waipori, South Otago, New Zealand

Abstract Veterinary antibiotics are widely used in New Zealand and around the world to treat bacterial infections and for non‐therapeutic use as growth promoters. There is growing concern that unmetabolised antibiotics pass through stock and enter the environment, facilitating antibiotic resistance in pathogenic bacteria and harming aquatic ecosystems. Bioassay experiments showed that filtered water from an agricultural drain reduced the abundance of aquatic bacteria in Lake Waipori, a shallow coastal lake, whereas most other planktonic organisms were not inhibited. This result was consistent with the presence in the drain water of bacte‐riolytic antibiotics (e.g., penicillin). Further experiments were conducted to examine the effects of admixtures of water from the same agricultural drain both on the abundance and respiration rate of aquatic bacteria in the lake. One of four experiments showed inhibition of bacterial respiration consistent with the presence of bacteriostatic antibiotics (e.g., tetracyclines, aminoglycosides, macrolides) in the drain water. No further significant bacteriolytic effects were observed. A mixture of commonly used antibiotics was not consistently effective at reducing bacterial abundance or inhibiting bacterial respiration in lake water. Although we found evidence of antibacterial activity in the drain water this was intermittent, indicating either that antibiotic inputs to the drain were also intermittent, that other environmental factors intermittently affected the potency of antibiotics in the drain water, and/or that aquatic bacteria exhibited temporally variable resistance to antibiotics.

Impact of Berm Breaching on Hyperbenthic Macroinvertebrate Communities in Intermittently Closed Estuaries

Berm breaching of intermittently closed estuaries, either naturally or due to management practices, results in a physicochemical disturbance due to the flushing of water, material and biota into the ocean and the subsequent tidal influx. In 2007 and 2008 comparative and controlled studies were employed in three New Zealand estuaries: Sawmill Creek (46°04′ S 170°12′ E), Otokia Creek (45°57′ S 179°20′ E) and Kaikorai Lagoon (45°56′ S 170°23′ E), to investigate the impact of berm breaching on the hyperbenthic macroinvertebrate community in intermittently closed estuaries. Significant changes in community structure occurred in both the weekly comparative and the controlled studies (ANOSIM P < 0.01). Furthermore, the catch per unit effort of both total and key invertebrate taxa significantly increased after breaching (ANOVA P < 0.01). However, substantial numbers of individuals were expelled into the ocean (5,800 individuals, 20-min sample) while new taxa immigrated into the estuaries. Along with migration-related changes to community structure, berm breaches also resulted in the loss of ∼80% of inundated habitat and the concentration of existing populations. Consequently, the management of intermittent estuary connections to the ocean has implications for the ecology of individual, managed estuaries and also for regional coastal populations of epibenthic invertebrates.