Zealand Lakes Research Articles

Characterizing carotenoids in cyanobacterial cultures – Opportunities and implications for paleolimnological studies

Cyanobacterial blooms are increasing in frequency and intensity globally, impacting lake ecosystem health and posing a risk to human and animal health due to the toxins they can produce. Cyanobacterial pigments preserved in lake sediments provide a useful means of understanding the changes that have led to cyanobacterial blooms in lakes. However, there is some uncertainty as to whether specific carotenoids are unique to certain genera or types of cyanobacteria. To fill this knowledge gap, we analyzed pigments in 34 cyanobacteria cultures and applied the findings to sediments from three New Zealand lakes. The cyanobacterial carotenoids canthaxanthin, echinenone and zeaxanthin were detected in all cultures, whereas myxoxanthophyll was only detected in ten cultures (Microcoleus, Planktothrix and the picocyanobacteria cultures; Synechococcaceae). The sum of the individual carotenoid concentrations provided the strongest relationship with cyanobacterial biomass (R2 = 0.58) and could be used in paleolimnology studies to evaluate general cyanobacterial abundance. Ratios of canthaxanthin, zeaxanthin and myxoxanthophyll relative to echinenone indicated that carotenoid ratios could be used to differentiate picocyanobacteria and bloom-forming cyanobacteria, to some degree. High zeaxanthin/echinenone ratios were measured in picocyanobacteria and low zeaxanthin/echinenone ratios were measured in bloom-forming cyanobacteria. The zeaxanthin/echinenone ratio was applied to sediment core samples where the cyanobacterial community was also evaluated by 16S rRNA gene metabarcoding, with the zeaxanthin/echinenone ratios showing similar patterns to those observed in the cultures. The preliminary assessment described here suggests that zeaxanthin/echinenone ratios could provide a valuable paleoecological proxy for evaluating historical shifts in cyanobacterial communities and warrants further exploration.

Heterogenous distribution of kākahi (freshwater musselEchyridella menziesii) environmental DNA in 5 New Zealand lakes of differing size and geomorphology

Heterogenous distribution of kākahi (freshwater mussel<i>Echyridella menziesii</i>) environmental DNA in 5 New Zealand lakes of differing size and geomorphology

Dynamics of pelagic mucilage produced by the invasive, cyclotelloid diatom, Lindavia intermedia, in oligotrophic lakes of New Zealand

Marine pelagic mucilages (e.g., marine snow) have been reported to a greater extent than their lacustrine counterparts. A pelagic mucilage primarily comprised of chitin secretions from the invasive centric diatom, Lindavia intermedia, has been reported since the early 2000s, primarily from large, oligotrophic pre-alpine lakes of the South Island of New Zealand. To better understand the factors related to mucilage abundance, we monitored its abundance as well as factors potentially related to mucilage production over time in four mucilage-afflicted lakes. Temporal mucilage dynamics were episodic, with peaks in abundance occurring during any season, but most often during summer and autumn. Chitin was confirmed to be an important component of the mucilage, but the chitin content varied between 1 and 12% of the mucilage dry mass in the lakes. An RT-qPCR assay for chitin synthase gene overexpression in L. intermedia showed that overexpression occurred in summer and autumn, often when peaks in mucilage abundance also occurred. A correlation between mucilage and phytoplankton abundance was only observed in one of the lakes. Both dissolved reactive and total phosphorus concentrations were often below analytical detection limits in these lakes. Nitrate concentrations were also low and showed negative correlations with mucilage abundance. This suggests either that the secrection of chitinous mucilage by L. intermedia significantly depleted the available N in the water column or that mucilage facilitated N uptake by L. intermedia and/or other microorganisms associated with the mucilage. Pelagic mucilage in New Zealand lakes shares many characteristics of other conspicuous mucilage phenomena, including lake snow and marine snow. While our correlational analyses revealed some relationships and associations with mucilage abundance, the strengths of these were quite variable, indicating that as yet unstudied mucilage loss processes in these lakes (e.g., sedimentation, disintegration, decomposition, assimilation) likely also play important roles in regulating mucilage abundance.

Diatom nutrient requirements change with lake nutrient limitation and enrichment in New Zealand dune lakes

ABSTRACT Nutrients are important determinants of diatom growth in lakes, and diatoms are considered reliable indicators of changing lake nutrient concentrations and eutrophication. However, diatom ecologies are not static, nor are they linked to single environmental variables, leading to imprecise diatom nutrient inferences. Anthropogenic nutrient enrichment is the principal issue facing New Zealand’s lakes. Thus, knowledge of diatom responses to nutrients in New Zealand lakes will be important for understanding contemporary and past changes in nutrient availability. Using a nutrient amendment experiment and diatom communities from dune lakes, here we show that the response of specific diatom species is not universal among lakes and is partly determined by lake nutrient concentrations and limitation status. The response of focal diatom species to nutrient additions differed from previously reported nutrient requirements, and did not align with published, assigned trophic statuses. This study highlights that the response of diatoms to nutrient enrichment is context-dependent, and that intraspecific generalisations of diatom ecologies between geographic locations or through time should be made with caution. To apply diatoms to making nutrient inferences, more work focusing on how physiochemical and biological factors influence diatom nutrient requirements is required.

Development of a triplex droplet digital polymerase chain reaction assay for the detection of three New Zealand native freshwater mussels (Echyridella) in environmental samples

AbstractThe freshwater mussel Echyridella (also known as kākahi) is the only freshwater mussel found in New Zealand's lakes and rivers and is endemic to the country. They play a crucial role in freshwater ecosystems and have high cultural significance. The three putative species of Echyridella are all classified as at risk. Monitoring is required to enhance knowledge on their distribution and to provide management, but conventional approaches (diving, wading, or swimming and visually looking for mussels) are time‐consuming, costly, and require good visibility. The use of environmental DNA (eDNA) in combination with PCR techniques offer advantages over conventional methods. In this study, we developed a triplex droplet digital PCR assay, targeting a region of the mitochondrial cytochrome oxidase subunit 1 gene, that differentiates all three kākahi species. The limits of quantification using gblocks were 0.6 × 10−03–6 × 10−03 fg/µl, yielding 2–8 copies/reaction, and for tissue DNA 10,000–100,000 fg/µl, yielding 9–15 copies/reaction. The method was applied to water samples from 48 lakes, lagoons, or ponds and two samples from streams. A total of 58% of samples from lakes, lagoons, or ponds and all samples from the streams were positive for kākahi. Sediment samples (n = 15) were also tested. Only those collected in close proximity (&lt;1 m) to living kākahi were positive highlighting the patchy distribution of eDNA in sediment. This new assay will assist in determining the current distribution of kākahi at large temporal and spatial scales and has the potential to be used for the assessment of historic distributions as well.

Isolation and characterisation of monoclonal picocyanobacterial strains from contrasting New Zealand lakes

ABSTRACT Freshwater picocyanobacteria form the base of microbial food webs in many lakes worldwide but have received less attention than other phytoplankton. Little is known about their potential response to environmental changes such as increased nutrient loading and climate change, due partly to the lack of available cultured and sequenced strains. Here, we isolated 25 monoclonal picocyanobacterial strains from 6 New Zealand lakes with contrasting trophic states. The use of MLA medium instead of BG11 proved highly successful for the rapid isolation of picocyanobacteria. Strains were characterised by sequencing of the 16S ribosomal RNA gene, spectrophotometry, and high-performance liquid chromatography. 16S rRNA gene analysis placed most strains within the cluster 5 picocyanobacterial lineage (sub-cluster 5.2, family: Synechococcaceae). Phylogenetic analysis showed that 12 isolates from Lakes Wakatipu, Hayes, Johnson, and Ellesmere/Te Waihora clustered with strains from a range of Northern Hemisphere locations, suggesting global dispersal of these strains. Pigment characterisation revealed that pink and brown cultures from oligotrophic and some eutrophic lakes were rich in phycoerythrin, while green cultures from eutrophic and hypertrophic lakes were rich in phycocyanin. This diverse group of freshwater cluster 5 picocyanobacterial cultures will provide a new resource to study how these critically important microbes function and respond to changing environmental stressors.

The Role of Environmental Processes and Geographic Distance in Regulating Local and Regionally Abundant and Rare Bacterioplankton in Lakes.

Bacteria are vital components of lake systems, driving a variety of biogeochemical cycles and ecosystem services. Bacterial communities have been shown to have a skewed distribution with a few abundant species and a large number of rare species. The contribution of environmental processes or geographic distance in structuring these components is uncertain. The discrete nature of lakes provides an ideal test case to investigate microbial biogeographical patterns. In the present study, we used 16S rRNA gene metabarcoding to examine the distribution patterns on local and regional scales of abundant and rare planktonic bacteria across 167 New Zealand lakes covering broad environmental gradients. Only a few amplicon sequence variants (ASVs) were abundant with a higher proportion of rare ASVs. The proportion of locally abundant ASVs was negatively correlated with the percentage of high productivity grassland in the catchment and positively with altitude. Regionally rare ASVs had a restricted distribution and were only found in one or a few lakes. In general, regionally abundant ASVs had higher occupancy rates, although there were some with restricted occupancy. Environmental processes made a higher contribution to structuring the regionally abundant community, while geographic distances were more important for regionally rare ASVs. A better understanding of the processes structuring the abundance and distribution of bacterial communities within lakes will assist in understand microbial biogeography and in predicting how these communities might shift with environmental change.

Lurking in the water: testing eDNA metabarcoding as a tool for ecosystem-wide parasite detection.

In the light of global biodiversity change and emerging disease, there is an urgent need to establish efficient monitoring programmes of parasites in aquatic ecosystems. However, parasite identification is time-consuming, requires a high degree of taxonomic expertize and in general requires lethal sampling. The use of environmental DNA methodology to identify parasites has the potential to circumvent these limitations. This study evaluates the use of eDNA metabarcoding to detect the presence of all species of nematode and platyhelminth parasites in two New Zealand lakes. We developed two novel metabarcoding primer pairs targeting a region of cytochrome oxidase I gene (COI) specific to platyhelminths and nematodes. We successfully detected parasite DNA in both lakes. Platyhelminth DNA yield was in general greater than nematode DNA yield. This most likely results from the larger biomass of the former quantified using traditional methods, or the presence of free-swimming life stages in the life cycle of many platyhelminths. By using eDNA, we did not detect all expected parasite families revealed through traditional methods, likely due to a lack of sequencing data available from public databases such as GenBank. As such, genetic resources need to include full reference sequences if parasitology is to truly harness eDNA to characterize and monitor parasite biodiversity in natural systems.

Nuisance mucilage produced by Lindavia intermedia (Bacillariophyceae) in New Zealand lakes

ABSTRACT The invasive centric diatom Lindavia intermedia arrived in New Zealand in recent decades. It produces a pelagic mucilage, which forms an adhesive substance known as lake snow. While determining cell concentrations of L. intermedia is relatively straightforward, methods to estimate mucilage concentration in lake water have not yet been developed. Two methods for lake snow quantification are reported here: a dragged line, or “snow tow,” and in situ filtration. A chemical assay for hexosamine, as an estimate of chitin content, and an atomic absorption method, which measures silicon, were used to measure these components of lake snow. Samples from 4 lakes revealed a correlation between snow tow and filtration data; in principle, the snow tow method (used by municipal authorities) could be calibrated and made quantifiable using the filtration method. Expression of the chitin synthase gene in summer/autumn (but not in winter/spring) correlated with abundance of the chitin component of lake snow, aligning with anecdotal evidence for the timing of its development in lakes. By contrast, cell densities correlated poorly with lake snow abundance. Cell concentrations relative to chitin concentrations were also higher in winter/spring than in summer/autumn across lakes. Dry weight and silicate in lake snow relative to chitin varied by lake and season. The quantification of lake snow and its adhesiveness are important parameters for assessing its nuisance value and fouling characteristics and for developing measures to prevent and remediate its incursion in lakes.

Spatial abundance and distribution of picocyanobacterial communities in two contrasting lakes revealed using environmental DNA metabarcoding.

Freshwater picocyanobacteria (Pcy) are important yet understudied components of lake ecosystems. Most previous studies have relied on cell abundances to assess Pcy dynamics in largely oligotrophic lakes, while little is known about spatial diversity and dynamics across different lake types. In the present study we assessed the horizontal-spatial abundance and community structure of Pcy in two contrasting (oligotrophic and hypertrophic) New Zealand lakes using epifluorescence microscopy and 16S rRNA metabarcoding. Pcy abundance and community composition differed significantly both between and within the oligotrophic and hypertrophic lakes. While spatial variability was observed in both study lakes, these differences were particularly pronounced in the oligotrophic, morphometrically complex Lake Wanaka where cell abundances were typically higher in bays than open-water sites and community structure differed significantly between sites. Community structuring appeared to be driven by localised environmental conditions, with different factors influencing each lake. These results suggest that single spot-samples are insufficient to gain an understanding of Pcy dynamics and consequently, phytoplankton dynamics in lakes.

The sediment fluorescence–trophic level relationship: using water-extractable organic matter to assess past lake water quality in New Zealand

ABSTRACT Lake sediments are the physical remnants of past allochthonous and autochthonous carbon and mineral inputs and therefore have the potential to illuminate both past terrestrial carbon cycling and within-lake biological productivity. However, there are currently no robust, rapid, and inexpensive methods to chemically characterise the organic matter (OM) components in lake sediments, which limits their utility for reconstructing past soil carbon export trends or trophic status. This study explores the use of 3D excitation–emission matrix (EEM) fluorescence spectroscopy of water extractable dissolved organic matter (WEDOM) from lake sediments as a method for reconstructing past soil dissolved organic matter (DOM) export and past lake water quality. Using contemporary lake sediments from 11 New Zealand lakes, we demonstrate that both overall WEDOM fluorescence and protein-like fluorescence intensity are strong functions of trophic status across lakes. We also demonstrate that protein-like fluorescence is a function of sedimentary total nitrogen concentrations in palaeo-sediments from a pristine, high-altitude lake (Adelaide Tarn). This approach has applications in the evaluation of the trophic status of infrequently monitored lakes and in palaeolimnology.

Predicting the potential distribution of the invasive freshwater diatom Lindavia intermedia in New Zealand lakes

Predicting the potential distribution of the invasive freshwater diatom Lindavia intermedia in New Zealand lakes

Sedimentary phosphorus in contrasting, shallow New Zealand lakes and its effect on water quality

ABSTRACT The eutrophication of lake ecosystems due to anthropogenic activities has impacted lakes worldwide and shallow lakes are particularly vulnerable. The retention of phosphorus (P) in lake sediments and its subsequent release to the water column is often a key factor in degraded water quality, algal blooms and delayed responses to lake restoration efforts. Despite this link between sedimentary P and poor ecosystem outcomes, a limited amount of research has been conducted on P dynamics in New Zealand’s lakes. In this study, sediments in six shallow lakes across the country were analysed for geochemistry and P fractionation. Total sedimentary P content varied widely and was related to inflow concentrations and hydrological retention times. The P binding capacity of the sediments was related to iron (Fe) and aluminium (Al) concentrations, while the Fe:P ratio was correlated to the release of P under anoxic conditions. P fractions and release rates were poorly correlated with traditional water quality parameters, however the mobile-PSL and reducible-P fractions were strongly correlated with the frequency of summertime algal blooms. This relationship may provide an indicator to assess harmful algal bloom frequency in unmonitored lakes, and a valuable tool to assess internal loading risk and inform lake restoration methods.

The application of stressor–response relationships in the management of lake eutrophication

ABSTRACT Since the 1960s, theoretical and empirical advances in limnology have offered lake managers different approaches to address lake eutrophication problems. The Vollenweider input–output model and the Scheffer model of alternative stable states are 2 well-known applications of the stressor–response (S-R) models. The 2 applications each utilise particular S-R relationship shapes. However, lake eutrophication response variables and shapes of S-R relationships may vary greatly from lake-to-lake, highlighting a key question for lake managers: What is the appropriate shape of the S-R relationship for a given lake eutrophication problem? This study develops an S-R lake framework that embraces multiple functional forms of S-R relationships. First, 3 New Zealand lake eutrophication case studies are presented in which different S-R relationships were used to inform management actions. Then, the different usages of the S-R framework illustrated by the case studies are discussed, including the different types of data used and how information about feedbacks and other mediating factors helped identify the S-R relationships. Finally, a lake typology is presented, linking specific lake types to specific S-R relationship shapes, to assist with managing lake eutrophication under conditions of changing stressors and stressor levels.

Editor's Introduction

An underlying theme in this issue is that of place and environment, but the articles build upon a wide range of conceptual approaches, locations, human activities and agency. We begin with Jonathan West’s article on New Zealand lakes. An environmental historian, and J.D. Stout Fellow at the Stout Research Centre in 2019, West’s research comes at a critical juncture when the declining quality of freshwater is the focus of intense national debate and argument. As West points out, the pollution in our lakes is the result of the farming practices and the residential uses of the land around them and resolving or mitigating problems decades in the making is going to pose very difficult questions for us all.

Reference and current Trophic Level Index of New Zealand lakes: benchmarks to inform lake management and assessment

ABSTRACT Knowledge of trophic status is fundamental to understanding the condition and function of lake ecosystems. We developed regression models to predict chlorophyll a concentrations (chl a) in New Zealand lakes for reference and current states, based on an existing dataset of total nitrogen (TN) and total phosphorus (TP) concentrations for 1031 lakes. Models were then developed to predict Secchi depth based on chl a and a sediment resuspension term applicable to shallow lakes. Estimates of all four Trophic Level Index (TLI) variables (chl a, TN, TP and Secchi depth) were analysed to estimate reference and current state TLI for the nationally representative sample of 1031 lakes. There was a trend of eutrophication between reference and current states, with systematic differences among lake geomorphic types. Mean chl a increased 3.5-fold (2.42 mg m−3 vs. 8.32 mg m−3) and mean Secchi depth decreased (indicating lower clarity) by approximately one-third (9.62 m vs. 6.48 m) between reference and current states. On average, TLI increased by 0.67, with the TLI increase >1 in approximately one-third (31%) of lakes. This study informs the status of lake ecosystems in NZ and provides benchmarks to guide management and assessment.

Quantifying the Extent of Anthropogenic Eutrophication of Lakes at a National Scale in New Zealand.

Quantifying environmental changes relative to ecosystem reference conditions (baseline or natural states) can inform assessment of anthropogenic impacts and the development of restoration objectives and targets. We developed statistical models to predict current and reference concentrations of total nitrogen (TN) and total phosphorus (TP) in surface waters for a nationally representative sample of ≥1033 New Zealand lakes. The lake-specific nutrient concentrations reflected variation in factors including anthropogenic nutrient loads, hydrology, geology, elevation, climate, and lake and catchment morphology. Changes between reference and current concentrations were expressed to quantify the magnitude of anthropogenic eutrophication. Overall, there was a clear increase in lake trophic status, with the most common trophic status being oligotrophic under a reference state and mesotrophic under current conditions. The magnitude of departure from reference state varied considerably within the sample; however, on average, the mean TN concentration approximately doubled between reference and current states, whereas the mean TP concentration increased approximately 4-fold. This study quantified the extent of water quality degradation across lake types at a national scale, thereby informing ecological restoration objectives and the potential to reduce anthropogenic nutrient loads, while also providing a modeling framework that can be applied to lakes elsewhere.

Dividing the algal soup: is there niche separation between native bivalves (Echyridella menziesii) and non-native Daphnia pulex in New Zealand?

ABSTRACTNew Zealand's native freshwater mussels (kākahi, kāeo) are considered to be in decline, yet the mechanisms driving this are unclear. The widespread establishment of highly efficient filter-feeding, non-native Daphnia in New Zealand lakes may have led to competition for algae with kākahi. We conducted a controlled laboratory experiment to determine whether differences exist in algal resources utilised by kākahi and North American Daphnia pulex. Echyridella menziesii (adults and juveniles) and D. pulex were exposed to mixed algal samples for three hours to determine whether similar algal resources were removed by the grazers. Relative to controls, both adult and juvenile E. menziesii removed a broad range of algal taxa including diatoms, green algae and filamentous species, ranging in size from 33.6 to 348.0 μm. High densities of D. pulex were unable to cause depletion of these same algae species. Our results suggest niche overlap is limited between the two grazers; E. menziesii utilises larger particles than D. pulex.

Increased Dust Deposition in New Zealand Related to Twentieth Century Australian Land Use

AbstractMineral aerosols (dust) generated in the dryland regions of Australia have the potential to reach New Zealand through atmospheric transport. Although a large portion of dust in New Zealand originates in Australia, little is known about how dust deposition has varied over time in New Zealand or what may have caused this variation. We used geochemical dust proxies to examine the recent history of dust deposition to two alpine lakes in Kahurangi National Park, South Island, New Zealand. Geochemical indicators suggest that dust deposition began to increase around 1900, with the greatest deposition rates occurring from ~1920 to ~1990. In subsequent decades, dust deposition rates to New Zealand lakes appear to have declined. This rise and fall of dust deposition recorded in New Zealand lakes is consistent with dust records from the Antarctic Ice Sheet, Eastern Australia, and incidents of low visibility due to dust events recorded at Australian climate stations. The dust deposition rate over time also follows the temporal pattern of land use in south and central Australia over the time scale of the twentieth century suggesting a causal linkage. It is possible, and perhaps likely, that drought cycles also affected both emissions and transport pathways but over shorter time periods this was difficult to discern at the temporal resolution of these lake sediment cores. The increase in dust deposition to the high‐elevation regions of New Zealand likely has implications for the biogeochemistry of alpine lakes in the Tasman Mountains.

Aquatic eutrophication indicators in LCA: Methodological challenges illustrated using a case study in New Zealand

ObjectiveThe objective of this work was to determine the effects and implications of generic and site-specific aquatic eutrophication potential indicators in the Life Cycle Assessment (LCA) of livestock farm systems using a New Zealand (NZ) lake catchment case study. MethodAverage dairy and sheep & beef farm systems in the Lake Taupo catchment were studied. Emissions of nitrogen (N) and phosphorus (P) to waterways, and ammonia and nitrogen oxides to air from these farms were calculated using the site-specific OVERSEER® nutrient budget model. These emissions data were then used to calculate the increase in nutrients in water bodies and aquatic Eutrophication indicators with a range of Life Cycle Impact Assessment (LCIA) methods. ResultsEutrophication indicator results varied considerably depending on the environmental mechanisms modelled by the LCIA method for the fate of N and P, accentuated by different choices for the inventory modelling. Using default emission factors instead of site-specific ones overestimated eutrophication impact results. The most recent methods are not only spatially-explicit and applicable beyond Europe, but they also account for more environmental mechanisms for the fate of the nutrients, giving relatively lower calculated impact results. However, the appropriate scale and spatial resolution is still a crucial question to address for these methods since they greatly affect results. Regarding eutrophication damage assessment, when the actual background nutrient concentration is very low, the end-point assessment method for freshwater eutrophication is not applicable. In this case, LCA fails to account for a high standard of water quality that is in a near-pristine state, but deteriorating. ConclusionsThe inventory of nutrient flows at a farm scale and fate factors modelled at a catchment scale should be site-specific. Freshwater eutrophication indicators should be based on a site-specific (and globally-valid) LCIA model rather than a generic one. Currently-accepted freshwater eutrophication indicators focus only on P, thus capturing only part of the problem for freshwater bodies that are co-limited by N and P (in terms of algal growth) such as Lake Taupo in NZ. Lake Taupo water quality concerns and regulations are not focused on P, but solely on N due to increasing N levels over time. Conclusions from this study are valid beyond NZ and beyond agricultural systems. Future work needs to investigate coupling N and P fate modelling based on the most recent globally-valid and spatially-explicit LCIA methods.