Avon-Heathcote Estuary Research Articles

Macroalgal Bioindicators of Recovery from Eutrophication in a Tidal Lagoon Following Wastewater Diversion and Earthquake Disturbance

Together, macroalgal tissue biochemical nitrogen indices (N-indices) and macroalgal abundance can be used as bioindicators of N-enrichment in estuaries. In this study, we examine the extent and rates of response of Ulva bioindicators during rapid N-enrichment perturbations in the eutrophic Avon-Heathcote Estuary (AHE) (Christchurch, New Zealand). With the diversion of the city’s wastewater discharge away from the estuary in March 2010, a ~ 90% reduction in the estuary’s N-concentration was expected. In turn, this was expected to reduce macroalgal biomass and improve the overall trophic condition of the estuary. We surveyed Ulva bioindicators over a five-year period spanning the diversion. There was a rapid (within one year) transition away from eutrophic condition reflected in N-indices (tissue-chlorophyll, -free amino acids, -N and -δ15N) following wastewater diversion, towards values corresponding with ‘cleaner’ water quality. This was accompanied by large reductions in Ulva percent cover, based on seasonal surveys conducted from 2001 to 2014. However, two large earthquakes in February and June 2011 caused a breakdown of the city’s wastewater infrastructure, resulting in overflows of untreated sewage into the estuary between February and November 2011. The re-enrichment of N and changes in N-sources (treated versus untreated sewage) were rapidly reflected in Ulva bioindicators, notably δ15N. Following repair of infrastructure, Ulva bioindicators again reverted towards a less eutrophic state. Overall, bioindicators were sensitive to changes in N-availability and N-source, and useful for identifying the position of algal populations on a eutrophic-to-oligotrophic gradient. These attributes demonstrated their utility as adjuncts to water quality monitoring and algal biomass surveys.

Trophic Indicators of Ecological Resilience in a Tidal Lagoon Estuary Following Wastewater Diversion and Earthquake Disturbance

Estuary ecological resilience can be gauged by response of estuary trophic state to abatement of nutrient pollution. Changes in trophic indicators were studied in the Avon-Heathcote Estuary (AHE) in Christchurch, New Zealand, over 6 years, spanning diversion of city wastewater inputs to an offshore outfall in 2010, and to temporary enrichment caused by the 2011 Christchurch earthquake. It was hypothesised that the tidally well-flushed and sandy AHE would not harbour a ‘legacy’ of eutrophication and would rapidly gain improved ecological function following the diversion. AHE sediments were coarse (156 μm median grain size) with low organic matter (OM 1.2%, N 0.03%, C 0.3%), which changed little either with diversion or earthquake. Upon diversion, median water column and porewater ammonium (36, 185 μmol) decreased by 87% and 57%, respectively, benthic microalgae (269 mg chlorophyll-a m−2) fell by 58%, and enrichment-affiliated polychaetes (3700–8000 m−2) fell by 60–80% at sites with largest benthic microalgal reductions, all within < 1–2 years. Oxygen and ammonium fluxes were usually oligotrophic and changed little upon diversion, except near the historic wastewater discharge site. Denitrification became more important for N loss, increasing from 5 to 29% of estuary N load. Responses to earthquake-driven enrichment were transient. Despite decades of heavy N loading and eutrophic growths of benthic microalgae and macroalgae, the AHE did not store a eutrophic legacy in its sediments. It reacted rapidly to improved water quality allowed by the outfall, showing that this common estuary type (sandy, well-flushed tidal lagoon) was resilient to eutrophication upon stressor removal.

Effects of local anthropogenic stressors on a habitat cascade in an estuarine seagrass system

Recent research has shown that co-occurring primary and secondary habitat-forming species typically support higher biodiversity than do monocultures of the primary habitat-former alone. However, these ‘habitat cascades’ may not be universal and it is important to know whether, when and where positive effects on biodiversity from secondary habitat-forming species change to negative effects. Here, we tested how anthropogenic stressors (fertilisation and sedimentation) and unattached secondary habitat-forming Ulva seaweeds affected the primary habitat-forming seagrass, Zostera muelleri, and its associated invertebrates in the Avon–Heathcote Estuary, New Zealand. We experimentally stressed Zostera by adding different fertilisation and sediment levels. Fertilisation had little impact, whereas even low sedimentation levels had strong negative effects on Zostera and its associated fauna. In a second experiment, sediments and Ulva were added to seagrass beds and unvegetated mudflats to test whether sediment stress modifies habitat cascades. We found again strong negative effects of sediments on Zostera, irrespective of spatio-temporal conditions, and that negative effects of sediments on invertebrates were enhanced in the presence of the secondary habitat former. These results highlighted that anthropogenic stressors can destabilise habitat cascades; processes that may be of particular importance in estuaries that are characterised by low biodiversity and stressful environmental conditions.

Evolutionary history of ssDNA bacilladnaviruses features horizontal acquisition of the capsid gene from ssRNA nodaviruses

Bacilladnaviruses have single-stranded (ss) DNA genomes and infect diatoms, a major group of unicellular algae widespread in aquatic habitats. Despite their ecological importance, the provenance and relationships of bacilladnaviruses to other eukaryotic viruses remain unclear. Accordingly, they are currently classified into the ‘floating’ genus Bacilladnavirus. Here we present three new bacilladnavirus genomes recovered from a mollusc Amphibola crenata and benthic sediments from the Avon-Heathcote estuary in New Zealand. Our analysis shows that the rolling-circle replication-initiation proteins of bacilladnaviruses display unique conserved motifs and in phylogenetic trees form a monophyletic clade separated from other groups of ssDNA viruses. Unexpectedly, distant homology detection combined with structural modeling indicates that bacilladnavirus capsid proteins are homologous to those of ssRNA viruses from the Nodaviridae family. Considering the sequence diversity within the expanding Bacilladnavirus genus, we argue that classification of these viruses has to be revised and the current genus upgraded to the family level.

Diverse small circular DNA viruses circulating amongst estuarine molluscs

Our understanding of the diversity and abundance of circular replication associated protein (Rep) – encoding single stranded (CRESS) DNA viruses has increased considerably over the last few years due to a combination of modern sequencing technologies and new molecular tools. Studies have used these to identify and recover CRESS DNA viruses from a range of different marine organisms, including copepods, shrimp and molluscs. In our study we identified 79 novel CRESS DNA viruses from three mollusc species (Austrovenus stutchburyi, Paphies subtriangulata and Amphibola crenata) and benthic sediments from the Avon-Heathcote estuary in Christchurch, New Zealand. The genomes recovered have varying genome architectures, with all encoding at least two major ORFs that have either unidirectional or bidirectional organisation. Analysis of the Reps of the viral genomes showed they are all highly diverse, with only one Rep sequence sharing 65% amino acid identity with the Rep of gastropod-associated circular DNA virus (GaCSV). Our study adds significantly to the wealth of CRESS DNA viruses recovered from freshwater and marine environments and extends our knowledge of the distribution of these viruses.

A dynamic growth model of macroalgae: Application in an estuary recovering from treated wastewater and earthquake-driven eutrophication

A dynamic growth model of macroalgae was developed to predict growth of the green macroalga Ulva sp. in response to changes in environmental variables. The model is based on common physiological behaviour of macroalgae and hence has general applicability to macroalgae. Three state variables (nitrogen, carbon and phosphorus) were used to describe physiological processes and functional differences between nutrient and carbon uptakes. Carbon uptake is modelled as a function of temperature, light, algal internal state and water current, while nutrient uptake depends on internal state, temperature and environmental nutrient level. Growth can only occur when nutrients in the environment and in the internal storage pools (N-quota and P-quota) reach threshold levels. Physiological rates follow the Arrhenius relationship and increase exponentially with increasing temperature within the temperature tolerance range of a species. When parameterised and applied to Ulva sp. in the eutrophic Avon-Heathcote Estuary, New Zealand, the model generally reproduced field observations of Ulva sp. growth and abundance. Growth followed a clear seasonal cycle with biomass increasing from early-middle summer, reaching peak values in early autumn and then decreasing. Conversely, N-quotient levels were maximal during the winter months, declining during summer peak growth. These seasonal patterns were collectively driven by temperature, light intensity and nutrients. The model captured the N-quota and growth responses of Ulva sp. to the N-reduction arising from diversion of treated wastewater from the Avon-Heathcote Estuary to an offshore outfall in 2010, and of raw sewage N-discharges resulting from wastewater infrastructure damage caused by the Canterbury earthquakes in 2011. Sensitivity analyses revealed that temperature-related parameters and maximum uptake rate of C were among the most sensitive parameters in predicting biomass. In addition, the earthquake-derived changes in reduction of immersion time and decrease in the start biomass prior to summer blooms were shown to drive considerable declines in summer growth and biomass of Ulva sp.

A review of palaeo-tsunamis for the Christchurch region, New Zealand

Recent earthquake activity in and around the Christchurch region, New Zealand, has raised concerns about tsunamis inundating the coastline. While the occurrence of historical tsunamis is well documented, information about palaeo-tsunamis is poorly understood. This review draws together data from numerous sources to outline our current understanding of palaeo-tsunamis for the region. Six probable and one possible Holocene palaeo-tsunamis are identified and proxy data are summarised with reference to all potential near-contemporaneous sites throughout New Zealand. The events cover a period of around 6500 years, occurring around 6250–6500 yr BP, 4800–5350 yr BP, 4050–4450 yr BP, 3400–3700 yr BP, 2200–2300 yr BP, 1250–1350AD and in 1604AD. The relative exposure of Christchurch city to tsunamis has however, fluctuated over time. This is most notable over the past 2000 years or so since the Brighton spit extended south to close off the bay, then retreated and formed again causing the Avon-Heathcote Estuary (Ihutai) to change from open to closed bay and then from open bay to estuary. The relative extent of the tsunami hazard is therefore controlled to a certain extent by the presence or absence of the spit, which is in turn governed by interactions between seismic activity and fluvial processes.Potential palaeo-sources vary from local (subduction fault rupture, nearshore submarine landslide, gas hydrate release, seamount flank collapse) to distant (subduction fault ruptures in Central and South America) candidates. In most cases more than one potential source was identified for each palaeo-tsunami. However, it appears that the most likely sources for most if not all of the palaeo-tsunamis were from Central and South America as opposed to more local alternatives. The identification of palaeo-sources was largely based upon historically-documented events and palaeoseismic research and as such was almost entirely limited to known local and distant fault ruptures. A review of other potential palaeo-sources with tsunamigenic potential reveals numerous additional candidates that need to be investigated in more detail.

Sediment–seawater solute flux in a polluted New Zealand estuary

We investigated the sediment–seawater solute flux at five sites in the polluted Avon–Heathcote Estuary, New Zealand, to provide a point of comparison for future studies of the effects of the closure of a major wastewater outfall into the estuary. Sediments collected in winters 2007 and 2008, and summer 2008, ranked consistently in organic matter content. Microelectrode profiling and sediment-core incubations revealed (1) a dominant role of microphytes in regulating solute flux causing significant differences in the dark and light sediment O2 consumption (Rd, Rl), total sediment O2 utilisation (TOUd, TOUl), and inorganic nutrient flux, (2) consistent ranking of sites in solute flux, and (3) a clear solute-flux signature of the wastewater effluent. Sediment near the wastewater outfall exhibited the highest absolute R and TOU, the lowest ratio Rl/Rd, the highest dark efflux of dissolved reactive phosphorus and ammonium, and the highest dark and light uptake of nitrate+nitrite.

Sand volcanoes in the Avon–Heathcote Estuary produced by the 2010–2011 Christchurch Earthquakes: implications for geological preservation and expression

Sand volcanoes produced by liquefaction of saturated sands were widespread in the Avon–Heathcote Estuary following individual major events of the Christchurch 2010–2011 Earthquake sequence. Sand volcanoes were composed of fine grey sands and varied in diameter over the range 0.2–5 m, fed by vertical to subvertical feeder pipes of 15–25 cm diameter that cross-cut mud and shell horizons. Tides and wind-driven waves reduced, and at times removed, the profile of surface features; however, subsurface features remained unaffected. The geological signature of these volcanoes, formed in wet sandy tidally influenced settings such as estuaries, would be preservation of straight-sided feeder pipes 15–25 cm in diameter, >30 cm in length that cross-cut undeformed strata with or without expression of the erupted cone. Sediments were not able to be excavated beneath the shallow water table, and all observed feeder conduits occurred as roughly cylindrical pipes rather than elongated planar dykes; this does not preclude dykes being present deeper in the subsurface, however. Coseismic subsidence may enhance the preservation potential of surface features by increasing relative water depth, thereby increasing sedimentary accommodation space, and decreasing the influence of wave action in removing cones.

Short-term study testing the resilience of an estuarine bivalve to macroalgal mats

Macroalgal mats occur seasonally in many estuaries worldwide but there is little information on their short- or long-term effects on the abundance or resilience of macrofauna. Within a small estuary, with a history of exposure to algal mats (Avon-Heathcote Estuary, Christchurch, New Zealand), we quantified the relationship between macroalgal mats and community composition. There was a high degree of species overlap between sites, and community analysis did not separate out areas that had been previously exposed to mats. Density of the cockle Austrovenus stutchburyi was negatively correlated with current abundances of sea lettuce Ulva and the red alga Gracilaria chilensis. A caging experiment at three sites with different sediment characteristics investigated the survival of the cockle (A. stutchburyi) to short-term exposure to mats of Ulva sp. and G. chilensis. Neither low or high algal biomass had any effect on cockle mortality, macroinvertebrate diversity or the sediment characteristics. Although the population structure of cockles differed amongst sites, bivalves followed normal seasonal development, regardless of the experimental treatment. The results confirm that the cockle has the ability to survive short-term exposure to algal mats.

An earth systems approach to understanding the tectonic and cultural landscapes of linked marine embayments: Avon‐Heathcote Estuary (Ihutai) and Lake Ellesmere (Waihora), New Zealand

AbstractAn earth systems study of the Avon‐Heathcote Estuary (Ihutai), New Zealand, shows that tectonic activity has a marked direct and indirect control upon its geomorphology and human settlement in the area. We discuss the Late Holocene history of the embayment in relation to large earthquakes and their after‐effects. Of particular note is the rapid fluvial transfer of sand to the coast causing dune formation and a more delayed pulse of coarser sediment causing channel avulsion of the Waimakariri River. While dune system development seems to occur soon after tectonic activity, river channel avulsion, spit/barrier formation and ongoing geomorphological changes may well relate to periods of tectonic activity that occurred 100–200 years previously. The interaction between these two sediment delivery systems causes significant, and often rapid, changes to coastal geomorphology and ecosystems that have serious implications for human populations living at or near the coast. We show a more region‐wide picture of the direct and indirect effects of tectonic activity, by comparing two embayments that represent coastal points of entry at opposite ends of the Waimakariri River floodplain: the Avon‐Heathcote Estuary (Ihutai) and Lake Ellesmere (Waihora). Copyright © 2005 John Wiley &amp; Sons, Ltd.

Trace metal concentrations in two New Zealand talitrid amphipods: effects of gender and reproductive state and implications for biomonitoring

This is the first in-depth investigation of whether the gender or reproductive state of talitrid amphipods affects the bioaccumulation of trace metals. Concentrations of copper, zinc, and cadmium were measured in the beach flea Transorchestia chiliensis (Milne-Edwards) and the sand hopper Talorchestia quoyana (Milne-Edwards) (Amphipoda: Talitridae) from sites in and near the Avon–Heathcote Estuary, Christchurch, New Zealand. For T. chiliensis, the whole body trace metals concentrations (μg g −1) were generally similar for nonbrooding, brooding, and brooding females that had the embryos removed. Where there were differences between female groups (3 out of 15 samples), concentrations in nonbrooding females were below those for brooding females. The trace metal concentrations of separated embryos did not follow those of their mothers. The body zinc concentration was similar for males and females. For copper and cadmium, body concentrations for females were higher than males at the two most contaminated sites. Cadmium body concentrations were similar between sites, and the lowest concentrations were from amphipods from one of the Estuary sites rather than the reference site. In T. quoyana, the trace metal concentrations in nonbrooding female and male sand hoppers were similar for copper and zinc, but cadmium concentrations were higher in nonbrooding females than in males. Copper and zinc concentrations within amphipod body tissues did not reflect those in the sediment or their food. The implications of these results are discussed in relation to previous studies and the use of beach fleas and sand hoppers as metal biomonitors. The beach flea T. chiliensis is recommended as a suitable trace metal biomonitor in New Zealand coastal waters with the potential to be affected by anthropogenic trace metal contamination.

The Impact of Christchurch City (New Zealand) on Heavy Metals in Sediments of the Avon-Heathcote Estuary

This paper reviews heavy metal (Cr, Cu, Fe, Mn, Ni, Pb, Zn) content in the clay fraction (&amp;lt;4 µm) of soils, suspended sediment, surface sediment, and core sediment associated with the Avon-Heathcote Estuary. Despite the estuary's low clay content (&amp;lt;10%), significant metal and organic matter trends are apparent in the clay fraction, which are less obvious in parallel studies of silt (4-63 µm), sand (&amp;gt;63 µm), and total sediment. Clay fraction depth profiles record periods of high heavy metal input in sediments deposited slowly but not in sediments deposited rapidly. Most metals, organic matter, mud, and Fe oxides accumulate in a broad anaerobic band across the western area of the estuary. Organic matter and metal concentrations are increasing towards the surface in depth profiles of this zone. This pattern combined with the increasingly eutrophic state of the estuary suggests more serious heavy metal contamination in the future.

Distribution, body size, and brood characteristics of four species of mysids (Crustacea: Peracarida) in the Avon‐Heathcote Estuary, New Zealand

Four species of mysids are resident in the Avon-Heathcote Estuary, Christchurch. Tenagomysis macropsis is by far the most abundant daytime species and has a wide distribution, not linearly correlated with salinity. Tenagomysis novae-zealandiae and T. chiltoni are much less abundant, increase in numbertoward the upper estuarineregion, and (especially T. chiltoni) have distributions significantly correlated with salinity (P < 0.05–0.001). T. chiltoni has a spring/summer population maximum. Gastrosaccus australis appears to be an obligate nocturnal plankter and its; distribution in the system is unresolved. The largest mysid was T. chiltoni and the smallest T. novae-zealandiae, although there was considerable intraspecific size variation. For all 3 Tenagomysis species, males were mature at a smaller size than females, whereas the opposite was true for G. australis. For each species, ovigerous females generally achieved the maximum size recorded. Embryo numbers carried in the marsupium ranged from 4 to 25 for T. macropsis, from 6 to 19 for T. novae-zealandiae, and from 22 to 39 for T. chiltoni. Embryo sizes for the New Zealand species are in accord with the range found generally for coastal mysids.

Carbon-13 depletion in an estuarine bivalve: Detection of marine and terrestrial food sources.

Stable carbon isotope analysis was used to define the food sources of bivalve Chione (Austrovenus) stutchburyi in the Avon-Heathcote Estuary, Christchurch, New Zealand. δ13C values of C. stutchburyi tissue were significantly different (from -16.7‰ to -23.5‰ relative to the PDB standard) at five locations separated by less than 4 km but subject to different hydrological regimes. This is related to differences in the isotopic composition of the suspended particulate matter of the inflowing water. C. stutchburyi is shown to utilise carbon of terrestrial and marine origin depending upon its position within the estuary and local hydrology.

Population and reproductive biology of the mud crab,Macrophthalmus hirtipes(Jacquinot, 1853) (Ocypodidae), from marine and estuarine habitats

Summary Monthly samples of the burrowing mud crab, Macrophthalmus hirtipes (Jacquinot 1853) were collected from February 1978 to April 1979 from a marine inlet, Governors Bay (43°38′S, 172°39′E) and from the Avon-Heathcote Estuary (43°33′S, 172°44′E), New Zealand. The estuarine population was generally unimodal and had an annual cycle of population change sustained by a concentrated summer recruitment. In contrast, the bay population was unimodal and bimodal at different times, and recruitment occurred thoughout the year with no clear peak. Both populations had equal sex ratios and were dominated by immature individuals (crabs⩽10·0 mm carapace width). Estuarine crabs were generally smaller than marine crabs. At both sites, ovigerous females were found from late May to early March; the smallest egg-bearing female measured CW 10·0 mm at the estuary and CW 10·5 mm at the bay. Cycles of ovarian and embryological development were similar at the two localities. Three peaks of egg oviposition occurred within one...

Habitat preferences of two estuarine burrowing crabs Helice crassa Dana (Grapsidae) and Macrophthalmus hirtipes (Jacquinot) (Ocypodidae)

The horizontal and vertical distributions of two species of endemic, burrowing mud crabs Helice crassa Dana 1851 (Grapsidae) and Macrophthalmus hirtipes (Jacquinot 1853) (Ocypodidae) are described for the Avon-Heathcote Estuary (43°33′S: 172°44′E), Christchurch, New Zealand. Substratum preference is shown to be the most important factor influencing mud crab distribution, but lack of tolerance to salinities below 4‰ is also a significant factor preventing M. hirtipes from occurring at points close to freshwater input. Both species had similar sediment organic content and particle size requirements. Helice crassa was concentrated in well-drained, compacted sediments above mid-tide level, whilst Macrophthalmus hirtipeswas found in waterlogged areas below mid-tide level. This vertical separation is shown not to be caused by differential desiccation tolerances, but by feeding and burrowing adaptations related to these different substrata.

Reproductive ecology of the estuarine burrowing mud crab Helice crassa (Grapsidae)

The reproductive cycle and population biology of the endemic, burrowing mud crab Helice crassa Dana, 1851 (Brachyura, Grapsidae) in the Avon-Heathcote Estuary (44°33′S, 172°44′E), Christchurch, New Zealand, was studied from April 1975 to December 1976. Juvenile crabs (≤4 mm carapace width) were present throughout the year, but were most numerous from February to April. Males of all sizes (4.1–18.0 mm carapace width) were significantly (tested by χ 2 ) more abundant than females and the overall sex ratio was 1.48♂♂: 1♀. Maximum carapace widths were 17.7 mm for male crabs, 15.8 mm for non-ovigerous females and 15.1 mm for ovigerous females. Ovigerous females occurred from August/September to March with maximum numbers present in November. Peaks of egg production were found in October and January. Egg volume at oviposition was constant throughout a breeding period; however, eggs from August–November 1975 ( volume=0.0099 μl±0.0032) had a significantly larger volume ( t =3.68, P <0.01 for 45 D.F.) than those from September–December 1976 ( volume=0.0074 μl±0.0021). Eggs did not increase in volume during development and had no measurable mortality. Egg numbers were not affected by season and were related to female carapace width according to the equation y =−13931.8+1890.8 x ( r 2 =0.886). These findings are compared with studies on the reproduction of this species from marine habitats elsewhere in New Zealand, and are considered with respect to the influence of latitude and environment on the breeding biology of H. crassa .

Response to urbanization of the avon-heathcote estuary, christchurch, New Zealand

The Avon-Heathcote is a small, microtidal, predominantly intertidal, weather-dominated estuary. It has experienced large alterations to its physical environment as a result of the establishment and growth the adjacent Christchurch City, on what was previously a swampy, dune-bordered coastal plain. During the first 25 years of settlement the volume of the tidal compartment of the estuary decreased from 7.7 × 106 m3 to about 5 × 106 m3. A combination of rapid drain laying in the 1880s and 1890s and the conversion of much of the catchment of the estuary to urban uses altered the sediment yields and runoff characteristics of the area and resulted in a reversal of the early trend. By 1925 the tidal compartment had returned to its original volume, and by 1975 it had reached a volume of 10.93 × 106 m3. The early decrease was accompanied by widespread deposition of a 30–60 cm thick layer of muddy sediment, some of which remains. The estuary inlet underwent major adjustments to accomodate the increasing tidal flow and now appears to be approaching a new, posturban equilibrium.

The effect of nutrient enrichment and temperature on the growth in culture of Ulva lactuca L.

The growth response of Ulva lactuca L. to different combinations of phosphorus and nitrogen was followed using discs cut from the expanded region of mature plants. Addition of either NO 3 -N or PO 4 -P stimulated growth, optimum levels being 0.6 g/m 3 for both nutrients. Below the optimum, N and P interacted in their effect on growth; above the optimum, increasing N concentration decreased growth while no change occurred with increasing P. These results are similar to those of Waite and Mitchell (1972), but their suggestion that the results fit a limiting factor equation was found to be true for only part of the P/N response surface. The growth response of U. lactuca to temperatures between 6 and 25° C was tested on plants from two localities which differed in water temperature. The plants from the locality with the higher mean monthly temperature had the higher temperature optimum in the experiments. The results support findings from field data which suggested that the high standing crop (up to 130 g/m 2 dry weight) of U. lactuca in the Avon-Heathcote Estuary (Christchurch, New Zealand) is related to eutrophic water conditions and that temperature is an important factor in controlling seasonal and annual fluctuations in growth.