P. A. Gillespie

Effects of mussel aquaculture on the nitrogen cycle and benthic communities in Kenepuru Sound, Marlborough Sounds, New Zealand

Nitrogen pools and transformations and benthic communities at a Perna canaliculus farm and a nearby reference site without direct influence of marine farming in Kenepuru Sound, New Zealand, were compared on four dates between September 1982 and May 1983. The organic nitrogen pool in the top 12 cm sediment was 7.4 to 10.8 mol m-2 at the mussel farm and 6.1 to 8.9 mol m-2 at the reference site. The nitrate and nitrite pools were similar in both sediments, but the ammonium pool in the mussel farm sediment was about twice as high as in the reference sediment. In January, the sediment ammonium concentrations ranged from 418 nmol cm-3 (surface) to 149 nmol cm-3 (12 cm depth) at the mussel farm and from 86 to 112 nmol cm-3 at the reference site. The molar C:N ratio of the sediment organic matter was 6.2 to 7.2 at the mussel farm and 7.9 to 10.0 at the reference site. The molar N:P ratio of the sediment organic matter was 4.3 to 7.2 and 3.3 to 6.1 at mussel farm and reference site, respectively. The total nitrogen mineralisation rate in the top 12 cm sediment ranged from 21.7 to 37.1 mmol m-2 d-1 at the mussel farm and from 8.5 to 25.0 mmol m-2 d-1 at the reference site. Ammonium excretion by mussels was about 4.7% (January) and 7.4% (May) of the combined nitrogen mineralisation by mussels and sediment. The sediment-denitrification rate was 0.7 to 6.1 mmol m-2 d-1 at the mussel farm and 0.1 to 0.9 mmol m-2 d-1 at the reference site. In January, 76 and 93% of the nitrate reduced in the sediments were denitrified at the mussel farm and reference site, respectively. The denitrification rate on the mussel lines (determined on detritus-covered mussels) was twice the mussel farm sediment-denitrification rate and 10 times the reference sediment-denitrification rate. Total denitrification at the mussel farm was 21% higher than at the reference site. The loss of nitrogen through mussel harvest and denitrification was 68% higher at the mussel farm. The surface layers of both sediments contained about 75 mg m-2 chlorophyll a. Sediment phaeophytin levels were 52 mg m-2 at the reference site and 137 mg m-2 at the mussel farm. While the benthic infauna of the mussel-farm sediment consisted only of polychaete worms, the reference sediment contained also bivalve molluscs, brittle stars and crustaceans.

Impacts of longline mussel farming on oxygen and nitrogen dynamics and biological communities of coastal sediments

Benthic communities and benthic mineralization were studied in two shallow coastal regions of New Zealand: Tasman Bay, a possible future site for mussel farm development, and Beatrix Bay, which already hosts several longline mussel farms. In Tasman Bay, microphytobenthic (MPB) production added significantly to the total primary production of the bay. The activity of benthic microalgae had a pronounced effect on oxic conditions, solute exchange and denitrification rates. Benthic mineralization, quantified as the dark oxygen uptake, was in the range of 675±11 μmol m−2 h−1. Denitrification rates were high and fueled entirely by nitrate produced by the nitrifying community within the sediment. Competition for inorganic nitrogen between benthic microalgae and nitrifiers/denitrifiers resulted in diel variation in nitrogen cycling and reduced the inorganic nitrogen efflux and denitrification activity in the light. Calculated in electron equivalents, denitrification accounted for 11–20% of the total carbon mineralization—one of the highest numbers reported for coastal sediments. Reduced sediments, containing low MPB biomass and few subsurface macroinvertebrate species, were observed below a mussel farm in Beatrix Bay, presumably due to the intensified sedimentation of organic matter. Oxygen consumption increased in the organic-rich sediments, and ammonium effluxes were up to 14 times higher than those of unaffected sediments 250 m away from the farm. Denitrification rates below the farm were low as the coupled nitrification–denitrification was inhibited by the presence of sulfide. The dissimilative reduction of nitrate to ammonium (DRNA) was, however, stimulated in the reduced sediment. The enhanced benthic mineralization was associated with sulfidic sediments and a lower nitrogen removal rate due to impeded benthic photosynthesis and denitrification activity. The described local conditions associated with mussel farming should be taken into account when new areas are considered for development.

Integrated catchment management—interweaving social process and science knowledge

This paper provides an overview of the Motueka integrated catchment management (ICM) research programme. This research was based on the thesis that achieving ecosystem resilience at a catchment scale requires active measures to develop community resilience. We define a generic adaptive planning and action process, with associated knowledge management and stakeholder involvement processes, and illustrate those processes with observations from five research themes: (1) water allocation; (2) land use effects on water; (3) land and freshwater impacts on the coast; (4) integrative tools and processes for managing cumulative effects; and (5) building human capital and facilitating community action. Our research clearly illustrates the benefits for effective decision-making of carrying out catchment scale science and management within collaborative processes which patiently develop trusting relationships. We conclude that coastal catchments should be managed as a holistic continuum from ridge tops to the sea and that some processes like floods or loss of community resilience have decadal consequences, which support the need for long-term monitoring and investment.

Tidal circulation in Tasman and Golden Bays: Implications for river plume behaviour

Abstract An investigation into the tidal residual circulation in the Tasman/Golden Bays system was performed. This investigation involved collecting hydrographic and current meter data, and configuring a numerical circulation model. The model was able to reproduce the gross features of the major tidal flows within the system revealed by the data. The simulated tidal residual circulation conformed to that previously suggested, except along the western side of Tasman Bay where this investigation suggests that residual flows move northwards. The validated model was then used to produce simulations of the fate of the plumes from the major rivers. Salinity field simulations describing different river flow and wind direction/velocity scenarios suggest that the Motueka River plume can cover considerable proportions of western side Tasman Bay, extending into Golden Bay during flood conditions. The embedded sediment transport model was also used to investigate the fate of fine sediments entering the bays. Simulated distribution patterns of fine sediments entering the bays from the four major tributaries were found to be consistent with existing bathymetric and seabed substrate characteristics.

Plankton ecology and productivity, nutrient chemistry, and hydrography of Tasman Bay, New Zealand, 1982–1984

Abstract The water column at a single near‐shore location in Tasman Bay was intensively sampled between April 1982 and March 1984 at 1–2 month intervals. Lowest salinities and highest dissolved nutrient concentrations occurred during the winter of both years. Nitrate‐N was the most commonly measurable inorganic nitrogen species. Inorganic N: P: Si ratios suggest that among the major nutrients nitrogen was in the greatest demand. The phytoplankton community structure and phenology was typical of a temperate neritic environment, though considerable year to year variations occurred in the specific composition and the magnitude of production. Periods of relative abundance of some potential nuisance species were documented. Small nannoplanktonic species (< 10 μm) were always an important and frequently a dominant component of the photosynthetic community. The winter/spring diatom bloom re‐occurred as the most productive event. In surface waters, phytoplankton biomass ranged from 19–208 mgC m‐3. In situ rates o...

Multiple indicators reveal river plume influence on sediments and benthos in a New Zealand coastal embayment

Abstract Multiple physico‐chemical and biological indicators were used to delineate the spatial influence of the Motueka River plume on coastal surface sediments and associated biota in Tasman Bay, New Zealand. Sediments were primarily muds at nearshore sites on all transects and comprised coarser sediments at the most seaward sites in Tasman Bay. Organic carbon/nitrogen ratios, stable carbon and nitrogen isotope signatures, and certain lipid biomarkers and trace metals provided suitable indicators of terrestrial and riverine influence on subtidal sediments. Analysis of these parameters revealed a discernible catchment influence extending at least 6 km offshore in the river outwelling plume, with a pronounced signature evident at two sampling stations within approximately 2km of the Motueka River mouth. At these two nearshore sites, nickel and chromium from natural upper‐catchment sources were present at concentrations greatly exceeding sediment quality thresholds for probable ecological effects. The infaunal assemblage at these sites comprised low densities of a few opportunistic taxa, with the spatial distribution of organisms strongly correlated with trace metal concentrations. Although a causal relationship with trace metals is possible, other unmeasured influences such as gradients of salinity, depth and physical disturbance could conceivably be the primary drivers of the biological pattern. By contrast with the effects on infauna, analyses of stable carbon and nitrogen isotopes and trace metals in epibenthic shellfish did not reveal any evidence of a direct terrestrial or riverine influence. Overall, the results from this work indicate a relatively localised river plume effect on subtidal sediments and the associated infaunal assemblage. However, because previous work has shown that the river plume can extend tens of kilometres offshore during flood flows, further investigation is required to understand changes in seabed parameters within the context of spatio‐temporal variation in catchment inputs and river plume discharge.

Microphytobenthic communities of subtidal locations in New Zealand: Taxonomy, biomass, production, and food‐web implications

Abstract Diatom mats dominated by large sig‐moid, raphid species of the genus Gyrosigma (Naviculaceae) and, in some instances, the tube‐former, Berkeleya rutilans (Naviculaceae) were observed in the semi‐enclosed coastal waters (depths 6–20 m) of Tory Channel, Marlborough Sounds, New Zealand. The latter species, not previously observed in New Zealand, is generally associated with intertidal environments where light intensities are relatively higher than subtidal locations. Its presence imparted a filamentous nature to the mat that may play a role in maintaining the integrity of the sediment/water interface. Sediment chlorophyll a concentrations ranged from c. 20 to 200 mg m‐2. Microphytobenthic (MPB) contributions to the total (benthic + planktonic) chlorophyll a equated to 92, 89, and 84% at depths of 8, 16, and 20 m, respectively. Oxygen production in intact cores often exceeded consumption (e.g., by up to 2.5 mmol m‐2h‐1) under near‐m situ conditions of light (8–30 μmol m‐2 s‐1). The feeding strategies of major components of the benthic macroinvertebrate fauna were used to identify possible pathways for utilisation of MPB production. MPB communities of more exposed subtidal locations in Tasman Bay were generally less dense and comprised of different species dominated by Pleurosigma amara and/or Paralia marina. We conclude that microalgal communities inhabiting the soft sediments in these regions can provide an important contribution to the benthic food web.

Source tracking faecal contamination in an urbanised and a rural waterway in the Nelson-Tasman region, New Zealand

Abstract Microbial contamination of New Zealands rivers, lakes and coastal waters can pose a risk to human health through both recreational contact and the consumption of contaminated shellfish. Microbial source tracking (MST) methods provide a means to identify potential contaminant sources, which can lead to high faecal indicator bacteria concentrations and elevated human health risk because of associated pathogens. Eight MST markers, including general, ruminant and human-associated Bacteroidales markers, a duck-associated E2 marker, a gull-associated Catellicoccus marimammalium marker and three additional human markers [Enterococcus faecium esp gene, Methanobrevibacter smithii nifH gene, and human polyomaviruses (HPyVs)] were tested for host specificity and sensitivity using an array of animal faecal samples of known origin and wastewater samples. The cross-reactivity identified for some of the markers, although limited, signals a need to validate overseas markers further in New Zealand before employing them in field studies. Application of MST markers on water samples collected from an urbanised section of the Maitai River (Nelson, New Zealand) identified the presence of faecal contamination originating from humans, ruminants and birds. Human faecal contamination was present in the lower section of the Matai River, and in stormwater drains entering the river, in association with elevated faecal coliform concentrations. Application of the markers to the rural Little Sydney Stream (near Motueka, Tasman district, NZ) identified faecal contamination derived from ruminants, which is consistent with the agricultural (pasture) use of the catchment. This study indicates that some of the markers developed overseas can be used effectively to track sources of microbial contamination in New Zealand watersheds.

Heterotrophic potentials and trophic status of ten New Zealand lakes

Abstract A comparative study of the heterotrophic potentials of ten New Zealand lakes was carried out. Two sampling periods were chosen, one during late August and early September 1972 (late winter, minimal thermal stratification) and another during February 1973 (mid summer, strong thermal stratification in all but two lakes). A wide range of heterotrophic potentials occurred which enabled the lakes to be placed in the following basic groups according to descending trophic levels: Group I: Rotowhero (thermal, acid lake) >Rotorua>Okaro Group II: Rotokakahi> Tikitapu >Okareka Group III: Rotoma = Rotoroa (S.I.) = Rotoiti (S.I.) = Okataina Maximum values for heterotrophic potential (Vm a x ) in micrograms of glucose per litre per hour were: Maximum heterotrophic activities were found within the metalimnion, except in Lakes Tikitapu and Rotokakahi, where maximum activities occurred within the hypolimnion.

Motueka River plume facilitates transport of ruminant faecal contaminants into shellfish growing waters, Tasman Bay, New Zealand

Hydrographic and water quality surveys of the Motueka River and its river plume were conducted during a moderate flood event (peak flow of 420 m3/s) to assess the source and fate of faecal contaminants transported into Tasman Bay. Escherichia coli (E. coli) and enterococci concentrations in the river were up to 10000 and 7300 Most Probable Number (MPN)/100 ml during peak flow, respectively. A coastal survey revealed a shallow low-salinity plume that extended at least 6 km into Tasman Bay and the regions largest aquaculture management areas (AMAs). Mussels within the influence of the river plume, including those collected within an AMA, had E. coli and enterococci concentrations as high as 1300 and 2200 MPN/100 g tissue, respectively. Application of microbial source tracking markers using end-point PCR assays identified the presence of faecal contamination from ruminant animals (cows, sheep) in water and mussel samples. The detection of ruminant faecal contamination within shellfish located 6 km offshore highlights the close connection between land use and the quality of New Zealands highly valued coastal resources.