Search

The McMurdo Dry Valleys are the largest single ice-free area in Antarctica, and of considerable scientific and conservation value as an extreme polar desert. This is recognised through the McMurdo Dry Valleys Antarctic Specially Managed Area (ASMA), where management's goals focus on protection of its unique features, while facilitating science access. Using a mix of remote sensing and existing cartography, we have identified over 6000 lakes and ponds in the ASMA. This study develops a classification of those aquatic ecosystems to provide a framework for management. It uses a limited top-down, hierarchical classification to define 13 class separations based on physical attributes that could largely be ascribed from existing databases or remotely sensed information. The first hierarchical level was based on landscape position, separating coastal kettle holes (reflecting recent glacial history), from other "topographic" water bodies. The second level was based on endorheic vs exorheic drainage, the third on mid-summer ice condition (no-ice cap; ice capped; frozen to base) and the fourth on source of inflow (glacial or non-glacial). Kettles were sub-classed by mid-summer ice only. Classes were tested against a set of field observations and an expert workshop validation process considered management implications for the ASMA. This study shows how the classification assists our understanding of Dry Valley landscapes and addresses management issues faced by researchers, environmental managers and policy makers. The approach to classification, rather than the detailed classes that may be specific to the Dry Valleys, has potential for wider use in other polar landscapes.

Protection of Antarctica's biodiversity and ecosystem values is enshrined in the Protocol on Environmental Protection to the Antarctic Treaty, which provides for the designation of Antarctic Specially Protected Areas (ASPAs) to areas with outstanding values. Concern has been raised that existing ASPAs fail to prioritize areas to maximize the likelihood of ensuring the long-term conservation of Antarctic ecosystems and biodiversity. The absence of systematic and representative protection is particularly acute for inland aquatic ecosystems, which support a disproportionate amount of inland biodiversity. This paper promotes the case for overt inclusion of inland waters as a critical component of a representative protected area framework for Antarctica, thereby addressing their current underrepresentation. We set out a structured approach to enable the selection of representative freshwater systems for inclusion in the ASPA framework that, with modification, could also be applied across other Antarctic habitats. We acknowledge an overall lack of information on the biogeography of inland aquatic diversity and recommend increased use of remote data collection along with classification tools to mitigate this, as well as the need for the consideration of catchment-scale processes. Changes that accompany contemporary and anticipated climate change make the need for the conservation of representative biodiversity increasingly urgent.

The ecological effects of wastewater treatment plant (WWTP) discharges into rivers typically include elevated periphyton biomass resulting from enrichment by dissolved reactive phosphorus (...

Rich in both microbial mat biomass and species diversity, the meltwater ponds of the McMurdo Ice Shelf (MIS) form important biodiversity and productivity elements in an otherwise barren landscape. These ponds are thought to be sensitive indicators of climate change-driven fluxes in pond water balance but our ability to predict such effects is confounded by our poor understanding of the inherent variability of these communities in response to the physico-chemical environment. Understanding how microbial communities are shaped across broad physico-chemical gradients may allow better predictions of the effects of climate change on the MIS wetlands. Our study found that distinct clustering of community types against environmental variables was apparent for both the diatom and cyanobacterial communities. For diatoms, conductivity was correlated with the separation of five significantly distinct communities. Significant differences in NH4–N concentrations were correlated to the three distinct cyanobacterial communities but many of the cyanobacteria morphotypes were recorded across a wide ecological range. More distinct community types suggested that diatoms were more sensitive to environmental change in these ponds than the cyanobacteria, despite the latter’s overall dominance. Distinct community clusters for diatoms, and to a lesser extent cyanobacteria, suggest that changes at a functional group level may be more important than at the level of individual species. Further understanding of diatom functional groups would provide us with the opportunity to hindcast past climates and water budgets within the Antarctic region. However, the disconnect between biomass and community composition currently prevents hindcasting past productivities in relation to environmental changes.

Many lakes world-wide suffer from eutrophication as a result of high external nutrient inputs from domestic sewage, industry and agricultural activities. Increased demands for water by a growing and developing human population as well as enhanced global warming may escalate the eutrophication on a global scale in the next century. Yet, in some countries large efforts are now being made to combat eutrophication by reducing the phosphorus input. Some lakes respond rapidly to such loading reductions, while others are highly resistant due to high internal phosphorus loading (chemical resistance) or homeostatic effects of the food web altered by eutrophication (biological resistance). Some general models have been developed for the response of lakes to reduced loading, but major advances within this field can be expected in the future when more case studies appear. While these models may be used as a core for evaluating response patterns, local factors should always be considered to avoid wrong and often expensive decisions. To precipitate recovery from chemical and biological resistance, several physico-chemical and biological restoration methods have been developed. The biological methods include removal of planktivorous and benthivorous fish, stocking of piscivorous fish, protection or planting of submerged macrophytes, introduction of artificial structures, or addition of mussels. A widely applied method is removal of planktivorous and benthivorous fish. In many cases such efforts have yielded major improvements in water quality and the ecological state of the lakes. Yet, the listed restoration methods have mainly been applied to northern temperate lakes and cannot readily be transferred to subtropical and tropical lakes where the eutrophication-related problems are going to be greatest in the future. There is thus a major need for development and adaptation of methods focusing on south temperate, subtropical and tropical lakes.

This special issue of the New Zealand Journal of Marine and Freshwater Research is a tribute to one of New Zealand’s eminent freshwater scientists, Dr John Quinn, who sadly passed away in November ...

The effect of stock origin and growing environment on growth and reproduction of the green-lipped mussel Perna canaliculus was investigated on the marine farms in the Marlborough Sounds, New Zealand. Following the normal commercial practice, mussel stocks from three widely separated origins in New Zealand were transplanted to six sites in Marlborough Sounds and grown on ropes hung from commercial longlines for eleven months. Stock origin had significant effects on growth rates as measured by shell length and flesh weight. Growing sites also showed a significant effect on flesh growth rate but only a small effect on shell length growth, with considerable variation among sites. Two sites (Beatrix Bay and Hallam Cove) had the fastest growth in flesh weight. One stock (Golden Bay) showed the fastest growth and lowest mid-winter reproductive rates, while the Kaitaia stock (the most commonly used one in industry) showed highest winter reproductive rate. Spawning was responsible for mid-winter declines in flesh weight among all stocks, but the Golden Bay stock recovered flesh weight more rapidly than other stocks after spawning. The stock differences in growth suggest that genetic traits of stock origin remained after mussels were grown in different environments (sites). In addition, we speculate that there would be a large variation of physiological rates between stocks including filtration, ingestion and respiration rates. The variation in growth and reproduction suggests that there would be a significant difference in energy allocation for reproduction, flesh and shell growth among stocks. The study has obvious application to the mussel industry for planning and selective seeding of stocks to maximise economic benefits. The use of fast-growing stocks and timing of harvesting in mid-winter can dramatically improve quality and quantity of production.

Consideration of the need and opportunities for restoration of freshwater lakes in New Zealand requires individualised approaches that account for lake type, invasive species and food web structure.

New Zealand has made significant contributions to scientific knowledge underpinning lake restoration work and to the development and testing of management tools. This introductory chapter provides an overview of the history, current context, and policy framework for lake restoration in New Zealand and makes international comparisons. The book draws on recent advances in modelling and monitoring tools, and highlights how improved understanding of lake processes and their interaction with biological communities applies to restoration. Restoration solutions must address catchment as well as in-lake issues, and the socio-cultural considerations which influence the development, implementation and monitoring of lake restoration actions. Accordingly, Chaps. 2– 16 are divided into five main sections: Management and modelling, Water quality restoration, Biodiversity restoration, Monitoring and indicators, and Socio-cultural considerations (including the roles of indigenous people and citizen science). New Zealand perspectives are complemented by international feature boxes which reinforce key concepts and highlight differences or similarities in restoration approaches. The feature boxes generally emphasise the ubiquity of the threats to lake ecosystems across the world but also the need to adapt restoration to the individual lake scale.

Widespread public concern in the last few decades over the state of freshwater ecosystems has driven a strong commitment to their rehabilitation in many countries. In New Zealand, this commitment is being expressed at levels from individual communities through to the government. Lake ecosystems are at the forefront of public discussions and policy development. Māori are integrally involved as the indigenous people of New Zealand who have rights and interests in water as well as environmental stewardship roles. New Zealand has acquired a substantial knowledge base on restoration actions, many of which integrate across environmental, social, cultural and policy domains, and which in some cases allow for a comprehensive evaluation of their effectiveness. Principal pathways to lake restoration identified in the chapters of this volume are through: 1. Reduction in contaminant loads and concentrations, particularly sediments and nutrients, where these have caused a decline in lake health 2. Reduction of internal nutrient loads in lakes 3. Alteration of lake stratification patterns where these exacerbate degradation 4. Control of invasive plant and animal pest species 5. Remediation of migration barriers to enhance connectivity for native species 6. Biodiversity enhancement 7. Lake monitoring and modelling to prioritise actions 8. Improved community participation processes

Stratification in lakes is a natural phenomenon caused by solar heating resulting in development of a thermocline. This becomes a barrier to heat, dissolved oxygen and dissolved nutrient transfer between the upper and lower water column. Nutrient runoff from land and phytoplankton growth in lakes can cause bottom waters to become oxygen depleted and potentially unsuitable as a habitat for aquatic biota. Conversely, reduced depth of mixing above the thermocline provides a high light field that enhances algal and cyanobacteria growth and, in nutrient rich conditions, the lake becomes degraded, the natural lake eutrophication process. Reducing the nutrient load on the lake may not be possible and alternative actions are required such as minimising or removing the magnifying effects of thermal stratification on the eutrophication process. This chapter describes issues associated with thermal stratification in lakes and examines the possible options for removing or preventing thermal stratification by mixing as a management strategy for the rehabilitation of degraded lakes. The most common mixing device is aeration, using bubble plumes to induce vertical movement of the water column. Sparge line aeration systems can be designed to suit most water bodies from small ponds to large reservoirs and natural lakes, with the maximum size being determined by economics: a generic design is described in detail. Also described are alternative water column mixing systems and the option of bottom water re-oxygenation without destratification. Discussions are based around strategies adopted for the ten water supply reservoirs for Auckland City (New Zealand), used as a case study.

Carbon limitation in domestic wastewater high rate algal ponds is thought to constrain microalgal photo-physiology and productivity, particularly in summer. This paper investigates the effects of CO₂ addition along a pH gradient on the performance of wastewater microalgae in high rate algal mesocosms. Performance was measured in terms of light absorption, electron transport rate, photosynthetic efficiency, biomass production and nutrient removal efficiency. Light absorption by the microalgae increased by up to 128% with increasing CO₂ supply, while a reduction in the package effect meant that there was less internal self-shading thereby increasing the efficiency of light absorption. CO₂ augmentation increased the maximum rate of both electron transport and photosynthesis by up to 256%. This led to increased biomass, with the highest yield occurring at the highest dissolved inorganic carbon/lowest pH combination tested (pH 6.5), with a doubling of chlorophyll-a (Chl-a) biomass while total microalgal biovolume increased by 660% in Micractinium bornhemiense and by 260% in Pediastrum boryanum dominated cultures. Increased microalgal biomass did not off-set the reduction in ammonia volatilisation in the control and overall nutrient removal was lower with CO₂ than without. Microalgal nutrient removal efficiency decreased as pH decreased and may have been related to decreased Chl-a per cell. This experiment demonstrated that CO₂ augmentation increased microalgal biomass in two distinct communities, however, care must be taken when interpreting results from standard biomass measurements with respect to CO₂ augmentation.

Carbon limitation in domestic wastewater high rate algal ponds (HRAPs) is thought to constrain both microalgal photosynthesis and biomass production. CO2 augmentation is one way of overcoming this carbon limitation; however, high carbon demands due to large microalgal biomass means that the frequency of CO2 supply is likely to be critical to its success. This paper investigates the hypothesis that decreasing the frequency of CO2 addition reduces the performance of wastewater microalgae. Microalgae were cultured in outdoor high rate algal mesocosms to assess the frequency of carbon dioxide (CO2) addition on photosynthetic performance, biomass production and nutrient removal. Microalgal productivity significantly increased with high frequency of CO2 addition. Organic biomass was 120 % higher, and total microalgal biovolume was 157 % higher at high-frequency compared to low-frequency CO2 addition. Photosynthetic efficiency increased, and algae were less photo-inhibited as the frequency of CO2 addition increased, while microalgae with low CO2 addition frequency did not differ from those without CO2 addition. In conclusion, low-frequency CO2 addition, such as that which could be expected in large HRAPs with long circuit times and a single point of CO2 addition, did not improve microalgal productivity. While CO2 addition enhances microalgal photosynthesis and productivity when good pH control is maintained through day-time, this study has demonstrated that, due to rapid assimilation of CO2 by the microalgae, having an effective CO2 addition system in a full-scale HRAP is important if the benefits of CO2 addition are to be realised.

There has been renewed interest in the combined use of high-rate algal ponds (HRAP) for wastewater treatment and biofuel production. Successful wastewater treatment requires year-round efficient nutrient removal while high microalgal biomass yields are required to make biofuel production cost-effective. This paper investigates the year-round performance of microalgae in a 5-ha demonstration HRAP system treating primary settled wastewater in Christchurch, New Zealand. Microalgal performance was measured in terms of biomass production, nutrient removal efficiency, light absorption and photosynthetic potential on seasonal timescales. Retention time-corrected microalgal biomass (chlorophyll a) varied seasonally, being lowest in autumn and winter (287 and 364 mg m−3day−1, respectively) and highest in summer (703 mg m−3day−1), while the conversion efficiency of light to biomass was greatest in winter (0.39 mg Chl-a per μmol) and lowest in early summer (0.08 mg Chl-a per μmol). The percentage of ammonium (NH4–N) removed was highest in spring (79 %) and summer (77 %) and lowest in autumn (47 %) and winter (53 %), while the efficiency of NH4–N removal per unit biomass was highest in autumn and summer and lowest in winter and spring. Chlorophyll-specific light absorption per unit biomass decreased as total chlorophyll increased, partially due to the package effect, particularly in summer. The proportional increase in the maximum electron transport rate from winter to summer was significantly lower than the proportional increase in the mean light intensity of the water column. We concluded that microalgal growth and nutrient assimilation was constrained in spring and summer and carbon limitation may be the likely cause.

Meltwater ponds are important biodiversity elements in continental Antarctica. Many occupy closed basins and are vulnerable to changes in the balance between water accrual, through melting of ice and snow, and water loss by ablation and evaporation. We use a two-decade long record of ponds on the McMurdo Ice Shelf to assess temporal variability in key limnological variables. Ponds underwent many-fold change in biologically conservative variables, such as conductivity, and changes were similar in ponds from different catchments but of comparable area. In contrast, biologically active variables (pH, inorganic nutrients and planktonic/benthic biomass) are buffered by in-pond processes and show consistency between years and no coherence across catchments. Coherent behaviour across catchments implies an overarching, climatic effect. However, we could identify no signature of summer air temperature or irradiance in pond dynamics, although winter snow deposition may leave a legacy of low conductivity to the following summer. While ponds are clearly affected by climate, our data show that ecosystem responses are complex and highlight the need for system-appropriate, long-term observation if directional environmental change is to be separated from inherent variability in systems that respond to multiple climatic variables and which have significant biological buffering capacity.

Nutrient ratios have been related to nutrient limitation of algal growth in lakes. Retention of nutrients in lakes, by sedimentation and by denitrification, reduces the nutrient concentrations in the water column, thereby enhancing nutrient limitation. Differential retention of nitrogen and phosphorus alters their ratios in lakes and thereby contributes to determine whether nitrogen or phosphorus limits algal growth. We examined the relationships between differential nutrient retention, nutrient ratios, and nutrient limitation in Lake Brunner, a deep oligotrophic lake. The observed retention of nitrogen (20%) and phosphorus (47%) agreed with predictions by empirical equations from literature. As a result of differential retention with a much larger proportion of phosphorus retained than that of nitrogen, the nitrogen:phosphorus ratio was higher in the lake (69) than in the inflows (46). While the mean ratio in the inflows suggested no or only moderate phosphorus limitation, the lake appeared to be severely phosphorus limited. Combining empirical equations from literature that predict nitrogen and phosphorus retention suggests that the nitrogen:phosphorus ratio is enhanced by greater retention of phosphorus compared to nitrogen only in deep lakes with relatively short residence times, such as Lake Brunner. In contrast, in most lakes differential retention is expected to result in lower nitrogen:phosphorus ratios.

Lake Chilwa produces between zero and 24,000 metric tons of fish per year, making it one of the most productive but variable lakes in Africa. The size of the lake varies seasonally and among years, sometimes drying completely. Its surrounding wetland and floodplain provide habitat for a diversity of birds and economically valuable grasses and reeds. When the lake has water, there is considerable activity on its shores and temporary fishing villages spring up. People move in and out of the lake basin in concert with these seasonal and longer term changes. This paper examines the environmental dynamics of Lake Chilwa and its surrounding wetlands, presents an overview of the socio-economic context of the area and discusses threats to this resilient system that might occur as a result of climate change. We conclude that management of Lake Chilwa must place the lake in the wider economic and ecological system in which it is situated. Ultimately, land-use practices within the basin present more of a threat to the resilience of the fishery and people's livelihoods than overfishing or a strict focus on the lake's resources. These perspectives present significant challenges to conventional fisheries governance.

After a decade of research, New Zealand’s Latitudinal Gradient Project (LGP) now includes primary sites from Cape Hallett (72°S) to the Darwin Glacier (80°S), while additional observations extend the latitudinal transect from 84°S to sub-Antarctic regions. The LGP has been structured around a hypothesis that, in a frigid continent, ice dynamics is the key ecosystem variable. For terrestrial environments, two aspects of ice dynamics appear to underlie much of the observed variability. Firstly, the aridity of the region makes the transition from ice to water a key ecological factor, and secondly, the legacy of ice dynamics dating as far back as the Pliocene is imprinted on biogeography. These factors operate at difference temporal and spatial scales and neither is monotonically related to latitude. Both are also complicated by meso-scale cross gradients of altitude and distance from the sea and micro-scale local variability. Whilst climate does vary on a broad-scale, differences within the northern and central parts of Victoria Land that the LGP has so far examined are insufficient to impose any overarching effect that can overwhelm these more local effects. The result is a multiple-scale patchwork of habitats and communities, more or less replicated across the transect, in which variability at any given latitude generally exceeds variability between latitudes. A lesser quantum of research has been directed at marine ecosystems, but here there is a similar picture of local variability dominating within the Ross Sea, with significant latitude-scale effects only emerging when transects are extended into maritime- and sub-Antarctic regions. It is implicit, but not specifically recognized in the LGP context, that a further confounding effect on the interpretation of ‘transect’ information is the multiple stressor concept that requires a simultaneous analysis of interacting (synergistic or antagonistic) factors and environmental responses. As the LGP continues to extend further south, climate is expected to become more extreme, and water availability may change sufficiently for loss of habitat and species diversity to occur. Here we discuss options for refining the LGP approach to optimize its potential for understanding variability, and the factors underpinning this, in the Ross Sea Sector.

Multi-year time-series were used to describe oceanic and riverine nutrient supply and primary biomass in Pelorus Sound, a 50 km long estuary supporting most of New Zealand's $200 mil- lion per annum mussel Perna canaliculus aquaculture industry. In the summer half-year (October to March), when the Southern Oscillation Index (SOI) was negative (El Nino), NNW along-shelf wind stress strengthened and sea surface temperature (SST) at the Sound entrance cooled, indicating upwelling. This triggered increases in phytoplankton biomass, particulate nitrogen (PN) and per capita yield of farmed mussels in the Sound. In the winter half-year (April to September), wind stress was unrelated to SOI, but during NNW winds Pelorus River flows increased, along with NO3 - , phyto- plankton biomass, PN and mussel yield. During an extended period of positive SOI (La Nina), SSE winds and drought during 1999 to 2002, seston (PN) abundance and its food quality decreased, con- comitant with a mussel yield decrease of ~25% throughout Pelorus Sound. Seston and mussel yield had recovered by 2003 without reductions in farming intensity, so over-grazing by mussels did not cause the yield minimum. Instead, climatic forcing of oceanic and riverine N supply and seston bio- mass underlay the inter-annual variation in mussel yield. As tracers of the relationship of nutrient loading and production, PN and mussel yield appeared more reliable than NO3 - or chl a concentra- tions. In Pelorus Sound, oceanic and riverine N supplies are seasonally complementary and sustain year-round mussel yield, although their inter-annual variability, linked to wider climate forcing, can drive considerable fluctuation in yield over the decadal scale.

In this review we consider the physical processes that shape inland aquatic ecosystems and how these affect ecosystem processes, with particular focus on the nitrogen cycle. Inland Antarctica is dominated by microbial communities that are usually concentrated in, or adjacent to, habitats with free water. The presence of free vs frozen water is dependent on very small changes in temperature around 0°C, so significant variability in the distribution of free water can be expected in response to variations in climate over diel, decadal, to millennial time scales and a range of spatial scales. Antarctic inland waters take many forms: snow-surface melt pockets, cryoconites, basal regions of wet-based glaciers, ponds (varying in salinity and degree of desiccation), melt streams, perennially and seasonally ice covered lakes and even hypersaline, ice free lakes. The important processes and transformations that characterize the nitrogen cycle worldwide have all been identified in Antarctic inland waters and in some cases (e.g. N-uptake, N-fixation), rates are similar to those at lower latitudes. The unique features of Antarctic ecosystems stem from the extreme and variable physical conditions under which these processes operate rather than any unique ecosystem processes per se.

In the face of climate variability and change, science in Antarctica needs to address increasingly complex questions. Individual small studies are being replaced by multinational and multidisciplinary research programmes. The Latitudinal Gradient Project (LGP) is one such approach that combines a series of smaller studies under a single broad hypothesis to provide information that uses a gradient in latitude as a surrogate for environmental gradients, particularly climate. In this way latitudinal differences can be used to indicate climate change differences. The Key Questions for the LGP were developed via national workshops in Italy, New Zealand, and the USA and via two international workshops at SCAR conferences. Science and logistics are currently jointly shared by New Zealand, Italy and the USA, and cover marine and inland ecosystem studies along the Victoria Land coast from 72° to 78°S with plans for extensions to 85°S. The LGP forms part of the SCAR Programme Evolution and Biodiversity in Antarctica. This Special Issue summarizes some of the work in the first three years of the LGP (2002–2005), between McMurdo Sound and Cape Hallett, to form a basis for future comparative studies as the research shifts along the latitudinal span in the next decade.

Environmental factors associated with deep chlorophyll maximum (DCM) layers were examined in five lakes of the McMurdo Dry Valleys, Antarctica, to test the hypothesis that DCM are more closely associated with resource limitations than water density. Because data could not be transformed to meet the assumption of normal distribution, distance matrices were constructed from vectors of observed chlorophyll-a (CHL), photosynthetic active radiation intensity (PAR), soluble reactive phosphorous (SRP), dissolved inorganic nitrogen (DIN), dissolved oxygen (DO), water density (DEN), and incremental change in water density/depth (DEL). Multiple regression analyses then were based on permutation evaluations of the relationships between distance matrices (partial Mantel analyses). Results indicated that resource availability (PAR and DIN) was most frequently related to chlorophyll-a, although DEN and DEL often were significant within individual lakes. Hence, resource relationships were strongest across lakes...

Phytoplankton blooms are fundamental features of coastal ecosystems, but the processes that select for blooms of certain species are not well understood. The aim of this work was to investigate experimentally the interaction of light and nutrients (nitrate) in structuring phytoplankton community composition in Pelorus Sound, New Zealand. Microcosm experiments were conducted in situ nine times throughout the year, providing controls and treatments for increased nutrients and decreased light. Nitrate availability was found to be limiting to phytoplankton growth during spring and summer. Small- to medium-sized, chain-forming diatom taxa such as Chaetoceros sp., Skeletonema sp., Pseudonitzschia sp. and Thalassiosira sp. responded most rapidly to nitrate enrichment, increasing their biovolume up to 32-fold during the 5-day experiments. A long-term phytoplankton monitoring database showed that these taxa have historically dominated the phytoplankton assemblage, suggesting that intense competition for nitrate is a key component in structuring the phytoplankton community. Many of the taxa that were able to withstand light reduction in the shaded treatments were rare historically in Pelorus Sound, suggesting that light is secondary to nitrate availability in structuring the phytoplankton community composition in this coastal embayment.

Field measurements were used to validate predictions for the initial dilution of negatively buoyant, cold-water inflows to Lake Taupo, as part of a study to quantify mixing processes associated with the two largest inflows to the lake. The predictions were made using a formulation originally derived for positively buoyant, warm-water inflows to cooling ponds. The formulation predicts the total dilution of an inflow during its inertia-dominated phase between its entrance to the lake and the point where buoyancy forces are great enough to cause the inflow to plunge and form a submerged density current. In one of the measured inflows, the inflowing jet was free to entrain from both sides; in the other, entrainment was restricted on one side by attachment of the inflowing jet to the shoreline of a bay just upstream of the plunge point. In the former example, the unmodified coefficients from the cooling pond formulation provided an excellent prediction of initial dilution. In the latter example, entrainment was reduced and different coefficients were derived. In both examples the inflows remained attached to the lake bed throughout their course until their lift-off at depths of 45-55 m to form interflows. The difference between coefficients for the two inflows indicates that the coefficient values should be considered site-specific. The formulation is not valid for inflows that separate from the bottom of the inflow channel before plunging. The entrance mixing formulation was incorporated in a more general model of lake stratification, DYRESM, which already includes a well-documented routine for routing underflows down submerged channels on the bed of a lake. Application of the model to the inflows measured in Lake Taupo gave good results for two model outputs that were not involved in the calibration of the entrance mixing formulation, but that are affected by the result of the initial dilution calculation-the temperatures in the river plume after it has plunged, and the insertion depth.

From the Paleocene to the Pliocene, Chlamys-like genera of scallops (pectinid bivalve molluscs) inhabited coastal areas around the Antarctic continent. Today, all of the Chlamys-like genera are extinct around Antarctica and restricted to lower latitude habitats along the surrounding continents. The only remaining scallop in the high Antarctic zone is the large (greater than 108 mm in height), endemic, thin-shelled Adamussium colbecki. Adamussium has a circumpolar distribution with its highest abundances (greater than 50 m−2 and 2 kg m−2) in Antarctic coastal areas, in contrast to the offshore habitats where its ancestors had predominated since the Oligocene. Shell morphology and substrate data indicate that the Chlamys-like faunas were largely exposed to high-energy conditions associated with open water in the coastal zone, while the Adamussium faunas have been associated with low-energy hydrodynamic conditions. Modern and mid-Holocene distributions in the Antarctic coastal zone further indicate that Adamussium is largely restricted to protected embayments and habitats with extensive sea-ice coverage. In addition, a decadal mark-and-recapture experiment demonstrates that Adamussium has extremely slow growth and a century-scale lifespan, which complement the life-history traits that are considered to be characteristic of species inhabiting predictable and constant environments in the deep sea. Stabilization of the water column by increased sea-ice extent—together with stenothermal conditions, prolonged darkness and limited primary production—would have enhanced the habitat similarities between polar coastal environments and the deep-sea after the Plio-Pleistocene climate threshold. Subsequently, the deep Antarctic continental shelf would have facilitated faunal shifts between deep-sea and coastal habitats as with the polar emergence of the Adamussium fauna. Such biogeographic interchanges across high-latitude continental shelves since the end of the Cenozoic would have contributed significantly to the latitudinal diversity gradients that have been noted from both deep-sea and shallow-water marine faunas.

The combined use of high rate algal ponds (HRAPs) for wastewater treatment and commercial algal production is considered to be an economically viable option. However, microalgal photosynthesis and biomass productivity is constrained in HRAPs due to light limitation. This paper investigates how the light climate in the HRAP can be modified through changes in pond depth, hydraulic retention time (HRT) and light/dark turnover rate and how this impacts light absorption and utilisation by the microalgae. Wastewater treatment HRAPs were operated at three different pond depth and HRT during autumn. Light absorption by the microalgae was most affected by HRT, significantly decreasing with increasing HRT, due to increased internal self-shading. Photosynthetic performance (as defined by Pmax, Ek and α), significantly increased with increasing pond depth and decreasing HRT. Despite this, increasing pond depth and/or HRT, resulted in decreased pond light climate and overall integrated water column net oxygen production. However, increased light/dark turnover was able to compensate for this decrease, bringing the net oxygen production in line with shallower ponds operated at shorter HRT. On overcast days, modelled daily net photosynthesis significantly increased with increased light/dark turnover, however, on clear days such increased turnover did not enhance photosynthesis. This study has showed that light absorption and photosynthetic performance of wastewater microalgae can be modified through changes to pond depth, HRT and light/dark turnover.

With microalgal biofuels currently receiving much attention, there has been renewed interest in the combined use of high rate algal ponds (HRAP) for wastewater treatment and biofuel production. This combined use of HRAPs is considered to be an economically feasible option for biofuel production, however, increased microalgal productivity and nutrient removal together with reduced capital costs are needed before it can be commercially viable. Despite HRAPs being an established technology, microalgal photosynthesis and productivity is still limited in these ponds and is well below the theoretical maximum. This paper critically evaluates the parameters that limit microalgal light absorption and photosynthesis in wastewater HRAPs and examines biological, chemical and physical options for improving light absorption and utilisation, with the view of enhancing biomass production and nutrient removal.

Carbon limitation in domestic wastewater high rate algal ponds is thought to constrain microalgal photo-physiology and productivity, particularly in summer. This paper investigates the effects of CO₂ addition along a pH gradient on the performance of wastewater microalgae in high rate algal mesocosms. Performance was measured in terms of light absorption, electron transport rate, photosynthetic efficiency, biomass production and nutrient removal efficiency. Light absorption by the microalgae increased by up to 128% with increasing CO₂ supply, while a reduction in the package effect meant that there was less internal self-shading thereby increasing the efficiency of light absorption. CO₂ augmentation increased the maximum rate of both electron transport and photosynthesis by up to 256%. This led to increased biomass, with the highest yield occurring at the highest dissolved inorganic carbon/lowest pH combination tested (pH 6.5), with a doubling of chlorophyll-a (Chl-a) biomass while total microalgal biovolume increased by 660% in Micractinium bornhemiense and by 260% in Pediastrum boryanum dominated cultures. Increased microalgal biomass did not off-set the reduction in ammonia volatilisation in the control and overall nutrient removal was lower with CO₂ than without. Microalgal nutrient removal efficiency decreased as pH decreased and may have been related to decreased Chl-a per cell. This experiment demonstrated that CO₂ augmentation increased microalgal biomass in two distinct communities, however, care must be taken when interpreting results from standard biomass measurements with respect to CO₂ augmentation.

Patterns of environmental spatial structure lie at the heart of the most fundamental and familiar patterns of diversity on Earth. Antarctica contains some of the strongest environmental gradients on the planet and therefore provides an ideal study ground to test hypotheses on the relevance of environmental variability for biodiversity. To answer the pivotal question, “How does spatial variation in physical and biological environmental properties across the Antarctic drive biodiversity?” we have synthesized current knowledge on environmental variability across terrestrial, freshwater, and marine Antarctic biomes and related this to the observed biotic patterns. The most important physical driver of Antarctic terrestrial communities is the availability of liquid water, itself driven by solar irradiance intensity. Patterns of biota distribution are further strongly influenced by the historical development of any given location or region, and by geographical barriers. In freshwater ecosystems, free water is also crucial, with further important influences from salinity, nutrient availability, oxygenation, and characteristics of ice cover and extent. In the marine biome there does not appear to be one major driving force, with the exception of the oceanographic boundary of the Polar Front. At smaller spatial scales, ice cover, ice scour, and salinity gradients are clearly important determinants of diversity at habitat and community level. Stochastic and extreme events remain an important driving force in all environments, particularly in the context of local extinction and colonization or recolonization, as well as that of temporal environmental variability. Our synthesis demonstrates that the Antarctic continent and surrounding oceans provide an ideal study ground to develop new biogeographical models, including life history and physiological traits, and to address questions regarding biological responses to environmental variability and change.

We have investigated the ecological importance of N2-fixation in cyanobacterial mats, dominated by oscillatorean species, in ponds of the Bratina Island area of the McMurdo Ice Shelf, Antarctica (78 degrees S, 166 degrees E). Nitrogenase activity, estimated as acetylene reducing activity (ARA), was found in all the mats investigated (n = 16). The average ARA was 75.9 mmol ethylene m-2 h-1, ranging from 6 to 201 mmol ethylene m-2 h-1. Nitrogenase activity was positively correlated with dissolved reactive phosphorus concentration in pondwater and the C/N ratio of the mat, and was negatively correlated with pondwater NH4+-N concentrations and natural abundance of 15N in the mats. ARA was restricted to the upper, oxic layer of the mats. Experiments conducted to ascribe ARA to different groups of prokaryotes suggested that ARA was mainly conducted by heterocystous cyanobacteria, since no activity was found in the dark and the activity was inhibited by the photosystem II inhibitor DCMU (3-[3,4-dichlorophenyl]-1,1-dimethyl urea). In spite of 24 h of daylight, nitrogenase activity showed a diel cycle with maximum activity at midday (10-18 h) and minimal activity at early morning (6-10 h) when pond temperatures were at their minima. Light dependency of nitrogenase activity for three cyanobacterial communities showed that the irradiance required for saturating ARA was low, in every case lower than 100 mmol photon m-2s-1. Irradiance rarely fell below 100 mmol photon m-2s-1 during Antarctic summer days and ARA was likely to be light saturated for much of the time. We estimate that N2 fixation represented on average a N input into the ponds of over 1 g m-2y-1. This value appears to be the highest N input to this Antarctic ecosystem.

Eleven lakes in the South Island of New Zealand were sampled in summer 1996. Water column profiles of ultraviolet radiation (UVR) at four wavelengths and photosynthetically available radiation (PAR) were obtained, along with analyses of dissolved organic carbon (DOC) concentration, total suspended solids (TSS), and catchment vegetation, including forest and natural grassland. Downward attenuation coefficients (Kd) and lake water transparency (1/Kd) for UVR were examined in relation to these variables. Consistent with other regions of the world, DOC concentration and variables related to DOC were the best predictors of UVR penetration. With our data set, we calculated ratios of water column integrals (RI) of UVR/PAR irradiance, using equations from the literature. At DOC concentrations below 4 g m−3, a progressive increase in RI shows that lakes become increasingly transparent to UVR. We also normalized chromophoric dissolved organic matter (CDOM) absorption of UVR at 380 nm (a380) to DOC concentration and found that the UVR-absorbing capacity per unit DOC increases with increasing percentage of forest in the catchment area. This indicates that not only DOC concentration but also DOC type or composition is important in determining the transparency of lake water to UVR, and that qualitative differences in DOC are dictated by the type and amount of vegetation present in the lake's catchment area.

Bacteria adhering to newly emerged and decomposing leaves ofPotamogeton pectinatus L. were examined using scanning electron microscopy. Bacteria obtained from mature leaves were isolated, grown in pure culture, and allowed to infect bacteria-free leaves. Infected leaves and individual isolates were examined by scanning electron microscopy. The method provided detail of the forms of bacterial attachment to leaf surfaces. Supernatants from isolate cultures were assayed for cellulase activity. Six out of eight isolates produced extracellular cellulase in medium containing carboxymethyl cellulose. In one isolate cellulase was produced at discrete intervals, at the beginning and end of the growth cycle. The adhesion of the isolates toP. pectinatus leaves, as well as their possession of cellulase, are considered as evidence of an active role of bacteria in the degradation ofP. pectinatus foliage. The system is unusual in that bacteria, as opposed to fungi, are primary colonizers of the leaves.

The Ward Hunt Ice Shelf (83 degrees N, 74 degrees W) is the largest remaining section of thick (10 m) land-fast sea ice along the northern coastline of Ellesmere Island, Canada. Extensive meltwater lakes and streams occur on the surface of the ice and are colonized by photosynthetic microbial mat communities. This High Arctic cryo-ecosystem is similar in several of its physical, biological and geochemical features to the McMurdo Ice Shelf in Antarctica. The ice-mats in both polar regions are dominated by filamentous cyanobacteria but also contain diatoms, chlorophytes, flagellates, ciliates, nematodes, tardigrades and rotifers. The luxuriant Ward Hunt consortia also contain high concentrations (10(7)-10(8) cm-2) of viruses and heterotrophic bacteria. During periods of extensive ice cover, such as glaciations during the Proterozoic, cryotolerant mats of the type now found in these polar ice shelf ecosystems would have provided refugia for the survival, growth and evolution of a variety of organisms, including multicellular eukaryotes.

Data from 63 New Zealand lakes were analysed to determine latitudinal and other patterns in the relationship between water clarity and the maximum recorded depths for submerged aquatic macrophytes (Zc). Vascular plants were encountered at Zc in 25% of the 63 lakes investigated. Characean algae extended to greater depths and occurred at Zc in 71% of the lakes, with a maximum depth of 34.4 m. There was a difference between North and South Island lakes, in values of Zc predicted from water clarity, that was not consistent with their latitudinal displacement. In clear North Island lakes, Zc was predicted to be less than in lakes of similar water clarity in the South Island and to reach an asymptotic maximum depth of 21 m. In contrast, the relationship between water clarity and Zc in South Island lakes was linear, with Zc of more than 30 m in some lakes at c. 2% of subsurface irradiance. Although the availability of light explained depth limits in most South Island lakes, other factors (e.g., grazing ...

Environmental conditions, both external to and within three shallow ponds of the McMurdo Ice Shelf, were measured over an annual cycle between January 1997 and January 1998. We combined this with a study of the response of the benthic microbial mat communities to the transition from summer conditions to winter freezing. Over the study period air temperature was above 0°C for a few days during summer. At this time pond temperatures were higher than air temperatures, with evidence of thermo-haline stratification. The shallow areas of ponds froze between late February and early March, with bottom waters in the deepest pond remaining unfrozen until early June. Minimum winter air temperatures were below −40°C. There was little evidence of freezing point depression due to freeze-concentration of solutes, except at the very bottom of ponds. In the most conductive pond investigated, the temperature of basal freezing was −4°C and conductivity did not exceed approximately 60 mS cm−1 immediately prior to freezing. Microbial mats remained photosynthetically active up to conductivities between 40 and 80 mS cm−1, and were able to acclimate to lowered irradiance associated with ice formation. Although photosynthesis and respiration were reduced by 11% and 40% respectively at temperatures of −2°C compared to 1°C, there was no difference in light harvesting efficiency. Results from this study suggest that light limitation of photosynthesis, or freezing, determine the growth season for the microbial communities, depending on depth.

Lake Coleridge is a deep monomictic lake in the Southern Alps of New Zealand which is affected by strong adiabatic winds. It receives significant inputs of inorganic suspended solids from rivers diverted into the lake for hydro‐electric generation. External inputs of wind energy and suspended solids to Lake Coleridge were quantified throughout 1 year and their impacts on hydrodynamics and the light climate were analysed. During stratification, the lake had a deep mixed layer, underlain by a complex metalimnion. High wind energy inputs caused large internal waves which resulted in the upwelling of hypolimnetic water, horizontal density gradients, and significant currents. Calculated vertical diffusivity and exchange coefficients were similar to those of much larger lakes. Analyses indicated that mixing in the metalimnion was often a result of shear stresses arising from vertical gradients in horizontal velocities. Whole lake total suspended solids (TSS) burdens were significantly correlated with t...

The migratory patterns of an Oscrllatoria sp. in a hypersaline microbial mat on Antarctica's McMurdo Ice Shelf, 78OS, 166" E, were examined under the natural solar irradiance of austral summer. Upward and downward migration was monitored in response to different intensities of full solar irradiance and of selected wavelengths achieved using a series of filter and screening treatments. ["C] photoincorporation rates, using freshly collected cell material, were also measured under different intensities and spectral regions of solar irradiance, as well as at several temperatures of incubation. Our objectives were two-fold: (1) to determine whether this cyanobacterium displays a pattern of migration, photosynthesis, and photoinhibition in response to solar UV and visible irradiance similar to that displayed by motile cyanobacteria in hypersaline ponds of middle latitudes (-28"N), and (2) to examine the impact of temperature on these activities. Oscillatoria sp. migrated completely to the surface under low visible irradiance ( 60 W n1r2, and blue light, which included 0.94 W m-' UV-A, caused complete downward migration. Photosynthetic saturation occurred at low visible light levels (-26 W m-'), and both photoand UV-inhibition was apparent. Photosynthetic rates increased in the order 2

Depth profiles of solar ultraviolet radiation (UVR), photosynthetically available radiation (PAR), and related variables were measured beneath the thick, permanent ice cover of four lakes in the McMurdo Dry Valleys (77°S, 162°E). These lakes span a range of phytoplankton concentrations (0.1-10 μg Chl a liter ') but receive little input of chromophoric dissolved organic matter (CDOM) from their barren, polar desert catchments. The diffuse attenuation coefficients for downwelling radiation (K d ) in the upper water column of the lakes were at or below those for clear natural waters elsewhere, with minimum values in Lake Vanda of 0.080 (305 nm), 0.055 (320 nm), 0.036 (340 nm), 0.023 (380 nm) and 0.034 (PAR) m -1 . The attenuation lengths (1/K d ) for these lakes and for a set of high latitude lakes in the northern hemisphere (tundra and boreal forest catchments) showed a close log-log relationship with dissolved organic carbon (DOC) concentrations (r 2 ≥ 0.90; n = 20); dry valley lakes were at the high transparency end of this polar-subpolar continuum. Phytoplankton exposure to UVR relative to PAR is known to rise steeply with decreasing DOC in the concentration range 2-4 g m -3 ; the addition of the dry valley lakes data shows the continuation of this upward, markedly nonlinear trend at lower DOC concentrations. Calculation of the biologically effective UVR dosage rate for the upper phytoplankton community of Lake Vanda indicated that sufficient UVR penetrates through the 3.5-m-thick lake ice to cause inhibition of algal growth. These results show that polar desert lakes are optical extremes in terms of their water-column transparency to UVR, and that their dilute, mostly autochthonous CDOM offers little protection against the ultraviolet-B radiation flux that is continuing to increase over the polar regions.