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Microcystin (MC) -producing and non-MC-producing Microcystisstrains typically coexist in Microcystis-dominated blooms. However, the interaction between submerged plants and Microcystis at strain level is not clear. This study aimed to assess the effects of a submerged macrophyte Myriophyllum spicatum on one MC-producing versus one non- MC-producing strains of the cyanobacterium Microcystis using plant-Microcystis co-culture experiments. The impacts of Microcystis on M. spicatum were also examined. It showed that the MC-producing Microcystis strain had a higher resistance to negative impacts by the cocultured submerged plant M. spicatum than the non-MC-producing strain. By contrast, the plant M. spicatum was impacted more by the MC-producing Microcystis than the non-MC-producer. The associated bacterioplankton community was affected more by the MC-producing Microcystis than the cocultured M. spicatum. The MC cell quotas were significantly higher in the coculture treatment (the PM+ treatment, p < 0.05), indicating that the production and release of MCs might be a key factor responsible for the reduced impact of M. spicatum. The higher concentrations of dissolved organic and reducing inorganic compounds might eventually exacerbate the recovering capacity of co-existing submerged plants. Overall, this study indicated that the capacity to produce MCs, as well as the density of Microcystis should be taken into account when attempting to re-establish submerged vegetation to undertake remediation works.

Around 36,000 km3 of freshwater flows through rivers and estuarine ecosystems and enter the world’s coastal fishing regions every year. The flow of freshwater and sediments creates regional changes in coastal circulation, stimulates marine productivity and helps define the hydrologic properties of estuarine and oceanic waters. These processes can affect different life stages of marine species either directly, through variations in salinity and temperature, or indirectly, due to changes in the availability of food and habitat. This paper reviews the relationship between freshwater flowing through estuarine and coastal ecosystems, and the variable productivity associated with global marine capture fisheries. The results of a global synthesis revealed that 72% of species representing 77% of the total catch (43 million tonnes) were linked to river flows for at least some part of their life cycle. Insights into how the relationship between flow and fishery production varies globally indicates wild capture fisheries and freshwater resources would benefit from an integrated planning and management approach.

The nuisance raphidophyte Gonyostomum semen (Ehrenberg) Diesing blooms in lakes and is known to produce a mucilage which can cause human skin irritation. Parameters such as water temperature, iron and high dissolved organic matter loads are shown to be important drivers in temperate regions. However, the causes of blooms in warmer latitudes are less well understood. Over a 6 mo study period, we used field monitoring and a nutrient addition experiment within a water reservoir to examine the role of nutrients in promoting G. semen growth. Early in the study, an inflow event delivered nutrients which increased dissolved inorganic nitrogen (DIN) concentrations 2-fold and filterable reactive phosphorus (FRP = phosphate) 4-fold. This event shifted the phytoplankton community from a mixed community to one dominated by G. semen. Two months after the inflow event, the effect of nutrients in promoting G. semen was confirmed with a nutrient addition experiment. Total biovolumes of this species across the study were strongly predicted by FRP and nitrate + nitrite concentrations. G. semen biovolumes also decreased as ratios of total nitrogen (TN):total phosphorus (TP) and DIN:FRP increased, highlighting the importance of P inputs. The stable isotope tracer 15N-nitrate was also used to trace N through the G. semen-dominated phytoplankton community. The tracer rapidly cycled through the G. semen-dominated phytoplankton community in 1-2 d, settled and remineralized, providing an ongoing source of DIN for maintaining blooms. Overall, the results highlight the importance of FRP, and to a lesser extent nitrate, in promoting blooms of this nuisance species.

Benthic diatoms are often included in bioassessment programs of river health as sensitive indicators of nutrient status and pollution. Many diatom‐based indices have been developed and are frequently used to infer conditions in water quality. However, concerns have been raised regarding the robustness of these indices in riverine systems that have natural variability in environmental conditions, including seasonal change of water quality parameters, especially in terms of physical and chemical characteristics of water, which also influence diatom community composition. Here, we used three diatom‐based indices (Diatom‐based eutrophication/pollution index, EPI‐D; Biological Diatom Index, IBD; Watanabe's Index, WAT), which have previously been validated as robust for water quality assessment in China, to explore their response to temporal changes in water quality and diatom community structure in a riverine network over time. Concentrations of total nitrogen (TN), nitrate nitrogen (NO3‐N), total phosphorus (TP), temperature (t), and turbidity in April 2010 were significantly higher than in November 2007. The 141 diatom taxa we found in April 2010 were fewer than the 194 taxa we found in November 2007. On both occasions, the three diatom indices responded to same water quality variables (phosphorus and chloride or nitrogen) as reported in previous studies. Of the three diatom indices tested, EPI‐D provided the most robust measure of natural seasonal changes in water quality and indicated the phosphorus and chloride. Our study confirms that these three diatom indices are effective for evaluating long‐term water quality in large rivers.

Floods are extreme weather events that can rapidly change water quality in receiving estuaries. The delivery of nutrients to the coastal zone via floods may stimulate productivity; however, in urban areas, the degradation of water quality and influx of contaminants can negatively affect inhabiting biota. Determining flood effects on inhabiting biota is important for informing catchment management practices. We investigated the body condition response of a commercially important prawn species, the brown tiger prawn Penaeus esculentus, to a large cyclone-driven flood in an urbanized subtropical coastal bay. Prawns were caught 10 days before the flood, 11 days after the flood, and 53 days after the flood in bare substrate areas of central Moreton Bay in Australia. Stable isotopes (δ15N and δ13C) were determined for prawn muscle tissue, and lipid content and a length-weight (Fulton’s K) index were used to assess prawn body condition. There were two distinct isotope signatures of tiger prawns living in either riverine or marine influenced areas, suggesting different residency areas within the bay. A flood signal (lower δ13C values post-flood) was detected in prawns in the southern area closest to the Logan River. Condition indices showed a short-term increase in condition of prawns in these southern sites, with no apparent condition change in prawns at other sites. A concurrent pulse in benthic primary productivity (chlorophyll a biomass) was measured in this southern area. Our results suggest that nutrients from the flood stimulated benthic primary production that was transferred through the food web, with positive impacts on prawn nutrition at southern sites. With an expected increase in unpredictable weather, including floods, under a changing climate, understanding short- and long-term ecosystem responses in modified catchments is important for mitigating sediment erosion and estuarine and coastal infilling effects, while maintaining productivity benefits to fisheries in receiving estuaries.

One goal of revegetating riparian zones is to mitigate nutrient movement into waterways, however release of dissolved nutrients and organic compounds from decaying leaf litter during rainfall may partially offset these benefits. We aim to understand how litter-derived nutrients and organics affect nutrient leaching from riparian soil, and how tree species affect these processes. In the laboratory we simulated large rainfall events through the leaf litter of two riparian woody tree species, Eucalyptus tereticornis and Casuarina cunninghamiana, with and without subsequent leaching through soil, as well as soil alone. We compared the forms and loads of nitrogen and phosphorus in leachate. Litter of both tree species stimulated additional nitrate release from soil (~100–200%) compared to bare soil. More ammonium and dissolved organic nitrogen also leached from soil with E. tereticornis litter, whereas less leached with C. cunninghamiana litter. More phosphate leached from soil with either species litter compared to bare soil. Increased nitrogen releases from soil with litter were greater than inputs from litter, suggesting they are driven by positive priming of soil microbial processes, whereas litter inputs increased phosphorus leaching. This information could be combined with rates of other riparian nutrient processes (e.g. plant uptake and denitrification) to quantify the net impact of trees on nutrient retention in riparian zones.

Plant-derived allelochemicals have the potential to be used as eco-friendly measures for control of Microcystis aeruginosa blooms. However, the susceptibility of M. aeruginosa to plant allelochemicals under a range of environmental factors, such as alkalinity, is not clear. This study investigated the effects of different alkalinity treatments on 1,2,3-trihydroxybenzene (pyrogallol) toxicity to a toxic strain of the cyanobacterium, M. aeruginosa (FACHB 905). Pyrogallol toxicity to M. aeruginosa cultures, both pre-adapted to a range of alkalinity levels and un-adapted, increased when alkalinity was increased from 0.09 to 1.51 meq L−1. The mean inhibition ratios calculated according to OD650, cell concentration, Chl a, and carotenoid concentrations of M. aeruginosa cultures were highest in the highest alkalinity treatment (1.51 meq L−1), i.e., up to 74%, 80%, 73%, and 87% for alkalinity-adapted cells on day 3. The lowest cell concentrations and photosynthesis pigment concentrations were found in the highest alkalinity treatment (1.51 meq L−1) for un-adapted cells in 12-day bioassays. This trend was more obvious over time. Pyrogallol and TPC (total phenolic compounds) concentrations measured immediately after pyrogallol addition into the culture medium decreased more rapidly in higher alkalinity treatments. In contrast, faster oxygen consumption and higher production of quinone end products occurred within the first 30 min after pyrogallol addition at higher alkalinity levels. Quinones and oxygen radicals have been shown previously to be more toxic to cyanobacteria than pyrogallol itself. This provides a potential explanation for the enhanced pyrogallol toxicity to M. aeruginosa under higher alkalinity. Therefore, it is important to take alkalinity into account when considering pyrogallol as a potential biocide.

Cyanobacteria species are sensitive to many plant allelochemicals, such as pyrogallol. However, little attention has been paid to the relative effects of these xenobiotics on co-occurring toxigenic and non-toxigenic cyanobacterial strains, despite their co-existence in blooms. Hence, the responses of one toxigenic (TS2) and two non-toxigenic (NS1, NS2) Microcystis aeruginosa strains to pyrogallol were tested under three conditions: mono-culture and co-cultured either directly or separately by dialysis membrane. The study showed that the inhibitory effects of pyrogallol on the growth and photosynthetic yield (Fv/Fm) of either toxigenic or non-toxigenic M. aeruginosa strains were lower in direct and dialysis co-culture conditions than those in mono-culture conditions. This result indicated that chemical-mediated reciprocal effects occur between the co-existing toxigenic and non-toxigenic strains. The toxigenic M. aeruginosa strain was more sensitive to pyrogallol than the non-toxigenic strains in both mono- and co-culture systems, though whether this outcome is due to the former's toxigenic status is unclear. Intracellular microcystin-LR (MC-LR) concentrations of the toxigenic strain decreased after pyrogallol addition in both mono- and co-culture systems, whereas extracellular MC-LR concentrations increased. This finding may reflect the cell damage of M. aeruginosa because of the pyrogallol. At the same initial number of cells, the extracellular MC-LR concentration released from the same amount of TS2 cells in mono-culture was slightly higher than that in dialysis co-culture conditions. Overall, this study shows that plant allelochemicals may have the potential to reduce bloom toxicity by reducing the proportion of toxigenic cyanobacterial strains, and the effects of co-existing strains must be considered when assessing the effects of plant allelochemicals on target strains.

David Schindler and his colleagues pioneered studies in the 1970s on the role of phosphorus in stimulating cyanobacterial blooms in North American lakes. Our understanding of the nuances of phosphorus utilization by cyanobacteria has evolved since that time. We review the phosphorus utilization strategies used by cyanobacteria, such as use of organic forms, alternation between passive and active uptake, and luxury storage. While many aspects of physiological responses to phosphorus of cyanobacteria have been measured, our understanding of the critical processes that drive species diversity, adaptation and competition remains limited. We identify persistent critical knowledge gaps, particularly on the adaptation of cyanobacteria to low nutrient concentrations. We propose that traditional discipline-specific studies be adapted and expanded to encompass innovative new methodologies and take advantage of interdisciplinary opportunities among physiologists, molecular biologists, and modellers, to advance our understanding and prediction of toxic cyanobacteria, and ultimately to mitigate the occurrence of blooms.

Trace element accumulation pathways are important in many ecological and toxicological studies on aquatic organisms, yet these pathways are often poorly understood. To study the influence of diet and environment on the trace element composition of species within estuarine food webs, we performed a community level assessment of 28 trace elements (including major and minor elements) in common fish and prawn taxa across four estuaries, and in fish, prawn, and other invertebrate taxa within a single estuary. Despite sediment substrates from the four estuaries having distinctly different geochemical compositions, food web samples showed no separation by estuary, but clear separation by taxa. Grouping of taxa by trace elements was related to feeding ecology, with pelagic taxa separated from benthic taxa, and mixed feeding by generalist taxa. Arsenic and selenium were more concentrated in benthic fish, while aluminium, barium, copper, iron, manganese, vanadium, and zinc were more concentrated in pelagic fish. Trophic level did not appear to influence trace element composition. Previous laboratory studies have shown that food sources influence trace element concentrations in marine taxa and this study confirms that this also occurs in natural food webs. These results improve our understanding of the dominant importance of diet and physiology in controlling the trace element composition of species within estuarine food webs.

RATIONALE The coupled analysis of δ13 C and δ15 N stable isotope values of blubber and skin biopsy samples is widely used to study the diet of free-ranging cetaceans. Differences in the lipid content of these tissues can affect isotopic variability because lipids are depleted in 13 C, reducing the bulk tissue 13 C/12 C. This variability in carbon isotope values can be accounted for either by chemically extracting lipids from the tissue or by using mathematical lipid normalisation models. METHODS This study examines (a) the effects of chemical lipid extraction on δ13 C and δ15 N values in blubber and skin of southern hemisphere humpback whales, (b) whether chemical lipid extraction is more favourable than mathematical lipid correction and (c) which of the two tissues is more appropriate for dietary studies. Strategic comparisons were made between chemical lipid extraction and mathematical lipid correction and between blubber and skin tissue δ13 C and δ15 N values, as well as C:N ratios. Six existing mathematical normalisation models were tested for their efficacy in estimating lipid-free δ13 C for skin. RESULTS Both δ13 C and δ15 N values of lipid-extracted skin (δ13 C: -25.57‰, δ15 N: 6.83‰) were significantly higher than those of bulk skin (δ13 C: -26.97‰, δ15 N: 6.15‰). Five of the six tested lipid normalisation models had small error terms for predicting lipid-free δ13 C values. The average C:N ratio of lipid-extracted skin was within the lipid-free range reported in other studies, whereas the average C:N ratio of blubber was higher than previously reported. CONCLUSIONS These results highlight the need to account for lipids when analysing δ13 C and δ15 N values from the same sample. For optimised dietary assessments using parallel isotope analysis from a single sample, we recommend the use of unextracted skin tissue. δ15 N values should be obtained from unextracted skin, whereas δ13 C values may be adequately lipid corrected by a mathematical correction.

Bacteria play key roles in the function and diversity of aquatic systems, but aside from study of specific bloom systems, little is known about the diversity or biogeography of bacteria associated with harmful cyanobacterial blooms (cyanoHABs). CyanoHAB species are known to shape bacterial community composition and to rely on functions provided by the associated bacteria, leading to the hypothesized cyanoHAB interactome, a coevolved community of synergistic and interacting bacteria species, each necessary for the success of the others. Here, we surveyed the microbiome associated with Microcystis aeruginosa during blooms in 12 lakes spanning four continents as an initial test of the hypothesized Microcystis interactome. We predicted that microbiome composition and functional potential would be similar across blooms globally. Our results, as revealed by 16S rRNA sequence similarity, indicate that M. aeruginosa is cosmopolitan in lakes across a 280 degrees longitudinal and 90 degrees latitudinal gradient. The microbiome communities were represented by a wide range of operational taxonomic units and relative abundances. Highly abundant taxa were more related and shared across most sites and did not vary with geographic distance, thus, like Microcystis, revealing no evidence for dispersal limitation. High phylogenetic relatedness, both within and across lakes, indicates that microbiome bacteria with similar functional potential were associated with all blooms. While Microcystis and the microbiome bacteria shared many genes, whole-community metagenomic analysis revealed a suite of biochemical pathways that could be considered complementary. Our results demonstrate a high degree of similarity across global Microcystis blooms, thereby providing initial support for the hypothesized Microcystis interactome.

Modification of freshwater flow regimes can impact estuarine ecosystems at the receiving end of these flows. This is particularly true in tropical areas, such as the wet-dry tropics, where major freshwater flows in the wet season may result in prolonged and large-scale flooding, followed by periods of little or no flow during an extended dry season. Estuarine species, such as the commercially important prawn Penaeus merguiensis, have lifecycles adapted to seasonal flows. The potential effects of flow regulation on estimated catches of P. merguiensis were explored using a Bayesian belief network (BBN) model. Probability statements were generated about the ecological implications of different magnitudes of natural flow, as well as three water-extraction scenarios: 1) reduced flow in the wet season; 2) the introduction of flow in the dry season; and 3) the combination of scenario one and two. Thresholds of freshwater flow that affect the likelihood of high prawn catches in the fishery were identified, and the cumulative effects explored. This is the first time that these thresholds have been identified and the model suggests there is little capacity to regulate or modify the freshwater flow without reducing the probability of high prawn catches.

Phosphorus (P) is a key driver of phytoplankton growth in lentic systems. During summer-stratified periods when dissolved inorganic P (DIP) is low, the phytoplankton assemblage often has elevated P uptake rates. Under these conditions, dissolved organic P (DOP) can become an important source of P for phytoplankton and a driver of phytoplankton succession. We examined how DOP mineralisation by alkaline phosphatase (AP) activity (APA), relative to phytoplankton P release (i.e., from exudation and lysis), meets phytoplankton P uptake and how it is associated with phytoplankton community composition changes under thermally stratified DIP-depauperate conditions in a large warm-monomictic lake. We found that when phytoplankton internal P stores were low (

Sediment denitrification plays an important role in nitrogen removal in aquatic systems. However, the importance in nitrogen removal in reservoirs, with a focus on seasonal differences of conditions such as macrophyte beds and environmental factors, is less well understood. This study examined sediment denitrification rate (D

Engineering solutions that aim to restore hydrological connectivity in river systems fragmented by dams and weirs frequently include the installation of fish passage facilities (i.e. fishways). Assessment of fish passage performance is often limited to single fishway designs and with a focus on species of commercial or conservation significance, meaning that conclusions regarding fishway success may not apply to all species that require access to fragmented habitats. We simultaneously compared the population structure and fish assemblage composition at two fishways (vertical slot and fish lock designs) at weirs in a subtropical coastal river system. We used hydrological and physico-chemical water quality data to explore if fishway performance was linked to particular environmental conditions. At both fishways, fish assemblage composition differed between fishway exit and downstream river samples, yet differences between exit and river samples were not associated with hydrological variables related to the size and frequency of weir drown-out events or water quality. Population structure of the most abundant species (sea mullet, Mugil cephalus; 61% of fish samples) also differed significantly among fishway exit and river habitats. A low-level structure spanning the river channel downstream of one weir was not associated with differences in fish assemblage composition indicating that access to the fishway entrance (and therefore fishway use) was not hindered by in-stream obstructions. Eight and seven species (predominantly small-bodied species that migrate within freshwater systems) were exclusively sampled in downstream river locations at the vertical slot and fish lock fishways, respectively, indicating that neither design was fully capable of facilitating the passage of the local fish fauna. Further assessment over a broader range of hydrological conditions will be necessary to determine if use of either fishway by fish is affected by low flows. Coupled with evidence produced from landscape-scale analysis of spatial and temporal variation in fish assemblage structure and dispersal patterns of diadromous species associated with river flow regime highlight that hydrological connectivity may be maintained by natural weir drown-out events. This study highlights that factors controlling hydrological connectivity for riverine biota need to be integrated among co-occurring anthropogenic impacts to identify and overcome constraints to effective conservation management in rivers subject to water resource development.

The coupled analysis of δThis study examines (a) the effects of chemical lipid extraction on δBoth δThese results highlight the need to account for lipids when analysing δ

Global warming and eutrophication contribute to the worldwide increase in cyanobacterial blooms, and the level of cyanobacterial biomass is strongly associated with rises in methane emissions from surface lake waters. Hence, methane-metabolizing microorganisms may be important for modulating carbon flow in cyanobacterial blooms. Here, we surveyed methanogenic and methanotrophic communities associated with floating Microcystis aggregates in 10 lakes spanning four continents, through sequencing of 16S rRNA and functional marker genes. Methanogenic archaea (mainly Methanoregula and Methanosaeta) were detectable in 5 of the 10 lakes and constituted the majority (~50%-90%) of the archaeal community in these lakes. Three of the 10 lakes contained relatively more abundant methanotrophs than the other seven lakes, with the methanotrophic genera Methyloparacoccus, Crenothrix, and an uncultured species related to Methylobacter dominating and nearly exclusively found in each of those three lakes. These three are among the five lakes in which methanogens were observed. Operational taxonomic unit (OTU) richness and abundance of methanotrophs were strongly positively correlated with those of methanogens, suggesting that their activities may be coupled. These Microcystis-aggregate-associated methanotrophs may be responsible for a hitherto overlooked sink for methane in surface freshwaters, and their co-occurrence with methanogens sheds light on the methane cycle in cyanobacterial aggregates.

Excess nitrogen (N) is one of the most widespread and serious pollutants in the environment, but wetlands can reduce N loads, ameliorating its damaging effects downstream. Tropical wetlands are highly productive and experience high temperatures year-round, resulting in potentially high denitrification rates. However, few measurements of denitrification have been reported for tropical wetlands. In this study, we measured denitrification within stands of macrophytes at the edge of a tropical lake (900 m length, 4 m deep) in Australia. We compared denitrification rates among sediments under emergent grass (giant bulrush, Actinoscirpus grossus), sediments under floating waterlilies (Nymphae spp.), and sediments from the deeper sections of the lagoon with no macrophytes. We also measured the denitrification and primary productivity of the epiphyton on macrophytes and compared the rates with those from the sediment. Denitrification in the sediment was higher (Dt = 3.3���52 mg m���2 h���1) than denitrification of the epiphyton (Dt = 1.9���3.6 mg m���2 h���1) and was mostly coupled with nitrification (Dn). Denitrification was highest in sediments rich in organic carbon (32.3%) and N (1.4%), and during times of the year when nitrates (NOx���-N = NO2���-N + NO3���-N) concentrations were relatively high (>0.10 mg L���1). Denitrification was lowest in sediments with no macrophytes, which comprised most of the lake area. Denitrification rates of sediments under these macrophyte stands were among the highest values measured for natural wetlands and highlight the potential role of this process in ameliorating N pollution in tropical catchments.

Cyanobacteria harmful blooms can represent a major risk for public health due to potential release of toxins and other noxious compounds in the water. A continuous and high-resolution monitoring of the cyanobacteria population is required due to their rapid dynamics, which has been increasingly done using in-situ fluorescence of phycocyanin (f-PC) and chlorophyll a (f-Chl a). Appropriate in-situ fluorometers calibration is essential because f-PC and f-Chl a are affected by biotic and abiotic factors, including species composition. Measurement of f-PC and f-Chl a in mixed species assemblages during different growth phases - representative of most field conditions - has received little attention. We hypothesized that f-PC and f-Chl a of mixed assemblages of cyanobacteria may be accurately estimated if taxa composition and fluorescence characteristics are known. We also hypothesized that species with different morphologies would have different fluorescence per unit cell and biomass. We tested these hypotheses in a controlled culture experiment in which photosynthetic pigment fluorescence, chemical pigment extraction, optical density and microscopic enumeration of four common cyanobacteria species (Aphanocapsa sp, Microcystis aeruginosa, Dolichospermum circinale and Raphidiopsis raciborskii) were quantified. Both monocultures and mixed cultures were monitored from exponential to late stationary growth phases. The sum of fluorescence of individual species calculated for mixed samples was not significantly different than measured fluorescence of mixed cultures. Estimated and measured f-PC and f-Chl a of mixed cultures had higher correlations and smaller absolute median errors when estimations were based on fluorescence per biomass instead of fluorescence per cell. Largest errors were overestimations of measured fluorescence for species with different morphologies. Fluorescence per cell was significantly different among most species, while fluorescence per unit biomass was not, indicating that conversion of fluorescence to biomass reduces species-specific bias. This study presents new information on the effect of species composition on cyanobacteria fluorescence. Best practices of deployment and operation of fluorometers, and data-driven models supporting in-situ fluorometers calibration are discussed as suitable solutions to minimize taxa-specific bias in fluorescence estimates.

Restoring woody vegetation to riparian zones helps to protect waterways from excessive sediment and nutrient inputs. However, the associated leaf litter can be a major source of dissolved organic matter (DOM) leached into surface waters. DOM can lead to the formation of disinfection by-products (DBPs) during drinking water treatment. This study investigated the DBPs formed during chlorination of DOM leached from leaf litter and assessed the potential toxicity of DBPs generated. We compared the leachate of two native Australian riparian trees, Casuarina cunninghamiana and Eucalyptus tereticornis, and a reservoir water source from a catchment dominated by Eucalyptus species. Leachates were diluted to dissolved organic carbon concentrations equivalent to the reservoir (~9 mg L-1). E. tereticornis leachates produced more trihalomethanes (THMs), haloacetic acids (HAAs), and haloketones after chlorination, while C. cunninghamiana produced more chloral hydrate and haloacetonitriles. Leachate from both species produced less THMs and more HAAs per mole of carbon than reservoir water. This may be because reservoir water had more aromatic, humic characteristics while leaf leachates had relatively more protein-like components. Using in vitro bioassays to test the mixture effects of all chemicals, chlorinated E. tereticornis leachate induced oxidative stress in HepG2 liver cells and bacterial toxicity more frequently and at lower concentrations than C. cunninghamiana and reservoir water. Overall, this study has shown that the DOM leached from litter of these species has the potential to generate DBPs and each species has a unique DBP profile with differing bioassay responses. E. tereticornis may pose a relatively greater risk to drinking water than C. cunninghamiana as it showed greater toxicity in bioassays. This implies tree species should be considered when planning riparian zones to ensure the benefits of vegetation to waterways are not offset by unintended increased DBP production and associated toxicity following chlorination at downstream drinking water intakes.

Many tropical river systems have altered water quality due to human land use, impacting the biodiversity of freshwater and coastal ecosystems. Long-term, catchment-scale monitoring is needed to understand pollutant sources, controls, and trends. This 12-year study monitored baseflow and flood event nutrient and sediment concentrations, and estimated sediment loads across the Normanby Basin in northern Australia. Suspended sediment concentrations and yields were highest in upper catchment areas where cattle grazing occurred on erosion-prone sodic soils. Mid- and lower catchment rivers and floodplains were a sink for sediments and nutrients, trapping around 75% of suspended sediments during events. Clays (

The growing demand for freshwater resources has led to dam construction and water diversions in a majority of the world's large rivers. With an increasing demand for freshwater, trade‐offs between water allocations and the preservation of ecological connections between terrestrial and marine ecosystems are inevitable. The ecological links formed by rivers flowing into the ocean benefit many commercially fished species. The degree to which different species and the livelihoods of fishers are negatively impacted by changes in river flows due to water extraction or diversion is important for management across terrestrial and marine boundaries. Our objective was to predict how changes in freshwater flows from three wet–dry tropical rivers in northern Australia, that is, the Mitchell, Gilbert, and Flinders rivers, affect the commercial banana prawn (Penaeus merguiensis) catch. We used a novel spatiotemporal Bayesian approach to model the effects of river flows and key climate drivers on banana prawn catch. We then predicted how the loss of flow due to water extraction or diversion affected prawn catch. Our analyses of three water development scenarios found that catch was most impacted by water extraction during low flows. The impact of water extraction was greatest for a scenario with dams on the Mitchell River, where we predicted catch would decline by 53% during a year with low flow. Overall, our results imply that maintenance of low‐level flows is a crucial requirement for sustained fishery yields. We suggest that water managers must balance agricultural demand for water during drier years against the impact of water extraction on prawn fisheries during low‐flow years. Protecting low‐level flows during drier years is a priority for maintaining terrestrial–marine linkages for adjacent marine fisheries.

Several cyanobacteria, including diazotrophic Raphidiopsis raciborskii, can form harmful blooms when dissolved inorganic phosphorus concentrations are very low. We hypothesized that R. raciborskii strains would vary in phosphorus (P) allocations to cell growth and storage, providing resilience of populations to continuously low or variable P supplies. We tested this hypothesis using six toxic strains (producing cylindrospermopsins) isolated from a field population using batch monocultures with and without P and dissolved inorganic nitrogen (DIN). Treatments replete with DIN, irrespective of P addition, had similar exponential growth rates for individual strains. P storage capacity varied 4-fold among strains and was significantly higher in DIN-free treatments than in replete treatments. P was stored by all R. raciborskii strains, in preference to allocation to increase growth rates. P stores decreased with increased growth rate across strains, but weeere not related to the time to P starvation in P-free treatments. The storage capacity of R. raciborskii, combined with strategies to efficiently uptake P, means that P controls may not control R. raciborskii populations in the short term. Intra-population strain variation in P storage capacity will need to be reflected in process-based models to predict blooms of R. raciborskii and other cyanobacteria adapted to low-P conditions.

Aquatic ecosystems are used for extensive rice-shrimp culture where the available water alternates seasonally between fresh and saline. Poor water quality has been implicated as a risk factor for shrimp survival; however, links between shrimp, water quality and their main food source, the natural aquatic biota inhabiting these ponds, are less well understood. We examined the aquatic biota and water quality of three ponds over an entire year in the Mekong Delta, Vietnam, where the growing season for the marine shrimp Penaeus monodon has been extended into the wet season, when waters freshen. The survival (30–41%) and total areal biomass (350–531 kg ha−1) of shrimp was constrained by poor water quality, with water temperatures, salinity and dissolved oxygen concentrations falling outside known optimal ranges for several weeks. Declines in dissolved oxygen concentration were matched by declines in both shrimp growth rates and lipid content, the latter being indicative of nutritional condition. Furthermore, as the dry season transitioned into the wet, shifts in the taxonomic composition of phytoplankton and zooplankton were accompanied by declines in the biomass of benthic algae, an important basal food source in these systems. Densities of the benthic invertebrates directly consumed by shrimp also varied substantially throughout the year. Overall, our findings suggest that the survival, condition and growth of shrimp in extensive rice-shrimp ecosystems will be constrained when poor water quality and alternating high and low salinity negatively affect the physiology, growth and composition of the natural aquatic biota. Changes in management practices, such as restricting shrimp inhabiting ponds to the dry season, may help to address these issues and improve the sustainable productivity and overall condition of these important aquatic ecosystems.

Terrestrial particulate nutrients transported during flood events are known to indirectly fuel phytoplankton blooms in rivers, lakes and coastal waters, although the mechanisms are poorly understood. Quantifying the response of phytoplankton to nutrients in sediments eroded from catchments is fundamental to prioritizing areas for erosion control. This study developed a novel bioassay technique for rapidly assessing the effects of nutrients released from suspended sediments on the growth of marine and freshwater phytoplankton communities. A range of sediment slurries were placed in bioassay bottles within dialysis tubing in the presence of phytoplankton and their photosynthetic efficiency (Fv/Fm) was measured over 72 h. This allowed an assessment of the effects of dissolved nutrients released from sediments without the confounding effects of suspended sediments. Chlorophyll a concentrations were also measured for comparison with Fv/Fm. Our study showed Fv/Fm was an effective method for measuring phytoplankton responses to sediment slurries. Photosynthetic efficiency was a more sensitive response metric than chlorophyll a. Applying the method to a range of suspended sediments from two tropical catchments in Australia that drain into Great Barrier Reef coastal waters, we identified a subset of sediment types (~40%) that increased Fv/Fm under the bioassay conditions. These sediments have the potential to stimulate marine and freshwater phytoplankton growth under the loads simulated in this study. The bioassay has the advantage of being a rapid and relatively simple method where a large number of sediments can be simultaneously tested for a phytoplankton response. To our knowledge this is the first time Fv/Fm has been used to assess phytoplankton responses to sediments in a bioassay. This approach advances the use of Fv/Fm as a sensitive indicator of phytoplankton responses to nutrients and could be used to develop indices of the relative risk various sediments pose, hence support decision making for erosion control measures.

Sediments delivered to freshwater and marine environments can make important contributions to the aquatic bioavailable nutrient pool. In the Great Barrier Reef (GBR) catchments, particulate nutrients comprise an important fraction of the end of catchment loads; however, their contribution to the bioavailable nutrient pool is not well understood. This research determined which particulate nutrient parameters are the best indicators of the potential effect of fine sediment (

The harmful cyanobacterium Cylindrospermopsis raciborskii is a widespread species increasingly being recorded in freshwater systems around the world. Studies have demonstrated some key attributes of this species which may explain its global dominance. It has a high level of flexibility with respect to light and nutrients, being capable of growth under low and variable light conditions. However, it is the strategy with respect to nutrient utilization that has received more attention. Unlike many bloom forming species, the dominance of this species is not simply linked to higher nutrient loads. In fact it appears that it is more competitive when phosphorus and nitrogen availability is low and/or variable. An important component of this flexibility appears to be the result of within-population strain variability in responses to nutrients, as well as key physiological adaptations. Strain variability also appears to have an effect on the population-level cell quota of toxins, specifically cylindrospermopsins (CYNs). Field studies in Australia showed that populations had the highest proportion of toxic strains when dissolved inorganic phosphorus was added, resulting in stoichiometrically balanced nitrogen and phosphorus within the cells. These strategies are part of an arsenal of responses to environmental conditions, making it a challenging species to manage. However, our ability to improve bloom prediction will rely on a more detailed understanding of the complex physiology and ecology of this species.

Cyanobacteria are oxygenic photosynthetic Gram-negative bacteria that can form potentially toxic blooms in eutrophic and slow flowing aquatic ecosystems. Bloom toxicity varies spatially and temporally, but understanding the mechanisms that drive these changes remains largely a mystery. Changes in bloom toxicity may result from changes in intracellular toxin pool sizes of cyanotoxins with differing molecular toxicities, and/or from changes in the cell concentrations of toxic and non-toxic cyanobacterial species or strains within bloom populations. We show here how first-order rate kinetics at the cellular level can be used to explain how environmental conditions drive changes in bloom toxicity at the ecological level. First order rate constants can be calculated for changes in cell concentration (μc: specific cell division rate) or the volumetric biomass concentration (μg: specific growth rate) between short time intervals throughout the cell cycle. Similar first order rate constants can be calculated for changes in nett volumetric cyanotoxin concentration (μtox: specific cyanotoxin production rate) over similar time intervals. How μc (or μg) covaries with μtox over the cell cycle shows conclusively when cyanotoxins are being produced and metabolised, and how the toxicity of cells change in response to environment stressors. When μtox/μc >1, cyanotoxin cell quotas increase and individual cells become more toxic because the nett cyanotoxin production rate is higher than the cell division rate. When μtox / μc =1, cell cyanotoxin quotas remains fixed because the nett cyanotoxin production rate matches the cell division rate. When μtox/μc

Saltwater intrusion has become a severe issue for the Mekong Delta in Vietnam, especially near the coastline. This issue has led to farmers diversifying from exclusively growing rice to adopting a mixed rice-shrimp system with rice only cultivated in the wet season. However, the nutrient (nitrogen, phosphorus and carbon) cycling and nutrient use efficiency of this system remain poorly understood. To address this knowledge gap, we examined nutrient budgets across 12 farms using integrated rice-shrimp ponds, and in some cases semi-intensive or intensive shrimp grow-out ponds (Penaeus monodon or Penaeus vannamei), over a two-year period (2014–2015). In terms of nutrient budgets, the main nutrient input (92% of the N input, 57% P and 95% C) in the integrated rice-shrimp ponds (IRSPs) came from intake water (excluding C from primary production), while water discharge accounted for the highest output (75% of N output, 41% P, 57% C, excluding C from respiration). The study showed that IRSPs had low dissolved oxygen and high nutrient concentrations which may affect shrimp production. Conversely, salinity levels in the wet season were too high for rice plants thereby affecting rice production. Shrimp survival in the IRSPs was low over the two years (6.3 ± 2.2%), which resulted in the low proportion of nutrients exported from the ponds as harvested shrimp (6% N, 5% P and 10% C). In contrast, the shrimp grow-out ponds (SGOPs), had much higher survival (77.1% for P. vannamei and 59.2% for P. monodon) in three of the six farms where the shrimp survived through to harvest. In these ponds, formulated feed was the highest nutrient input (P. vannamei: 82% N, 75% P and 85% C; P. monodon: 75% N, 55% P and 77% C) with approximately a third of the nutrients being in the shrimp harvest. In our study, nutrients in the IRSPs were used less efficiently than in SGOPs, hence mechanisms to improve shrimp survival and production in IRSPs are urgently needed.

Estuaries in the tropical Gulf of Carpentaria (GOC) in Australia are under increasing pressure from catchment water development, potentially affecting productivity. We examined the potential effect of changes in freshwater inputs on the primary productivity of three estuaries (Flinders, Gilbert and Mitchell Rivers). The addition of nutrients stimulated mudflat primary production in all estuaries at multiple sampling times, suggesting chronic nutrient limitation. All three estuaries were productive with the Flinders estuary being the most productive of the three estuaries, compared to the Gilbert and Mitchell estuaries. This is despite the fact that the Flinders estuary has the shortest period of freshwater flow and more variable flows from year-to-year compared with the other estuaries. This makes the Flinders highly vulnerable to excessive water development. This study suggests that water extraction which significantly reduces freshwater inputs and associated nutrients has the potential to impact on productivity within these estuaries.

Agricultural activities in catchments can cause excessive nutrient loads in waterways. Catchment nitrogen (N) and phosphorus (P) flows may be intercepted and assimilated by riparian vegetation. While prior studies suggest that woody vegetation is preferable for reducing P loads, the question remains: is woody vegetation or grass cover more effective at reducing catchment N and P exports to waterways. To address this we investigated the relative importance of vegetation type, hydrologic and soil microbial processes on N and P losses from soil to a stream. The study involved the analysis of data from two soil microcosm experiments, and a field case study. We found P leaching loss from riparian zones depended significantly on vegetation type (woody vs. grass cover), with lower P exported from wooded riparian zones, irrespective of the scale of rainfall. For N leaching losses, the scale of rainfall had an effect. During high rainfall, vegetation type had a major effect on N leaching loss, with lower N exported from grassed verses wooded riparian zones. However, under low rainfall conditions, soil type and soil C and N stores, potential indicators of soil microbial activity, rather than vegetation cover, affected N leaching. It is hypothesized that soil microbes were reducing N removal under these conditions. We reason that nitrifiers may have played an important role in soil N cycling, as increased soil ammonium had a strong positive effect on nitrate leaching loads, mediated through soil nitrate stores. Whereas, N immobilization, via incorporation into microbial biomass, and denitrification processes appeared to be limited by C availability, with increased C associated with reduced N leaching. Overall, this study identified that N leaching losses from riparian zones appeared to be affected by two different processes, vegetative uptake and soil microbial processes, the relative importance of which was driven by hydrological conditions.

Sustained water level drawdown followed by rewetting has the potential to shift macrophytes from a nutrient sink to a source, but the fate of macrophyte-derived nutrients after rewetting is not well understood. We investigated the fate of released nitrogen (N) from isotopically labeled macrophyte litter over a 4-week period after rewetting. We used three treatments: (1) different species in the litter (invasive Cabomba caroliniana vs. native Hydrilla verticillata); (2) sediment desiccation history (“dried then rewetted” vs. “constantly wet”); (3) living macrophytes (presence vs. absence). Our results showed that the Cabomba litter treatment had a significantly higher percentage of macrophyte-derived 15N in the dissolved fraction of the water column and assimilated by phytoplankton (higher chlorophyll a concentrations), compared to the Hydrilla litter. The treatments with sediment desiccation also had a significantly higher percentage of 15N in the dissolved fraction and used by phytoplankton after rewetting, but less in the sediment, compared to the constantly wet treatment. The presence of living macrophytes partially reduced the 15N increase in the water column and/or sediment, but the scale of the effect was species- and biomass-dependent. Our study showed that sediment pre-desiccation changed the fate of macrophyte-derived 15N after rewetting, increasing the impact on water quality. This was further exacerbated by the presence of litter from an invasive species. This study highlights the need to manage water levels to maintain healthy macrophyte beds and thereby addressing water quality issues in lakes and reservoirs.

In recent years, across tropical regions of the world, there has been an expansion of integrated farming systems that combine rice and shrimp production. While these systems were developed as a form of crop-rotation – growing rice in the wet season and shrimp in the dry season – some farmers grow both rice and brackish-water shrimp simultaneously during the wet season. Climatic variability has resulted in considerable crop losses in this system across many regions. Research has yet to identify the complete array of key risk factors, and their potential interactions, for integrated rice-shrimp farming. Consequently, different farming practices and environmental factors that may affect crop production need to be clarified to guide research efforts. We applied a staged, iterative process to develop a probabilistic Bayesian belief network based on expert knowledge that describes the relationships that contribute to the risk of failure of both crops in integrated rice-shrimp farming systems during the wet season. We applied the approach in the Southern Mekong Delta, Vietnam, in the context of a broader research program into the sustainability of the rice-shrimp farming system. The resulting network represents the experts' perceptions of the key risk factors to production and the interactions among them. While both farmers and extension officers contributed to the identification of the processes included in the network, the farmers alone provided estimates of the probability of the relationships among them. The network identified the challenges to minimise the risk of failure for both crops, and the steps farmers can take to mitigate some of them. Overall, farmers perceived they have a better chance to minimise risk of failure for shrimp rather than rice crops, and limited opportunities appear to exist for successful production of both. By engaging the farmers in this process of model development, we were able to identify additional research questions for the broader research team and to identify simple steps the farmers could take to reduce the risk of crop failure. Integrating additional empirical data into this network, as it becomes available, will help identify clear opportunities for improvements in farming practices which should reduce the risk of crop failure into the future.

Here we link plant source phylogeny to its chemical characteristics and determine parameters useful for predicting DOM phytotoxicity towards algal monocultures. We found that DOM characterised using UV–visible spectroscopic indices and elemental analysis is useful for distinguishing DOM plant sources. Specifically, combined values of absorbance at 440 nm and coefficients for the spectral slope ratio, were used to distinguish between gymnosperm-leached DOM and that from angiosperms. In our bioassays, DOM leached from 4 g leaf L −1 resulted in over 40% inhibition of photosynthetic yield for the cyanobacterium, Cylindrospermopsis raciborskii , for eight of the nine plants tested. Significant variables for predicting inhibition of yield were DOM exposure time and plant source, or using an alternate model, exposure time and spectroscopic and elemental measures. Our study proposes spectroscopic indices which can estimate a plant source's contribution to aquatic DOM, may provide insights into ecological outcomes, such as phytotoxicity to algae. The cyanobacterium ( C. raciborskii) was more sensitive to DOM than a green algae ( Monoraphidium spp .), as identified in a subsequent dose-response experiment with five different DOM plant sources. Low level additions of angiosperm derived-DOM (i.e. 0.5 g L −1 ) were slight phytotoxic to Monoraphidium spp . causing 30% inhibition of yield, while C. raciborskii was not affected. Higher DOM additions (i.e. 2 g L −1 ) caused 100% inhibition of yield for C. raciborskii , while Monoraphidium spp . inhibition remained under 30%. The divergence in algal sensitivity to DOM indicates that in aquatic systems, DOM derived from catchment vegetation has the potential to affect algal assemblages.

The freshwater cyanobacterium Microcystis is a nuisance species. It forms large blooms on the water surface and overwhelmingly dominates the ecosystem through the formation of colonies from single cells surrounded by mucilage; however, the mechanism of colony formation is poorly understood. Two mechanisms of Microcystis colony formation have been proposed: cell-division, where cells remain attached after binary fission; and cell-adhesion, where single cells stick together. This paper examined the published literature on Microcystis colony formation to clarify the mechanism of colony formation and its relationship to environmental drivers. This meta-analysis showed that in laboratory experiments, colony formation by cell-division was mainly induced by zooplankton filtrate, high Pb2+ concentrations, the presence of the cyanobacterium Cylindrospermopsis raciborskii, heterotrophic bacteria, and low temperature and low light intensities. Alternatively, colony formation by cell-adhesion was mainly induced by zooplankton grazing, high Ca2+ concentrations, and microcystins. Therefore, colony formation by cell-division appears to be a slower process and to occur under an environmental stress factor, while cell-adhesion occurs more quickly to an environmental threat. Applying the criteria to the different morphospecies of Microcystis, it was found that under natural conditions M. ichthyoblabe colonies formed predominantly through cell-division, whereas M. wesenbergii colonies formed predominantly through cell-adhesion. This study provides new insights into the mechanisms and environmental drivers of colony formation by Microcystis.

Tropical floodplains are one of the most productive ecosystems on earth. Studies on floodplain productivity have primarily focused on trees and macrophytes, rather than algae, due to their greater biomass. However, epiphyton—algae and bacteria attached to the submerged portion of aquatic macrophytes—is a major source of energy in many tropical floodplains. Epiphyton productivity rates are unknown for most tropical floodplain wetlands, and spatial variability is not well understood. In this study, we measured primary productivity of epiphyton in Kakadu National Park in northern Australia. We estimated the relative contribution of epiphyton to aquatic production (epiphyton, + phytoplankton + macrophytes). We sampled sites dominated by different macrophyte structural types: vertical emerging grasses, horizontal emerging grasses, submerged macrophytes, and macrophytes with floating leaves. Epiphyton productivity was highly influenced by the structural type of the macrophyte. Highest potential productivity per weight was measured from epiphyton growing on macrophytes with floating leaves and horizontal grasses (1.52 ± 0.53 and 1.82 ± 0.61 mgC/dw g epiphyton/h, respectively) and lowest in submerged macrophytes and vertical grasses (0.57 ± 0.26 and 0.66 ± 0.47 mgC/dw g epiphyton/h, respectively). When considering the areal biomass of the macrophyte and the amount of epiphyton attached, epiphyton on horizontal grasses and submerged macrophytes had productivity values approximately ten times higher (45–219 mgC/m2/d) compared to those on vertical grasses and macrophytes with floating leaves (2–18 mgC/m2/d). Epiphyton contributed between 2 to 13 percent to the aquatic production of these tropical floodplain wetlands.