Factors driving impacts of different nitrogen sources on freshwater and marine green algae.

The response of marine and freshwater algal species to both point and non-point sources of nitrogen have not been directly compared. We compared the photosynthetic yield response (Fv/Fm) of nitrogen-starved freshwater and marine green microalgae after a 3-day exposure to fourteen treated wastewater and nine aquaculture farm effluent as well as twenty-three soil erosion sources. The combination of inorganic and organic nutrients, organic carbon, and carbon-to‑nitrogen ratios were most highly correlated with algal responses across all nitrogen sources (R = 0.

Sources of nutrients fuelling post-flood phytoplankton biomass in a subtropical bay.

Extreme rainfall from an ex-tropical cyclone caused a major flood event in the Logan River system in southeast Queensland, Australia. This resulted in a significant flood plume, containing nutrients and sediment, being discharged into the adjacent estuary/Bay system. The spatial extent of higher phytoplankton biomass (Chl a) matched the distribution of higher nutrient and sediment concentrations post-flood, suggesting nutrients fuelled phytoplankton production.

How do small dams alter river food webs? A food quality perspective along the aquatic food web continuum.

Damming of rivers poses a significant threat to freshwater ecosystems. Previous studies about the impact of damming on river ecosystems have mostly focused on large dams, with the impact of small dams largely unknown. Further, while the impacts of dams on aquatic communities have been widely studied, the effect on energy flow across river food webs remains unclear.

Phosphorus storage and utilization strategies of two bloom-forming freshwater cyanobacteria.

The inter-relationships between cellular phosphorus (P) storage, dissolved inorganic P (DIP) uptake affinity, alkaline phosphatase activity (APA) and dissolved inorganic nitrogen (DIN) concentrations were studied in two ubiquitous diazotrophic freshwater cyanobacteria, (six strains) and (two strains). DIP uptake kinetics were measured using rates of incorporation of the radio-isotope, P and APA as a proxy for DOP-ester utilization. The study showed that DIP uptake of individual strains followed Michaelis-Menten kinetics (modified in our study to incorporate cellular P quotas), but differed with DIN and P availability, and between growth stages.

A slurry approach to identify nutrient critical source areas from subtropical catchment erosion.

Targeting catchment nutrient critical source areas (CSAs) (areas contributing most of the nutrients in a catchment) is an efficient way to prioritize remediation sites for reducing nutrient runoff to waterways. We tested if the soil slurry approach - with particle sizes and sediment concentrations representative of those in streams during high rainfall events - can be used to identify potential CSAs within individual land use types, examine fire impacts, and identify the contribution of leaf litter in topsoil to nutrient export in subtropical catchments. We first confirmed the slurry approach met the prerequisite to identify CSAs with relatively higher nutrient contribution (not absolute load estimation) by comparing the slurry sampling with stream nutrient monitoring data.

Scientific challenges and biophysical knowledge gaps for implementing nutrient offset projects.

Nutrient offsetting allows nutrient point source polluters to pay for diffuse source nutrient reductions, or improvements in nutrient load reductions from alternative point sources. These programs have the potential to provide a more cost-effective approach to achieve water quality goals in waterways compared to infrastructure upgrades. However, worldwide adoption of nutrient offset/trading has not been realized.

Higher resistance of a microcystin (MC)-producing cyanobacterium, Microcystis, to the submerged macrophyte Myriophyllum spicatum.

Outbreaks of Microcystis blooms can affect growth of submerged plants, which in turn can inhibit cyanobacterial growth. Microcystin (MC)-producing and non-MC-producing Microcystis strains typically coexist in Microcystis-dominated blooms. However, the interaction between submerged plants and Microcystis at strain level is not clear.

Schindler's legacy: from eutrophic lakes to the phosphorus utilization strategies of cyanobacteria.

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.

Effects of macrophytes and environmental factors on sediment denitrification in a subtropical reservoir.

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), and their potential controlling factors were determined in both macrophyte beds and deeper waters in the subtropical reservoir.

Chlorophyll and phycocyanin in-situ fluorescence in mixed cyanobacterial species assemblages: Effects of morphology, cell size and growth phase.

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.

Global co-occurrence of methanogenic archaea and methanotrophic bacteria in Microcystis aggregates.

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.

Comparing the importance of freshwater flows driving primary production in three tropical estuaries.

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.

Assessing the effects of lipid extraction and lipid correction on stable isotope values (δ C and δ N) of blubber and skin from southern hemisphere humpback whales.

Rationale: The coupled analysis of δ C and δ 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 C, reducing the bulk tissue C/ 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.

Terrestrial dissolved organic matter source affects disinfection by-product formation during water treatment and subsequent toxicity.

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.

Identification of compounds from terrestrial dissolved organic matter toxic to cyanobacteria.

There is emerging evidence for the phytotoxicity of terrestrial dissolved organic matter (DOM), however its sources, transformations and ecological effects in aquatic ecosystems are poorly understood. DOM characterization by Nuclear Magnetic Resonance (NMR) spectroscopy has typically involved solid-state techniques, but poor resolution has often precluded identification of individual components. This study is the first to directly identify individual phytotoxic components using a novel combined approach of preparative HPLC fractionation of DOM (obtained from leaves of two common riparian trees, Casuarina cunninghamiana and Eucalyptus tereticornis).

Rice-shrimp ecosystems in the Mekong Delta: Linking water quality, shrimp and their natural food sources.

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.

Intra-population strain variation in phosphorus storage strategies of the freshwater cyanobacterium Raphidiopsis raciborskii.

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.

Are laboratory growth rate experiments relevant to explaining bloom-forming cyanobacteria distributions at global scale?

Predicting algal population dynamics using models informed by experimental data has been used as a strategy to inform the management and control of harmful cyanobacterial blooms. We selected toxic bloom-forming species Microcystis spp. and Raphidiopsis raciborskii (basionym Cylindrospermopsis raciborskii) for further examination as they dominate in 78 % and 17 %, respectively, of freshwater cyanobacterial blooms (cyanoHABs) reported globally over the past 30 years.

Enhanced resistance of co-existing toxigenic and non-toxigenic Microcystis aeruginosa to pyrogallol compared with monostrains.

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 global interactome.

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 during blooms in 12 lakes spanning four continents as an initial test of the hypothesized interactome.

Subtropical freshwater phytoplankton show a greater response to increased temperature than to increased pCO.

Global increases in atmospheric CO and temperatures will impact aquatic systems, with freshwater habitats being affected. Some studies suggest that these conditions will promote cyanobacterial dominance. There is a need for a clearer picture of how algal species and strains within species will respond to higher temperatures and CO, especially in combination.

Plant source and soil interact to determine characteristics of dissolved organic matter leached into waterways from riparian leaf litter.

Wetting of leaf litter accumulated in riparian zones during rainfall events provides pulses of dissolved organic matter (DOM) to rivers. Restoring riparian vegetation aims to reduce sediment and nutrient transport into rivers, however DOM from leaf litter can stimulate phytoplankton growth and interfere with water treatment processes. Improved understanding of the loads and chemical composition of DOM leached from leaf litter of different plant species, and how subsequent leaching through soils affects DOM retention or transformation, is needed to predict the outcomes of riparian revegetation.

Effects of photochemical and microbiological changes in terrestrial dissolved organic matter on its chemical characteristics and phytotoxicity towards cyanobacteria.

Previous studies have shown that under laboratory conditions, dissolved organic matter (DOM) leached from plants can be differentially more phytotoxic to cyanobacteria, compared to green algae. This study examined how DOM source and transformation processes (microbial and photochemical) affect its chemical composition and phytotoxicity towards a cultured species of cyanobacteria (Raphidiopsis raciborskii) using a factorial experimental design. To complement cyanobacterial bioassays, the chemical composition and associated changes in DOM were determined using spectroscopic (nuclear magnetic resonance (NMR) and absorbance) and elemental analyses.

Comparison of DET, DGT and conventional porewater extractions for determining nutrient profiles and cycling in stream sediments.

Determining inorganic nutrient profiles to support understanding of nitrogen transformations in stream sediments is challenging, due to nitrification and denitrification being confined to particular conditions in potentially heterogeneous sediment influenced by benthic microalgae, rooted aquatic plants and/or diel light cycles. The diffusive gradients in thin films (DGT) and diffusive equilibration in thin films (DET) techniques allow in situ determination of porewater concentration profiles, and distributions for some solutes. In this study, DGT, DET and conventional porewater extraction (sectioning and centrifugation) methods were compared for ammonium and nitrate in stream sediments under light and dark conditions.

Stoichiometric control on riparian wetland carbon and nutrient dynamics under different land uses.

Riparian wetland provides important ecosystem function, such as water filtration and nutrient retention. When land use change in upland from native forest to sugarcane cultivation have important impacts on carbon (C) and nutrient availability in downstream wetland systems. Here, we examined concentrations and stoichiometry of C and nutrients in total, labile, biomass pools in upland soil, riparian wetland and sediment along two distinct transects (sugarcane versus forest).