Algal blooms: Algae are organisms that live in the water. Algae can rapidly grow out of control, or “bloom,” when water is warm, slow-moving, and full of nutrients.

Autotroph: An organism that serves as a primary producer in a food chain. Autotrophs obtain energy and nutrients by harnessing sunlight through photosynthesis (e.g. algae, cyanobacteria, vascular plants).

Basal resources: Food webs are often thought of hierarchically like a pyramid, with the basal resources from primary production and detritus providing that large stable base that supports all the animals that comprise the rest of the food web.

Bioenergetics: A term that refers to the processes in food webs that include how energy is transferred between organisms and the environment, and the other environmental and physical aspects that control and influence those processes in the water.

Biomass: describes the energy in living organisms. Biomass is transferred when organisms eat each other, from producers to consumers.

Cyanobacteria: A phylum of gram-negative bacteria that obtain energy via photosynthesis (autotrophs). Commonly referred to as Blue-green Algae, cyanobacteria are not scientifically classed as algae. Some cyanobacteria produce toxins that can cause acute illness following consumption or skin exposure. Cyanobacteria blooms usually form in warm, slow-moving waters rich in nutrients and can cause significant problems for water users.

Dissolved oxygen (DO): A measure of how much oxygen is dissolved in the water – the amount of oxygen available to living aquatic organisms. The amount of dissolved oxygen in a stream or lake can tell us a lot about its water quality.

Ecosystem Respiration (ER): The mineralisation of organic matter by autotrophs and heterotrophs – measured by the consumption of dissolved oxygen. High levels of ecosystem respiration has the potential to lead to low oxygen levels.

Net Ecosystem Production (NEP): the difference between GPP and ER and specifies how much carbon accrues (ecosystem is autotrophic) or is depleted (ecosystem is heterotrophic).

Eutrophication: A process where water has an overabundance of nutrients – especially that of nitrogen and phosphorus. Algae and other plants feed on these nutrients causing excessive growth, in some instances resulting in algal blooms. Eutrophication can have severe consequences for water quality.

Food web: A network of interconnecting links of feeding relationships within an ecosystem. Food webs describe how matter and energy from food are transferred from one organism to another (referred to as a trophic relationship). Food webs are often illustrated hieratically with many basal resources at the bottom, such as algae and detritus, gradually leading to smaller numbers of apex predators at the top, such as Murray Cod.

Gross Primary Production (GPP): Represents the generation of new biomass by autotrophs (e.g. algae, cyanobacteria, vascular plants) via photosynthesis—the process by which solar energy, water, and carbon dioxide are transformed into reduced carbon compounds that sustain life and form the basis of food webs. GPP is usually expressed as the rate of carbon generation and, in aquatic ecosystems, can be estimated from changes in dissolved oxygen concentration.

Food web productivity: refers more generally to the rate at which energy is added to the food web in the form of biomass.

Heterotroph: An organism that consumes other organisms or organic matter in a food chain. In contrast to autotrophs, heterotrophs cannot produce organic substances from inorganic ones (e.g. bacteria, fungi, animals).

Hypoxic blackwater: ‘Blackwater’ occurs when there is a very high concentration of dissolved organic carbon (DOC) in the water column. Usually this happens when large quantities of terrestrial litter (e.g. leaves) are submerged (similar effect to tea bags in water). If conditions are suitable (e.g. high water temperature), consumption of DOC by bacteria can use up large quantities of oxygen, leading to ‘hypoxic conditions’ – where dissolved oxygen concentration can drop below 2 mg L-1, sometimes leading to fish deaths.

Labile carbon: Labile carbon is the fraction of organic carbon with most rapid turnover, as it is more readily decomposed by microorganisms.

Metabolic regime/pattern: patterns of gross primary productivity and ecosystem respiration for a water body.

Mixotroph: An organism, often tiny microbes, that can meet their energy requirements via photosynthesis or consuming other animals or organic matter

Organic carbon: Whilst most of the biomass of most living organisms is composed of organic carbon (or organic matter), in aquatic science, organic carbon is usually referring to the non-living fraction. This can include a dissolved organic carbon fraction (DOC) or particulate (POC) fraction. This material is often comprised of detritus from plants and algae or dissolved materials leached from soil or plant material.

Photic zone of autotrophic biofilms: The photic zone is the uppermost layer of water that receives sunlight, which allows organisms like phytoplankton and other autotrophic organisms, to photosynthesis. Biofilms are a layer of microorganisms joined together in what appears like slime, which form on surfaces in contact with water.

Phytoplankton: an autotrophic organism that contains chlorophyll and can photosynthesise. They are considered the foundation of an aquatic food web.

Secondary production: the formation of heterotrophic organisms.

Stream Metabolism: The transformation of organic matter used to measure food resource availability. Comprised of two key ecological processes – GPP as an indicator of how much is being produced through photosynthesis, and ER, which is an indicator of how much energy is consumed. These processes generate and recycle organic matter, respectively. Monitored in a river reach using measurement of the production and consumption of oxygen.

Trophic: The tropic level of an organism is the position it occupies in a food web, which is determined by the food relationship or feeding habitats of different organisms (i.e., who eats whom).