Freshwater

This metric refers to the number of people and/or buildings that can be identified as being in a lower flood risk category than they would have been in the absence of the ecosystem providing the flood mitigation service. Usually this involves an assumption that the relevant ecosystem would otherwise have been bare land (see SEEA-EA 2021, Table 7.7), and requires some form of hydrological modelling to determine risk exposure in the existing situation as well as the baseline scenario.

River flood mitigation services may be provided along with water flow regulation services (including baseline flow maintenance services and peak flow mitigation services).

Annual average, seasonal average or even daily average flow rates can be compared with natural (undisturbed) flow rates or ‘environmental flows’ determined to protect ecological integrity.

There are various ways in which river/stream fragmentation could be measured. Relatively simple proxies could include the maximum river/stream length without barriers such as dams, or the number of barriers per unit river/stream length.

More sophisticated proxies can be based on measured differences between natural upstream and downstream discharge rates, and the discharge rate at the barrier – see Grill, G. et al. (2019) ‘Mapping the world’s free-flowing rivers’, Nature, 569(7755), pp. 215–221.

Species richness can be defined as “The number of species within a given sample, community, or area” (IPBES). It is one way of measuring species diversity, which is itself only one aspect of overall biodiversity. The concept of richness can also be applied at other levels, from genetic (e.g. the number of distinct genotypes within a species) to the number of represented genera, families, etc. It can be useful to supplement richness information with information on abundances or relative abundance distributions.

Depending on the purpose of measurement, and the measurement resources available, the concept of species richness may be applied to certain sets (e.g. plants, mammals, birds, invertebrates, endemic species, etc.). It is important to recognise that observations from one set may not apply to other sets in the same area.

It is usually not feasible to count all species, even within a limited set, within a given area. Therefore some form of sampling method is usually applied to come up with a sample set that can feasibly be measured. Many different sampling methods may be used, and the number of samples required will depend on the measurement objectives (e.g. desired accuracy and confidence), the sample measurement method (e.g. size of sample areas), and the actual variation in the measured quantity across the given area. There are also many different measurement methods and technologies at the sample measurement level (e.g. pit traps for insects, camera traps for animals, acoustic methods for birds). There is no single ‘right’ method that applies in all circumstances. Whatever method is used, it is important that it should be applied consistently for a given site over time, and appropriate to the measurement objectives and ecosystem type. Measurements using different methods may not necessarily be comparable.

Water abstracted may be considered an ecosystem service (e.g. where ecosystems provide essential water purification services or flow regulation services); or an abiotic flow (not dependent on any particular ecological processes). Either way, the volume extracted is the relevant measure, unless water purification services and flow regulation services can be measured separately (see SEEA-EA s.6.4.2, pp. 138-139), in which case water supply should not be measured as a separate ecosystem service, but rather as an abiotic flow (water abstracted). If water abstracted can be separated into different uses (e.g. human drinking water, livestock drinking water, irrigation) then it can be helpful to measure these amounts separately.

Relevant water quality metrics and thresholds depend on the use of the water and known threats to water quality. Example Tier 1/Tier 2 metrics might include Turbidity, Dissolved Oxygen, Organic and inorganic compounds, Nutrients, Acidity, Salinity/Total Dissolved Solids. Tier 3 could also include additional, more difficult or costly to measure metrics such as concentrations of cyanobacteria, pathogens and parasites, heavy metals and organic contaminants, where appropriate.

See Australian and New Zealand Guidelines for Fresh and Marine Water Quality for information and guidance on how to identify relevant water quality metrics and thresholds or ‘guideline values’ for Australian and New Zealand waters.

See also: Standard Methods for the Examination of Water and Wastewater; UN Environment (2017) A Framework for Freshwater Ecosystem Management (especially Volume 2, Tables 4 and 5 which list example water quality metrics for different freshwater ecosystem types).