Freshwater

• Innhold
• Description of freshwater
• Assessed Ecosystem Types
• Red-listed ecosystem types
• Impact factors
• Existing knowledge
• Expert Committee
• Acknowledgements
• References

A total of 6 % of the area of mainland Norway is covered by lakes and rivers. The lake area is calculated to be 18 312 km² and comprises 5.7 % of the area of Norway (Norwegian Mapping Authority 2010). This includes only lakes with an area greater than 300 m². River surfaces, excluding lesser rivers and streams that are narrower than 15 m, comprise 0.5 % of the area of Norway (Norwegian Mapping Authority 2010). Most of the rivers in Norway are small with a watershed <10 km² and a length of some few kilometres, while only 14 watercourses have a length of more than 200 km (Schartau et al. 2008). Inland surface waters in Norway are clearly dominated by lime-deficient and oligotrophic lakes and rivers (Henriksen et al. 2007). The flora and fauna are therefore characterized by species that are adapted to this environment.

Description of freshwater

In Nature in Norway (NiN 2.1) freshwater systems are divided into two major groups: Freshwater bed systems L and Limnic waterbody systems F (Halvorsen et al. 2016). Freshwater bed systems, also called lacustrine bottom systems, are divided into eight major types and encompass ecosystems in freshwater that are found in or closely connected to the bottom of rivers and lakes. Limnic waterbody systems are divided into five major types and encompass ecosystems of floating, free-floating and swimming organisms in the open water of rivers and lakes. Two major types in both Freshwater bed systems and Limnic waterbody systems encompass modified or changed ecosystem types. These are ecosystems that are irreversibly changed through anthropogenic physical interventions and alterations such as watercourse regulation, as well as chemical and biological changes, and which are not to be assessed for the Red List (Halvorsen et al. 2016).

Assessed Ecosystem Types

Freshwater bed systems that are assessed include Euphotic freshwater rock L1, Euphotic freshwater sediment L2, Aphotic freshwater sediment L3, Freshwater swamp L4 and Freshwater spring L5.

The major types Euphotic freshwater rock and Euphotic freshwater sediment encompass river and lake bottoms with sufficient light penetration for positive net photosynthesis, with either a stable bottom substrate and organic sediment, peat, or unstable inorganic bottom sediment. Aphotic freshwater sediment encompasses natural systems associated with lake bottoms. The bottom water does not experience regular periods of stagnation with a level of oxygen-depletion significant enough to influence the species composition. Freshwater swamp encompasses water entities with compact stands of large swamp plants in terrestrial or wetland systems, while Freshwater springs includes limnocrene springs, helocrene springs, and fluvial and lacustrine bottoms that are influenced by groundwater discharge.

Limnic waterbody systems that are assessed include River and stream waterbody F1, Circulating lake waterbody F2 and Anoxic lake waterbody F3.

River and stream waterbody encompasses ecosystems in all lotic environments (running water). Circulating lake waterbody encompasses lentic (still water) ecosystems i.e. waterbodies with low flow rates, long hydrological retention times, and more or less without water currents. These are types we often describe as lakes, tarns, ponds and vernal pools. Anoxic lake waterbody encompasses permanent, stagnant bottom water in lakes i.e. a cold, heavy and oxygen-depleted layer of water that never mixes with the rest of the water in the lake. This water often has a high content of different salts, eg. old sea-water.

The remaining assessment entities in limnic waterbody system were selected after an initial analysis of existing data (VannNett 2018, Mjelde unpublished data, Dervo unpublished data). These entities were deemed to be affected differently than the major type limnic waterbody system and to such a degree that they were assigned to a higher Red List category than the major type.

Minor types which were assessed were Lime-poor, humus-rich waterbody in small or shallow lake F2-16 and deep lake F2-13, as well as Lime-poor, turbid waterbody in small or shallow lake F2-12. Furthermore, the four minor types that encompass lime-rich ponds, vernal pools and small shallow lakes (F2-6, F2-9, F2-18 and F2-21) were combined into a single assessment entity, because ecosystems in lime-rich water entities are impacted differently than water entities with less lime (eg. DN 2011). An additional assessment was undertaken for lime-rich ponds, vernal pools and small shallow lakes with a calcium content of 20 mg Ca/L, since these are considered to be more exposed to anthropogenic influence than lakes with a calcium content of mg Ca/L. Lime-rich freshwater swamp L4-3 was also assessed for the Red List since this ecosystem type is found exclusively in lime-rich waterbodies and can therefore be assessed on the basis of the same data.

Challenges with the selection of types for assessment

In NiN, a nature complex is a composite of natural systems consisting of a functional ecological or geomorphological entity within a well-defined area. It would be most natural to assess freshwater ecosystem types as a nature complex for the Red List. Examples of a nature complex in NiN could be an entire stream, or parts of the stream, a river, a pond, a tarn, or a lake. A nature complex will therefore contain several major or minor types from the natural system level. As the nature complex level in NiN is still being developed, it is landforms and the natural system level down to minor (ecosystem) types that form the basis of the Red List assessment of freshwater in 2018.

A large part of the data that has been collected for ecosystem types in freshwater, for example via the Water Management Regulations (NN 2015; VannNett 2018), is at the water entities level, something which corresponds to the nature complex level in NiN. In addition the definitions of minor types in NiN harmonise only partially with the definitions of ecosystem entities in other classification systems. Existing data at the water entities level can be used to assess waterbodies but not to assess bottom types since the distribution and occurrence of bottom types within water entities are not adequately surveyed. Neither have survey guidelines been developed yet for freshwater ecosystem types. Variables from the descriptive system in NiN (subordinate local environmental variables and regional natural landscape variation) that can be used to define or describe assessment entities were assessed as being irrelevant, or unable to be used, due to a lack of data.

Insufficient surveying, and existing data for freshwater mostly at the nature complex level have limited the opportunities to assess Red List ecosystem types in freshwater. The Red List assessment 2018 cannot therefore be considered to completely cover ecosystem types in freshwater.

Red-listed ecosystem types

Of the 14 assessed ecosystem types, 6 are assessed as Endangered EN, Vulnerable VU or Near Threatened NT.

For the major type River and stream waterbody F1, 53 % of the occurrences are assessed as more than 30 % degraded over the last 50 years. This corresponds to the Red List category Near Threatened NT with reference to the C1 criterion. River and stream waterbodies encompass all running water in Norway, from small streams in the mountains to large rivers in the lowlands, in other words a broad spectrum of different lotic ecosystems. Some of these ecosystems are heavily influenced by anthropogenic activity and can thus be deemed to be threatened to a considerably greater degree than that which is indicated by the assessment of the major type.

With a basis in the existing knowledge which has been collected in accordance with the Water Management Regulations, Circulating lake waterbody F2 was assessed as being of Least Concern LC.

Three minor types under Circulating lake waterbody F2 were assessed as Vulnerable VU, Endangered EN or Near Threatened NT. Lime-poor, humus-rich small or shallow lake F2-16 and Lime-poor, humus-rich deep lakes F2-13 were assessed as Vulnerable VU and Endangered EN, respectively. Both minor types have a limited distribution with few localities combined with an ongoing decline in area and quality. They are also particularly vulnerable to acidification at the same time as the distribution is limited to that region of Norway which receives the most acid rain. Lime-poor shallow and deep lakes F2-16 & F2-13 were allocated to their respective Red List categories on the basis of the B2-criterion. For the shallow type (F2-16), 22 % of the estimated ecologically intact area in 1969 is assessed as > 30 % degraded in the past 50 years. This indicates an ongoing decline, and the number of occurrences is less than 50. An occurrence in this context is the number of 10 x 10 km² grids where the ecosystem type exists. For the deep type (F2-13), 9 % of the area estimated to have disappeared in the past 50 years is something that indicates an ongoing decline, whilst the number of occurrences is less than 20. Lime-poor, turbid waterbody in small or shallow lake F2-12 is assessed as Near Threatened NT on the basis of the C1-criterion because 32 % of the estimated intact area in 1969 is assessed as > 50 % degraded in the past 50 years. Turbid lakes are to a large degree representative of glacier-influenced waterbodies.

Lime-rich ponds, vernal pools and shallow lakes (F2-6, F2-9, F2-18 and F2-21) were on the basis of data from Vann-Nett assessed as being of Least Concern LC. It has nevertheless been estimated that more than 30 % of lime-rich ponds and lakes with a Ca-content > 20 mg have been lost in the past 50 years. The entity is therefore assessed as Vulnerable VU according to the A1 criterion. The ecosystem type is also assessed as Vulnerable VU on the basis of the C1 criterion because more than 30 % is more than 80 % degraded in the past 50 years.

Lime-rich (helophyte) swamp L4-3 is found almost exclusively in lime-rich ponds and lakes. If this type of waterbody disappears, then lime-rich (helophyte) swamp will also disappear, either because the dominant species of sedge (Carex genus), is replaced by other species of sedge, or because the ecosystem type disappears due to being filled in or drying up. Lime-rich (helophyte) swamp is assessed for the Red List as Vulnerable VU based on the same criteria as lime-rich ponds and lakes.

Impact factors

The most important impacts on freshwater on the mainland are hydropower regulation, long-distance pollution and runoff from agriculture and households (Vann-Nett 2018; Miljøstatus 2018). Around a third of the surface water areas in Norway are impacted by hydropower development, and watercourse regulation is deemed to be the largest impact factor. This includes regulation of water flows and water levels, as well as the transfer of water from one watercourse to another. The reason that Lime-poor, turbid waterbody in small or shallow lake is assessed as near threatened NT is partly due to hydropower regulation. A considerable area, especially in southern Norway, is still influenced by acid rain and extensive liming is is necessary to counteract the damage. Run-off from agriculture and built-up areas leads to increased additions of nutrients (eutrophication) and pollutants to water entities. Digging ditches and the draining of mires and woodland areas have influenced many ponds and vernal pools. Especially in woodland areas with slightly higher soil quality, many ponds and vernal pools have disappeared (Dervo et al. 2016). Climate change also influences freshwater ecosystems to an increasing degree and the effects are at this stage difficult to predict.

A significant proportion of the impacts on freshwater took place prior to 1969 and are therefore not taken into consideration as the Red List assessment in 2018 only goes back 50 years in time. This applies particularly to hydropower development, where approximately three-quarters of the affected waterbody area was regulated more than 50 years ago.

Existing knowledge

With the exception of Lime-rich ponds, Vernal pools, Small shallow lakes and Lime-rich freshwater swamp L4-3, the Red List assessment of limnic waterbody systems is based on data collected via environmental monitoring in accordance with the Water Management Regulations (NN 2015, Vann-Nett 2018). This data encompasses ecological condition assessments of 58% of the freshwater lake area in Norway, and includes both heavily modified and natural water entities. A water resource that has changed character to a considerable degree due to anthropogenic physical changes is defined as a heavily modified water entity (HMWE – heavily modified water entity).

With use of the A-criterion (reduction in total area), a proportion of the heavily modified water entities are defined as lost. Heavily modified waterbodies are categorized into four classes based on their ecological condition: very poor, poor, moderate or good ecological potential (Vann-nett 2018). We have estimated that the proportion of the ecological type that has disappeared corresponds to the sum of the area with a very poor or poor ecological potential and 50 % of the area with moderate ecological potential. This comprises 29 % of the heavily modified water entities.

Data from NVE (www.nve.no/karttjenester) regarding lakes in Norway has been used to estimate the proportion of lakes that have been regulated in the past 50 years (25 % of the lake area, based on the year of regulation). The regulated proportion is further deemed to represent variation in general impact over time. HMWE-areas that have disappeared in the past 50 years do not encompass areas that were regulated before 1969 in the Red List assessment (75 % of the lake area). This means that 29 % of the HMWE-area acquired after 1968 is deemed to represent the area that has disappeared in the past 50 years.

With assessment on the basis of criterion B2, the area data from Vann-Nett is used along with map data to decide the area of occurrence for surface waterbodies. The results from assessments using criteria A and C are used to document that the assessment entity is in persistent decline.

With assessment on the basis of criterion C1, the proportion of the area of the ecosystem type that is degraded is evaluated. Different degrees of degradation are estimated based on data collected for the purpose of undertaking ecological condition assessments in accordance with the Water Management Regulations. See the table below: 

Lime-rich ponds, Vernal pools and Small, shallow lakes, as well as Lime-rich freshwater swamp L4-3 is assessed for the Red List based on ecological condition assessments contained in the NIVA database of lime-rich lakes in Norway (Mjelde 2016, and Mjelde unpublished data), as well as the NINA database of occurrences of Northern crested newt Triturus cristatus (Dervo unpublished data).

With the exception of the major type Lime-rich (helophyte) swamp (L-4) the existing data is limited to Red List assessments carried out for major types under the major-type group Freshwater bed systems (L), as well as for Meromictic lakes F-3.

Knowledge gaps

Surveying of inland surface waters currently takes place in accordance with the Water Management Regulations (NN 2015). Surveying of ecosystem types in freshwater using NiN has not yet been implemented at the national level, with the exception of research and development (R&D) activities that include the aim of developing a survey guide. To be able to assess changes over time, as required with Red List assessments, the establishment of long time series should be emphasized, something which is currently undertaken at a national level to satisfy the requirements of the Water Management Regulations. Consequently, there is a clear need to harmonize future NiN-surveying with surveying carried out in accordance with the Water Management Regulations so that available resources can be used most effectively. In this context, it is crucial to take into account that it is likely that there are endangered ecosystem types, in freshwater, that are not covered by environmental monitoring carried out in accordance with the Water Management Regulations alone.

Expert Committee

The expert committee for freshwater ecosystem types was comprised of Ingebrigt Uglem (chair), Børre Dervo, Marit Mjelde, Ann Kristin Schartau and Martin Svenning. 

Acknowledgements

To Erik Brandrud and Anders Lyngstad from the wetlands committee contributed to the work. Bjørnar Dervo contributed with map analysis. We would also like to thank Rune Halvorsen, Lars Erikstad, Snorre Henriksen, Anne-Britt Storeng and Lars Stasberg for contributing with data, good discussions and useful suggestions.

References

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DN (2011). Handlingsplan for kalksjøer. Direktoratet for naturforvaltning, rapport 6-2011. [In Norwegian.]

Halvorsen R, et al. (2016). NiN – typeinndeling og beskrivelsessystem for natursystemnivået. – Natur i Norge, Artikkel 3 (versjon 2.1.0): 1–528 (Artsdatabanken, Trondheim; http://www.artsdatabanken.no.) [In Norwegian.]

Henriksen A, Skjelkvåle BL, Mannio J, Wilander A, Jensen JP, Moiseenko T, Harriman R, Traaen T, Fjeld E, Vuorenmaa J, Kortelainen P, Forsius M (1997). Results of national lake surveys (1995) in Finland, Norway, Sweden, Denmark, Russia Kola, Russia Karelia, Scotland and Wales. NIVA-report OR-3645.

Miljøstatus (2018). www.miljostatus.no  [In Norwegian.]

Mjelde M (2016). Oppsummering av kunnskap om kalksjølokaliteter som er «utvalgt naturtype». NIVA-rapport lnr. 6998-2016. [In Norwegian.]

NN (2015). Klassifisering av miljøtilstand i vann, Økologisk og kjemisk klassifiseringssystem for kystvann, grunnvann, innsjøer og elver. Veileder 02:2013, revidert 2015. hwww.vannportalen.no/veiledere/ [In Norwegian.]

Schartau AK, Dolmen D, Hesthagen T, Mjelde M, Walseng B, Ødegård F, Økland J, Økland KA, Bongard T (2008). Ferskvann. In: Miljøforhold og påvirkninger på rødlistearter. Artsdatabanken, Norge (www.artsdatabanken.no). [In Norwegian.]

Statens kartverk (2010). Arealstatistikk for Norge. [In Norwegian.]

Vann-nett (2018). www.vann-nett.no/portal, 06.03.2018. [In Norwegian.]