| Tayside Biodiversity - Tayside
Biodiversity Action Plan - Water - Mesotrophic Lochs |
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INTRODUCTION
Mesotrophic lochs were identified
by the UK Biodiversity Group as a key habitat of particular national
importance that required specific work over and above that detailed
in the standing open waters broad habitat plan. Much of the Standing
Open Waters Habitat Action Plan therefore applies, but issues particularly
relevant to mesotrophic lochs are examined here.
DEFINITION
Mesotrophic lochs are defined either as those with a moderately rich plant nutrient
environment, particularly nitrogen and phosphorus, or those having a range of
submerged plant communities, principally NVC (National Vegetation Classification)
types 5A and 5B.
Type 5A is characterised by Shore-weed Littorella uniflora, Alternate flowered
water milfoil Myriophyllum alterniflorum, Stoneworts Nitella spp., Small pondweed
Potamogeton berchtoldii and Canadian pondweed Elodea canadensis, (an alien
species). Type 5B is characterised by Floating pondweed Potamogeton natans, and
White water lilies Nymphaea alba.
However, lochs may be historically mesotrophic but have been subsequently changed
to eutrophic by human activity. This type of loch has been included within this
Plan as it may be possible in the long term to return them to a more natural
nutrient status. |
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CURRENT STATUS
AND EXTENT OF HABITAT
There are several mesotrophic lochs in Tayside, mainly located along the fringe
of the uplands. These are listed under key sites, together with a brief assessment
of their current status. It is apparent from the list that many lochs that were
probably historically mesotrophic have now become eutrophic and others are threatened
by nutrient enrichment. The Lowes chain of lochs between Dunkeld and Blairgowrie,
which is of international significance, remains of high quality, but is threatened.
Remediation of culturally eutrophic lochs is usually difficult, but efforts are
being made, for example, to restore Loch Leven to a more natural nutrient status.
Naturally mesotrophic lochs are severely threatened and positive action is required
to ensure the survival of this important habitat. Formerly mesotrophic lochs
which have lost their characteristic animal and plant communities are not regarded
as a national priority for remediation as it is considered that resources are
best directed at maintaining and improving relatively unimpacted examples.
KEY SITES
The national rarity and decline of naturally mesotrophic lochs means that all
of those present within the region merit inclusion as key sites. However, a few
that particularly stand out are the Lowes chain of lochs between Dunkeld and
Blairgowrie (Craiglush, Lowes, Butterstone, Clunie and Marlee), the Black Loch
at Cleish, and Loch Moraig. These represent relatively unpolluted or pristine
examples. Loch Leven, possibly once a mesotrophic loch, but now highly eutrophic,
is of considerable importance and represents a classic example of the challenges
faced in restoring lochs such as these to their natural status. |
Loch
Moraig (SSSI) -
Black Loch, Cleish (SSSI)
The Lowes chain of lochs of between Dunkeld and Blairgowrie
of international
significance (SSSIs and increasing candidate SAC):
Loch of Lintrathen (SSSI)
Long Loch of Lundie (SSSI)
Crombie Reservoir
Loch Monzievaird
Drumore Loch (SSSI)
Laird’s Loch (SSSI)
Loch Leven (SSSI, SPA,
RAMSAR)
Rescobie Loch
Balgavies Loch |
Mesotrophic,
very high quality. A naturally mesotrophic loch, but there
are indications that land use within the catchment is having
an effect on the ecology of the loch.
Mesotrophic, very high quality. The only known naturally
mesotrophic loch in Tayside that has had no recent agricultural
improvement or afforestation within its catchment.
- Loch of Craiglush - oligo/mesotrophic, high quality.
- Loch of Lowes - mesotrophic, high quality, but indications
of increasing nutrient levels.
- Butterstone Loch - mesotrophic, high quality, but indications
of nutrient levels.
- Loch Clunie - mesotrophic, high quality, but indications
of elevated nutrient levels.
- Loch of Drumellie or Marlee - mesotrophic, high quality,
but indications of increasing nutrient levels.
Mesotrophic/eutrophic, artificial loch.
High quality, mesotrophic with notable fringing fen.
Artificial waterbody.
Status uncertain.
Mesotrophic loch.
Status uncertain.
Now eutrophic, may historically have been mesotrophic. Still
of very high conservation value.
Eutrophic, may historically have been mesotrophic.
Eutrophic, may historically have been mesotrophic. |
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Slender Niaid
A Naiad, the water nymph and lake dweller of Greek myth,
is found in Scotland...
An inconspicuous plant, the wonderfully named Slender Naiad
Najas flexillis is typically found growing submerged in clear
mesotrophic lochs where there is soft silty substrata.
Classed as ‘scarce’ in Britain, all the UK populations
are now only found in Scotland. Most of these populations
are found on the islands off the west coast, but there are
a few sites on the mainland. Tayside’s only known population
is found in the Lunan chain of lochs. It is thought to be
in decline because of eutrophication, but it may also be
due to excessive growth of other plants such as the invasive
Canadian pondweed Elodea canadensis. |
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NATURE
CONSERVATION IMPORTANCE
Mesotrophic lochs are frequently of particular nature conservation importance
for the exceptionally diverse plant communities they support and for rare species
such as Slender naiad Najas flexilis. Most mesotrophic lochs have SSSI status
and the Lowes chain of lochs is a candidate Special Area of Conservation (SAC)
for its populations of Slender naiad. These designations reflect the importance
and scarcity of this habitat.
KEY SPECIES
Some species, such as the Slender naiad are very characteristic of mesotrophic
lochs and their distribution is restricted
to these types of waterbodies. They, therefore, merit inclusion as key species
for their nationally important populations.
Many of the key species associated with mesotrophic lochs such as the Common
scoter Melanitta nigra, Black-necked
grebe Podiceps nigricollis and the Osprey Pandion haliaetus are also associated
with other open standing water, but
mesotrophic lochs provide good habitat and may maintain significant populations.
P = UK Priority species C = UK species of conservation concern |
| Mammals |
Water vole |
Arvicola terrestris |
P |
| Otter |
Lutra lutra |
P |
| Daubenton’s bat |
Myotis daubentoni |
C |
| Birds |
Common scoter |
Melanitta nigra |
P |
| Osprey |
Pandion haliaetus |
C |
| Black-necked grebe |
Podiceps nigricollis |
C |
| Whooper swan |
Cygnus cygnus |
C |
| Wigeon |
Anas penelope |
C |
| Gadwall |
Anas strepera |
C |
| Pink-footed goose |
Anser brachyrhynchos |
C |
| Greylag goose |
Anser anser |
C |
| Pochard |
Aythya ferina |
C |
| Goosander |
Mergus merganser |
C |
| Amphibians |
Palmate newt |
Triturus helveticus |
C |
| Plants |
Slender naiad |
Najas flexilis |
P |
| Slender stonewort |
Nitella gracilis |
P |
| Pillwort |
Pilularia globulifera |
P |
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NATIONAL
BIODIVERSITY CONTEXT
There is a UK Habitat Action Plan for mesotrophic lochs. This has the following
objectives:
Maintain
the characteristic plant and animal communities of current
mesotrophic lochs.
Identify and implement effective remedial action to address
nutrient enrichment and pollution in mesotrophic lochs
by 2010. |
ECOLOGY AND MANAGEMENT
The ecology of mesotrophic lochs is critically dependent on nutrient levels.
The diverse macrophyte communities they support are due to the excellent conditions
they have for rooted plant growth. The moderate levels of nutrients they have
encourage plant growth, whilst not generally being sufficient to cause algal
blooms which can shut light out from rooted plants. Maintenance of natural nutrient
levels is, therefore, a key element in the management of mesotrophic lochs. To
achieve this a catchment based approach is required. |
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