H3.1 OPEN-WATER LOTIC (RIVERS AND STREAMS)

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Habitats Natural History of Nova Scotia, Volume I

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© Nova Scotia Museum of Natural History

H3.1Open-waterLotic (Rivers andStreams)

H3.1 OPEN-WATER LOTIC (RIVERS AND STREAMS)

The open-water habitat in rivers and streams is thebody of water flowing through the channel. The char-acteristics of the water can vary considerably in rela-

tion to the morphology of the channel. Rivers andstreams in Nova Scotia are not deep enough to createlayering in the water column.

Plate H3.1.1: Drysdale Falls, Colchester County (sub-Unit 521a). An open-water stream habitat with a waterfall and associated cliff habitat (H5.3).The forest is a spruce, hemlock, pine association (H6.2.6). Photo: R. Merrick

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Natural History of Nova Scotia, Volume I Habitats

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FORMATION

The dominant feature of all lotic environments is thecontinuous movement of water and currents, whichcuts the channel, molds the character of the streamand influences the chemical and organic composi-tion of the water.1 Water running off the land followscourses of least resistance and develops these asdistinct channels by erosion. Young or rejuvenatedstreams, with a high velocity, erode more than theydeposit.

Water in slow-moving rivers reflects the charac-teristic of the terrain; nutrient level and sedimentload vary according to region. The slow-movingstream often develops a floodplain, meanders, andassociated features and terminates in a lake orestuary.

PHYSICAL ASPECTS

1. Water conditions: variables include conductiv-ity, temperature, turbidity, light, seasonal varia-tions. (Chemical composition, includingdissolved nutrients, depends on bedrock in rap-idly-moving streams.)

2. Air-water interaction: wind influences turbulenceand gas exchange (O2 and CO2 ).

3. Land-water interaction: variable conditions aredetermined by enclosing land forms, turbidity,runoff with products of erosion and nutrientsupply.

4. Bottom-water interaction: turbidity, nutrientsupply.

ECOSYSTEM

The lotic is primarily determined by the velocity ofthe current, which can create either slow-moving orfast-moving streams; each has very distinct charac-teristics. The base of the food chain is dependent ondetritus from upstream or from the edges. In slow-moving streams, plant and animal communitieslargely resemble those found in lentic (lake andpond) habitats. The significant phytoplanktonpopulations that usually exist contribute to a higherrate of primary productivity than that found in fast-moving steams. The level of productivity is depend-ent upon water temperature and the amount of nu-trient input received from the surrounding environ-ment, and therefore subject to seasonal variation.The diversity of consumer organisms varies accord-ing to the physical conditions and vegetation. Plank-tonic populations are relatively high, although notas dense as those found in lakes.

In fast-moving streams, there is very little pri-mary production in the open-water habitat, due tothe velocity and turbulence of the current.Populations of consumer organisms (mainlyparticulate feeders) are low. Riffle areas providevaluable habitat for juvenile trout and salmon. Poolsare important resting areas for several fish species,including Atlantic Salmon. The quality of these ar-eas can be adversely affected when shade trees areremoved from the banks.

SUCCESSIONAL SEQUENCE

The normally understood process of ecological suc-cession does not apply to open water. In slow-mov-ing steams, the development of habitat dependsupon the depositional and erosional characteristicsof the river. The fast-flowing, young stages ofstreams will always be present as the river erodesthe landscape. Over time, the young stage will ma-ture into a slow-moving stream, but it can be reju-venated when a geological obstacle (e.g., a water-fall) is encountered. In mature streams, there is aprogressive downstream movement of meanders,leaving shallow or deep pools, backwaters, braidedchannels and oxbow ponds. There is an associatedchange in the character of the open water.

PLANTS

Vegetation in the lotic open-water habitat consistsmainly of phytoplankton found in slow-movingstreams. There are no plankton species unique torivers; those found there originate mostly from back-waters or lakes. Several species of desmids and dia-toms are present in slow-moving rivers, althoughabundance is much lower than in lakes.

ANIMALS

Some zooplankton species and rotifers can be foundin slow-moving streams. Their abundance dependson the amount of the predation from invertebratesand small fish.

Most fish inhabiting fresh water in Nova Scotiawill utilize this environment at some stage in theirlife cycle. Fish species such as Redbelly Dace andWhite Sucker, and introduced species such as BrownTrout are commonly found in slow-moving streams.Fast-moving streams provide excellent habitat formany kinds of fish, including Brook Trout, AtlanticSalmon parr, Common Shiner, White Suckers andYellow Perch.

H3.1Open-water

Lotic (Rivers andStreams)

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Bird species associated with rivers include mer-gansers, Black Ducks, Spotted Sandpipers and BeltedKingfisher. Mammals commonly found in rivers areWater Shrews, Star-nosed Moles, Muskrats, otters,mink and beavers.

SPECIAL FEATURES

• Tidal rivers occur when the lower reaches of thehabitat are influenced by the sea. The mixing offresh and salt water creates conditions suitablefor brackish water species.

• Some marine-fish species enter freshwatersystems through estuaries.

• Special adaptations of stream organisms.• The effects of acid precipitation on rivers and

streams occurs mainly in southwesternNova Scotia.

• The heating effect of shade removal due totree cutting.

• River rejuvenation, including the occurrenceof rapids and falls, especially along theAtlantic coast.

• Important recreational fisheries, particularlyAtlantic Salmon and Brook Trout.

• Stream flow is harnessed for milling or hydro-electric-power generation.

DISTRIBUTION

Slow-moving streams are found in all regions of theprovince, except where high ground occurs close tothe sea. Some of the well-developed larger river sys-tems include the Tusket, Medway, Mersey, LaHave,

St. Marys (Region 400); the Shubenacadie andStewiacke (Region 500); the Cornwallis andAnnapolis (Region 600).

Fast-moving streams occur throughout the prov-ince in upland areas. These include the Cape Bretonhighlands (Regions 100 and 200), the Cobequid Hills(Region 300), North Mountain (District 710), andSouth Mountain (District 420). Slow-movingstreams flowing to the Atlantic Ocean are often re-juvenated as they pass through the Meguma bed-rock near the Atlantic Coast. Examples of this oc-currence are the Musquodoboit River (Units 413aand 453) and the St. Marys River (Unit 842).

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Associated TopicsT6.1 Ocean Currents, T6.4 Estuaries, T8.1 Freshwa-ter Hydrology, T8.2 Freshwater Environments, T10.9Algae, T11.5 Freshwater Wetland Birds and Water-fowl, T11.11 Small Mammals, T11.13 Fresh WaterFishes, T11.15 Amphibians and Reptiles, T11.16Land and Freshwater Invertebrates, T12.8 Freshwa-ter and Resources

Associated HabitatsH3.2 Open-water Lentic (Lakes and Ponds), H3.3Bottom Lotic (Rivers and Streams), H3.5 Water’sEdge Lotic (Rivers and Streams)

References1 Smith, R.L. (1990) Ecology and Field Biology.

Harper and Row, New York.

H3.1Open-waterLotic (Rivers andStreams)

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H3.2 OPEN WATER LENTIC (LAKES AND PONDS)

Plate H3.2.1: A pond at Northport, Cumberland County (sub-Unit 521a). Aquatic plants include Potamogeton and Juncus. Photo: D.S. Davis

The open-water habitat of lentic environments (i.e.,lakes and ponds) includes the limnetic and profundalzones of the water column (see Figure T8.2.2). Thelimnetic zone is the area beyond which rooted plantsgrow and extends vertically to the depth of maximum

sunlight penetration. The profundal zone is the deeper(and often colder) water below the level of light pen-etration. Most lakes in Nova Scotia are deep enoughto have open-water habitats. Most ponds are shallowand support submerged vegetation throughout.

H3.2Open-water

Lentic (Lakesand Ponds)

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FORMATION

The formation of open-water habitats in lentic en-vironments relates to the origin of the lake or pond.Lakes in Nova Scotia tend to be of glacial origin.Ice-scouring results in depressions in the bedrockor surface irregularities in glacial drift. Lakes andponds can also be formed due to damming by land-slides, flood debris, or hydroelectric dams. Pondscan form when a lake is infilled with organic debrisor mineral sediment; by the natural cutoff of a me-andering river (oxbow), or by solution of gypsum orlimestone (sinkhole). The open water is influencedby precipitation, flushing rates, and drainage. Wa-ter levels can fluctuate seasonally.

PHYSICAL ASPECTS

1. Water conditions: conductivity, temperature,turbidity, light, seasonal variations. (Chemicalcomposition, including dissolved nutrients,depends on bedrock.)

2. Air-water interaction: (O2 and CO2 ), windinduces mixing of water column, turbulenceand gas exchange.

3. Land-water interaction: enclosing land forms,turbidity, runoff with products of erosion andnutrient supply, flushing rates.

4. Drainage: open water (lakes); poorly drained,partially open water (ponds)

ECOSYSTEM

Most primary production occurs in the limneticzone of the open-water habitat. Phytoplankton car-ries out photosynthesis in the limnetic zone andproduces oxygen in the water. Zooplankton con-sumes the phytoplankton and is, in turn, eaten byhigher animals, such as insects and fish.

The amount of primary production byphytoplankton relates to the nutrients, the contentmorphology and the flushing rate of the lake orpond. In the spring, a large influx of nutrients canproduce a rapid growth of phytoplankton, knownas a “bloom”. Herbivorous zooplankton respondsto the increase in phytoplankton. The amount ofbloom (i.e., how green the lake appears) is thoughtto be controlled by the amount of grazing done bythe zooplankton.

The profundal zone is a cooler, low-productivityenvironment characterized by a high abundance andlow diversity of oxygen-demanding species. Thesespecies may depend on the limnetic zone for food.

In deep lakes, vertical stratification is commonin summer, and the cool-water organisms accumu-late at the thermocline (see Figure T8.2.1), wherethey depend on the limnetic zone for their foodsources. Temperature and wind changes (e.g., infall and spring) create a mixing, and the nutrientsdeposited on the bottom rise and are available tophytoplankton for production.


The normally understood process of ecological suc-cession does not apply to open water. In the earlystages of succession, lakes slowly begin to infill fromeroding shoreline materials. A vertical erosional-depositional process also takes place within the lake.Infilling of the lake basin results from suspendedsediment being brought into the system by inflowingstreams and rivers. This sediment is deposited inthe deeper parts of the lake until the bottom is slowlybuilt up to a flat surface. The water level then be-comes so shallow that wave action decreases anderosion declines to a very slow rate. At this point,the lake begins to resemble a pond. The siltationprocess continues until the open-water habitat dis-appears, giving rise to bog, fen, swamp or marshhabitats. The rate at which this occurs depends uponthe amount of siltation, the rate of production oforganic material and the rate of decomposition.

PLANTS

The open water of lakes and ponds contains nu-merous phytoplankton species. Diatoms anddesmids are common in oligotrophic and distrophicconditions, while blue-green algae are abundant ineutrophic lakes (see Topic T8.2). Duckweeds(Lemma) and Spirodella.

ANIMALS

The planktonic community of the open water con-sists primarily of cladocerans (water fleas),copepods, rotifers, air-breathing insects in adultform (e.g., water beetles) and larval form (e.g. mos-quitoes). The zooplankton is a primary source offood for open-water fish species, such as BrookTrout, Golden Shiner and Yellow Perch. Black Duckis common in the open water during the summer.Osprey, Bald Eagles, cormorants and loons also uti-lize the open water for feeding.

H3.2Open-waterLentic (Lakesand Ponds)

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SPECIAL FEATURES

• Amphibian populations in ponds• Ponds are greatly affected by local climatic and

geological conditions and are quite different invarious regions of the province. It is importantto understand the origin of a pond (e.g.,sinkhole, river oxbow, beaver dam)

• Landlocked populations of marine fish species(e.g., Atlantic Salmon)

• Freshwater jellyfish in Dartmouth lakes

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Associated TopicsT8.1 Freshwater Hydrology, T8.2 FreshwaterEnvironments, T10.2 Successional Trends in Veg-etation, T10.5 Seed-bearing Plants, T11.5 Freshwa-ter Wetland Birds and Waterfowl, T11.13 Freshwa-ter Fishes, T11.16 Land and Freshwater Inverte-brates

Associated HabitatsH3.1 Open-water Lotic (Rivers and Streams), H3.4Bottom Lentic (Lakes and Ponds), H3.6 Water’s EdgeLentic (Lakes and Ponds), H4.1 Bog, H4.2 Fen, H4.3Swamp

H3.2Open-water

Lentic (Lakesand Ponds)

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H3.3 BOTTOM LOTIC (RIVERS AND STREAMS)

H3.3Bottom Lotic(Rivers andStreams)

The streambed can comprise a variety of physicaland organic materials and can be either aneroding basin or a depositional environment. Thesesituations can alternate in the same stream, as maybe seen in riffles or ponds.

The bottom habitat of a lotic environment is thestreambed. In some conditions, this habitat can ex-tend across the entire width of the bed. In deeperchannels with sloped edges, zonation may create alittoral or edge habitat. In shallow channels or low-water conditions, the streambed can be exposed in-termittently.

Plate H3.3.1: LaHave River north of Bridgewater (Unit 433). Hard rock bottom is exposed due to low water levels in late summer. Photo: R. Merrick

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are six to seven metres wide.1 This is one reasonwhy small headwater streams are important spawn-ing and nursery areas for salmon and trout.


In slow-moving steams, the development of habitatdepends upon the depositional and erosional char-acteristics of the river. There is a progressive, down-stream movement of meanders, leaving shallow ordeep pools, backwaters, braided channels and ox-bow ponds. Sediment is deposited on the floodplainduring periods of high water, slowly filling up olderosional features. The plants and animals of theriver ecosystem are constantly adjusting to thesechanging conditions (see Figure T8.2.2).

The fast-flowing young stages of streams will al-ways be present as the river erodes the landscape.Over time, the young stage will mature into a slow-moving stream, but it can be rejuvenated when ageological obstacle (e.g., a waterfall) is encountered.

PLANTS

In slow-moving streams, vegetation is generallyabsent from the bottom habitat, except alongthe stream bank or hydrosere (see H3.5). In rap-idly moving streams, diatoms, blue-green algaeand green algae frequently are found on the rocksurfaces, and there may be dense growths ofliverworts and water mosses (e.g., Fontinalis), es-pecially near the stream banks. The floweringplants bur reed (Sparganium spp.) and pondweed(Potomogeton spp.) are firmly rooted into thegravel bottom and have narrow leaves to pro-vide the least amount of resistance to the cur-rent. The Riverweed (Podostemum cerato-phyllum), found on the LaHave River, is speciallyadapted to adhere to rock surfaces in fast-flow-ing water.

ANIMALS

In slow-moving streams, there is an abundance ofinvertebrates, dominated by aquatic insects.Nymphs and larvae of insects such as blackfly, drag-onfly, mayfly, stonefly and caddisfly, as well as adultand larval stages of waterbugs and water beetles,can be found. Many species of crustaceans, rotifers,nematodes and protozoans may also be present.Leeches, oligochaete worms and molluscs are plen-tiful in oligotrophic waters. Freshwater mussels maybe abundant in some areas and include some spe-cies with limited distribution. Various sponges and

FORMATION

The nature of a lotic environment is primarily de-termined by the velocity of the current, which cancreate either slow-moving or fast-flowing streams;each has very distinct characteristics. Fast-flowingstreams are often comprised of two interrelated en-vironments: the turbulent riffle area and the quietpool.

The bottom of slow-moving streams is comprisedmainly of sedimentary rock and thick glacial till.Soils consist of fluvial sediments; silt, mud, sand,gravel and varying amounts of organic material. Infast-moving streams, the bedrock is primarily re-sistant metamorphic or igneous rocks, with boul-der or coarse gravel bottom. Soils consist of sandand gravel, with some organic material, and are of-ten mobile due to water velocity.

PHYSICAL ASPECTS

1. Bedrock: (more important in fast-movingstreams) exposures of bedrock; particularlyresistant metamorphic or igneous rocks andboulder or coarse gravel bottom.

2. Soil: (more important in slow-moving streams)sand and gravel, with some organic material;often mobile due to water flow.

3. Relief: in hilly country, giving steep streamprofiles or, on plains, giving low profiles.

ECOSYSTEM

In slow-moving environments, silt and decaying or-ganic material accumulates on the bottom and be-comes the main food source for invertebrates. Pro-ductivity is associated mainly with the breakdownof this imported material, such as leaf litter, by her-bivores. Some of the organic material is exported,but some remains on site and can develop into peat.

In fast-moving streams, the riffle areas are re-sponsible for most of the primary production.Groups of plants that cling to the bottom are domi-nant and become as important to streams asphytoplankton is to lakes. They consist mainly ofmicroscopic and filamentous algae and can form aslippery cover on rocks during the summer months.However, this production is only temporary, as it issoon exported downstream by the strong currents.Populations of consumer organisms (chieflyparticulate feeders) are relatively low.

The width of the stream also affects the amountof production. Streams two metres wide are fourtimes as rich in bottom organisms as those which

H3.3Bottom Lotic

(Rivers andStreams)

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ectoprocts are also commonly found. All of theseorganisms are significant, as they consume organicdetritus and provide food for other bottom-dwell-ing animals. Adult newts and tadpoles inhabit theorganic debris in pools and slow-moving sectionsof streams.

In fast-moving streams, aquatic animals are welladapted to withstand the fast current and seasonalvariations in water level. The most important inver-tebrates are the aquatic larvae and nymphs of in-sects, especially stoneflies, mayflies and caddisflies.Blackfly larvae develop on rocks in the well-aeratedwater and form their pupae on the leaves of sub-merged plants. Other invertebrates include severalsponges (e.g., Spongilla) and freshwater mussels(e.g., Margaritifera), which are found in patches ofgravel. The larvae of river mussels are parasitic onthe gills of fish, an adaptation that counteracts thetendency for populations to be carried downstreamby the current.

The insect larvae of fast- and slow-movingstreams provides the primary food source for manyfish species, including White Sucker, American Eeland Bullhead Catfish (see Topic T11.16).

SPECIAL FEATURES

• The adaptation of plants and animals to resistcurrent flow and maintain their populations inthe stream.

• Important recreational fisheries, particularlyAtlantic Salmon and Brook Trout.

• Hibernation of Wood Turtles in slow-movingstreams.

• The association of the parasitic (glochidia)larval stage of mussels and fish. A rare mussel(Lampsilis cariosa) is found in the Sydney River.

• Modification of river courses by human activi-ties, such as gravel extraction and dam con-struction.

DISTRIBUTION

Slow-moving streams are found in all regions of theprovince, except where high ground is located closeto the sea. Some of the well-developed larger riversystems include the Tusket, Medway, Mersey,LaHave, St. Marys (Region 400); the Shubenacadieand Stewiacke (Region 500); the Cornwallis andAnnapolis (Region 600).

Fast-moving streams occur throughout the prov-ince in upland areas. These include the Cape Bretonhighlands (Regions 100 and 200), the Cobequid Hills(Region 300), North Mountain (Region 710), andSouth Mountain (Region 420). Slow-moving streamsflowing to the Atlantic Ocean are often rejuvenatedas they pass through the Meguma quartzite nearthe Atlantic Coast (Region 800). Examples of thisoccurrence are the Musquodoboit River and the St.Marys River.

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Associated TopicsT8.1 Freshwater Hydrology, T8.2 Freshwater Envi-ronments, T11.5 Freshwater Wetland Birds and Wa-terfowl, T11.11 Small Mammals, T11.13 FreshwaterFishes, T11.15 Amphibians and Reptiles, T11.16Land and Freshwater Invertebrates

Associated HabitatsH3.1 Open-water Lotic (Rivers and Streams), H3.4Bottom Lentic (Lakes and Ponds), H3.5 Water’s EdgeLotic (Rivers and Streams)

Reference1 Smith, R.L. (1990) Ecology and Field Biology.


H3.3Bottom Lotic(Rivers andStreams)

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© Nova Scotia Museum of Natural History Natural History of Nova Scotia, Volume I Habitats

H3.4 BOTTOM LENTIC (LAKES AND PONDS)

H3.4Bottom Lentic

(Lakes andPonds)

The bottom habitat of lentic environments (lakes andponds) is the depositional environment in the benthiczone (see Figure T7.2.2). The benthic zone is the areawhere decomposition takes place. It is associated withabundant biological activity and very little oxygen.

The dominant organisms are anaerobic bacteria.Closely associated with the benthic zone is the

profundal zone, which lies directly abovethe benthic zone but beneath the depth of light pen-etration (see H3.3).

Plate H3.4.1: Warren Lake in Victoria County, Cape Breton County (sub-Unit 552b). The steep-sided lake levels off at 31m and provides a high proportion ofbottom habitat compared to edge habitat. Photo: D. Davis

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FORMATION

The formation of the bottom habitat in lentic envi-ronments is closely associated with the origin of thelake or pond (see H3.2). Most lakes and pondbottoms in Nova Scotia are covered with “lake-bot-tom muck” (i.e., silt, clay or organic matter).

PHYSICAL ASPECTS

1. Bedrock: may occur in all bedrock types, as wellas in alluvial or glacial deposits.

2. Soil: deposition of silt, clay, etc.3. Relief: depressional topography4. Drainage: ponds and shallow lakes exhibit

seasonal fluctuation of water levels.

ECOSYSTEM

Although the abundance of life in the lentic bottomzone is not great, it is still significant. Organismsliving there have adapted to the conditions of softmud and low oxygen levels. During the summer, athermocline often develops in eutrophic lakes, caus-ing the bottom waters to become anerobic. How-ever, in deep oligotrophic lakes, where productivityis low, the supply of oxygen is not depleted bydecomposers. Under these conditions, theprofundal zone can support life, particularly fish,some plankton and certain cladocerans, which livein the bottom ooze.1


Succession relates to the deposition of sedimentsand organic material. As the deposits accumulate,the water level becomes more shallow and the zoneof light penetration (limnetic) increases. The nutri-ent supply in the bottom becomes available for pri-mary production, and plants begin to take root. Thebenthic zone is thus replaced by an extension of thelittoral zone. The character of the water columnalso changes.

PLANTS

No vegetation is associated with this habitat, sinceit lies beyond the depth of light penetration.

ANIMALS

The benthic community of this habitat, includingthe microscopic or meiofauna, have becomeadapted to conditions of soft mud and low oxygen.

The primary constituents are in three groups:1. bloodworms, including chironomid larvae

(midges) and annelids (worms)2. small clams of the family Sphaeriidae3. Chaoborus or “phantom midges”Many species of crustaceans, rotifers, nematodes,beetle larvae and protozoans may also be present.These organisms are significant, as they consumeorganic matter and provide food for other bottom-dwelling animals (see Topic T11.16). Fish species,such as Lake Whitefish and Brown Bullheads, arefound in oligotrophic lakes with sufficient oxygen.The bottoms of ponds are important habitats forthe larvae of amphibians such as salamanders andfrogs (tadpoles).

SPECIAL FEATURES

• Chironomid larvae (midges) have adapted tomany benthic habitats that have low concentra-tions of oxygen. The bright-red-coloured larvaehave a pigment which binds to oxygen andenables the storage of oxygen in this type ofhabitat. Their abundance may be an indicatorof poor water quality.

DISTRIBUTION

Deep-water lakes are found throughout Nova Scotia;however, they are more abundant on the hard, ig-neous and metamorphic bedrocks of the AtlanticInterior (Region 400).

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Associated TopicsT8.1 Freshwater Hydrology, T8.2 FreshwaterEnvironments, T9.1 Soil-forming Factors, T11.13Freshwater Fishes, T11.16 Land and FreshwaterInvertebrates

Associated HabitatsH3.2 Open-water Lentic (Lakes and Ponds), H3.6Water’s Edge Lentic (Lakes and Ponds)

References1 Smith, R.H. (1990) Ecology and Field Biology.


H3.4Bottom Lentic(Lakes andPonds)

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H3.5 WATER’S EDGE LOTIC(RIVERS AND STREAMS)

H3.5Water’s Edge


The water’s edge habitat, or hydrosere, of lotic envi-ronments is the extension of the streambed habitatonto the shore and is also referred to as the water’sedge component of riparian zones, characterized by

hydrophytic vegetation. The edge habitat in riversand streams is most obvious where deposition orstreambed gradient allows for zonation to occur.

Plate H3.5.1: Slow-moving section of MacLellan’s Brook, Inverness County (sub-Unit 551b). The stream margins are defined by energy changes.The left bank is permanently steep, undercut and has overhanging vegetation; the inward curve of the right bank fluctuates with seasonal water flow anddepositional activity, creating an ephemeral environment. Herbaceous plants colonize the cobble bar briefly during the height of summer.The elms in the background are the remnants of a floodplain forest (H6.1.3). Photo: R. Merrick

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FORMATION

The formation is influenced by water flow and depo-sition. During periods of high discharge, the edgehabitat will increase shorewards, possibly extend-ing to the edge of the floodplain. During periods oflow water or intermittent streams, the edge habitatdecreases, allowing dry-land vegetation to grow rightup to the water’s edge. The aquatic extension of thishabitat is also influenced by water levels, streamgradient and water clarity. This habitat supports avariety of plant species and provides food and coverfor animals that occupy the area and for those foundin adjacent aquatic or upland habitats. The habitatalso aids in reducing pollution from surroundingland areas by slowing runoff and decreasing ero-sion. In addition, the hydrosere provides shade thathelps maintain suitable water temperatures foraquatic life.

PHYSICAL ASPECTS

1. Bedrock: any bedrock and glacial till (fast-mov-ing stream–exposed bedrock; particularly resist-ant metamorphic or igneous rocks, and boulderor coarse gravel bottoms).

2. Soil: fluvial sediments, silt, mud, sand and gravel,with varying amounts of organic material; oftenmobile in fast-moving streams.

3. Relief: in depressions, gently undulating and slop-ing towards the coast.

4. Drainage: wet shoreline; seasonal fluctuation ofwater levels.

5. Water conditions: turbidity, deposition.

ECOSYSTEM

In slow-moving streams, the lotic hydrosere containsa diversity of plant communities, many of which arelocated in the numerous shallow channels and back-waters of the floodplain margins. Some of the organicmaterial produced is exported downstream; some,which may develop into peat, remains on site; some isconsumed by herbivores, such as aquatic insects.

In fast-moving streams, primary production islow because adverse conditions, such as coarse, mo-bile substrate, restrict plant growth. Production fromplants near the stream bank and marginal terres-trial vegetation is soon exported by the current. Fewconsumer organisms (mainly aquatic insects) canbe found. The quality of the ecosystem is directlyaffected by an increase in water temperature causedby the removal of shade trees from the stream banks.


In slow-moving steams, the development of habitatdepends upon the depositional and erosional char-acteristics of the river. There is a progressive down-stream movement of meanders, leaving shallow ordeep pools, backwaters, braided channels and ox-bow ponds. Sediment is deposited on the floodplainduring periods of high water, slowly filling up olderosional features. The plants and animals of theriver ecosystem are constantly adjusting to thesechanging conditions (see Figure T8.2.3).

The fast-flowing young stages of streams will al-ways be present as the river erodes the landscape.Over time, the young stage will mature into a slow-moving stream, but can be rejuvenated when ageological obstacle (e.g., a waterfall) is encountered.

PlantsIn slow-moving streams, the variable condition ofthe habitat results in a diversity of plant communi-ties along the stream bank. A distinct zonation inthe type of vegetation usually occurs. This is di-rectly related to substrate stability and drainage forplants located on the bank and to the current forthose found in the water. The type of vegetationfound along the bank is characteristic of other fresh-water habitats, including the hydrosere of ponds(H3.6), bogs (H4.1), fens (H4.2), swamps (H4.3) andfloodplain forest (H6.1). Aquatic plants adjacent tothe stream bank include rushes and sedges foundmainly in stony shallows. Water mosses (Fontinalisspp.) are often abundant. In calcareous water thealga Chara may also be present.

In fast-moving streams, emerging aquatic plantsmay be found along the stream banks where thecurrent is reduced. Aquatic mosses are also com-mon in this habitat.

AnimalsSimilar to plants of the hydrosere, the aquatic ani-mals of the slow-moving stream include the richdiversity described for bog, fen, and the hydrosereof ponds. There is an abundance of aquatic inverte-brates dominated by insects. Nymphs and larvae ofinsects such as blackfly, dragonfly, mayfly, stoneflyand caddisfly, as well as adult and larval stages ofwaterbugs and water beetles, can be found. Leeches,oligochaete worms and molluscs are plentiful inoligotrophic waters. Freshwater mussels may beabundant in some areas and include some specieswith limited distribution. Various sponges andectoprocts are also commonly found.

H3.5Water’s EdgeLotic (Rivers andStreams)

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Amphibians such as Mink Frogs, are commonand may breed and develop in the shallow backwa-ters and oxbow ponds. Wood Turtles often lay theireggs on sand stream banks. Most bird species aremainly associated with the adjacent forest habitats;exceptions to this are mergansers, Black Duck, Spot-ted Sandpiper, and Belted Kingfisher. A few mam-mals, such as the Water Shrew, Star-nosed Mole,Muskrat, otter, mink, and beaver, are characteristicof this environment.

In fast-moving streams, aquatic animals of thehydrosere are well adapted to withstand the sea-sonal variations in water level. The most importantinvertebrates are the aquatic larvae and nymphs ofinsects, especially stoneflies, mayflies andcaddisflies. Blackfly larvae develop on rocks in thewell-aerated water and form their pupae on theleaves of submerged plants. Other aquatic inverte-brates include sponges (e.g., Spongilla), althoughfewer in number than lakes or slow moving streams,and freshwater mussels (e.g. Margaritifera), whichare found in patches of gravel. The larvae of rivermussels are parasitic on the gills of fish, an adapta-tion that counteracts the tendency for populationsto be carried downstream by the current.

The insect larvae of fast- and slow-movingstreams provides the primary food source for manyfish species, including Lake Chub, White Sucker andThreespine Stickleback. During times of low water,fish tend to concentrate in the larger pools.

SPECIAL FEATURES

• Special adaptations of stream organisms.• Breeding habitat for Wood Turtles.• The heating effect of shade removal due to

tree cutting.• Modification of river courses by human

activities, such as gravel extraction and damconstruction.

DISTRIBUTION

Slow-moving streams are found in all regions of theprovince, except where high ground is located closeto the sea. Some of the well-developed larger riversystems include the Tusket, Medway, Mersey,LaHave, St. Marys (Region 400); the Shubenacadieand Stewiacke (Region 500); the Cornwallis andAnnapolis (Region 600).

Fast-moving streams occur throughout the prov-ince in upland areas. These include the Cape Bretonhighlands (Regions 100 and 200), the Cobequid Hills(Region 300), North Mountain (District 710) andSouth Mountain (District 420). Slow-movingstreams flowing to the Atlantic Ocean are often re-juvenated as they pass through the Meguma bed-rock near the Atlantic Coast. Examples of this oc-currence are the Musquodoboit River (Units 413aand 453) and the St. Marys River (Unit 842).

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Associated TopicsT8.1 Freshwater Hydrology, T8.2 FreshwaterEnvironments, T9.1 Soil-forming Factors,T10.5 Seed-bearing Plants, T10.7 Pteridophytes(Ferns and Their Allies), T10.8 Bryophytes Mosses,Liverworts and Hornwarts, T10.9 Algae, T11.5 Fresh-water Wetland Birds and Waterfowl, T11.11 SmallMammals, T11.13 Freshwater Fishes, T11.15Amphibians and Reptiles, T11.16 Land and Fresh-water Invertebrates

Associated HabitatsH3.1 Open-water Lotic (Rivers and Streams), H3.3Bottom Lotic (Rivers and Streams), H3.6 Water’sEdge Lentic (Lakes and Ponds), H4.1 Bog, H4.2 Fen,H4.3 Swamp, H6.1 Hardwood Forest.

H3.5Water’s Edge


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H3.6 WATER’S EDGE LENTIC (LAKES AND PONDS)

H3.6Water’s EdgeLentic (Lakesand Ponds)

The water’s edge, or hydrosere, habitat of lentic eco-systems is the marginal edge of lakes and ponds, whererooted plants can grow. The habitat includes shallowwater, where sunlight can penetrate to the bottom,

commonly known as the littoral zone (see FigureT8.2.2). The littoral zone often applies to the entirearea of ponds, which are generally shallow enough tosupport submerged vegetation throughout.

Plate H3.6.1: A sheltered lake shore at Lake Egmont, Halifax County (sub-Unit 511a), showing floating leaves of pond-lilies and emergent Pickerel-weed andrushes. Photo: D.S. Davis.

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FORMATION

The water’s edge habitat forms at the edge of a lakeor pond and is always wet, though the water levelmay vary seasonally and is invariably frozen forsome period during the winter. It is best developedin open, shallow conditions on glacial till in areas oflow relief.

PHYSICAL ASPECTS

1. Bedrock: any bedrock and glacial till (particu-larly resistant metamorphic or igneous rocks, andboulder or coarse gravel bottoms).

2. Soil: fluvial sediments, silt, mud, sand and gravel,with varying amounts of organic material; oftenmobile.

3. Relief: in depressions, gently undulatingsandscape.

4. Drainage: wet shoreline; seasonal fluctuation ofwater levels; variations in water levels can varyin relation to hydrodams – lake levels fluctuateartificially.

5. Water conditions: turbidity, deposition

ECOSYSTEM

Aquatic life is most abundant in the shallow wateraround the edges of lentic environments. Plants andanimals generally establish a distinct zonation whichvaries mainly according to water depth (FigureH3.6.1). Rooted macrophytes, such as sedges, liliesand rushes, which grow in shallow, sheltered areas,are the primary producers. They contribute substan-tially to the productivity of lentic environments andprovide a large input of organic material to the eco-system.

Plant growth relies primarily on the availabilityof nutrients from sediments found in the benthichabitat (see H3.4). Macrophytes enhance therecycling of nutrients such as phosphorus byputting them back into circulation from thesediments. This process can produce a buildup ofnutrients, resulting in increased productivity andthe eutrophication of lakes and ponds. Thehydrosere also provides favourable habitat for nu-merous animal species, including invertebrates,amphibians, fish, waterfowl, and small mammals.


The process of succession slowly converts thehydrosere into a terrestrial habitat. The sedimenta-tion and subsequent infilling of a shallow water zone

occurs from several sources. These include organicmaterial produced by plants, silt imported from sur-face runoff, and the input of suspended sedimentfrom streams. In the early stages of succession, thereis a relatively large area of water with distinct zonesof plants around the margins. As the pond silts up,these zones progress toward the middle, reducingthe amount of water, giving rise to bog, fen, swampor marsh habitats. The pace at which this takes placedepends upon the rates of siltation, the rate of or-ganic production and the rate of decomposition.

PLANTS

The plants occupying the lentic hydrosere can beclassified according to four main zones, as shownin Figure H3.6.1.1. The terrestrial zone of vegetation is character-

ized by members of the sedge family and sphag-num mosses, and is associated with various fenor swamp plants. In lakeshore areas with a min-eral substrate, an association between two plants,Water Lobelia (Lobelia dortmanna) andLoosestrife (Lysimachia spp.),often develops.This relationship remains dormant until latesummer, when water levels are lowest. At thistime, these two species become the dominantvegetation in this zone. Other types of plantsinclude Twig-Rush (Cladium), Pipewort(Eriocaulon) and Broad-leaf (Spartina pectinata).

2. The zone of emergent vegetation is character-ized by rooted plants with most of their surfaceabove the water. Some of the more commonemergent plants found in Nova Scotia includePickerel-weed (Pontedaria), Spike Rush (Eleo-charis), Bog Buckbean (Menyanthes), Pipewort(Eriocaulon), Arrowhead (Sagittaria), cattail(Typha) and bulrush (Scirpus). Plant growthrelates to the pH of the water, the degree of ex-posure and geographic location. The emergentplants, together with those on the shoreline, forman important link between water and land envi-ronments. They are used for food and shelter byamphibians and aquatic mammals, and providea convenient means for acquatic insects to enterand exit the water.1

3. The zone of floating plants is characterized byplants with leaves on or just below the watersurface, and emergent flowers. These may beeither rooted or not rooted. Common species in-clude Water-lily (Nymphaea), pond lily (Nuphar),and pondweed (Potamogeton). In small ponds withlittle surface movement, duckweed (Lemna) isusually found covering the surface. The

H3.6Water’s EdgeLentic (Lakes

and Ponds)

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undersurfaces of lily pads provide suitable rest-ing and oviposit sites for various animals.

4. The zone of submerged vegetation is locatedbetween the open-water habitat (see H3.2) andthe shore. The character of the zone varies withthe region. The plants generally require oligotro-phic water conditions, rather than the distrophicsituations which receive input from acidic envi-ronments, such as bogs. Some of the commonlyfound plants include pondweed (Potamogetonspp.), milfoil (Myriophyllum spp.), White Water-crowfoot (Ranunculus trichophyllus), CanadianPondweed (Elodea canadensis), and the calcare-ous algae Stonewort (Chara spp.). Found mainlyin gypsum or limestone bedrock areas (Region500), Stonewort often indicates the inner bound-ary of the littoral zone, as it is able to grow inrelatively deep water.

ANIMALS

The plant growth at the edges of lakes and pondsprovides food for a wide variety of invertebrates, themost important of which are insects. Adult beetlesand bugs are common and are mostly predatory, feed-ing mainly upon the aquatic larvae and nymphs ofother insects, such mosquitos, mayflies, caddisfliesand dragonflies. Other species include planktonic andbenthic species of crustaceans, as well as numerousostracods, cladocerans and copepods. Other inverte-brates include one widespread species of amphipod(Hyalella azteca) and one isopod (Caecidotea com-

munis) which is found only in southwestern Nova Scotiaand Sydney River (Unit 531). Other invertebrates in-clude species of oligochaete worms, leeches, gastro-pods (snails) and bivalve molluscs (clams). The diver-sity of species other than flying insects is generally lim-ited. In small, isolated ponds, species require some formof introduction via a carrier (e.g., the pea clams may beintroduced by birds, insects or amphibians). During thesummer, small ponds generally experience long dryperiods, which requires many invertebrates either toestivate or hibernate until water levels rise.

The number of vertebrate species will vary ac-cording to the degree of isolation from larger watersystems and the geographic region. Most of the big-ger lakes provide for several distinct types of faunaassociated with different habitat conditions. The shel-tered shores where there is sediment deposition inthe hydrosere provide a habitat similar to that foundin ponds, and hence the types of animals present arequite similar. However, the diversity of fish species isgreater and the predation of invertebrates more sig-nificant in lakes than in ponds. Fish include BandedKillifish, Golden Shiner and young White Sucker. Insmall isolated ponds, fish may be totally absent,which is a distinct advantage for the larvae of sala-manders and tadpoles of frogs that utilize the pondsduring their early stages of development. Turtles arealso mobile and may colonize the larger ponds. Theyuse the sand and gravel banks to lay their eggs. Someamphibians, such as the Green Frog, stay in the edgehabitat of ponds as adults; others may disperse tothe woods.

H3.6Water’s EdgeLentic (Lakesand Ponds)

Figure H3.6.1a Zonation of aquatic vegetation at the edge of a dystrophic pond or lake in association with a bog.

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Lakes with exposed rocky or cobble shorelinesare subject to considerable wave action, which makesthe habitat largely unsuitable for rooted vegetation,with the result that animals are correspondinglysparse. Some insect larvae, such as the caddisfly(Helicopsyche spp.), and snails (Physa spp., Lymnaeaspp., and Amnicola limosa) are found attached tostones. This is generally an impoverished state of thesheltered shore fauna. Mussels such as Elliptiocomplanata burrow in patches of gravel. In addition,the Green Sponge and several species of ectoproctscan be found. Spotted Sandpipers are commonly seenalong the shore. Migratory waterfowl, such as BlackDucks and Canada Geese, as well as species of loons,cormorants and gulls are also found in this habitat.Other birds common to the pond habitat include theRed-winged Blackbird, herons, bitterns, smallpasserines and aerial foragers, such as Tree Swal-lows. Mammals that may be present include mink,beaver, otter, and Muskrat.

DISTRIBUTION

Found throughout Nova Scotia

H3.6Water’s EdgeLentic (Lakes

and Ponds)

SPECIAL FEATURES

• The rare flora of the coastal-plain shoreline(southwestern Nova Scotia) includes PlymouthGentian and Pink Coreopsis.

• The hydrosere habitat of lakes and pondssupports the developmental and adult stages ofnumerous invertebrates and vertebrates. Manyof these would not exist without the presence ofthe hydrosere.

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Associated TopicsT8.1 Freshwater Hydrology, T8.2 Freshwater Envi-ronments, T9.1 Soil-forming Factors, T10.2 Succes-sional Trends in Vegetation, T10.5 Seed-bearingPlants, T10.9 Algae, T11.5 Freshwater Wetland Birdsand Waterfowl, T11.11 Small Mammals, T11.13Freshwater Fishes, T11.15 Amphibians and Reptiles,T11.16 Land and Freshwater Invertebrates

Associated HabitatsH3.2 Open-water Lentic (Lakes), H3.4 Bottom Lentic(Lakes and Ponds), H3.5 Water’s Edge Lotic (Riversand Streams)

References1 Odum, E.P. (1971) Fundamentals of Ecology.

W.B. Saunders, Philadelphia.

Figure H3.6.1b: Zonation of aquatic vegetation at the edge of an oligotrophic pond or lake in association with a fen.

H3.1 OPEN-WATER LOTIC (RIVERS AND STREAMS)

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