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H3.1 Open-Water Lotic (Rivers and Streams)

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H3.1 Open-Water Lotic (Rivers and Streams) PAGE .............................................................. 428 ▼ H3.1 OPEN-WATER LOTIC (RIVERS AND STREAMS) The open-water habitat in rivers and streams is the tion to the morphology of the channel. Rivers and body of water flowing through the channel. The char- streams in Nova Scotia are not deep enough to create acteristics of the water can vary considerably in rela- layering in the water column. H3.1 Open-water Lotic (Rivers and Streams) 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 Habitats Natural History of Nova Scotia, Volume I © Nova Scotia Museum of Natural History .............................................................. PAGE 429 ▼ FORMATION In fast-moving streams, there is very little pri- mary production in the open-water habitat, due to The dominant feature of all lotic environments is the the velocity and turbulence of the current. continuous movement of water and currents, which Populations of consumer organisms (mainly cuts the channel, molds the character of the stream particulate feeders) are low. Riffle areas provide and influences the chemical and organic composi- valuable habitat for juvenile trout and salmon. Pools tion of the water.1 Water running off the land follows are important resting areas for several fish species, courses of least resistance and develops these as including Atlantic Salmon. The quality of these ar- distinct channels by erosion. Young or rejuvenated eas can be adversely affected when shade trees are streams, with a high velocity, erode more than they removed from the banks. deposit. Water in slow-moving rivers reflects the charac- SUCCESSIONAL SEQUENCE teristic of the terrain; nutrient level and sediment load vary according to region. The slow-moving The normally understood process of ecological suc- stream often develops a floodplain, meanders, and cession does not apply to open water. In slow-mov- associated features and terminates in a lake or ing steams, the development of habitat depends H3.1 estuary. upon the depositional and erosional characteristics Open-water Lotic (Rivers and of the river. The fast-flowing, young stages of Streams) PHYSICAL ASPECTS streams will always be present as the river erodes the landscape. Over time, the young stage will ma- 1. Water conditions: variables include conductiv- ture into a slow-moving stream, but it can be reju- ity, temperature, turbidity, light, seasonal varia- venated when a geological obstacle (e.g., a water- tions. (Chemical composition, including fall) is encountered. In mature streams, there is a dissolved nutrients, depends on bedrock in rap- progressive downstream movement of meanders, idly-moving streams.) leaving shallow or deep pools, backwaters, braided 2. Air-water interaction: wind influences turbulence channels and oxbow ponds. There is an associated and gas exchange (O2 and CO2 ). change in the character of the open water. 3. Land-water interaction: variable conditions are determined by enclosing land forms, turbidity, PLANTS runoff with products of erosion and nutrient supply. Vegetation in the lotic open-water habitat consists 4. Bottom-water interaction: turbidity, nutrient mainly of phytoplankton found in slow-moving supply. streams. There are no plankton species unique to rivers; those found there originate mostly from back- ECOSYSTEM waters or lakes. Several species of desmids and dia- toms are present in slow-moving rivers, although The lotic is primarily determined by the velocity of abundance is much lower than in lakes. the current, which can create either slow-moving or fast-moving streams; each has very distinct charac- ANIMALS teristics. The base of the food chain is dependent on detritus from upstream or from the edges. In slow- Some zooplankton species and rotifers can be found moving streams, plant and animal communities in slow-moving streams. Their abundance depends largely resemble those found in lentic (lake and on the amount of the predation from invertebrates pond) habitats. The significant phytoplankton and small fish. populations that usually exist contribute to a higher Most fish inhabiting fresh water in Nova Scotia rate of primary productivity than that found in fast- will utilize this environment at some stage in their moving steams. The level of productivity is depend- life cycle. Fish species such as Redbelly Dace and ent upon water temperature and the amount of nu- White Sucker, and introduced species such as Brown trient input received from the surrounding environ- Trout are commonly found in slow-moving streams. ment, and therefore subject to seasonal variation. Fast-moving streams provide excellent habitat for The diversity of consumer organisms varies accord- many kinds of fish, including Brook Trout, Atlantic ing to the physical conditions and vegetation. Plank- Salmon parr, Common Shiner, White Suckers and tonic populations are relatively high, although not Yellow Perch. as dense as those found in lakes. © Nova Scotia Museum of Natural History Natural History of Nova Scotia, Volume I Habitats PAGE .............................................................. 430 ▼ Bird species associated with rivers include mer- St. Marys (Region 400); the Shubenacadie and gansers, Black Ducks, Spotted Sandpipers and Belted Stewiacke (Region 500); the Cornwallis and Kingfisher. Mammals commonly found in rivers are Annapolis (Region 600). Water Shrews, Star-nosed Moles, Muskrats, otters, Fast-moving streams occur throughout the prov- mink and beavers. ince in upland areas. These include the Cape Breton highlands (Regions 100 and 200), the Cobequid Hills SPECIAL FEATURES (Region 300), North Mountain (District 710), and South Mountain (District 420). Slow-moving • Tidal rivers occur when the lower reaches of the streams flowing to the Atlantic Ocean are often re- habitat are influenced by the sea. The mixing of juvenated as they pass through the Meguma bed- fresh and salt water creates conditions suitable rock near the Atlantic Coast. Examples of this oc- for brackish water species. currence are the Musquodoboit River (Units 413a • Some marine-fish species enter freshwater and 453) and the St. Marys River (Unit 842). systems through estuaries. • Special adaptations of stream organisms. ○○○○○○○○ H3.1 • The effects of acid precipitation on rivers and Open-water streams occurs mainly in southwestern Associated Topics Lotic (Rivers and Streams) Nova Scotia. T6.1 Ocean Currents, T6.4 Estuaries, T8.1 Freshwa- • The heating effect of shade removal due to ter Hydrology, T8.2 Freshwater Environments, T10.9 tree cutting. Algae, T11.5 Freshwater Wetland Birds and Water- • River rejuvenation, including the occurrence fowl, T11.11 Small Mammals, T11.13 Fresh Water of rapids and falls, especially along the Fishes, T11.15 Amphibians and Reptiles, T11.16 Atlantic coast. Land and Freshwater Invertebrates, T12.8 Freshwa- • Important recreational fisheries, particularly ter and Resources Atlantic Salmon and Brook Trout. • Stream flow is harnessed for milling or hydro- Associated Habitats electric-power generation. H3.2 Open-water Lentic (Lakes and Ponds), H3.3 Bottom Lotic (Rivers and Streams), H3.5 Water’s DISTRIBUTION Edge Lotic (Rivers and Streams) Slow-moving streams are found in all regions of the References province, except where high ground occurs close to 1 Smith, R.L. (1990) Ecology and Field Biology. the sea. Some of the well-developed larger river sys- Harper and Row, New York. tems include the Tusket, Medway, Mersey, LaHave, Habitats Natural History of Nova Scotia, Volume I © Nova Scotia Museum of Natural History .............................................................. PAGE 431 ▼ H3.2 OPEN WATER LENTIC (LAKES AND PONDS) The open-water habitat of lentic environments (i.e., sunlight penetration. The profundal zone is the deeper lakes and ponds) includes the limnetic and profundal (and often colder) water below the level of light pen- zones of the water column (see Figure T8.2.2). The etration. Most lakes in Nova Scotia are deep enough limnetic zone is the area beyond which rooted plants to have open-water habitats. Most ponds are shallow grow and extends vertically to the depth of maximum and support submerged vegetation throughout. 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 © Nova Scotia Museum of Natural History Natural History of Nova Scotia, Volume I Habitats PAGE .............................................................. 432 ▼ FORMATION In deep lakes, vertical stratification is common in summer, and the cool-water organisms accumu- The formation of open-water habitats in lentic en- late at the thermocline (see Figure T8.2.1), where vironments relates to the origin of the lake or pond. they depend on the limnetic zone for their food Lakes in Nova Scotia tend to be of glacial origin. sources. Temperature and wind changes (e.g., in Ice-scouring results in depressions in the bedrock fall and spring) create a mixing, and the nutrients or surface irregularities in glacial drift. Lakes and deposited on the bottom rise and are available to ponds can also be formed due to damming by land- phytoplankton for production. slides, flood debris, or hydroelectric dams. Ponds can form when a lake is infilled with organic debris SUCCESSIONAL SEQUENCE or mineral sediment; by the natural cutoff of a me-
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