Presentation on theme: "Hydrological Cycle. Streams Stream = water flowing downhill in a defined channel. (River = large stream; Creek & Brook = small streams) Lotic system ="— Presentation transcript:
Streams Stream = water flowing downhill in a defined channel. (River = large stream; Creek & Brook = small streams) Lotic system = flowing (fresh)water system; Riparian system = of/around river/stream; Fluvial = river/stream ; Rheos/Rrheic = stream
Gradient = meters of drop per kilometer of stream High gradient = fast Low gradient = slow Discharge = the amount of water carried by a stream (often varies seasonally and with precipitation) Usually measured as m 3 per second at a given point of the stream. Quantifying Stream Flow
Streams Basin/Drainage/Catchment = area drained by a stream. Headwaters = small source streams that originate from springs (groundwater) or runoff from the basin. Mouth = terminus of a stream at another body of water. Floodplain = level area along a stream that is frequently flooded. Riparian Zone = area where vegetation is influenced by the stream.
Stream Order often streams begin at a spring (ground-water becomes surface water). Stream Order = pattern of stream branching. 1st Order Stream = headwater streams. 2nd Order Stream = streams formed by uniting of 1st order streams. Etc. Usually lower order = high gradient, cool, low turbidity, few species, small discharge, more variable flows over time.
Typical Stream Section Flood Plain = area around a higher order stream covered by water during floods. Channel = area where a stream usually flows. Main Channel (thalweg?) = deepest part. Levee = raised area on either side of a stream channel. Channel Main Channel
Streams, Runoff, & Groundwater More surface runoff greater discharge Stream at groundwater level more continuous discharge (wont go dry; if channel above groundwater, then may go dry) If stream higher than groundwater and channel, then may re-charge groundwater (especially if lower flow). groundwater
Channel & Flow Water flows faster further away from the substrate which causes turbulence. More irregular channels slow flow more than regular channels. Straighter channel sustains higher flow.
Meanders/Bends Channel composition determines erosion Channels of evenly erodable material... still form regular meanders/bends.
Oxbow Lakes Oxbow lake = Portion of a bend cut off from the main flow of the stream.
Braided Channels Braided Channel = multiple channels in a large (high order) stream separated by islands/bars.
Pools, Riffles, & Runs Pool = relatively deep portion with slower water flow (lower dO 2 ) Riffle = relatively shallow portion with faster water flow where the water ripples or breaks on the substrate (higher dO 2 ) Run = relatively deep portion with faster water flow.
Substrate & Cover Substrate usually composed of larger elements the lower the order. Cover = the percent of the sky above the stream that is shielded by vegetation. % cover usually higher the lower the order.
Drift (Stream) Drift = normally benthic organisms in the water column moving downstream. Allows re-positioning and/or benthic predator avoidance (but makes vulnerable to large predators). - Always one way.
Drought and Floods Effects usually most dramatic on low and mid- order streams. Drought – problem = too little water; surface flow may be very low or absent drought refugia - isolated pools often connected by subsurface flow or connected higher order stream Floods – problem = scouring flow; surface flow in channel very rapid flood refugia – inundated floodplain or water behind large structure (i.e., boulders) or connected higher order stream
In-Stream Primary Production Very high flow, intermittent stream flow, and high turbidity reduce (or eliminate) in-stream photosynthesis. In clear streams, periphyton (microphytes) & macrophytes may be able to undergo in- stream photosynthesis). Phytoplankton (& zooplankton) only rarely present in very high order streams (consistent low flow but… high turbidity). Marginal emergent vegetation and riparian zone vegetation can undergo significant production, especially in higher order streams.
Allochthonous Inputs In most streams most nutrients come from surrounding terrestrial environments (dead parts of organisms, such as leaves, or dissolved molecules) Allochthonous material = organic matter from a different habitat ; CPOM – coarse particulate organic matter FPOM – fine particulate organic matter DOM – dissolved organic matter Detritivores (animals that eat detritus) and decomposers (bacteria & fungi that decompose dead organisms) are very important in most streams. Flow washes detritus downstream, more FPOM and less CPOM in higher order streams.
N. Amer. Decapod Crustaceans When crayfishes, crabs, and/or shrimps are present, they often have significant ecological effects as feeding generalists (acting as shredders, collectors, grazers, AND predators).
Differences in Tropical Streams Bacterial and fungal decomposition of allochthonous material is more rapid. Allochthonous inputs are often (but not always) less seasonal. Fewer aquatic insects. Fishes ( and in some places decapod crustaceans) serve as the major shredders, collectors, and grazers.
Human Impacts: Runoff/Erosion Increased nutrient inputs via agricultural fertilizers – favors algal periphyton and bacteria (can result in anoxia) Increased turbidity due to erosion – less in- stream photosynthesis
Human Impacts: Channelization Channelization and elimination of flood plains – reduces groundwater recharge, increases water velocity in flood and severity of floods when levees breached
Human Impacts: Impoundments Formation of Lakes via damming of rivers. Greatly changes conditions, especially downstream. (e.g., hypolimnetic release)