Disturbance

Complex Diagram Magnetocaloric Effect

Hurricanes, fires, floods, and droughts are well-known examples of extreme disturbances that episodically cause high mortality to populations of many species in forest, grassland, coral reef, river, and other ecosystems. Because species vary in their resistance to disturbance, as well as rates of recolonization and recovery, disturbance can ameliorate strong biological interactions and help to maintain populations of species that might otherwise be eliminated by their consumers or competitors....

Nitrogen sources and quantities

Nitrogen is abundant in the environment as N2, but it is N bonded to oxygen, hydrogen, or C such as nitrate, ammonium, and organic N that comprises reactive N, and until recently this originated mainly by biological N fixation (Wet-zel 2001). As a consequence of the synthesis of nitrogenous fertilizers, burning of fossil fuels, and wide cultivation of crops such as soybeans that have N-fixing microbial symbionts, annual N fixation from anthropogenic sources now exceeds natural fixation...

Rivers are the Product of their Landscapes

Valley Rules The Stream

In a prescient essay published in 1975, Noel Hynes wrote that ''in every respect the valley rules the stream.'' Geology determines the availability of ions and the supply of sediments, topography determines slope and degree of containment, climate and soils determine vegetation and hence the availability of organic matter and extent of shade, and so on. Decades of research support this view. The river continuum concept describes how basal resources and thus consumer assemblages and stream...

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River Bank Straightening

FIGURE 13.4 Decline in spawning populations of Chinook salmon (Oncorhynchus tshawytscha) since the construction of four dams on the lower Snake River, western United States (Reproduced from Kareiva et al. 2000.) tamed river due to six mainstem reservoirs on the middle river and channelization and levee construction along the lower river, the Missouri historically experienced March and June flood pulses that inundated the extensive bottomland forests, occasional prairies, oxbow lakes, and...

The Bicarbonate Buffer System

Buffer Capacity

Dissolved CO2 reacts with H2O to form carbonic acid H2CO3 , a weak inorganic acid that occurs at low concentrations relative to unhydrated CO2 at pH lt 8 Wetzel 2001 . H2CO3 further FIGURE 4.4 A classification of surface waters of the world based on ratios of sodium to calcium and chloride to bicarbonate, in relation to total dissolved salts. As one proceeds from left to right along the lower arm, inputs shift from a dominance of rock dissolution to a dominance of precipitation. The majority of...

Fluvial Processes along the River Continuum

River Bed Morphology

We are now familiar with many of the principal features of streams, including the shape of their channels, the lateral connection to the flood-plain, the presence of riffles, pools, and meanders, and the sediments of the streambed and its banks. These features vary along the river's course from headwaters to lowlands, and with regional differences in climate and terrain. As stated earlier, streams seek a state of dynamic equilibrium between the imposed conditions of valley slope, discharge, and...

Consumers of CPOM

Shredders Ecology

Figure 8.3 depicts the shredder-CPOM linkage typical of a small stream in the temperate zone. The series of events culminating in the disappearance of leaf CPOM has already been discussed Section 7.1 , and the critical role that microorganisms play both directly and indirectly in influencing the nutritional quality of this resource is elaborated below. CPOM that becomes available in wetlands and larger rivers following macrophyte dieback enters the decomposer trophic web in a very similar...

Consumers of FPOM

Detrital Breakdown Streams

The collector-FPOM linkage Figure 8.5 depends on FPOM captured from suspension or from substrates. As discussed in Chapter 7, FPOM is a poorly characterized food source, and it originates in a number of ways. Categories considered to be richest in quality include sloughed periphyton and biofilm, and particles produced in the breakdown of CPOM. Morphological and behavioral specializations for suspension feeding including setae, mouthbrushes, and fans are diverse and well studied Wallace and...

Preface to the Second Edition

The diversity of running water environments is enormous. When one considers torrential mountain brooks, large rivers of lowlands, and great rivers whose basins occupy subcontinents, it is apparent how location-specific environmental factors contribute to the sense of uniqueness and diversity of running waters. At the same time, however, our improved understanding of ecological, biogeochemical, hydrological, and geomorphological processes provides insight into the structural and functional...