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About UNEP
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United Nations Environment Programme
Division of Technology, Industry and Economics
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Newsletter and Technical Publications
Freshwater Management Series No. 5

Guidelines for the Integrated Management of the Watershed
- Phytotechnology and Ecohydrology -


Kriging - an interpolation technique based on a theory of the semivariogram.

Layer - a logical set of thematic data covering one subject.

Map projection - a set of mathematical equations for converting geographical coordinates to Cartesian plane coordinates. The equations allow the depiction of spherical, three-dimensional objects on a flat map.

Metrics - a characteristic that changes in some predictable way with increased human influence (e.g., a scoring system).

Model - a simplification and abstraction of reality. Models can be seen as a data set representing the structure of geographical objects, as well as a set of logical expressions and mathematical equations used to simulate processes. Models may also be physical representations of geographic features.

Multimetric approaches - an analysis technique using several measurable characteristics of a biological assemblage.

Multispectral - the remote sensing technique for obtaining images over number of distinct narrow bands of the electromagnetic spectrum.

Multivariate community analysis - statistical methods (e.g., ordination or discriminant analysis) for analysing physical and biological community data using multiple variables (quantitative or nominal).

Node - the end points of a line.

Nonpoint source pollution - pollution entering water bodies from diffused sources, including surface and sub-surface runoff, nutrient leaching, and erosion, mainly from degraded landscapes (e.g., landscapes degraded due to agriculture, deforestation, etc.).

Nutrients (Biogenics) - chemical elements necessary for growth and development of vegetation. The main nutrients are phosphorus, nitrogen, and carbon. Increased nutrient concentrations stimulate the process of eutrophication in aquatic ecosystems.

Nutrient concentration - the amount of a nutrient in a given volume of water.

Nutrient load - the amount of a nutrient transported into a water body by rivers, sewage discharges, etc., over a given period of time, calculated as concentration multiplied by discharge.

Phycocyanin - a photosynthetic pigment characteristic of cyanobacteria.

Phytoplankton- the algal component of plankton, which are free-living organisms within the aquatic environment.

Phosphatase - a group of hydrolytic enzymes liberating the orthophosphate ion from organic compounds.

Piesometer - a pipe-like trap for ground waters with perforated ends, placed in water bearing layers to measure ground water elevations; when placed in fields, ground water flows can be measured using tracers.

Pixel - one picture element (or cell) in a set of grid data.

Point source pollution - pollution entering water bodies from concentrated outflows (e.g., pipes transporting municipal and industrial sewerage, water from purification plants, irrigation channels, etc.).

Polygon - a vector representation of an enclosed area written as a set of vertices or given by a mathematical function.

Radical zone - the surface layers of the soil within the reach of plant roots.

Raster - a computer readable format used for representing images or grid data.

Rasterization - the process of converting data from vector format to raster format.

Reflectance - the ratio of energy reflected by a surface to that incident upon it.

Retention time [also Water retention time, WRT] - the ratio of volume and flow of a reservoir or lake.

Rubbersheeting - the procedure for adjusting the geometry of an image by non-uniform transformations.

Reference condition - the chemical, physical, or biological quality, exhibited at either a single site or an aggregation of sites, representing a semi-natural or reasonably attainable condition at the least impaired reference sites.

Scale - a relationship between the distance on a map and in reality.

Scanning - the process by which analogue maps are converted to raster format by an optical device.

Semivariogram - a graph showing the relationship between variance and separation for a pair of data points.

Shoal - a great number of fish swimming together.

Spatial interpolation - the procedure of estimating values in certain areas using existing observations.

Stream microhabitat system - the distribution of pools, riffles, and runs, having relatively homogenous substrate types, water depths, and velocities, within a stream course (after Frissell et al. 1986)

Stream order - the dendritic arrangement of channels of a river throughout its drainage basin. The most popular hierarchy is defined such that first order streams are those having no tributaries, second order streams are those formed by the union of two first order streams, third order streams are those formed by the union of second order streams, and so on.

Stream pool-riffle-run system - a subsystem of a reach having characteristic bed topography, water surface slope, depth, and velocity patterns. In the natural meandering watercourse, the shallow zones or riffles and the deeper zones or pools lie in a regular pattern connected by runs. The distance between two neighbouring riffles or pools is approximately one half of the wavelength of one full meander, or about 5 to 7 times the width of the watercourse. In-stream habitats at this level are complex hydrological units (after Frissell et al. 1986).

Stream reach - a length of stream or a stream segment lying between breaks in channel slope, local side-slopes, valley floor widths, riparian vegetation, and bank materials (after Frissell et al. 1986).

Stream segment - the portion of a stream system flowing through a single bedrock type and bounded by tributary junctions or major waterfalls.

Stream system - all running surface waters in a watershed (after Frissell et al. 1986); standing waters within stream systems may be wetlands or lakes depending upon their depth, hyrdologic conditions, soil types, and vegetation cover.

Succession - the biological concept implying a sequence in which species or groups of species dominate a community.

Surface - a representation of geographical object as set of continuous data (also, a data field).

Surface runoff - surface flow caused by rainfall, transporting solids, nutrients, and pollutants downhill into aquatic systems.

Topology - the spatial relationship between nodes, lines, and polygons.

Vector - a data structure in which lines are represented as a list of ordered coordinates.

Vectorization - the process of converting data from raster to vector formats.

Vertex (vertices) - a point or series of points with given coordinates on a line.

Wetland - a natural or constructed system, permanently or periodically flooded, that can act as water purification systems or nutrient sinks. Purification is enhanced by the activity of vegetation and variety of microbiological and biogeochemical processes taking place within the substrate of the wetland. Wetlands are defined by the presence of hydric soils, characteristic types of vegetation, and an high water table.

 

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