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==Optical measurements in coastal waters==
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==Biogeomorphology of aquatic systems==
  
This article gives an introduction of the instruments available (and the application of these instruments) to measure optical properties in coastal waters. Attention is paid to optical measurements in general, regional characteristics and implications for [[remote sensing]].
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[[Image:seagrasswaddensea.jpg|thumb|20x|Seagrass meadow]]
  
Optical measuments using satellite and airborne sensors is a powerful, operational tool for monitoring [[coastal zone]]s. This technology can provide accurate, large-scale, synoptic environmental information essential for understanding and managing marine [[ecosystems]].  
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[[Biogeomorphology]] considers the interactions between the ecology and geomorphology of a system. Ecology is the study of relationships between the biota and their environment, and geomorphology examines landforms and how they are formed. Biogeomorphology can be studied in terrestrial as well as aquatic systems. Within aquatic systems biogeomorphological relationships can be found for both hard substrates (rocky shores / coral reefs) and soft substrates (muddy / sandy coastal sediments). Biota can alter geomorphology by creating hard substrates (e.g. coral reefs) or by modifying the stability or erodability of soft substrates.  Key species in the benthic communities of sediment shores can influence geomorphology by acting as '''biostabilizers''' or '''biodestabilizers''' of sediment. The impact of organisms on coastal morphology can be both dramatic (e.g. coral reefs, [[saltmarsh]]es, mussel beds) and more subtle by modifying rates of sediment [[erosion]] and accretion. Biota are not only influenced by various environmental factors (abiotic – physical & chemical; biotic – other organisms; [[anthropogenic]] – humans), but organisms also act as [[ecosystem]] engineers and modify their environment (physical, chemical and biological aspects). [[Ecosystem]] engineers create valuable habitats (e.g. coral reefs and saltmarshes) that are important for fish and birds and serve as a vital part of our natural coastal defence against storm surges and [[sea level rise]].
Optical sensor data allows the assessment of in-water properties, such as suspended matter or [[phytoplankton]] concentration, [[benthic]] substrate type, vegetation composition, and [[bathymetry]]. Optical sampling methods enable for example the continuous and contactless measurement of sediment concentrations, which is an important advantage compared to the mechanical sampling methods.
 
 
 
[[image:uw_optics04.jpg|thumb|right|200px|Figure 1: Downward irradiance spectra measured using a TRIOS Ramses sensor in a shelf sea ]]
 
 
 
Optical characteristics of a light-transmitting medium can be specified in terms of its inherent optical properties (IOPs). The main IOPs are:
 
* the absorption coefficient (a) (m<sup>-1</sup>)
 
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* the scattering coefficient (b) (m<sup>-1</sup>)
 
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* the attenuation coefficient (c), with c = a + b (m<sup>-1</sup>)
 
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* the scattering phase function (&beta;) (sr<sup>-1</sup>)
 

Revision as of 12:14, 22 December 2008

Biogeomorphology of aquatic systems

Seagrass meadow

Biogeomorphology considers the interactions between the ecology and geomorphology of a system. Ecology is the study of relationships between the biota and their environment, and geomorphology examines landforms and how they are formed. Biogeomorphology can be studied in terrestrial as well as aquatic systems. Within aquatic systems biogeomorphological relationships can be found for both hard substrates (rocky shores / coral reefs) and soft substrates (muddy / sandy coastal sediments). Biota can alter geomorphology by creating hard substrates (e.g. coral reefs) or by modifying the stability or erodability of soft substrates. Key species in the benthic communities of sediment shores can influence geomorphology by acting as biostabilizers or biodestabilizers of sediment. The impact of organisms on coastal morphology can be both dramatic (e.g. coral reefs, saltmarshes, mussel beds) and more subtle by modifying rates of sediment erosion and accretion. Biota are not only influenced by various environmental factors (abiotic – physical & chemical; biotic – other organisms; anthropogenic – humans), but organisms also act as ecosystem engineers and modify their environment (physical, chemical and biological aspects). Ecosystem engineers create valuable habitats (e.g. coral reefs and saltmarshes) that are important for fish and birds and serve as a vital part of our natural coastal defence against storm surges and sea level rise.