Sediment

Monitoring sediment focuses on:

1) Pools and deposition of nutrients in the sediment,

2) the sediment's hydrogen sulphide buffering capacity, and

3) organic matter metabolism and internal nutrient load from the sea floor.

Unlike the water column the sediment is site specific, i.e. it is possible to study the same estuarine or marine sediment from year to year. Thus, marine or estuarine sediments are an important element of marine ecosystems and measurements of the state of the sediment and the most important sediment processes provide valuable information on changes in the marine environment when the development in marine systems is assessed.

1) Determination of pools and nutrients in the sediment

comprise total nitrogen, total phosphorus, dry matter, loss on ignition and iron-bound phosphate. The latter is the most significant phosphorus pool regarding the potential internal load to the near-shore marine environment.

2) The sediment's hydrogen sulphide buffering capacity

or its oxidation reserve describes the sediment's ability to retain reduced compounds, especially hydrogen sulphide, the immediate oxidation of which requires high consumption of O₂.

The sediment's hydrogen sulphide buffering capacity depends on the content of oxidised iron and is affected by the load of organic matter, microbial and chemical processes in the sediment and on meteorological and hydrographical conditions. Along with the hydrogen sulphide buffering capacity, the hydrogen sulphide front within the sediment is measured.

3) Organic matter metabolism within the sediment and internal nutrient load

comprise measurements of oxygen flux, and fluxes of NO₃^-, NH₄⁺, PO₄^3- and Si across the sediment/water interface.

The oxygen flux across the sediment/water interface provides valuable information on the amount of organic matter reaching the sediment, and from measurements of nutrient fluxes the significance of the sediment as an internal nutrient source can be assessed. Release of nutrients from marine and estuarine sediments may lead to an increased production of algae in the exact same way as the external load from land and atmosphere.

Data

Information on sampling locations within the Danish national marine monitoring program (NOVA 2003) and download of data can be accessed.

Inquires concerning data or comments on the page can be sent to Henrik Fossing.