GEMS-GLORI world river discharge database

The GEMS-GLORI register, circulated by UNEP for review in 1996, lists 555 world major rivers discharging to oceans (Q > 10 km**3/year, or A > 10 000 km**2, or sediment discharge > 5Mt/year, or basin population >5M people). Up to 48 river attributes are listed, including major ions and nutrients (C, N, P) in both dissolved, particulate, organic and inorganic forms. For many rivers, two or three sets of data are provided with relevant periods of records and references. Although half of the selected rivers are not yet documented for water quality, most of the first 40 rivers are well described (Irrawady, Zambezi, Ogooue, Magdalena, are noted exceptions). Altogether about 10 000 individual data from 500 references are listed. The global coverage in terms of river discharge and/or drainage area ranges from 40 to 67% for most major water quality attributes but drops to 25% for some organic and/or particulate forms of N and P. Planned development of the register includes collection of information on particulate chemistry and data on endorheic rivers and selected tributaries.

Tab. 3: Concentrations of selected chemical species at various depths in Ace Lake

This article reviews the history, chemical stratification, biology and biogeochemistry of Ace Lake, which is one of the many marine-derived meromictic (permanently stratified) lakes in the Vestfold Hills, Eastern Antarctica. The lake has an area of 18 ha, a maximum depth of 25 m, and a salinity range from 7 to 43 g l**-1. The lake mixes to a depth of 7 m in late winter as a result of brine freeze out during ice formation. Deeper mixing is precluded by a sharp halocline. The water beneath 12 m is permanently anoxic, The lake was formed approximately 10,800 yr BP as the polar ice cap melted. Sea level rise 7,800 yr BP resulted in invasion of seawater into the initially freshwater lake. Subsequently, sea level dropped, and the now saline lake became isolated from the ocean. The biota of the lake was derived from species trapped when the connection between the lake and the ocean was cut off. The oxic zone above 12 m supports a relatively simple community which includes microbial mats, four major species of phytoplankton (including a picocyanobacterium), two copepod species, and a variety of heterotrophic flagellates and ciliates. The anoxic zone contains populations of photosynthetic sulfur, sulfate reducing, fermentative and methanogenic bacteria, which combine to remineralise organic carbon which sediments from the upper waters. Research on the physics, biology and chemistry of Ace Lake has contributed significantly to knowledge of Antarctic meromictic lakes.