The ability of sponges to feed in diverse (including oligotrophic) ecosystems significantly contributes to their ubiquitous aquatic distribution. It was hypothesized that sponges that harbour small amounts of symbiotic bacteria in their mass feed mainly on particulate organic matter (POM). We examined the nearly symbiont-free (by microscopic observation) filter-feeding Red Sea sponge Negombata ...

In the Baltic Sea, floating blooms of nitrogen-fixing cyanobacteria occur yearly during late summer. These blooms can sometimes be limited by iron. Due to extensive foresting around the Baltic Sea, iron is entering the Baltic Sea partly bound to dissolved organic material (DOM) via rivers. An experiment was performed in 300 l laboratory mesocosms to test the hypothesis that riverine highmolecul...

-~~~~~~~ ~ ~ r~~~ ~~~ ~~~~ ~ ~ ~~~~ ~~ ~~~~ ~~~~~~~~~~~ -~~~ ~ ~.~ ~ . . . ~~substrates. The watershed is underlain bv ice-bonded till and is hvdrolo~icallv water~ ~~ ~~ ~ , tight. Because of low rates of weatherine. bedrock and lill do no1 contribute sienifi~~~ ~~ ~ ~~ -~~~~~ c&tly to ionic composition of the stream-water. Breakup occurs in late May to early June with surface flow until Seprem...

[1] Here we describe, test, and apply a system of spatially explicit, global models for predicting river export of three dissolved organic matter (DOM) components: dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and dissolved organic phosphorus (DOP). The DON and DOP models represent the first attempt to model DON and DOP export in a spatially explicit, global manner. DOC, DON...

The marine autotroph Aureococcus anophagefferens (Pelagophyceae) was rendered axenic in order to investigate hydrolysis rates of peptides, chitobiose, acetamide, and urea as indicators of the ability to support growth on dissolved organic nitrogen. Specific rates of hydrolysis varied between 8 and 700% of rates observed in associated heterotrophic marine bacteria.

Conventional wisdom postulates that leaching losses of N from agriculture systems are dominated by NO3 – . Although the export of dissolved organic nitrogen (DON) into the groundwater has been recognized for more than 100 yr, it is often ignored when total N budgets are constructed. Leaching of DON into stream and drinking water reservoirs leads to eutrophication and acidifi cation, and can pos...

[1] Hydrologic losses can play a key role in regulating ecosystem nutrient balances, particularly in regions where baseline nutrient cycles are not augmented by industrial deposition. We used first-order streams to integrate hydrologic losses at the watershed scale across unpolluted old-growth forests in New Zealand. We employed a matrix approach to resolve how stream water concentrations of di...

The importance of resource limitation in controlling bacterial growth in the high-nutrient, low-chlorophyll (HNLC) region of the Southern Ocean was experimentally determined during February and March 1998. Organic- and inorganic-nutrient enrichment experiments were performed between 42 degrees S and 55 degrees S along 141 degrees E. Bacterial abundance, mean cell volume, and [(3)H]thymidine and...