The NTA/EDTA fractionation of sediment-bound, inorganic phosphate was improved and made more effective . The iron-bound phosphate is now extracted with Ca-EDTA plus dithionite and followed by an extraction of calciumbound phosphate by Na2-EDTA at pH = 4.5 . A comparison is made with two other sequential extraction procedures : the SEDEX and the Hieltjes & Lijklema extractions . The EDTA extractions have an advantage over the other two methods .Abbreviations o-P = ortho phosphate EDTA =Ethylene dinitrilo tetraacetic acid(or its salts) ASOP = Acid Soluble Organic Phosphate Fe(OOH)NP = iron-bound phosphate TRIS-buffer=tris (hydroximethyl)-amino methane CaCO3 ;ZZ~P=calcium-bound phosphate NTA = Nitrilo triacetic acid (or its salts) NaOH-Pextr = phosphate extracted with NaOH (etc .) Throughout this article : M = mol dm 3 .

The accumulation of inorganic phosphate in lake sediments and a possible following release is due to the adsorption of phosphate onto Fe(OOH) and, especially in hard waters, to the precipitation of apatite . Attempts are made to quantify both processes .For the quantification of the P adsorbed, Pads, onto Fe(OOH) the Freundlich adsorption isotherm, P ads A(0P)B, gave good results . The constants A and B could be quantified . Constant A appeared to depend on the pH and the Ca 2+ and Mg 2+ concentrations in the water. Constant B appeared to approach 0 .333 . The full equation becomes then: P ads =23600 .(10 -o .4P H )(2 .77-1 .77 ; e-c ')~/o -P, with the Ca concentration in mmol 1 -1 and the o-P and Pads concentrations in mg 1 -1 .For the quantification of the solubility of calcium-bound phosphate the solubility product of apatite being 10 -50 as found in the two hard water rivers Rhine and Rhone, was used . With this solubility product the solubility of o-P can be calculated as function of the Ca 2+ concentration and the pH. The two equations, for adsorption and precipitation, are put together in a so-called solubility diagramme, which describes the o-P concentration as function of the Fe(OOH) concentration in the sediments, and the pH and the Ca 2+ concentration in the overlying water .The release of phosphate from the Fe(OOH) : P complex under anoxic conditions after adding H2S in inorganic suspensions was shown to be limited . Only when a large excess of H2S was added there was some release, but if less than 75% of the Fe(OOH) was converted into FeS, there was no release . The possibility of organic phosphate as the source of phosphate release under anoxic conditions is discussed . For a full understanding of this possibility, fractionation of sediment bound phosphate must be carried out in such a way, that these organic phosphates are not hydrolysed .

The organic phosphate pool of some Camargue sediments (South of France) was studied, after removal of inorganic phosphate, with Ca-NTA/dithionite (Fe bound phosphate) and Na-EDTA (Ca bound phosphate). The organic phosphate was divided into an acid soluble organic phosphate fraction (ASOP) and a residual organic phosphate fraction (ROP). The extraction of organic matter with 2.0 M NaOH (90 C) from ROP yielded considerable quantities of Org-P. In this extract the presence of phytate (inositol hexa phosphate) could be demonstrated using phytase to hydrolyse the phytate. Phytate was shown to account for a considerable part of organic phosphate in sediments of freshwater marsh sediments as well as in the sediment of the brackish/salt water lake 'Etang de Vaccares'. In laboratory experiments phytate was found to precipitate with all poly-valent cations tested. Furthermore, phytate was found to be strongly adsorbed onto Fe(OOH), which may explain its accumulation and its stability in sediments.Considerable quantities of ASOP were found; the chemical stucture of this pool remains unknown.Abbreviations: In this paper the standard abbreviations are used, as suggested by the editor (see page vi):chem-Xphys (inorg-Pdiss, Tot-Nsed)Additional abbreviations used: ASOP = acid soluble organic phosphate CaCO 3 ; P = calcium bound phosphateFe(OOH) P = iron bound phosphate NaOHextr-P = phosphate extracted with NaOH (90 C) after ASOP extraction.Phyt-P = phytate bound phosphate ROP = residual organic phosphate 118

Wetlands, especially in the Mediterranean area, are subject to severe eutrophication . T h i s m a y u p s e t t h e e q u i l i b r i u m b e t w e e n p h y t o p l a n k t o n p r o d u c t i o n i n u n d e s i r a b l e q u a n t i t i e s a n d a q u a n t i t a t i v e l y d e s i r a b l e m a c r o p h y t e p r o d u c t i o n . I n o r d e r t o m a n a g e t h i s e q u i l i b r i u m , a q u a n t i t a t i v e k n o w l e d g e o f n u t r i e n t i n p u t a n d f l u x e s i s e s s e n t i a l a n d t h e r o l e of sediments in these processes must be understood . This knowledge can be useful even for agriculture, e .g. rice cultivation, where optimal utilization of fertilizers can lead to an economic benefit .In this article different aspects of nutrient cycles are discussed in view of approaching a sufficiently precise q u a n t i f i c a t i o n . The nutrient input balance of the Camargue was therefore measured which showed that the input of n u t r i e n t s w i t h t h e i r r i g a t i o n w a t e r , t a k e n f r o m t h e r i v e r R h o n e , r o u g h l y e q u a l s t h e q u a n t i t y o f f e r t i l i z e r s a d d e d . Phytoplankton growth can be approached reasonably with the Monod model, although there are still many practical problems, such as the influence of the pH on P uptake and the problem of measuring P uptake in the field. The situation is worse for macrophyte growth ; q u a n t i t a t i v e d a t a a r e s c a r c e a n d s t u d i e s h a v e o f t e n b e e n c a r r i e d o u t with unrealistic nutrient concentrations or without addressing the influence of the sediment . This influence can also include negative factors, such as high concentrations of Fe e+ , H 2 S o r F e S , b u t c a n n o t y e t b e q u a n t i f i e d . The nitrogen cycle in wetlands is dominated by denitrification . Most wetlands have sediments with high concentrations of organic matter, therefore with a large reducing capacity. Besides this process, we have shown that denitrification can also be controlled by FeS . In the Camargue sediments this denitrification is mediated by bacteria from the sulfur cycle ; this appeared to be the major pathway . It was shown that a stoicheiometric relation exists between nitrate reduced and sulphate produced . T h e i n f l u e n c e o f t h e t e m p e r a t u r e w a s q u a n t i f i e d a n d a p p e a r e d t o b e stronger at high organic matter concentrations than at lower ones . Denitrification with FeS means that the bacteria use nitrate also for their N demands, while this is not necessarily the case during denitrification with organic matter .Mineralization of macrophytes is a much slower process than that of phytoplankton, probably because of their high C/N ratio . We could, however, not confirm the general assumption that the addition of nitrogen stimulates this mineralization . On the contrary, we found that two amino acids both with a C/N ratio of 6 had different mineralization rates . T h e a m i n o a c i d c o m p o s i t i o n o f d ...

By means of sequential extractions with Ca-NTA and EDTA, a separation was performed between Fe(OOH) z P and CaCO 3 z P in a few sediments ; the remaining fraction, considered to be organic phosphate, was quantified as well . We found that with the commonly used method of extraction with NaOH and H2S04, less Fe(OOH) z P and much more CaCO 3 z P was found than with the chelating extractants . The organic phosphate pool in live and dead algal material and in some mud samples was partly hydrolysed and therefore recovered as inorganic phosphates with classical extractions . The difference between chelating extractants and the classical ones is discussed .