Dear Debashish,


Not having carried out anything like your study myself, the best I can offer
is a swag (= scientific wild ass guess).

I don't think there is a Direct causal link between 15N and 13C that would
result in inversely coupled isotope abundance for the two determining for
d13C to always become more -ve if d15N if going up (more +ve).

That is not to say there may not be a common link for your observation.

When looking at plant products such as sugars and fatty acids, I have
noticed that d13C-values seem to reflect how well a plant is doing;
ultimately reflecting enzyme activity and gene expression. If memory serves,
people at the Scottish Crop Research Institute have looked at this
(www.scri.sari.ac.uk). Same species plant grown under -favourable and
+favourable conditions yield more -ve and more +ve d13C-values for the same
biogenic material (e.g. oils), respectively.

If we say your polluted estuary stunts growth (hampers development) one
could argue this is the reason why you find highly -ve d13C-values in fish
tissue from this estuary. If we furthermore say part of the pollution is
caused by fertilizer washout (and/or sewage) then this would explain the
highly +ve d15N-values.

By the same token, the opposite situation in the cleaner estuary (less
fertilizer/sewage pollution) and more life conducive conditions in general
will lead to the fish doing better (less -ve d13C-values) while at the same
incorporating less fertilizer/sewage derived N (less +ve d15N-values).


Best regards,

Wolfram



> -----Original Message-----
> From: Stable Isotope Geochemistry 
> [mailto:[log in to unmask]] On Behalf Of MAZUMDER, Debashish
> Sent: 02 March 2007 07:14
> To: [log in to unmask]
> Subject: Re: d13C depleted and d15N enriched
> 
> Hi
> 
> I would highly appreciate if you give me a clue in the 
> following situation?
> 
> I have analysed 5 fish species from two estuaries. One 
> estuary is polluted other is clean. I found highly enriched 
> dN15 and highly depleted d13C values for all fish species 
> from the polluted estuary. Relatively less enriched d15N and 
> less depleted d13C values from the cleaner estuary. Why d13C 
> is depleted when d15N is enriched? Any suggestion/reference 
> would be highly appreciated. Thanks in advance
> 
> Kind regards
> Debashish    
> 
> Debashish Mazumder, PhD
> Institute for Environmental Research
> Australian Nuclear Science & Technology Organisation (ANSTO) 
> PMB 1, Lucas Heights Menai 2234, New South Wales AUSTRALIA 
> 
> Phone: +61 2 9717 9219
> Fax: +61 2 9717 9260
> Email: [log in to unmask] 
> 
> "Important: This transmission is intended only for the use of 
> the addressee.
> It is confidential and may contain privileged information or 
> copyright material. If you are not the intended recipient, 
> any use or further disclosure of this communication is 
> strictly forbidden. If you have received this transmission in 
> error, please notify me immediately by telephone and delete 
> all copies of this transmission as well as any attachments".
> 
>  
>