[R-sig-eco] Mixed model for coastal waters

[enrico.barbone at unisalento.it]

Dear ecologgers,

we have 15 transects with 3 stations (500, 1000, 3000 m from the
coastline) each one (globally 45 stations). For each stations we have
taken, for two years, monthly samples of water columns chemical and
physical measures that we have used for the calculus of a trophic index. 5
transects are situated in correspondence of small river mouths while the
10 remaining don’t have a freshwater input (we call this coastal). From
the literature we have that the trophic index values are positively linked
to the runoff of large river.

Our questions are:

1)      Are there differences among trophic index values for the two
typologies of transect (river mouth and coastal)?

2)      If difference are significant, this Is true all over the year or
only in particular season?

3)      For the river mouth transects, the runoff river effect on trophic
index is observed for the three station (500, 1000, 3000)?



My idea is to use a linear mixed models with the transects as a random
factor and, as fixed factor: 1) the distance from the coast 2) the river
mouth or coastal 3) the months. Moreover, the interaction among fixed
factors.

My question his: can I answer to my 3 question with the model that I have
proposed?

Do you have some suggestions?

I was wondering if someone could help me.


Many thanks for your help,

Enrico