Nested ANOVA in R

Hi, I am a master's student in Biology (Ecology and Evolution) and for a statistics course I have to do a case study using real data (datafiles are attached). The dataset containts (among others) measurements of inorganic N, in NO3, NO4 and N, in 8 different valleys. Of these 8 valleys, 4 have been rewetted after drainage, and 4 haven't, but they all have a similar groundwater level. Per valley, 3 measurements were made at a place with a high groundwater level, 3 at a place with a medium level, and three with a low level. I want to answer the question whether soil N-levels are affected by rewetting or by the position within the gradient (or maybe there is an interaction). I figured I should do this in R using a nested ANOVA. Unfortunately, we didn't get a very good lecture on nested ANOVAs, so I'm still not sure how to do it.
Should I nest position (H, M, L) in location (which valley) and location in water management (rewetted/not rewetted), or should I only nest postion in location? And how would this work in R?
I tried this script, it seems to find significant results but I'm not sure whether this is correct:
summary(aov(N ~ Rewetted + Location/Position)) #here I tried nesting position in location

It would be great if someone could help me with this.
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