Hi Leela

My first thought was also to wonder about the regression.  What is your
range of values and the r-squared value?  (goodness of fit). And are there
outliers at either extreme?  They can have a big effect.

Warm regards
  -Mark Schurr

from my phone

On Sun, Sep 15, 2019, 2:25 PM Tom Millican <[log in to unmask]>

> Hi Leela,
> If the values of your samples are confined to a narrow range, compared to
> the range of what falls in that watershed over the course of a year, it
> could result in odd slopes with a small sample set. Is the range of values
> you obtained wide enough?
> If snowmelt is involved, it could have an effect on your slope as well.
> This is intriguing. I'll be watching for the water isotope experts' ideas.
> -tom millican
> On Sun, 15 Sep 2019 10:56:34 -0400
> Leela <[log in to unmask]> wrote:
> > I measured several ground water samples from a temperate region (Lat 42
> deg). The hydrogen vs oxygen gives a slope of 3.5 and an intercept of -5. I
> can understand such a behavior from an arid region. Many samples from an
> nearby filed gave a slope of 7.7 and intercept of 11. Any suggestions