and15NPl"</span><span class="op">]</span> <span class="op">+</span> <span class="va">source_sds_c</span><span class="op">[</span>, <span class="st">"SDd15N"</span><span class="op">]</span></span>
<span><span class="op">)</span></span>
<span><span class="va">new_df3</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/data.frame.html" class="external-link">data.frame</a></span><span class="op">(</span></span>
<span>  x <span class="op">=</span> <span class="va">x</span>,</spa