Why there is chloride retention in diarrhea?

The salt load in diarrhea is higher because there was not enough time for more absorption of chloride prior to the expulsion of stool.

Increased motility of gut causes proFuse watery diarrhea which is rich in bicarbonate. Further, loss of bicarbonate causes further secretion of bicarbonate from pancreas and small intestine. To correct the dehydration, person drinks salt heavy liquids. Na+k+unmeasured anions—hco3+chloride+um cations if Na increases or bicarbonate decreases, it results in increased chlorine. Hope it helps.