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The hydrogeochemical processes controlling groundwater evolution in theDaweijia area of Dalian, northeast China, were characterised usinghydrochemistry and isotopes of carbon and sulfur (δ13CDIC and δ34SSO4). The aim was to distinguish anthropogenic impacts as distinct from natural processes, with a particular focus on sulfate, which is found at elevated levels (range: 54.4 to 368.8 mg L−1; mean: 174.4 mg L−1) in fresh and brackish groundwater. The current investigation reveals minor seawater intrusionimpact (not exceeding 5 % of the overall solute load), in contrast withextensive impacts observed in 1982 during the height of intensiveabstraction. This indicates that measures to restrict groundwater abstractionhave been effective. However, hydrochemical facies analysis shows that thegroundwater remains in a state of ongoing hydrochemical evolution (towardsCa–Cl type water) and quality degradation (increasing nitrate andsulfate concentrations). The wide range ofNO3 concentrations (74.7–579 mg L−1) in the Quaternary aquifer indicates considerable input of fertilisers and/or leakage from septicsystems. Both δ13C (−14.5 to −5.9 ‰) andδ34SSO4 (+5.4 to +13.1 ‰) values in groundwater show increasing trends along groundwater flow paths. While carbonate minerals may contribute to increasing δ13CDIC and δ34SSO4 values in deep karstic groundwater, highloads of agricultural fertilisers reaching the aquifer via irrigation returnflow are likely the main source of the dissolved sulfate in Quaternarygroundwater, as shown by distinctive isotopic ratios and a lack of evidencefor other sources in the major ion chemistry. According to isotope massbalance calculations, the fertiliser contribution to overall sulfate hasreached an average of 62.1 % in the Quaternary aquifer, which has a stronghydraulic connection to the underlying carbonate aquifer. The results pointto an alarming level of impact from the local intensive agriculture on thegroundwater system, a widespread problem throughout China

hydrology and earth system sciences

Identification of anthropogenic and natural inputs of sulfate into a karstic coastal groundwater system in northeast China: evidence from major ions, &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C&amp;lt;sub&amp;gt;DIC&amp;lt;/sub&amp;gt; and &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;34&amp;lt;/sup&amp;gt;S&amp;lt;sub&amp;gt;SO&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;&amp;lt;/sub&amp;gt;