Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes of organic matter (OM) in bed sediments and suspended solids are thoroughly investigated in the Pulicat lagoon, India, in pre-South West (SW) monsoon (June 2018) and post-North East (NE) monsoon (March 2019) to understand the response of OM in salt stress conditions. A near absence of an external supply of water and intense evaporation, as suggested by higher hydrogen and oxygen isotope values (δD and δ¹⁸O) of the lagoon water, led to hypersaline conditions in the lagoon. Despite a long period of osmotic stress, a high OM concentration in suspended solids in post-NE monsoon suggests that autochthonous production is unaffected by salt stress conditions. Locally at different sites, the difference in δ¹³C (−4.9‰ to +1.4‰) and δ¹⁵N (−4.1‰ to +1.6‰) values of OM between suspended solids and bed sediments are higher in pre-SW monsoon compared to post-NE monsoon. The negative isotopic difference is caused by benthic respiration of OM and cation exchange with clay bound ammonium in bed sediments, whereas the positive difference is the result of cellulose decomposition in areas dominated by seagrasses. However, in post-NE monsoon, wind-induced re-suspension of bed sediments reduce the differences in δ¹³C (−2.3‰ to −0.1‰) and δ¹⁵N (−2.1‰ to +3‰) values. The source apportionments of δ¹⁵N values suggest inputs from sewage and fertilizers. Additionally, seagrass-detritus dislodged by fishing activities favors primary production. Overall, we suggest that the impact of the hypersaline conditions on in-situ productivity can be suppressed if wind activity and nutrient re-cycling are dominant. The present study is unique as it addresses the processes that operate in a hypersaline lagoon during the short-term failure of monsoon.

在西南 (SW) 季风前的印度普利卡特泻湖 (2018 年 6 月) 中，彻底调查了床层沉积物和悬浮固体中有机物 (OM) 的稳定碳 (δ ¹³ C) 和氮 (δ ¹⁵ N) 同位素和东北（NE）季风后（2019 年 3 月），以了解 OM 在盐胁迫条件下的响应。正如泻湖水的较高氢和氧同位素值（δD 和 δ ¹⁸ O）所表明的那样，几乎没有外部水供应和剧烈蒸发，导致泻湖中的高盐度条件。尽管长期存在渗透胁迫，但东北季风后悬浮固体中的高 OM 浓度表明，本土生产不受盐胁迫条件的影响。局部在不同地点，δ 的差异与东北季风后相比，西南季风前的悬浮固体和床层沉积物之间的¹³ C（-4.9‰ 至 +1.4‰）和 δ ^{15 N（-4.1‰ 至 +1.6‰）值较高。}负同位素差异是由 OM 的底栖呼吸和与床沉积物中粘土结合的铵的阳离子交换引起的，而正差异是由海草为主的地区纤维素分解的结果。然而，在东北季风后，风引起的床层沉积物再悬浮减少了 δ ¹³ C（-2.3‰ 至 -0.1‰）和 δ ¹⁵ N（-2.1‰ 至 +3‰）值的差异。^{δ 15}的源解析N 值表明来自污水和化肥的投入。此外，因捕鱼活动而脱落的海草碎屑有利于初级生产。总体而言，我们建议如果风活动和养分循环占主导地位，则可以抑制高盐条件对原位生产力的影响。本研究是独一无二的，因为它解决了在季风短期失败期间在高盐泻湖中运行的过程。