Effects of salt marsh vegetation zonation on carbon and nitrogen cycling in Connecticut

Coastal marshes fringing the Long Island Sound (Connecticut, USA) are dynamic ecosystems positioned at the interface between land and sea, and provide an array of essential ecosystem services to society associated with improved water quality, carbon sequestration, and disturbance regulation. However, these wetlands are increasingly altered by rising seas and invasive species, and have been affected by historical management such as tidal manipulation. We conducted a survey of 20 Connecticut salt marshes (10 tidally restored, 10 unrestricted references) in 2017 to quantify carbon mineralization, denitrification potential, microbial community composition, above and belowground biomass and a suite of sediment characteristics. Carbon density was our only paramenter that differed between unrestricted and tidally restored marshes, but we observed strong differences across vegetation zones, with vegetation being a top predictor of microbial respiration and potential denitrification rates. Based on sea-level rise model projections, the replacement of S. patens by short-form S. alterniflora is expected to be widespread across the Connecticut coastline, decreasing statewide potential denitrification from the low-to-high marsh transitional zone. Our results suggest that changes in vegetation zones can serve as landscape-scale predictors of the rapid changes occurring in salt marshes.环绕美国康涅狄格州长岛海湾（Long Island Sound）的滨海盐沼是坐落于海陆交界带的动态生态系统，可为人类社会提供一系列至关重要的生态系统服务，涵盖水质改善、碳封存（carbon sequestration）以及扰动调控等功能。然而，这类湿地正日益受到海平面上升与入侵物种的干扰，同时也曾受历史上潮汐调控等人类管理活动的影响。本研究团队于2017年对康涅狄格州的20处盐沼开展了调查，其中10处为潮汐修复（tidally restored）样地，10处为未受干扰的对照（unrestricted references）样地，旨在量化碳矿化作用（carbon mineralization）、反硝化潜力（denitrification potential）、微生物群落组成（microbial community composition）、地上与地下生物量（biomass）以及一系列沉积物特征（sediment characteristics）参数。碳密度（carbon density）是唯一在未受干扰样地与潮汐修复样地间存在显著差异的参数，但研究团队观察到不同植被带间存在显著分化，且植被是微生物呼吸速率与潜在反硝化速率的核心预测因子。基于海平面上升模型的预测结果，短型S. alterniflora取代S. patens的现象预计将在康涅狄格州沿海全域广泛发生，进而导致全州盐沼高低潮过渡带的潜在反硝化能力出现下降。本研究结果表明，植被带的变化可作为盐沼快速演变过程的景观尺度预测指标。