Comprehensive sampling of the carbonate system in estuaries and coastal waters can be difficult and expensive because of the complex and heterogeneous nature of near-shore environments. We show that sample collection by community science programs is a viable strategy for expanding estuarine carbonate system monitoring and prioritizing regions for more targeted assessment. ‘Shell Day’ was a single-day regional water monitoring event coordinating coastal carbonate chemistry observations by 59 community science programs and seven research institutions in the northeastern United States, in which 410 total alkalinity (TA) samples from 86 stations were collected. Field replicates collected at both low and high tides had a mean standard deviation between replicates of 3.6 0.3 mol kg⁻¹ (σ _mean SE, n = 145) or 0.20 0.02%. This level of precision demonstrates that with adequate protocols for sample collection, handling, storage, and analysis, community science programs are able to collect TA samples leading to high-quality analyses and data. Despite correlations between salinity, temperature, and TA observed at multiple spatial scales, empirical predictions of TA had relatively high root mean square error >48 mol kg⁻¹. Additionally, ten stations displayed tidal variability in TA that was not likely driven by low TA freshwater inputs. As such, TA cannot be predicted accurately from salinity using a single relationship across the northeastern US region, though predictions may be viable at more localized scales where consistent freshwater and seawater endmembers can be defined. There was a high degree of geographic heterogeneity in both mean and tidal variability in TA, and this single-day snapshot sampling identified three patterns driving variation in TA, with certain locations exhibiting increased risk of acidification. The success of Shell Day implies that similar community science based events could be conducted in other regions to not only expand understanding of the coastal carbonate system, but also provide a way to inventory monitoring assets, build partnerships with stakeholders, and expand education and outreach to a broader constituency.

由于近岸环境的复杂性和异质性，对河口和沿海水域的碳酸盐系统进行全面采样可能既困难又昂贵。我们表明，通过社区科学计划收集样本是扩大河口碳酸盐系统监测和优先考虑区域以进行更有针对性的评估的可行策略。“贝壳日”是美国东北部 59 个社区科学计划和 7 个研究机构协调沿海碳酸盐化学观测的单日区域水监测活动，其中收集了来自 86 个站点的 410 个总碱度 (TA) 样本。在低潮和高潮时采集的田间重复样本的平均标准偏差为 3.6 0.3mol kg ^-1 ( σ _平均SE, n = 145) 或 0.20 0.02%。这种精确度表明，通过适当的样本收集、处理、储存和分析协议，社区科学项目能够收集 TA 样本，从而实现高质量的分析和数据。尽管在多个空间尺度上观察到盐度、温度和 TA 之间存在相关性，但 TA 的经验预测具有相对较高的均方根误差 >48摩尔公斤^-1. 此外，十个站点显示了 TA 的潮汐变化，这不太可能是由低 TA 淡水输入驱动的。因此，无法使用美国东北部地区的单一关系从盐度准确预测 TA，尽管在可以定义一致的淡水和海水端元的更局部的尺度上预测可能是可行的。TA 的平均和潮汐变异性都存在高度的地理异质性，这一单日快照抽样确定了 TA 变化的三种模式，某些位置的酸化风险增加。壳牌日的成功意味着可以在其他地区开展类似的基于社区科学的活动，不仅可以扩大对沿海碳酸盐系统的了解，还可以提供一种库存监测资产的方法，