Hourly water chemistry measurements at the mouth of West Falmouth Harbor, MA, USA from 2005 to 2019 and 2023

West Falmouth Harbor (West Falmouth, MA, USA) has been experiencing a dramatic increase in nitrogen loading from an upgradient municipal wastewater treatment facility since the early 2000s. As part of a long-term study into the effects of this nitrogen enrichment, we have been measuring water chemistry at the mouth of the harbor to calculate exchange between the harbor and adjacent coastal waters of Buzzards Bay. Water samples were taken hourly over 24- to 48-hour periods during several periods in 2005-2009, 2014, 2017, 2019, and 2023. Data from 2005-2009 were collected year-round; samples from 2014 and later were collected during June through August. Samples were processed for ammonium, phosphate, nitrate + nitrite, total nitrogen, and total phosphorus unless otherwise notated. During some sampling years, additional samples were run for silicate, chlorophyll, total dissolved nitrogen, total dissolved phosphorus, dissolved organic carbon, particulate organic carbon, and particulate organic nitrogen. Salinity is reported for all samples. Samples were collected with an ISCO autosampler and stored on ice until analysis. Full analysis details and quality control methods are available in Hayn et al. 2014 (doi: 10.1007/s12237-013-9699-8) and Hayn 2025 (doi: 10.7298/btm6-ba76).