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Headwater streams are known sources of methane (CH4) to the atmosphere, but their contribution to global scale budgets remains poorly constrained. While efforts have been made to better understand diffusive fluxes of CH4 in streams, much less attention has been paid to ebullitive fluxes. We examine the temporal and spatial heterogeneity of CH4 ebullition from four lowland headwater streams in the temperate northeastern United States over a 2‐yr period. Ebullition was observed in all monitored streams with an overall mean rate of 1.00 ± 0.23 mmol CH4 m−2 d−1, ranging from 0.01 to 1.79 to mmol CH4 m−2 d−1 across streams. At biweekly timescales, rates of ebullition tended to increase with temperature. We observed a high degree of spatial heterogeneity in CH4 ebullition within and across streams. Yet, catchment land use was not a simple predictor of this heterogeneity, and instead patches scale variability weakly explained by water depth and sediment organic matter content and quality. Overall, our results support the prevalence of CH4 ebullition from streams and high levels of variability characteristic of this process. Our findings also highlight the need for robust temporal and spatial sampling of ebullition in lotic ecosystems to account for this high level of heterogeneity, where multiple sampling locations and times are necessary to accurately represent the mean rate of flux in a stream. The heterogeneity observed likely indicates a complex set of drivers affect CH4 ebullition from streams which must be considered when upscaling site measurements to larger spatial scales. [ABSTRACT FROM AUTHOR]

Previous studies have shown that watersheds with significant human development (i.e., urban and agricultural land use) generally have higher concentrations and fluxes of dissolved inorganic nitrogen (DIN) in comparison to less-developed or forested watersheds. However, the impact of watershed development on dissolved organic nitrogen (DON) concentrations in drainage waters has received little attention. We present data from 39 watersheds in Massachusetts (Ipswich River watershed) encompassing a gradient of developed land use (0%-92% urban plus agriculture) and wetland abundance (0%-32%) to assess controls on mean annual DON concentrations and DON/ total dissolved nitrogen (TDN) in drainage waters. In addition, we compiled published data from 119 northeastern U.S. watersheds to evaluate broader-scale relationships between DON, developed land use, and wetlands. The percentage of developed land is a poor predictor of DON concentrations in the Ipswich watersheds (r² = 0.09) and the compiled dataset (r² = 0.27). In contrast, wetland percentage explains 56% of the variability in DON concentrations in the Ipswich watersheds, and 60% when all literature data are included. Excluding watersheds with direct wastewater inputs to surface waters improves the regional relationship significantly (r² = 0.79). The DON:TDN ratio is best explained by a multiple regression of wetland percentage and developed land use percentage for both the Ipswich watersheds (r² = 0.73) and the compiled dataset (r² = 0.50). Watersheds with abundant wetlands may therefore have high DON concentrations and DON:TDN ratios despite elevated anthropogenic nitrogen inputs associated with human development. [ABSTRACT FROM AUTHOR]