ABSTRACT. Enhanced phytoplankton production and algal blooms, symptoms of eutrophication, are frequently caused by elevated nutrient loading, usually a s nitrogen, to coastal waters. This nitrogen is derived primarily from anthropogenic sources (urban, industrial, and agricultural) but is delivered to coastal waters through meteorological and hydrological means. We utilized a 4 yr monthly data set to investigate the effect of these upstream physical forces upon primary productivity of the Neuse River Estuary (North Carolina. USA), a large temperate coastal plain estuary Our results indicate that the magnitude of estuarine primary production and the periodicity of algal blooms can be directly related to variations in upper watershed rainfall and its subsequent regulation of downstream nver flow Future changes in preclpitatlon patterns for coastal regions may thus lead to substantlal alterations in coastal primary productiv~ty rates and patterns.

Nutrient limitation of phytoplankton production was assessed monthly from 1987 through 1990 in the lower Neuse River Estuary, North Carolina, USA, a well-mixed, mesotrophic system. Nutrient addition bioassays indicated that the lower estuary experienced a general state of nitrogen limitation, with especially pronounced limitation during summer months, a period of high phytoplankton productivity. Bioassays conducted during spring months showed significantly greater stimulation of algal productivity with the addition of nitrogen and phosphorus than that found with nitrogen addition alone. This CO-stimulation occurred during periods when surface-water dissolved inorganic nitrogen : dissolved inorganic phosphorus ratios were elevated above typical values of < 5. Seasonal patterns in ambient nutrient concentrations revealed nitrogen maxima associated with spring, fall, and winter runoff events, with summer minima Hydrologically driven nitrogen loading exerted a strong, yearround influence on primary production and nutrient limitation characteristics. High-flow events acted to oversaturate the upper estuarine nutrient filtering capacity, resulting in increased delivery of nitrogen to the lower estuarine environment. The phytoplankton community responded to increased flow and concomitant nutrient loadings by increasing production and b~omass levels, often very rapidly. In this regard, hydrologic factors influencing nitrogen loading (terrigenous runoff, point source inputs, and wet and dry atmospheric deposition) are key determinants of the trophic state of this estuary.

SignificanceMethane from global rice cultivation currently accounts for one-half of all crop-related greenhouse gas emissions. Several international organizations are advocating reductions in methane emissions from rice by promoting intermittent flooding without accounting for the possibility of large emissions of nitrous oxide (N2O), a long-lived greenhouse gas. Our experimental results suggest that the Indian subcontinent’s N2O emissions from intermittently flooded rice fields could be 30–45 times higher than reported under continuous flooding. Net climate impacts of rice cultivation could be reduced by up to 90% through comanagement of water, nitrogen, and carbon. To do this effectively will require a careful ongoing global assessment of N2O emissions from rice, or we will risk ignoring a very large source of climate impact.

Abstract. Recent evaluations of estuarine and coastal nutrient budgets implicate atmospheric deposition as a potentially significant (20 to

Across many cities, estimates of methane emissions from natural gas (NG) distribution and end use based on atmospheric measurements have generally been more than double bottom-up estimates. We present a top-down study of NG methane emissions from the Boston urban region spanning 8 y (2012 to 2020) to assess total emissions, their seasonality, and trends. We used methane and ethane observations from five sites in and around Boston, combined with a high-resolution transport model, to calculate methane emissions of 76 ± 18 Gg/yr, with 49 ± 9 Gg/yr attributed to NG losses. We found no significant trend in the NG loss rate over 8 y, despite efforts from the city and state to increase the rate of repairing NG pipeline leaks. We estimate that 2.5 ± 0.5% of the gas entering the urban region is lost, approximately three times higher than bottom-up estimates. We saw a strong correlation between top-down NG emissions and NG consumed on a seasonal basis. This suggests that consumption-driven losses, such as in transmission or end-use, may be a large component of emissions that is missing from inventories, and require future policy action. We also compared top-down NG emission estimates from six US cities, all of which indicate significant missing sources in bottom-up inventories. Across these cities, we estimate NG losses from distribution and end use amount to 20 to 36% of all losses from the US NG supply chain, with a total loss rate of 3.3 to 4.7% of NG from well pad to urban consumer, notably larger than the current Environmental Protection Agency estimate of 1.4% [R. A. Alvarez et al., Science 361, 186–188 (2018)].