Response of metabolism and fluvial carbon flux to anomalous low flows in New Hampshire streams

Abstract:

Under a changing climate, greater variability in precipitation patterns is predicted for the northeastern United States, with heavy rainfall events, short seasonal droughts, and extended drought all likely to become more frequent. Fluvial networks are important sites of carbon processing and retention, but it remains unclear how extended dry periods will alter the metabolic regime of perennial streams and rivers. In this study we used continuous, high-frequency measurements of fluorescent dissolved organic matter and dissolved oxygen in nine streams across New Hampshire that vary in size, nutrient loading, and landscape context, with the goal of better understanding the influence of low flows in 2015 and an anomalous extreme drought in 2016 on the metabolism and carbon export from perennial streams. For one forested headwater stream in southern New Hampshire, fluorescent dissolved organic matter was flushed upon re-wetting after a 10-day stream drying event, but ecosystem respiration was suppressed for almost two weeks before recovering to levels observed prior to stream drying. Overall, low flows reduced dissolved carbon export by 30 percent compared to prior years. This study will increase our understanding of the impacts that low-flow events have on carbon transport and transformation in streams and rivers.