Streams provide a physical linkage between land and downstream river networks, delivering solutes derived from multiple catchment sources. We analyzed high‐frequency time series of stream solutes to characterize the timing and magnitude of major ion, nutrient, and organic matter transport over event, seasonal, and annual timescales as well as to assess whether nitrate ( NO3−) and dissolved organic carbon (DOC) transport are coupled in catchments, which would be expected if they are subject to similar biogeochemical controls throughout the watershed. Our data set includes in situ observations of NO3−, fluorescent dissolved organic matter (DOC proxy), and specific conductance spanning 2–4 years in 10 streams and rivers across New Hampshire, including observations of nearly 700 individual hydrologic events. We found a positive response of NO3− and DOC to flow in forested streams, but watershed development led to a negative relationship between NO3− and discharge, and thus a decoupling of the overall NO3− and DOC responses to flow. On event and seasonal timescales, NO3− and DOC consistently displayed different behaviors. For example, in several streams, FDOM yield was greatest during summer storms while NO3− yield was greatest during winter storms. Most streams had generalizable storm NO3− and DOC responses, but differences in the timing of NO3− and DOC transport suggest different catchment sources. Further, certain events, including rain‐on‐snow and summer storms following dry antecedent conditions, yielded disproportionate NO3− responses. High‐frequency data allow for increased understanding of the processes controlling solute variability and will help reveal their responses to changing climatic regimes.

Colony structure and reproductive investment were studied in a population of Myrmica punctiventris. This species undergoes a seasonal cycle of polydomy. A colony overwinters in entirety but fractionates into two or more nest sites during the active season and then coalesces in the fall. Colony boundaries were determined by integrating data on spatial pattern, behavioral compatability, and genetic relatedness as revealed by protein electrophoresis. Colonies contained at most one queen. Consequently, a colony consisted of one queenright nest and one or more queenless nests. Furthermore, estimates of relatedness were fully consistent, with queens being single mated. M. punctiventris therefore has a colony genetic structure that conforms to the classical explanation of the maintenance of worker sterility by kin selection. Kin selection theory predicts that workers would favor a female-biased allocation ratio while selection on queens would favor equal investment in males and females. We predicted that in polydomous populations, queenless nests would rear more female reproductives from diploid larvae than queenright nests. There was a significant difference between queenright and queenless nests in sexual allocation; queenless nests allocated energy to reproductive females whereas queenright nests did not. At neither the nest nor colony levels did worker number limit sexual production. We also found that nests tended to rear either males or females but when colony reproduction was summed over nests, the sexes were more equally represented. The difference in allocation ratios between queenless and queenright nests was attributed solely to queen presence/absence. Our work shows that polydomy provides an opportunity for workers to evade queen control and thereby to sexualize brood.

A state‐of‐the‐art network of water quality sensors was established in 2012 to gather year‐round high temporal frequency hydrochemical data in streams and rivers throughout the state of New Hampshire. This spatially extensive network includes eight headwater stream and two main stem river monitoring sites, spanning a variety of stream orders and land uses. Here we evaluate the performance of nitrate, fluorescent dissolved organic matter (fDOM), and turbidity sensors included in the sensor network. Nitrate sensors were first evaluated in the laboratory for interference by different forms of dissolved organic carbon (DOC), and then for accuracy in the field across a range of hydrochemical conditions. Turbidity sensors were assessed for their effectiveness as a proxy for concentrations of total suspended solids (TSS) and total particulate C and N, and fDOM as a proxy for concentrations of dissolved organic matter. Overall sensor platform performance was also examined by estimating percentage of data loss due to sensor failures or related malfunctions. Although laboratory sensor trials show that DOC can affect optical nitrate measurements, our validations with grab samples showed that the optical nitrate sensors provide a reliable measurement of NO3 concentrations across a wide range of conditions. Results showed that fDOM is a good proxy for DOC concentration (r2 = 0.82) but is a less effective proxy for dissolved organic nitrogen (r2 = 0.41). Turbidity measurements from sensors correlated well with TSS (r2 = 0.78), PC (r2 = 0.53), and PN (r2 = 0.51).

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Diurnal trends in hydrochemical components of stream and river water, especially nutrients, is growing in interest as instrumentation capable of measuring at fine time scales becomes increasingly available. In this growing body of work, there are few studies that simultaneously report the dynamics of the major nutrients nitrate, phosphate, and ammonium through time. We used an in situ nutrient autoanalyzer to simultaneously measure nitrate, phosphate, and ammonium concentrations with wet chemistry methods in an arctic headwater stream. We operated the analyzer under two sampling regimes: (1) time interval (hourly) sampling to examine fine time scale nutrient dynamics and (2) continuous sampling (1 s data) to evaluate nutrient uptake from a pulse solute addition experiment. Hourly sampling showed inverse diurnal oscillating trends of nitrate and ammonium concentrations for several days during base flow conditions. We propose that this trend is a result of in-stream nutrient processing (autotrophic demand and nitrification) combined with increased lateral inputs of water from the active (thawed) soil layer at night, after evapotranspiration (ET) has ceased. Pulse additions of ammonium resulted in rapid increases in nitrate concentration, confirming potential magnitude of nitrification in this system. Phosphate concentrations were usually at or below detection limits, consistent with results from previous manual sampling of this stream. We conclude that as studies examining fine time scale nutrient trends in streams and rivers increase, the ability to examine the behavior of multiple nutrients simultaneously will be pertinent to assess the underlying mechanisms driving those trends.

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Efforts to estimate air‐water carbon dioxide (CO2) exchange on regional or global scales are constrained by a lack of direct, continuous surface water CO2 observations. Sensor technology for the in situ measurement of the partial pressure of carbon dioxide (pCO2) has progressed, but still poses limitations including expense and biofouling concerns. We describe a simple, inexpensive, in situ pCO2 method (SIPCO2) in which a non‐dispersive infrared (NDIR) detector is paired with an air pump in an enclosed housing to produce air‐sea equilibration. We first evaluated this approach in a laboratory setting, then in an estuarine‐coastal ocean laboratory for several months to continuously monitor aquatic pCO2. An accepted, accurate NDIR‐based CO2 measurement technique was employed alongside SIPCO2 to provide an assessment of sensor performance. SIPCO2 allows for low‐cost, relatively accurate measurements of pCO2 (mean difference of −5 ± 5 μatm from validation system after laboratory calibration) without reagents or membranes, and can be assembled and operated with a minimal amount of technical skill. While not suitable for some exacting applications, this SIPCO2 approach could rapidly and effectively increase the number of quality CO2 observations in a range of aquatic environments. We also provide detailed instructions for the assembly of SIPCO2 from commercially available components.

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