ABSTRACT:

Continuous data is collected at 9 sites throughout New Hampshire. At each site data is collected every 15 minutes by the datalogger from a HOBO Stage logger (or site is paired with USGS site), Satlantic SUNA and YSI EXO2. Data is collected and transmitted to UNH by cell telemetry once a day where it is stored on the NH EPSCoR data server. The data that is collected from the SUNA are Nitrate in mg/L and is corrected by grab sample NO3 analyzed by IC. Data that is collected by the YSI are Stream Temperature, Specific Conductance, and fDOM in QSU. The fDOM is corrected by temperature, turbidity (not included), and absorbance.

This data set was used to analyze the high-frequency time series of stream solutes to characterize the timing and magnitude of nutrient and organic matter transport over event, seasonal, and annual timescales as well as to assess to whether nitrate (NO3-) and dissolved organic carbon (DOC) transport are coupled in watersheds. Our dataset includes in situ observations spanning 2 – 4 years in 10 streams and rivers across New Hampshire, including observations of nearly 700 individual hydrologic events. These events are identified in the files.

Methods and findings are described in the associated WRR manuscript.

ABSTRACT:

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 through the NH EPSCoR project. This spatially-extensive network includes eight headwater stream and two main-stem river monitoring sites, spanning a variety of stream orders and land uses. We evaluated the performance of nitrate, fluorescent dissolved organic matter (fDOM), and turbidity sensors included in the sensor network and the data is shared here.

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).

ABSTRACT:

The Central Siberia Plateau (CSP) is undergoing rapid climate change resulting in increasing frequency of forest fires, which have uncertain effects on organic matter and nutrient delivery from headwater streams to downstream ecosystems. Across a fire chronosequence (3 to >100 years) underlain by continuous permafrost, we quantified the effects of wildfire on quantity and quality of dissolved organic matter (DOM) and inorganic nutrients in streams. Wildfire decreased DOM concentrations for about 50 years, but elevated nitrate (NO3-) concentrations lasted only 10 years; ammonium and phosphate concentrations were unchanged. This increase in NO3- and decrease in dissolved organic carbon (DOC) results in a wide range of DOC:NO3-, a ratio that is known to regulate NO3- uptake and denitrification in streams. Ultrahigh-resolution mass spectrometry and DOM optical properties showed that the composition of stream DOM changes after fire, with decreased abundance of polyphenols and aliphatic forms of DOM that are typically more biolabile than other forms of OM. Increasing wildfire frequency is thus likely to have major shifts in the metabolism, carbon flux, and nutrient balance of Arctic fluvial systems.

ABSTRACT:

The Central Siberian Plateau (CSP) is undergoing rapid climate change that has resulted in increased frequency of forest fires and subsequent alteration of watershed carbon and nutrient dynamics. Across a watershed chronosequence (3 to >100 years since wildfire) we quantified the effects of fire on quantity and composition of dissolved organic matter composition (DOM), stream water nutrients concentrations, as well as in-stream nutrient uptake. Wildfires increased concentrations of nitrate for a decade, while decreasing concentrations of dissolved organic carbon and nitrogen (DOC and DON) and aliphatic DOM contribution for five decades. These post-wildfire changes in stream DOM result in lower uptake efficiency of in-stream nitrate in recently burned watersheds. Nitrate uptake (as uptake velocity) is strongly dependent on DOM quality (e.g. polyphenolics), ambient dissolved inorganic nitrogen (DIN), and DOC to DIN ratios. Our observations and experiments suggest that a decade-long pulse of inorganic nitrogen and a reduction of DOC export occur following wildfires in streams draining the CSP. Increased fire frequency in the region is thus likely to both decrease DOM and increase nitrate delivery to the main stem Yenisei River, and ultimately the Arctic Ocean, in the coming decades.

ABSTRACT:

Tropical forests store large amounts of Earth’s terrestrial carbon (C), but many tropical montane streams have low dissolved organic matter (DOM). This low availability of energy likely limits certain pathways of inorganic nitrogen (N) uptake, as evidenced by high rates of nitrification and predominance of nitrate (NO3-) in the total pool of dissolved nitrogen, seen in many tropical montane forests. To test this hypothesis of energy limitation to N cycling, we conducted a series of experiments to explore the influence of DOM availability on tropical stream N cycling. Nutrient pulse additions of NO3- with or without an added carbon (C) source (acetate or urea) were conducted in streams of the Luquillo Experimental Forest, Puerto Rico. In the absence of added DOM, NO3- uptake was either undetectable or had very long (>3,000 m) uptake lengths (Sw). When DOM was added with NO3-, NO3- Sw were much shorter (80 to 1,200 m), with the shortest lengths resulting from additions of acetate. Comparing uptake metrics of the added C sources, there was greater demand for acetate compared to urea and measurable urea uptake was detected much less frequently. During additions of NO3--only, ambient concentrations of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) decreased in some cases, suggesting increased metabolic demand for energy from the ambient organic matter pool under elevated levels of inorganic nutrients. Collectively, these results demonstrate that pathways of inorganic nitrogen cycling are tightly tied to energy availability at this tropical site. The response of ambient DOC and DON to increases in NO3- concentrations points to important feedbacks between inorganic nitrogen and DOM including organic nitrogen. Understanding the controls on NO3- processing in these streams is important to predict network-scale exports of nitrogen from tropical ecosystems.

ABSTRACT:

Inland waters can be significant sources of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) to the atmosphere. However, considerable uncertainty remains in regional and global estimates of greenhouse gas (GHG) emissions from freshwater ecosystems, particularly streams. Controls on GHG production in streams, such as water chemistry and sediment characteristics, are also poorly understood. The main objective of this study was to quantify spatial and temporal variability in GHG concentrations in 20 streams across a landscape with considerable variation in land use and land cover in New England, USA. Stream water was consistently supersaturated in CO2, CH4, and N2O, suggesting that these small streams are sources of GHGs to the atmosphere in this landscape. Results show that concentrations of dissolved CO2, CH4 and N2O differed in their spatial and temporal patterns and in their relationship to stream chemistry. Both bivariate and multivariate analyses revealed a unique combination of predictor variables for each gas, suggesting variation in the landscape attributes and in-stream processes that control GHG concentrations. Although hydrologic conditions did not explain variation among sites, temporal patterns in GHG concentrations align with seasonal phenologies in flow and temperature. We developed a conceptual model based on these data that describes the spatial variability in GHG production from streams and that can elucidate the dominant controls on each gas. Developing an understanding of the factors controlling GHG dynamics in streams can help assess and predict how fluvial ecosystems will respond to changes in climate and land use and can be used to incorporate emissions from streams into regional and global GHG emission inventories.

ABSTRACT:

The major greenhouse gases in streams and rivers, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), can contribute significantly to regional greenhouse gas (GHG) budgets, and each appears to be responding to multiple drivers. Recent work suggests that tropical water bodies may be hot spots of GHG emissions due to high primary productivity in their watersheds, but tropical streams and rivers have historically been underrepresented in studies of GHG concentration and emissions. We use a five-year record of weekly water chemistry and dissolved gas data from eight tropical watersheds of varying lithology and redox conditions in the Luquillo Mountains of Puerto Rico to examine controls on GHG variability and estimate gas flux. Streams were frequently supersaturated in all three gases indicating that streams in this tropical landscape are sources of GHGs to the atmosphere. Concentrations of CO2 and N2O were associated with lateral inputs from the surrounding landscape, whereas CH4 concentrations correlated with in-stream oxygen availability and lithology. Our results underscore the importance of including tropical sites in global syntheses and budgets and the role of both in-stream biological and physical processes as well as landscape attributes that contribute to the export of gases to the fluvial network and atmosphere.