Helium-4 is produced in the Earth’s crust and degassed to the atmosphere. Measurements of 4 He and 81 Kr dating in an aquifer in Brazil suggest that most crustal 4 He reaches the atmosphere by the discharge of deep groundwater at the surface.

We assembled data from a global network of automated lake observatories to test hypotheses regarding the drivers of ecosystem metabolism. We estimated daily rates of respiration and gross primary production (GPP) for up to a full year in each lake, via maximum likelihood fits of a free‐water metabolism model to continuous high‐frequency measurements of dissolved oxygen concentrations. Uncertainties were determined by a bootstrap analysis, allowing lake‐days with poorly constrained rate estimates to be down‐weighted in subsequent analyses. GPP and respiration varied considerably among lakes and at seasonal and daily timescales. Mean annual GPP and respiration ranged from 0.1 to 5.0 mg O2 L−1 d−1 and were positively related to total phosphorus but not dissolved organic carbon concentration. Within lakes, significant day‐to‐day differences in respiration were common despite large uncertainties in estimated rates on some lake‐days. Daily variation in GPP explained 5% to 85% of the daily variation in respiration after temperature correction. Respiration was tightly coupled to GPP at a daily scale in oligotrophic and dystrophic lakes, and more weakly coupled in mesotrophic and eutrophic lakes. Background respiration ranged from 0.017 to 2.1 mg O2 L−1 d−1 and was positively related to indicators of recalcitrant allochthonous and autochthonous organic matter loads, but was not clearly related to an indicator of the quality of allochthonous organic matter inputs.

4 He accumulated in fluids is a well established geochemical tracer used to study crustal fluid dynamics. Direct fluid samples are not always collectable; therefore, a method to extract rare gases from matrix fluids of whole rocks by diffusion has been adapted. Helium was measured on matrix fluids extracted from sandstones and mudstones recovered during the San Andreas Fault Observatory at Depth (SAFOD) drilling in California, USA. Samples were typically collected as subcores or from drillcore fragments. Helium concentration and isotope ratios were measured 4–6 times on each sample, and indicate a bulk 4 He diffusion coefficient of 3.5 ± 1.3 × 10 –8 cm 2 s –1 at 21°C, compared to previously published diffusion coefficients of 1.2 × 10 –18 cm 2 s –1 (21°C) to 3.0 × 10 –15 cm 2 s –1 (150°C) in the sands and clays. Correcting the diffusion coefficient of 4 He water for matrix porosity (∼3%) and tortuosity (∼6–13) produces effective diffusion coefficients of 1 × 10 –8 cm 2 s –1 (21°C) and 1 × 10 –7 (120°C), effectively isolating pore fluid 4 He from the 4 He contained in the rock matrix. Model calculations indicate that <6% of helium initially dissolved in pore fluids was lost during the sampling process. Complete and quantitative extraction of the pore fluids provide minimum in situ porosity values for sandstones 2.8 ± 0.4% (SD, n = 4) and mudstones 3.1 ± 0.8% (SD, n = 4).

The present study investigated the habituation rate of Atlantic salmon parr to a daily sudden transition from darkness to light during the 6-week “winter signal” period of alternating light (L12, D:12) in commercial smolt production. Increase in oxygen consumption when the light was turned on was used as a measure of activity, and habituation rate was estimated from the day to day decrease of this hyper-consumption. A non-linear regression model was fitted to the data, where an initial response of 4.36mg O2 kg−1 min−1 declined at a rate corresponding to 24% day−1, and approached a response level of 1.33mg O2 kg−1 min−1 over the course of the experiment. The results show that parr effectively habituated to the strong stimulus, but that 31% of the initial response was sustained over weeks and not subject to habituation.

The existing measures of the 4He flux from the Earth's continental solid surface have been evaluated collectively. The lognormal mean of continental crustal flux measurements (n = 33) globally covering many geological environments is 4.18 × 1010 4He atoms m−2 s−1 with an estimated one sigma variance of */45X based on an assumption of symmetric error bars (lognormal distribution provides a standard deviation with a multiplication or division factor (*/) by which the mean may statistically vary). The range of the continental 4He degassing flux (95th percentile) increases with decreasing time scales (to */∼106X at 0.5 year) and decreasing space scales (to */∼106X at 1 km). The statistics can be interpreted as reflecting natural variability and suggest that the mechanisms transporting the crustal helium degassing flux contain a high degree of both spatial and temporal variability. This lognormal mean of the continental degassing flux of 4He as well as the (n = 271) estimate of degassing from Precambrian Shield lakes are both approximately equivalent to the radiogenic production rate for 4He in the whole crust. Large‐scale vertical mass transport in continental crust is estimated as scaled values of the order 10−5 cm2 s−1 for helium (over 2 Gyr and 40 km vertically) versus 10−2 cm2 s−1 for heat. This rate of mass transport requires not only release of He from the solid phase via diffusion, fracturing, or comminution but also an enhanced rate of mass transport facilitated by some degree of fluid advection. This further implies a separation of heat and mass during transport which will significantly influence the interpretations of heat and 3He/4He relations.

Raman spectra distributed temperature sensing (DTS) by fiber‐optic cables has recently shown considerable promise for the measuring and monitoring of surface and near‐surface hydrologic processes such as groundwater–surface water interaction, borehole circulation, snow hydrology, soil moisture studies, and land surface energy exchanges. DTS systems uniquely provide the opportunity to monitor water, air, and media temperatures in a variety of systems at much higher spatial and temporal frequencies than any previous measurement method. As these instruments were originally designed for fire and pipeline monitoring, their extension to the typical conditions encountered by hydrologists requires a working knowledge of the theory of operation, limitations, and system accuracies, as well as the practical aspects of designing either short‐ or long‐term experiments in remote or challenging terrain. This work focuses on providing the hydrologic user with sufficient knowledge and specifications to allow sound decisions on the application and deployment of DTS systems.

Small, shallow, inland water bodies are ubiquitous on the landscape and may be significant hotspots for biogeochemical transformations. However, the coupled physical and biogeochemical dynamics of these systems have received little attention compared with larger and deeper systems. Here, we examine the coupling between physical dynamics, sediment dynamics and oxygen-carbon dynamics in Mirror Lake, a small shallow pond in Storrs, CT, USA, using high frequency monitoring data and a simple coupled physical-biogeochemical model. The physical dynamics are characterised by a diurnal pattern of daytime thermal stratification and nighttime mixing. Observations show that the distribution of oxygen is tightly coupled with both the diurnal physical dynamics and photosynthesis-respiration reactions. Two 24-h periods in the summer of 2003 with similar meteorological conditions but distinctly different oxygen dynamics were simulated with a coupled physical-biogeochemical model. The model results suggest that the dynamics of sediment resuspension during nighttime convective overturn and subsequent settling during daytime stratification are critical in explaining the observed oxygen and dissolved inorganic carbon distributions. The diurnal dynamics provide a biogeochemical hot spot and hot moment by coupling meterologic forcing, resuspension of sediments, physical mixing and biological activity to hypoxia and anoxia in Mirror Lake.

Diurnal thermal stratification in shallow lakes and ponds is well documented and affects biogeochemical gradients. The onset of thermal stratification should occur when the stratification parameter I S  =−HB/u* rises above a critical value, I crit . Previous applications of the stratification parameter lack a common definition for the onset stratification and include assumptions inappropriate for shallow inland waterbodies. Here, the onset of stratification is defined relative to a practical threshold given by the Rohr-Stillinger criterion, N2 = ε/(20v). Using this definition, the utility of I S for predicting stratification in two shallow ponds was evaluated using select periods from over 600 days of temperature profiles, standard weather data and measured light attenuation coefficients. Though uncertainties in B and u* can produce errors in I S on the order of 40–60%, the parameter is robust for predicting the onset of stratification. Accuracy can be improved by sitespecific determinations of wind sheltering. The critical value for the onset of stratification was found to be approximately 1. The stratification parameter can be an effective screening tool for 1) predicting the presence of significant chemical gradients, and 2) determining the minimum wind speed required to prevent diurnal thermal stratification from developing.

The fortuitous presence of in situ equipment capable of high-resolution (time/space) measures of O(2) and total dissolved inorganic carbon (TDIC) enabled the response and recovery of a small pond to copper algaecide application to be monitored. Algaecide application to the pond significantly impacted the gross primary productivity (GPP) of the pond over a timescale of less than 4 days. By day 3-4 (postapplication), GPP had recovered to preherbicide levels and net ecosystem productivity (NEP) returned to a positive value. This indicated a timescale for copper algaecide impact on GPP of the order 1+ day and duration of impact of the order 3 days. Observed timescales for GPP recovery (3-4 days) indicate that algaecide effectiveness is not significantly controlled by mixing processes in this pond but is most likely influenced by the rate of removal of Cu to the sediment and the rate of Cu release from the chelating agent in K-tea. Observed recovery timescales for GPP (3-4 days) occurring during minimal inflow also indicate that significant nutrient recycling (internal loading) occurs to fuel the recovery of GPP. Thus, as an agent for the overall reduction in primary productivity of a polymictic pond ecosystem, a single copper application may not have a significant long-term impact on primary productivity.

Mesopelagic acoustic scattering layers (SLs) in 2 fjords were studied from a stationary research vessel. Diel vertical movements of SLs were assessed by hull-mounted transducers, while in situ behavior of individuals constituting the SLs was resolved by a submerged echo sounder. The study focused on SLs made up of the lightfish Maurolicus muelleri and the lanternfish Benthosema glaciale. Individual fish migrated in a pronounced stepwise manner, alternating between vertical movements and stationary phases both during ascent and descent. Mean lengths of steps varied between 2.01 and 0.40 m, and mean duration of stationary phases between 69 and 36 s for fish in different SLs. Such travel-pause behavior concords with saltatory search, where fish scan the water for prey during the stationary phases, relocate and scan a new water parcel. Little activity was recorded among individuals in deep water, apart from infrequent, short shifts in vertical distribution. This study shows that stationary submerged echo sounders can provide detailed information on in situ behavior of mesopelagic fish.

Because of the relative strength of sediment processes compared to water column processes, natural and anthropogenic ponds represent an important component of the terrestrial hydrologic cycle and a site for recycling carbon to the atmosphere. Over 250 d of dissolved oxygen and carbon dioxide concentrations were measured on the 0.5 h timescale in a small Connecticut pond. Using approximately 8000 half‐hour time intervals, Mirror Lake (Storrs, Connecticut) exhibits net annual fluxes for 2002 and 2003 of 80 and 86 mmol CO2 m−2 d−1 (±26%) and 25 and −7.5 mmol O2 m−2 d−1 (±20%), respectively (positive flux is to the atmosphere). The instantaneous (0.5 h) fluxes of both CO2 and O2 to the atmosphere exhibit a standard deviation in the flux (measured every 0.5 h) of the order 100%, indicating a high degree of daily, weekly, and seasonal variability in the controlling processes, and the two gases rarely follow Redfield ratio stoichiometry. This net carbon flux to the atmosphere agrees with the range of carbon fluxes from various shallow inland aquatic waters. Using CO2 and O2 mass balances, the minimum bacterial production of CO2 in the pond is estimated to be 100 and 81mmol CO2 m−2 d−1 for 2002 and 2003 (same order as the net CO2 flux from the pond), indicating the importance of the bacterial processes in pond carbon dynamics. Bacterial pathways that utilize NO3−1 or fermentation strongly favor CO2 production relative to O2 consumption and may provide a mechanistic explanation for the (instantaneous to annual) CO2 to O2 imbalance relative to the Redfield ratio. Thus, while natural and man‐made ponds do provide advantages for flood control, sediment settling, and some degree of contaminant removal, ponds may also provide a locus for the processing of terrestrial carbon into a CO2 source to the atmosphere. Given the number of small ponds and their location in the hydrologic cycle, pond systems represent a coupling of hydrology and the carbon cycle worthy of greater investigation.

Spatially and temporally continuous temperature measurements were collected over 32 h using a fiber-optic distributed temperature sensing (DTS) system deployed along 330 m of two intertidal saltmarsh channel beds in northern California. Measured temperature gradients imparted ecosystem-scale structure to the saltmarsh tidal channel thermal regime, which was punctuated by potential warm and cold refugia. Anomalous bed temperatures of 2-4 degrees C occurred throughout the 1.3 tidal cycles at some locations. Discrete locations of consistently warm temperatures characterized sustained seepage of recently infiltrated tidal waters. Low-variance temperature anomalies were typically collocated with hidden microtopographic tributaries that facilitated mixing of warm surface waters and cold groundwater. Bed temperature gradients (approximately 2 degrees C/100 m, average) decreased from high temperatures similar to bay water at the channel mouths to low inland temperatures comparable to groundwater. The trends were maintained by cold groundwater discharge throughout the channels, which affected bed temperatures in proportion to channel reach exposure time; the opposing effect, conductive bed-warming by tidal waters, was proportional to flood duration. DTS is a promising tool for identifying spatial and temporal temperature patterns of hydroecological importance amidst complex natural systems.

In shallow aquatic systems subject to heavy allochthonous (terrestrial) organic loading, bacterial processing of organic matter can be a significant component in the ecosystem C‐cycle. Because this bacterial processing of organic matter also produces reduced species (Fe+2, Mn+2, S−2, NH3, etc.), these processes also create an additional chemical oxygen demand. Hence, net ecosystem operation can deviate significantly from the “Redfield Line” defined by the traditional photosynthesis/respiration reaction stoichiometry. Here, a 3D process vector concept is presented in terms of (gas‐exchange‐corrected) CO2 or O2‐TDIC‐time to characterize significant bacterial contributions to the net O2 and TDIC dynamics of the ecosystem. The direction of the process vector provides an important clue to the internal process dynamics and the biogeochemical pathways that govern the net ecosystem function. Using instrumented in situ measures of O2 and TDIC in a small pond (ca. 0.7 m deep), this ecosystem is shown to operate significantly off the “Redfield Line” with multiple periods producing a net increase in both (gas‐exchange‐corrected) O2 and CO2 and exporting of both to the atmosphere. A methodology for the quantification of the minimum bacterially produced TDIC in the ecosystem (MBP) is developed. The rates (38–91 mmoles C m−2 day−1) are consistent with measured carbon fluxes from shallow terrestrial aquatic systems as well as anticipated cell numbers in the sediment that likely contribute to this bacterially produced carbon. The process vector concept can be extended to additional dimensions (CH4, NO3−, NH4+, Fe+2, etc.) and may provide a tool for visualization of observatory data streams.

Vertical migration of the mesopelagic jellyfish Periphylla periphylla (Scyphozoa: Coronatae) was studied by use of hull‐mounted and submerged echosounders in a ~440 m deep Norwegian fjord. The research vessel was kept at a fixed position so that individual jellyfish remained in the acoustic beam for prolonged periods in the low advective environment of the deep fjord basin. The population of jellyfish was divided into different vertical modes with different migration behavior. A scattering layer (SL) of P. periphylla was located at 150‐200 m during the day; it migrated coherently to the upper 50 m at night and returned to depth the next morning. A deeper SL seemed to remain below 250 m both day and night. However, focus on individuals revealed additional, asynchronous migration activity. A pulse of P. periphylla left upper layers already a few hours after sunset, and there was interchange of individuals between shallow and deep water throughout the night, including ascent of individuals from the apparent nonmigrating deepest SL. Vertical migration velocities were ~2 cm s−1 both during ascent and descent, irrespective of time. Different types of swimming behavior were reflected in the acoustic records, affecting the recorded backscatter.

I present a mechanistic predation model with explicit representation of predator aggregation for analysing the relationship between mortality rate of prey and their vulnerability (e.g., conspicuousness, escape ability). The model is developed for an aquatic setting with plankton as prey and planktivores as predators, but the principle is general. When predators are aggregated, encounters between prey and predators are not independent events. This means that a prey that runs into one predator is more likely to run into more predators, and any prey that runs into a high number of predators will eventually be perceived and captured, almost irrespective of how cryptic it is or how well it escapes attacks. A prey that has not run into a predator yet is more likely to continue to not run into predators and may therefore avoid predation even if it displays no crypsis or anti predation behaviour. Therefore, the predation risk from aggregated predators is less dependent on prey vulnerability than the intuitive proportionality relationship that applies to predation risk from solitary predators. This has important implications for patterns of mortality within prey communities (e.g., size dependency of plankton mortality).

Multiple issues in hydrologic and environmental sciences are now squarely in the public focus and require both government and scientific study. Two facts also emerge: (1) The new approach being touted publicly for advancing the hydrologic and environmental sciences is the establishment of community‐operated “big science” (observatories, think tanks, community models, and data repositories). (2) There have been important changes in the business of science over the last 20 years that make it important for the hydrologic and environmental sciences to demonstrate the “value” of public investment in hydrological and environmental science. Given that community‐operated big science (observatories, think tanks, community models, and data repositories) could become operational, I argue that such big science should not mean a reduction in the importance of single‐investigator science. Rather, specific linkages between the large‐scale, team‐built, community‐operated big science and the single investigator should provide context data, observatory data, and systems models for a continuing stream of hypotheses by discipline‐based, specialized research and a strong rationale for continued, single‐PI (“discovery‐based”) research. I also argue that big science can be managed to provide a better means of demonstrating the value of public investment in the hydrologic and environmental sciences. Decisions regarding policy will still be political, but big science could provide an integration of the best scientific understanding as a guide for the best policy.